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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.

Objective To establish and optimize a stable 3 Tesla (T) glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging protocol for assessing the articular cartilage of the tibiotalar joint in healthy volunteers and patients after a sustained injury to the ankle. Methods Using Bloch–McConnell simulations, we optimized the sequence protocol for a 3 T MRI scanner for maximum gagCEST effect size within a clinically feasible time frame of less than 07:30 min. This protocol was then used to analyze the gagCEST effect of the articular cartilage of the tibiotalar joint of 17 healthy volunteers and five patients with osteochondral lesions of the talus following ankle trauma. Reproducibility was tested with the intraclass correlation coefficient. Results The mean magnetization transfer ratio asymmetry (MTRasym), i.e., the gagCEST effect size, was significantly lower in patients than in healthy volunteers (0.34 ± 1.9% vs. 1.49 ± 0.11%; p < 0.001 [linear mixed model]). Intra- and inter-rater reproducibility was excellent with an average measure intraclass correlation coefficient (ICC) of 0.97 and a single measure ICC of 0.91 (p < 0.01). Discussion In this feasibility study, pre-morphological tibiotalar joint cartilage damage was quantitatively assessable on the basis of the optimized 3 T gagCEST imaging protocol that allowed stable quantification gagCEST effect sizes across a wide range of health and disease in clinically feasible acquisition times.

Purpose:To characterize the proton exchange in aqueous urea solutions using a modified version of the WEX II filter at high magnetic field, and to assess the feasibility of performing quantitative urea CEST MRI on a 3T clinical MR system. Methods: In order to study the dependence of the exchange-rate constant k sw of urea as a function of pH and T, the WEX-spectra were acquired at 600 MHz from urea solutions in a pH range from 6.4 to 8.0 and a temperature range from T = 22 • C to 37 • C. The CEST experiments were performed on a 3T MRI scanner by applying a train of 50 Gaussian-shaped pulses, each 100-millisecond long with a spacing of 100 milliseconds, for saturation. Exchange rates of urea were calculated using the (extended) AREX metric. Results: The results showed that proton exchange in aqueous urea solutions is acid and base catalyzed with the rate constants: k a = (9.95 ± 1.1) × 10 6 l/(mol·s) and k b = (6.21 ± 0.21) × 10 6 l/(mol·s), respectively. Since the urea protons undergo a slow exchange with water protons, the CEST effect of urea can be observed efficiently at 3T. However, in neutral solutions the exchange rate of urea is minimal and cannot be estimated using the quantitative CEST approach. Conclusions: By means of the WEX-spectroscopy, the kinetic parameters of the proton exchange in urea solutions have been determined. It was also possible to estimate the exchange rates of urea in a broad range of pH values using the CEST method at a clinical scanner. K E Y W O R D SCEST, exchange rate, proton exchange, urea, urCEST, WEX