Diffusion tensor imaging in renal artery stenosis: a preliminary report

Abstract

Objective: To investigate the diffusion properties in the kidneys affected by renal artery stenosis (RAS) using diffusion tensor imaging (DTI).

Methods: In this prospective study, 35 patients with RAS and 15 patients without renal abnormalities were enrolled and examined using DTI. Cortical and medullary regions of interest (ROIs) were located to obtain the corresponding values of the apparent diffusion coefficient (ADC) and fractional anisotropy (FA). The cortical and medullary ADC and FA were compared in the kidney affected by variable degrees of stenosis (RAS 50-75% and >75%) vs controls, using the one-way ANOVA and Student's t-test. The Spearman correlation test was used to correlate the mean ADC and FA values in the cortex and medulla with the estimate glomerular filtration rate (eGFR).

Results: For the controls, the ADC value was significantly (p = 0.03) higher in the cortex than in the medulla; the FA value was significantly (p = 0.001) higher in the medulla than in the cortex. Compared with the controls, a significant reduction in the cortical ADC was present with a RAS of 50-75% and >75% (p = 0.001 and 0.041, respectively); a significant reduction in the medullary FA was verified only for RAS >75% (p = 0.023). The Spearman correlation test did not show a statistically significant correlation between the cortical and medullary ADC and FA, and the eGFR.

Conclusion: The alterations of the diffusional parameters caused by RAS can be detected by DTI and could be useful in the diagnostic evaluation of these patients.

Advances in knowledge: 1. Magnetic resonance DTI could provide useful information about renal involvement in RAS.2. Magnetic resonance DTI allows non-invasive repeatable evaluation of the renal parenchyma, without contrast media.

Figure 1.

Diffusion tensor imaging analysis in a control group patient (eGFR of 105 mL/min). Circular ROIs were defined in the cortex and medulla on the ADC (A) and FA (B) maps of the right kidney, by using the T2 sequence for the correct placement (C): the corresponding values of the ADC were 2.54 and 2.23 × 10⁻³ mm²/s and the corresponding values of the FA were 0.26 and 0.40. ADC, apparent diffusion coefficient; eGFR, estimated glomerular filtration rate; FA, fractional anisotropy; ROIs, regions of interest.

Figure 2.

A patient of subgroup A with an eGFR of 56 mL/min. (A) The contrast-enhanced Magnetic Resonance Angiography shows left RAS of 60% (white arrow). DTI analysis of the right kidney (not shown) did not find alterations of the diffusion parameters. On the left side, the ADC map (B) shows a significant reduction in the cortical ADC (2.29 × 10⁻³ mm²/s) as compared to the reference standard values; the medullary ADC was 2.46 × 10⁻³ mm²/s. The FA map (C) did not show significant alteration in the cortical and medullary FA (0.28 and 0.33, respectively). ADC, apparent diffusion coefficient; DTI, diffusion tensor imaging; eGFR, estimated glomerular filtration rate; FA, fractional anisotropy; RAS, renal artery stenosis; ROIs, regions of interest.

Figure 3.

A patient of subgroup B with an eGFR of 40 mL/min. (A) The contrast-enhanced Magnetic Resonance Angiography shows bilateral RAS > 80% (white arrows). The DTI analysis shows a bilaterally significant reduction in the cortical ADC and the medullary FA calculated on the ADC and FA maps. Here, the DTI analysis of the right kidney is shown: on the ADC map (B) the ADC values were 2.24 (cortex) and 2.30 (medulla) x 10⁻³mm²/s; on the FA map (C), the FA values were 0.36 (cortex) and 0.20 (medulla). ADC, apparent diffusion coefficient; DTI, diffusion tensor imaging; eGFR, estimated glomerular filtration rate; FA, fractional anisotropy; RAS, renal artery stenosis.