Magnetic resonance imaging (MRI) and pathophysiology of the rat kidney in streptozotocin-induced diabetes.

Proton magnetic resonance imaging was performed on rats before induction of diabetes with streptozotocin (STZ) and at 2 and 12 days postinduction. Images revealed an increase in maximal longitudinal and axial dimensions of the kidneys at 2 days and a further increase at 12 days. Similarly, an increase in the size of the remaining kidney was seen in a rat which underwent uninephrectomy as a positive control. Two major differences were observed between the kidney undergoing compensatory hypertrophy and those developing diabetic nephropathy: (i) Expansion of the renal vasculature was seen only in images of the diabetic rat; (ii) A loss in conspicuity of the normal corticomedullary junction was seen in the T2-weighted images of the diabetic rat but not in the uninephrectomized rat. Histologic examination revealed that the medulla increased to a size greater than the cortex during diabetic nephropathy whereas the medullary volume was less than that of the cortex during compensatory hypertrophy. In vitro T1 relaxation times in cortex, outer medulla and inner medulla of kidneys from control rats were measured and compared with the same respective regions in diabetic rats. When these values were correlated with tissue water content, a linear increase in relaxation rate versus percent water content from cortex to inner medulla was found in the control kidneys, but this correlation was absent in diabetic nephropathy. These studies demonstrate that MRI is an effective noninvasive tool for studying the course of renal hypertrophy and hydration changes in the development of renal disease in STZ-induced diabetes in the rat.     

NMR imaging study of the pharmacodynamics of polylysine-gadolinium-DTPA in the rabbit and the rat

The pharmacodynamics of polylysine-(Gd-DTPA) (Schering, Berlin, Germany), a new blood pooling contrast agent for MRI, were studied in the rabbit and the rat. Polylysine-(Gd-DTPA) is a compound with high LD50. Due to its high molecular weight (50.000) and physico-chemical properties, it remains in the vascular system; during the first hour, the plasma level is three times higher than for Gd-DTPA. MRI was performed at 1.5 T using a SE sequence with TR/TE = 300/15 or 20 msec. Signal intensities of muscle, liver and kidney were measured before and after intravenous injection of the contrast agent (0.1 mmol/kg) during 8 hours in the rat (n = 3) and up to 2 wk in the rabbit (n = 3). A dose response study in three additional rabbits confirmed that the 0.1 mmol/kg dose was optimal. The pharmacodynamics results show that the effects of polylysine-(Gd-DTPA) are similar in both the rabbit and the rat. The liver signal is enhanced by about 60% immediately after injection in both species. This enhanced signal decays to half its maximal value in about one hour, which makes the contrast agent useful for clinical applications at a dose of 0.1 mmol/kg. In the kidney medulla and cortex the signals are enhanced by much larger factors (about 3 to 4); it takes at least one day for the kidney to clear the contrast agent in both species.     

Magnetic resonance tissue analysis of acute renal vascular occlusion in the rabbit: enhancement with gadolinium-DTPA complex

In order to assess the sensitivity of nuclear magnetic resonance (NMR) in detecting acute renal vascular insufficiency, in vitro NMR spectroscopy (at 0.25 T) was performed on rabbit renal cortices following 45 min of unilateral renal artery (RAO) or renal vein occlusion (RVO). Data were obtained both with and without paramagnetic enhancement with gadolinium-DTPA (Gd-DTPA). In the absence of contrast material, RVO was distinguished by markedly elevated spin-lattice (T1) and spin-spin (T2) relaxation times when compared to the contralateral control kidney [mean increase of 29% in T1 (p less than 0.001) and 19% in T2 (p less than .001)]. RAO produced no change in T1 (p = N.S.) and a small change in T2 (mean increase of 11%, p less than .01). Five min following injection of 0.05 mM/kg of Gd-DTPA, relaxation times of control kidneys were markedly shortened [mean decrease 75% in T1 (p less than .001) and 12% in T2 (p less than 0.01)]. With Gd-DTPA, kidneys with RVO continued to have elevated T1 and T2 relaxation time, and kidneys with RAO maintained their essentially normal pre-contrast relaxation time values. We conclude that non-contrast NMR tissue analysis clearly differentiated normal from congested (RVO) kidneys, but not from acutely ischemic (RAO) kidneys. Paramagnetic enhancement with Gd-DTPA allows the differentiation of normally perfused from acutely ischemic or congested kidneys.     

