Extravascular chest wall technetium 99m diethylene triamine penta-acetic acid: implications for the measurement of renal function during renography

Abstract

Measurement of individual kidney glomerular filtration rate (IKGFR) from the gamma-camera technetium 99m diethylene triamine penta-acetic acid (99mTc-DTPA) renogram requires a continuous measurement of arterial activity. This is usually based on a region of interest (ROI) placed over the cardiac blood pool on the posterior view, with the assumption of negligible contamination from activity in the extravascular space of the chest wall. By injecting a small dose of technetium 99m human serum albumin (HSA) before the 99mTc-DTPA in 12 patients undergoing routine renography, the contribution of extravascular activity to the total signal recorded over the cardiac blood pool was calculated to be 11.0% (SE 2.1%) 1.5 min after DTPA injection, rising to 35.1% (SE 2.5%) at 15 min. Subtraction of the time-activity curve recorded from a ROI of the same size over the right lung generated a "pure" blood signal as shown by almost identical HSA/DTPA signal ratios recorded in blood samples taken 5 min after HSA and 15 min after DTPA and from the gamma-camera at the corresponding times. The effect of using a cardiac blood pool time-activity curve uncorrected for extravascular activity was to overestimate IKGFR by an average factor of 1.17 (SE 0.03).

Noninvasive measurement of tracer extraction efficiency in tissue, illustrated with Tc-99m-MAG3

“…This is negligible over first-pass and would have no effect on F’ . Bell and Peters [11] found with Tc-99m-DTPA that the extravascular activity signal recorded in a small ROI over the LV was 11, 27, 36 and 35% of total signal at 1.5, 5, 10 and 15 min postinjection, respectively. Although high plasma protein binding would be expected to minimise diffusion of Tc-99m-MAG3 into the interstitial space, we nevertheless found it to be significant, being 25–30% of the counts recorded over the LV at 15 min postinjection (Fig.…”

The direct measurement of glomerular filtration rate from the continuous monitoring of DTPA clearance

“…Hence, although the proposed method still gives a biased estimate of the GFR, it appears more accurate than our routinely applied slope method. The most probable reason for this error in the proposed method is the well recognized limitation of using an external detector that the observed count rates do not accurately reflect plasma activity while the intra-and extra-vascular pools are not in equilibrium (Bell and Peters 1991). This will lead to an overestimate of the GFR from our proposed method, and with more complete data a correction factor could he empirically determined if necessary.…”

Non-invasive techniques for the measurement of extraction fraction and permeability surface area product of99TcmDTPA in the human forearm

“…stable) HSA count rates recorded over the one minute period prior to the DTPA injection. The left ventricular curves were corrected for chest wall extravascular activity by subtraction of the right lung curves to produce 'pure' left ventricular curves for both HSA and DTPA (Bell and Peters 1991).…”