⁸²Rb tissue kinetics in humans

Abstract

Aim The study aim was to compare the kinetics of the potassium analogue, 82Rb, between spleen, liver and kidney. Methods Patients had myocardial stress/rest perfusion imaging using adenosine (n = 45) or regadenoson (n = 33) for stressing. Hepatic arterial (HAP), splenic (SP) and renal (RP) perfusions were measured from first‐pass and blood 82Rb clearances (Ki) from Gjedde–Patlak–Rutland graphical analysis of data between 1 and 2 min postinjection, using regions of interest over left ventricular cavity or abdominal aorta to monitor arterial concentration. Tissue 82Rb extraction efficiency (E) was calculated as [Ki/perfusion]*100. Tissue extracellular fluid volume (ECV) was derived from the GPR plot intercept. Results SP (24%) and RP (23%) increased after regadenoson but decreased (−41% and −19%) after adenosine. HAP increased after adenosine (91%) and regadenoson (68%). Resting E was high in kidney (69%) and low in spleen (26%). After adenosine, it increased to 91% in kidney and 49% in spleen. Assuming an arterial contribution of 25% to hepatic blood flow, resting E in liver was estimated as 23%. Relationships between Ki and perfusion in spleen and kidney were consistent with the Crone–Renkin equation (Ki = [1 − A.e‐B/perfusion]*perfusion), with respective values of A of 0.95 and 0.94 and B of 31 and 186 ml/min/100 ml. Splenic ECV decreased following adenosine from 62 to 39 ml/100 ml and showed a logarithmic correlation with SP. Conclusion Kidney, spleen and liver display contrasting tissue kinetics. E is high in kidney and low in spleen and liver. Spleen is erectile, collapsing when perfusion decreases.

Dynamic rubidium‐82 PET/CT as a novel tool for quantifying hemodynamic differences in renal blood flow using a one‐tissue compartment model

“…38,39 Gregg et al reported the relation between K 1 and flow in kidney tissue, showing that the extraction function by Gregg deflects more strongly with increasing flow. 25 Future studies comparing K 1 values obtained using 82 Rb as flow tracer with a gold standard reference radiopharmaceutical with a linear extraction such as [ 15 O]H 2 O is therefore crucial in order to establish a more robust relationship between K 1 values and flow of 82 Rb in renal tissue. Moreover, it is essential to further investigate the extraction of 82 Rb in the kidney and the conversion of K 1 to flow before the clinical implementation of 82 Rb PET/CT measurements can take place.…”

“…40 Previous research showed that adenosine has various effects on the renal perfusion. 25,28,[41][42][43] Ultimately, we need a well-established renal stressor that can also be effectively combined with imaging from logistical and technical perspectives.…”

“…(i) assuming a constant extraction fraction of 0.9 as determined in canine experiments, 7 (ii) using the values found by Gregg et al 25 for the kidney: a = 0.94 and b = 1.86.…”

“…CT-or PET-based kidney VOI delineation methods (region growing and iso-contouring), IDIFs (AA, ATA, and LVBP), and Gregg's 25 and constant 7 extraction fractions. Applying iso-contouring as the PET-based VOI of the kidney and using AA as an IDIF is suggested for consideration in further studies.…”

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

“…injection of contrast. By combining F with the tissue blood clearance ( Ki ) of tracer measured, for example, from Gjedde–Patlak–Rutland (GPR) graphical analysis, the tissue extraction efficiency ( E ) of a tracer can be measured [3].…”