Kirk W. Beach

Quantitative segmental evaluation of venous valvular reflux with duplex ultrasound scanning

The duration of deep venous valvular reflux was studied in 192 venous segments of the legs of 32 patients in good health. Three methods were used to elicit reflux in the supine and upright positions--Valsalvas maneuver, proximal limb compression, and release of distal limb compression. Standardized compressions were achieved with pneumatic cuffs. When this approach was used to study valve function, the time to complete closure of the valve and cessation of retrograde flow was found to be shorter than that for conventional methods of closure. The distal cuff deflation method is the only one that permits a quantitative and reproducible method to measure duration of venous reflux at all levels of the lower limb. Normal values obtained with this test are presented for the common femoral, deep femoral, and superficial femoral veins and for the popliteal and posterior tibial veins midway between knee and ankle level and the posterior tibial vein at the ankle. In the popliteal vein, median duration of reflux is 0.19 second; 95% of the values in the popliteal vein are less than 0.66 second. In distal areas, duration of reflux is short and uniform. The advantage of the cuff deflation test over the Valsalva method is that the cuff method is not hindered by the presence of ileofemoral valves. A better understanding of the relative importance of deep valve dysfunction at different levels and the expected benefit of valve repair may be obtained with this test.

The natural history of carotid arterial disease in asymptomatic patients with cervical bruits.

A prospective study was initiated in January 1980 to follow with Duplex scanning a consecutive series of 167 asymptomatic patients with cervical bruits. Patients were seen at six month intervals for the first year and yearly thereafter. Based on previously validated criteria, disease at the carotid bifurcation was classified into 6 categories: Normal, 1-15% diameter reduction, 16-49%, 50-79%, 80-99%, and occlusion. Patients were evaluated to assess: the occurrence of new neurological symptoms, the stability of the lesions at the carotid bifurcation, and the possible role of risk indicators on disease changes. During follow-up, ten patients became symptomatic (6 with TIAs and 4 with stroke). The development of symptoms was accompanied by disease progression in 8 patients. By life table analysis, the annual rate occurrence of symptoms was 4%. The mean annual rate of disease progression to a greater than 50% stenosis was 8%. When progression in all categories was considered, 60% of the sides showed some disease aggravation. The presence of or progression to a greater than 80% stenosis was highly correlated (p = 0.00001) with either the development of a total occlusion of the internal carotid artery or new symptoms. The major risk factors associated with disease progression were cigarette smoking, diabetes mellitus, and age. Those patients under 65 years of age were most likely to show progression. Despite high rates of disease progression, this study further supports the contention that it is prudent to follow a conservative course in the management of asymptomatic patients presenting with a cervical bruit.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of Atherosclerotic Carotid Plaque Size In Vivo Using High Resolution Magnetic Resonance Imaging

BACKGROUND Current imaging modalities, such as contrast angiography, accurately determine the degree of luminal narrowing but provide no direct information on plaque size. Magnetic resonance imaging (MRI), however, has potential for noninvasively determining arterial wall area (WA). This study was conducted to determine the accuracy of in vivo MRI for measuring the cross-sectional maximum wall area (MaxWA) of atherosclerotic carotid arteries in a group of patients undergoing carotid endarterectomy. METHODS AND RESULTS Fourteen patients scheduled for carotid endarterectomy underwent preoperative carotid MRI using a custom-made phased-array coil. The plaques were excised en bloc and scanned using similar imaging parameters. MaxWA measurements from the ex vivo MRI were used as the reference standard and compared with MaxWA measurements from the corresponding in vivo MR study. Agreement between the in vivo and ex vivo measurement was analyzed using the Bland-Altman method. The paired in vivo and ex vivo MaxWA measurements strongly agreed: the mean difference (in vivo minus ex vivo) in MaxWA was 13.1+/-6.5 mm2 for T1-weighted (T1W) imaging (mean MaxWA in vivo=94.7 mm2, ex vivo=81.6 mm2) and 14.1+/-11.7 mm2 for proton density-weighted (PDW) imaging (mean MaxWA in vivo=93.4 mm2, ex vivo=79.3 mm2). Intraobserver and interobserver variability was small, with intraclass correlation coefficients ranging from 0.90 to 0.98. CONCLUSIONS MRI is highly accurate for in vivo measurement of artery WA in atherosclerotic carotid lesions. This imaging technique has potential application monitoring lesion size in studies examining plaque progression and/or regression.

