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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 wash-out 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.

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.

Abscesses are walled-off collections of infected fluids that often develop as complications in the setting of surgery and trauma. Abscess care depends on size, location, composition and complexity, among other patient factors. The goal of this work is to describe, using the latest ultrasound imaging technologies, the progression of 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. The abscesses were imaged at least weekly with B-mode, 3D B-mode, shear-wave elastography (SWE) and color flow 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. Size and shape changes during development were quantified with 3D imaging. With SWE, the lesion stiffness varied interiorly and generally decreased over time. These ultrasound features potentially provide biomarkers to facilitate improved selection of treatment strategies for abscesses.

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 wash-out 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.

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.

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.

Objective:We developed a duplex ultrasound simulator and used it to assess accuracy of volume flow measurements in dialysis access fistula (DAF) models.Methods:The simulator consists of a mannequin, computer, and mock transducer. Each case is built from a patient’s B-mode images that are used to create a 3-dimensional surface model of the DAF. Computational fluid dynamics is used to determine blood flow velocities based on model vessel geometry. The simulator displays real-time B-mode and color-flow images, and Doppler spectral waveforms are generated according to user-defined settings. Accuracy was assessed by scanning each case and measuring volume flow in the inflow artery and outflow vein for comparison with true volume flow values.Results:Four examiners made 96 volume flow measurements on four DAF models. Measured volume flow deviated from the true value by 35 ± 36%. Mean absolute deviation from true volume flow was lower for arteries than veins (22 ± 19%, N = 48 vs. 58 ± 33%, N = 48, p < 0.0001). This finding is attributed to eccentricity of outflow veins which resulted in underestimating true cross-sectional area. Regression analysis indicated that error in measuring cross-sectional area was a predictor of error in volume flow measurement (β = 0.948, p < 0.001). Volume flow error was reduced from 35 ± 36% to 9 ± 8% ( p < 0.000001) by calculating vessel area as an ellipse.Conclusions:Duplex volume flow measurements are based on a circular vessel shape. DAF inflow arteries are circular, but outflow veins can be elliptical. Simulation-based analysis showed that error in measuring volume flow is mainly due to assumption of a circular vessel.

Ultrasonographic (US) assessment of abdominal aortic aneurysms is typically performed by measuring maximal aneurysm diameter from two-dimensional images. These measurements are prone to inaccuracies owing to image planes and interobserver variability. The purpose of this study was to compare the variability in diameter, cross-sectional area (CSA), and volume measurements of abdominal aortic aneurysms obtained using a three-dimensional (3D) US imaging system with those obtained using computed tomographic (CT) angiography, and to determine the reliability of these measures.Seven patients in whom endovascular aneurysm repairs were performed underwent CT angiography in addition to a 3D US scan. Measurements computed using 3D surface reconstructions of CT and 3D US scans included maximum diameter, CSA, and aneurysm volume. The seven matched CT and 3D US scans were compared at baseline and 6 to 8 weeks later.The average aneurysm measured 57.2 mm on CT and 56.2 mm on US (P = 0.14). Correlation coefficients for diameter, CSA, and volume were 0.88, 0.90, and 0.93, respectively (all P values0.001). A Bland-Altman analysis demonstrated a strong agreement between 92% of the diameter, 96.4% of the CSA, and 100% of the volume measurements. The interrater reliability was remarkably high comparing the modalities (CT vs. US), and ranged from 0.934 to 0.997 for single measurements and 0.965 to 0.998 for all measurements together; moreover, there was a strong reliability when the tests were reviewed 6 to 8 weeks later, with a reliability of 0.962 to 0.998 for single measurements and 0.992 to 0.999 for all tests (all P values0.001).The 3D US is an accurate and noninvasive method of determining aneurysm size and geometry that is reproducible. Volumetric measurements may represent a significant advancement in long-term follow-up after endovascular aneurysm repair.

