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Functional Evaluation of Transplanted Kidneys with Diffusion-weighted and BOLD MR Imaging: Initial Experience¹

¹ From the Departments of Radiology, Neuroradiology, and Nuclear Medicine (H.C.T., S.S., P. Vock); Clinical Research (D.Z., C.B., P. Vermathen); and Nephrology and Hypertension (U.E., L.H., F.J.F.), University Hospital of Bern, Inselspital, Freiburgstrasse 10, CH-3010 Bern, Switzerland; and Department of Radiology, University Hospitals Leuven, Leuven, Belgium (F.D.K.). Received January 17, 2006; revision requested March 22; revision received April 8; final version accepted June 8. H.C.T. supported by a research grant from the Swiss National Foundation, National Center of Competence in Research, "Computer-aided and image-guided medical interventions", NCCR CO-ME. F.J.F. supported by grant no. 31-102153 from the Swiss National Foundation for Scientific Research. P. Vermathen and H.C.T. supported by grant no. 320000-111959/1 from the Swiss National Foundation for Scientific Research. Address correspondence to H.C.T. (e-mail: Harriet.Thoeny{at}insel.ch).

View larger version (60K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Parameter maps generated from DW MR images of a transplanted kidney. A, Native DW image obtained with a b value of 0 sec/mm2 corresponding to a measurement obtained without diffusion-sensitizing gradients, B, ADCtot calculated with Equation (1), C, ADCD calculated with Equation (2) and reflecting mainly pure diffusion, and, D, perfusion fraction calculated with Equation (2). Relatively homogeneous signal intensity is depicted in the ADC maps and, to a lesser extent, in the perfusion fraction map.

View larger version (10K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Graphs show correlation between ADCtot in cortex and medulla of transplanted and native kidneys. Correlation between ADC values was significant (P < .001) in the cortex and medulla of transplanted (r = 0.83) and native (r = 0.95) kidneys.

View larger version (18K): [in this window] [in a new window] [Download PPT slide]   Figure 3: Graphs show medullary and cortical ADCtot in all patients and volunteers. In transplanted kidneys, no significant difference between cortical and medullary ADCtot is observed; however, in native kidneys, ADCtot is higher in the cortex than in the medulla (P < .0001). The mean ADCtot of the cortex is slightly lower in transplanted kidneys than in native kidneys.

View larger version (11K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Graphs show correlation of perfusion fraction (FP), ADCD, and R2* between the first and second measurements (mean interval, 65 days) in the cortex and medulla of seven patients with renal transplants. Most values are close to the identity line. Circled points indicate data were obtained in the patient with hemoglobinopathy.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 5: A, BOLD MR image (multiple gradient-recalled-echo sequence with an echo time of 6 msec), and, B, corresponding calculated R2* image of a transplanted kidney. The cortex and medulla are differentiated.

View larger version (13K): [in this window] [in a new window] [Download PPT slide]   Figure 6: Graph of medullary R2* versus ADCtot derived from measurements obtained in renal allografts shows a significant negative correlation (r = –0.66, P < .01). Each symbol represents a patient ( = patient 1, = patient 2, = patient 3, = patient 4, gray diamond = patient 5, gray square = patient 6, gray triangle = patient 7, gray circle = patient 8, = patient 9, = patient 10, = patient 11, = patient 12, + = patient 13, x = patient 14, * = patient 15). In some patients measurements were obtained twice. For the regression analysis (dashed line), the mean value of repeated measurements was considered.

View larger version (15K): [in this window] [in a new window] [Download PPT slide]   Figure 7: Graphs show relationship between serum creatinine (s-Crea) concentrations and functional MR parameters in transplanted kidneys (tp) and native kidneys (nk). With increasing serum creatinine concentrations, the cortical perfusion fraction (FP cortex) (r = –0.82, P < .01) and corticomedullary differences in ADCtot (ADCtot (cortex-medulla)) (r = –0.78, P < .01) declined in transplanted kidneys, indicating that increasing serum creatinine concentrations are accompanied by reduced cortical diffusion and microperfusion. For regression analyses, only transplanted kidneys were considered. The circled point indicates datum obtained in the patient with hemoglobinopathy.