Biomedical subjects

K W Beach

Publications and source records attributed to K W Beach.

At least 37 records · Page 2Linked to original sources

PubMed1995

Demonstration of three-dimensional vector flow estimation using bandwidth and two transducers on a flow phantom.

A method of performing three-dimensional (3-D) velocity vector estimation with two transducers is demonstrated on a flow phantom using the Doppler spectra's mean frequencies and bandwidths. The results are compared with 3-D vector estimates computed from Doppler mean frequencies obtained with a five-transducer system. It is shown that the two-transducer vector Doppler system which uses bandwidth can improve on the accuracy of a three-transducer vector Doppler system which relies only on Doppler mean frequencies.

Blood Flow Velocity↗

PubMed1995

Hemodynamic parameters of failing infrainguinal bypass grafts.

PURPOSE: To assess the relationship of duplex ultrasound hemodynamic parameters in stenotic vein grafts with events such as graft thrombosis or surgical revisions. PATIENTS AND METHODS: We studied 35 patent infrainguinal bypass grafts that were observed by means of color duplex graft mapping using a surveillance protocol. RESULTS: During the 11.2 month mean follow-up interval, 10 grafts developed complications. Two stenotic grafts (1 already revised) thrombosed spontaneously, and arteriography was obtained on the basis of either clinical indications or a decreased ankle/brachial index of greater than 0.15 on 9 bypasses, leading to 12 procedures (multiple procedures on 2 grafts). The 14 duplex examinations preceding an event showed these bypasses had increased focal peak systolic velocities that ranged from 250 to 600 cm/s and velocity ratios that ranged from 3.4 to 25.0 at the stenotic segment of the graft, anastomosis, or outflow artery. None of the grafts with a stenotic peak systolic velocity less than 250 cm/s or a velocity ratio less than 3.4 thrombosed spontaneously or required revision. CONCLUSION: We conclude that stenotic vein grafts with a focal peak systolic velocity of at least 250 cm/s or a velocity ratio of at least 3.4 are at increased risk for thrombosis or need for revision. Asymptomatic stenotic vein grafts with focal peak systolic velocities and ratios less than the above values may be safely observed without immediate risk for thrombosis.

Adult↗

PubMed1995

A new method for studying plaque morphology.

A histologic method was developed for three-dimensional (3-D) analysis of atherosclerotic plaques removed from the carotid bifurcation during endarterectomy. By sectioning the plaque at frequent intervals (0.5 to 1.0 mm), it is possible to obtain important information on plaque constituents with regard to their volume and distribution within the lesion. These data from each section are combined with those from other sections and displayed in a 3-D format for the entire length of the lesion. The tissues making up each of the 10 carotid plaques were outlined and digitized for each histologic section by position along the lesion. From the areas outlined a 3-D model was created by a computer-aided design program. Quantitative information on tissue distribution within the plaque was measured. Fibrous tissue constituted between 35% and 70% of plaque volume; loose necrosis from 0.5% to 30% of the plaque and thrombus occupied, at a maximum, 10% even though if was present in six of the 10 plaques. To investigate the distribution of constituents about the long axis, measurements were also made from each of the four quadrants of each section. The reproducibility of the measurements of three sets of sections at 10-mm separation showed that estimates of the amount of some constituents were very reproducible whereas others had considerable variation related to the small volume they occupied within the lesion. By generating a complete 3-D reproduction of the contents of atherosclerotic plaques, it may be possible to identify those features of the plaque that are most responsible for the development of ischemic events.

Arteriosclerosis↗

PubMed1994

Ultrasonic three-dimensional reconstruction: in vitro and in vivo volume and area measurement.

This study validates the use of an ultrasound three-dimensional reconstruction system to measure phantom and blood conduit geometry. Independently determined uniform and stenotic phantom dimensions are compared with reconstruction-based measurements. Lower extremity saphenous vein bypass graft reconstructions were performed to demonstrate clinical application. Uniform phantom independent and reconstructed volume correlation was high (r = 0.989), the average volume difference was 4.68 mm3 and the average area difference was 0.4 mm2. An in vitro 28% diameter reduction was detected. Stenotic bypass graft segment volume was 795 mm3; following successful angioplasty the volume increased to 1419 mm3. Advantages of this technique are its accuracy, the luminal information it provides and the absence of mechanical arm or acoustic transmitter limitations. We are exploring the possibility that measurement of luminal change over time may allow stenosis detection prior to hemodynamic disturbance, in an ongoing clinical saphenous vein bypass graft surveillance study.

