Elizabeth A. Sadowski

Blood oxygen level-dependent and perfusion magnetic resonance imaging: detecting differences in oxygen bioavailability and blood flow in transplanted kidneys

Functional magnetic resonance imaging (fMRI) is a powerful tool for examining kidney function, including organ blood flow and oxygen bioavailability. We have used contrast enhanced perfusion and blood oxygen level-dependent (BOLD) MRI to assess kidney transplants with normal function, acute tubular necrosis (ATN) and acute rejection. BOLD and MR-perfusion imaging were performed on 17 subjects with recently transplanted kidneys. There was a significant difference between medullary R2 values in the group with acute rejection (R2=16.2/s) compared to allografts with ATN (R2=19.8/s; P=.047) and normal-functioning allografts (R2=24.3/s;P=.0003). There was a significant difference between medullary perfusion measurements in the group with acute rejection (124.4+/-41.1 ml/100 g per minute) compared to those in patients with ATN (246.9+/-123.5 ml/100 g per minute; P=.02) and normal-functioning allografts (220.8+/-95.8 ml/100 g per minute; P=.02). This study highlights the utility of combining perfusion and BOLD MRI to assess renal function. We have demonstrated a decrease in medullary R2 (decrease deoxyhemoglobin) on BOLD MRI and a decrease in medullary blood flow by MR perfusion imaging in those allografts with acute rejection, which indicates an increase in medullary oxygen bioavailability in allografts with rejection, despite a decrease in blood flow.

Frequency of malignancy in lesions classified as probably benign after dynamic contrast-enhanced breast MRI examination.

To determine the chance of malignancy in lesions classified as “probably benign” by dynamic magnetic resonance imaging (MRI), in a heterogeneous population.

Arterial spin labeling MRI for assessment of perfusion in native and transplanted kidneys

PURPOSE To apply a magnetic resonance arterial spin labeling (ASL) technique to evaluate kidney perfusion in native and transplanted kidneys. MATERIALS AND METHODS This study was compliant with the Health Insurance Portability and Accountability Act and approved by the institutional review board. Informed consent was obtained from all subjects. Renal perfusion exams were performed at 1.5 T in a total of 25 subjects: 10 with native and 15 with transplanted kidneys. A flow-sensitive alternating inversion recovery (FAIR) ASL sequence was performed with respiratory triggering in all subjects and under free-breathing conditions in five transplant subjects. Thirty-two control/tag pairs were acquired and processed using a single-compartment model. Perfusion in native and transplanted kidneys was compared above and below an estimated glomerular filtration rate (eGFR) threshold of 60 ml/min per 1.73 m² and correlations with eGFR were determined. RESULTS In many of the transplanted kidneys, major feeding vessels in the coronal plane required a slice orientation sagittal to the kidney. Renal motion during the examination was observed in native and transplant subjects and was corrected with registration. Cortical perfusion correlated with eGFR in native (r=0.85, P=.002) and transplant subjects (r=0.61, P=.02). For subjects with eGFR >60 ml/min per 1.73 m², native kidneys demonstrated greater cortical (P=.01) and medullary (P=.04) perfusion than transplanted kidneys. For subjects with eGFR <60 ml/min per 1.73 m², native kidneys demonstrated greater medullary perfusion (P=.04) compared to transplanted kidneys. Free-breathing acquisitions provided renal perfusion measurements that were slightly lower compared to the coached/triggered technique, although no statistical differences were observed. CONCLUSION In conclusion, FAIR-ASL was able to measure renal perfusion in subjects with native and transplanted kidneys, potentially providing a clinically viable technique for monitoring kidney function.

Noninvasive assessment of early kidney allograft dysfunction by blood oxygen level-dependent magnetic resonance imaging.

Background. Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) is a noninvasive method to assess tissue oxygen bioavailability, using deoxyhemoglobin as an endogenous contrast agent. We hypothesized that BOLD-MRI could accurately discriminate different types of rejection early after kidney transplantation. Methods. Twenty-three patients underwent imaging in the first four months posttransplant. Five had normal functioning transplants and 18 had biopsy-proven acute allograft dysfunction (acute tubular necrosis [ATN, n=5] and acute rejection [n=13] including borderline rejection: n=3; IA rejection: n=4; IIA rejection: n=6: C4d(+) rejection: n=9). Results. Mean medullary R2* (MR2*) levels (a measure directly proportional to tissue deoxyhemoglobin levels) were significantly higher in normal functioning allografts (R2*=24.3/s±2.3) versus acute rejection (R2*=16.6/s±2.1) and ATN (R2*=20.9/s±1.8) (P<0.05). The lowest MR2* levels were observed in acute rejection episodes with vascular injury i.e. IIA and C4d (+). Similarly, the lowest medullary to cortical R2* ratios (MCR2*) were present in allografts with IIA (1.24±0.05) and C4d(+) rejection (1.26±0.06). ROC curve analyses suggested that MR2* and MCR2* values could accurately discriminate acute rejection in the early posttransplant period. Conclusions. BOLD-MRI demonstrated significant changes in medullary oxygen bioavailability in allografts with biopsy-proven ATN and acute rejection, suggesting that there may be a role for this noninvasive tool to evaluate kidney function early after transplantation.

Comparing kidney perfusion using noncontrast arterial spin labeling MRI and microsphere methods in an interventional swine model.

