Quantitative renal PET imaging with Rubidium-82 can discriminate individuals with different degrees of renal impairment

Background: While non-invasive quantitative (K1) renal imaging with Rubidium-82 (Rb-82) PET has been shown to be feasible in healthy volunteers, its clinical application remains uncertain.Objective:The aim of the study was to investigate changes in renal K1 (as marker of blood flow; quantified in Rb-82 PET images) across various degrees of renal impairment.Methods: We studied 102 patients (mean age 60 ± 12 years; LVEF 62 ± 14%; median creatinine 1.13 mg/dL [IQR 0.89 - 4.58]; male 56%; blacks 44%; diabetes 38%; hypertension 81%; coronary disease 25%; heart failure 15%) who underwent list-mode rest/stress Rb-82 myocardial perfusion PET/CT for evaluation of inducible ischemia, and in whom the right and/or left kidney were partial or fully included in the field of view of the heart. On both the rest and stress delayed images, volumes of interest were drawn along the entire left ventricular (LV) wall, the visualized right and/or left kidneys, and the center of the left atrial blood pool. Tissue and blood pool time activity curves were generated from the dynamic datasets, and a two-compartment model was applied for quantitative evaluation of tracer kinetics at rest and during stress.

Results: Patients were divided into 5 groups according to their glomerular filtration rate (GFR): group 1 (n=54; GFR ≥ 60 ml/min/1.73m2), group 2 (n=6; GFR 45-59 ml/min/1.73m2), group 3 (n=5; GFR 30 - 44 ml/min/1.73m2), group 4 (n=3; GFR 15 - 29 ml/min/1.73m2), and group 5 (n=34; GFR <15 ml/min/1.73m2). Overall, renal K1 did not vary between rest and stress (0.83 ± 0.43 vs. 0.84 ± 0.46 ml/min/g; P=0.42) or between the right and left kidney (0.84 ± 0.44 vs. 0.85 ± 0.43 ml/min/g; P=0.42). Renal K1 showed a clear correlation with renal function (r = -0.64; P<0.001) with a stepwise reduction across GFR 1-5 groups (1.12 ± 0.35, 0.93 ± 0.30, 0.68 ± 0.18, 0.49 ± 0.15, 0.44 ± 0.20 mL/min/gr, respectively; P<0.0001). The renal-to-LV K1 ratio showed that flow was significantly higher in the kidney in groups 1 and 2, comparable between organs in group 3, and lower in the kidney than the heart in groups 4 and 5 (1.82 ± 0.54, 1.50 ± 0.27, 1.17 ± 0.56, 0.79 ± 0.25, 0.66 ± 0.25, respectively; P<0.0001).Conclusion:Non-invasive evaluation of renal flow with Rb-82 PET is feasible during cardiac evaluations and can discriminate patients with varying degrees of renal dysfunction. Further studies are necessary to better delineate the relationship between absolute renal blood flow and the perfusion coefficient K1, as well as its predictive role in the development of renal dysfunction.

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