Humans↗

PubMed1994

Pseudocolor B-mode arterial images to quantify-echogenicity of atherosclerotic plaque.

Based on the differences between tissue impedances in atherosclerotic plaques and on the scattering of ultrasound from blood, colors were assigned to the echo strength scale, replacing the usual gray scale in 2-D B-mode ultrasound images. Using a "green tag" indicating -55 dB to mark blood, other echo strength values from atherosclerotic plaque were assigned specific colors, creating a B-mode color ultrasound display that highlights selected echogenicities. The color scale permits the use of a wider dynamic range in the B-mode image, and allows the instrument gains to be set reproducibly.

Arteries↗

PubMed1994

Echolucent regions in carotid plaque: preliminary analysis comparing three-dimensional histologic reconstructions to sonographic findings.

This study compares sonographic and histologic findings within defined spatial regions in carotid artery plaque, using computer generated three-dimensional reconstructions. Twenty-four patients (14 asymptomatic, 10 symptomatic) with angiographically documented 70% to 99% carotid artery stenosis were examined with ultrasonic B-mode imaging prior to endarterectomy. Using a standardized protocol for instrument set-up and scanning technique, echolucent regions in the plaque were identified. After endarterectomy, each plaque was sectioned at 0.5 to 1.0 millimeter increments throughout its length. Sites containing intraplaque hemorrhage, cholesterol clefts, foam cells, necrotic cores, dense calcification and speckled calcification were identified. These areas were outlined on a template, digitized and imported into a computer program that created three-dimensional reconstructions of the histologic findings. Each carotid plaque was divided into quadrants for analysis: (1) lateral wall proximal to the common carotid bifurcation (flow divider); (2) medial wall proximal to the flow divider; (3) lateral wall distal to the flow divider; and (4) medial wall distal to the flow divider. The odds of finding intraplaque hemorrhage, foam cells, necrotic cores and speckled calcification were significantly higher in quadrants with an echolucent region identified by ultrasonography (odds ratio (95% confidence interval) for intraplaque hemorrhage = 3.5 (1.4-8.6); foam cells = 4.0 (1.6-9.9); necrotic cores = 3.2 (1.2-8.4); speckled calcification = 4.0 (1.6-9.8). This preliminary analysis demonstrates the potential of these newly developed techniques for comparing ultrasonic imaging to histology.

Aged↗

PubMed1994

3D ultrasonic image feature localization based on magnetic scanhead tracking: in vitro calibration and validation.

The basis of a three-dimensional (3D) ultrasound imaging system was constructed from a commercially available magnetometer-based position and orientation measurement (POM) device, a standard B-Mode ultrasound instrument and a personal computer. To evaluate the system's performance, a novel method was devised using an iterative, least-squares technique to simultaneously determine the system's calibration parameters and measure its precision in locating points in three-dimensional space. When tested separately, the POM system located single points with a root mean squared (RMS) uncertainty of from 1.4 mm to 3.2 mm over the 610 mm working radius of the system. When combined with the ultrasound instrument, the RMS uncertainty in locating point targets varied from 2.1 mm to 3.5 mm. These results establish the lower limits of variability to be expected from this system when locating fiducial anatomical landmarks for repeated examinations of the same region of the body, and when making numerical 3D reconstructions from multiple planar images.

Calibration↗

PubMed1994

Transesophageal echocardiography and carotid ultrasound in patients with cerebral ischemia: prevalence of findings and recurrent stroke risk.

