Parametric renal blood flow imaging using [15O]H2O and PET

Quantitative Total-Body Imaging of Blood Flow with High Temporal Resolution Early Dynamic 18F-Fluorodeoxyglucose PET Kinetic Modeling

Quantitative total-body PET imaging of blood flow can be performed with freely diffusible flow radiotracers such as 15O-water and 11C-butanol, but their short half-lives necessitate close access to a cyclotron. Past efforts to measure blood flow with the widely available radiotracer 18F-fluorodeoxyglucose (FDG) were limited to tissues with high 18F-FDG extraction fraction. In this study, we developed an early-dynamic 18F-FDG PET method with high temporal resolution kinetic modeling to assess total-body blood flow based on deriving the vascular transit time of 18F-FDG and conducted a pilot comparison study against a 11C-butanol reference.

Methods

The first two minutes of dynamic PET scans were reconstructed at high temporal resolution (60×1 s, 30×2 s) to resolve the rapid passage of the radiotracer through blood vessels. In contrast to existing methods that use blood-to-tissue transport rate (K 1 ) as a surrogate of blood flow, our method directly estimates blood flow using a distributed kinetic model (adiabatic approximation to the tissue homogeneity model; AATH). To validate our 18F-FDG measurements of blood flow against a flow radiotracer, we analyzed total-body dynamic PET images of six human participants scanned with both 18F-FDG and 11C-butanol. An additional thirty-four total-body dynamic 18F-FDG PET scans of healthy participants were analyzed for comparison against literature blood flow ranges. Regional blood flow was estimated across the body and total-body parametric imaging of blood flow was conducted for visual assessment. AATH and standard compartment model fitting was compared by the Akaike Information Criterion at different temporal resolutions.

Results

18F-FDG blood flow was in quantitative agreement with flow measured from 11C-butanol across same-subject regional measurements (Pearson R=0.955, p<0.001; linear regression y=0.973x-0.012), which was visually corroborated by total-body blood flow parametric imaging. Our method resolved a wide range of blood flow values across the body in broad agreement with literature ranges (e.g., healthy cohort average: 0.51±0.12 ml/min/cm3 in the cerebral cortex and 2.03±0.64 ml/min/cm3 in the lungs, respectively). High temporal resolution (1 to 2 s) was critical to enabling AATH modeling over standard compartment modeling.

Conclusions

Total-body blood flow imaging was feasible using early-dynamic 18F-FDG PET with high-temporal resolution kinetic modeling. Combined with standard 18F-FDG PET methods, this method may enable efficient single-tracer flow-metabolism imaging, with numerous research and clinical applications in oncology, cardiovascular disease, pain medicine, and neuroscience.

Ex Vivo Simultaneous H215O Positron Emission Tomography and Magnetic Resonance Imaging of Porcine Kidneys-A Feasibility Study

The aim was to establish combined H215O PET/MRI during ex vivo normothermic machine perfusion (NMP) of isolated porcine kidneys. We examined whether changes in renal arterial blood flow (RABF) are accompanied by changes of a similar magnitude in renal blood perfusion (RBP) as well as the relation between RBP and renal parenchymal oxygenation (RPO).

METHODS

Pig kidneys (n = 7) were connected to a NMP circuit. PET/MRI was performed at two different pump flow levels: a blood-oxygenation-level-dependent (BOLD) MRI sequence performed simultaneously with a H215O PET sequence for determination of RBP.

RESULTS

RBP was measured using H215O PET in all kidneys (flow 1: 0.42-0.76 mL/min/g, flow 2: 0.7-1.6 mL/min/g). We found a linear correlation between changes in delivered blood flow from the perfusion pump and changes in the measured RBP using PET imaging (r2 = 0.87).

CONCLUSION

Our study demonstrated the feasibility of combined H215O PET/MRI during NMP of isolated porcine kidneys with tissue oxygenation being stable over time. The introduction of H215O PET/MRI in nephrological research could be highly relevant for future pre-transplant kidney evaluation and as a tool for studying renal physiology in healthy and diseased kidneys.

