Ultrasonography in Carotid Artery Stenosis
Although ultrasonography (US) advantageously portrays lumen and wall thickness, velocity criteria have been used primarily to interpret carotid artery stenosis. The relationship of US and velocity measurements was investigated.
Peak-systolic and end-diastolic velocities (PSV, EDV) increase exponentially as the lumen of the internal carotid artery narrows and the percent stenosis (%S) increases. We tested the consistency of the relationship between carotid velocities and US %S in two distinct data sets. One data set was used to obtain regression equations relating velocity parameters and %S based on US. Validation of these equations was conducted using a separate, independent data set. US measurements were classified in 12 %S intervals. PSV, EDV, the ratio of the internal carotid artery to the common carotid artery PSV, and %S were entered consecutively until 10 records for each %S interval were obtained. Regression equations obtained in the first data set were used to predict %S in the second data set. Predicted %S was then compared with actual US %S.
The highest correlation in the first data set ( r = .89) was between %S and the natural logarithm (ln) of PSV. This ln PSV -%S equation was then applied to a second data set of an additional 120 carotid duplex images. In the second data set, actual %S and PSV-predicted %S differed by > 10% in 38 cases (32%). When all velocity-%S regression equations were used for comparison, differences between actual and at least one velocity-predicted %S were > 10% in 19% of the arteries. Conversely, actual %S matched at least one prediction of %S based on velocity data in 81% of the cases.
US %S differed significantly from single velocity-based estimates of %S in at least one-third of the cases. On the other hand, four of five US measurements were confirmed by at least one velocity parameter. Emphasis on US, in addition to velocity data, is recommended for the interpretation of duplex US carotid examinations.
Duplex ultrasonography (US) has become the most common screening and diagnostic test to evaluate extracranial carotid artery stenosis. US has also been employed alone or together with other noninvasive techniques for definitive decision making prior to carotid endarterectomy. Most criteria for grading internal carotid artery stenosis rely on velocity measurements. Velocity criteria, however, vary among laboratories, most likely owing to differences in instrumentation, protocol technique, and the degree of carotid stenosis considered severe enough to warrant endarterectomy. Multielement transducers with different designs produce a variety of instrument-related spectral broadening, altering the true physiologic blood velocity spectrum.
Multicenter randomized trials justified carotid endarterectomy as the most appropriate treatment of severe or even moderate carotid artery stenosis. These trials, however, employed several arteriographic criteria and provoked re-evaluation of duplex US velocity criteria. As a consequence, several different velocity criteria have been created. Furthermore, sample populations included in the studies may have a different prevalence of patients with bilateral stenosis, carotid kinking or curvatures, and age. All of these factors affect carotid velocities. A simpler alternative to protocols dependent on velocity determinations is US imaging.
Focus on imaging emphasizes direct visualization of residual lumen and pathology. Imaging also allows for evaluation of percent stenosis (%S) in intervals of about 10%, an improvement in decision-making detail, and plaque follow-up. This study was conducted to test if direct US measurements differ from velocity-related estimates of carotid stenosis. For this purpose, two data sets were analyzed. A first data set was used to obtain regression equations linking velocity parameters and %S measured by US. These regression equations were used in a second data set to predict %S. This predicted %S based on velocity measurements was compared with the actual %S US measurements.
Although ultrasonography (US) advantageously portrays lumen and wall thickness, velocity criteria have been used primarily to interpret carotid artery stenosis. The relationship of US and velocity measurements was investigated.
Peak-systolic and end-diastolic velocities (PSV, EDV) increase exponentially as the lumen of the internal carotid artery narrows and the percent stenosis (%S) increases. We tested the consistency of the relationship between carotid velocities and US %S in two distinct data sets. One data set was used to obtain regression equations relating velocity parameters and %S based on US. Validation of these equations was conducted using a separate, independent data set. US measurements were classified in 12 %S intervals. PSV, EDV, the ratio of the internal carotid artery to the common carotid artery PSV, and %S were entered consecutively until 10 records for each %S interval were obtained. Regression equations obtained in the first data set were used to predict %S in the second data set. Predicted %S was then compared with actual US %S.
The highest correlation in the first data set ( r = .89) was between %S and the natural logarithm (ln) of PSV. This ln PSV -%S equation was then applied to a second data set of an additional 120 carotid duplex images. In the second data set, actual %S and PSV-predicted %S differed by > 10% in 38 cases (32%). When all velocity-%S regression equations were used for comparison, differences between actual and at least one velocity-predicted %S were > 10% in 19% of the arteries. Conversely, actual %S matched at least one prediction of %S based on velocity data in 81% of the cases.
US %S differed significantly from single velocity-based estimates of %S in at least one-third of the cases. On the other hand, four of five US measurements were confirmed by at least one velocity parameter. Emphasis on US, in addition to velocity data, is recommended for the interpretation of duplex US carotid examinations.
Duplex ultrasonography (US) has become the most common screening and diagnostic test to evaluate extracranial carotid artery stenosis. US has also been employed alone or together with other noninvasive techniques for definitive decision making prior to carotid endarterectomy. Most criteria for grading internal carotid artery stenosis rely on velocity measurements. Velocity criteria, however, vary among laboratories, most likely owing to differences in instrumentation, protocol technique, and the degree of carotid stenosis considered severe enough to warrant endarterectomy. Multielement transducers with different designs produce a variety of instrument-related spectral broadening, altering the true physiologic blood velocity spectrum.
Multicenter randomized trials justified carotid endarterectomy as the most appropriate treatment of severe or even moderate carotid artery stenosis. These trials, however, employed several arteriographic criteria and provoked re-evaluation of duplex US velocity criteria. As a consequence, several different velocity criteria have been created. Furthermore, sample populations included in the studies may have a different prevalence of patients with bilateral stenosis, carotid kinking or curvatures, and age. All of these factors affect carotid velocities. A simpler alternative to protocols dependent on velocity determinations is US imaging.
Focus on imaging emphasizes direct visualization of residual lumen and pathology. Imaging also allows for evaluation of percent stenosis (%S) in intervals of about 10%, an improvement in decision-making detail, and plaque follow-up. This study was conducted to test if direct US measurements differ from velocity-related estimates of carotid stenosis. For this purpose, two data sets were analyzed. A first data set was used to obtain regression equations linking velocity parameters and %S measured by US. These regression equations were used in a second data set to predict %S. This predicted %S based on velocity measurements was compared with the actual %S US measurements.
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