ABSTRACT
OBJECTIVES: The aim of this study was to noninvasively evaluate changes in renal stiffness, diffusion, and oxygenation in patients with chronic, advanced stage immunoglobulin A nephropathy (IgAN) by multiparametric magnetic resonance imaging using tomoelastography, diffusion-weighted imaging (DWI), and blood oxygen level-dependent (BOLD) imaging. MATERIALS AND METHODS: In this prospective study, 32 subjects (16 patients with biopsy-proven IgAN and 16 age- and sex-matched healthy controls) underwent multifrequency magnetic resonance elastography with tomoelastography postprocessing at 4 frequencies from 40 to 70 Hz to generate shear wave speed (meter per second) maps reflecting tissue stiffness. In addition, DWI and BOLD imaging were performed to determine the apparent diffusion coefficient in square millimeter per second and T2* relaxation time in milliseconds, respectively. Regions including the entire renal parenchyma of both kidneys were analyzed. Areas under the receiver operating characteristic (AUCs) curve were calculated to test diagnostic performance. Clinical parameters such as estimated glomerular filtration rate and protein-to-creatinine ratio were determined and correlated with imaging findings. RESULTS: Success rates of tomoelastography, DWI, and BOLD imaging regarding both kidneys were 100%, 91%, and 87%, respectively. Shear wave speed was decreased in IgAN (-21%, P < 0.0001), accompanied by lower apparent diffusion coefficient values (-12%, P = 0.004). BOLD imaging was not sensitive to IgAN (P = 0.12). Tomoelastography detected IgAN with higher diagnostic accuracy than DWI (area under the curve = 0.9 vs 0.8) and positively correlated with estimated glomerular filtration rate (r = 0.66, P = 0.006). CONCLUSIONS: Chronic, advanced stage IgAN is associated with renal softening and restricted water diffusion. Tomoelastography is superior to DWI and BOLD imaging in detecting IgAN.
Subject(s)
Elasticity Imaging Techniques/methods , Glomerulonephritis, IGA/diagnostic imaging , Image Interpretation, Computer-Assisted/methods , Multiparametric Magnetic Resonance Imaging/methods , Adult , Aged , Area Under Curve , Diffusion Magnetic Resonance Imaging/methods , Female , Glomerular Filtration Rate , Humans , Kidney/diagnostic imaging , Male , Middle Aged , Prospective Studies , ROC Curve , Young AdultABSTRACT
The purpose of this study was to analyze full-field-of-view maps of renal shear wave speed (SWS) measured by time-harmonic elastography (THE) in healthy volunteers in terms of reproducibility, regional variation and physiologic effects. The kidneys of 37 healthy volunteers were investigated by multifrequency THE. The complete renal parenchyma, as well as cortex and medulla, was analyzed. A subgroup was investigated to test reproducibility (n = 3). Significant differences between SWS in cortex, medulla and full parenchyma were observed (2.10 ± 0.17, 1.35 ± 0.11 and 1.71 ± 0.16 m/s, all p values < 0.001) with mean intra-volunteer standard deviations of repeated measurements of 0.04 m/s (1.6%), 0.06 m/s (4.0%) and 0.08 m/s (4.5%), respectively. No effects of kidney anatomy, age, body mass index, blood pressure and heart rate on SWS were observed. THE allows generation of full-field-of-view SWS maps of native kidneys with high reproducibility.
Subject(s)
Elasticity Imaging Techniques/methods , Image Processing, Computer-Assisted/methods , Kidney/anatomy & histology , Adult , Female , Humans , Male , Middle Aged , Prospective Studies , Reference Values , Reproducibility of Results , Young AdultABSTRACT
PURPOSE: To measure normal renal stiffness in adults, taking into account regional variation, hydration, and urinary status. METHODS: Thirty-six healthy volunteers were examined by tomoelastography based on MR elastography at four frequencies, from 40 to 70 Hz and multifrequency shear wave speed recovery. Regional wave speeds were derived for the medulla, cortex (inner cortex and outer cortex), and renal pelvis, and examined for age-related effects. Subgroups were repeatedly examined for reproducibility, amount of prior water drinking, and urinary status. Variations in renal perfusion were simulated ex vivo using a porcine kidney subjected to venous water inflow at different pressures. RESULTS: Shear wave speed (stiffness) of renal parenchyma was 2.46 ± 0.12 m/s (inner cortex: 2.91 ± 0.17 m/s; outer cortex: 2.52 ± 0.11 m/s; medulla: 2.15 ± 0.08 m/s) without side differences and a tendency toward softening with age (P = 0.028). Corresponding intraclass correlation for reproducibility coefficients were 0.78 (inner cortex: 0.80; outer cortex: 0.81; medulla: 0.80). Water drinking resulted in slightly higher values in inner cortex and lower values in medulla (both P = 0.039), which was consistent with the results in perfused specimens. A full bladder led to higher renal pelvis stiffness (P = 0.004), whereas renal parenchyma remained uninfluenced. Stiffness of the porcine renal cortex increased with venous inflow pressure, whereas medulla stiffness decreased. CONCLUSIONS: Tomoelastography provides full field of view maps of renal stiffness with highly detailed resolution and sensitivity to physiological effects related to age and fluid-solid tissue interactions. These basic data could be used to compare pathological conditions in the future. Magn Reson Med 79:2126-2134, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