Assessment of renal perfusion with 82-rubidium PET in patients with normal and abnormal renal function

BACKGROUND

Noninvasive measurement of renal blood flow (RBF) and renal vascular resistance (RVR) is challenging, yet critical in renal pathologies. This study evaluates the correlation between serum renal function markers and RBF/RVR assessed using rubidium PET.

METHODS

Dynamic images from 53 patients who underwent rubidium PET for nonrenal indications were analyzed. RBF was determined using a one-compartment model, and RVR was calculated by dividing mean arterial pressure by RBF.

RESULTS

The study included 51 patients (31 females and 20 males). Among them, 35 had normal renal function [estimated glomerular filtration rate (eGFR) ≥60 ml/min/1.73 m2], and 16 had abnormal renal function (eGFR <60 ml/min/1.73 m2). Patients with normal renal function had significantly higher RBF [median (interquartile range): 443 (297-722) vs 173 (108-380) ml/min/100 g, P = 0.022] and lower RVR [19.1 (12.4-27.2) vs 49.6 (24.4-85.7) mmHg×min×g/ml, P = 0.0011) compared with those with abnormal renal function. There was a moderate correlation between RBF and eGFR (r = 0.62, P < 0.0001) and between RVR and eGFR (r = -0.59, P < 0.0001) in both groups. Among patients with normal renal function, RBF was negatively correlated with age (r = -0.51, P = 0.0017) but there was no correlation among patients with abnormal renal function (r = 0.21, P = 0.44).

CONCLUSION

PET-measured RBF and RVR correlate with renal function markers and differ significantly by renal function status. Further studies are needed to validate rubidium PET's precision and clinical applicability.

Optimization of Fair Arterial Spin Labeling Magnetic Resonance Imaging (ASL-MRI) for Renal Perfusion Quantification in Dogs: Pilot Study

Arterial spin labeling (ASL) MRI allows non-invasive quantification of renal blood flow (RBF) and shows great potential for renal assessment. To our knowledge, renal ASL-MRI has not previously been performed in dogs. The aim of this pilot study was to determine parameters essential for ALS-MRI-based quantification of RBF in dogs: T1, blood (longitudinal relaxation time), λ (blood tissue partition coefficient) and TI (inversion time). A Beagle was scanned at 3T with a multi-TI ASL sequence, with TIs ranging from 250 to 2500 ms, to determine the optimal TI value. The T1 of blood for dogs was determined by scanning a blood sample with a 2D IR TSE sequence. The water content of the dog's kidney was determined by analyzing kidney samples from four dogs with a moisture analyzer and was subsequently used to calculate λ. The optimal TI and the measured values for T1,blood, and λ were 2000 ms, 1463 ms and 0.91 mL/g, respectively. These optimized parameters for dogs resulted in lower RBF values than those obtained from inline generated RBF maps. In conclusion, this study determined preliminary parameters essential for ALS-MRI-based RBF quantification in dogs. Further research is needed to confirm these values, but it may help guide future research.

Mapping 18F-FDG Kinetics Together with Patient-Specific Bootstrap Assessment of Uncertainties: An Illustration with Data from a PET/CT Scanner with a Long Axial Field of View

The purpose of this study was to examine a nonparametric approach to mapping kinetic parameters and their uncertainties with data from the emerging generation of dynamic whole-body PET/CT scanners. Methods: Dynamic PET 18F-FDG data from a set of 24 cancer patients studied on a long-axial-field-of-view PET/CT scanner were considered. Kinetics were mapped using a nonparametric residue mapping (NPRM) technique. Uncertainties were evaluated using an image-based bootstrapping methodology. Kinetics and bootstrap-derived uncertainties are reported for voxels, maximum-intensity projections, and volumes of interest (VOIs) corresponding to several key organs and lesions. Comparisons between NPRM and standard 2-compartment (2C) modeling of VOI kinetics are carefully examined. Results: NPRM-generated kinetic maps were of good quality and well aligned with vascular and metabolic 18F-FDG patterns, reasonable for the range of VOIs considered. On a single 3.2-GHz processor, the specification of the bootstrapping model took 140 min; individual bootstrap replicates required 80 min each. VOI time-course data were much more accurately represented, particularly in the early time course, by NPRM than by 2C modeling constructs, and improvements in fit were statistically highly significant. Although 18F-FDG flux values evaluated by NPRM and 2C modeling were generally similar, significant deviations between vascular blood and distribution volume estimates were found. The bootstrap enables the assessment of quite complex summaries of mapped kinetics. This is illustrated with maximum-intensity maps of kinetics and their uncertainties. Conclusion: NPRM kinetics combined with image-domain bootstrapping is practical with large whole-body dynamic 18F-FDG datasets. The information provided by bootstrapping could support more sophisticated uses of PET biomarkers used in clinical decision-making for the individual patient.

