99mTc-DTPA dynamic SPECT/CT renogram in adults. Feasibility and diagnostic benefit

Abstract

Objective To investigate the feasibility, quantitative parameters and potential advantages of dynamic SPECT/CT renogram with ^99mTc-DTPA in adults. Methods Fifty-five (55) patients aged 19–80 y.o. most of them with obstructive uropathy were enrolled. The imaging protocol included: Day 1: a) Conventional ^99mTc-DTPA planar renogram, followed by b) ^99mTc-DMSA injection and static planar imaging 3 hrs post injection. Day 3: c) Dynamic SPECT/CT renogram post injection of 333–444 MBq of ^99mTc-DTPA. This included an initial CT scan followed by 12 consecutive SPECT sessions acquired via continuous acquisition mode for a total of 24 minutes. CT-derived maps were used for attenuation compensation of SPECT data dSPECT(AC). Renal activity was measured in the total kidney volume by Regions of Interest (ROIs) drawn manually on consecutive transaxial CT slices of the 3rd SPECT, which were then copied on the whole 12-SPECT series. Corresponding time-activity curves were created. Renographic dSPECT(AC) parameters were compared to those of conventional renogram. The reference method for split renal function was ^99mTc-DMSA (geometrical mean of anterior and posterior projection counts) and for Glomerular Filtration Rate (GFR) the 2-blood sample clearance method with Cr-51 EDTA. Results dSPECT(AC) images were of good quality. There was good correlation between renogram parameters (time to peak activity and NORA20) comparing the two techniques (Pearson’s r = 0.959 and 0.933, respectively). In 21 cases with > 30% absolute difference between the two kidneys, spilt renal function calculation by dSPECT(AC) correlated perfectly (r = 0.968) with the reference method, whereas planar renogram was less accurate (r = 0.843). Anatomic information provided by non-enhanced CT offered an integrated structural-functional view valuable for final diagnosis. dSPECT(AC) early kidney uptake as a fraction of injected dose correlated better with reference GFR (r = 0.789) than that estimated by the Gates’ method (r = 0.642). Conclusions ^99mTc-DTPA dynamic 3D renogram corrected for attenuation and fused with CT images is feasible with conventional gamma cameras incorporated into hybrid SPECT/CT systems. It allows accurate split renal function measurement, is enriched by useful anatomical information and can be used for closer approximation of GFR compared with Gates’ method.