Background Changes in renal blood flow (RBF) may play a pathophysiological role in hypertension and kidney disease. However, RBF determination in humans has proven difficult. We aimed to confirm the feasibility of RBF estimation based on positron emission tomography/computed tomography (PET/CT) and rubidium-82 (82Rb) using the abdominal aorta as input function in a 1-tissue compartment model. Methods Eighteen healthy subjects underwent two dynamic 82Rb PET/CT scans in two different fields of view (FOV). FOV-A included the left ventricular blood pool (LVBP), the abdominal aorta (AA) and the majority of the kidneys. FOV-B included AA and the kidneys in their entirety. In FOV-A, an input function was derived from LVBP and from AA, in FOV-B from AA. One-tissue compartmental modelling was performed using tissue time activity curves generated from volumes of interest (VOI) contouring the kidneys, where the renal clearance of 82Rb is represented by the K1 kinetic parameter. Total clearance for both kidneys was calculated by multiplying the K1 values with the volume of VOIs used for analysis. Intra-assay coefficients of variation and inter-observer variation were calculated. Results For both kidneys, K1 values derived from AA did not differ significantly from values obtained from LVBP, neither were significant differences seen between AA in FOV-A and AA in FOV-B, nor between the right and left kidneys. For both kidneys, the intra-assay coefficients of variation were low (~ 5%) for both input functions. The measured K1 of 2.80 ml/min/cm3 translates to a total clearance for both kidneys of 766 ml/min/1.73 m2. Conclusion Measurement of renal perfusion based on PET/CT and 82Rb using AA as input function in a 1-tissue compartment model is feasible in a single FOV. Based on previous studies showing 82Rb to be primarily present in plasma, the measured K1 clearance values are most likely representative of effective renal plasma flow (ERPF) rather than estimated RBF values, but as the accurate calculation of total clearance/flow is very much dependent on the analysed volume, a standardised definition for the employed renal volumes is needed to allow for proper comparison with standard ERPF and RBF reference methods.
Background: Changes in renal blood flow (RBF) may play a pathophysiological role in hypertension and kidney disease. However, RBF determination in humans has proven difficult. We aimed to confirm the feasibility of RBF estimation based on positron emission tomography/ computed tomography (PET/CT) and rubidium-82 (82Rb) using the abdominal aorta as input function in a 1-tissue compartment model. Methods: Eighteen healthy subjects underwent two dynamic 82Rb PET/CT scans in two different fields of view (FOV). FOV-A included the left ventricular blood pool (LVBP), the abdominal aorta (AA) and the majority of the kidneys. FOV-B included AA and the kidneys in their entirety. In FOV-A, an input function was derived from LVBP and from AA; in FOV-B from AA. 1-tissue compartmental modeling was performed using tissue time activity curves generated from volumes of interest contouring the kidneys, where the renal clearance of 82Rb is represented by the K1 kinetic parameter. To investigate the correct interpretation of K1, we assumed to first estimate effective renal plasma flow (ERPF) by extrapolating clearance values (ml/min/cm3) to whole kidney values (ml/min) using the estimated total kidney volume. Thereafter, RPF was estimated from ERPF using an assumed extraction fraction (0.89). Lastly, RBF was estimated from RPF using measured haematocrit values. Intra-assay coefficients of variation and inter-observer variation were calculated.Results: For both kidneys, K1 values derived from AA did not differ significantly from values obtained from LVBP, neither were significant differences seen between AA in FOV-A and AA in FOV-B, nor between the right and left kidneys. For both kidneys, the intra-assay coefficients of variation were low (~ 5%) for both input functions. The measured K1 of 2.80 ml/min/cm3 suggests, for young healthy subjects, an estimated total renal perfusion normalized to body surface area of 860 ± 129 ml/min/1.73 m2 and subsequently an estimated RBF of 1494 ± 221 ml/min/1.73 m2. Conclusion: RBF estimation based on PET/CT and 82Rb using AA as input function in a 1-tissue compartment model is feasible in a single FOV. The measured K1 clearance values are most likely representative of ERPF rather than estimated RBF values.