Total-Body Perfusion Imaging with [11C]-Butanol

Tissue perfusion can be affected by physiology or disease. With the advent of total-body PET, quantitative measurement of perfusion across the entire body is possible. [11C]-butanol is a perfusion tracer with a superior extraction fraction compared with [15O]-water and [13N]-ammonia. To develop the methodology for total-body perfusion imaging, a pilot study using [11C]-butanol on the uEXPLORER total-body PET/CT scanner was conducted. Methods: Eight participants (6 healthy volunteers and 2 patients with peripheral vascular disease [PVD]) were injected with a bolus of [11C]-butanol and underwent 30-min dynamic acquisitions. Three healthy volunteers underwent repeat studies at rest (baseline) to assess test-retest reproducibility; 1 volunteer underwent paired rest and cold pressor test (CPT) studies. Changes in perfusion were measured in the paired rest-CPT study. For PVD patients, local changes in perfusion were investigated and correlated with patient medical history. Regional and parametric kinetic analysis methods were developed using a 1-tissue compartment model and leading-edge delay correction. Results: Estimated baseline perfusion values ranged from 0.02 to 1.95 mL·min-1·cm-3 across organs. Test-retest analysis showed that repeat baseline perfusion measurements were highly correlated (slope, 0.99; Pearson r = 0.96, P < 0.001). For the CPT subject, the largest regional increases were in skeletal muscle (psoas, 142%) and the myocardium (64%). One of the PVD patients showed increased collateral vessel growth in the calf because of a peripheral stenosis. Comorbidities including myocardial infarction, hypothyroidism, and renal failure were correlated with variations in organ-specific perfusion. Conclusion: This pilot study demonstrates the ability to obtain reproducible measurements of total-body perfusion using [11C]-butanol. The methods are sensitive to local perturbations in flow because of physiologic stressors and disease.

Renal Perfusion, Oxygenation and Metabolism: The Role of Imaging

Thanks to technical advances in the field of medical imaging, it is now possible to study key features of renal anatomy and physiology, but so far poorly explored due to the inherent difficulties in studying both the metabolism and vasculature of the human kidney. In this narrative review, we provide an overview of recent research findings on renal perfusion, oxygenation, and substrate uptake. Most studies evaluating renal perfusion with positron emission tomography (PET) have been performed in healthy controls, and specific target populations like obese individuals or patients with renovascular disease and chronic kidney disease (CKD) have rarely been assessed. Functional magnetic resonance (fMRI) has also been used to study renal perfusion in CKD patients, and recent studies have addressed the kidney hemodynamic effects of therapeutic agents such as glucagon-like receptor agonists (GLP-1RA) and sodium-glucose co-transporter 2 inhibitors (SGLT2-i) in an attempt to characterise the mechanisms leading to their nephroprotective effects. The few available studies on renal substrate uptake are discussed. In the near future, these imaging modalities will hopefully become widely available with researchers more acquainted with them, gaining insights into the complex renal pathophysiology in acute and chronic diseases.

The utilization of positron emission tomography in the evaluation of renal health and disease

Purpose

Positron emission tomography (PET) is a nuclear imaging technique that uses radiotracers to visualize metabolic processes of interest across different organs, to diagnose and manage diseases, and monitor therapeutic response. This systematic review aimed to characterize the value of PET for the assessment of renal metabolism and function in subjects with non-oncological metabolic disorders.