MRI findings of primary small-cell carcinoma of kidney

We report the MRI findings of primary small-cell carcinoma of the kidney (PSCCK) in a 59-year-old female. This tumor appeared as a 16-cm mass that arose from the right kidney. This lesion had diminished signal on T1-weighted images and heterogeneous mixed signal on T2-weighted images. The tumor primarily involved the renal medulla with persistent thin renal cortex. Despite the tumors' large size, no substantial central necrosis was present. The predominant medullary location and the lack of central necrosis in this large tumor were features unusual for renal cell carcinoma and should raise the suspicion of another malignancy, the differential diagnosis of which should contain extrapulmonary small-cell carcinoma of the kidney.     

Paramagnetic enhanced proton magnetic resonance measurement in rats: correlates with renal function

Renal cortical, medullar and papillary T1 and T2 relaxation times were measured in rats with normal (n = 13) and impaired renal function (n = 11) with a Bruker Multispec, 20 MHz at 37 degrees C. In one group of seven rats, decreased renal function was obtained by 50% glycerol solution administration (10 ml/kg-body weight) 24 hours before the experiment, while in another group of four rats the renal function was decreased, by ureteral ligation for 72 hours. Immediately after the excision of one kidney, Gadolinium-DTPA (70 mumole/kg body weight) was injected intravenously. The second kidney was excised 5 min later. From the T1 and T2 relaxation times measured in the cortex, medulla, and papilla, their respective ratios before and after GdDTPA administration were calculated and correlated with GFR determined by creatinine clearance (Ccr range was between 0 and 850 microliters/min/g kidney weight). For T1: the ratios in the cortex, medulla, and papilla the correlation coefficients were r = 0.81 (p less than 0.001), r = 0.85 (p less than 0.001), and r = 0.87 (p less than 0.0001), respectively. The respective correlation coefficient r values for T2 were r = 0.38 (NS), r = 0.76 (p less than 0.001), and r = 0.73 (p less than 0.001). The present study indicates that a combination of MR measurements, with and without GdDTPA paramagnetic enhancement, can offer a new possibility for obtaining information on renal function and suggest the possibility of concomitant anatomo functional magnetic resonance imaging.     

Proton MR study of different types of experimental acute renal failure in rats

Kidney cortical and medullary spin-lattice (T1) and spin-spin (T2) relaxation times were measured in several types of experimental acute renal failure in rats with a Bruker PC "Multispec." Gentamicin ARF was obtained after one i.p. injection of 100mg Gentamicin/kg BW/day for 8 days. Glycerol ARF: 24 hours after one i.m. injection of 10 ml 50% Glycerol/kg BW. Obstruction ARF: 3 days after complete ureteral ligation. Renal tissue total water content, hydration fraction, fraction bound, blood urea and creatinine were measured at the end of the experiments. Shortened T1 and prolonged T2 were found in both cortex and medulla in the Glycerol ARF group. Gentamicin renal toxicity and the non-functioning kidney with ureteral obstruction are characterized by significant prolongation of T1 and T2 in cortex, while the medullary T1 and T2 were prolonged only in obstruction ARF. The highest T1 and T2 were found in the obstructed non-functioning kidney. The total water content decreased in the Glycerol ARF, increased in the obstruction and remain unchanged in Gentamicin ARF. The hydration fraction and the fraction bound changed significantly in the opposite direction with the total water content. Different profiles of renal cortical and medullary magnetic resonance properties found in several models of experimental ARF in rats indicate that MR properties may provide etiopathogenetic diagnostic possibilities.     

A preliminary study of blood-oxygen-level-dependent MRI in patients with chronic kidney disease

Background

Blood-oxygen-level-dependent (BOLD) magnetic resonance imaging (MRI) can provide regional measurements of oxygen content using deoxyhemoglobin paramagnetic characteristics. The apparent relaxation rate or R2*(=1/T2*) can be determined from the slope of log (intensity) versus echo time and is directly proportional to the tissue content of deoxyhemoglobin. Thus, as the level of deoxyhemoglobin increases, T2* will decrease, leading to an increase in R2*. Chronic kidney disease (CKD) can affect oxygenation levels in renal parenchyma, which influences the clinical course of the disease. The goal of this study was to detect and assess renal oxygenation levels in CKD using BOLD MRI.

