Early detection of acute tubular injury with diffusion-weighted magnetic resonance imaging in a rat model of myohemoglobinuric acute renal failure

Noninvasive evaluation of diabetic patients with high fasting blood glucose using DWI and BOLD MRI

PURPOSE

To investigate the renal microstructure changes and hypoxia changes in type 2 diabetic patients and the relationship between them and glucose using both diffusion-weighted imaging (DWI) and blood oxygenation level-dependent magnetic resonance imaging (BOLD MRI).

METHODS

After measuring morning fasting blood glucose, DWI and BOLD MRI were performed in 57 patients with type 2 diabetes mellitus (DM group) and 14 healthy volunteers (NC group). According to the fasting blood glucose levels, diabetic patients were divided into a normoglycemic diabetes group (group A), a less hyperglycemic diabetes group (group B) and a more hyperglycemic diabetes group (group C). The renal parenchymal apparent diffusion coefficient (ADC), renal cortical R2* (CR2*), and medullary R2* (MR2*) were measured, and the R2* ratio between the medulla and cortex (MCR) was calculated. To test for differences in ADC, R2*, and MCR among the four groups, the data were analyzed by separate one-way ANOVAs. The correlations between ADC, R2*, and MCR and the clinical index of renal function were analyzed.

RESULTS

Groups B and C had significantly lower ADC values in the renal parenchyma (P = 0.048, 0.002) and significantly higher MR2* and MCR values (P < 0.000, P = 0.001, 0.001, and 0.005, respectively) than the NC group. ADC was negatively correlated with glucose, and MR2*, MCR and glucose showed a weak positive correlation.

CONCLUSION

DWI and BOLD may indirectly and qualitatively reflect the kidney microstructure status and hypoxia level of diabetic patients at different blood glucose levels to a certain extent, and possibly guide the clinical treatment of diabetic patients with different blood glucose levels.

Diffusion tensor imaging of renal ischemia reperfusion injury in an experimental model

Renal ischemia reperfusion injury (IRI) is a major cause of acute renal failure. It occurs in various clinical settings such as renal transplantation, shock and vascular surgery. Serum creatinine level has been used as an index for estimating the degree of renal functional loss in renal IRI. However, it only evaluates the global renal function. In this study, diffusion tensor imaging (DTI) was used to characterize renal IRI in an experimental rat model. Spin-echo echo-planar DTI with b-value of 300 s/mm(2) and 6 diffusion gradient directions was performed at 7 T in 8 Sprague-Dawley (SD) with 60-min unilateral renal IRI and 8 normal SD rats. Apparent diffusion coefficient (ADC), directional diffusivities and fractional anisotropy (FA) were measured at the acute stage of IRI. The IR-injured animals were also examined by diffusion-weighted imaging with 7 b-values up to 1000 s/mm(2) to estimate true diffusion coefficient (D(true)) and perfusion fraction (P(fraction)) using a bi-compartmental model. ADC of injured renal cortex (1.69 +/- 0.24 x 10(-3) mm(2)/s) was significantly lower (p < 0.01) than that of contralateral intact cortex (2.03 +/- 0.35 x 10(-3) mm(2)/s). Meanwhile, both ADC and FA of IR-injured medulla (1.37 +/- 0.27 x 10(-3) mm(2)/s and 0.28 +/- 0.04, respectively) were significantly less (p < 0.01) than those of contralateral intact medulla (2.01 +/- 0.38 x 10(-3) mm(2)/s and 0.36 +/- 0.04, respectively). The bi-compartmental model analysis revealed the decrease in D(true) and P(fraction) in the IR-injured kidneys. Kidney histology showed widespread cell swelling and erythrocyte congestion in both cortex and medulla, and cell necrosis/apoptosis and cast formation in medulla. These experimental findings demonstrated that DTI can probe both structural and functional information of kidneys following renal IRI.