Background Changes in renal perfusion may play a pathophysiological role in hypertension and kidney disease, however to date, no method for renal blood flow (RBF) determination in humans has been implemented in clinical practice. In a previous study, we demonstrated that estimation of renal perfusion based on a single positron emission tomography/computed tomography (PET/CT) scan with Rubidium-82 (82Rb) is feasible and found an approximate 5% intra-assay coefficient of variation for both kidneys, indicative of a precise method.This study’s aim was to determine the day-to day variation of 82Rb PET/CT and to test the method’s ability to detect increased RBF induced by infusion of amino acids. Methods Seventeen healthy subjects underwent three dynamic 82Rb PET/CT scans over two examination days comprising: Day A, a single 8-minute dynamic scan and Day B, two scans performed before (baseline) and after RBF stimulation by a 2-hour amino acid-infusion. The order of examination days was determined by randomization. Time activity curves for arterial and renal activity with a 1-tissue compartment model were used for flow estimation; the K1 kinetic parameter representing renal 82Rb clearance. Day-to-day variation was calculated based on the difference between the unstimulated K1 values on Day A and Day B and paired t-testing was performed to compare K1 values at baseline and after RBF stimulation on Day B. Results Day-to-day variation was observed to be 5.5% for the right kidney and 6.0% for the left kidney (n = 15 quality accepted scans). K1 values determined after amino acid-infusion were significantly higher than pre-infusion values (n = 17, p = 0.001). The mean percentage change in K1 from baseline was 13.2 ± 12.9% (range − 10.4 to 35.5) for the right kidney; 12.9 ± 13.2% (range − 15.7 to 35.3) for the left kidney. Conclusion Day-to-day variation is acceptably low. A significant K1 increase from baseline is detected after application of a known RBF stimulus, indicating that 82Rb PET/CT scanning can provide a precise method for evaluation of RBF and it is able to determine changes herein. Clinical Trial Registration EU Clinical Trials Register, 2017-005008-88. Registered 18/01/2018.
There is no difference in variance between GFR estimated from single-head renography and that estimated using dual-head renography. Hence, dual-head camera renography might be useful in daily practice with the potential to provide a better estimate of absolute function in each kidney and the relative kidney function in patients with differing kidney depths and/or malformed kidneys.
<b><i>Introduction:</i></b> Invasive bone biopsy to assess bone metabolism in patients with chronic kidney disease-mineral and bone disorder may be replaced by the noninvasive <sup>18</sup>F-NaF PET/CT and biomarkers of bone metabolism. We aimed to compare parameters of bone turnover, mineralization, and volume assessed by bone biopsies with results derived from <sup>18</sup>F-NaF PET/CT and biomarkers (bone-specific alkaline phosphatase, osteocalcin, fibroblast growth factor 23, and osteoprotegerin). <b><i>Methods:</i></b> A cross-sectional study included 17 dialysis patients, and results from <sup>18</sup>F-NaF PET/CT scans and the biomarkers were directly compared with the results of histomorphometric analyses of tetracycline double-labeled trans-iliac bone biopsies. <b><i>Results:</i></b> Bone biopsies showed 40% high, 20% normal, and 40% low bone turnover. No biopsies had generalized abnormal mineralization, and the bone volume/total tissue volume was low in 80% and high in 7%. The pelvic skeletal plasma clearance (K<sub>i</sub>) from <sup>18</sup>F-NaF PET/CT correlated with bone turnover parameters obtained by bone biopsy (activation frequency: <i>r</i> = 0.82, <i>p</i> < 0.01; bone formation rate/bone surface: <i>r</i> = 0.81, <i>p</i> < 0.01), and K<sub>i</sub> defined low turnover with high sensitivity (83%) and specificity (100%). CT-derived radiodensity correlated with bone volume, <i>r</i> = 0.82, <i>p</i> < 0.01. Of the biomarkers, only osteocalcin showed a correlation with turnover assessed by histomorphometry. <b><i>Conclusion:</i></b> In conclusion, <sup>18</sup>F-NaF PET/CT may be applicable for noninvasive assessment of bone turnover and volume in CKD-MBD.
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