Pilot MR evaluation of pharmacokinetics and relaxivity of specific blood pool agents for MR angiography

RATIONALE AND OBJECTIVES: To evaluate the use of two new blood pool contrast agents (P760, P775) compared with a low-molecular-weight gadolinium chelate in MR angiography. METHODS: The r1 efficiency of P760 was evaluated in vitro at 1.5 T; 3D abdominal contrast-enhanced MR angiography with qualitative analysis was compared in four rabbits after injection of incremental doses of P760 and in one rabbit after Gd-DOTA. A dynamic MR study was performed using a 2D T1-weighted turbo-flash MR sequence after injection of P760, P775, and Gd-DOTA. Each compound was tested at equivalent doses in three rabbits to assess r1 efficiency. Quantitative analysis of signal intensity in the aorta, the inferior vena cava, the renal cortex, and the medulla was performed. RESULTS: In vitro, the r1 efficiency of P760 was 23.3 mmol(-1) x L x sec(-1) at 1.5 T. Injection of a dose of P760 10 times less than Gd-DOTA allowed similar vessel visualization. The signal intensity peak and first-pass contrast kinetics in the aorta and the inferior vena cava were similar with the three products. Compared with P760 and Gd-DOTA, P775 allowed a greater renal cortex signal intensity at the first pass and a faster decrease on delayed images. CONCLUSIONS: The superior r1 efficiency of P760 and P775 was confirmed in vitro and in vivo at 1.5 T compared with Gd-DOTA, and P775 proved to be a rapid-clearance blood pool agent.     

Magnetic resonance imaging of experimental renal hemorrhage

Experimental renal hemorrhage was induced by injecting autologous blood into the left kidney of 13 rats. To investigate the magnetic resonance (MR) characteristics of acute renal hemorrhage and subsequent stages of resolution, repetitive MR images were obtained using a 0.35 Tesla imager during a period of 21 days postinduction. A dual spin-echo imaging (TR 500 and 2,000 msec, TE 28 and 56 msec) was used to calculate the relaxation times and record the intensities in the renal medulla and cortex. Histologic examination (n = 9) indicated that blood was dispersed intrarenally, and no encapsulated hematoma developed. The signal intensity on the T1- and T2-weighted images, as well as the relaxation times in the hemorrhagic renal parenchyma were unchanged during 21 days when compared with intact kidney values. Subcapsular fresh blood had a high signal intensity on T2-weighted images. A marked overlap of the relaxation parameters between intact kidney parenchyma and diffuse intrarenal hemorrhage was observed. Detection of dispersed intrarenal blood using spin echo MR imaging may be difficult.     

Paramagnetic contrast enhancement at 0.02 T: An experimental study using Gd-DOTA in normal and hydronephrotic kidneys

Both normal and experimentally hydronephrotic rabbits were imaged at 0.02 T using partial saturation (PS 160/30) and inversion recovery (IR 1000/200/40) sequences. The signal intensity of normal renal medulla and cortex markedly increased after the injection of 0.1 mmol/kg of Gd-DOTA. In the unilateral total hydronephrosis the dilated renal pelvis did not contrast enhance after 15 and 35 min of Gd-DOTA injection. The enhancement pattern was similar in 1- and 3-week-old hydronephrosis. The effect of Gd-DOTA on renal T1 times at 0.02 T was studied using rats. Fifteen minutes after the Gd-DOTA injection (0.1 mmol/kg) the TI times of excised rat kidneys decreased from 311 to 90 ms. The authors conclude that the enhancement of the MR signal of the kidney by Gd-DOTA at an ultralow magnetic field (0.02 T) is similar to its enhancement at higher fieldss (>0.15 T). © 1988 Academic Press, Inc.     

Renal functional contrast-enhanced magnetic resonance imaging: evaluation of a new rapid-clearance blood pool agent (p792) in sprague-dawley rats