Effects of chitosan oligosaccharide (COS) on the glycerol-induced acute renal failure in vitro and in vivo

The purpose of this study was to investigate the effects of chitosanoligosaccharide (COS) on the change of inflammatory response, renal function factor, and renal oxidative stress in glycerol-induced ARF in vitro and in vivo. The molecular weight of COS was approximately below 10 kDa with 90% degree of deacetylation. Renal proximal tubular cells were treated with only COS (0, 0.01, 0.025, 0.05, 0.075 and 0.1%) or COS in the presence of glycerol (4mM). And rats were administered with glycerol (50%, 8 ml/kg) by intramuscular injection for the induction of ARF. For identification the protection effect of COS in the glycerol-induced ARF, rats were administered by COS (0.05 and 0.1%) using P.O. injection. The enzymatic activity of the released RDPase was assayed by the fluorometric method. The level of TNF-alpha in kidney or the culture medium was quantified using ELISA kit (R&D Systems, Minneapolis, USA) and, nitrite concentration was determined by the Griess reaction. We showed that COS stimulated the production of TNF-alpha, NO and the released RDPase. Glycerol increased the concentration of RDPase in kidney and decreased the released RDPase in proximal tubular cells. And, glycerol increased the production of NO, TNF-alpha, creatinine, and MDA, and decreased SOD. However, COS recovered the glycerol-induced inflammatory response, renal function factor, and antioxidant effect in kidney. COS had the antioxidant activity and the anti-inflammatory effect. And maybe that characteristics could help recover the glycerol-induced ARF.

Furosemide increases water content in renal tissue

The present study was designed to evaluate the short-term effects of intravenous administration of furosemide on key functions in the kidney cortex and the outer and inner medulla of rats by using magnetic resonance imaging (MRI). Renal tissue water content, renal tissue oxygenation (in relation to the magnetic resonance spin-spin relaxation rate), the apparent diffusion coefficient (ADC) of water, and volume of renal blood flow were measured. Furosemide administration resulted in an increased water content in all regions of the kidney. In parallel with this, we found a significant reduction in ADC in the cortex (2.7 +/- 0.1 x 10(-3) to 2.3 +/- 0.1 x 10(-3) mm(2)/s; P < 0.01) and in the outer medulla (2.3 +/- 0.1 x 10(-3) to 2.0 +/- 0.1 x 10(-3) mm(2)/s; P < 0.01), indicating that the intra- to extracellular volume fraction of water increased in response to furosemide administration. Furosemide also decreased the blood oxygenation in the cortex (49.1 +/- 2.9 to 40.9 +/- 2.0 s(-1); P < 0.01), outer medulla (41.9 +/- 2.8 to 33.2 +/- 1.6 s(-1); P < 0.01) and in the inner medulla (37.1 +/- 2.9 to 26.7 +/- 1.8 s(-1); P < 0.01), indicating an increased amount of oxygenated Hb in the renal tissue. Moreover, renal blood flow decreased in response to furosemide (6.9 +/- 0.2 to 4.4 +/- 0.2 ml/min; P < 0.001). In conclusion, furosemide administration was associated with increased renal water content, an increase in the intra- to extracellular volume fraction of water, an increased oxygen tension, and a decrease in the renal blood flow. Thus MRI provides an integrated evaluation of changes in renal function, leading to decreased renal water and solute reabsorption in response to furosemide, and, in addition, MRI provides an alternative tool to monitor noninvasively changes at the cellular level.

Functional renal imaging: nonvascular renal disease

Functional renal imaging-a fast-growing field of MR-imaging-applies different sequence types to gather information about the kidneys other than morphology and angiography. This update article presents the current status of different functional imaging approaches and presents current and potential clinical applications. Apart from conventional in-phase and opposed-phase imaging, which already yields information about the tissue composition, BOLD (blood-oxygenation level dependent) sequences, DWI (diffusion-weighted imaging) sequences, perfusion measurements, and dedicated contrast agents are used.

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.

