Magnetic resonance imaging in prostate cancer: the value of apparent diffusion coefficients for identifying malignant nodules

N M desouza, S A Reinsberg, E D Scurr, J M Brewster, G S Payne
2007 British Journal of Radiology  
The aim of this work was to determine the potential of diffusion-weighted magnetic resonance imaging (DW-MRI) for identifying prostate cancer by comparing apparent diffusion coefficients (ADC's) from malignant peripheral zone (PZ) nodules with values from non-malignant PZ and predominantly benign central gland (CG). Thirtythree patients with elevated prostate specific antigen (PSA) aged 52-78 years (30 with biopsy proven prostate cancer) underwent endorectal MRI with T2-weighted and echo-planar
more » ... DW (b = 0, 300, 500 and 800 s/mm 2 ) sequences. ADC's were measured from 30 malignant PZ nodules (identified on T2-weighting and positive biopsy; median ROI size 41mm 2 ), 33 CG regions (predominantly benign nodules; median ROI size 218mm 2 ) and 18 non-malignant PZ regions (ipsilateral biopsies all benign; median ROI size 54.5mm 2 ). ADC's were (mean ±sd; mm 2 /s): malignant PZ nodules INTRODUCTION: Cancer of the prostate currently accounts for 30% of new cancer cases [1] and requires 6-8 tissue cores obtained under transrectal ultrasound (TRUS) guidance for diagnosis. T2-weighted magnetic resonance imaging (MRI) delineates prostate cancer as a region of low signal intensity (indicative of a shorter T2 relaxation time constant for tumour) surrounded by high signal intensity (longer T2) of normal peripheral zone tissue [2;3]. However, although the sensitivity of T2-weighted images for tumour detection is high, specificity is poor [4] . Furthermore, the 30% of tumours that occur in the central gland cannot be detected on T2-weighted imaging because it is not possible to differentiate them from the low signal-intensity benign nodules of prostatic hyperplasia. Potential advantages of improved discrimination of malignant tissue in both the peripheral and central zones of the prostate include better local staging performance, increased accuracy in performing biopsy, improved focusing of irradiation for intensity-modulated radiotherapy, improved follow-up of therapy response, and earlier detection of tumour recurrence. An alternative to T2-weighted MRI is to develop image contrast through "apparent diffusivity" (tissue water incoherent displacement over distances of 1-20 µm). Diffusion-weighted magnetic resonance imaging (DW-MRI) has been used in both clinical and research settings for detecting cerebral [5-8] as well as cancer-related pathologies [9] [10] [11] [12] [13] . In cancer imaging, it has been used primarily in characterizing brain tumours [7] and in differentiating brain lesions based on diffusivity of peritumoural edema [14] . However, there are a few recent reports of the utility of DW-MRI in prostate cancer [15] [16] [17] [18] [19] where its role appears promising but has not been established. The extensive branching ductal structure of the normal prostate compared with the highly restricted intracellular and interstitial spaces encountered in prostate cancers produces a substantial differential in apparent diffusion coefficient (ADC) and, thus, the potential for high image contrast. The purpose of this study was to investigate the potential of DW-MRI in identifying malignant nodules by comparing apparent diffusion coefficients (ADC's) of malignant peripheral zone (PZ) nodules with values from non-malignant PZ and from the central gland (CG), which is primarily composed of benign nodules.
doi:10.1259/bjr/24232319 pmid:17303616 fatcat:eihm7tiagvc3he74dga6e4b3ne