OBJECTIVES: The objective of the present study was to compare P792, a new rapid clearance blood pool agent characterized by negligible interstitial diffusion but unrestricted glomerular filtration, with Gd-DOTA in both qualitative and quantitative aspects of renal functional magnetic resonance imaging. MATERIALS AND METHODS: Dynamic imaging was performed with a fast T1-weighted gradient-echo sequence on a 1.5-T magnet in 25 Sprague-Dawley rats, after injection of 13 micromol Gd/kg-1 of P792 (n = 10), 100 (n = 10), or 50 micromol Gd/kg-1 of Gd-DOTA (n = 5). Signal-time curves from 6 regions of interest (ROIs), including renal parenchyma and contents, were analyzed. RESULTS: Qualitative analysis depicted a typical pattern of temporal enhancement as previously described with extracellular gadolinium chelates, including early and brief enhancement of the aorta, renal vessels and cortex, quickly followed by enhancement of the medulla and then renal pelvis. However, a decrease in signal intensity was noted in the inner medulla and the renal pelvis approximately 90 seconds after bolus injection, being more marked when using the full dose of Gd-DOTA. Curve analysis showed a similar vascular phase within each parenchymal ROI, confirmed by similar upslopes, which ranged from 0.015 +/- 0.007 to 0.019 +/- 0.005. Following this initial phase, T1-enhancement appeared greater and longer within the medulla and renal pelvis, and subsequently in the whole kidney ROI with P792 (time to maximal enhancement (sec)/ enhancement rate: 85.5 +/- 15.9/3.1 +/- 0.4) as compared with Gd-DOTA full (53.0 +/- 18.9/ 2.7 +/- 0.3) or half dosage (65.2 +/- 20.1/ 2.2 +/- 0.2). The subsequent decrease in signal intensity, characterized by a downslope during the minute following maximal enhancement, was faster with Gd-DOTA (0.006 +/- 0.002) as compared either to P792 or half dosage Gd-DOTA (0.003 +/- 0.001). CONCLUSIONS: Due to its physicochemical and pharmacokinetic properties, P792 allows the use of a reduced dosage of gadolinium, resulting in less T2* effect without compromising T1 enhancement. Thus, P792 appears suitable for renal functional MR imaging.     

USPIO-enhanced MR imaging of macrophage infiltration in native and transplanted kidneys: initial results in humans

The purpose of this study was to evaluate the detection and characterization of macrophage infiltration in native and transplanted kidneys using ultrasmall superparamagnetic iron oxide particles (USPIO). Among 21 patients initially enrolled, 12 scheduled for renal biopsy for acute or rapidly progressive renal failure (n = 7) or renal graft rejection (n = 5) completed the study. Three magnetic resonance (MR) sessions were performed with a 1.5-T system, before, immediately after and 72 h after i.v. injection of USPIO at doses of 1.7–2.6 mg of iron/kg. Signal intensity change was evaluated visually and calculated based on a region of interest (ROI) positioned on the kidney compartments. Histological examination showed cortical macrophage infiltration in four patients (>5 macrophages/mm²), two in native kidneys (proliferative extracapillary glomerulonephritis) and two in transplants (acute rejection). These patients showed a 33 ± 18% mean cortical signal loss on T2*-weighted images. In the remaining eight patients, with <5 macrophages/mm², there was no cortical signal loss. However, in three of these, presenting with ischemic acute tubular necrosis, a strong (42 ± 18%) signal drop was found in the medulla exclusively. USPIO-enhanced MR imaging can demonstrate infiltration of the kidneys by macrophages both in native and transplanted kidneys and may help to differentiate between kidney diseases.     

Functional evaluation of normothermic ischemia and reperfusion injury in dog kidney by combining MR diffusion-weighted imaging and Gd-DTPA enhanced first-pass perfusion

PURPOSE: To evaluate functional alterations of renal ischemia and reperfusion injury using MR diffusion-weighted imaging and dynamic perfusion imaging. MATERIALS AND METHODS: Twelve dogs were randomly divided into four groups. Animal renal ischemia was respectively induced for 30 (group 1), 60 (group 2), 90 (group 3), and 120 (group 4) minutes by left renal artery ligation under anesthesia. Using a 1.5 T MR system, true-FISP, TSE, EPI, and DWI sequences were acquired in five different periods; specifically, pre-ischemia, onset-ischemia, late ischemia, onset-reperfusion, and post-reperfusion. Moreover, a turbo-FLASH sequence (TR/TE/TI/FA = 5.8/3.2/400 msec/10 degrees ) with a temporal resolution of 1.16 seconds was acquired. Signal intensity (SI) was measured in the cortex, outer medulla, and inner medulla of kidney. Apparent diffusion coefficient (ADC) values were calculated, and SI was plotted as a function of time. RESULTS: In all animals, significant SI changes of the left kidney on T2/T2*WI were detected following ischemia-reperfusion insult compared to corresponding values of the right kidney. Following ligation, the ADC values decreased in all layers of the left kidney. Immediately after the release of ligation, ADC values in both outer and inner medulla of the left kidney remained lower than those of the right kidney in those animals which were induced with renal ischemia for 60, 90, and 120 minutes. In all groups, a uniphasic enhancement pattern was observed in the outer and inner medulla of the left kidney, accompanied by a decrease of the area under the curve. CONCLUSION: Our results suggest that MR diffusion-weighted imaging and dynamic perfusion imaging are useful in identifying renal dysfunction following normothermic ischemia and reperfusion injury.     