OBJECTIVES: This study was conducted to determine the yield of transesophageal echocardiographic findings in a consecutive series of patients with stroke and transient ischemic attack, with and without carotid stenosis, and to estimate the recurrent stroke risk associated with specific echocardiographic findings. BACKGROUND: Transesophageal echocardiography has a high yield for identification of potential sources of cardiac embolism in patients with cerebral ischemia; however, the clinical significance of the most commonly detected abnormalities is uncertain. METHODS: We evaluated 145 consecutively admitted patients with stroke or transient ischemic attack with both transesophageal echocardiography and carotid ultrasound. Patients were followed up prospectively for a mean duration of 18 months to document the rate of recurrent cerebral ischemia. RESULTS: Transesophageal echocardiography detected at least one potential cardiac source of embolism in 45% of the patients. Atrial septal aneurysm and interatrial shunt were detected more frequently in patients who did not have a significant carotid stenosis that could account for their ischemic event. During follow-up, a higher rate of recurrent stroke or transient ischemic attack occurred in patients with positive transesophageal echocardiographic findings, particularly atrial septal aneurysm, interatrial shunt and left atrial thrombus. CONCLUSIONS: These data support recent studies that suggest that atrial septal aneurysm and interatrial shunts may be a significant source of cardioembolic stroke. Further studies are needed to clarify the optimal management of patients with these abnormalities.

Carotid Stenosis↗

PubMed1994

Ultrasound determination of total arterial wall thickness.

PURPOSE: Ultrasonic measurement techniques for determining intima-media thickness and total arterial wall thickness have been described. The intima-media thickness measurements are currently in use in large epidemiologic trials. Intima-media thickness does not evaluate extramedial atherosclerotic change and so may not fully reflect pathologic changes in the arterial wall. METHODS: After we performed variability studies of B-mode image acquisition and measurement, we measured total wall thickness and intima-media thickness of the common carotid arteries in 60 adult subjects in three groups: a control group aged 20 to 29 years, a control group aged 60 to 79 years, and a claudication group aged 60 to 79 years. Measurements were made with B-mode ultrasound images. RESULTS: No statistical difference between sexes was noted. A statistically significant (p < or = 0.05) increase in intima-media thickness and wall thickness was found with increasing age, and an additional increase was observed with clinically significant lower extremity arterial occlusive disease (p < or = 0.05). Image quality had an effect on measurement accuracy. CONCLUSIONS: The finding that the wall thickness of common carotid arteries is increased in those patients with clinically significant lower extremity disease supports the theory that atherosclerosis affects the arterial wall in a systemic fashion. Because intima-media thickness also increases across subject groups without change in its proportional contribution to the total arterial wall thickness, extramedial arterial changes also occur with aging and the development of atherosclerosis. We propose that because increases in wall thickness measurements of common carotid arteries follow intima-media thickness increase (but do not necessarily measure the same physiologic change) and the wall thickness method can be used in cases when the intima-media thickness cannot be measured, arterial wall thickness measurement may serve as an alternate or confirmatory test of peripheral artery atherosclerotic severity.

Adult↗

PubMed1993

Carotid artery intraplaque hemorrhage and stenotic velocity.

BACKGROUND AND PURPOSE: One of the proposed mechanisms for sudden expansion of a carotid bifurcation plaque is hemorrhage within the lesion. It has been postulated that the sudden increase in plaque size will acutely reduce blood flow to the ipsilateral hemisphere and induce either a transient ischemic attack or a stroke. In this study, the relation between peak systolic velocity at the site of narrowing and its potential role in the development of intraplaque hemorrhage were investigated. METHODS: Ten patients who had carotid endarterectomy were examined by duplex Doppler sonography before surgery to determine the peak systolic velocity at the site of maximal narrowing. The excised carotid plaques were sectioned at 1-mm intervals and examined for histological evidence of intraplaque hemorrhage. The recorded peak systolic velocities in patients with intraplaque hemorrhage were compared with the velocities in cases in which no hemorrhage was identified. RESULTS: Five of the ten patients had intraplaque hemorrhage. Four of the five patients with intraplaque hemorrhage had a peak systolic velocity of > 420 cm/sec and diastolic velocities of > 160 cm/sec; none of the patients without intraplaque hemorrhage had such high values. CONCLUSIONS: Peak systolic velocity is significantly higher in patients with intraplaque hemorrhage. The specificity and sensitivity of a peak systolic velocity of > 420 cm/sec in predicting intraplaque hemorrhage remains to be determined.

