3T boosts MR's ability to pinpoint prostate cancer

April 15, 2005

The higher resolution of 3T MR may propel it into routine use in an arena that has been slow to adopt it: prostate imaging. Challenged by the discomfort of endorectal coils and the possibility of artifacts at 1.5T, many urologists have relied on clinical examination, the prostate-specific antigen (PSA) test, an ultrasound examination, and biopsy. Results from work with 3T scanners, however, may persuade more clinicians to refer patients to the MR suite.

The higher resolution of 3T MR may propel it into routine use in an arena that has been slow to adopt it: prostate imaging. Challenged by the discomfort of endorectal coils and the possibility of artifacts at 1.5T, many urologists have relied on clinical examination, the prostate-specific antigen (PSA) test, an ultrasound examination, and biopsy. Results from work with 3T scanners, however, may persuade more clinicians to refer patients to the MR suite.

The higher signal-to-noise ratio with high-field magnets means that the endorectal coil is not strictly necessary, said Dr. Hui Mao, an assistant professor of radiology at Emory University in Atlanta. Mao and his colleagues at Emory have found that use of a phased-array surface coil with parallel imaging for 3T prostate MRI generates images with sensitivity comparable to those from a 1.5T endorectal examination without increasing scan time. Problems with motion artifacts are reduced, blooming from the endorectal coil is no longer an issue, and patient tolerance is higher.

Mao is already using the novel approach in clinical practice, scanning prostate cancer patients to assess possible extracapsular extension of the tumor and patients with equivocal test results such as a high PSA and negative biopsy. He is confident that once urologists appreciate the quality of 3T prostate MR studies, they will refer a far wider range of patients.

"People talk about using this exam for monitoring and for staging prostate cancer. But I would recommend it for screening, too. I would recommend it for screeining if it could be comfortable and affordable, because it shows the prostate structure so clearly," he said.

Prof. Dr. Arend Heerschap, head of experimental biomedical MR at the University Medical Center St. Radboud in Nijmegen, the Netherlands, is also interested in the prospect of nonendorectal prostate examinations at 3T. Heerschap would like to test the procedure primarily for MR spectroscopy. High-field MR scanners make it far easier to interpret MRS data because peaks relating to key metabolites are more easily distinguished. The peaks from choline and citrate, for example, which are believed to be markers for prostate tumors, may be obscured by large nearby signals generated from fats and lipids on 1.5T MRS spectra. These peaks can be distinguished more clearly when the scan is performed at 3T.

Dr. Bruce Daniel, an assistant professor of radiology at Stanford University, continues to use the endorectal approach for both prostate MRI and MRS at 3T. Rather than emulating results already possible with 1.5T, he prefers to use the higher SNR to boost the information gained from MR prostate assessment.

"You can get some truly phenomenal images of the prostate where you are looking at microstructure you have never seen before," Daniel said. "We're trying to push the imaging and the spectroscopy to the ultimate performance you can get."