Duplex ultrasound scanning in the diagnosis of renal artery stenosis: A prospective evaluation

Since ultrasonic energy can be used to interrogate vessels at great depth, it is only natural that it should be applied to deeply placed arteries in the abdomen. Early studies suggested that high-grade stenoses of the renal artery could be detected by this approach as long as the peak systolic velocity in the renal artery was normalized by that measured in the abdominal aorta. A retrospective study comparing the peak velocity in the renal artery to that from the adjacent abdominal aorta (the renal aortic ratio) showed that if this value exceeded 3.5, it is likely to be associated with a greater than 60% diameter-reducing stenosis. To test this hypothesis, we used duplex scanning to prospectively evaluate 58 renal arteries in 29 patients in whom arteriograms were available. There were 39 renal arteries with 0% to 59% stenosis, 14 with 60% to 99% stenosis, and five occlusions by angiography. Renal duplex scanning accurately diagnosed 38 of 39, 11 of 14, and four of five of these, respectively, giving a sensitivity of 84%, a specificity of 97%, and a positive predictive value of 94% for the detection of a greater than 60% diameter-reducing stenosis. The overall agreement with angiography was 93%. These data show that renal duplex scanning can be used to diagnose renal artery stenosis in patients with hypertension or renal dysfunction, thus providing a rational basis for the selection of patients for angiography.

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 systems performance, a novel method was devised using an iterative, least-squares technique to simultaneously determine the systems 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.

Noninvasive diagnosis of renal artery stenosis by ultrasonic duplex scanning.

We retrospectively studied the results of duplex scanning for evaluation of renal artery disease in 158 patients. Satisfactory examinations were achieved in 144 patients (90%). Arteriograms were available for 43 renal arteries. We used the ratio of the peak velocities in the renal artery and the aorta (RAR) to separate nonstenotic arteries (less than 60% diameter reduction) from stenotic arteries (greater than 60% diameter reduction). With an RAR of greater than 3.5 to indicate stenotic lesions, duplex scanning had a sensitivity of 91% (20 of 22 diseased arteries correctly identified) and specificity of 95% (20 of 21 normal or insignificantly diseased arteries correctly identified). One of four occluded arteries was incorrectly interpreted as patent because of misidentification of a collateral vessel. Prospective studies will be necessary to validate this test and establish other criteria for a more detailed classification of renal artery stenosis. The ratio of the end-diastolic to peak systolic velocities in the renal artery (EDR) tended to decrease with increasing serum creatinine levels, presumably because renal vascular resistance increases with end-stage parenchymal disease. EDR may prove useful in the detection of advanced parenchymal disease before renal artery revascularization is attempted.

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.

Cross-beam vector Doppler ultrasound for angle-independent velocity measurements

Combining Doppler measurements taken along multiple intersecting ultrasound (US) beams is one approach to obtaining angle-independent velocity. Over 30 laboratories and companies have developed such cross-beam systems since the 1970s. Early designs focused on multiple single-element probes. In the late 1980s, combining multiple color Doppler images acquired from linear-array transducers became a popular modality. This was further expanded to include beam steering and the use of subapertures. Often, with each change in design, came a new twist to calculating the velocity. This article presents a review of most proposed cross-beam systems published to date. The emphasis is on the basic design, the approach used to determine the angle-independent velocity, the advantages of the design, and the disadvantages of the design. From this, requirements needed to convert the idea of angle-independent vector Doppler into a commercial system are suggested.

Carotid Plaque Morphology and Clinical Events

BACKGROUND AND PURPOSE Studies have suggested that B-mode ultrasonography can be used to determine carotid plaque composition and that specific plaque characteristics are associated with a worse clinical outcome. However, histological studies examining the relationship between carotid plaque morphology and clinical outcome have reported conflicting findings. Furthermore, few investigators have described plaque morphology in quantifiable terms. This study examines the association between the volume of carotid plaque constituents and preoperative ischemic neurological symptoms. Constituents examined were chosen based on their potential for identification by current diagnostic imaging modalities such as ultrasound or MRI. METHODS Atherosclerotic plaques from 43 patients undergoing carotid endarterectomy were examined histologically, with sections obtained every 0.5 to 1 mm. The lesions were examined for the presence and quantity of fibrous intimal tissue, intraplaque hemorrhage, lipid core, necrotic plaque core, and calcification. The quantity of each constituent was compared in plaques removed from symptomatic patients with those excised from asymptomatic individuals. Differences were analyzed with a Kolmogorov-Smirnov statistic. RESULTS There was no difference between plaques removed from asymptomatic and symptomatic patients with regard to the presence and volume of fibrous intimal tissue, intraplaque hemorrhage, the lipid core, the necrotic core, or calcification. CONCLUSIONS In patients with highly stenotic carotid lesions who are undergoing carotid endarterectomy, gross plaque composition is similar regardless of preoperative symptom status. Given this similarity, it is unlikely that differences in the volume of intraplaque hemorrhage, lipid core, necrotic core, or calcification in atherosclerotic carotid plaques explain their embolic history.

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.