Objective:The purpose of this study was to assess the ability of a flow-sensitive alternating inversion recovery–arterial spin labeling (FAIR-ASL) technique to track renal perfusion changes during pharmacologic and physiologic alterations in renal blood flow using microspheres as a gold standard. Materials and Methods:Fluorescent microsphere and FAIR-ASL perfusion were compared in the cortex of the kidney for 11 swine across 4 interventional time points: (1) under baseline conditions, (2) during an acetylcholine and fluid bolus challenge to increase perfusion, (3) initially after switching to isoflurane anesthesia, and (4) after 2 hours of isoflurane anesthesia. In 10 of the 11 swine, a bag of ice was placed on the hilum of 1 kidney at the beginning of isoflurane administration to further reduce perfusion in 1 kidney. Results:Both ASL and microspheres tracked the expected cortical perfusion changes (P < 0.02) across the interventions, including an increase in perfusion during the acetylcholine challenge and decrease during the administration of isoflurane. Both techniques also measured lower cortical perfusion in the iced compared with the noniced kidneys (P ≤ 0.01). The ASL values were systematically lower compared with microsphere perfusion. Very good correlation (r = 0.81, P < 0.0001) was observed between the techniques, and the relationship appeared linear for perfusion values in the expected physiologic range (microsphere perfusion <550 mL/min/100 g) although ASL values saturated for perfusion >550 mL/min/100 g. Conclusion:Cortical perfusion measured with ASL correlated with microspheres and reliably detected changes in renal perfusion in response to physiologic challenge.

Reproducibility of renal perfusion MR imaging in native and transplanted kidneys using non-contrast arterial spin labeling.

To examine both inter‐visit and intra‐visit reproducibility of a MR arterial spin labeling (ASL) perfusion technique in native and transplanted kidneys over a broad range of renal function.

Quantitative MR Measures of Intrarenal Perfusion in the Assessment of Transplanted Kidneys: Initial Experience

RATIONALE AND OBJECTIVES The purpose of this study was to evaluate prospectively a gadolinium-based perfusion technique for intrarenal blood flow in transplanted kidneys and to determine if magnetic resonance imaging (MRI) measurements of intrarenal perfusion could be used to differentiate between normal-functioning kidney allografts and allografts with acute tubular necrosis (ATN) or acute rejection. MATERIALS AND METHODS Twenty-one subjects were enrolled within 4 months of receiving a kidney transplant. A biopsy was performed on subjects to diagnose each allograft as having either ATN or acute rejection. A group of subjects with normal functioning transplants was also enrolled in our study. MRI perfusion images were acquired on a 1.5 T MRI system within 48 hours after biopsy using an echo planar, T2*-weighted sequence, and an injection of gadodiamide contrast agent administered at a dose of 0.1 mmol/kg. Scan parameters were: repetition time/echo time/flip = 1000 ms/30 ms/60 degrees , field of view = 340 x 340 mm, matrix = 128 x 64, slice thickness = 10 mm, and temporal resolution = 1.0 seconds. Cortical and medullary blood flow values were calculated. RESULTS Medullary blood flow values were significantly (P = .02) lower in allografts undergoing acute rejection (121 +/- 41 mL/100 g/min) compared to normal-functioning allografts (221 +/- 96 mL/100 g/min) and those with ATN (247 +/- 124 mL/100 g/min). Cortical blood flow values were also significantly (P = .03) reduced in allografts with acute rejection (243 +/- 116 mL/100 g/min) compared to those with normal function (413 +/- 116 mL/100 g/min). CONCLUSIONS Preliminary results indicate that MRI perfusion techniques may provide a means of determining noninvasively the viability of renal allografts, potentially alleviating the need for biopsy in some patients.

Detection of acute renal ischemia in swine using blood oxygen level-dependent magnetic resonance imaging.

To determine the feasibility and sensitivity of blood oxygen level‐dependent (BOLD) magnetic resonance imaging (MRI) to detect acute renal ischemia, using a swine model, and to present the causes of variability and assess techniques that minimize variability introduced during data analysis.

Evaluation of Uterine Anomalies: 3D FRFSE Cube Versus Standard 2D FRFSE

OBJECTIVE The purpose of this study was to compare a novel MRI sequence-3D fast-recovery fast spin-echo (FRFSE) cube-with a standard 2D FRFSE sequence for the investigation of uterine anomalies. CONCLUSION Compared with 2D FRFSE, 3D FRFSE cube provides superior image quality and improved 3D reconstructions in a shorter acquisition time and enables excellent visualization of uterine anatomy in any orientation, regardless of the original scanning plane.

Update on nephrogenic systemic fibrosis: are we making progress?

Nephrogenic systemic fibrosis is a rare fibrosing disorder associated with the use of gadolinium‐based contrast agents in patients with renal dysfunction. However, only a small proportion of at‐risk patients develops the disorder, and the exact determinants of disease are still not completely clear. Here, we present an update on emerging evidence for the role of gadolinium‐based contrast agents, renal dysfunction, and background inflammation in disease expression, with a focus on current experimental models. Based on these findings, significant progress has been made in our understanding of the pathophysiology of this disorder over the last few years. This review provides a summary of these developments with discussion of the implications for clinical practice and directions for additional study.