MRI of acute myocardial infarction with injection of Gd-DOTA (15 patients)

We studied 15 patients 4 to 8 days after myocardial infarction by using ECG gated MR before and after administration of 0.2 mmol/kg Gd-DOTA. The diagnosis in each patient was confirmed by electrocardiographic criteria, elevated levels of fractionated creatine kinase (CK) isoenzyme, thallium scintigraphy, ventriculography and coronarography. T1-weighted, spin-echo images, were obtained before and immediately after injection of Gd-DOTA and were repeated 15 min later. The site of infarction was visualised in 10 patients as an area of high signal intensity after the injection of Gd-DOTA. Contrast between normal and infarcted myocardium was greatest 15 min after injection. Three patients were excluded because of failure to acquire adequate MR studies. In 2 other patients, the infarct were not detected. Before injection of Gd-DOTA, only 2 infarcts were detected. These results suggest that Gd-DOTA can improve MR visualisation and detection of acute myocardial infarction.     

Acute tubular necrosis: use of gadolinium-DTPA and fast MR imaging to evaluate renal function in the rabbit

Sequential fast magnetic resonance (MR) images (repetition time = 33 ms, echo time = 7 ms, alpha = 22 degrees, one image every 12 s) were acquired using gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) (10 or 100 mumol/kg) to study perfusion and concentrating ability in normal rabbit kidneys and in kidneys with HgCl2-induced acute tubular necrosis (ATN). In normal rabbits receiving 100 mumol Gd-DTPA/kg a concentric region of decreased MR signal was observed. In sequential images the dark ring pattern migrated centripetally through the kidney moving from the corticomedullary junction to the inner medulla. The decrease in MR signal intensity occurred as a consequence of T2 relaxation (magnetic susceptibility) due to high concentration of Gd-DTPA within the tubules. This suggests that the dark ring pattern may serve as a qualitative feature indicative of the ability of the kidneys to concentrate. With the onset of HgCl2-induced ATN the pattern of enhancement due to Gd-DTPA administration changed markedly. Although the kidneys with ATN did continue to be perfused, the concentric dark ring pattern seen in normal kidneys receiving 100 mumol Gd-DTPA/kg was not observed. These results suggest that Gd-DTPA and fast imaging MR may provide a method of assessing perfusion and concentrating ability within the healthy or diseased kidney.     

Magnetic resonance imaging in the diagnosis of acute renal allograft rejection and its differentiation from acute tubular necrosis. Experimental study in the dog

This study was designed to evaluate the potential utility of magnetic resonance imaging (MRI) for the diagnosis of acute renal allograft rejection and its differentiation from acute tubular necrosis (ATN). Eighteen canines were used. Five animals served as controls. ATN was induced in six animals by cross-clamping of the left renal artery for 90 minutes. In order to study acute renal allograft rejection, seven animals were subjected to exchange allograft transplantation of the left kidney. MRI was performed with a 0.35T superconductive magnet. A double spin-echo technique was used with varying TR and TE parameters. The spin echo images were analyzed for morphology, signal intensity, T1 and T2 relaxation times, and spin density. The most useful MRI criteria for the diagnosis of ATN and acute rejection were found to be the renal size, the intensity difference between cortex and medulla (corticomedullary contrast), and the T1 relaxation time of the cortex. Normal kidneys showed maximal corticomedullary contrast (19% +/-2) on images obtained with TR = 0.5 sec and TE = 28 msec. Cortical T1 relaxation time was 551 msec + /-73. In the ATN group, the kidneys were slightly swollen (P = ns) and the corticomedullary contrast (11% + /-3) was reduced by 42% (P less than .01). T1 of the cortex (689 + /-142) was increased by 25% (P less than .10). In acute rejection, significant renal enlargement was noted (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative signal intensity measurements in dynamic gadolinium-enhanced MR mammography

