Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

Abstract

Renal fibrosis is a useful biomarker for diagnosis and guidance of therapeutic interventions of chronic kidney disease (CKD), a worldwide disease that affects more than 10% of the population and is one of the major causes of death. Currently, tissue biopsy is the gold standard for assessment of renal fibrosis. However, it is invasive, and prone to sampling error and observer variability, and may also result in complications. Recent advances in diagnostic imaging techniques, including magnetic resonance imaging (MRI) and ultrasonography, have shown promise for noninvasive assessment of renal fibrosis. These imaging techniques measure renal fibrosis by evaluating its impacts on the functional, mechanical, and molecular properties of the kidney, such as water mobility by diffusion MRI, tissue hypoxia by blood oxygenation level dependent MRI, renal stiffness by MR and ultrasound elastography, and macromolecule content by magnetization transfer imaging. Other MR techniques, such as T 1 /T 2 mapping and susceptibility-weighted imaging have also been explored for measuring renal fibrosis. Promising findings have been reported in both preclinical and clinical studies using these techniques. Nevertheless, limited specificity, sensitivity, and practicality in these techniques may hinder their immediate application in clinical routine. In this review, we will introduce methodologies of these techniques, outline their applications in fibrosis imaging, and discuss their limitations and pitfalls.

Multiparametric magnetic resonance imaging shows promising results to assess renal transplant dysfunction with fibrosis

“…A multiparametric MRI approach has the unique potential to identify changes in renal tissue structure, perfusion, and oxygen consumption that occur in parallel in renal fibrosis. 9,10 Previous validation studies showed the association of MRI parameters with renal allograft dysfunction and histopathology, 4,6,7,[9][10][11] with few studies focusing on comparisons of diagnostic performance among techniques 7,12 or the prediction of allograft outcome. Our preliminary study identified cortical ADC and T 1 as the parameters with the best diagnostic performance for chronic allograft dysfunction, association to histopathology, renal function decline, and graft survival.…”

“…We did not include emerging MRI modalities with utility in renal fibrosis, such as magnetization transfer imaging (MTR) or MR elastography. 10 MR elastography data were acquired, and detailed analysis will be presented in a separate paper.…”

Renal fibrosis detected by diffusion-weighted magnetic resonance imaging remains unchanged despite treatment in subjects with renovascular disease

“…Contrarily, renal revascularization seems to be effective in selective cohorts of patients with RVD, such as those with low levels of albuminuria 13 . Renal fibrosis is also considered to be an important biomarker, determinant of renal outcomes, and a therapeutic target in CKD 9 , which can predict outcomes in renal transplant recipients and native kidney disease.…”

“…In addition, the b-values were collected during separate acquisitions, which may lead to some motion or misregistration artifacts. Newer DWI methods allow for acquisition of multiple b-values during a single acquisition period 9 . However, we excluded most b-values less than 300 s/mm 2 to minimize the effects of renal perfusion on ADC.…”

“…Apparent diffusion coefficient (ADC) is a quantitative index derived from DWI by fitting diffusion-weighted images to the respective MR signal using a mono-exponential decay model 8 . ADC is simple to implement and is achievable by as few as two different sets of diffusion-weighted images in renal pathological conditions 9 . Low ADC values, reflecting impediment to water diffusion, are considered to indicate changes in microstructure, such as tubular atrophy or interstitial fibrosis 8 .…”