Diffusion-weighted MR imaging of kidneys in renal artery stenosis

doi:10.1016/j.ejrad.2007.03.007

European Journal of Radiology

Volume 65, Issue 1, January 2008, Pages 148-153

https://doi.org/10.1016/j.ejrad.2007.03.007 Get rights and content

Abstract

Objective

The purpose of our study was to evaluate perfusion and diffusion of kidneys in renal artery stenosis (RAS) and any correlation between stenosis and ADC values and whether this imaging modality may be a noninvasive complementary assessment technique to MR angiography before interventional procedures.

Materials and methods

Twenty consecutive patients suspected of having renal artery stenosis were evaluated with renal MR angiography to exclude stenosis and were then included in the study. Transverse DW multisection echo-planar MR imaging was performed. In the transverse ADC map, rectangular regions of interest were placed in the cortex on 3 parts (upper, middle, and lower poles) in each kidney. ADCs of the kidneys were calculated separately for the low, average, and high b-values to enable differentiation of the relative influence of the perfusion fraction and true diffusion. The ADC values of 39 kidneys (13 with renal artery stenosis and 26 normal renal arteries) were compared, and the relationship between stenosis degree and ADC values was calculated.

Results

RAS was detected in 11 of 20 (55%) patients with MRA. Thirteen of 39 kidneys demonstrated RAS, and 26 were normal. The ADC_low (1.9 ± 0.2 versus 2.1 ± 0.2; P = .020), ADC_average (1.7 ± 0.2 versus 1.9 ± 0.1; P = .006), and ADC_high (1.8 ± 0.2 versus 2.0 ± 0.1; P = .012) values were significantly lower in patients with kidneys with arterial stenosis than that in patients with kidneys with normal arteries. Statistical analysis revealed that stenosis degree correlated strongly with ADC_low (r = −.819; P = .001), ADC_average (r = −.754; P = .003), and ADC_high (r = −.788; P = .001). The ADC_low, ADC_average, and ADC_high values were significantly lower in patients with kidneys with arterial stenosis than that in patients with kidneys with normal arteries.

Conclusion

We think that DW MR imaging of kidneys with RAS can help determine the functional status of a renal artery stenosis.

Introduction

The widespread availability of MRA has led to its increasing use in the evaluation of patients with suspected renal artery stenosis. One of the limitations of renal MRA, as currently performed, was its tendency to overestimate the degree of stenosis [1].

Diffusion-weighted (DW) magnetic resonance (MR) imaging is used to show molecular diffusion, which is the Brownian motion of the spins in biologic tissues [1]. The apparent diffusion coefficient (ADC), as a quantitive parameter calculated from DW MR images, combines the effects of capillary perfusion and water diffusion in the extracellular extravascular space [2]. Thus, DW MR imaging can be used to differentiate normal and abnormal structures of tissues, and it might help in characterizing various abnormalities [3].

Recently, DW MR imaging has been used in extracranial organs; for example, it has been used to perform functional evaluation of kidneys [4], [5], [6], [7], [8]. The feasibility and reproducibility of DW MR imaging of kidneys in healthy volunteers and different renal abnormalities has been well reported by Harriet and colleagues [3].

The purpose of this study was to evaluate perfusion and diffusion of kidneys in renal artery stenosis (RAS) and any correlation between stenosis and ADC values and whether this imaging modality may be a noninvasive complementary assessment technique to MR angiography before interventional procedures.

Section snippets

Patients and method

Twenty consecutive patients (11 male, 9 female) suspected of having renal artery stenosis were evaluated with renal MR angiography to exclude stenosis and were then included in the study. The clinical criteria for suspicion of renovascular hypertension were recent onset, difficult to control, end organ damage, renal dysfunction, recurrent pulmonary edema and continuous abdominal bruit. The mean age of patients with RAS was 53.1 ± 10.3 years and 62.6 ± 8.0 years in those with a normal kidney. MR

Statistical analyses

Power analysis revealed that when 10% change in ADC value was considered clinically important, mean ± S.D. ADC value = 2.01 ± 0.2, two tailed α = 0.05. For 80% statistical power, adequate subject count was calculated as 12 subjects.

The ADC values of kidneys with and without arterial stenosis were compared using the Student's t-test. In kidneys with arterial stenosis, correlations between ADC values and stenosis degree were tested using Spearman's correlation analysis. A P-value of less than .05 was

Results

All patients were hypertensive (8 of whom were newly diagnosed and 12 had chronic hypertension). Six patients had diabetes mellitus (DM) and two had diabetic nephropathy (DN). The serum creatinine levels and blood urine nitrogen levels of four patients were elevated. Three of these four patients had DM and two had DN.

RAS was detected in 11 of 20 (55%) patients with MRA. Two patients had bilateral RAS. One patient had undergone a right nephrectomy due to nephrolithiasis 15 years earlier.

Discussion

The feasibility of DW MR imaging of kidney using different technical approaches has been examined in several previously published articles [5], [9], [10], [11]. However, few studies were performed in patients [4], [6]. The reproducibility of DW MR imaging of kidney in healthy volunteers has been shown by Thoeny et al. [3]. Also in our study the inter observer variability values and coefficient of variability values were highly acceptable, and it supports the feasibility and reproducibility of

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DWI is a robust technique that revealed no tissue diffusion and perfusion impairment in mild TRAS. ADC_T has good sensitivity and specificity for identifying patients with severe TRAS. DWI is potentially an alternative radiologic biomarker for assessing microstructural and perfusion alterations in TRAS. DWI is useful in detecting renal functional recovery following successful angioplasty.
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Diffusion-weighted MR imaging of kidneys in renal artery stenosis

Abstract

Objective

Materials and methods

Results

Conclusion

Introduction

Section snippets

Patients and method

Statistical analyses

Results

Discussion

Radiol Clin North Am

Kidney Int

Functional magnetic resonance imaging in renal artery stenosis

Abdom Imaging

Separation of diffusion and perfusion in intravoxel incoherent motion MR imaging

Radiology

Diffusion-weighted MR imaging of kidneys in healthy volunteers and patients with parenchymal diseases: initial experience

Radiology

Measurement of the apparent diffusion coefficient in diffuse renal disease by diffusion-weighted echo-planar MR imaging

J Magn Reson Imaging