Methods

This review was conducted and reported in accordance with the PRISMA statement. Research articles reporting “kidney” or “renal” metabolism evaluated with PET imaging between 1980 and 2021 were systematically searched in Medline/PubMed, Science Direct, and the Cochrane Library. Search results were exported and stored in RefWorks, the duplicates were removed, and eligible studies were identified, evaluated, and summarized.

Results

Thirty reports met the inclusion criteria. The majority of the studies were prospective (73.33%, n = 22) in nature. The most utilized PET radiotracers were 15O-labeled radio water (H215O, n = 14) and 18F-fluorodeoxyglucose (18F-FDG, n = 8). Other radiotracers used in at least one study were 14(R,S)-(18)F-fluoro-6-thia-heptadecanoic acid (18F-FTHA), 18F-Sodium Fluoride (18F-NaF), 11C-acetate, 68-Gallium (68Ga), 13N-ammonia (13N-NH3), Rubidium-82 (82Rb), radiolabeled cationic ferritin (RadioCF), 11C‐para-aminobenzoic acid (11C-PABA), Gallium-68 pentixafor (68Ga-Pentixafor), 2-deoxy-2-F-fluoro-d-sorbitol (F-FDS) and 55Co-ethylene diamine tetra acetic acid (55Co-EDTA).

Conclusion

PET imaging provides an effective modality for evaluating a range of metabolic functions including glucose and fatty acid uptake, oxygen consumption and renal perfusion. Multiple positron emitting radiolabeled racers can be used for renal imaging in clinical settings. PET imaging thus holds the potential to improve the diagnosis of renal disorders, and to monitor disease progression and treatment response.

Quantitative Analysis of Renal Perfusion by Arterial Spin Labeling

The signal intensity differences measured by an arterial-spin-labelling (ASL) magnetic resonance imaging (MRI) experiment are proportional to the local perfusion, which can be quantified with kinetic modeling. Here we present a step-by-step tutorial for the data post-processing needed to calculate an ASL perfusion map. The process of developing an analysis software is described with the essential program code, which involves nonlinear fitting a tracer kinetic model to the ASL data. Key parameters for the quantification are the arterial transit time (ATT), which is the time the labeled blood takes to flow from the labeling area to the tissue, and the tissue T₁. As ATT varies with vasculature, physiology, anesthesia and pathology, it is recommended to measure it using multiple delay times. The tutorial explains how to analyze ASL data with multiple delay times and a T₁ map for quantification.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This analysis protocol chapter is complemented by two separate chapters describing the basic concept and experimental procedure.

Quantitative transport mapping (QTM) of the kidney with an approximate microvascular network

Purpose

Proof‐of‐concept study of mapping renal blood flow vector field according to the inverse solution to a mass transport model of time resolved tracer‐labeled MRI data.

Theory and Methods

To determine tissue perfusion according to the underlying physics of spatiotemporal tracer concentration variation, the mass transport equation is integrated over a voxel with an approximate microvascular network for fitting time‐resolved tracer imaging data. The inverse solution to the voxelized transport equation provides the blood flow vector field, which is referred to as quantitative transport mapping (QTM). A numerical microvascular network modeling the kidney with computational fluid dynamics reference was used to verify the accuracy of QTM and the current Kety’s method that uses a global arterial input function. Multiple post‐label delay arterial spin labeling (ASL) of the kidney on seven subjects was used to assess QTM in vivo feasibility.

Results

Against the ground truth in the numerical model, the error in flow estimated by QTM (18.6%) was smaller than that in Kety’s method (45.7%, 2.5‐fold reduction). The in vivo kidney perfusion quantification by QTM (cortex: 443 ± 58 mL/100 g/min and medulla: 190 ± 90 mL/100 g/min) was in the range of that by Kety’s method (482 ± 51 mL/100 g/min in the cortex and 242 ± 73 mL/100 g/min in the medulla), and QTM provided better flow homogeneity in the cortex region.

