Elsevier

Clinical Radiology

Volume 66, Issue 5, May 2011, Pages 420-425
Clinical Radiology

Original Paper
Ability and utility of diffusion-weighted MRI with different b values in the evaluation of benign and malignant renal lesions

https://doi.org/10.1016/j.crad.2010.11.013Get rights and content

Aim

To evaluate the ability and the utility of diffusion-weighted (DW) magnetic resonance imaging (MRI) with high and low b values to visualize benign and malignant renal lesions, and to determine which b value (b = 100, 600, or 1000 s/mm2) was most useful in differentiating benign from malignant renal lesions.

Materials and methods

Fifty-eight patients with 67 renal lesions and 50 normal contralateral kidneys (as control) were enrolled in the study. DW imaging was performed with b values of 100, 600, and 1000 s/mm2. Results of the histopathological evaluation were compared with the DW MRI results. Apparent diffusion coefficient (ADC) values, and the sensitivity and specificity for differentiating malignant renal lesions from benign renal lesions were calculated for each b value.

Results

The mean ADC values of normal renal parenchyma with b = 100, 600, and 1000 s/mm2 values were (3.14 ± 0.54) × 10−3, (2.52 ± 0.30) × 10−3, and (2.16 ± 0.43) × 10−3 mm2/s, respectively. The mean ADC values of benign renal lesions (n = 35) with b = 100, 600, and 1000 s/mm2 values were (2.88 ± 0.88) × 10−3, (2.58 ± 0.91) × 10−3, and (2.10 ± 0.93) × 10−3 mm2/s, respectively. The mean ADC values of malignant renal lesions (n = 32) with b = 100, 600, and 1000 values were (2.74 ± 0.58) × 10−3, (2.09 ± 0.63) × 10−3, and (1.66 ± 0.51) × 10−3 mm2/s, respectively. Using DW imaging malignant renal lesions could be differentiated from benign renal lesions, and also angiomyolipomas and oncocytomas could be differentiated from renal cell carcinoma.

Conclusions

DW MRI with quantitative ADC measurements can be useful in the differentiation of benign and malignant renal lesions. High b values (b = 600 and 1000 s/mm2) had the best specificity and sensitivity.

Introduction

Diffusion-weighted (DW) magnetic resonance imaging (MRI) is an MRI technique used to show molecular diffusion, which is the Brownian motion of the spins in biological tissues. The apparent diffusion coefficient (ADC), as a quantitative parameter calculated from the DW MRI images, combines the effects of capillary perfusion and water diffusion in the extracellular extravascular space.1, 2

Recently, DW imaging (DWI) of the abdomen and pelvis, which has a widespread usage for diagnostic purposes, has provided a new contrast mechanism to evaluate patients with abdominal disease and solid abdominal and pelvic organs.3 Current articles show that adding DWI to routine MRI examination increases diagnostic accuracy.4, 5, 6 Most tumours show restricted diffusion because of the higher cellularity of solid tumours and their increase in cell membranes per unit volume, resulting in restriction of water movement and corresponding high signal intensity on DWI.7 The ADC value has been reported to be valuable for quantitatively distinguishing malignancy from benign lesions.8, 9

DWI simultaneously provides information on diffusion and perfusion. When applying a high b value, the ADC value approximates the true diffusion. Low b values are influenced by both perfusion and diffusion.9

The aim of this study was to evaluate the role of DW MRI with high and low b values to visualize renal lesions and to determine which b value (ie., b = 100, 600, or 1000 s/mm2) was most useful in differentiating benign from malignant renal lesions.

Section snippets

Patients

Fifty-eight consecutive patients (25 men, 33 women, mean age 53 ± 19 years, range 1–76 years) with 67 renal lesions who underwent conventional MRI and DW MRI for renal indications between August 2006 and December 2009 were enrolled in the study. DWI has been systematically used as part of our renal mass MRI protocol since 2006. Informed consent was not acquired from all patients due to the retrospective design of the study. The study received institutional review board approval. The renal lesions

Results

Sixty-seven renal lesions (mean diameter 42 ± 24 mm; range 13–160 mm) were analysed in 58 patients.

For each lesion, the measured total ROIs had a mean size of 64 ± 24 mm2 (range 25–200 mm2) and were oval or round, depending on the lesion morphology. For each normal kidney, the measured ROIs had a mean size of 76 ± 24 mm2 (range 39–124 mm2).

DW images were of sufficient diagnostic quality in all patients, and none of the patients was excluded from this study. All renal lesions and mean ADC values are listed

Discussion

RCCs represent 85% of all renal tumours with an incidence of approximately 30,000 new cases a year and a mortality of 12,000 deaths per year in the USA. Differential diagnosis between malignant tumours, angiomyolipomas, oncocytomas, and complex cysts is not always easy.15

ADC values have been reported to be related to the cellular density of a tumour, and a reduced ADC value has been reported for most malignant tumors.16, 17 Thus DWI using b values of 100, 600 or 1000 s/mm2 was included in the

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    Hence, they were easily recognized on conventional MRI with typical fat components. Their mean ADC value (0.95 ± 0.3 × 10 − 3 mm2/s) was significantly lower than that of RCC, and our findings were in concordance with previous studies (11,12,18,19). Contrasting results have been reported by Kilickesmez et al., (29) who have found that mean ADC value was higher for AMLs (1.40 ± 0.21) than for RCCs (1.06 ± 0.39).

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    However, other studies indictaed that the use of b = 1000 s/mm2 is diagnostically optimal. The study by Doganay et al. showed that higher b values (600 and 1000 s/mm2) led to increased sensitivity and specificity in the differential diagnosis of malignant and benign renal lesions [8]. Regardless, higher b causes significantly decreased signal-to-noise ratio (SNR) and suppresses the background signal, unable to display anatomical parts [39].

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