IMAGING

MRI of prostate cancer at 1.5 and 3.0 T: comparison of image quality in tumor detection and staging
Beyersdorff D, Taymoorian K, Knosel T, Schnorr D, Felix R, Hamm B, Bruhn H
Department of Radiology, Charite, Universitatsmedizin Berlin, Berlin, Germany
AJR Am J Roentgenol. 2005; 185: 1214-20

• Objective: This prospective study was performed to compare the image quality, tumor delineation, and depiction of staging criteria on MRI of prostate cancer at 1.5 and 3.0 T.
• Subjects and Methods: Twenty-four patients with prostate cancer underwent MRI at 1.5 T using the combined endorectal-body phased-array coil and at 3.0 T using the torso phased-array coil, among them 22 before undergoing radical prostatectomy. The prostate was imaged with T2-weighted sequences in axial and coronal orientations at both field strengths and, in addition, with an axial T1-weighted sequence at 1.5 T. Preoperative analysis of all MR images taken together was compared with the histologic findings to determine the accuracy of MRI for the local staging of prostate cancer. In a retroanalysis, the image quality, tumor delineation, and conspicuity of staging criteria were determined separately for both field strengths and compared. Statistical analysis was performed using Wilcoxon’s and the McNemar tests.
• Results: In the preoperative analysis, MRI (at both 1.5 and 3.0 T) had an accuracy of 73% for the local staging of prostate cancer. The retroanalysis yielded significantly better results for 1.5-T MRI with the endorectal-body phased-array coil in terms of image quality (p < 0.001) and tumor delineation (p = 0.012) than for 3.0-T MRI with the torso phased-array coil. Analysis of the individual staging criteria for extracapsular disease did not reveal a superiority of either of the two field strengths in the depiction of any of the criteria.
• Conclusion: Intraindividual comparison shows that image quality and delineation of prostate cancer at 1.5 T with the use of an endorectal coil in a pelvic phased-array is superior to the higher field strength of 3.0 T with a torso phased-array coil alone. As long as no endorectal coil is available for 3-T imaging, imaging at 1.5 T using the combined endorectal-body phased-array coil will continue to be the gold standard for prostate imaging.
  
  
• Editorial Comment
  The best results for local staging of prostate cancer with MR imaging is obtained using 1.5 T MR scanner and an integrated endorectal pelvic-phased array coil. Using this combination of coils and following strict and definite criteria for extraprostatic disease, a high degree of specificity can be obtained (97%). As 3T MR units are becoming more available, and offering higher signal-to-noise ratios and increased temporal and spatial resolution it would be useful to have a study comparing both techniques.
  The authors present a very interesting paper where they did a prospective analysis comparing the results of both equipments in a group of 22 patients who underwent prostatectomy. Since endorectal coils are not yet approved for clinical use at 3.0 T, they performed a direct comparison between 1.5 T MR scanner and an integrated endorectal pelvic-phased array coil with a 3.0 T MR scanner and the torso phased-array coil alone. Among these patients 15 had stage T2 tumor, and 7 had stage T3 tumor. The accuracy of staging using the MR images obtained at both field strengths was 73%. The author’s conclusion was that at this moment, 1.5-T MRI of the prostate with the endorectal coil will continue to be the gold standard for MRI of the prostate because of its superior overall image quality compared with MRI at 3.0 T using only the torso phased-array coil.
  It has been shown that in experimental studies, the initial results of endorectal 3T MR imaging in prostate cancer is potentially useful (1). This should be expected since with this new endorectal coil, we would obtain an increase in spatial and temporal resolution and also an increase in spectral resolution (better MR spectroscopic imaging). Endorectal 1.5 T MR imaging combined with spectroscopic imaging has already demonstrated a potential for improved diagnosis and staging of prostate cancer. Thus it is all right to predict that the 3.0 T MR scanner with adequate endorectal coil will very soon offer a significant improvement in conventional MR images and also in spectroscopic analysis causing a significant impact in the evaluation of patients with prostate cancer.

Reference
1. Futterer JJ, Scheenen TW, Huisman HJ, Klomp DW, van Dorsten FA, Hulsbergen-van de Kaa CA, Witjes JA, Heerschap A, Barentsz JO: Initial experience of 3 tesla endorectal coil magnetic resonance imaging and 1H-spectroscopic imaging of the prostate. Invest Radiol. 2004; 39: 671-80.

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