Two recent studies are helpful in clarifying the issue of when specific types of magnetic resonance imaging (MRI) meothds may be useful in the diagnosis and prognosis of prostate cancer.
First, and perhaps most importantly, a study by Jung et al. from the University of California, San Francisco, suggests that standard T2-weighted, endorectal MRI studies appear to be no better (or worse) that so-called “B-mode” transrectal ultrasound (TRUS) imaging in the detection of locally invasive prostate cancer (i.e., whether the cancer presents a significant risk of extracapsular extension).
This study was based on data from 101 patients with biopsy proven prostate cancer. Each patients was given both types of imaging tests prior to a radical prostatectomy. Retrospective assessment of all images was carried out (by three experienced readers for the MRI data and by a single experience reader for the ultrasound data). The accuracy of staging based on the MRI and ultrasound data was then compared to the pathological stage found after prostatectomy. There was no significant difference between the accuracy of the clinical stages based on MRI data as compared to the stages based on TRUS data.
The second study — by Ohgiya et al. — was designed to investigate the diagnostic accuracy of 3.0-T, diffusion-weighted MRI (3TDW-MRI) for detection of prostate cancer by using different b-values. (From a technical point of view, the higher the b-value, the greater of the strength of the effect of diffusion weighting, but this is a very technical issue better left to electrical engineers who specialize in imaging technology.)
In this study, 73 men with biopsy-proven prostate cancer were given three MRIs at 3.0 T. However, the b-value varied from MRI to MRI:
- In Protocol A, the b-value was set at 500 s/mm2.
- In Protocol B, the b-value was set at 1,000 mm2.
- In Protocol C, the b-value was set at 2,000 s/mm2 .
All the MRI sets were reviewed by two experienced radiologists.
Ohgiya et al. report that data from Protocol C were clearly superior to data from Protocols A and B. They conclude that 3TDW-MRI at a b-value of 2000 mm2 can improve the diagnostic accuracy of this technique (compared to use of 3TDW-MRI at lower b-values) in the diagnosis of prostate cancer. This may be important to the appropriate application of MRI in the diagnosis and prognosis of men on active surveillance and to men who need MRI methods to assess risk for progressive forms of prostate cancer prior to treatment during the course of their disease.