Doppler angle correction in the measurement of intrarenal parameters

Jing Gao¹, Keith Hentel¹, Qiang Zhu², Teng Ma², George Shih¹, Kevin Mennitt¹, Robert Min¹
¹Department of Radiology, New York Presbyterian Hospital, Weill Cornell Medical College, NY, USA; ²Division of Diagnostic Ultrasound, Department of Radiology, Beijing Tongren Hospital, Capital Medical University, Beijing, China

Background: The aim of this study was to assess differences in intrarenal artery Doppler parameters measured without and with Doppler angle correction.
Methods: We retrospectively reviewed color duplex sonography in 30 normally functioning kidneys (20 native kidneys in 10 subjects and 10 transplanted kidneys in 10 subjects) performed between January 26, 2010 and July 26, 2010. There were 10 age-matched men and10 age-matched women (mean 39.8 ± 12.2, range 21–60 years) in this study. Depending on whether the Doppler angle was corrected in the spectral Doppler measurement, Doppler parameters including peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI) measured at the interlobar artery of the kidney were divided into two groups, ie, initial Doppler parameters measured without Doppler angle correction (Group 1) and remeasured Doppler parameters with Doppler angle correction (Group 2). Values for PSV, EDV, and RI measured without Doppler angle correction were compared with those measured with Doppler angle correction, and were analyzed statistically with a paired-samples t-test.
Results: There were statistical differences in PSV and EDV at the interlobar artery in the upper, mid, and lower poles of the kidney between Group 1 and Group 2 (all P < 0.001). PSV and EDV in Group 1 were significantly lower than in Group 2. RI in Group 1 was the same as that in Group 2 in the upper, mid, and lower poles of the kidneys.
Conclusion: Doppler angle correction plays an important role in the accurate measurement of intrarenal blood flow velocity. The true flow velocity converted from the maximum Doppler velocity shift is produced only when the Doppler angle is 0°, so that the emission sound beam is parallel to the direction of blood flow at the sampled artery. Therefore, the Doppler angle correction should be routinely applied and displayed on renal color duplex sonography.

Keywords: color duplex sonography, blood flow velocity, Doppler angle, Doppler shift, kidney