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Matthew Bruce Principal Scientist/Engineer mbruce@apl.washington.edu Phone 206-685-2283 |
Education
B.S. Electrical and Computer Engineering, Michigan Technological University, 1991
M.S. Electrical and Computer Engineering, Virginia Polytechnic University, 1993
Ph.D. Bioengineering, University of Washington, 2004
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Publications |
2000-present and while at APL-UW |
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Glibenclamide treatment improved intraspinal blood volume, tissue sparing, and functional recovery after cervical spinal cord injury in rats Prasse, T., and 11 others including M.F. Bruce, "Glibenclamide treatment improved intraspinal blood volume, tissue sparing, and functional recovery after cervical spinal cord injury in rats," Brain Res. Bull., 246, doi:10.1016/j.brainresbull.2026.112162, 2026. |
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1 Nov 2026
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Limiting the expansion of the primary injury after a traumatic spinal cord injury (SCI) can offer improved functional outcomes. Glibenclamide (glyburide) has been shown to limit intraspinal bleeding and promote vascular stability after SCI in rats, but its impact on intraspinal hemodynamics has not been investigated. Here, we hypothesized that acute glibenclamide treatment would improve intraspinal hemodynamics after a cervical contusion SCI in a rat model (200 kdyn). Intravital ultrafast contrast-enhanced ultrasound (CEUS) imaging revealed that glibenclamide treatment significantly increased total blood volume (i.e., tissue perfusion) at 72-hours post-injury (hpi) compared to vehicle treated controls (p < 0.05, Cohen's d >1.2). Histological data confirmed that glibenclamide treatment significantly lowered caspase-8-positive cells in the white matter at 72-hpi (p < 0.05, Cohen's d>1.2). Weekly forelimb locomotor scoring revealed significant functional improvements in animals treated with glibenclamide at 4-weeks post-injury (wpi) (p < 0.001, Cohen's d>1.2), which continued through to 8-wpi compared to vehicle treated animals (p < 0.05, Cohen's d>1.2). Glibenclamide intervention significantly reduced lesion size by 8-wpi compared to controls (p < 0.05, Cohen's d>1.2). This study is the first to report in vivo improvements in intraspinal blood volume associated with glibenclamide treatment after acute cervical SCI in rats. |
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Contrast-enhanced ultrasound demonstrates a severity-dependent hemodynamic response to acute dural decompression in concussive rodent spinal cord injury Ramkumar, R., and 7 others including M.F. Bruce, "Contrast-enhanced ultrasound demonstrates a severity-dependent hemodynamic response to acute dural decompression in concussive rodent spinal cord injury," Neurotrauma Rep., 7, doi:10.1177/2689288X261479412, 2026. |
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25 Aug 2026
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Traumatic spinal cord injury (tSCI) is characterized by early microvascular disruption and regional perfusion failure that contribute to secondary tissue loss. The physiological effects of early decompression on spinal cord perfusion across injury severities remain incompletely defined. This study examined the influence of injury severity on perfusion dynamics and the impact of durotomy using contrast-enhanced ultrasound (CEUS) in a rat model of tSCI. Female Long–Evans rats underwent contusive injuries of graded severity (100, 150, 200 kDyn) at the T8 level, followed by decompressive durotomy or no further intervention. CEUS was performed at baseline, immediately after injury, 1 and 24 h postinjury to derive spatially resolved perfusion metrics, including normalized area under the curve (AUC) and spinal perfusion index (SPI). Perfusion was analyzed across defined regions: injury center, perilesional transition zone, and distal spinal cord. Functional recovery was assessed longitudinally using Basso, Beattie, and Bresnahan locomotor scoring and ladder walk testing, and spared myelin was quantified histologically at 8 weeks postinjury (wpi). Contusive tSCI produced an immediate, severity-dependent reduction in spinal cord perfusion at the lesion epicenter, with progressive involvement of adjacent segments at higher injury severities. Decompressive durotomy selectively improved perilesional perfusion following moderate injury (150 kDyn), reflected by a higher SPI (0.49 vs. 0.30, p = 0.005) and a concordant increase in perilesional AUC at 1 h. These perfusion changes were spatially restricted and transient. In exploratory analyses of chronic outcomes, moderate-injury cohort showed focal, nonsignificant trends toward greater perilesional myelin preservation and improved motor performance; total spared white matter and locomotor scores did not differ significantly between groups. These findings demonstrate that the perfusion benefits of early decompression are severity-dependent, with maximal effects in perilesional tissue following moderate injury. Quantitative CEUS provides a physiologically grounded approach for assessing therapeutic responsiveness in acute tSCI and may help guide optimization of decompressive strategies. |
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Sound decisions: real-time ultrasound in the management of traumatic spinal cord injury Hofstetter, C.P., A. Sadeghi, R. Ramkumar, M. Bruce, and Z.Z. Khaing, "Sound decisions: real-time ultrasound in the management of traumatic spinal cord injury," Curr. Opin. Neurobiol., 38, 635-643, doi:10.1097/WCO.0000000000001432, 2025. |
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1 Dec 2025
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Traumatic spinal cord injury (tSCI) is a devastating neurological emergency with high morbidity and no proven therapies that reliably improve recovery. While early decompression and hemodynamic optimization are standard, clinicians lack imaging tools to stratify injury severity or monitor physiological responses in real time. Advances in high-resolution B-mode, contrast-enhanced ultrasound, and multiparametric approaches offer a unique opportunity to close this gap and improve patient-specific treatment strategies. |
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Contrast-enhanced ultrasound imaging detects anatomical and functional changes in rat cervical spine microvasculature with normal aging Harmon, J.N., and 7 others including M.F. Bruce, "Contrast-enhanced ultrasound imaging detects anatomical and functional changes in rat cervical spine microvasculature with normal aging," J. Gerontol. A, 80, doi:10.1093/gerona/glae215, 2025. |
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1 Jan 2025
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Normal aging is associated with significant deleterious cerebrovascular changes; these have been implicated in disease pathogenesis and increased susceptibility to ischemic injury. Although these changes are well documented in the brain, few studies have been conducted in the spinal cord. Here, we utilize specialized contrast-enhanced ultrasound (CEUS) imaging to investigate age-related changes in cervical spinal vascular anatomy and hemodynamics in male Fisher 344 rats, a common strain in aging research. Aged rats exhibited significant tortuosity in the anterior spinal artery and elevated vascular resistance compared to adults. Baseline blood volume was lower in both larger vessels and the microcirculation in the aged cohort, specifically in white matter. To elucidate functional differences, animals were exposed to a hypoxia challenge, whereas adult rats exhibited significant functional hyperemia in both gray matter (GM) and white matter (WM), aged rats showed no response. Immunohistochemistry revealed reduced pericyte coverage and activated microglia behavior in aged rats, which may partially explain the lack of vascular response. This study provides the first in vivo description of age-related hemodynamic differences in the cervical spinal cord. |
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Advancing boiling histotripsy dose in ex vivo and in vivo renal tissues via quantitative histological analysis and shear wave elastography Ponomarchuk, E., G. Thomas, M. Song, Y.-N. Wang, S. Totten, G. Schade, J. Thiel, M. Bruce, V. Khokhlova, and T. Khokhlova, "Advancing boiling histotripsy dose in ex vivo and in vivo renal tissues via quantitative histological analysis and shear wave elastography," Ultrasound Med. Biol., 50, 1936-1944, doi:10.1016/j.ultrasmedbio.2024.08.022, 2024. |
