Renal background correction and measurement of split renal function: The challenge : Editorial Comment: EJNM-D-15-00322, M Donald Blaufox, MD, PhD.

One of the sources of error in performing quantitative nuclear medicine studies is correction for the presence of background activity surrounding the area of interest. This problem is particularly difficult to resolve in evaluating the kidney because of its location deep within the body surrounded by other highly vascular organs including the liver and spleen. The difficulty in determining quantitative individual renal function measurements accurately and subtracting the correct background activity was noted in a consensus report from the International Society of Radionuclides and Nephrourology (ISCORN) [1]. They stated that BBackground subtraction is particularly critical in some methods, since intraand extravascular activity is rapidly changing (in opposite directions) during the timewhen individual function is usually calculated and the contribution of each type of activity varies within different regions of interest^. They also pointed out that renal depth may influence the amount of measured activity through attenuation. Taylor et al. [2] suggested improved formulas for correction of renal depth, but there remains an error from this source, which is fortunately small in most patients. It is noted in a later consensus report from ISCORN that many of the disagreements about how and where to choose background activity to quantitate individual renal function have been resolved [3]. Unlike the previous report, the group at this time was able to achieve a consensus, but did not endorse one single method as the method of choice. Measurements of total renal function with in vivo methods remain subject to significant error [4]. The Patlak Rutland plot method was found to be accurate [5, 6], but it was not chosen as the preferred method. Absolute proof of the accuracy of these techniques is not available and they remain essentially theoretical approaches that have achieved some degree of general acceptance with indirect methods of validation. The Patlak Rutland technique for correcting for renal background (interstitial and vascular) suffers from the requirement for five separate regions of interest. Regions of interest including both kidneys, two perirenal regions and the aorta are needed to calculate the correction and determine the relative renal function. Certainly a simpler technique with equivalent accuracy is desirable. The authors of the article in this issue of the European Journal of Nuclear Medicine [7] present a technique that requires only three regions of interest including the two kidneys and liver to facilitate subtraction of the background activity (including the vascular component) and calculation of individual renal function. The technique is presented with a firm theoretical basis and has been shown both to correlate very well with the Patlak Rutland technique and to be easily performed with good agreement among different observers. The data presented suggest that it may well be a useful alternative to the Patlak Rutland method, especially since by avoiding the necessity for an area of interest over the heart, the camera can be positioned lower over the patient allowing the full genitourinary system to be included in the field of view. The paper reports the study with MAG3 and does not resolve the question as to whether it would be valid for measurement of glomerular filtration rate (GFR) with DTPA. There is also a potential source of error at very low levels of renal function due to some hepatic uptake. This does not appear to have been a problem in the present study. At the present time there is no method available to This Editorial Commentary refers to the article http://dx.doi.org/10.1007/ s00259-015-3216-1