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Biomedical subjects

J M Rubin

Publications and source records attributed to J M Rubin.

At least 19 recordsLinked to original sources
PubMed2005

Standardization of power Doppler quantification of blood flow in the human fetus using the aorta and inferior vena cava.

OBJECTIVE: This study aimed to test the applicability to the fetus of mathematical techniques developed to standardize power Doppler indices of adult regional perfusion. METHOD: Fetal power Doppler imaging was performed on 14 fetuses (25-37 weeks' gestation) using a standardized parasagittal plane, examining renal and aortic blood flow, and additionally inferior vena caval (IVC) flow in one fetus. Images were stored and transferred for off-line computer analysis using purpose-designed software. We first tested the need for techniques to remove the effects of red blood cell clumping on power Doppler amplitude, then performed further analyses to: (1) investigate cardiac cycle effects on aortic amplitude; (2) determine the spatial consistency of, and influence of angle of insonation on, maximal pixel value; (3) quantify temporal consistency; and (4) compare peak pixel values in the fetal aorta and IVC. RESULTS: No rouleaux effect on the vascular profile was detectable, in contrast to that identified in the adult. Within each fetus a consistent value was seen in the center of the aorta corresponding to 100% vascular amplitude, which was unaltered by the phase of the cardiac cycle, with a coefficient of variation of 28.9% at 89 degrees and 6.5% at 73 degrees . This value was constant in the aorta and IVC. CONCLUSION: Fetal blood does not appear to form rouleaux to any significant degree, so there is no artificially elevated maximal value for power Doppler amplitude as seen in the adult. We propose that the value representing 100% amplitude may be consistently measured in the center of large fetal vessels such as the aorta, allowing the direct measurement of fractional moving blood volumes in the human fetus.

Adult↗
PubMed2005

Renal advances in ultrasound elasticity imaging: measuring the compliance of arteries and kidneys in end-stage renal disease.

BACKGROUND/AIMS: Ultrasound elasticity imaging visually represents tissue hardness measurements using high-resolution ultrasound speckle-tracking algorithms. This method has recently been applied in the renal setting to measure arterial compliance in end-stage renal disease (ESRD) and the mechanical properties of transplant kidneys in vivo. METHODS: Ultrasound radio-frequency signal measurements were made of the brachial artery in 5 ESRD subjects and 5 healthy controls and renal transplant measurements in 2 subjects, 1 with chronic allograft nephropathy (CAN) and 1 with normal graft function. RESULTS: Maximal brachial artery percent strain measurements for healthy controls were 32.9 +/- 10.2% (mean +/- SD) and for ESRD subjects maximal percent strains were 4.9 +/- 1.8%. Transplant renal cortical strain for the subject with CAN was approximately one third that of the healthy transplant recipient. CONCLUSION: Ultrasound elasticity imaging offers the potential to noninvasively measure the mechanical properties of structures within the body.

Adult↗
PubMed2005

3-D correlation-based speckle tracking.

Widely-used 1-D/2-D speckle tracking techniques in elasticity imaging often experience significant speckle decorrelation in applications involving large elevational motion (i.e., out of plane motion). The problem is more pronounced for cardiac strain rate imaging (SRI) since it is very difficult to confine cardiac motion to a single image plane. Here, we present a 3-D correlation-based speckle tracking algorithm. Conceptually, 3-D speckle tracking is just an extension of 2-D phase-sensitive correlation-based speckle tracking. However, due to its high computational cost, optimization schemes, such as dynamic programming, decimation and two-path processing, are introduced to reduce the computational burden. To evaluate the proposed approach, a 3-D bar phantom under uniaxial compression was simulated for benchmark tests. A more sophisticated 3-D simulation of the left ventricle of the heart was also made to test the applicability of 3-D speckle tracking in cardiac SRI. Results from both simulations clearly demonstrated the feasibility of 3-D correlation-based speckle tracking. With the ability to follow 3-D speckle in 3-D space, 3-D speckle tracking outperforms lower-dimensional speckle tracking by minimizing decorrelation caused by pure elevational translation. In other words, 3-D tracking can push toward solely deformation-limited, decorrelation-optimized speckle tracking. Hardware implementation of the proposed 3-D speckle tracking algorithm using field programmable gate arrays (FPGA) is also discussed.