The association between ambient fine particulate matter (PM) air pollution [particles with aerodynamic diameter ≤ 2.5 μm (PM2.5)] and increased cardiovascular morbidity and mortality in epidemiologic studies (Dominici et al. 2006; Miller et al. 2007; Pope et al. 2002) has led to investigation of underlying mechanisms, which remain cryptic (Bhatnagar 2006). Several studies link ambient (especially combustion-derived) PM with increased vascular tone (Brook et al. 2002; Campen et al. 2005; Proctor et al. 2006), and animal studies showed possible involvement of sympathetic nervous system activation (Proctor et al. 2006) and vasoconstriction pathways (Bouthillier et al. 1998; Li et al. 2005). Evidence suggests that the effect of PM on vascular reactivity may be greater in individuals at risk for coronary artery disease (O’Neill et al. 2005). Human studies to date have provided limited insight into the mechanism of the vascular effects of PM, although recent evidence has documented enhanced exercise-induced ischemia with controlled exposure to diesel exhaust (DE) (Mills et al. 2007). DE is a complex mixture of particulate and gaseous pollutants that comprise a substantial and biologically active fraction of urban ambient air pollution (Health Effects Institute 1995) and is a very appropriate experimental model exposure, especially with the current interest in traffic-related air pollution. Evidence suggests that inhalation of DE is associated with perturbation in endothelial function (Campen et al. 2005; Mills et al. 2005; Tornqvist et al. 2007). We exposed young adults, healthy or with metabolic syndrome, to DE under controlled settings. Young adults with metabolic syndrome have increased subclinical atherosclerosis (Tzou et al. 2005) and are at increased risk for cardiovascular morbidity and mortality (Isomaa et al. 2001). We focused on individuals with metabolic syndrome because they might be more susceptible to DE effects. We hypothesized that DE inhalation would result in vaso-constriction and decreased endothelium-dependent flow-mediated dilation (FMD) of the brachial artery within 30 min of exposure. We also hypothesized that vascular effects of DE might be related to activation of the sympathetic nervous system or increased release of the endothelium-dependent vasoconstrictor endothelin-1 (ET-1).

Women who develop preeclampsia have a higher risk of future cardiovascular disease and diabetes compared to women who have uncomplicated pregnancies. We hypothesized that women with prior preeclampsia would have increased visceral adiposity that would be a major determinant of their metabolic and cardiovascular risk factors.We compared intraabdominal fat (IAF) area, insulin sensitivity index (SI), fasting lipids, low-density lipoprotein relative flotation rate, and brachial artery flow-mediated dilatation in 49 women with prior preeclampsia and 22 controls who were at least 8 months postpartum and matched for age, parity, body mass index, and months postpartum. Women were eligible if they did not smoke tobacco, use hormonal contraception, have chronic hypertension, or have a history of gestational diabetes.The groups were similar for age (mean ± SD: prior preeclampsia 33.4 ± 6.6 vs control 34.6 ± 4.3 years), parity (median: 1 for both), body mass index (26.7 ± 5.9 vs 24.0 ± 7.3 kg/m(2)), and months postpartum (median [25th-75th percentile]: 16 [13-38] vs 16.5 [13-25]). There were no significant differences in IAF area and SI. Despite this, women with preeclampsia had lower high-density lipoprotein (46.0 ± 10.7 vs 51.3 ± 9.3 mg/dL; P.05), smaller/denser low-density lipoprotein relative flotation rate (0.276 ± 0.022 vs 0.289 ± 0.016; P = .02), higher systolic (114.6 ± 10.9 vs 102.3 ± 7.5 mm Hg) and diastolic (67.6 ± 7.5 vs 60.9 ± 3.6 mm Hg; P.001) blood pressures, and impaired flow-mediated dilatation (4.5 [2-6.7] vs 8.8 [4.5-9.1] percent change, P.05) compared to controls. In a subgroup analysis, women with nonsevere preeclampsia (n = 17) had increased IAF (98.3 [60.1-122.2]) vs 63.1 [40.1-70.7] cm(2); P = .02) and decreased SI (4.18 [2.43-5.25] vs 5.5 [3.9-8.3] × 10(-5) min(-1)/pmol/L; P = .035) compared to the controls, whereas women with severe preeclampsia (n = 32) were not different for IAF and SI. IAF was negatively associated with SI and positively associated with cardiovascular risk factors even after adjusting for the matching variables and total body fat.Women with prior preeclampsia have an atherogenic lipid profile and endothelial dysfunction compared to matched control subjects despite having similar adiposity and insulin sensitivity, suggesting that there are mechanisms separate from obesity and insulin resistance that lead to their cardiovascular risk factors. Visceral adiposity may have a role in contributing to these risk factors in the subgroup of women who have preeclampsia without severe features.

