Functional Evaluation of Transplanted Kidneys with Reduced Field-of-View Diffusion-Weighted Imaging at 3T

Objective: To determine the feasibility of reduced field-of-view diffusion-weighted imaging (rFOV DWI) with multi-b values to detect functional variability in transplanted kidneys. Materials and Methods: Using a 3T MRI scanner, multi-b rFOV DWI of transplanted kidney or native kidney was performed in 40 renal transplantation recipients and 18 healthy volunteers. The patients were stratified, according to an estimated glomerular filtration rate (eGFR): Group 1, $eGFR{\geq}60mL/min/1.73m^2$ ; Group 2, $eGFR{\geq}30mL/min/1.73m^2$ and < $60 mL/min/1.73m^2$; Group 3, eGFR < $30mL/min/1.73m^2$. Total apparent diffusion coefficient ($ADC_T$), perfusion-free ADC ($ADC_D$) and perfusion fraction ($F_P$) of kidneys were calculated and compared among the four groups. Correlations between the imaging results and eGFR were assessed. Results: All volunteers had $eGFR{\geq}60mL/min/1.73m^2$, while 16, 16, and 8 patients were included in Groups 1, 2, and 3, respectively. In the renal cortex, $ADC_T$ was higher in Group 1 ($[1.65{\pm}0.13]{\times}10^{-3}mm^2/s$) than Group 3 ($[1.44{\pm}0.11]{\times}10^{-3}mm^2/s$) (p < 0.05), and the inter-group differences of FP values were significant (all p < 0.05) ($0.330{\pm}0.024$, $0.309{\pm}0.019$, $0.278{\pm}0.033$, and $0.250{\pm}0.028$ for control group, Groups 1, 2, and 3, respectively). Renal cortical $ADC_T$, $ADC_D$, $F_P$, and renal medullary $ADC_T$ and $F_P$ correlated positively with eGFR (r = 0.596, 0.403, 0.711, 0.341, and 0.323, respectively; all p < 0.05). When using 0.278 as the cutoff value, renal cortical $F_P$ had a sensitivity of 97.1% and a specificity of 66.7% for predicting decreased renal function. Conclusion: Multi-b rFOV DWI presents transplanted kidneys with high resolution, which is a promising functional tool for non-invasively monitoring function of transplanted kidneys.