Intravoxel Incoherent Motion-Diffusion-Weighted MRI for Investigation of Delayed Graft Function Immediately after Kidney Transplantation

Abstract

Purpose: A non-invasive way of assessing post-transplant renal graft function has been needed. This study aimed to assess the micro-structural and micro-functional status of graft kidneys by using intravoxel incoherent motion- (IVIM-) diffusion-weighted imaging (DWI) to investigate delayed graft function (DGF) immediately after transplantation.

Method: A prospective study was conducted on 37 patients, 14 with early graft function (EGF) and 23 with DGF (9 with complication, 14 without) who underwent IVIM-DWI, most often within 1-7 days after kidney transplantation. A total of 37 cases were collected and all the participants have been well-informed and signed their consents. In addition, the study conducted in this paper was approved by the Ethics Committee of Clinical Research, Taichung Veterans General Hospital (IRB number: CE14065). Using biexponential analysis of slow diffusion coefficient (D _slow), fast diffusion coefficient (D _fast), and perfusion fraction was performed. The apparent diffusion coefficient (ADC) was calculated by use of a monoexponential model. All parameters were measured from three different regions-of-interest (ROI), covering the entire renal parenchyma, cortex, and medulla.

Results: D _slow, perfusion fraction, and ADC were significantly higher in patients with EGF than DGF (all p values values <0.001). Especially, ADC measured from ROI covering the entire kidney parenchyma had the best cut-off value (1.93μm²/msec) with the highest area under the receiver operating characteristic curve (AUC 0.943) in differentiating EGF from DGF. For analysis of pair-wise differences, only the perfusion fraction values, measured from the ROI covering the renal cortex, were significantly higher in 14 DGF patients with no complications than in the 9 DGF patients with complications, with the best cut-off value of 12.3% and the AUC of 0.844.

Conclusion: Noninvasive IVIM-DWI reliably differentiates DGF from EGF after kidney transplantation, and it may aid in identifying posttransplant complications and indications for renal biopsy.

Figure 1

Morphological images of allograft kidneys from two subjects with early graft function (EGF) and delayed graft function (DGF). On the left, top and bottom are long-axis coronal fast-spin-echo T1WIs (TR/TE 500/9 ms). The images show distinct corticomedullary differentiation (CMD) in a patient with EGF (a) and loss of CMD in a patient with DGF (b).On the right, top and bottom, in the same two patients, no CMD was noted in fast-spin-echo T2WIs (TR/TE 3000/80 ms).

Figure 2

The long-axis coronal images of intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) in two allograft kidneys with early graft function (b = 0, 300 and 800 s/mm², followed by D_slow, D_fast, f, and ADC). Typically, in IVIM-DWI images, signal intensities are relatively homogeneous within the graft kidney (a), as seen in a 38-year-old male subject shown in the top row. The 2 lower rows show different slices from a 53-year-old female subject (b). Note that wedge-shaped high signal intensities on the IVIM-DWI images and multifocal defects on D_slow, f, and ADC maps.

Figure 3

Receiver operating characteristic (ROC) curves analysis for the relationship in the different IVIM parameters of renal parenchyma, renal cortex, and renal medulla. D_slow: slow diffusion coefficient; f: perfusion fraction; ADC: apparent diffusion coefficient.