Conclusions

QTM flow velocity mapping is feasible from multi‐delay ASL MRI data based on inverting the transport equation. In a numerical simulation, QTM with deconvolution in space and time provided more accurate perfusion quantification than Kety’s method with deconvolution in time only.

Renal vascular resistance is increased in patients with kidney transplant

BACKGROUND

Despite improvement in short-term outcome of kidney transplants, the long-term survival of kidney transplants has not changed over past decades. Kidney biopsy is the gold standard of transplant pathology but it's invasive. Quantification of transplant blood flow could provide a novel non-invasive method to evaluate transplant pathology. The aim of this retrospective cross-sectional pilot study was to evaluate positron emission tomography (PET) as a method to measure kidney transplant perfusion and find out if there is correlation between transplant perfusion and histopathology.

METHODS

Renal cortical perfusion of 19 kidney transplantation patients [average time from transplantation 33 (17-54) months; eGFR 55 (47-69) ml/min] and 10 healthy controls were studied by [15 O]H2O PET. Perfusion and Doppler resistance index (RI) of transplants were compared with histology of one-year protocol transplant biopsy.

RESULTS

Renal cortical perfusion of healthy control subjects and transplant patients were 2.7 (2.4-4.0) ml min- 1 g- 1 and 2.2 (2.0-3.0) ml min- 1 g- 1, respectively (p = 0.1). Renal vascular resistance (RVR) of the patients was 47.0 (36.7-51.4) mmHg mL- 1min- 1g- 1 and that of the healthy 32.4 (24.6-39.6) mmHg mL- 1min-1g-1 (p = 0.01). There was a statistically significant correlation between Doppler RI and perfusion of transplants (r = - 0.51, p = 0.026). Transplant Doppler RI of the group of mild fibrotic changes [0.73 (0.70-0.76)] and the group of no fibrotic changes [0.66 (0.61-0.72)] differed statistically significantly (p = 0.03). No statistically significant correlation was found between cortical perfusion and fibrosis of transplants (p = 0.56).

CONCLUSIONS

[15 O]H2O PET showed its capability as a method in measuring perfusion of kidney transplants. RVR of transplant patients with stage 2-3 chronic kidney disease was higher than that of the healthy, although kidney perfusion values didn't differ between the groups. Doppler based RI correlated with perfusion and fibrosis of transplants.

Renal hemodynamics and fatty acid uptake: effects of obesity and weight loss

Human studies of renal hemodynamics and metabolism in obesity are insufficient. We hypothesized that renal perfusion and renal free fatty acid (FFA) uptake are higher in subjects with morbid obesity compared with lean subjects and that they both decrease after bariatric surgery. Cortical and medullary hemodynamics and metabolism were measured in 23 morbidly obese women and 15 age- and sex-matched nonobese controls by PET scanning of [¹⁵O]-H₂O (perfusion) and 14(R,S)-[¹⁸F]fluoro-6-thia-heptadecanoate (FFA uptake). Kidney volume and radiodensity were measured by computed tomography, cardiac output by MRI. Obese subjects were re-studied 6 mo after bariatric surgery. Obese subjects had higher renal volume but lower radiodensity, suggesting accumulation of water and/or lipid. Both cardiac output and estimated glomerular filtration rate (eGFR) were increased by ~25% in the obese. Total renal blood flow was higher in the obese [885 (317) (expressed as median and interquartile range) vs. 749 (300) (expressed as means and SD) ml/min of controls, P = 0.049]. In both groups, regional blood perfusion was higher in the cortex than medulla; in either region, FFA uptake was ~50% higher in the obese as a consequence of higher circulating FFA levels. Following weight loss (26 ± 8 kg), total renal blood flow was reduced (P = 0.006). Renal volume, eGFR, cortical and medullary FFA uptake were decreased but not fully normalized. Obesity is associated with renal structural, hemodynamic, and metabolic changes. Six months after bariatric surgery, the hemodynamic changes are reversed and the structural changes are improved. On the contrary, renal FFA uptake remains increased, driven by high substrate availability.