Methods

Fifteen healthy subjects and 11 patients with CKD underwent a renal scan using multigradient-recalled-echo sequence with eight echoes. R2* (1/s) of the renal cortex and medulla was measured on BOLD images. Of the 11 patients, nine had biopsy-proven chronic glomerulonephritis, and two had a similar diagnosis based on clinical symptoms and investigations.

Results

Mean medullary R2* (MR2*) and cortex R2* (CR2*) levels were significantly higher in patients (22 kidneys, MR2*=24.79±4.84 s⁻¹, CR2*=18.97±2.72 s⁻¹) than in controls (30 kidneys, MR2*=19.98±1.19 s⁻¹, CR2*=16.03±1.23 s⁻¹) (P<.01), and MR2* was increased more than CR2*. Medullary to cortical R2* ratios (MCR2*) of patients were significantly increased when compared with those of controls (P<.01). In the patient group, estimated glomerular filtration rate levels were greater than or equal to 60 ml/min/1.73 m² in six patients (12 kidneys), whose MR2* and CR2* were also significantly higher than those of controls (P<.01). Serum creatinine levels were normal in seven patients (14 kidneys), whose MR2*, CR2* and MCR2* were also higher than those of controls (P<.01).

Conclusions

BOLD MRI can be used to evaluate changes in renal oxygenation in CKD, suggesting that it has the potential to be an excellent noninvasive tool for the evaluation of renal function.     

GD-enhanced 3D phase-contrast MR angiography and dynamic perfusion imaging in the diagnosis of renal artery stenosis

The objective of this study was to investigate the role of contrast enhancement using a three-dimensional (3D) phase-contrast (PC) magnetic resonance (MR) sequence (3D PC-MRA) and to assess the value of a dynamic MR perfusion study of the kidneys to determine the hemodynamic relevance of unilateral renal artery stenosis (RAS). Seventeen patients with unilateral RAS were examined on a standard 1.0 T imaging system using a phase shift and magnitude sensitive 3D PC sequence (TR = 160 ms, TE = 9 ms, venc. 30 cm/s). Following the initial pre-contrast 3D PC-MRA a dynamic first pass perfusion study was performed using a Turbo-FLASH 2D sequence (TR = 4.5 ms, TE = 2.2 ms, TI = 400 ms) after bolus injection of 0.15 mmol gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)/kg body weight. The 3D PC-MRA was then repeated during infusion of 0.15 mmol Gd-DTPA/kg body weight. Evaluation by three independent readers was based on maximum intensity projection images. Source images were rendered on request. Signal intensity (SI) over time curves of the renal cortex were obtained from the dynamic perfusion study and analyzed for maximum signal enhancement as well as temporal relationship to the aortic SI curve. Results from 3D PC-MRA revealed a sensitivity (pre-/post-contrast) of 100%/89%, specificity of 76%/63%, positive predictive value of 80%/69%, negative predictive value of 90%/78%, and accuracy of 85%/75% (p = 0.07). Interobserver agreement was κ = 0.61/κ = 0.47 (pre/post Gd-DTPA), respectively. Increased signal-to-noise was present in all segments of the renal arteries post contrast (p = 0.0003). This came along with image degradation due to aliasing and elevated SI of venous flow that partially obscured the renal arteries. Dynamic SI curves showed a significantly decreased maximum SI in RAS (p = 0.01–0.001). A temporal delay of cortical signal intensity enhancement could not be confirmed in this setting. Gd-enhanced 3D PC-MRA did not yield a superior diagnostic value in the diagnosis of RAS compared to pre-contrast measurements. Dynamic perfusion imaging of the kidneys, in combination with 3D PC-MRA, can contribute additional information in suspected unilateral RAS.     

MRI anatomy of the rat kidney at 1.5 T in different states of hydration

The objective of this study was to determine correlation between structural anatomy and surface coil spin-echo MR imaging of the rat kidney and the effect of hydration state on MR signal intensities of the cortex and medulla. Twelve rats were studied in a pilot study with a 3-inch surface coil in a 1.5 T magnet under five different states of hydration. Serum and urine osmolality measurements were obtained immediately prior to each scan. Signal intensity measurements were made from both T₁- and T₂-weighted images of the cortex and medulla of both kidneys in each state of hydration. Gross and histological anatomy of the rat kidneys was correlated with the MR images. Four distinct layers were detected in vivo on MRI images of the rat kidney; these correlated with the histological layers. T₁-weighted cortico-medullary differentiation was most pronounced at 48 h dehydration; T₂ cortico-medullary differentiation was greatest at 72 h of dehydration. We concluded that different parts of the mammalian nephron can be identified by MR imaging and that cortico-medullary differentiation is affected by the hydration state of the animal.     