Objective: Remodeling of vein grafts in the lower limb can lead to stenotic lesions that threaten long-term graft patency. Progressive changes in vein graft geometry were measured at sites of repaired stenoses with three-dimensional (3D) ultrasound imaging. Methods: Ten vein graft revisions with patch angioplasty were followed up for 31 to 47 weeks. Four revisions were at valve sites, and six were at sites of diffuse intimal hyperplasia. Sets of spatially registered two-dimensional (2D) cross-sectional ultrasound images were assembled to create 3D computer models of each vein graft. Cross-sectional area measurements in planes normal to the vessel center axis were calculated from the 3D surface reconstructions. Data sets from serial studies were registered in a common coordinate system, and cross-sectional area measurements were compared at matched sites. Results: Three of the four vein graft revisions at valve sites changed by less than 18%, and one decreased in cross-sectional area by 61%. Five of the six revisions at sites of diffuse intimal hyperplasia demonstrated significant decreases in lumen area ranging from 26% to 61%, and one revision exhibited no significant change in cross-sectional area. Reproducibility of the cross-sectional area measurements derived from the 3D imaging technique was 6.9%. Conclusions: Sequential area measurements from 3D ultrasound scans demonstrated different remodeling patterns and rates of change among revision sites within the vein grafts. Lumen narrowing documented with 3D scanning was not associated with consistent flow velocity changes on conventional duplex graft surveillance scans. (J Vasc Surg 2003;37:798-807.)

Physician-modified endovascular grafts, with fenestrations added to accommodate major branch vessels, provide a means for endovascular treatment of abdominal aortic aneurysms that are adjacent to the renal arteries. Manual measurements of vessel origin locations from computed tomography images, however, take time and can lead to errors in the positions of the fenestrations. To make the fenestration process faster and more accurate, we have developed a procedure to create custom templates that serve as patient-specific guides for graft fenestration. We use a three-dimensional printer to create a clear rigid sleeve that replicates the patient's aorta and includes holes placed precisely at the locations of the branch vessels. The sleeve is slipped over the graft, the locations of the openings are marked with a pen, and the fenestrations are created after the sleeve is removed. Custom fenestration templates can potentially save procedural costs and make minimally invasive aortic aneurysm repair available to more patients.

The objective of this study was to develop and validate a three-dimensional technique of left ventricular shape analysis. Geometric phantoms and left ventricles of excised calf hearts, normal human subjects, and one subject each with aortic stenosis and dilated cardiomyopathy were reconstructed from three-dimensional echocardiograms. The fit between the reconstructions and true surfaces of the geometric phantoms and excised ventricles was determined. To evaluate in vivo left ventricular shape, a center axis was constructed from the centroid of the mitral annulus to the furthest endocardial point. Regional shape was evaluated as the relative distances of 16 separate myocardial segments from the center axis compared with a population-derived mean value. Global shape was evaluated as the average standard deviation from the normal value over the 16 segments. The system precisely reproduced the shapes of the phantoms and excised left ventricles (root-mean-square error between true and reconstructed surface 1.0 0.2 mm and 1.2 0.8 mm, respectively). The in vivo shape analysis differentiated the pathological from normal left ventricles. (J Am Soc Echocardiogr 1998;11:761-9.)

Accurate measurement of left-ventricular (LV) volume and function are important to monitor disease progression and assess prognosis in patients with heart disease. Existing methods of three-dimensional (3-D) imaging of the heart using ultrasound have shown the potential of this modality, but each suffers from inherent restrictions which limit its applicability to the full range of clinical situations. The authors have developed a technique for image acquisition using a magnetic-field system to track the 3-D echocardiographic imaging planes and 3-D image analysis software including the piecewise smooth subdivision method for surface reconstruction. The technique offers several advantages over existing methods of 3-D echocardiography. The results of validation using in vitro LV's show that the technique allows accurate measurement of LV volume and anatomically accurate 3-D reconstruction of LV shape and is, therefore, suitable for analysis of regional as well as global function.

Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patients with End-Stage Renal Disease (ESRD). Producing an autogenous shunt linking an artery and a vein in the peripheral circulation bypasses the high resistance capillary bed in order to provide the necessary flow rates at sites easily accessible for dialysis. It has long been recognized that hemodynamics constitute the primary external influence on the remodeling process of anastomosed vascular tissue [1, 2]. The high flow rate, together with the exposure of the venous tissue to the high arterial pressure, leads to a rapid process of wall remodeling that may lead to a mature access or end in failure. Recent hemodynamic simulations [3, 4] have computed very high viscous wall shear stresses within dialysis access fistulae; Stresses >15 Pa have been reported. These are much higher than what is typically considered normal or homeostatic (i.e. ≈ 1–1.5 Pa). The abnormal stresses in the fistulae have been hypothesized to cause pathological venous remodeling (i.e. intimal hyperplasia) which causes stenoses and threatens fistula patency. Given the high failure rate of dialysis access sites (up to 50% require surgical revision within one year), understanding the dynamics of blood flow within the fistula is a necessary step in understanding remodeling, and ultimately, in improving clinical outcomes.

Arteriovenous fistulae are created surgically to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is in part a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. The current study presents fluid–structure interaction (FSI) simulations of a patient-specific model of a mature arteriovenous fistula reconstructed from 3D ultrasound scans. The FSI results are compared with previously published data of the same model but with rigid walls. Ultrasound-derived wall motion measurements are also used to validate the FSI simulations of the wall motion. Very large time-averaged shear stresses, 10–15 Pa, are calculated at the fistula anastomosis in the FSI simulations, values which are much larger than what is typically thought to be the normal homeostatic shear stress in the peripheral vasculature. Although this result is systematically lower by as much as 50 % compared to the analogous rigid-walled simulations, the inclusion of distensible vessel walls in hemodynamic simulations does not reduce the high anastomotic shear stresses to “normal” values. Therefore, rigid-walled analyses may be acceptable for identifying high shear regions of arteriovenous fistulae.

Background: Duplex ultrasound with Doppler velocimetry is widely used to evaluate the presence and severity of internal carotid artery stenosis; however, a variety of velocity criteria are currently being applied to classify stenosis severity. The purpose of this study is to compare published Doppler velocity measurements to the severity of internal carotid artery stenosis as assessed by x-ray angiography in order to clarify the relationship between these 2 widely used approaches to assess carotid artery disease. Methods: Scatter diagrams or “scattergrams” of correlations between Doppler velocity measurements and stenosis severity as assessed by x-ray contrast angiography were obtained from published articles for native and stented internal carotid arteries. The scattergrams were graphically digitized, combined, and segmented into categories bounded by 50% and 70% diameter reduction. These data were combined and divided into 3 sets representing different velocity parameters: (1) peak systolic velocity, (2) end-diastolic velocity, and (3) the internal carotid artery to common carotid artery peak systolic velocity ratio. The horizontal axis of each scattergram was transformed to form a cumulative distribution function, and thresholds were established for the stenosis categories to assess data variability. Results: Nineteen publications with 22 data sets were identified and included in this analysis. Wide variability was apparent between all 3 velocity parameters and angiographic percent stenosis. The optimal peak systolic velocity thresholds for stenosis in stented carotid arteries were higher than those for native carotid arteries. Within each category of stenosis, the variability of all 3 velocity parameters was significantly lower in stented arteries than in native arteries. Conclusion: Although Doppler velocity criteria have been successfully used to classify the severity of stenosis in both native and stented carotid arteries, the relationship to angiographic stenosis contains significant variability. This analysis of published studies suggests that further refinements in Doppler velocity criteria will not lead to improved correlation with carotid stenosis as demonstrated by angiography.

