Interobserver variability in the measurement of internal carotid stenosis.

OBJECTIVE: To assess interobserver variability in the measurement of carotid stenoses from digital subtraction angiograms displayed in different ways (nonmagnified or magnified, white or black arteries); and to compare human readers with computer-generated densitometric measurements of vessel stenosis. METHODS: Digital subtraction angiograms of 20 proximal internal carotid artery stenoses were laser printed in the following ways: (1) Nonmagnified white artery on a black background; (2) Magnified white artery on a black background; (3) Nonmagnified black artery on a white background; (4) Magnified black artery on a white background. This resulted in 80 images of internal carotid artery stenoses. These stenoses were independently measured by 4 radiologists using the North American Symptomatic Carotid Endarterectomy Trial method. A computer-generated densitometric measurement of the black nonmagnified images was also obtained. RESULTS: The most reliable stenosis measurements were obtained from the nonmagnified black and white artery images. The interobserver variability in the measurement of internal carotid stenoses using these images was quite small. Variability increased with the use of magnification. The computer-generated stenosis measurements were consistently much higher than those of the radiologists. CONCLUSION: There was significant variability in measurements made from magnified images and between human readers and computer-generated measurements. This has great clinical significance. Readers of digital angiographic images must determine the most reliable, reproducible images generated by their equipment, as these measurements significantly affect treatment of patients with symptomatic internal carotid artery stenosis.     

Three-dimensional color Doppler sonography in carotid artery stenosis

BACKGROUND AND PURPOSE: Color Doppler sonography (CDS) suffers from such disadvantages as high interobserver variability and problems with data presentation and storage. We therefore performed a prospective trial to assess the role of three-dimensional CDS (3D-CDS) in the evaluation of internal carotid artery stenosis (ICAS). METHODS: We included 32 consecutive patients with sonographically verified ICAS (30-99%) and 16 asymptomatic volunteers. All underwent CDS and 3D-CDS, and 23 patients also underwent intraarterial angiography. The sensitivity, specificity, positive predictive value, and negative predictive value for the detection of high-grade ICAS were analyzed by three blinded readers, who also graded the percentage of ICAS. RESULTS: CDS revealed 14 patients with mild to moderate ICAS and 18 patients with high-grade ICAS. Mean sensitivity of 3D-CDS was 81.5%, mean specificity was 98.9%, mean positive predictive value was 97.9%, and mean negative predictive value was 89.9%. 3D-CDS correlated significantly with CDS (mean r=0.85; P<.001) and angiography (mean r=0.57; P=.01). CONCLUSION: 3D-CDS findings correlate with those obtained by CDS and angiography; 3D-CDS also offers excellent interobserver correlation, positive predictive value, and specificity, approaching 100% for the detection of high-grade ICAS.     

Nonstenotic internal carotid arteries: effects of age and blood pressure at the time of scanning on Doppler US velocity measurements.

PURPOSE: To assess the effects of age and blood pressure at the time of scanning on internal carotid artery velocities and cross-sectional diameter at Doppler ultrasonography (US). MATERIALS AND METHODS: During 12 months, 1,020 consecutive patients underwent internal carotid artery Doppler US. No or minimal arterial disease was found in 142 patients (67 women, 75 men). Blood pressure was recorded prior to examination. The angle-corrected internal carotid artery peak systolic and end-diastolic velocities were obtained. The effects of systolic blood pressure, diastolic blood pressure, pulse pressure, age, chronic hypertension, and medications for hypertension on velocities were evaluated by using linear regression analysis. RESULTS: Peak systolic velocity was influenced by age (P =.008), systolic blood pressure (P =.009), diastolic blood pressure (P =.003), and pulse pressure (P =.017) but not history of hypertension (P =.53) or antihypertensive medication use (P =.77). Increasing age decreased peak systolic velocity by 0.34 cm/sec/y. End-diastolic velocity was influenced by age (P <.001) but not by systolic, diastolic, or pulse pressure (all P values were >.13). CONCLUSION: Internal carotid artery peak systolic velocities decrease with advancing age and increase with increasing pulse pressure. The effects of blood pressure at the time of scanning are small, but isolated systolic hypertension could cause increases in spurious velocity.     