Increases in signal intensity enhancement were measured in defined regions of interest (ROIs) to allow distinction between malignant and benign tumors with dynamic gadolinium-enhanced magnetic resonance (MR) mammography. Twenty patients with palpable breast lesions (15 malignant, five benign) underwent MR mammography. The dynamic gradient-echo sequence was performed with intravenous bolus injection of gadopentetate dimeglumine and consisted of 25 images with a time resolution of 30 seconds. Contrast enhancement was calculated by comparing user-defined ROIs on pre- and postcontrast images. An increase in signal intensity of 70% or more on the 1-minute postcontrast image was used as the criterion of malignancy. MR mammographic results correlated with histopathologic findings in all patients when the defined ROI was in the most enhancing part of the tumor. For the ROI in areas of submaximal enhancement or when the ROI surrounded the whole lesion, only five and nine tumors, respectively, fulfilled the malignancy criterion. All malignant tumors showed large variations in signal intensity enhancement that depended on the position of the ROI in the tumor. Dynamic, gadolinium-enhanced MR mammography allows distinction of benign from malignant breast tumors when the selected ROI is in the most enhancing part of the lesion.     

CT derived Patlak images of the human kidney.

This study aimed to produce Patlak images of the kidney from dynamic CT data and to determine whether such images are substantially affected by fluid movement between renal tubular segments. Renal permeability was measured in 31 kidneys by applying Patlak analysis to time-density data from kidney and aorta during dynamic CT. Permeability parameters were correlated against plasma urea. The renal region (cortex or medulla) with the greatest permeability was determined from parametric images generated using pixel by pixel analysis. The mean value for whole kidney permeability was 517.5 microliters min-1 ml-1. A correlation was found between whole kidney permeability and plasma urea (p < 0.01). Permeability values were highest in the renal medulla in 24 (77%) kidneys. The higher medullary values of permeability are artefactual, resulting from movement of fluid and contrast medium between cortex and medulla. Although Patlak images do not reflect true intrarenal permeability values, the apparent medullary permeability may provide diagnostically useful information about the concentrating ability of the kidney. CT measurements of whole kidney permeability reflect filtration function but the apparent intrarenal variations in permeability will result in measurement errors dependent upon the relative amounts of renal cortex and medulla included in the CT slice studied.     

Evaluation of changes in intrarenal oxygenation in rats using multiple gradient-recalled echo (mGRE) sequence.

Changes in intrarenal oxygenation in rats during pharmacological stimuli were evaluated with a multiple gradient-recalled echo (mGRE) sequence. With administration of the loop diuretic furosemide, oxygenation in the medulla improved; acetazolamide, a proximal tubular diuretic, produced no significant change. These results are consistent with our previous studies in humans and resemble earlier studies of medullary oxygenation using oxygen microelectrodes in anesthetized rats. The technique may be useful in the evaluation of therapeutic strategies in animal models of pathophysiological states such as acute renal failure.     

Study of acute renal ischemia in the rat using magnetic resonance imaging and spectroscopy

Magnetic resonance (MR) imaging and spectroscopy, chemical lactate measurements, and microscopic examinations were performed to investigate acute renal ischemia in rats. MR images (1H) and spectra (31P and 1H) were acquired on a 2.0-T superconducting small-bore magnet by using implanted coils. Occlusion of the renal artery induced a significant decrease in signal intensity of the renal parenchyma on T2-weighted images, which was most obvious in the outer medulla (-50 +/- 15%, n = 8, P less than 0.001) and was the result of venous congestion, as verified histologically, 31P spectroscopy demonstrated a drop in pH from 7.3 +/- 0.2 to 6.6 +/- 0.2 (n = 18, P less than 0.001), characterized by a time constant (Tc) in the same range as that of the depletion of ATP (2.3 +/- 1.3 min versus 1.9 +/- 1.2 min, n = 10, P = ns). By means of 1H spectroscopy, a lactate peak was detected within 1.5 to 4 min of ischemia, still increasing in intensity after 1 h of ischemia. The Tc of the lactate buildup (15.9 +/- 7.5 min, n = 8) was significantly longer than that of the drop in pH (P less than 0.005). The chemically measured intrarenal concentration of lactate was 1.3 +/- 0.5 mumol/g in control kidneys and 8.7 +/- 3.2 mumol/g (P less than 0.005) in kidneys made ischemic for 1 h. The present study demonstrated important features of acute renal ischemia: (a) acute ischemia induces venous congestion in the medulla; (b) accumulation of lactate is not the main cause of the intracellular acidification observed during ischemia.     