Quantitative assessment of rat kidney function by measuring the clearance of the contrast agent Gd(DOTA) using dynamic MRI

Magnetic resonance imaging (MRI) has been applied to assess kidney function in normal rats by monitoring the passage of the extracellular contrast agent GdDOTA. High-resolution images have been obtained using either the rapid acquisition with relaxation enhancement (RARE) or the snapshot pulse sequence. The latter was superior in anatomic definition due to the shorter echo delays used. The GdDOTA induced signal enhancements in the various renal structures were theoretically modeled and the results of the regression analysis then used to estimate local tissue concentrations in renal cortex, inner medulla and outer medulla/pelvis. The concentration-time curves in vena cava and renal cortex were similar and distinctly different from the ones in medulla and pelvis. This is reflected in the time-to-peak (TTP) values, which were TTP (blood) = 0.18 +/- 0.03 < TTP (cortex) = 0.26 +/- 0.05 < TTP (outer medulla) = 0.62 +/- 0.03 < TTP (inner medulla/pelvis) = 0.92 +/- 0.16 min. The initial tracer uptake rates depended linearly on the dose of GdDOTA administered, the value of the uptake rate in the cortex being significantly higher than those in the outer and inner medulla, which were identical within error limits. The initial medullar tracer uptake followed a first-order kinetics. The rate constant k(cl) = (dc[medulla]/dt)/c[cortex] = 3.4 +/- 0.5 min(-1) for the transition from cortex (predominantly blood signal) to medulla (predominantly urine) was considered a measure for the renal clearance. Intravenous administration of furosemide at doses 2.5, 5, and 10 mg/kg led to a dose-dependent decrease of k(cl). This reflects the inhibitory effect of the diuretic furosemide on medullary water resorption and thus the dilution of the GdDOTA in urine.     

Assessment of renal fibrosis in a rat model of unilateral ureteral obstruction with diffusion kurtosis imaging: Comparison with α-SMA expression and 18F-FDG PET

PurposeTo investigate the utility of diffusion kurtosis imaging (DKI) MRI for evaluation of renal fibrosis in rats with unilateral ureteral obstruction (UUO).MethodsTwenty-five rats had UUO, and ten rats were subjected to sham operation as control. DKI was performed on a 3.0 T MRI scanner on days 1, 3, 5, and 7 after ligation. All rats then underwent ¹⁸F-FDG dynamic PET to evaluate unilateral renal function, followed by histological analysis to examine α-smooth muscle actin (α-SMA) expression. DKI metrics were assessed among the time points and between two sides, and compared with maximum standardized uptake value (SUV_max), serum levels of creatinine and urea, and fibrosis marker α-SMA.ResultsMean kurtosis (MK) on day 7, axial kurtosis (Ka) on days 3 and 7, mean diffusivity (MD) on days 1, 3, 5, and 7, and fractional anisotropy (FA) on days 3, 5, and 7 of cortex and medulla between the UUO and contralateral sides were significantly different (all p < 0.05). Over the course of UUO progression, there were significant changes in Ka, MD and FA of medulla (all p < 0.05). FA of medulla was positively correlated with SUV_max (r = 0.641, p < 0.001), and MD of cortex was negatively correlated with urea (r = −0.534, p = 0.001). MD of cortex was negatively correlated with α-SMA on UUO sides (r = −0.710, p < 0.001).ConclusionsDKI shows the potential for noninvasive assessment of renal fibrosis and unilateral renal function induced by UUO.     