Algorithms↗
PubMed2004

Vascular intramural strain imaging using arterial pressure equalization.

Peripheral vascular strain imaging has limited strain dynamic range because arterial wall deformations only exhibit small strains under physiologic pressures. A noninvasive freehand ultrasound (US) scanning procedure was performed to apply external force, comparable to the force generated in measuring a subject's blood pressure, to achieve higher strains by equalizing the internal arterial baseline pressure. When the applied pressure matched the internal baseline diastolic pressure, intramural strain and strain rate increased by a factor of 10 over a cardiac cycle. Radial arterial strain was assessed within the vessel wall over the entire deformation procedure using a phase-sensitive 2-D speckle-tracking algorithm. The feasibility of this technique to assess vascular nonlinear elastic properties is demonstrated in an ex vivo experiment and further supported by in vivo measurements. With some uncertainty associated with the elastic properties of surrounding tissue, an elastic modulus reconstruction procedure was developed to estimate the nonlinear elastic properties of the vascular wall.

Adult↗
PubMed2002

Triplex ultrasound: elasticity imaging to age deep venous thrombosis.

Deep venous thrombosis (DVT), and its sequela, pulmonary embolism (PE), is the leading cause of preventable in-hospital mortality in the USA and other developed countries. After it is detected, acute clots must be differentiated from chronic DVT for appropriate treatment. However, there are no reliable thrombus staging methods presently available in clinical practice. In this study, we tested the hypothesis that blood clots can be detected and staged using a triplex ultrasound (US) test. Triplex US is based on a "gold standard" duplex US technique augmented by US-based reconstructive elasticity imaging. Fibrin-composed blood clots harden with development and organization. By imaging clot elasticity, it may be possible to both detect and differentiate clots and, therefore, provide an urgently needed noninvasive means of DVT staging.

Animals↗
PubMed2001

Analysis of three-dimensional ultrasound Doppler for the detection of prostate cancer.

OBJECTIVES: To investigate the relative effectiveness of Doppler ultrasound quantitative measures in discriminating prostate cancer from normal prostate tissue. The true locations of prostate cancer within these prostates were determined by histologic examination after radical prostatectomy. METHODS: Three-dimensional Doppler ultrasound data were acquired from 39 men before radical prostatectomy. The removed prostates were sectioned and all cancerous regions in each prostate were identified on whole-mount hematoxylin-eosin-stained slides. The ultrasound and histologic data were then spatially registered. Biopsy results were simulated on a grid of potential sites within each prostate. Along each simulated biopsy site, the amount of cancer was computed from the hematoxylin-eosin-identified cancerous regions and the peak speed-weighted pixel density (SWD) was compared. RESULTS: By selecting the biopsy sites with higher associated SWDs within each sextant, the probability of having at least one positive biopsy within a prostate increased from 75% if the SWD was ignored to 85% if only the top 15% of potential biopsy sites in each sextant were selected. This trend was seen within each sextant individually as well. CONCLUSIONS: Doppler ultrasound provides discriminatory information for prostate cancer using the SWD. Translating this into a practical strategy that might improve the yield of prostate biopsy remains under development. The results of our study indicate that biopsying regions of high Doppler color could potentially increase the cancer yield to a small degree and improve the accuracy of the biopsy results. These results also objectively verify previous visual studies suggesting a modest improvement with the use of color Doppler.

Aged↗
PubMed2001

Volume flow measurement using Doppler and grey-scale decorrelation.

A technique for volumetric blood flow measurement was developed by combining standard Doppler measurements with grey-scale decorrelation. Steered Doppler is used to determine the in-plane velocities, which are then used to extract the out-of-plane velocities from the temporal A-line decorrelation. As a result, a three-dimensional (3-D) vector flow field can be computed over the imaging plane using a single clinical transducer without knowledge of the vessel orientation. Volume flow is computed by integrating the out-of-plane flow over the vessel cross-section. The algorithm was tested using a scattering-enhanced fluid in a 6.4-mm diameter dialysis tubing. For a wide range of transducer angles, the volume flow was accurately measured to within 28% in these preliminary tests.