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1 Dec 2024
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Histotripsy-induced bactericidal activity correlates to size of cavitation cloud in vitro Ambekar, P.A., Y.-N. Wang, T.D. Khokhlova, G.P.L. Thomas, P.B. Rosnitskiy, K. Contreras, D.F. Leotta, A.D. Maxwell, M. Bruce, S. Pierson, S. Totten, Y.N. Kumar, J. Thiel, K.T. Chan, W.C. Liles, E.P. Dellinger, A. Adedipe, W.L. Monsky, and T.J. Matula, "Histotripsy-induced bactericidal activity correlates to size of cavitation cloud in vitro," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 71, 1868-1878, doi:10.1109/TUFFC.2024.3476438, 2024. |
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9 Oct 2024
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Large abscesses are walled-off collections of pus and bacteria that often do not respond to antibiotic therapy. Standard of care involves percutaneous placement of indwelling catheter(s) for drainage, a long and uncomfortable process with high rehospitalization rates. The long-term goal of this work is to develop therapeutic ultrasound approaches to eradicate bacteria within abscesses as a noninvasive therapeutic alternative. Inertial cavitation induced by short pulses of focused ultrasound (histotripsy) is known to generate lethal mechanical damage in bacteria. Prior studies with Escherichia coli (E. coli) in suspension demonstrated that bactericidal effects increase with increasing peak negative amplitude, treatment time, and duty cycle. The current study investigated correlates of bactericidal activity with histotripsy cavitation cloud size. Histotripsy was applied to E. coli suspensions in 10-mL sample vials at 810 kHz, 1.2 MHz, or 3.25 MHz for 40 min. The cavitation activity in the sample vials was separately observed with high-speed photography. The cavitation cloud area was quantified from those images. A linear relationship was observed between bacterial inactivation and cavitation cloud size ( R2 = 0.98 ), regardless of the acoustic parameters (specifically frequency, pulse duration, and power) used to produce the cloud. |
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Perfusion imaging metrics after acute traumatic spinal cord injury are associated with injury severity in rats and humans Khaing, Z.Z., and 9 others including M. Bruce, "Perfusion imaging metrics after acute traumatic spinal cord injury are associated with injury severity in rats and humans," Sci. Transl. Med., 16, doi:10.1126/scitranslmed.adn4970, 2024. |
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18 Sep 2024
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Traumatic spinal cord injury (tSCI) causes an immediate loss of neurological function, and the prediction of recovery is difficult in the acute phase. In this study, we used contrast-enhanced ultrasound imaging to quantify intraspinal vascular disruption acutely after tSCI. In a rodent thoracic tSCI model, contrast-enhanced ultrasound revealed a perfusion area deficit that was positively correlated with injury severity and negatively correlated with hindlimb locomotor function at 8 weeks after injury. The spinal perfusion index was calculated by normalizing the contrast inflow at the injury center to the contrast inflow in the injury periphery. The spinal perfusion index decreased with increasing injury severity and positively correlated with hindlimb locomotor function at 8 weeks after injury. The feasibility of intraoperative contrast-enhanced ultrasound imaging was further tested in a cohort of 27 patients with acute tSCI of varying severity and including both motor-complete and motor-incomplete tSCIs. Both the perfusion area deficit and spinal perfusion index were different between motor-complete and motor-incomplete patients. Moreover, the perfusion area deficit and spinal perfusion index correlated with the injury severity at intake and exhibited a correlation with extent of functional recovery at 6 months. Our data suggest that intraoperative contrast-enhanced, ultrasound-derived metrics are correlated with injury severity and chronic functional outcome after tSCI. Larger clinical studies are required to better assess the reliability of the proposed contrast-enhanced ultrasound biomarkers and their prognostic capacity. |
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A comparative study of histotripsy parameters for the treatment of fibrotic ex-vivo human benign prostatic hyperplasia tissue Kumar, Y.N., Z. Singh, Y.-N.Wang, D. Kanabolo, L. Chen, M. Bruce, E. Vaisavljevich, L. True, A.D. Maxwell, and G.R. Schade, "A comparative study of histotripsy parameters for the treatment of fibrotic ex-vivo human benign prostatic hyperplasia tissue," Sci. Rep., 14, doi:10.1038/s41598-024-71163-2, 2024. |
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2 Sep 2024
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Histotripsy is a noninvasive focused ultrasound therapy that mechanically fractionates tissue to create well-defined lesions. In a previous clinical pilot trial to treat benign prostatic hyperplasia (BPH), histotripsy did not result in consistent objective improvements in symptoms, potentially because of the fibrotic and mechanically tough nature of this tissue. In this study, we aimed to identify the dosage required to homogenize BPH tissue by different histotripsy modalities, including boiling histotripsy (BH) and cavitation histotripsy (CH). |
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Quantifying injury expansion in the cervical spinal cord with intravital ultrafast contrast-enhanced ultrasound imaging Harmon, J.N. J.E. Hyde, D.E. Jensen, E.C. D'cessare, A.A. Odarenko, M.F. Bruce, and Z.Z. Khaing, "Quantifying injury expansion in the cervical spinal cord with intravital ultrafast contrast-enhanced ultrasound imaging," Exper. Neurol., 374, doi:10.1016/j.expneurol.2024.114681, 2024. |
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1 Apr 2024
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Spinal cord injury is characterized by hemodynamic disruption at the injury epicenter and hypoperfusion in the penumbra, resulting in progressive ischemia and cell death. This degenerative secondary injury process has been well-described, though mostly using ex vivo or depth-limited optical imaging techniques. Intravital contrast-enhanced ultrasound enables longitudinal, quantitative evaluation of anatomical and hemodynamic changes in vivo through the entire spinal parenchyma. Here, we used ultrasound imaging to visualize and quantify subacute injury expansion (through 72 h post-injury) in a rodent cervical contusion model. Significant intraparenchymal hematoma expansion was observed through 72 h post-injury (1.86 ± 0.17-fold change from acute, p < 0.05), while the volume of the ischemic deficit largely increased within 24 h post-injury (2.24 ± 0.27-fold, p < 0.05). Histology corroborated these findings; increased apoptosis, tissue and vessel loss, and sustained tissue hypoxia were observed at 72 h post-injury. Vascular resistance was significantly elevated in the remaining perfused tissue, likely due in part to deformation of the central sulcal artery nearest to the lesion site. In conjunction, substantial hyperemia was observed in all perilesional areas examined except the ipsilesional gray matter. This study demonstrates the utility of longitudinal ultrasound imaging as a quantitative tool for tracking injury progression in vivo. |
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Comparative study of histotripsy pulse parameters used to inactivate Escherichia coli in suspension Ambedkar, P.A., Y.-N. Wang, T. Khokhlova, M. Bruce, D.F. Leotta, S. Totten, A.D. Maxwell, K.T. Chan, W.C. Liles, E.P. Dellinger, W. Monsky, A.A. Adedipe, and T.J. Matula, "Comparative study of histotripsy pulse parameters used to inactivate Escherichia coli in suspension," Ultrasound Med. Biol., 49, 2451-2458, doi:10.1016/j.ultrasmedbio.2023.08.004, 2023. |
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1 Dec 2023
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Bacterial loads can be effectively reduced using cavitation-mediated focused ultrasound, or histotripsy. In this study, gram-negative bacteria (Escherichia coli) in suspension were used as model bacteria to evaluate the effectiveness of two regimens of histotripsy treatments: cavitation histotripsy (CH) and boiling histotripsy (BH).The results of this study suggest that both CH and BH can be used to inactivate E. coli in suspension, with the optimal regimen depending on the attainable peak negative focal pressure at the target. |