Synthesis of N-(6-[18F]Fluoropyridin-3-yl)glycine as a potential renal PET agent

OBJECTIVE

Given the requirements of high sensitivity and spatial resolution, the development of new positron emission tomography (PET) agents is required for PET renography. The objective of this study was to investigate a new fluorine-18 labeled hippurate analogue of picolinamide, N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine, as a new renal PET agent for evaluating renal function.

METHODS

N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine was prepared via a two-step reaction, including the nucleophilic substitution reaction of Br with ¹⁸F using methyl 2-(6-bromonicotinamido)acetate as a precursor followed the hydrolysis with sodium hydroxide and purification by preparative-HPLC. The in vitro and in vivo stability were determined using HPLC, and the plasma protein binding (PPB) and erythrocyte uptake of N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine were determined using blood collected from healthy rats at 5 min post-injection. Biodistribution and dynamic micro-PET/CT imaging studies were conducted in healthy rats.

RESULTS

N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine was prepared within 45 min with an uncorrected radiochemical yield of 24.5 ± 6.7% (n = 6, based on [¹⁸F]F^-) and a radiochemical purity of >98%. N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine demonstrated good stability both in vitro and in vivo. The results of the biodistribution and dynamic micro-PET/CT imaging studies in normal rats indicated that N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine was rapidly and exclusively excreted via the renal-urinary pathway.

CONCLUSION

N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine is has been shown to be a promising renal PET agent and warrants further evaluation of renal function.

The renal blood flow reserve in healthy humans and patients with atherosclerotic renovascular disease measured by positron emission tomography using [15O]H2O

BACKGROUND

Microvascular function plays an important role in ARVD (atherosclerotic renovascular disease). RFR (renal flow reserve), the capacity of renal vasculature to dilate, is known to reflect renal microvascular function. In this pilot study, we assessed PET (positron emission tomography)-based RFR values of healthy persons and renal artery stenosis patients. Seventeen patients with ARVD and eight healthy subjects were included in the study. Intravenous enalapril 1 mg was used as a vasodilatant, and the maximum response (blood pressure and RFR) to it was measured at 40 min. Renal perfusion was measured by means of oxygen-15-labeled water PET. RFR was calculated as a difference of stress flow and basal flow and was expressed as percent [(stress blood flow - basal blood flow)/basal blood flow] × 100%.

RESULTS

RFR of the healthy was 22%. RFR of the stenosed kidneys of bilateral stenosis patients (27%) was higher than that of the stenosed kidneys of unilateral stenosis patients (15%). RFR of the contralateral kidneys of unilateral stenosis patients was 21%. There was no difference of statistical significance between RFR values of ARVD subgroups or between ARVD subgroups and the healthy. In the stenosed kidneys of unilateral ARVD patients, stenosis grade of the renal artery correlated negatively with basal (p = 0.04) and stress flow (p = 0.02). Dispersion of RFR values was high.

CONCLUSIONS

This study is the first to report [15O]H2O PET-based RFR values of healthy subjects and ARVD patients in humans. The difference between RFR values of ARVD patients and the healthy did not reach statistical significance perhaps because of high dispersion of RFR values. [15O]H2O PET is a valuable non-invasive and quantitative method to evaluate renal blood flow though high dispersion makes imaging challenging. Larger studies are needed to get more information about [15O]H2O PET method in evaluation of renal blood flow.

Organ-specific physiological responses to acute physical exercise and long-term training in humans

Virtually all tissues in the human body rely on aerobic metabolism for energy production and are therefore critically dependent on continuous supply of oxygen. Oxygen is provided by blood flow, and, in essence, changes in organ perfusion are also closely associated with alterations in tissue metabolism. In response to acute exercise, blood flow is markedly increased in contracting skeletal muscles and myocardium, but perfusion in other organs (brain and bone) is only slightly enhanced or is even reduced (visceral organs). Despite largely unchanged metabolism and perfusion, repeated exposures to altered hemodynamics and hormonal milieu produced by acute exercise, long-term exercise training appears to be capable of inducing effects also in tissues other than muscles that may yield health benefits. However, the physiological adaptations and driving-force mechanisms in organs such as brain, liver, pancreas, gut, bone, and adipose tissue, remain largely obscure in humans. Along these lines, this review integrates current information on physiological responses to acute exercise and to long-term physical training in major metabolically active human organs. Knowledge is mostly provided based on the state-of-the-art, noninvasive human imaging studies, and directions for future novel research are proposed throughout the review.