Algorithms↗
PubMed2001

Retrograde hemodialysis access flow during dialysis as a predictor of access pathology.

We have detected retrograde flow by Doppler ultrasound within the hemodialysis access of 10 patients during routine dialysis. Nine of these accesses were prosthetic grafts, and 1 was an autogenous fistula. All 9 of the grafts had access pathology demonstrated by angiography. The single patient with the fistula exhibiting reversed access flow had a poorly developed access with no focal stenoses on angiogram, but 18% recirculation by ultrasound dilution. All patients with retrograde flow had access flow rates below 650 mL/min. While 3 of these patients had substantial access recirculation (2 grafts, 12% and 40%; and 1 fistula, 18%) 2 of these patients had 3% recirculation (2 needle urea method), and 4 patients had 0% access recirculation (ultrasound dilution and 2 needle urea method). We report that retrograde access flow during dialysis may be a specific indicator of access dysfunction. These findings further suggest that retrograde access flow develops before access recirculation, indicating that this finding is more sensitive than recirculation for detecting access dysfunction. Further study is needed to determine the utility of this finding in access surveillance.

Adult↗
PubMed2001

Analysis of variable flow Doppler hemodialysis access flow measurements and comparison with ultrasound dilution.

The variable flow (VF) Doppler method determines access blood flow from the pump speed-induced change in Doppler signal between the arterial and venous needles. This study evaluated 35 patients in two analyses to assess VF Doppler measurement reproducibility (54 paired measurements) and compared VF Doppler and ultrasound dilution flow measurements (24 paired measurements). VF Doppler measurement variations were 4% for access flow less than 800 mL/min (n = 17), 6% for access flow of 801 to 1,600 mL/min (n = 22), and 11% for access flow greater than 1,600 mL/min (n = 15). The mean measurement coefficient of variation was 7% for VF Doppler compared with 5% for ultrasound dilution. Correlation coefficients (r) between VF Doppler and ultrasound dilution access flow measurements were 0.79 (n = 24; P < 0.0001), 0.84 for access flow less than 2,000 mL/min (n = 20; P < 0.0001), and 0.91 for access flow less than 1,600 mL/min (n = 18, P < 0.0001). VF Doppler measurements using indicated versus measured pump flow rates correlated highly (r = 0.99; P < 0.0001). VF Doppler therefore yields reproducible access volume flow measurements that correlate with ultrasound dilution measurements. The VF Doppler method is dependent on the pump-induced change in access Doppler signal and therefore is inherently most accurate and reproducible at lower access blood flow rates. This method appears capable of determining access flow rates in the clinically useful range.

Blood Flow Velocity↗
PubMed2001

Analysis of three-dimensional Doppler ultrasonographic quantitative measures for the discrimination of prostate cancer.

OBJECTIVE: The purpose of this study was to determine whether several quantitative ultrasonographic measures have potential to discriminate prostate cancer from normal prostate and to determine the best combination of these measures. The true spatial distributions of cancer within the prostates studied were obtained histologically after radical prostatectomy. The relationship between Doppler ultrasonography and microvessel count was also investigated. METHODS: Three-dimensional Doppler ultrasonographic data were acquired from 39 patients before radical prostatectomy. The removed prostate was sectioned, and whole-mount hematoxylineosin-stained slides were used to identify all regions of cancer within each prostate. These histologic and ultrasonographic data were spatially registered. Doppler ultrasonographic measures were calculated within uniformly sized three-dimensional regions that were either entirely cancerous or noncancerous, and receiver operating characteristic analysis was performed on the results. Microvessel counts were made within each contiguous cancerous region and correlated with ultrasonographic measures. RESULTS: Color pixel density was the best simple measure for discriminating prostate cancer (accuracy, 80%). The mean power mode value (normalized mean power in color pixels) was inversely related to cancer with an accuracy of 1--normalized mean power in color pixels = 65% (low mean power is more cancerous). When color pixel density was combined with the normalized mean power in color pixels, its accuracy improved slightly to 84%. The peak microvessel count had a negative correlation with color pixel density as well as with cancer stage. CONCLUSION: Doppler ultrasonography does provide discriminatory information for prostate cancer, with color pixel density being the most promising measure.