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Quantitative tissue perfusion imaging using nonlinear ultrasound localization microscopy Harmon, J.S., Z.Z. Khaing, J.E. Hyde, C.P. Hofstetter, C. Tremblay-Darveau, and M.F. Bruce, "Quantitative tissue perfusion imaging using nonlinear ultrasound localization microscopy," Sci. Rep., 12, doi:10.1038/s41598-022-24986-w, 2023. |
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19 Dec 2022
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Ultrasound localization microscopy (ULM) is a recent advancement in ultrasound imaging that uses microbubble contrast agents to yield vascular images that break the classical diffraction limit on spatial resolution. Current approaches cannot image blood flow at the tissue perfusion level since they rely solely on differences in velocity to separate tissue and microbubble signals; lower velocity microbubble echoes are removed during high pass wall filtering. To visualize blood flow in the entire vascular tree, we have developed nonlinear ULM, which combines nonlinear pulsing sequences with plane-wave imaging to segment microbubble signals independent of their velocity. Bubble localization and inter-frame tracking produces super-resolved images and, with parameters derived from the bubble tracks, a rich quantitative feature set that can describe the relative quality of microcirculatory flow. Using the rat spinal cord as a model system, we showed that nonlinear ULM better resolves some smaller branching vasculature compared to conventional ULM. Following contusion injury, both gold-standard histological techniques and nonlinear ULM depicted reduced in-plane vessel length between the penumbra and contralateral gray matter (–16.7% vs. –20.5%, respectively). Here, we demonstrate that nonlinear ULM uniquely enables investigation and potential quantification of tissue perfusion, arguably the most important component of blood flow. |
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Development of tough hydrogel phantoms to mimic fibrous tissue for focused ultrasound therapies Kumar, Y.N., Z. Singh, Y.-N. Wang, G.R. Schade, W. Kreider, M. Bruce, E. Vlaisavljevich, T.D. Khokhlova, and A.D. Maxwell, "Development of tough hydrogel phantoms to mimic fibrous tissue for focused ultrasound therapies," Ultrasound Biol. Med., 48, 1762-1777, doi:10.1016/j.ultrasmedbio.2022.05.002, 2022. |
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1 Sep 2022
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Tissue-mimicking gels provide a cost-effective medium to optimize histotripsy treatment parameters with immediate feedback. Agarose and polyacrylamide gels are often used to evaluate treatment outcomes as they mimic the acoustic properties and stiffness of a variety of soft tissues, but they do not exhibit high toughness, a characteristic of fibrous connective tissue. To mimic pathologic fibrous tissue found in benign prostate hyperplasia (BPH) and other diseases that are potentially treatable with histotripsy, an optically transparent hydrogel with high toughness was developed that is a hybrid of polyacrylamide and alginate. The stiffness was established using shear wave elastography (SWE) and indentometry techniques and was found to be representative of human BPH ex vivo prostate tissue. Different phantom compositions and excised ex vivo BPH tissue samples were treated with a 700-kHz histotripsy transducer at different pulse repetition frequencies. Post-treatment, the hybrid gels and the tissue samples exhibited differential reduction in stiffness as measured by SWE. On B-mode ultrasound, partially treated areas were present as hyperechoic zones and fully liquified areas as hypoechoic zones. Phase contrast microscopy of the gel samples revealed liquefaction in regions consistent with the target lesion dimensions and correlated to findings identified in tissue samples via histology. The dose required to achieve liquefaction in the hybrid gel was similar to what has been observed in ex vivo tissue and greater than that of agarose of comparable or higher Young's modulus by a factor >10. These results indicate that the developed hydrogels closely mimic elasticities found in BPH prostate ex vivo tissue and have a similar response to histotripsy treatment, thus making them a useful cost-effective alternative for developing and evaluating different treatment protocols. |
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Blood flow changes associated with spinal cord injury assessed by non-linear Doppler contrast-enhanced ultrasound Bruce, M., D. Dewees, J. Harmon, L. Cates, Z.Z. Khaing, and C.P. Hofstetter, "Blood flow changes associated with spinal cord injury assessed by non-linear Doppler contrast-enhanced ultrasound," Ultrasound Med. Biol., 48, 1410-1419, doi:10.1016/j.ultrasmedbio.2022.03.004, 2022. |
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1 Aug 2022
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Contrast-enhanced ultrasound (CEUS) is clinically used to image the microcirculation at lower imaging frequencies (<2 MHz). Recently, plane-wave acquisitions and Doppler processing have revealed improved microbubble sensitivity, enabling CEUS use at higher frequencies (15 MHz) and the ability to image simultaneously blood flow in the micro- and macrocirculations. We used this approach to assess acute and chronic blood flow changes within contused spinal cord in a rodent spinal cord injury model. Immediately after spinal cord injury, we found significant differences in perfusion deficit between moderate and severe injuries (1.73 ± 0.1 mm2 vs. 3.2 ± 0.3 mm2, respectively), as well as a delay in microbubble arrival time in tissue adjacent to the injury site (0.97 ± 0.1 s vs. 1.54 ± 0.1 s, respectively). Acutely, morphological changes to central sulcal arteries were observed where vessels rostral to the contusion were displaced 4.8 ± 2.2° and 8.2 ± 3.1° anteriorly, and vessels caudal to the contusion 17.8 ± 3.9° and 24.2 ± 4.1° posteriorly, respectively, for moderate and severe injuries. Significant correlation of the acute perfusion deficit and arrival time were found with the chronic assessment of locomotive function and histological estimate of spared spinal cord tissue. |
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Sonographic features of abscess maturation in a porcine model Leotta, D.F., M. Bruce, Y.-N. Wang, J. Kucewicz, T.K. Khokhlova, K. Chan, W. Monsky, and T.J. Matula, "Sonographic features of abscess maturation in a porcine model," Ultrasound Med. Biol., 47, 1920-1930, doi:10.1016/j.ultrasmedbio.2021.03.011, 2021. |
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1 Jul 2021
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Abscesses are walled-off collections of infected fluids that often develop as complications in the setting of surgery and trauma. Treatment is usually limited to percutaneous catheterization with a course of antibiotics. As an alternative to current treatment strategies, a histotripsy approach was developed and tested in a novel porcine animal model. The goal of this article is to use advanced ultrasound imaging modes to extract sonographic features associated with the progression of abscess development in a porcine model. Intramuscular or subcutaneous injections of a bi-microbial bacteria mixture plus dextran particles as an irritant led to identifiable abscesses over a 2 to 3 wk period. Selected abscesses were imaged at least weekly with B-mode, 3-D B-mode, shear-wave elastography and plane-wave Doppler imaging. Mature abscesses were characterized by a well-defined core of varying echogenicity surrounded by a hypoechoic capsule that was highly vascularized on Doppler imaging. 3-D imaging demonstrated the natural history of abscess morphology, with the abscess becoming less complex in shape and increasing in volume. Furthermore, shear-wave elastography demonstrated variations in stiffness as phlegmon becomes abscess and then liquefies, over time. These ultrasound features potentially provide biomarkers to aid in selection of treatment strategies for abscesses. |
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Super-resolution ultrasound localization microscopy through deep learning van Sloun, R.J.G., O. Solomon, M. Bruce, Z.Z. Khaing, H. Wijkstra, Y.C. Eldar, and M. Mischi, "Super-resolution ultrasound localization microscopy through deep learning," IEEE Trans. Med. Imaging, 40, 829-838, doi:10.1109/TMI.2020.3037790, 2021. |
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1 Mar 2021
