Biomedical subjects
Publications and source records attributed to J M Rubin.
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.
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.
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.
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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.
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OBJECTIVE: To evaluate the effects of loteprednol etabonate (LE) 0.2% in reducing the signs and symptoms of seasonal allergic conjunctivitis. DESIGN: Randomized, double-masked, placebo-controlled, parallel group multicenter study of 6 weeks duration. PARTICIPANTS: A total of 135 patients with signs and symptoms of seasonal allergic conjunctivitis participated. INTERVENTION: All patients received either LE 0.2% or placebo (vehicle) four times a day in both eyes for 42 days. MAIN OUTCOME MEASURES: Bulbar conjunctival injection (primary sign) and itching (primary symptom) over the first 2 weeks of treatment was measured. RESULTS: A reduction in severity was seen in both LE and placebo groups for bulbar conjunctival injection (1.5 vs. 1.0 units on a 0-3 scale) and itching (3.4 vs. 3.0 units on a 0-4 scale) over the first 2 weeks. The treatment effect by these measures was -0.5 and -0.4 units in favor of LE (P < or = 0.008). Resolution (i.e., the proportion of patients with signs or symptoms no longer present) at day 14 strongly favored LE-treated patients (36% and 15%; 58% and 38%, for injection and itching, respectively). Both treatments were well tolerated. One patient in each treatment group (1 of 67 and 1 of 68, respectively) had an elevation of intraocular pressure of 10 mmHg or greater during the 6 weeks of treatment. CONCLUSIONS: Loteprednol etabonate 0.2% was more effective than placebo in the treatment of seasonal allergic conjunctivitis. Loteprednol etabonate 0.2% had a safety profile comparable to placebo.
A texture discriminant based on spatial frequencies is proposed for characterizing B-scans of Achilles' tendon. The anisotropic echo texture of normal tendon has an ellipsoidal spatial spectrum that can be quantified by the ratio of the major-to-minor axis and by the direction of the major axis. Applying a moving window to the B-scan, a corresponding tissue elliptical axis ratio (TEAR) image is derived that segments out tendon. The algorithm was applied to B-scan images taken from 13 volunteers, 6 of whom had tendon abnormalities: tendon rupture (n = 3) or cholesterol deposits (xanthomas) in patients with heterozygous familial hypercholesterolemia (n = 3). The average TEAR value was 1.75 +/- 0.17 for normal tendon, 1.04 +/- 0.06 for torn tendon, and 1.31 +/- 0.16 for tendons with xanthomas. The dispersion of the directionality vectors was used to further differentiate tendons with xanthomas from normal tendons. This technique appears to be useful for characterizing both diffuse and focal tendon abnormalities.
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PURPOSE: To evaluate the dependence of the resistive index (RI) on not only vascular resistance but also vascular compliance. MATERIALS AND METHODS: An in vitro model that made use of a pulsatile pump, blood-mimicking fluid, and variable compliance and resistance was used to investigate the relationship between the RI and both vascular compliance and resistance. RESULTS: In the absence of vascular compliance, the RI was independent of vascular resistance. With vascular compliance, the RI was dependent on vascular resistance and increased with increasing resistance. The higher the compliance, the more the RI was affected by resistance. CONCLUSION: The RI is misnamed and should actually be called the "impedance index" because resistance and compliance interact to alter the Doppler arterial waveform. A greater understanding of this relationship may enable future studies that take both resistance and compliance into account to better detect pathologic conditions.
PURPOSE: To test the hypothesis that increased end-organ vascular resistance reduces blood flow to the kidney, thus reducing the mean velocity in the renal artery and secondarily lowering the peak systolic velocity (PSV). MATERIALS AND METHODS: An in vitro hydraulic model with a pulsatile pump, blood-mimicking fluid, interchangeable stenoses, and variable compliance and resistance was used to investigate the relationship between end-organ vascular resistance and poststenotic PSV. RESULTS: Poststenotic PSV was mildly dependent on end-organ vascular resistance and decreased with increasing resistance. CONCLUSION: The results help explain some of the reported variability from using poststenotic PSV to detect hemodynamically significant renal arterial stenoses, but the effect is not great enough to completely explain the variability. Other factors not investigated in this study must be at work as well.
PURPOSE: To evaluate the effect of the increase in total cross-sectional area of arteries as they branch beyond the main trunks on the resistive index (RI) and early systolic acceleration (ESA). MATERIALS AND METHODS: An essentially noncompliant in vitro model that used a pulsatile pump, blood-mimicking fluid, and a branching tubing network that could be configured to produce a downstream cross-sectional area one, two, four, or eight times that of the feeding vessel was used to investigate the relationship, if any, between arterial bed cross-sectional area and the RI and ESA. RESULTS: The mean ESA in the branching network was inversely proportional to cross-sectional area, decreasing by approximately a factor of two for every doubling of the cross-sectional area. The mean RI in the branching network decreased with increasing cross-sectional area, but not as greatly as the ESA did; the mean RI in the bed with eight times the upstream cross-sectional area had an RI that was approximately three-fourths the upstream RI. These relationships are real, as the slopes of the plots (ESA vs cross-sectional area, P = .001; RI vs cross-sectional area, P < .02) are significantly different from zero. CONCLUSION: RI and ESA decrease as a result of increasing downstream cross-sectional diameter of the arterial bed.