Effect of field strength on gadolinium enhancement in MR imaging

This studv was designed to evaluate the influence of magnetic field strength on the relative enhancement effect (RE) of gadolinium (Gd)-chelates. Dilution series of two paramagnetic contrast agents (Gd-DTPA and Gd-DOTA) were examined in three commercially available MR systems. operating at different field strengths (02 T, 1. T, and 1.5 T). The RE was plotted against Gd concentration. The highest increases in signal intensity occurred with Gd concentrations of approximately L.0 mmol/L. No significant difference in RE was observed between MR systems ranging in field strength from 0.? T to 1.5 T. The RE of Gd-DTPA and Gd-DOTA was found to he equivalent.     

Hemorrhagic fever with renal syndrome: MR imaging of the kidney

Magnetic resonance (MR) imaging of the kidneys was performed in 14 patients with a severe form of hemorrhagic fever with renal syndrome (HFRS), a major public health problem in Far Eastern Asia. To the authors' knowledge, this is the first report of renal assessment with MR imaging in HFRS. Three MR imaging studies were done while patients were in the oliguric phase, 19 were done during the diuretic phase, and three were done during the convalescent phase. The authors differentiated the cortex and the medulla in all 21 T1-weighted examinations and all 25 T2-weighted examinations. Seven T1-weighted examinations (33%) and 20 T2-weighted examinations (80%) showed low signal intensity along the outer portion of the medulla, which thus enabled differentiation from the inner medulla. Low signal intensity along the medulla (especially the outer medulla) on T2-weighted images, possibly representing medullary hemorrhage, is fairly constant and characteristic on MR images of the kidneys in patients with HFRS.     

Atypical low-signal-intensity renal parenchyma: causes and patterns.

Certain renal diseases manifest as low signal intensity of the renal parenchyma on magnetic resonance images. Sometimes, the appearance is sufficiently characteristic to allow a specific radiologic diagnosis to be made. The causes of this finding can be classified into three main categories on the basis of the pathophysiology: hemolysis, infection, and vascular disease. The first category includes paroxysmal nocturnal hemoglobinuria (PNH), hemosiderin deposition in the renal cortex from mechanical hemolysis, and sickle cell disease. The second category includes hemorrhagic fever with renal syndrome (HFRS). The third category includes acute renal vein thrombosis, renal cortical necrosis, renal arterial infarction, rejection of a transplanted kidney, and acute nonmyoglobinuric renal failure with severe loin pain and patchy renal vasoconstriction. These disease processes have different patterns of low signal intensity. PNH, hemosiderin deposition from mechanical hemolysis, and sickle cell disease involve the entire cortex including the columns of Bertin. HFRS involves the medulla, especially the outer medulla, whereas cortical necrosis involves the inner cortex including the columns of Bertin. In renal vein thrombosis, low-signal-intensity lesions involve the outer medulla, an appearance resembling that of HFRS. Wedge-shaped low-signal-intensity regions involving both the cortex and the medulla are seen in arterial infarction.     

The role of technetium-99m MAG3 renal imaging in the diagnosis of acute tubular necrosis of native kidneys

The differential diagnosis for patients with acute renal failure of their native kidneys, as a result of primary intrarenal disease, includes acute tubular necrosis, glomerulonephritis, and interstitial nephritis. The role of MAG3 renography has not been studied in this setting. The authors describe four patients with acute renal failure in whom MAG3 renal imaging reliably identified acute tubular necrosis, as confirmed by follow-up kidney biopsies. In contrast to the poor parenchymal uptake observed in glomerulonephritis and interstitial nephritis, MAG3 shows a distinctive pattern in patients with acute tubular necrosis. For patients with acute renal failure, a renal scan can facilitate decision-making regarding the initiation of therapy.     

Gadolinium-enhanced MR imaging of normal renal transplants. An evaluation of a T1-weighted dynamic echo-planar sequence.

