ACCURACY OF MAXIMUM VELOCITY ESTIMATES MADE USING DOPPLER ULTRASOUND SYSTEMS

This study was performed in order to provide quantitative data on the estimation of maximum velocity made using modern Doppler ultrasound sy stems. This is important since the degree of stenosis within arteries is commonly assessed from the maximum velocity. A string phantom was u sed as the source of Doppler signals. This enables direct comparison b etween the Doppler estimated maximum velocity and the true filament ve locity. Six modern commercial Doppler systems were used. Measurements were made under standard conditions for each probe. In addition a numb er of factors were varied in turn (beam-filament angle, filament depth , filament velocity and Doppler aperture position). Under standard con ditions the maximum velocity was overestimated in all cases (0-29% err or). For all measurements maximum velocity errors ranged from -4% to 4 7%. There was a large intraprobe variation in maximum velocity estimat ion (mean variation of 25%), and a large interprobe variation (mean va riation of 18%). These results indicate that, at present, errors in ma ximum velocity estimation may be directly translated into significant errors in the estimate of the degree of arterial stenosis made from ve locity measurements. As a consequence, some patients may be incorrectl y categorized. Consideration should be given to applying angle depende nt correction factors to maximum velocity measurements, and to the use of conversion from Doppler frequency shift to velocity using the angl e derived from the edge of the Doppler aperture.