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MR Elastography, Diffusion Imaging and BOLD-Imaging for the Detection of Early Changes of Renal Stiffness in Patients with Lupus Nephritis1Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, 2Rheumatology, Charité - Universitätsmedizin Berlin, Berlin, Germany, 3Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany
Synopsis
Renal stiffness was investigated using MR elastography (MRE) and tomoelastography data processing in healthy controls and patients with lupus nephritis (LN). Our results showed that patients had lower renal stiffness than controls, while subregions such as medulla and inner cortex allowed to differentiate early chronic kidney disease (CKD=1) from progressed disease stages based on MRE values. The observed reduction in renal stiffness is associated with decreased ADC-values and increased T2*-values due to LN with CKD≥2. The decreased stiffness due to CKD=1 was reflected by T2*-values but not by ADC-values. MRE provided the highest diagnostic accuracy for detection of LN.
Purpose:
To investigate renal stiffness in patients with lupus nephritis (LN) using multifrequency magnetic resonance elastography (MRE) and comparison to diffusion-weighted imaging (DWI) and blood oxygen level-dependent (BOLD) imaging, taking into account regional variation.Background:
Renal manifestation (LN) in systemic lupus erythematosus (SLE) is the strongest predictor for morbidity and mortality. Pathogenic antibodies against renal tissue were identified being the primary cause of damage in LN, followed by a local inflammation, which can lead to end-stage kidney disease. Histological damage occurs often clinically silent. Therefore, the early identification of a renal manifestation of SLE is of great importance.Methods:
In this prospective study 25 patients with LN (subgrouped, based on chronic kidney disease (CKD) stage: normal (LN-nRF, CKD 1) and compromised renal function (LN-cRF, ≥CKD 2) and 16 age- and sex-matched healthy volunteers (CTR) were examined by multifrequency MRE (1) and tomoelastography data processing (2) at four vibration frequencies from 40–70 Hz, and further by DWI and BOLD-imaging. All experiments were conducted on a 1.5-T MRI scanner equipped with a 12-channel phased array surface coil. Shear wave speed (SWS) was given in m/s. DWI and BOLD-imaging were performed with a spin echo-echo planar imaging (SE-EPI) sequence and multiple gradient-recalled-echo (mGRE) sequence, respectively. For DWI, 11 slices with 2.7×2.7×5 mm3 resolution were recorded with 2 averages and b values of 0 and 500 s/mm2 in 17 seconds. For BOLD MRI, 3 slices with 2.8×2.8×5 mm3 resolution were recorded with 8 echo times (2.38-37.72 ms) in 20 seconds. All imaging protocols were executed in a paracoronal slice orientation covering both kidneys. Regions of interest (ROI) were placed in the inner cortex (CoI), outer cortex (CoO) and medulla (ME). The diagnostic accuracy was calculated for MRE, DWI and BOLD.Results:
Figure 1 shows representative maps of MRE, DWI and BOLD imaging. The stiffness maps demonstrate that kidneys of LN are softer than those of CTR. Compared to CTR (SWS: CoI, 2.92±0.25 m/s; ME, 2.41±0.13 m/s), an early decrease of SWS due to LN-nRF was observed in ME (2.20±0.21 m/s, p = 0.007) (fig. 2A), accompanied by an increase in T2* (CTR, 61.5±6.0 ms; LN, 69.2±7.2 ms, p = 0.046) (fig. 2B). In LN-cRF a further decline in SWS in ME and additionally in CoI (2.84±0.4 m/s, p = 0.019) was observed (fig. 2A). DWI was only sensitive to changes in ME in LN-cRF (CTR, 170.3±11.8 mm2/s; LN, 148.5±20.1 mm2/s, p = 0.006) (fig. 2C). MRE showed the highest sensitivity to detect LN-nRF (AUROC: MRE, 0.81; DWI, 0.63; BOLD, 0.76). No differences were found in CoO.Discussion:
In our study cohort, mainly consisting of well to moderate functioning renal filtration, ME stiffness was identified as the decisive factor for discriminating CKD stage 1 from CTR. Disease progression is characterized by further CoI-stiffness reduction which is associated with impaired renal function (glomerular filtration rate < 90 mL/min/1.73m2). This observation agrees with a previous MRE study on patients with CKD (3). We hypothesize that a reduction in renal perfusion could mask an increase in fibrosis, resulting in an overall decrease in SWS. Our hypothesis is in line with previous findings showing the influence of renal perfusion to SWS (4). The observed reduction in renal stiffness is associated with decreased ADC-values and increased T2*-values due to LN with CKD stage ≥2. The decreased stiffness due to CKD stage 1 was reflected by T2*-values but not by ADC-values. MRE provided the highest diagnostic accuracy for detection of LN.Conclusion:
MRE is sensitive to renal tissue changes involved in the progression of lupus nephritis and allows the early detection of those structural changes at stages when renal function is still preserved. MRE has a better diagnostic accuracy for the detection of lupus nephritis than DWI and BOLD.Acknowledgements
The author would like to thank the Deutsche Forschungsgemeinschaft (DFG) for their financial support (Funding Nr: GU 1726/1-1).References
1. Muthupillai R, Ehman RL. Magnetic resonance elastography. Nat Med 1996;2(5):601-603.
2. Tzschatzsch H, Guo J, Dittmann F, Hirsch S, Barnhill E, Johrens K, Braun J, Sack I. Tomoelastography by multifrequency wave number recovery from time-harmonic propagating shear waves. Med Image Anal 2016;30:1-10.
3. Marticorena Garcia SR, Fischer T, Durr M, Gultekin E, Braun J, Sack I, Guo J. Multifrequency Magnetic Resonance Elastography for the Assessment of Renal Allograft Function. Invest Radiol 2016;51(9):591-595.
4. Marticorena Garcia SR, Grossmann M, Lang ST, Tzschatzsch H, Dittmann F, Hamm B, Braun J, Guo J, Sack I. Tomoelastography of the native kidney: Regional variation and physiological effects on in vivo renal stiffness. Magn Reson Med 2017.
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