Evaluation of carotid stenosis by angiography: potential bias toward overestimated measurements introduced by prior interpretation of Doppler sonograms

BACKGROUND AND PURPOSE: Doppler sonography of the carotid arteries is routinely performed before catheter angiography, and its results may bias the subsequent interpretation of angiograms. We attempt to establish that Doppler sonography may show an exaggerated degree of carotid stenosis, introducing bias to the evaluation of carotid stenosis by subsequent catheter angiography. METHODS: Angiograms of the carotid arteries obtained to evaluate potential carotid stenosis in patients who had undergone Doppler sonography of the carotid arteries were retrospectively reviewed (from 1993 to 1998). Readers who were blinded to the previous interpretations of the angiography and Doppler sonography results measured carotid stenosis. The results of Doppler sonography of the carotid arteries were not re-evaluated. Based on the original Doppler sonograms, stenoses were categorized as normal/mild (<30%), moderate (30-59%), severe (60-79%), and critical (80-99%). Within these categories, the differences between the original percent stenosis, as determined by angiography, and the blinded measurements were determined. RESULTS: A total of 106 patients with angiographically measurable stenoses in 128 vessels were identified. The difference between the blinded readers was 3% (+/-8%), with no category statistically different from the other. The difference between original and remeasured stenoses in carotid arteries in the Doppler categories were as follows: mild stenosis, 2% (+/-9%); moderate stenosis, 6% (+/-15%); severe stenosis, 8% (+/-15%); and critical stenosis, 22% (+/-12%). A significant overestimation occurred in the severe (P < .05) and critical (P < .0001) stenosis categories. One third of patients with stenoses in the severe or critical Doppler category had significant stenoses on the original angiograms that were less than 60%, according to blinded remeasurement. CONCLUSION: Doppler sonography of the carotid arteries has the potential to bias the subsequent interpretation of catheter angiography. Care must be taken to measure stenosis accurately, using strict criteria to determine the potential benefit of carotid endarterectomy for the individual patient and to ensure that the criteria for Doppler sonography of the carotid arteries are based on accurate catheter angiography measurements.     

Variability of Doppler US measurements along the common carotid artery: effects on estimates of internal carotid arterial stenosis in patients with angiographically proved disease

PURPOSE: To determine the effect of variability of common carotid arterial (CCA) velocities on velocity ratios used to assess internal carotid arterial (ICA) stenosis. MATERIALS AND METHODS: Doppler ultrasonographic (US) velocity measurements were obtained at three levels in the CCA and in the carotid bulb and ICA in all patients referred for carotid US between September 1996 and October 1997. Only ICAs (n = 98, in 57 patients) without ipsilateral CCA disease at angiography were analyzed. The range of CCA peak systolic velocities (PSVs) and end diastolic velocities (EDVs) and velocity ratios were calculated for each CCA measurement. For each ICA/CCA velocity ratio, receiver operating characteristic analysis was performed. RESULTS: CCA PSV and EDV ranges averaged 23.1 cm/sec +/- 15.7 (SD) and 5.1 cm/sec +/- 3.6, respectively. For a given side, the difference averaged 1.0 +/- 1.3 for PSV ratios and 2.7 +/- 6.9 for EDV ratios, depending on where CCA measurements were taken. By using a threshold of 60% stenosis as indication for endarterectomy, variability in CCA velocities could have altered recommendations in 16 (28%) of 57 patients. Receiver operating characteristic analysis showed that ratios made by using the three CCA velocities or their mean were not significantly different. CONCLUSION: Variability in velocity measurements along the course of the CCA in patients with ICA disease can be substantial and can result in inaccuracies in assessment of carotid stenosis.     