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Ultrasound localization microscopy has enabled super-resolution vascular imaging through precise localization of individual ultrasound contrast agents (microbubbles) across numerous imaging frames. However, analysis of high-density regions with significant overlaps among the microbubble point spread responses yields high localization errors, constraining the technique to low-concentration conditions. As such, long acquisition times are required to sufficiently cover the vascular bed. In this work, we present a fast and precise method for obtaining super-resolution vascular images from high-density contrast-enhanced ultrasound imaging data. This method, which we term Deep Ultrasound Localization Microscopy (Deep-ULM), exploits modern deep learning strategies and employs a convolutional neural network to perform localization microscopy in dense scenarios, learning the nonlinear image-domain implications of overlapping RF signals originating from such sets of closely spaced microbubbles. Deep-ULM is trained effectively using realistic on-line synthesized data, enabling robust inference in-vivo under a wide variety of imaging conditions. We show that deep learning attains super-resolution with challenging contrast-agent densities, both in-silico as well as in-vivo. Deep-ULM is suitable for real-time applications, resolving about 70 high-resolution patches (128 x 128 pixels) per second on a standard PC. Exploiting GPU computation, this number increases to 1250 patches per second. |
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Treating porcine abscesses with histotripsy: A pilot study Matula, T.J., Y.-N. Wang, T. Khokhlova, D.F. Leotta, J. Kucewicz, A.A. Brayman, M. Bruce, A.D. Maxwell, B.E. MacConaghy, G. Thomas, V.P. Chernikov, S.V. Buravkov, V.A. Khokhlova, K. Richmond, K. Chan, W. Monsky, "Treating porcine abscesses with histotripsy: A pilot study," Ultrasound Med. Biol., 47, 603-619, doi:10.1016/j.ultrasmedbio.2020.10.011, 2021. |
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1 Mar 2021
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Infected abscesses are walled-off collections of pus and bacteria. They are a common sequela of complications in the setting of surgery, trauma, systemic infections and other disease states. Current treatment is typically limited to antibiotics with long-term catheter drainage, or surgical washout when inaccessible to percutaneous drainage or unresponsive to initial care efforts. Antibiotic resistance is also a growing concern. Although bacteria can develop drug resistance, they remain susceptible to thermal and mechanical damage. In particular, short pulses of focused ultrasound (i.e., histotripsy) generate mechanical damage through localized cavitation, representing a potential new paradigm for treating abscesses non-invasively, without the need for long-term catheterization and antibiotics. In this pilot study, boiling and cavitation histotripsy treatments were applied to subcutaneous and intramuscular abscesses developed in a novel porcine model. Ultrasound imaging was used to evaluate abscess maturity for treatment monitoring and assessment of post-treatment outcomes. Disinfection was quantified by counting bacteria colonies from samples aspirated before and after treatment. Histopathological evaluation of the abscesses was performed to identify changes resulting from histotripsy treatment and potential collateral damage. Cavitation histotripsy was more successful in reducing the bacterial load while having a smaller treatment volume compared with boiling histotripsy. The results of this pilot study suggest focused ultrasound may lead to a technology for in situ treatment of acoustically accessible abscesses. |
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Histotripsy treatment of abscesses Matula, T.J., Y.-N. Wang, T. Khokhlova, D.F. Leotta, J. Kucewicz, A.A. Brayman, M. Bruce, A.D. Maxwell, B.E. MacConaghy, G. Thomas, K. Richmond, K. Chan, and W. Monsky, "Histotripsy treatment of abscesses," in Proc., IEEE International Ultrasonics Symposium, 7-11 September, Las Vegas, NV, doi:10.1109/IUS46767.2020.9251683 (IEEE, 2020). |
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7 Sep 2020
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Abscesses are walled-off collections of infected fluids containing pus and bacteria. They are often treated with percutaneous drainage in which a drainage catheter may be sutured in place for up to several weeks. Complications such as clogged drains or secondary infections require rehospitalization and wound management. Bacteria are susceptible to mechanical damage, and thus we hypothesize that histotripsy may be a potential new paradigm for treating abscesses noninvasively, without the need for long term catheterization and antibiotics. We developed a porcine animal model that recapitulates some of the features of human abscesses (including size and loculations). Boiling and cavitation histotripsy treatments were applied to subcutaneous and intramuscular abscesses in this porcine model. Ultrasound imaging was used to evaluate abscess maturity, for treatment monitoring and assessment of post-treatment outcomes. Disinfection was quantified by counting bacteria colonies from samples aspirated before and after treatment. Histopathological evaluation of the abscesses was performed to identify changes resulting from histotripsy treatment and potential collateral damage. The results of this pilot study suggest focused ultrasound may lead to a technology for in situ treatment of acoustically accessible abscesses. |
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Ultrasound imaging of abscesses before and during histotripsy treatment Bruce, M., D.F. Leotta, Y.-N. Wang, T. Khokhlova, J. Kucewicz, A.D. Maxwell, K. Chan, W. Monsky, and T.J. Matula, "Ultrasound imaging of abscesses before and during histotripsy treatment," in Proc., IEEE International Ultrasonics Symposium, 7-11 September, Las Vegas, NV, doi:10.1109/IUS46767.2020.9251386 (IEEE, 2020). |
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7 Sep 2020
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Abscesses are walled-off collections of infected fluids most often treated with percutaneous drains placed under CT guidance. Complications such as clogged drains or secondary infections require rehospitalization and wound management. Histotripsy treatment has the potential to eliminate the need for long term catheterization and antibiotics. The progression of abscess development has yet to be fully described. The objective of this study was to use the latest advances in non-contrast ultrasound technologies to characterize abscess development in a porcine animal model. Intramuscular or subcutaneous injections of bacteria plus dextran particles as an irritant led to identifiable abscesses over a 2- to 3-week period. Ultrasound imaging was performed at least weekly, in some cases with a 3D tracking device that provided quantifiable size and shape measurements. Abscess progression was also measured with a plane-wave Doppler mode providing increased sensitivity to low-velocity flows, while abscess stiffness was quantified using shear wave elastography. Most of the mature abscesses were characterized by a rounded core of varying echogenicity surrounded by a hypoechoic capsule that was highly vascularized on Doppler imaging. A treatable abscess was defined by its hypervascular rim and avascular core. Stiffness varied within the abscess but generally decreased over time. Abscess echogenicity, shape, stiffness and vascularity potentially provide features to identify lesions suitable for treatment. |
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High-frequency nonlinear Doppler contrast-enhanced ultrasound imaging of blood flow Bruce, M., A. Hannah, R. Hammond, Z.Z. Khaing, C. Tremblay-Darveau, P.N. Burns, and C.P. Hofstetter, "High-frequency nonlinear Doppler contrast-enhanced ultrasound imaging of blood flow," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 67, 1778-1784, doi:10.1109/TUFFC.2020.2986486, 2020. |
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1 Sep 2020
