Objective: To evaluate the feasibility of in-vivo quantitative susceptibility mapping (QSM) of the human kidney. Methods: An axial single-breath-hold 3D multi-echo sequence (acquisition time 33 s) was completed on a 3 T-MRI-scanner (Magnetom Prisma, Siemens Healthineers, Erlangen, Germany) in 19 healthy volunteers. Graph-cut-based unwrapping combined with the T₂*-IDEAL approach was performed to remove the chemical shift of fat and to quantify QSM of the upper abdomen. Mean susceptibility values of the entire, renal cortex and medulla in both kidneys and the liver were determined and compared. Five subjects were measured twice to examine the reproducibility. One patient with severe renal fibrosis was included in the study to evaluate the potential clinical relevance of QSM. Results: QSM was successful in 17 volunteers and the patient with renal fibrosis. Anatomical structures in the abdomen were clearly distinguishable by QSM and the susceptibility values obtained in the liver were comparable to those found in the literature. The results showed a good reproducibility. Besides, the mean renal QSM values obtained in healthy volunteers (0.04 ± 0.07 ppm for the right and − 0.06 ± 0.19 ppm for the left kidney) were substantially higher than that measured in the investigated fibrotic kidney (− 0.43 ± − 0.02 ppm). Conclusion: QSM of the human kidney could be a promising approach for the assessment of information about microscopic renal tissue structure. Therefore, it might further improve functional renal MR imaging.

Contrast-induced nephropathy (CIN) resembles an important complication of radiographic contrast medium (XCM) displayed by a rise in creatinine levels 48–72 h after XCM administration. The purpose of the current study was to evaluate microstructural renal changes due to CIN in high-risk patients by diffusion weighted (DWI) and diffusion tensor imaging (DTI). Fifteen patients (five CIN and ten non-CIN) scheduled for cardiological intervention were included in the study. All patients were investigated pre- and post-intervention on a clinical 3T scanner. After anatomical imaging, renal DWI was performed by a paracoronal echo-planar-imaging sequence. Renal clinical routine serum parameters and advanced urinary injury markers were determined to monitor renal function. We observed a drop in cortical and medullar apparent diffusion coefficient (ADC) and fractional anisotropy (FA) before and after XCM administration in the CIN group. In contrast, the non-CIN group differed only in medullary ADC. The decrease of ADC and FA was apparent even before serum parameters of the kidney changed. In conclusion, DWI/DTI may be a useful tool for monitoring high-risk CIN patients as part of multi-modality based clinical protocol. Further studies, including advanced analysis of the diffusion signal, may improve the identification of patients at risk for CIN.

Purpose: To evaluate partial volume correction (PVC) techniques for sodium MRI of the Achilles tendon in situ and in vivo. Methods: Five PVC methods were evaluated including a volume ratio of the proton and sodium segmentations (PSSR), a modified least trimmed square (3D‐mLTS) linear regression, a geometric transfer matrix (GTM) approach, a single target correction (STC), and a novel estimated single target correction (eSTC). Their performance was tested using simulated data and 3 T MR data of two volunteers' Achilles tendons acquired at different resolutions: 1.5, 2.0, 3.0, and 4.5 mm ³ . Since there was no in vivo ground truth, the highest‐resolution apparent tissue sodium contents (aTSC) were used. Results: In the simulation, all PVC methods reduced the difference between the actual and calculated concentrations and were 11.69 ± 6.17 mM without PVC, 4.90 ± 5.40 mM with the PSSR, 4.86 ± 5.19 mM with the mLTS, 1.72 ± 4.13 mM with the GTM, 0.36 ± 1.77 mM with STC and 0.26 ± 1.63 mM with the eSTC. In vivo, the difference in aTSCs between the lower and the highest resolution decreased with all PVCs ranging from 3.6 to 38.8 mM without PVC, 2.8–20.4 mM with PSSR, 4.5–25.9 mM with mLTS, 0.9–7.8 mM with GTM, 0.1–23.8 mM with STC, and 0.7–7.7 mM with eSTC. Conclusion: PVC generally improved the accuracy of aTSC calculations. The newly introduced eSTC produced the most accurate results for the Achilles tendon.

Purpose: ²³Na MRI is a functional imaging technique that facilitates measurements of the renal corticomedullary sodium gradient (CMSG). The CMSG can be determined by a region of interest (ROI) in the renal parenchyma along the corticomedullary axis (Line method) or by dividing the renal parenchyma into concentric layers, using the twelve‐layer concentric objects (TLCO) method. The aim of this study was to investigate the differences, strengths, and weaknesses in determining the CMSG using these methods.Methods: Ten healthy volunteers were examined on a 3 T MRI‐system. ²³Na images were acquired using a double‐tuned ²³Na/¹H surface coil and a golden angle (GA) density‐adapted 3D radial (DA‐3D‐RAD) sequence. The CMSG was determined with the Line and TLCO methods. Intra‐ and inter‐reader analyses were performed by two radiologists.Results: The evaluated CMSG by the two methods does not differ statistically significantly. Compared to the Line method, the TLCO method provides improved results in terms of reliability, precision, reproducibility, and concordance in intra‐ and inter‐reader analyses. A CMSG of (6.7 ± 2.6) mM/mm was determined using the TLCO method in the segmentation process with the lowest standard deviation.Conclusion: The TLCO method shows superior performance in determining the CMSG compared to the Line method. Accordingly, the use of the TLCO method is recommended for future renal CMSG studies.