Percutaneous angioplasty of atherosclerotic and postsurgical stenosis of carotid arteries

A technique for safe angioplasty of atherosclerotic stenosis of internal and common carotid arteries is described in which temporary balloon occlusion of the internal carotid artery is used to prevent cerebral embolization during manifestation of ulcerated plaques. Its successful use in six atherosclerotic stenosis is described. Five angioplasties of postsurgical stenoses are also reported in which the technique of temporary occlusion was not used. The future of carotid artery angioplasty is discussed.     

Magnetic resonance velocity measurements in small arteries. Comparison with Doppler ultrasonic measurements in the aortas of normal rabbits.

RATIONALE AND OBJECTIVES. Magnetic resonance imaging (MRI) can be used to measure motion. This study compares MRI blood flow velocity measurements to Doppler ultrasound velocity measurements in an animal model. MATERIALS AND METHODS. Blood flow in the abdominal aortas of nine normal rabbits was measured using 16-frame, velocity-resolved MRI and Doppler ultrasound. The MRI data were processed into velocity spectra to aid in their interpretation. RESULTS. Maximum velocity measurements made by range-gated Doppler ultrasound were predicted by the maximum velocity values derived from MR velocity spectra with a slope of 0.861, an intercept of -2.78 cm/second, and an R-value of 0.935 in 70 measurements. CONCLUSIONS. Despite the longer time required for the MR measurement, the MR velocity measurement may be useful in the assessment of deep vessels or those obscured by other structures, which are difficult to measure with ultrasound.     

Increased variability of watershed areas in patients with high-grade carotid stenosis

Purpose

Watershed areas (WSAs) of the brain are most susceptible to acute hypoperfusion due to their peripheral location between vascular territories. Additionally, chronic WSA-related vascular processes underlie cognitive decline especially in patients with cerebral hemodynamic compromise. Despite of high relevance for both clinical diagnostics and research, individual in vivo WSA definition is fairly limited to date. Thus, this study proposes a standardized segmentation approach to delineate individual WSAs by use of time-to-peak (TTP) maps and investigates spatial variability of individual WSAs.

Methods

We defined individual watershed masks based on relative TTP increases in 30 healthy elderly persons and 28 patients with unilateral, high-grade carotid stenosis, being at risk for watershed-related hemodynamic impairment. Determined WSA location was confirmed by an arterial transit time atlas and individual super-selective arterial spin labeling. We compared spatial variability of WSA probability maps between groups and assessed TTP differences between hemispheres in individual and group-average watershed locations.

Results

Patients showed significantly higher spatial variability of WSAs than healthy controls. Perfusion on the side of the stenosis was delayed within individual watershed masks as compared to a watershed template derived from controls, being independent from the grade of the stenosis and collateralization status of the circle of Willis.

Conclusion

Results demonstrate feasibility of individual WSA delineation by TTP maps in healthy elderly and carotid stenosis patients. Data indicate necessity of individual segmentation approaches especially in patients with hemodynamic compromise to detect critical regions of impaired hemodynamics.

     

Variability of clinical CT perfusion measurements in patients with carotid stenosis

Introduction CT perfusion imaging (pCT) may be used to detect and monitor hemodynamic abnormalities due to cerebrovascular disease. The magnitude of variability in clinical measurements has been insufficiently evaluated. The purpose of this study was to measure the long-term variability of clinical pCT measurements in patients with cerebrovascular disease. Methods pCT parameters were calculated for the cerebral hemisphere contralateral to a carotid stenosis before and after stent treatment of stenosis in 33 consecutive patients. Mean transit time (MTT), cerebral blood flow (CBF), and cerebral blood volume (CBV) calculated from pCT data from both a small and large region of interest (ROI) using both manual and automated methods were compared before and after stent treatment. Differences between the first and second measurement were tested for statistical significance with at-test. Variability was calculated as the standard deviation of the differences divided by the mean of the pre- and post-stent treatment values. To adjust for proportional bias, the Bland–Altman analysis was applied. Results The differences between the two measurements of MTT, CBF, and CBV averaged 2.5 to 7.7% when a manual method was used and was higher with automatic methods (p > 0.07). The variability of the values was 18% for MTT, 19% for CBV, and 25% for CBF with the large ROI and the manual method of calculation. The magnitude was larger when the small ROI and automatic methods were employed. Conclusion Longitudinal measurements of MTT, CBV, or CBF by pCT may vary by 20–25%. To detect changes in treatment-related changes in perfusion, pCT studies must be designed to achieve statistical significance based on this variability.     