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Current methods for in vivo microvascular imaging (<1 mm) are limited by the tradeoffs between the depth of penetration, resolution, and acquisition time. Ultrasound Doppler approaches combined at elevated frequencies (<7.5 MHz) are able to visualize smaller vasculature and, however, are still limited in the segmentation of lower velocity blood flow from moving tissue. Contrast-enhanced ultrasound (CEUS) has been successful in visualizing changes in microvascular flow at conventional diagnostic ultrasound imaging frequencies (<7.5 MHz). However, conventional CEUS approaches at elevated frequencies have met with limited success, due, in part, to the diminishing microbubble response with frequency. We apply a plane-wave acquisition combined with the non-linear Doppler processing of ultrasound contrast agents at 15 MHz to improve the resolution of microvascular blood flow while compensating for reduced microbubble response. This plane-wave Doppler approach of imaging ultrasound contrast agents also enables simultaneous detection and separation of blood flow in the microcirculation and higher velocity flow in the larger vasculature. We apply singular value decomposition filtering on the nonlinear Doppler signal to orthogonally separate the more stationary lower velocity flow in the microcirculation and higher velocity flow in the larger vasculature. This orthogonal separation was also utilized to improve time-intensity curve analysis of the microcirculation, by removing higher velocity flow corrupting bolus kinetics. We demonstrate the utility of this imaging approach in a rat spinal cord injury model, requiring submillimeter resolution. |
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Blind source separation for clutter and noise suppression in ultrasound imaging: Review for different applications Wildeboer, R.R., and 11 others including M. Bruce, "Blind source separation for clutter and noise suppression in ultrasound imaging: Review for different applications," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 67, 1497-1512, doi:10.1109/TUFFC.2020.2975483, 2020. |
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1 Aug 2020
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Blind source separation (BSS) refers to a number of signal processing techniques that decompose a signal into several "source" signals. In recent years, BSS is increasingly employed for the suppression of clutter and noise in ultrasonic imaging. In particular, its ability to separate sources based on measures of independence rather than their temporal or spatial frequency content makes BSS a powerful filtering tool for data in which the desired and undesired signals overlap in the spectral domain. The purpose of this work was to review the existing BSS methods and their potential in ultrasound imaging. Furthermore, we tested and compared the effectiveness of these techniques in the field of contrast-ultrasound super-resolution, contrast quantification, and speckle tracking. For all applications, this was done in silico , in vitro , and in vivo . We found that the critical step in BSS filtering is the identification of components containing the desired signal and highlighted the value of a priori domain knowledge to define effective criteria for signal component selection. |
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Effect of stiffness of large extravascular hematomas on their susceptibility to boiling histotripsy liquefaction in vitro Khokhlova, T.D., J.C. Kucewicz, E.M. Ponomarchuk, C. Hunter, M. Bruce, V.A. Khokhlova, T.J. Matula, and W. Monsky, "Effect of stiffness of large extravascular hematomas on their susceptibility to boiling histotripsy liquefaction in vitro," Ultrasound Med. Biol., 46, 2007-2016, doi:10.1016/j.ultrasmedbio.2020.04.023, 2020. |
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1 Aug 2020
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Large intra-abdominal, retroperitoneal and intramuscular hematomas are common consequences of sharp and blunt trauma and post-surgical bleeds, and often threaten organ failure, compartment syndrome or spontaneous infection. Current therapy options include surgical evacuation and placement of indwelling drains that are not effective because of the viscosity of the organized hematoma. We have previously reported the feasibility of using boiling histotripsy (BH) — a pulsed high-intensity focused ultrasound method — for liquefaction of large volumes of freshly coagulated blood and subsequent fine-needle aspiration. The goal of this work was to evaluate the changes in stiffness of large coagulated blood volumes with aging and retraction in vitro, and to correlate these changes with the size of the BH void and, therefore, the susceptibility of the material to BH liquefaction. Large-volume (55–200 mL) whole-blood clots were fabricated in plastic molds from human and bovine blood, either by natural clotting or by recalcification of anticoagulated blood, with or without addition of thrombin. Retraction of the clots was achieved by incubation for 3 h, 3 d or 8 d. The shear modulus of the samples was measured with a custom-built indentometer and shear wave elasticity (SWE) imaging. Sizes of single liquefied lesions produced with a 1.5-MHz high-intensity focused ultrasound transducer within a 30-s standard BH exposure served as the metric for susceptibility of clot material to this treatment. Neither the shear moduli of naturally clotted human samples (0.52 ± 0.08 kPa), nor their degree of retraction (ratio of expelled fluid to original volume 50%––58%) depended on the length of incubation within 0–8 d, and were significantly lower than those of bovine samples (2.85 ± 0.17 kPa, retraction 5%–38%). In clots made from anticoagulated bovine blood, the variation of calcium chloride concentration within 5––40 mmol/L did not change the stiffness, whereas lower concentrations and the addition of thrombin resulted in significantly softer clots, similar to naturally clotted human samples. Within the achievable shear modulus range (0.4–1.6 kPa), the width of the BH-liquefied lesion was more affected by the changes in stiffness than the length of the lesion. In all cases, however, the lesions were larger compared with any soft tissue liquefied with the same BH parameters, indicating higher susceptibility of hematomas to BH damage. These results suggest that clotted bovine blood with added thrombin is an acceptable in vitro model of both acute and chronic human hematomas for assessing the efficiency of BH liquefaction strategies. |
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Imaging methods for ultrasound contrast agents Averkiou, M.A., M.F. Bruce, J.E. Powers, P.S. Sheeran, and P.N. Burns, "Imaging methods for ultrasound contrast agents," Ultrasound Med. Biol., 46, 498-517, doi:10.1016/j.ultrasmedbio.2019.11.004, 2020. |
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1 Mar 2020
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Microbubble contrast agents were introduced more than 25 years ago with the objective of enhancing blood echoes and enabling diagnostic ultrasound to image the microcirculation. Cardiology and oncology waited anxiously for the fulfillment of that objective with one clinical application each: myocardial perfusion, tumor perfusion and angiogenesis imaging. What was necessary though at first was the scientific understanding of microbubble behavior in vivo and the development of imaging technology to deliver the original objective. And indeed, for more than 25 years bubble science and imaging technology have evolved methodically to deliver contrast-enhanced ultrasound. Realization of the basic bubbles properties, non-linear response and ultrasound-induced destruction, has led to a plethora of methods; algorithms and techniques for contrast-enhanced ultrasound (CEUS) and imaging modes such as harmonic imaging, harmonic power Doppler, pulse inversion, amplitude modulation, maximum intensity projection and many others were invented, developed and validated. Today, CEUS is used everywhere in the world with clinical indications both in cardiology and in radiology, and it continues to mature and evolve and has become a basic clinical tool that transforms diagnostic ultrasound into a functional imaging modality. In this review article, we present and explain in detail bubble imaging methods and associated artifacts, perfusion quantification approaches, and implementation considerations and regulatory aspects. |
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Transcutaneous contrast-enhanced ultrasound imaging of the posttraumatic spinal cord Khaing, Z.Z., L.N. Cates, J.E. Hyde, R. Hammond, M. Bruce, and C.P. Hofstetter, "Transcutaneous contrast-enhanced ultrasound imaging of the posttraumatic spinal cord," Spinal Cord, 56, 695-704, doi:10.1038/s41393-020-0415-9, 2020. |
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21 Jan 2020