Longitudinal assessment of mouse renal injury using high-resolution anatomic and magnetization transfer MR imaging

The purpose of this study is to evaluate the utility of high-resolution non-invasive endogenous high-field MRI methods for the longitudinal structural and quantitative assessments of mouse kidney disease using the model of unilateral ureter obstruction (UUO). T₁-weighted, T₂-weighted and magnetization transfer (MT) imaging protocols were optimized to improve the regional contrast in mouse kidney. Conventional T₁ and T₂ weighted images were collected in UUO mice on day 0 (~ 3 h), day 1, day 3 and day 6 after injury, on a 7 T small animal MRI system. Cortical and medullary thickness, corticomedullary contrast and Magnetization Transfer Ratio (MTR) were assessed longitudinally. Masson trichrome staining was used to histologically assess changes in tissue microstructure. Over the course of UUO progression there were significant (p < 0.05) changes in thickness of cortex and outer medulla, and regional changes in T₂ signal intensity and MTR values. Histological changes included tubular cell death, tubular dilation, urine retention, and interstitial fibrosis, assessed by histology. The MRI measures of renal cortical and medullary atrophy, cortical–medullary differentiation and MTR changes provide an endogenous, non-invasive and quantitative evaluation of renal morphology and tissue composition during UUO progression.     

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.     

USPIO-Enhanced MR imaging of glycerol-induced acute renal failure in the rabbit

Enhanced-MR imaging in combination with ultrasmall superparamagnetic iron oxide (USPIO) was used in the glycerol-induced model of acute renal failure (ARF) in the rabbit to detect renal perfusion abnormalities. A control group (n = 5) and an ARF group (n = 5) were studied after intramuscular injection of glycerol (10 ml/kg) with T₂-weighted spin-echo sequence at 1.5 T and a 27 μmol/kg IV dose of iron. The signal intensity (SI) was quantified in the cortex, the outer medulla (OM), and the inner medulla (IM). In control rabbits, the maximum SI decrease after USPIO injection was in the OM (76% ± 3.6), as this is the region of maximal vascular density, then in the IM (73.4% ± 2.9). In the glycerol group, SI loss in the OM (61% ± 12.6) and the IM (45.2% ± 16.24) was significant less than in the control group (p < .05). Pathology results showed fibrinous thrombus in the efferent arterioles and congestive aspect of the vasa recta in the medulla. We argue that a reduced medullary concentration of USPIO in the renal failure group is indicative of medullary hypoperfusion.     

Hypothermic renal preservation with a sucrose/ polyethylene glycol solution in a rabbit renal transplant model

Renal preservation at for 24 hours at hypothermia was studied in a rabbit model after flush cooling with sucrose-based solution (SBS), compared with a standard preservation solution (in this case, Marshall's Hypertonic Citrate solution - HCA). Polyethylene glycol supplementation to SBS (SBS-PEG) was also investigated. Renal function was measured by plasma creatinine assays during 1 months post transplantation, and pathology of the explanted kidneys was undertaken. Results showed that survival at 28 days was similar in all groups, (HCA - 3 out of 6; SBS - 2 out of 5; SBS-PEG - 3 out of 5), and there were no differences in recovery of plasma creatinine values. Histopathological evaluation of the grafts indicated that SBS preservation resulted in more severe damage after transplantation (P less than 0.05 in both corticomedullary region and medulla compared to HCA), whilst addition of PEG reduced the damage score to that seen with HCA. SBS can be used as a simple, inexpensive preservation solution for kidney cold storage provided that PEG is used as an additional colloid.     

In vivo estimation of relaxation processes in benign hyperplasia and carcinoma of the prostate gland by magnetic resonance imaging

Tissue characterization for separating malignant from benign tissue is a clinically very important potential of magnetic resonance imaging (MRI). In this study quantitative determination of T1- and T2-relaxation processes was accomplished in five healthy volunteers, 10 patients with benign hyperplasia of the prostate gland and eight patients with prostatic carcinoma. Histological verification was obtained in all the patients. The measurements were performed on a wholebody MR-scanner operating at 1.5 T using six inversion recovery sequences (TR = 4000 msec) for T1-determination and a 32 spin-echo sequence (TR = 3000 or 2000 msec) for T2-estimation. The T1-relaxation curves all appeared monoexponential, whereas the T2-curves in most cases showed a multiexponential behaviour. A considerable overlap of the relaxation curves was seen. Consequently, we found no statistically significant differences between the T1- or the T2-relaxation times of the three groups investigated. It is concluded that tissue characterization based on relaxation time measurements with MRI does not seem to have a clinically useful role in prostatic disease.     

Renal perfusion in acute kidney injury with DCE-MRI: Deconvolution analysis versus two-compartment filtration model

Purpose

To investigate the results of different pharmacokinetic models of a quantitative analysis of renal blood flow (RBF) in acute kidney injury using deconvolution analysis and a two-compartment renal filtration model.