PURPOSE: To use speckle decorrelation in the presence of ultrasonographic (US) contrast agent as an alternative flow measurement technique to Doppler US. MATERIALS AND METHODS: In vivo and in vitro studies were performed. A tube with flowing saline solution containing contrast agent was positioned horizontally across a US image. The amount of decorrelation between a series of images was recorded. The flow profile across the tube was generated by averaging the decorrelation values and was compared with a Doppler frequency shift image. In addition, B-mode images of six rabbit kidneys were obtained during and after intravenous injection of contrast agent. Images were analyzed to compute the correlation between successive points in time. RESULTS: The velocity profiles across the tube were parabolic, with the fastest flow rates measured in the center of the tube. In the rabbit kidneys, measurements indicated the largest decorrelation rates occurred in the larger vessels. The cortical decorrelation rates were significantly slower than those for the hilar vessels (P < .05) and were relatively angle independent. CONCLUSIONS: Decorrelation flow measurements can be used to estimate flow in vitro and in vivo similar to measurements obtained with Doppler US but with less angle dependence. These measurements could lead to a US perfusion technique.
Prior studies have shown variable results using poststenotic peak systolic velocity to detect hemodynamically significant renal artery stenoses. We postulated that vascular compliance, which affects the arterial waveform and varies by a factor of at least 5 in vivo, affects the peak systolic velocity, perhaps explaining the aforementioned variable results using peak systolic velocity to detect stenoses. A hydraulic model was used to investigate the relationship between end-organ vascular compliance and the peak systolic velocity. The peak systolic velocity was found to be mildly dependent on vascular compliance, decreasing with decreasing compliance. These results help explain some of the reported variability using peak systolic velocity to detect hemodynamically significant renal artery stenoses, but the effect is not great enough to explain the variability completely. Other factors not investigated in this study must exist that also affect peak systolic velocity.
OBJECTIVE: To evaluate how well transabdominal power Doppler sonography, a new method of colour Doppler sonography, visualizes the vasculature of the early placenta. METHODS: Evaluation of intrachorionic/intraplacental vasculature in 15 normal, singleton gestations of 8 to 18 weeks. RESULTS: Intrachorionic/intraplacental vessels were identified in all gestations, except the earliest (8 weeks). The number of vessels detected increased with increasing gestational age. Intrachorionic/intraplacental Doppler waveforms of maternal arterial origin were identified in gestations of 8.5, 9.5, and 11.5 weeks. CONCLUSIONS: Transabdominal power Doppler sonography detects intrachorionic/intraplacental vasculature at least as early as 8.5 weeks. Intervillous arterial flow of maternal origin is present in the first trimester, confirming the results of a recent transvaginal colour Doppler sonographic study, and contradicting earlier studies suggesting that such flow is not present in the first trimester.
In this article, new measures obtained from color Doppler images are introduced and a pilot study is described, in which these and previously published indices are evaluated for use in future work. Twenty women with breast masses observed on mammography and going to surgical biopsy were studied. Of the masses, 11 proved to be benign and 9 were malignant. Both 3-D mean frequency shift (f-CDI) and power mode Doppler (p-CDI) imaging were performed. To identify the mass and other regions of interest, vessels were displayed as rotatable 3-D color volumes, superimposed on selectable grey-scale/color flow slices. Doppler signals were recorded in each of 6 ellipsoidal regions of interest in and around the mass and 2 in normal tissues. Seven measures were computed in each region, three from power mode, two from mean frequency and two from combinations of both. Radiologists rated the grey-scale appearances of the masses on a scale of 1 to 5 (5=most suspicious) for each of 6 conventional grey-scale criteria. Of the individual vascularity measures in individual ROIs, the log speed-weighted pixel density and log power-weighted pixel density in the lesion internal periphery showed the greatest discrimination of malignancy, although neither was statistically significant nor as good as the peak variables described below. The mean visual grey-scale rating was the best discriminator overall, but two peak vascularity measures each made promising scatterplots in conjunction with the average visual grey-scale rating. These two vascularity measures were the log peak normalized power-weighted pixel density (peak NPD) and log of peak mean Doppler frequency times the peak NPD (vM x NPD(M)). Each of these two values was the maximum in any one of the five chosen ROIs closely associated with the mass. A possible rationale for the relative success of these peak values is the blood signal's normalization and the inhomogeneity of most breast cancers and the expectation that the highest velocities (shunting) and largest collections of blood are not necessarily in the same region in and around the tumor. Peak NPD of cancers varied with age, decreasing by a factor of 45 from 33 to 77 y.