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The current study aims to test whether the blood flow within the contused spinal cord can be assessed in a rodent model via the acoustic window of the laminectomy utilizing transcutaneous ultrasound. |
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Modeling the acoustic field produced by diagnostic ultrasound arrays in plane and diverging wave modes Lai, T.-Y., M. Bruce, M.A. Averkiou, "Modeling the acoustic field produced by diagnostic ultrasound arrays in plane and diverging wave modes," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 66, 1158-1169, doi:10.1109/TUFFC.2019.2908831, 2019. |
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1 Jul 2019
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Recent advances in ultrafast contrast imaging have facilitated innovations, such as superresolution imaging and ultrafast contrast-enhanced Doppler imaging. Combining plane and diverging wave imaging (PWI/DWI) with tissue harmonic imaging (THI) may offer improvements in image quality in applications such as 3-D THI and harmonic color flow. However, no studies have reported simulations of the nonlinear acoustic fields produced by diagnostic arrays in either plane or diverging wave mode. The aim of this study is to model three typical diagnostic arrays that are used in clinical practice and research, Verasonics L11-4v linear array, C5-2v convex array, and P4-2v phased array with the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation. We have two specific objectives: first, to investigate whether there is increased bubble destruction due to the nature of the plane and diverging fields in contrast imaging; and second, to investigate the feasibility of combining PWI/DWI and THI by quantifying the second harmonic generated by these fields. We showed in linear simulations that using such arrays for ultrafast contrast imaging produced pressures that are greater in the near field and lower in the far field than those of focused beams and thus may induce more near-field bubble destruction. In nonlinear simulations, the second harmonic produced by ultrafast THI was found to be 2–16 dB lower than that of focused beams for all arrays considered when operated at the same MI. This moderate difference of the second harmonic between PWI/DWI and focused ultrasound suggests that it is feasible to combine PWI/DWI and THI. |
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Deep learning for super-resolution vascular ultrasound imaging van Sloun, R.J.G., O. Solomon, M. Bruce, Z.Z. Khaing, Y.C. Eldar, and M. Mischi, "Deep learning for super-resolution vascular ultrasound imaging," Proc., IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 12-17 May, Brighton, United Kingdom, doi:10.1109/ICASSP.2019.8683813 (IEEE, 2019). |
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12 May 2019
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Based on the intravascular infusion of gas microbubbles, which act as ultrasound contrast agents, ultrasound localization microscopy has enabled super resolution vascular imaging through precise detection of individual microbubbles across numerous imaging frames. However, analysis of high-density regions with significant overlaps among the microbubble point spread functions typically yields high localization errors, constraining the technique to low-concentration conditions. As such, long acquisition times are required for sufficient coverage of the vascular bed. Algorithms based on sparse recovery have been developed specifically to cope with the overlapping point-spread-functions of multiple microbubbles. While successful localization of densely-spaced emitters has been demonstrated, even highly optimized fast sparse recovery techniques involve a time-consuming iterative procedure. In this work, we used deep learning to improve upon standard ultrasound localization microscopy (Deep-ULM), and obtain super-resolution vascular images from high-density contrast-enhanced ultrasound data. Deep-ULM is suitable for real-time applications, resolving about 1250 high-resolution patches (128 x 128 pixels) per second using GPU acceleration. |
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Ultrasound imaging of micro bubble activity during sonoporation pulse sequences Keller, S., M. Bruce, and M.A. Averkiou, "Ultrasound imaging of micro bubble activity during sonoporation pulse sequences," Ultrasound Med. Biol., 45, 833-845, doi:10.1016/j.ultrasmedbio.2018.11.011, 2019. |
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1 Mar 2019
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Ultrasound-mediated drug delivery using the mechanical action of oscillating and/or collapsing microbubbles has been studied on many different experimental platforms, both in vitro and in vivo; however, the mechanisms remain to be elucidated. Many groups use sterile, enclosed chambers, such as Opticells and Clinicells, to optimize acoustic parameters in vitro needed for effective drug delivery in vivo, as well as for mechanistic investigation of sonoporation or the use of sound to permeate cell membranes. In these containers, cell monolayers are seeded on one side, and the remainder of the volume is filled with a solution containing microbubbles and a model drug. Ultrasound is then applied to study the effect of different parameters on model drug uptake in cell monolayers. Despite the simplicity of this system, the field has been unable to appropriately address what parameters and microbubble concentrations are most effective at enhancing drug uptake and minimizing cellular toxicity. In this work, a common in vitro sonoporation experimental setup was characterized through quantitative analysis of microbubble-dependent acoustic attenuation in combination with high-frame-rate and high-resolution imaging of bubble activity during sonoporation pulse sequences. The goal was to visualize the effect that ultrasound parameters have on microbubble activity. It was observed that under literature-derived sonoporation conditions (0.1–1 MPa, 20–1000 cycles and 10,000 to 10,000,000 microbubbles/mL), there is strong and non-linear acoustic attenuation, as well as bubble destruction, gas diffusion and bubble motion resulting in spatiotemporal pressure and concentration gradients. Ultimately, it was found that the acoustic conditions in common in vitro sonoporation setups are much more complex and confounding than often assumed. |
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Spontaneous nucleation of stable perfluorocarbon emulsions for ultrasound contrast agents Li, D.S., S. Schneewind, M. Bruce, Z. Khaing, M. O'Donnell, and L. Pozzo, "Spontaneous nucleation of stable perfluorocarbon emulsions for ultrasound contrast agents," Nano Lett., 19, 173-181, doi:10.1021/acs.nanolett.8b03585, 2019. |
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9 Jan 2019
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Phase-change contrast agents are rapidly developing as an alternative to microbubbles for ultrasound imaging and therapy. These agents are synthesized and delivered as liquid droplets and vaporized locally to produce image contrast. They can be used like conventional microbubbles but with the added benefit of reduced size and improved stability. Droplet-based agents can be synthesized with diameters on the order of 100 nm, making them an ideal candidate for extravascular imaging or therapy. However, their synthesis requires low boiling point perfluorocarbons (PFCs) to achieve activation (i.e., vaporization) thresholds within FDA approved limits. Minimizing spontaneous vaporization while producing liquid droplets using conventional methods with low boiling point PFCs can be challenging. In this study, a new method to produce PFC nanodroplets using spontaneous nucleation is demonstrated using PFCs with boiling points ranging from –37 to 56°C. Sometimes referred to as the ouzo method, the process relies on saturating a cosolvent with the PFC before adding a poor solvent to reduce solvent quality, forcing droplets to spontaneously nucleate. This approach can produce droplets ranging from under 100 nm to over 1 μm in diameter. Ternary plots showing solvent and PFC concentrations leading to droplet nucleation are presented. Additionally, acoustic activation thresholds and size distributions with varying PFC and solvent conditions are measured and discussed. Finally, ultrasound contrast imaging is demonstrated using ouzo droplets in an animal model. |
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3D perfusion imaging using principal curvature detection rendering Tremblay-Darveau, C., P.S. Sheeran, C.K. Vu, R. Williams, M. Bruce, and P.N. Burns, "3D perfusion imaging using principal curvature detection rendering," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 65, 2286-2295, doi:10.1109/TUFFC.2018.2854727, 2018. |