Materials and methods

MRI data of ten male Lewis rats were analyzed retrospectively. Six animals were subjected to unilateral acute kidney injury and underwent perfusion imaging by dynamic contrast-enhanced MRI (DCE-MRI). Renal blood flow was estimated from regions-of-interest depicting the cortex in the DCE-MRI perfusion maps. The perfusion models were compared by a paired t-test and Bland–Altman plots.

Results

No significant difference was found between the two compartment model and the deconvolution analysis (P = 0.2807). Differences between healthy and diseased kidney in the AKI model were significant for both methods (P < 0.05). A Bland–Altman plot showed no systematic errors, and values were equally distributed around the mean difference between the methods lying within the range of 1.96 standard deviations.

Conclusion

Both quantification strategies could detect the kidneys that were impaired by AKI. When just aiming at RBF as a marker, a deconvolution analysis can provide similar values as the 2CFM. If functional parameters beyond RBF like glomerular filtration rate are needed, the 2CFM should be employed.     

In vivo MR evaluation of Gd-DTPA conjugated to dextran in normal rabbits.

A dextran-Gd-DTPA compound has been recently synthesized utilizing 70,800 Da molecular weight dextran. This polymeric contrast agent for magnetic resonance imaging has been found chemically to be very stable and to demonstrate in vitro improved relaxivities of 1.5 to 2.3 times that of monomeric Gd-DTPA at 100 MHz. This MR experiment examines the in vivo distribution and relaxivity of the 70,800 Da molecular weight dextran-Gd-DTPA compound in a rabbit model by measuring the change in signal-to-noise ratio of a variety of organs (renal cortex, renal medulla, liver, brain, and torcula herophile) compared to the preinjection state. Results demonstrate prolonged (beyond 60 min) enhancement of the renal cortex, renal medulla, liver and torcula, and no enhancement of brain parenchyma.     

Visualization of myocardial infarction and subsequent coronary reperfusion with MRI using a dog model

Twelve anesthetized mongrel dogs underwent left thoracotomy with placement of a removable ligature around the left circumflex coronary artery. Following a 3 to 6 hour delay, ECG-gated spin-echo MRI was performed. The ligature was then removed reperfusing the heart, and after a 10-15 min period, MRI repeated. Finally, post-sacrifice images were obtained, and the hearts chemically stained for infarct evaluation. The MR images were subjectively and quantitatively evaluated for visibility of the endocardial border and of the injured myocardium, and for changes after reperfusion. The injured tissue was variably visible in vivo, the major limitation a result of motion blurring and artifact. The abnormal tissue was easily visible on MRI in 11 animals, and not clearly visible in one. The endocardial border was easily seen in 10 animals. The variation of calculated relaxation times was high for both normal and ischemic/infarcted myocardium in the beating hearts (normal: T1 = 566 +/- 288, T2 = 38 +/- 6; injured myocardium: T1 = 637 +/- 250, T2 = 41 +/- 12) in contrast, relatively stationary skeletal muscle measured in the same images had narrower ranges (T1 = 532 +/- 199, T2 = 28 +/- 2). Changes with reperfusion were seen, but not reliably. The infarcted or ischemic zones were easily visible on post-sacrifice images in all animals imaged. Post-sacrifice relaxation times were T1 = 564 +/- 69 msec, T2 = 39 +/- 3 msec for normal heart muscle, and 725 +/- 114, T2 = 47 +/- 5 for ischemic/infarcted tissue.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantitation of renal perfusion using arterial spin labeling with FAIR-UFLARE

Quantitative perfusion imaging of human kidneys was performed using arterial spin labeling MRI with a fast spin echo readout-sequence. Perfusion maps of centrally located single slices were obtained in axial and coronal orientations. In ten healthy volunteers, the mean value of perfusion was 213+/-55 mL/(100g min) with a range from 140 to 319 mL/(100g min). These results are in accordance with literature data, considering the fact that FAIR only measures the perfusion component normal to the imaging plane. Intra-individual reproducibility errors of +/-11% were smaller than the natural interindividual variability of renal perfusion (SD = +/- 25%). Perfusion in the cortex was approximately 3-4 times higher compared to the medulla. Considering the relatively high resolution of 2x2x10 mm3, the ability to quantify perfusion, and the lack of ionizing radiation and contrast media, this technique should prove useful in diagnosing renal pathologies that are associated with reductions in tissue perfusion.