Expression and function of P-glycoprotein in rats with glycerol-induced acute renal failure

The effect of glycerol-induced acute renal failure on P-glycoprotein expression and function was evaluated in rats. The in vivo function of P-glycoprotein was evaluated by measuring renal secretory and biliary clearance and brain distribution of rhodamine 123 (Rho-123), a P-glycoprotein substrate, under a steady-state plasma concentration. In acute renal failure rats, the P-glycoprotein level increased 2.5-fold in the kidney, but not in the liver and brain. In contrast, P-glycoprotein function in these tissues was suppressed. Interestingly, not only the renal but also the biliary clearance of Rho-123 was correlated with the glomerular filtration rate. In Caco-2 cells, plasma from renal failure rats exhibited a greater inhibitory effect on P-glycoprotein-mediated transport of Rho-123 than did plasma from control rats. In conclusion, P-glycoprotein function was systemically suppressed in acute renal failure, even though the level of P-glycoprotein remained unchanged or rather increased. This may be due to the accumulation of some endogenous P-glycoprotein substrates/modulators in the plasma in disease states.

Measurement of the apparent diffusion coefficient in diffuse renal disease by diffusion-weighted echo-planar MR imaging

The purpose of this study was to determine the relationship between the apparent diffusion coefficient (ADC) and diffuse renal disease by diffusion-weighted echolanar magnetic resonance (MR) imaging (EPI). Thirty-four patients were examined with diffusion-weighted EPI. The average ADC values were 2.55 x 10(-3) mm2/sec for the cortex and 2.84 x 10(-3) mm2/sec for the medulla in the normal kidneys. The ADC values in both the cortex and medulla in chronic renal failure (CRF) kidneys and in acute renal failure (ARF) kidneys were significantly lower than those of the normal kidneys. In renal artery stenosis kidneys, the ADC values in the cortex were significantly lower than those of the normal and the contralateral kidneys. In the cortex, ADC values were above 1.8 x 10(-3) mm2/sec in all 32 normal kidneys, ranging from 1.6 to 2.0 x 10(-3) mm2/sec in all 8 ARF kidneys, and below 1.5 x 10(-3) mm2/sec in 14 of 15 CRF kidneys. In the medulla, there was considerable overlap in the ADC values of the normal and diseased kidneys. There was a linear correlation between ADC value and sCr level in the cortex (r = 0.75) and a weak linear correlation in the medulla (r = 0.60). Our results show that diffusion-weighted MR imaging may be useful to identify renal dysfunction.

Delayed reduction of tissue water diffusion after myocardial ischemia

The apparent diffusion coefficient (ADC) of water after regional myocardial ischemia was measured in isolated, perfused rabbit hearts by using magnetic resonance imaging (MRI) techniques. After ligation of the left anterior descending coronary artery, the ADC of the nonperfused region showed a gradual but significant decreasing trend over time, whereas that of the normally perfused myocardium remained constant. Morphological analysis revealed that the ADC decrease reflected the expansion of a subregion of reduced ADC within the nonperfused myocardium. The dynamics of the diffusion change and the morphological progression of the affected tissue suggest that the ADC decrease may be linked to the onset of myocardial infarction, which is known to involve myocyte swelling. The ADC reduction provides a potentially valuable MRI tissue-contrast mechanism for noninvasively determining the viability of the ischemic myocardium and assessing the dynamics of acute myocardial infarction.

Physiologic measurements by contrast-enhanced MR imaging: expectations and limitations

Contrast-enhanced magnetic resonance imaging (MRI) offers the opportunity to quantitatively assess physiologic properties of tissue, such as perfusion, blood volume, and capillary permeability. Use of such quantitation potentially allows tissues to be characterized in terms of pathophysiology and to be monitored over time, during the course of therapeutic intervention. The degree to which such quantitation is applicable relies heavily on simplified model descriptions of the tissue space and assumptions relating the signal intensity observed to the contrast agent concentration. This article presents a perspective on the use of quantitative contrast-enhanced MRI, analysis of the accuracy of derived physiologic parameters, and recommendations for pulse sequence choice.