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1 Dec 2018
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Three-dimensional contrast-enhanced ultrasound (CEUS) imaging presents a clear advantage over its 2D counterpart in detecting and characterizing suspicious lesions as it properly surveys the inherent heterogeneity of tumours. However, 3D CEUS is also slow compared to 2D CEUS and tends to undersample the microbubble wash-in. This makes it difficult to resolve the feeding vessels, an important oncogenic marker, from the background perfusion cloud. Contrast-enhanced Doppler is helpful in isolating this conduit flow, but requires too many pulses in conventional line-by-line beamforming design. Recent breakthroughs in plane-wave imaging have greatly accelerated the volumetric imaging frame rate, but volumetric Doppler angiography still remains challenging when considering realtime limitations on the Doppler ensemble length. In this work, we demonstrate the feasibility of volumetric CEUS angiography subjected to real-time imaging constraints. Namely, we show how principal curvature detection can significantly improve 3D rendering of relatively noisy ultrasound angiograms without degrading the spatial resolution while subjected to a reasonable Doppler ensemble size. Singular Value Decomposition is also shown to be capable of identifying the quasi-stationary capillary perfusion. |
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Contrast-enhanced ultrasound to visualize hemodynamic changes after rodent spinal cord injury Khaing, Z.Z., L.N. Cates, D.M. DeWees, A. Hannah, P. Mourad, M. Bruce, and C.P. Hofstetter, "Contrast-enhanced ultrasound to visualize hemodynamic changes after rodent spinal cord injury," J. Neurosurg. Spine, 29, 235-350, doi:10.3171/2018.1.SPINE171202, 2018. |
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1 Sep 2018
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Traumatic spinal cord injury (tSCI) causes an almost complete loss of blood flow at the site of injury (primary injury) as well as significant hypoperfusion in the penumbra of the injury. Hypoperfusion in the penumbra progresses after injury to the spinal cord and is likely to be a major contributor to progressive cell death of spinal cord tissue that was initially viable (secondary injury). Neuroprotective treatment strategies seek to limit secondary injury. Clinical monitoring of the temporal and spatial patterns of blood flow within the contused spinal cord is currently not feasible. The purpose of the current study was to determine whether ultrafast contrast-enhanced ultrasound (CEUS) Doppler allows for detection of local hemodynamic changes within an injured rodent spinal cord in real time. |
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The role of microbubble echo phase lag in multipulse contrast-enhanced ultrasound imaging Tremblay-Darveau, C., P.S. Sheeran, C.K. Vu, R. Williams, Z. Zhang, M. Bruce, and P.N. Burns, "The role of microbubble echo phase lag in multipulse contrast-enhanced ultrasound imaging," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 65, 1389-1401, doi:10.1109/TUFFC.2018.2841848, 2018. |
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1 Aug 2018
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In this paper, we assess the importance of microbubble shell composition for contrast-enhanced imaging sequences commonly used on clinical scanners. While the gas core dynamics are primarily responsible for the nonlinear harmonic response of microbubbles at diagnostic pressures, it is now understood that the shell rheology plays a dominant role in the nonlinear response of microbubbles subjected to low acoustic pressures. Of particular interest here, acoustic pressures of tens of kilopascal can cause a reversible phase transition of the phospholipid coatings from a stiff elastic organized state to a less stiff disorganized buckled state. Such a transition from elastic to buckled shell induces a steep variation of the shell elasticity, which alters the microbubble acoustic scattering properties. We demonstrate in this paper that this mechanism plays a dominant role in contrast pulse sequences that modulate the amplitude of the insonifying pulse pressure. The contrast-to-tissue ratio (CTR) for amplitude modulation (AM), pulse inversion (PI), and amplitude modulation pulse inversion (AMPI) is measured in vitro for Definity, Sonazoid, both lipid-encapsulted microbubbles, and the albumin-coated Optison. It is found that pulse sequences using AM significantly enhanced the nonlinear response of all studied microbubbles compared to PI (up to 15 dB more) when low insonation pressures under 200 kPa were used. Further investigation reveals that the origin of the hyperechoicity is a small phase lag occurring between the echoes from the full-and half-amplitude driving pulses, and that the effect could be attributed to the shell softening dynamics of lipid and albumin coatings. We assess that this additional phase in microbubble ultrasound scattering can have a dominant role in the CTR achieved in contrast sequences using AM. We also show that the pressure dependent phase lag is a specific marker for microbubbles with no equivalent in tissue, which can be used to segment microbubbles from the tissue harmonics and significantly increase the CTR. |
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PD37-09 kidney stone contrast with color-Doppler twinkling artifact as a function of mechanical index Cunitz, B., J. Dai, M. Sorenson, R. Sweet, B. Dunmire, J. Thiel, M. Bruce, M. Bailey, Z. Liu, and J. Harper, "PD37-09 kidney stone contrast with color-Doppler twinkling artifact as a function of mechanical index," J. Urol., 199, e734, doi:10.1016/j.juro.2018.02.1744, 2018. |
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1 Apr 2018
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Kidney stones can exhibit a twinkling artifact under color-flow Doppler ultrasound. There has been much work that suggests the mechanism for this artifact is micron sized bubbles trapped in the cracks of the stone cavitating from the incident Doppler pulses. We hypothesize that the signal-to-clutter ratio (SCR) of stone-to-background in Doppler mode increases with the ultrasound mechanical index (MI), a metric of the likelihood of cavitation, and that a minimum MI is needed for visibility under Doppler. |
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Quantification of renal stone contrast with ultrasound in human subjects Cunitz, B.W., J.D. Harper, M.D. Sorensen, Y.A. Haider, J. Thiel, P.C. May, Z. Liu, M.R. Bailey, B. Dunmire, and M. Bruce, "Quantification of renal stone contrast with ultrasound in human subjects," J. Endourol., 31, 1123-1130, doi:10.1089/end.2017.0404, 2017. |
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1 Nov 2017
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Purpose: Greater visual contrast between calculi and tissue would improve ultrasound (US) imaging of urolithiasis and potentially expand clinical use. The color Doppler twinkling artifact has been suggested to provide enhanced contrast of stones compared with brightness mode (B-mode) imaging, but results are variable. This work provides the first quantitative measure of stone contrast in humans for B-mode and color Doppler mode, forming the basis to improve US for the detection of stones. |
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Contrast enhanced ultrasound(CEUS) imaging of rat spinal cord injury Bruce, M., A. Hannah, Z. Khaing, C. Tremblay-Darveau, C. Hofstetter, and P. Burns, "Contrast enhanced ultrasound(CEUS) imaging of rat spinal cord injury," Proc., IEEE International Ultrasonics Symposium, 6-9 September, Washington, D.C., doi:10.1109/ULTSYM.2017.8092033 (IEEE, 2017). |
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6 Sep 2017
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Traumatic spinal cord injury (tSCI) often leads to debilitating neurological disabilities that in addition to the loss of sensory and motor capabilities, also includes other issues with the bladder, heart and respiration. Overall, tSCI results in a drastic decrease in the quality of life. Traumatic spinal cord injury causes an almost complete loss of blood flow at the site of injury (primary injury) as well as significant ischemia surrounding the injury, resulting in progressive additional cell death over time (secondary injury). Counteracting secondary injury of spinal cord tissue surrounding tSCI is an active area of research to improve outcomes. There are no existing techniques to assess simultaneously both temporal and spatial changes in blood flow of contused spinal cord tissue in experimental settings. The goal of this work was to visualize temporal and spatial changes in blood flow following tSCI in a rat spinal cord injury model. |