PURPOSE: To evaluate the potential usefulness of dynamic MR with echoplanar imaging (EPI) in assessing the renal function in patients with renal allografts. MATERIAL AND METHODS: Using a T1-weighted sequence, EPI was performed after injection of a Gd-chelate in 17 patients with normally functioning renal allografts. Time-intensity curves were plotted from the signal intensity (SI) measurements of the cortex and the medulla. RESULTS: The pattern of corticomedullar differentiation (CMD) observed after contrast enhancement was divided into four phases using the T1-EPI. After a rapid decrease in the SI of cortical structures, and a subsequent return to precontrast levels, a gradual fall in the SI of the medulla was observed. The average time between the two periods of signal loss was 60 s. CONCLUSION: This study illustrated the potential use of dynamic T1-EPI to demonstrate contrast-induced CMD in renal allografts.     

Gadolinium-DTPA enhanced dynamic MR imaging in the evaluation of cisplatinum nephrotoxicity

Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) enhanced dynamic magnetic resonance (MR) imaging was used to monitor the nephrotoxic effects of cis-platinum (cis-diamminedichloroplatinum; CDDP), a chemotherapeutic agent that produces damage in the proximal convoluted tubule. Ten New Zealand white rabbits (NZWs) were divided into two groups and were evaluated at two clinically relevant doses of CDDP. Group 1 (four NZWs) received CDDP intravenously at 125 mg/m2 over 1 h. Rabbits in Group 2 (six NZWs) were infused with CDDP at 40 mg/m2 each day for 5 consecutive days. Dynamic MR images were performed in the axial plane at 1.5 T using a gradient recalled acquisition in the steady state sequence with an echo time of 11 ms, a repetition time of 20 ms, and a flip angle of 10 degrees after a bolus injection of Gd-DTPA 0.1 mmol/kg. Thirty-two sequential post Gd-DTPA images (5.12 s/image) were obtained over 2 min 45 s at a single location. All rabbits underwent baseline normal and serial post CDDP Gd-DTPA enhanced dynamic MR scans. Analysis of the alterations in the normal pattern of renal enhancement caused by CDDP was facilitated by using a stacked profile image and quantitative region of interest measurements of signal intensity. Normally, after the injection of Gd-DTPA, a dark band promptly appears in the outer cortex of the kidneys and migrates centripetally toward the papilla, reflecting the tubular concentration of Gd-DTPA. In Group 1 rabbits, nephrotoxicity due to CDDP was observed as early as 9 h after administration of the drug, with a complete disappearance of the dark band by 7 days. In Group 2 rabbits, the band disappeared gradually and reappeared 2-10 days after the completion of CDDP treatment, indicative of tubular damage and recovery with return of the concentrating ability of the kidney. These results illustrate the feasibility of using Gd-DTPA dynamic MR as a sensitive monitor of drug induced alterations of renal function.     

Evaluation of a new ultrasmall superparamagnetic iron oxide contrast agent Clariscan, (NC100150) for MRI of renal perfusion: experimental study in an animal model

PURPOSE: To determine the diagnostic value of a new ultrasmall superparamagnetic iron oxide Clariscan, (NC100150) for the evaluation of renal perfusion in an animal model using a 3D-FFE-EPI sequence. MATERIALS AND METHODS: Four groups of four rabbits each were imaged after bolus injection of NC100150, using a 1.5 T MR system (Gyroscan ACS-NT). T2*w MR images in the coronal plane were acquired over 60 seconds with an echo-shifted 3D-FFE-EPI sequence (TR/TE/alpha = 18/25 msec/8 degrees ). Data were transferred to a workstation and converted into concentration curves. Based on the fitted concentration time curves, parameter maps were calculated pixelwise: bolus arrival time (T0), time-to-peak (TTP), mean transit time (MTT), and relative bolus volume (rBV). Maximum signal decrease was determined with respect to the baseline value. RESULTS: Mean MTT increased from 4.2 seconds at a dose of 0.25 mg to 5.9 seconds at 1.0 mg (P < .0001). The maximum signal decrease was observed at 0.75 mg, corresponding to 85% of the baseline value. Transit times of the contrast bolus were accurately calculated for the cortex and the outer medulla, but at the level of the inner medulla no arterial flow profile was identified. No significant difference between the cortex and the outer medulla was found for either T0 or rBV, but medullar TTP and MTT were prolonged with regard to cortical TTP and MTT (6.3 seconds vs. 5.7 seconds, P < .001; 5.7 seconds vs. 4.2 seconds, P < .0001). CONCLUSION: The employed intravascular contrast agent is well suited to assess renal perfusion. By the use of a T2*w3D perfusion sequence, cortical and medullar transit times can be quantified and physiologic information on regional perfusion differences can be obtained.