Investigation of prostate cancer using diffusion weighted IVIM imaging

Introduction: Diffusion-weighted Imaging (DWI) and the derived apparent diffusion coefficient (ADC) were reported by several groups [1,2] to differentiate cancerous and healthy tissue in the prostate. The Intravoxel Incoherent Motion (IVIM) Theory, which predicts an additional component in the signal equation due to perfusion [3], could recently be applied to the liver and the pancreas [4,5]. Furthermore, it was possible to identify lesions by means of the extracted parameters. In this work, the decrease of the ADC in prostate cancer compared to healthy tissue is investigated using the IVIMTheory. Moreover, the extracted parameters and the calculated parameter maps are analyzed with regard to the differentiation between cancerous and healthy tissue. Methods: Diffusion-weighted images of the prostate were acquired from 9 patients with histologically proven prostate carcinoma (prostatectomy) using an optimized single-shot echo planar imaging (EPI) sequence at 3 Tesla (Magnetom Tim Trio, Siemens Medical Solutions, Erlangen, Germany) with an endorectal coil: TR/TE = 3300/88 ms, 20 slices with 3 mm thickness, matrix = 136x136, bandwidth = 1600 Hz/Px and an isotropic inplane resolution of 1.5 mm. The diffusion weighting was performed applying four b-values (b = 0, 50, 500, 800 s/mm2). Anatomical scans included an axial T2weighted turbo spin-echo sequence (TR/TE = 3580/101 ms, slice thickness = 3.8 mm). The following parameters were extracted from the diffusion weighted images: The ADC via a mono-exponential fit and the diffusion coefficient D, the pseudo diffusion coefficient D*, and the perfusion fraction f via a bi-exponential fit according to [3]. On the parameter maps, calculated with a home-written Matlab program (The MathWorks, Natick, Massachusetts), regions of interest (ROIs) were placed in cancerous and healthy tissue using the information of histological findings. A non-parametric Wilcoxon test was used to analyze whether differences existed between the tumor and the healthy prostate tissue. Results: Fig.1 shows a T2-weighted anatomical slice of a patient with prostate cancer, Fig. 2 the calculated ADC map of the same slice. The ADC of the tumor (red ROI) is considerably decreased compared to the surrounding tissue (green ROI). Fig. 4 shows the signal decay against the b-value in the two ROIs of Fig. 2. Both the perfusion fraction f and the pseudo diffusion coefficient D* are lower in cancerous than in healthy tissue. Hence, in the f map (Fig. 3) the carcinoma appears darker than the surrounding tissue (red arrow). Tab.1 shows that the ADC and f are significantly decreased in cancerous tissue compared to healthy tissue for all examined patients (P ≤ 0.0039), whereas D and D* were not significantly different in both tissues.