Hemodialysis is a common treatment for approximately 370,000 patients in the United States with end-stage renal disease [1]. To optimize the procedure, the dialysis access site must be easily accessible but must also be able to continuously provide high blood flow rates: >250 mL/min [2]. If there is insufficient blood flow through the access, then the dialysis procedure becomes impractical or ineffective. To provide these features, an arteriovenous (AV) fistula is typically surgically created in the arm: an artery and a vein are anastomosed together, bypassing the high flow resistance of the capillary bed and providing enhanced flow through the artery and into the access vein. Unfortunately, as many as 60% of AV fistulae require an intervention within one year to maintain clinical patency [3,4]. There are two major causes of patency loss: thrombotic occlusion, brought on by aggressive intimal hyperplasia and stenotic lesions, or impaired dilation, whereby impaired venous remodeling does not provide a sufficient flow rate at the access site [2]. In the United States alone, it is estimated that the total expenditures related to access site complications and revisions exceed $2 billion per year [1]. After the creation of the fistula, the vein undergoes a rapid remodeling process, leading to an increase in the diameter of the lumen and increased muscular thickness in the wall, which is a process referred to as vein arterialization [5]. It has long been hypothesized that hemodynamic forces constitute the primary external influence on the remodeling process [6,7]. Since an AV fistula causes a dramatic rise in the flow rate and wall shear stress outside of normal physiological values, it is hypothesized that the vein and artery lumens chronically increase as a way to renormalize the value of the wall shear stress. The remodeling of the vessels has been shown to correlate with the initial time-averaged wall shear stress as evidenced by animal models of AV fistulae [6,7] and ultrasound surveillance in dialysis patients [5,8]. These studies hypothesized that the remodeling stops once the mean wall shear stress in the fistulae reach about 1.5 Pa in the radial artery and about 1.0 Pa in the cephalic vein. The renormalization of shear stress in the fistula vessels has been interpreted as evidence of a “mechanical homeostasis” [9]: the vessels seek to maintain a preferred mechanical state through a process of growth and remodeling. The shear-induced remodeling is widely hypothesized to be regulated in part by the vascular endothelium [10]. Despite the pervasive use of the AV fistula for dialysis access, the mechanisms which drive a fistula to either successful remodeling and patency versus occlusion and failure remain unclear [11]. Even though blood flow is thought to play an important role in fistula remodeling, the characterization of the hemodynamic stresses occurring within fistulae remain ambiguous [12], even within functioning accesses [13]. Characterizing the fistula hemodynamics has been hindered, in part, due to the relative complexity of the flow, including separation, vortex shedding, and swirling flows [14]. In this study, we use 3D ultrasound imaging and computational fluid dynamics to determine the hemodynamics in four mature AV fistulae of hemodialysis patients. The hemodynamic analysis aims to quantify the mechanical stresses occurring due to complex secondary flows. It is important to first characterize the hemodynamics in patent accesses in order to eventually understand the negative influence of hemodynamics in failing accesses [11]. It is furthermore unlikely that effective clinical treatments for fistula maturation will be successful until a more precise characterization of fistula hemodynamics is articulated [10].

Objective The mechanisms of restenosis in autogenous vein bypass grafts placed for peripheral artery disease are not completely understood. We investigated the role of hemodynamic stress in a case study of a revised bypass graft that failed due to restenosis. Methods The morphology of the lumen was reconstructed from a custom three-dimensional ultrasound system. Scans were taken at 1, 6, and 16 months after a patch angioplasty procedure. Computational hemodynamic simulations of the patient-specific model provided the blood flow features and the hemodynamic stresses on the vessel wall at the three times studied. Results The vessel was initially free of any detectable lesions, but a 60% diameter-reducing stenosis developed during the 16-month study interval. As determined from the simulations, chaotic and recirculating flow occurred downstream of the stenosis due to the sudden widening of the lumen at the patch location. Curvature and a sudden increase in the lumen cross-sectional area induced these flow features that are hypothesized to be conducive to intimal hyperplasia. Favorable agreement was found between simulation results and in vivo Doppler ultrasound velocity measurements. Conclusions Transitional and chaotic flow occurs at the site of the revision, inducing a complex pattern of wall shear as computed with the hemodynamic simulations. This supports the hypothesis that the hemodynamic stresses in the revised segment, produced by the coupling of vessel geometry and chaotic flow, led to the intimal hyperplasia and restenosis of the graft.

Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patients with End-Stage Renal Disease. Producing an autogenous shunt linking an artery and a vein in the peripheral circulation bypasses the high resistance capillary bed in order to provide the necessary flow rates at sites easily accessible for dialysis. In successful fistulae, venous flow rates can easily exceed 1000 mL/min. It has long been recognized that the hemodynamics constitute the primary external influence on the remodeling process [1, 2]; The high flow rate, together with the exposure of the venous tissue to the high arterial pressure, leads to a rapid process of wall remodeling that may end in a mature access or in stenosis and failure. Given the high failure rate of dialysis access (up to 50% require surgical revision within one year [3]), understanding the dynamics of blood flow within the fistula is a necessary step in understanding the remodeling, and ultimately, in improving clinical outcomes.Copyright © 2011 by ASME

We report a study of the role of hemodynamic shear stress in the remodeling and failure of a peripheral artery bypass graft. Three separate scans of a femoral to popliteal above-knee bypass graft were taken over the course of a 16 month period following a revision of the graft. The morphology of the lumen is reconstructed from data obtained by a custom 3D ultrasound system. Numerical simulations are performed with the patient-specific geometries and physiologically realistic flow rates. The ultrasound reconstructions reveal two significant areas of remodeling: a stenosis with over 85% reduction in area, which ultimately caused graft failure, and a poststenotic dilatation or widening of the lumen. Likewise, the simulations reveal a complicated hemodynamic environment within the graft. Preliminary comparisons with in vivo velocimetry also showed qualitative agreement with the flow dynamics observed in the simulations. Two distinct flow features are discerned and are hypothesized to directly initiate the observed in vivo remodeling. First, a flow separation occurs at the stenosis. A low shear recirculation region subsequently develops distal to the stenosis. The low shear region is thought to be conducive to smooth muscle cell proliferation and intimal growth. A poststenotic jet issues from the stenosis and subsequently impinges onto the lumen wall. The lumen dilation is thought to be a direct result of the high shear stress and high frequency pressure fluctuations associated with the jet impingement.

Tissue pulsatility imaging (TPI) is an ultrasonic technique that is being developed at the University of Washington to measure tissue displacement or strain as a result of blood flow over the cardiac and respiratory cycles. This technique is based in principle on plethysmography, an older nonultrasound technology for measuring expansion of a whole limb or body part due to perfusion. TPI adapts tissue Doppler signal processing methods to measure the “plethysmographic” signal from hundreds or thousands of sample volumes in an ultrasound image plane. This paper presents a feasibility study to determine if TPI can be used to assess cerebral vasoreactivity. Ultrasound data were collected transcranially through the temporal acoustic window from four subjects before, during and after voluntary hyperventilation. In each subject, decreases in tissue pulsatility during hyperventilation were observed that were statistically correlated with the subject's end-tidal CO 2 measurements. (E-mail: kucewicz@u.washington.edu )

Doppler measurement of tissue vibrations (ultrasonic vibrometry) can provide clinical information about vascular pathology that may be otherwise difficult to obtain using conventional duplex ultrasound. Vibrometry can provide improved sensitivity, since the scattering strength from tissue is significantly higher than that from blood. In addition, detection of tissue vibrations has reduced angle dependency and does not require visualization of the vessel lumen, making the exam less dependent on operator skill and less time-consuming. The fundamental sources of error that can affect the measurement accuracy of the vibration characteristics are Doppler spectral broadening and tissue acceleration. Parametric simulation studies analyzing the effect of these sources of error and their implications are presented. We also present preliminary results from renal artery stenosis (RAS), demonstrating that a diagnosis based on the characteristics of measured tissue vibrations correlates well with the routine clinical diagnosis