Doppler ultrasound and contrast-enhanced magnetic resonance angiography in assessing carotid artery stenosis

PURPOSE: This study prospectively compares Doppler ultrasound (Doppler US) and contrast-enhanced magnetic resonance angiography (CE-MRA) with digital subtraction angiography (DSA) and endarterectomy findings to determine the accuracy in assessing carotid artery stenosis. MATERIALS AND METHODS: Thirty-two patients underwent carotid endarterectomy, 21 studied with Doppler US, CE-MRA and DSA and 11 with Doppler US and CE-MRA. In 41 carotid arteries, the degree of stenosis was analysed with Doppler US and CE-MRA and compared with DSA by using the Spearman rank correlation coefficient. Nine out of 32 endarterectomies were done using the eversion technique, and it was possible to compare Doppler US, CE-MRA and DSA with the specimen measurement. Twenty-three out of 32 endarterectomies were done using the standard technique, and the presence of ulcers was documented. RESULTS: There was a significant Doppler US/DSA (Rs=0.86; p<0.001) and CE-MRA/DSA (Rs=0.81; p<0.001) correlation for the degree of stenosis. The diagnostic accuracy of the three methods was the same (89%). Ulcers were most frequently seen at CE-MRA, with a diagnostic accuracy of 85%. CONCLUSIONS: These data suggest that endarterectomy on the basis of Doppler US and CE-MRA can be considered appropriate. CEMRA was the best noninvasive imaging modality to detect plaque ulceration.     

Color-flow Doppler sonography in the identification of ulcerative plaques in patients with high-grade carotid artery stenosis.

PURPOSE: To assess the ability of color-flow Doppler sonography (CFDS) to detect plaque ulcerations in patients who had high-grade to thread-like carotid artery stenosis and who underwent carotid endarterectomy. METHODS: CFDS is a noninvasive diagnostic technique that allows, in addition to spatial visualization of blood flow, the identification of abnormal blood flow patterns such as vortex formation. There is evidence that pathologic anatomic changes in the vascular wall (such as ulcerations) may result in characteristic hemodynamic alterations. Therefore, solely hemodynamic criteria (detection of vortices) were used to diagnose ulceration. The results of preoperative examinations were compared to the intraoperative findings in 89 patients in a prospective and blinded way. RESULTS: CFDS proved highly sensitive (95.3%), specific (93.5%), and accurate (94.0%) for demonstrating ulcerative plaques. CONCLUSION: CFDS may be of significant advantage for examining plaque morphology in patients who have high-grade internal carotid artery stenosis, and in whom accurate, noninvasive diagnosis of plaque ulceration was previously difficult, if not impossible.     

Effect of heart rate on Doppler measurements of resistive index in renal arteries

The effect of heart rate on Doppler measurements of the resistive index (RI) in renal arteries was studied in eight patients by varying paced heart rate to eliminate intrinsic and extrinsic factors influencing renal vascular resistance. A Doppler spectrum was obtained in renal segmental arteries. The RI was calculated at increasing heart rates from 70 to 120 beats per minute. There was a statistically significant decrease in RI with increasing heart rate (heart rate of 70: RI = 0.7 +/- 0.06; heart rate of 120: RI = 0.57 +/- 0.06; P less than .001), while blood pressure and cardiac output remained constant. To overcome this source of variance, the observed RI can be corrected for heart rate by using the following regression equation. For a heart rate of 80 beats per minute, corrected RI = observed RI - 0.0026(80 - observed heart rate). In interpreting the RI in renal allograft examinations, the actual heart rate of a patient must be taken into account. However, the clinical significance of standardizing the RI for heart rate requires further investigation.