HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

No abstract

No abstract

Purpose:To investigate the possibility of using combined blood oxygen level-dependent (BOLD) imaging and diffusion-weighted imaging (DWI) to detect pathological and physiological changes in renal tissue damage of the kidney induced by chronic renal hyperfiltration. Materials and Methods:The apparent diffusion coefficient (ADC) and the T 2 * value within the inner compartments of the kidneys of 17 rats with diabetes mellitus were compared with the results obtained from a control group (N ϭ 16). The influence of dynamic changes of the renal function on the blood-oxygen saturation was evaluated by comparing the T 2 * values before and after the active reduction of tubular transport by furosemide injection.Results: All compartments of the diabetic kidney showed significantly (P Ͻ 0.05) lower T 2 *-values compared to the control group. In particular, the very low values in the outer stripe (OS) of the outer medulla (OM) (T 2 *-normal: 69.4 Ϯ 10.9 msec; T 2 *-diabetic: 51.4 Ϯ 13.9 msec) indicated either hypoxia due to hyperfiltration, or renal blood volume changes. Diffusion imaging of the same area showed significantly lower ADC values (ADC-normal: 1.45 Ϯ 0.26; ADCedema: 1.19 Ϯ 0.25 [10 -9 m 2 /s]) that correlated with pathological findings on histopathology. The injection of furosemide significantly (P Ͻ 0.05) increased T 2 * in all compartments of both populations while the ADC remained unchanged.Conclusion: BOLD-contrast imaging appears to be able to depict tissue at risk from ischemia by revealing information about the balance between tubular workload and delivery of oxygen, and thus may reflect a measure of the reserve capacity. The diffusion measurements apparently reveal complementary information. Although ADC imaging is not sensitive to the current energy metabolism, it appears toreflect the pathological changes within the tissue. Therefore, ADC measurements may be a sensitive indicator of the severity of ischemic lesions.

This study characterizes the diffusion anisotropy of the human kidney using a diffusion-weighted, single-shot echo planar imaging (EPI) sequence in order to access the full apparent diffusion tensor (ADT) within one breathhold. The fractional anisotropy (FA) of the cortex and the medulla were found to be 0.22 ؎ 0.12 and 0.39 ؎ 0.11, respectively (N ‫؍‬ 10), which emphasizes the need for rotationally invariant diffusion measurements for clinical applications. Additional limitations for clinical diffusion imaging on the kidney are the strong susceptibility variations within the abdomen that restrict the use of imaging techniques employing long echo trains, and the severe motion sensitivity that limits the available imaging time to one breath-hold. To overcome these problems an isotropic, diffusion-weighted, segmented EPI protocol that facilitates the acquisition of high-resolution diffusion-weighted images within a single breath-hold was implemented. Using this method, the apparent diffusion coefficient (ADC) of the cortex and medulla were found to be 2. 89 Index terms: diffusion; magnetic resonance imaging; kidney; EPI; fractional anisotropy WATER TRANSPORT is the predominant phenomenon throughout the kidney due to the kidney's major role in water reabsorption and concentration-dilution functions. These movements are mainly located in the tubular cells and are controlled either by active or passive mechanisms, depending on their location in the nephrons. Consequently, the measurement of the diffusion characteristics of the kidney may provide useful insights into the mechanisms of various renal diseases, including chronic renal failure, renal artery stenosis, and uretral obstruction. However, renal diffusion imaging is very challenging due to the extreme motion sensitivity of diffusion-weighted sequences, and the clinical use of this technique has been hampered by both the severe motion artifacts caused by arterial pulsations and respiratory motion. Diffusion-weighted single-shot-EPI (DW-SSEPI) (1), in conjunction with single breath-hold imaging (2-6) and peripheral pulse unit (PPU) triggering, (7) has been suggested as a possible means of overcoming these problems. However, the restriction of the diffusion experiment to a single breathhold limits the possible spatial resolution and the precision of the diffusion measurement (the number of directions for the diffusion weighting, the number of b-values, and the number of averages). As a result, most studies in the literature have measured the ADC in only one direction (2,4 -7), and hence have implicitly assumed that the diffusion characteristics of the kidney are isotropic. Hydration has been shown to increase global ADC values (3), while renal artery stenosis or ureteral obstruction decreased the values (2,3). In cases of acute or chronic renal failure, the cortical and medullary ADC values were significantly lower than in normal kidneys, and the cortical values were highly correlated with the serum creatinine levels (2).Although some studies have implied that t...

MR imaging can aid in monitoring of intravascularly administered SPIO-labeled MSCs in vivo in kidney and liver.

BOLD MRI provides noninvasive estimates of regional renal oxygen content and our study demonstrates that this technique may provide a useful tool in UUO which is associated with altered renal oxygen consumption.

Chronic kidney disease (CKD) incidence and prevalence are increasing in Western countries, due particularly to diabetes mellitus and hypertension-related nephropathies. CKD may lead to end-stage renal failure, with extensive morbidity, mortality and increasing health costs. Primary and secondary prevention requires a better knowledge of mechanisms underlying renal scarring, the development of specific therapies to slow down the progression of the disease and the development of non-invasive diagnostic tools to characterize the process. Ultrasound elastography is a new imaging technique under development that provides information about renal stiffness. Kidney elasticity measurements with ultrasound should be performed with a quantitative technique, such as Shearwave techniques. However kidney stiffness is not only related to fibrosis, as it also sensitive to mechanical and functional parameters such as anisotropy, vascularization, hydronephrosis and external pressure. This paper reviews the existing ultrasound elastography techniques. Elastography is a new tool under development for renal tissue characterization and needs further validation in clinical practice.