Objective: Accurate measurements of abdominal aortic aneurysms (AAAs) are required for surgical planning and monitoring over time. We have examined the feasibility of using a three-dimensional (3-D) ultrasound imaging system to derive quantitative measurements of interest from AAAs. Methods: A normal aorta, a small AAA, and an AAA repaired with an endovascular stent graft were scanned with a 3-D ultrasound imaging system. For each case, a 3-D surface reconstruction was generated from manual outlines of a sequence of two-dimensional ultrasound images, registered in 3-D space with a magnetic tracking system. The surfaces were resampled in planes perpendicular to the vessel center axis to calculate cross-sectional area and maximum diameter as a function of distance along the length of the aorta. Results: Cross-sectional area and maximum diameter were plotted along the length of the aneurysmal aortas from the renal arteries to the aortic bifurcation. The overall maximum diameter was found for both aneurysms. For the small AAA, the distances of the aneurysm from the renal arteries and the bifurcation were measured. For the repaired AAA, the location of the stent graft relative to the renal arteries was measured. Conclusions: 3-D surface reconstructions from ultrasound images show promise for quantitatively characterizing the geometry of AAAs both before surgery and after endovascular repair. (J Vasc Surg 2001;33:700-7.)

Objective : To develop a non-invasive method for evaluating gastric emptying and duodenogastric reflux stroke volumes using three-dimensional (3D) guided digital color Doppler imaging. Methods : The technique involved color Doppler digital images of transpyloric flow in which the 3D position and orientation of the images were known by using a magnetic location system. Results: In vitro, the system was found to slightly underestimate the reference flow (by average 8.8%). In vivo (five volunteers), stroke volume of gastric emptying episodes lasted on average only 0.69 s with a volume on average of 4.3 ml (range 1.1–7.4 ml), and duodenogastric reflux episodes on average 1.4 s with a volume of 8.3 ml (range 1.3–14.1 ml). Conclusion : With the appropriate instrument settings, orientation determined color Doppler can be used for stroke volume quantification of gastric emptying and duodenogastric reflux episodes.

Introduction Serial monitoring of patients participating in clinical trials of carotid artery therapy requires noninvasive precision methods that are inexpensive, safe and widely available. Noninvasive ultrasonic duplex Doppler velocimetry provides a precision method that can be used for recruitment qualification, pre-treatment classification and post treatment surveillance for remodeling and restenosis. The University of Washington Ultrasound Reading Center (UWURC) provides a uniform examination protocol and interpretation of duplex Doppler velocity measurements. Methods Doppler waveforms from 6 locations along the common carotid and internal carotid artery path to the brain plus the external carotid and vertebral arteries on each side using a Doppler examination angle of 60 degrees are evaluated. The UWURC verifies all measurements against the images and waveforms for the database, which includes pre-procedure, post-procedure and annual follow-up examinations. Doppler angle alignment errors greater than 3 degrees and Doppler velocity measurement errors greater than 0.05 m/s are corrected. Results Angle adjusted Doppler velocity measurements produce higher values when higher Doppler examination angles are used. The definition of peak systolic velocity varies between examiners when spectral broadening due to turbulence is present. Examples of measurements are shown. Discussion Although ultrasonic duplex Doppler methods are widely used in carotid artery diagnosis, there is disagreement about how the examinations should be performed and how the results should be validated. In clinical trails, a centralized reading center can unify the methods. Because the goals of research examinations are different from those of clinical examinations, screening and diagnostic clinical examinations may require fewer velocity measurements.

At the 105th ASA meeting we presented results of our research on the Tadoma method of tactile speech reception and described our ongoing development of a “synthetic Tadoma system” for use as a research tool in studying transformations of Tadoma [Reed et al., J. Acoust. Soc. Am. Suppl. 1 73, S26 (1983)]. In the synthetic Tadoma system, signals recorded from a talker's face are used to control an artificial mechanical face. Preliminary evaluation of the system has involved roving ABX discrimination tests among sets of 15 vowels in CVC contexts and among sets of 24 consonants in CV contexts. Two naive adult subjects, with simulated deafness and blindness, have been tested. Average results for vowel discrimination (68%) were equal to those obtained in a comparable study of natural Tadoma [Reed et al., J. Speech Hear. Res. 21, 625–637 (1978)]. Results for consonant discrimination were lower for the synthetic system (68% vs 78%), but were improved (to 74%) following certain modifications to the system. [Work supported by NSF.]