Purpose or Case Report: Renal dysfunction in a transplant kidney is a common clinical problem which is usually attributed to either rejection or arterial stenosis. While the overall incidence of transplant renal artery stenosis is low, the question of stenosis remains after Doppler examinations although abnormal Doppler ultrasounds are often later proven to be false positives. In the author's experience, these false positive cases are almost always associated with high correction angles (at or near 60 degrees). Conversely, repeating a positive Doppler study by maneuvering the transducer to produce a lower correction angle often resolves the apparently elevated velocity.

A contributing factor to the usage of high correction angles is the actual angle of takeoff of the transplant renal artery relative to the external iliac artery. This can make performing the study with a low correction angle a physically challenging task for the sonographer. Nevertheless, proper effort when scanning these cases is indicated to save the patients from unnecessary follow-up studies and possibly unnecessary invasive procedures.


This educational exhibit aims to address the following learning points:

1) The basis for avoiding high correction angles can be traced to back to basic trigonometric principles which we must keep in mind during image acquisition and interpretation
2) The mechanism for false positive Doppler studies in post-transplant renal artery stenosis is often an unnecessarily high Doppler correction angle
3) Repeating a positive Doppler study with the aim of minimizing the correction angle through optimal probe placement can help avoid unnecessary further testing including possibly invasive procedures
4) The angle of takeoff and variable trajectories of transplant renal arteries can pose difficult physical and cognitive problems for the ultrasound operator
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