Humans↗
PubMed2001

History of intraoperative ultrasound in neurosurgery.

This article chronicles the development of real-time ultrasound for use in operations in the central nervous system. Described are the technology and the various applications of ultrasound in the neurosurgical operating room. The use of real-time ultrasound to localize, characterize, and instrument lesions of the brain and spinal chord are discussed.

Brain Neoplasms↗
PubMed2000

Ultrasound detection of microembolic signals in hemodialysis accesses.

Microembolic signals (MES) detected by ultrasound, thought to be of gaseous or solid origin, have been described with decompression illness and in the intracranial and cardiopulmonary circulation. We describe the first reported cases of MES occurring in hemodialysis accesses. Two hemodialysis patients, one with a synthetic graft and one with an arteriovenous fistula, showed MES during a dialysis session detected by duplex ultrasound. We postulate that these MES represent cavitation bubbles developing from turbulent blood flow around the venous needle in the access. However, other potential causes exist, including air introduced into the circulation from the dialysis circuit or microemboli arising from thrombus or atheroma.

Aged↗
PubMed2000

Doppler US gating of cardiac MR imaging.

RATIONALE AND OBJECTIVES: Electrocardiographic (ECG) gating of cardiac magnetic resonance (MR) imaging has been problematic for many reasons. The purpose of this study was to demonstrate the feasibility of using Doppler ultrasound (US) gating, either directly off the moving cardiac wall or the systolic upstroke of the arterial signal from the great vessels in neck, in alternative gating modes. MATERIALS AND METHODS: A 2.5-MHz, range-gated Doppler US device was used with A-mode guidance for gating directly off left ventricular wall motion. A 4- or 8.1-MHz, continuous-wave (CW) Doppler US device was used for gating off the systolic upstroke from the great vessels in the neck. The subject undergoing imaging held the transducer against his chest for range-gated Doppler US and against his neck for 8.1-MHz CW Doppler US. The 4-MHz transducer was strapped to the subject's neck. Modified Doppler signals were fed back into the gating circuitry of the MR imager to achieve cardiac synchrony. RESULTS: Cardiac gating was achieved by using both the range-gated technique directly off the cardiac wall and the CW method off blood flow from the great vessels. Problems occurred with radiofrequency shielding during the range-gated method; however, these problems were almost completely removed by use of the CW Doppler probes. CONCLUSION: Doppler US gating of MR images is possible and potentially could overcome many shortcomings of ECG gating. Subsequent embodiments of the technique will require improved radiofrequency shielding in the range-gated technique.

Echocardiography, Doppler↗
PubMed1999

MRA contrast bolus timing with ultrasound bubbles.

The purpose of this study was to determine the feasibility of using an ultrasound contrast agent test bolus to determine optimum bolus timing for three-dimensional (3D) gadolinium (Gd)-enhanced magnetic resonance angiography (MRA). Small test doses of ultrasound contrast agent (0.3 ml Optison) were injected intravenously followed immediately by a 20 ml saline flush. Arrival of the contrast agent was detected by spectral Doppler ultrasound (US). This technique was implemented in patients undergoing peripheral vascular MRA and carotid MRA. Arrival of the US contrast agent test bolus was readily detected by the change in amplitude of the Doppler spectrum and by a huge increase in the audio signal amplitude. This contrast travel time measurement accurately guided bolus timing for 3D Gd MRA. Bolus timing for 3D contrast-enhanced MRA can be performed using US, thereby eliminating the problems and MR scanner time required for injecting a test bolus of Gd contrast.

Albumins↗
PubMed1999

Power doppler.

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Blood Flow Velocity↗