Image accuracy and quality test in rate constant depending on reconstruction algorithms with and without incorporating PSF and TOF in PET imaging

OBJECTIVE

Positron emission tomography allows imaging of patho-physiological information as a form of rate constants from scanned and reconstructed dynamic image. Some reconstruction algorithms incorporated with time of flight and point spread function have been developed, and quantitative accuracy and quality in the image have been investigated. However, feasibility of the rate constants from the dynamic image has not been directly investigated. We investigated the accuracy and quality in the rate constant by scanning a phantom filled simultaneously with (11)C and (18)F.

METHOD

We utilized a phantom filled with (18)F-F(-) solution in the main cylinder and with (11)C-flumazenil solution in seven sub-cylinders. The phantom was scanned by a Biograph mCT and the scanned data were reconstructed with FBP- and OSEM-based algorithms incorporating with and without TOF and/or PSF corrections. Decay rate images as kinetic rate constant were computed for all the reconstructed images and quantitative accuracy and quality in the rate images were investigated.

RESULTS

The obtained decay rates were not significantly different from the reference values for both isotopes for all applied algorithms when noise on image was not large. Respective SD was smaller in OSEM with TOF in the (11)C-filled region.

CONCLUSION

The present study suggests that OSEM incorporating with TOF provides reasonable quantitative accuracy and image quality regarding decay rates.

Quantitative mouse renal perfusion using arterial spin labeling

Information on renal perfusion is essential for the diagnosis and prognosis of kidney function. Quantification using gadolinium chelates is limited as a result of filtration through renal glomeruli and safety concerns in patients with kidney dysfunction. Arterial spin labeling MRI is a noninvasive technique for perfusion quantification that has been applied to humans and animals. However, because of the low sensitivity and vulnerability to motion and susceptibility artifacts, its application to mice has been challenging. In this article, mouse renal perfusion was studied using flow-sensitive alternating inversion recovery at 7 T. Good perfusion image quality was obtained with spin-echo echo-planar imaging after controlling for respiratory, susceptibility and fat artifacts by triggering, high-order shimming and water excitation, respectively. High perfusion was obtained in the renal cortex relative to the medulla, and signal was absent in scans carried out post mortem. Cortical perfusion increased from 397 ± 36 (mean ± standard deviation) to 476 ± 73 mL/100 g/min after switching from 100% oxygen to carbogen with 95% oxygen and 5% carbon dioxide. The perfusion in the medulla was 2.5 times lower than that in the cortex and changed from 166 ± 41 mL/100 g/min under oxygen to 203 ± 40 mL/100 g/min under carbogen. T1 decreased in both the cortex (from 1570 ± 164 to 1377 ± 72 ms, p < 0.05) and medulla (from 1788 ± 107 to 1573 ± 144 ms, p < 0.05) under carbogen relative to 100% oxygen. The results showed the potential of the use of ASL for perfusion quantification in mice and in models of renal diseases.

The effect of revascularization of renal artery stenosis on renal perfusion in patients with atherosclerotic renovascular disease

BACKGROUND

Only a small fraction of patients with atherosclerotic renovascular disease (ARVD) treated with revascularization have improved renal function after the procedure. It has been suggested that this may be due to effects of renal microvascular disease. Our aim was to measure the effect of renal artery stenosis (RAS) revascularization on renal perfusion in patients with renovascular disease.

METHODS

Seventeen renovascular disease patients were treated by dilatation of unilateral (N = 8) or bilateral (N = 9) RAS (N = 23 kidneys), mainly because of uncontrolled or refractory hypertension. The patients were studied before and after (103 ± 29 days) the procedure. Renal perfusion was measured using quantitative positron emission tomography (PET) perfusion imaging.

