Is there no future for renal BOLD-MRI?

Abstract

To the Editor: We read with interest the recent article by Michaely et al. in which it was stated that renal blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) does not reflect renal function in chronic kidney disease (CKD), a conclusion that is in direct contrast to our recent results. We strongly support the statement from the same issue that renal tissue oxygenation appears to be dependent on CKD severity as well as on the etiology of the underlying kidney disease. The causes of chronic renal hypoxia are remarkably multifactorial, and while we have verified a relationship between BOLD-MRI T2* values and estimated glomerular filtration rates in nondiabetic nephropathy, no association has been shown in cases of diabetic nephropathy. Thus, etiological diversity in CKD might have a far greater, and more pernicious, influence on BOLD-MRI results than thought by Michaely et al. As the kidney is surrounded by adipose tissue, removal of the out-of-phase subtraction effect caused by this tissue is vital to minimizing fluctuations in T2* values. We, therefore, used in-phase echo time (TE) of the longest possible duration to limit the T2* errors and provide more accurate data, while balancing the signal-to-noise ratio. Michaely et al. used an unusually short TE of just 40ms. We, and other similarly focused groups, understand the limitations of this novel modality and hope that the article does not discourage the application of BOLD-MRI to CKD assessment.