Detection of renal allograft fibrosis with MRI: arterial spin labeling outperforms reduced field-of-view IVIM.

OBJECTIVE: To compare the value of reduced field-of-view (FOV) intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) and arterial spin labeling (ASL) for assessing renal allograft fibrosis and predicting long-term dysfunction. METHODS: This prospective study included 175 renal transplant recipients undergoing reduced FOV IVIM DWI, ASL, and biopsies. Renal allograft fibrosis was categorized into ci0, ci1, ci2, and ci3 fibrosis according to biopsy results. A total of 83 participants followed for a median of 39 (IQR, 21-42) months were dichotomized into stable and impaired allograft function groups based on follow-up estimated glomerular filtration rate. Total apparent diffusion coefficient (ADCT), pure diffusion ADC, pseudo-perfusion ADC, perfusion fraction f from IVIM DWI, and renal blood flow (RBF) from ASL were calculated and compared. The area under the receiver operating characteristic curve (AUC) was calculated to assess the diagnostic and predictive performances. RESULTS: RBF was different in ci0 vs ci1 (147.9 ± 46.3 vs 126.0 ± 49.4 ml/min/100 g, p = .02) and ci2 vs ci3 (92.9 ± 46.9 vs 70.8 ± 37.8 ml/min/100 g, p = .03). RBF in the stable group was higher than that in the impaired group (144.73 ± 49.33 vs 102.19 ± 47.58 ml/min/100 g, p < .001). AUCs in distinguishing renal allograft fibrosis and predicting long-term allograft dysfunction for RBF were higher than cortical ADCT (ci0 vs ci1-3, 0.76 vs 0.59, p < .001; ci0-1 vs ci2-3, 0.79 vs 0.68, p = .01; ci0-2 vs ci3, 0.79 vs 0.68, p = .01; 0.76 vs 0.60, p = .04, respectively). CONCLUSION: Compared to reduced FOV IVIM DWI, ASL was a more promising technique for noninvasively distinguishing renal allograft fibrosis degree and predicting long-term allograft dysfunction. KEY POINTS: • Compared to total ADC from rFOV IVIM DWI, RBF from ASL can distinguish no fibrosis (ci0) vs mild fibrosis (ci1) (p = .02) and moderate fibrosis (ci2) vs severe fibrosis (ci3) (p = .04). • RBF had superior performance than diffusion parameters in discriminating fibrosis (no fibrosis [ci0] vs fibrosis [ci1-3], mild fibrosis [ci0-1] vs moderate to severe fibrosis [ci2-3], non-severe [ci0-2] vs severe [ci3] fibrosis; AUC = 0.76 vs 0.59, p < .001; 0.79 vs 0.68, p = .01; 0.79 vs 0.68, p = .01). • Compared to reduced FOV IVIM DWI, ASL was a more promising technique for noninvasively predicting long-term allograft dysfunction (AUC = 0.76 vs 0.60, p = .04).

Non-contrast-enhanced magnetic resonance angiography: a reliable clinical tool for evaluating transplant renal artery stenosis.

PURPOSE: To evaluate image quality of non-contrast-enhanced magnetic resonance angiography (MRA) and compare transplant renal artery stenosis (TRAS) seen by non-contrast-enhanced MRA with digital subtraction angiography (DSA) as the gold standard. MATERIALS AND METHODS: 330 patients receiving 369 non-contrast-enhanced MRA examinations from July 2014 to June 2017 were included. Thirty patients received at least two MRA examinations. Image quality was independently assessed by two radiologists. Inter-observer agreement was analyzed. Transplant renal artery anatomy and complications were evaluated and compared with DSA. If possible, accuracy was calculated on a per-artery basis. RESULTS: Good or excellent image quality was found in 95.4 % (352/369) of examinations with good inter-observer agreement (K=0.760). Twenty-two patients with DSA had 28 non-contrast-enhanced MRA examinations within a 2-month period. Of these, 19 patients had TRAS, two patients had pseudoaneurysms, and one patient had a normal transplant renal artery but an occluded external iliac artery. Non-contrast-enhanced MRA correctly detected 19 TRAS and nine normal arteries, giving 96.6 % accuracy on a per-artery basis. CONCLUSIONS: Non-contrast-enhanced MRA demonstrates a good depiction of the transplanted renal artery and shows good correlation with DSA in cases where there was TRAS. KEY POINTS: • Good or excellent image quality was found in 95.4 % of examinations. • Non-contrast-enhanced MRA can clearly map transplant renal artery anatomy. • Non-contrast-enhanced MRA is a reliable tool to detect TRAS.

Multiparametric Functional Magnetic Resonance Imaging for Evaluating Renal Allograft Injury.

Kidney transplantation is the treatment of choice for patients with end-stage renal disease, as it extends survival and increases quality of life in these patients. However, chronic allograft injury continues to be a major problem, and leads to eventual graft loss. Early detection of allograft injury is essential for guiding appropriate intervention to delay or prevent irreversible damage. Several advanced MRI techniques can offer some important information regarding functional changes such as perfusion, diffusion, structural complexity, as well as oxygenation and fibrosis. This review highlights the potential of multiparametric MRI for noninvasive and comprehensive assessment of renal allograft injury.