RESULTS

Although renal perfusion correlated inversely with the degree of RAS in patients with renovascular disease, it did not change after revascularization.

CONCLUSIONS

Our data support the notion of former clinical trials that angiographic severity of RAS does not determine the response to revascularization. Quantitative PET perfusion imaging is a promising tool to noninvasively measure renal perfusion for the assessment of physiological impact of RAS.

Evaluating the effects of diclofenac sodium and etodolac on renal hemodynamics with contrast-enhanced ultrasonography: a pilot study

PURPOSE

Contrast-enhanced ultrasonography (CEUS) is a novel approach used for measuring organ perfusion changes. Studies using CEUS to assess the effects of non-steroidal anti-inflammatory drugs (NSAIDs) on renal blood flow (RBF) have not yet been conducted. We aimed to evaluate the effects of NSAIDs on the renal hemodynamics of healthy subjects with CEUS.

METHODS

We performed CEUS using the bolus injection method in a total of 10 healthy subjects. Measurements were completed over two study days in a randomized, crossover manner. On each study day, CEUS was performed twice, before and after the administration of NSAIDs. Subjects received an injection of contrast medium and images were recorded. A region-of-interest (ROI) was selected within the renal cortex, signal intensity in the ROI of the kidney was measured and a time-intensity curve (TIC) was automatically generated with attached software.

RESULTS

The mean (±SD) peak intensity decreased significantly after an administration of diclofenac sodium (from 26.0 × 10(-4) ± 17.4 × 10(-4) AU to 19.2 × 10(-4) ± 12.0 × 10(-4) AU; P = 0.022), but not significantly with etodolac (from 26.5 × 10(-4) ± 9.7 × 10(-4) AU to 25.9 × 10(-4) ± 20.8 × 10(-4) AU; P = 0.474). The mean (±SD) percent reduction in intensity following diclofenac sodium administration was significantly reduced compared with etodolac administration (22.2 ± 20.5 % vs. 3.4 ± 8.9 %, P = 0.037).

CONCLUSIONS

These finding suggests that diclofenac sodium (P = 0.022), but not etodolac (P = 0.474), affects renal hemodynamics even in healthy subjects.

In vivo, label-free, three-dimensional quantitative imaging of kidney microcirculation using Doppler optical coherence tomography

Doppler optical coherence tomography (DOCT) is a functional extension of optical coherence tomography (OCT) and is currently being employed in several clinical arenas to quantify blood flow in vivo. In this study, the objective was to investigate the feasibility of DOCT to image kidney microcirculation, specifically, glomerular blood flow. DOCT is able to capture three-dimensional (3D) data sets consisting of a series of cross-sectional images in real time, which enables label-free and non-destructive quantification of glomerular blood flow. The kidneys of adult, male Munich-Wistar rats were exposed through laparotomy procedure after being anesthetized. Following exposure of the kidney beneath the DOCT microscope, glomerular blood flow was observed. The effects of acute mannitol and angiotensin II infusion were also observed. Glomerular blood flow was quantified for the induced physiological states and compared with baseline measurements. Glomerular volume, cumulative Doppler volume, and Doppler flow range parameters were computed from 3D OCT/DOCT data sets. Glomerular size was determined from OCT, and DOCT readily revealed glomerular blood flow. After infusion of mannitol, a significant increase in blood flow was observed and quantified, and following infusion of angiontensin II, a significant decrease in blood flow was observed and quantified. Also, blood flow histograms were produced to illustrate differences in blood flow rate and blood volume among the induced physiological states. We demonstrated 3D DOCT imaging of rat kidney microcirculation in the glomerulus in vivo. Dynamic changes in blood flow were detected under altered physiological conditions demonstrating the real-time imaging capability of DOCT. This method holds promise to allow non-invasive imaging of kidney blood flow for transplant graft evaluation or monitoring of altered-renal hemodynamics related to disease progression.