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High resolution ultrafast imaging of microbubble destruction during sonoporation Keller, S., R. Zong, A. Hannah, M. Bruce, and M. Averkiou, "High resolution ultrafast imaging of microbubble destruction during sonoporation," Proc., IEEE International Ultrasonics Symposium, 6-9 September, Washington, D.C., doi: 10.1109/ULTSYM.2017.8091583 (IEEE, 2017). |
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6 Sep 2017
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Ultrasound-mediated drug delivery using microbubbles is a growing field with applications ranging from targeted chemotherapy delivery to permeating the blood brain barrier. However, the precise parameters that induce increased cellular permeability are not fully understood. For sonoporation efficiency, a high microbubble concentration is preferred, but acoustic shadowing limits the ultrasound delivery to the cells. Our hypothesis is that high-resolution ultrafast imaging will demonstrate the interaction of ultrasound with microbubbles during the sonoporation process to carefully control the ultrasound dose. This work has two aims: 1) to accurately image the ultrasound delivery to cells with high-resolution ultrafast imaging, and 2) to determine the dependence of microbubble concentration and acoustic environment on cavitation activity. This will lead to optimization of sonoporation. |
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Improved contrast-enhanced power Doppler using a coherence-based estimator Tremblay-Darveau, C., A. Bar-Zion, R. Williams, P.S. Sheeran, L. Milt, T. Loupas, D. Adam, M. Bruce, and P.N. Burns, "Improved contrast-enhanced power Doppler using a coherence-based estimator," IEEE Trans. Med. Imaging, 36, 1901-1911, doi:10.1109/TMI.2017.2699672, 2017. |
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1 Sep 2017
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While plane-wave imaging can improve the performance of power Doppler by enabling much longer ensembles than systems using focused beams, the long-ensemble averaging of the zero-lag autocorrelation R(0) estimates does not directly decrease the mean noise level, but only decreases its variance. Spatial variation of the noise due to the time-gain compensation and the received beamforming aperture ultimately limits sensitivity. In this paper, we demonstrate that the performance of power Doppler imaging can be improved by leveraging the higher lags of the autocorrelation [e.g., R(1), R(2),...] instead of the signal power (R(0)). As noise is completely uncorrelated from pulse-to-pulse while the flow signal remains correlated significantly longer, weak signals just above the noise floor can be made visible through the reduction of the noise floor. Finally, as coherence decreases proportionally with respect to velocity, we demonstrate how signal coherence can be targeted to separate flows of different velocities. For instance, we show how long-time-range coherence of microbubble contrast-enhanced flow specifically isolates slow capillary perfusion (as opposed to conduit flow). |
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Limitations and artifacts in shear-wave elastography of the liver Bruce, M., O. Kolokythas, G. Ferraioli, C. Filice, and M. O'Donnell, "Limitations and artifacts in shear-wave elastography of the liver," Biomed. Eng. Lett., 7, 81-89, doi:, 2017. |
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1 May 2017
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Recent studies have shown that real-time, two-dimensional shear-wave elastography (2D-SWE) can monitor liver fibrosis by measuring tissue elasticity (i.e., elastic modulus). Two clinical studies of 2D-SWE in the liver have shown that there are several practical issues that can compromise quantitation of liver tissue elasticity. Both general ultrasound (US) limitations and limitations in the 2D-SWE method itself resulted in significant variability in estimated liver elasticity. The most common US limitations were: poor acoustic window, limited penetration, and rib/lung shadows. The most common 2D-SWE limitations were: reverberations under the liver capsule, respiratory/cardiac motion, and vessel pulsation/loss of SWE signal. Based on these studies, scan protocols have been optimized to minimize the influence of these limitations on liver elasticity quantification. These refined protocols should move non-invasive SWE closer to becoming the preferred tool to diagnose and manage many chronic diseases of the liver. |
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Feasibility of pulse wave velocity estimation from low frame rate US sequences in vivo Zontak, M., M. Bruce, M. Hippke, A. Schwartz, and M. O'Donnell, "Feasibility of pulse wave velocity estimation from low frame rate US sequences in vivo," Proc. SPIE 10139, Medical Imaging: Ultrasonic Imaging and Tomography, 13 March, Orlando, FL, doi:10.1117/12.2255535 (SPIE, 2017). |
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13 Mar 2017
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The pulse wave velocity (PWV) is considered one of the most important clinical parameters to evaluate CV risk, vascular adaptation, etc. There has been substantial work attempting to measure the PWV in peripheral vessels using ultrasound (US). This paper presents a fully automatic algorithm for PWV estimation from the human carotid using US sequences acquired with a Logic E9 scanner (modified for RF data capture) and a 9L probe. Our algorithm samples the pressure wave in time by tracking wall displacements over the sequence, and estimates the PWV by calculating the temporal shift between two sampled waves at two distinct locations. Several recent studies have utilized similar ideas along with speckle tracking tools and high frame rate (above 1 KHz) sequences to estimate the PWV. To explore PWV estimation in a more typical clinical setting, we used focused-beam scanning, which yields relatively low frame rates and small fields of view (e.g., 200 Hz for 16.7 mm filed of view). For our application, a 200 Hz frame rate is low. In particular, the sub-frame temporal accuracy required for PWV estimation between locations 16.7 mm apart, ranges from 0.82 of a frame for 4 m/s, to 0.33 for 10 m/s. When the distance is further reduced (to 0.28 mm between two beams), the sub-frame precision is in parts per thousand (ppt) of the frame (5 ppt for 10 m/s). As such, the contributions of our algorithm and this paper are: |
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Elastography of diffuse liver diseases Dighe, M., and M. Bruce, "Elastography of diffuse liver diseases," Sem. Roentgenol., 51, 358-366, doi:10.1053/j.ro.2016.05.002, 2016. |
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1 Oct 2016
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Liver elastography is a noninvasive marker for liver fibrosis and cirrhosis with good and excellent diagnostic accuracy. It has several advantages over liver biopsy, however, elastography still needs to find its place in clinical practice. In etiologies other than HCV, there is a large potential for further research. Alcoholic and nonalcoholic liver diseases now account for most liver disease, large, well-performed diagnostic accuracy studies of elastography in this population are missing. Elastography would be used in an increasing number of clinical situations, however, elastography has be performed by experienced operators and the results should be interpreted with the techniques limitations in mind. |
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In The News
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Harnessing the 'ouzo effect' for better ultrasound imaging UW Chemical Engineering, Lindsey Doermann CIMU scientists are collaborating with engineering and neurological surgery researchers to develop new ultrasound contrast agents. They dissolve perfluorocarbons (PFCs) in ethanol and then add a water-based solution, causing the PFC to come out of solution and form nanodroplets on the order of 100 nm in diameter, which is small enough to diffuse out of blood vessels. |
3 Jan 2019
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