Arteriosclerosis↗

PubMed1992

Vector Doppler: accurate measurement of blood velocity in two dimensions.

An ultrasound Doppler system capable of determining both the magnitude and direction of complex blood velocities has been developed and demonstrated. This system uses a single transmitter and two receivers to resolve orthogonal velocity vector components. The system has been tested on a moving string phantom and on a carotid artery. The method may improve the detection of early vascular diseases and improve the accuracy of volumetric blood flow measurements in peripheral arteries.

Blood Flow Velocity↗

PubMed1992

1975-2000: a quarter century of ultrasound technology.

The most popular forms of ultrasonic diagnostic technology experienced a major transition around 1975 with the introduction of real-time B-mode imaging and the combination of real-time imaging with pulsed Doppler in the Ultrasonic Duplex Scanner. At about the same time, the superposition of Doppler data as color on the gray-scale B-mode image was conceived and demonstrated. Since that time, the instruments have been commercialized and distributed broadly. Except for advancements in scanhead design, the introduction of dynamic focussing on echo receive, and conversion of the instruments from analog to digital processing, little has changed in ultrasound instruments; their size, price, features, and portability have been constant. A fully trained examiner using the most modern instrument made in 1978 can easily adapt the same examination methods to instruments made in 1990. The major change in ultrasound technology has been the increased application of ultrasound examination, specifically Doppler examinations to new organ systems. These trends will change in this final decade of the century. The comments here are from a perspective of noninvasive vascular diagnosis. Each of the advancements in ultrasound technology have resulted from the combined efforts and cooperation of many people. I will not attempt to credit those people here.

Forecasting↗

PubMed1990

Testing ultrasonic pulsed Doppler instruments with a physiologic string phantom.

The spatial, temporal, and frequency resolution of conventional ultrasonic Doppler instruments and the time/space distortions in two-dimensional color Doppler imaging systems can be measured using a pulsatile moving string target. The diameter of the string is small compared with the Doppler sample volume, the velocity (speed and direction), acceleration and timing of the string motions are precisely known with reference to the R wave timing mark, and the spatial location of the string is known. A loop of surgical thread or monofilament fishline running between pulleys is driven by a motor that provides constant string speeds from 0.05 to 150 cm/s and variable string speeds programmed to mimic arterial velocity waveforms from the carotid, aortic, and femoral arteries. Constant string speeds are used to evaluate the Doppler sensitivity, frequency processing, and sample volume size; pulsatile movement of the string provides a physiologic model to evaluate the temporal performance of conventional Doppler systems and the temporal and spatial performance of two-dimensional color Doppler imaging scanners.

Blood Flow Velocity↗

PubMed1989

Should results of ultrasound Doppler studies be reported in units of frequency or velocity?

There is a current tendency to report the results of ultrasound Doppler studies in units of velocity instead of Doppler frequency. This is probably motivated by the intuitive feeling that blood flow studies should naturally be reported in cm/s and the notion that "velocity" is a normalizing factor for Doppler ultrasound studies. In order to determine velocity, the Doppler angle theta or angle formed by the ultrasound beam and flow velocity vector, must be known. It is not possible, using currently available systems, to obtain an accurate estimate of this angle. The physics related to the Doppler equation are reviewed in this paper along with examples to illustrate the origin and magnitude of errors that could arise when reporting in units of velocity. Guidelines are provided for thinking about and reporting results of Doppler studies in units of velocity. An understanding of the Doppler equation and its use in clinical studies are promoted in this paper to enhance the diagnostic usefulness of Doppler ultrasound studies and to reduce serious errors which could lead to faulty information dictating patient management.

Blood Flow Velocity↗

PubMed1989

An ultrasonic measurement of superficial femoral artery wall thickness.

An ultrasonic measurement of the superficial femoral artery wall thickness was performed on 16 volunteers. The measurement included all echogenic tissue between the lumen of the superficial femoral artery and the lumen of the superficial femoral vein. The average arterial wall plus vein wall thickness in volunteers with peripheral arterial disease was 2.13 +/- 0.87 mm, significantly greater than the 1.27 +/- 0.50 mm found in those without detectable peripheral arterial disease.

