Three‐year follow‐up of human transplanted kidneys by diffusion‐weighted MRI and blood oxygenation level‐dependent imaging

Abstract

Purpose: To prospectively determine the 3-year stability and potential changes of functional parameters in renal allograft recipients obtained from diffusion-weighted imaging (DWI) and blood oxygenation level-dependent (BOLD) MRI. Materials and Methods:Nine renal allograft recipients underwent DWI and BOLD-MRI twice, once 7 6 3 months after transplantation, and again 32 6 2 months after the first MRI. DWI yielded an apparent diffusion coefficient (ADC) and the perfusion contribution (F P ). BOLD imaging yielded R2*, providing an estimation of renal oxygenation. Coefficients of variation between (CV b ) and within subjects (CV w ) were calculated.Results: The parameters were stable after 32 months in eight of the nine patients, who had well-functioning allografts. Mean diffusion values were very similar in the first and second scan. CV w and CV b for ADC values were less than 3.5% and 5.9%, respectively, in cortex and medulla, but were higher for F P (15%-18%). CV w and CV b of R2* were also low (medulla: CV w ¼ 10.8%, CV b ¼ 11.4%; cortex: CV w and CV b ¼ 7.2%). R2* increased significantly (P ¼ 0.035) in cortex but not in medulla, suggesting reduced cortical oxygen content. One subject with decreased glomerular filtration rate demonstrated strongly altered parameters. Conclusion:In the absence of graft dysfunction, DWI and BOLD imaging yield consistent results over 3 years in stable human renal allograft recipients.

Renal Allograft Fibrosis: Biology and Therapeutic Targets

“…From personal experience, we know that kidney stiffness is much less altered compared to the liver during fibrosis, suggesting that elastography in kidneys might not be sensitive enough for assessment of fibrosis. A third approach suggested to measure renal fibrosis is diffusion-weighted MRI (427)(428)(429)(430)(431)(432)(433)(434)(435)(436)(437). Presently it is unclear whether any of these modalities specifically reflects renal fibrosis.…”

Blood oxygenation level-dependent MRI for assessment of renal oxygenation

“…81 Similarly, medullary oxygenation was increased in renal allografts (n=9) on average 7 months after renal transplantation compared with native kidneys. 82 When BOLD MRI was repeated at 32 months postoperatively, cortical, but not medullary oxygenation declined as compared with the first scan. 82 These data on the state of renal oxygenation in normally functioning renal allografts are inconsistent and do not provide clear insights.…”

“…82 When BOLD MRI was repeated at 32 months postoperatively, cortical, but not medullary oxygenation declined as compared with the first scan. 82 These data on the state of renal oxygenation in normally functioning renal allografts are inconsistent and do not provide clear insights. Results may have been influenced by the time of study and calcineurin inhibitor dosing.…”

Diffusion tensor imaging of the human kidney: Does image registration permit scanning without respiratory triggering?

“…[4][5][6] Its derived quantitative parameter, the apparent diffusion coefficient (ADC) parameter, documents changes like fibrosis or edema. Moreover, DWI may also provide information on concurrent micro-circulation, including capillary perfusion, quantified with the "fraction of the perfusion" (F P ).…”