IMAGING

Combined T2-weighted and diffusion-weighted MRI for localization of prostate cancer
Haider MA, van der Kwast TH, Tanguay J, Evans AJ, Hashmi AT, Lockwood G, Trachtenberg J
Joint Department of Medical Imaging, Princess Margaret Hospital, University Health Network and Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada
AJR Am J Roentgenol. 2007; 189: 323-8

• Objective: The objective of our study was to compare T2-weighted MRI alone and T2 combined with diffusion-weighted imaging (DWI) for the localization of prostate cancer.
• Subjects and Methods: T2-weighted imaging and DWI (b value = 600 s/mm2) were performed in 49 patients before radical prostatectomy using an endorectal coil at 1.5 T in this prospective trial. The peripheral zone of the prostate was divided into sextants and the transition zone into left and right halves. T2 images alone and then T2 images combined with apparent diffusion coefficient (ADC) maps (T2 + DWI) were scored for the likelihood of tumor and were compared with whole-mount histology results. Fixed window and level settings were used to display the ADC maps. Only tumors with an area of more than 0.13 cm2 (> 4 mm diameter) and a Gleason score of > or = 6 were considered significant. The area under the receiver operating characteristic curve (A(z)) was used to assess accuracy.
• Results: In the peripheral zone, the A(z) value was significantly higher (p = 0.004) for T2 plus DWI (A(z) = 0.89) than for T2 imaging alone (A(z) = 0.81). Performance was poorer in the transition zone for both T2 plus DWI (A(z) = 0.78) and T2 (A(z) = 0.79). For the whole prostate, sensitivity was significantly higher (p < 0.001) with T2 plus DWI (81% [120/149]) than with T2 imaging alone (54% [81/149]), with T2 plus DWI showing only a slight loss in specificity compared with T2 imaging alone (84% [204/243] vs 91% [222/243], respectively).
• Conclusion: Combined T2 and DWI MRI is better than T2 imaging alone in the detection of significant cancer (Gleason score > or = 6 and diameter > 4 mm) within the peripheral zone of the prostate.
  
  
• Editorial Comment
  Localization of prostate cancer is important for adequate tumor staging, adequate targeting for transrectal ultrasound biopsy and for adequate conservative therapies such as intensity-modulated radiation therapy, interstitial brachytherapy and cryosurgery. Endorectal magnetic resonance techniques that can be used for identification of prostate cancer are conventional T2-weighted image, 3D-spectroscopy, diffusion-weighted image (DWI) and dynamic contrast enhanced technique (DCE). Since the appearance of cancer on T2-weighted image is not specific, several studies have demonstrated that the combination of endorectal MR imaging and magnetic resonance spectroscopic imaging, can lead to high sensitivity and specificity for peripheral zone tumor localization. DWI is a technique of imaging prostate cancer based on the fact that cancer tissue presents with restriction of the movements of the molecules of water compared with the movement of the molecules of water within normal prostatic tissue. In other words, cancer appears with low apparent diffusion-coefficient values (ADC).Though the authors state that sensitivity of combined T2 and DWI MRI is significantly higher than with T2 imaging alone, we should be alert because both techniques can present false positive (due to prostatitis, focal prostatic atrophy, etc) or false negative results. In our institution, we have been using routinely, in the last 3 years, the combination of these four different techniques: T2-weighted image, 3D-spectroscopic imaging, DWI and dynamic contrast enhanced imaging. Preliminary analysis of our materials has been shown that combining these four techniques provides better sensitivity and specificity for cancer detection and localization.

Dr. Adilson Prando
Chief, Department of Radiology and
Diagnostic Imaging
Vera Cruz Hospital
Campinas, São Paulo, Brazil