Aged↗

PubMed1989

Diagnosis of deep venous thrombosis. A prospective study comparing duplex scanning to contrast venography.

Duplex scanning has been proposed as a safe alternative to contrast venography for diagnosing deep venous thrombosis, but its accuracy has not been proved. In this prospective, double-blind study of 47 patients, the sensitivity and specificity of duplex scan criteria were determined relative to contrast venography for lower extremity deep venous thrombosis. Criteria considered to show the presence of deep venous thrombosis included visualization of thrombus (T), absence of spontaneous flow by Doppler ultrasonography (F), absence of phasicity of flow with respiration (P), and incompressibility of the vein with probe pressure (VC). When analyzed individually, the variables T and F had low sensitivities (50% and 76%) but high specificities (92% and 100%). VC had low values for both (79% and 67%, respectively). The best single variable was P (sensitivity and specificity = 92%). The best combinations of variables were T+P (sensitivity = 95%, specificity = 83%), T+F+P (sensitivity = 95%, specificity = 83%), F+P (sensitivity and specificity = 92%), and F+T (sensitivity = 92%, specificity = 87%). The low specificity of vein incompressibility was secondary to cases in which normal veins were difficult to compress in the thigh. All false-negative cases were from isolated calf vein thrombi. We conclude that isolated criteria from duplex scanning should not be used to diagnose deep venous thrombosis. In cases of suspected calf vein thrombosis, repeat duplex examination should be obtained in 3-4 days to determine the most appropriate therapy. In equivocal cases of proximal vein thrombosis, a contrast venogram should be obtained.

Adult↗

PubMed1989

Spontaneous lysis of deep venous thrombi: rate and outcome.

Ultrasonic duplex scanning was used to study the rates at which lysis of thrombi, valvular incompetence, and symptoms of the postthrombotic syndrome (edema) developed in 21 patients after deep venous thrombosis (DVT). Lysis of thrombi occurred rapidly in most patients. In 11 of 21 patients (53%), recanalization occurred in all segments by 90 days after presentation. In four patients, extension of the initial DVT occurred between 30 and 180 days, despite treatment with warfarin. Valvular incompetence developed in 13 patients during the study period. The number of patent venous segments with incompetent valves increased from the initial presentation to 180 days, at which time 25% of patent segments contained incompetent valves. Valvular incompetence developed in previously thrombosed segments that were initially competent after recanalization and in segments not previously thrombosed. This suggested that although incompetence may occur as a result of a direct effect of the thrombus on the valve, other mechanisms must also be involved. Patients with edema early after DVT (from 7 to 30 days) were more likely to have residual occlusion than valvular incompetence. The late development of edema (from 90 to 270 days) was more closely correlated with valvular incompetence.

Humans↗

PubMed1988

Progression of lower-extremity arterial occlusive disease in type II diabetes mellitus.

The prevalence of lower-extremity arterial occlusive disease (LEAOD), the progression of LEAOD, and the incidence of new LEAOD were determined by noninvasive method in 410 volunteers between the ages of 50 and 70 yr; 252 individuals had type II (non-insulin-dependent) diabetes, 158 were control subjects. LEAOD was monitored with the ankle/arm systolic blood pressure index in combination with Doppler arterial velocity waveform analysis. LEAOD was much more prevalent in the type II patients (22%, 55 of 252) than in the control subjects (3%, 4 of 158) (P less than .00001). The prevalence of risk factors for LEAOD was much higher in the type II patients, including elevated triglyceride, depressed high-density lipoprotein (HDL) cholesterol, hypertension, smoking, and elevated systolic blood pressure. In type II diabetic patients the incidence of new LEAOD over a 2-yr period (14%, 28 of 197) was lower than the incidence of LEAOD progression (87%, 45 of 52). Type II patients with LEAOD also had a high incidence of mortality (22%, 12 of 55) compared with those without LEAOD (4%, 8 of 197) (P less than .0005). A risk score including smoking history, duration of diabetes, depressed HDL cholesterol, total cholesterol, elevated systolic blood pressure, and low obesity index is related to LEAOD. After accounting for the effect of all of the risk factors, we suggest that type II diabetes contributes additional risk for LEAOD.

Aged↗