Health Imaging & IT
May 13, 2011
By Clint vanSonnenberg
Researchers at the University of California, Los Angeles (UCLA) have demonstrated preliminary accuracy in the use of 3D ultrasound tracking and MR image fusion for biopsy of suspected prostate cancers, according to a study published in the May-June issue of Urologic Oncology.
“Virtually all major cancers can be easily imaged within the organ of origin, but not [prostate cancer],” noted Shyam Natarajan, MS, from the Biomedical Engineering Interdepartmental Program at UCLA, and co-authors. “Imaging prostate cancer (CaP), while in a curable state, has proven elusive, despite a half-century of interest and effort.”
Natarajan pointed to similarity between benign and cancerous tissue in the prostate, heterogeneity of prostate tissue in aging men and limited resolving power of imaging as posing significant challenges to accurate imaging and diagnosis of prostate cancer.
Highlighting advances such as 3T MRI, the researchers performed a trial on 218 patients of an ultrasound biopsy tracking device. Developed by Eigen (Grass Valley, Calif.), the Artemis tracking system was attached to the ultrasound probe and 3D images were reconstructed. All patients also underwent trans-rectal ultrasound prior to tracking and 47 had images co-registered with MRI.
Systematic 3D biopsy was successfully completed in 180 of 218 patients, though the success rate was closer to 95 percent among the last 50 patients, the authors noted. Biopsy took an average of 15 minutes with an additional 5 minutes required for MRI fusion and biopsy targeting.
The mean error—distance from the target to the center of the re-biopsy core—was measured at 1.2 mm. Error was found to be independent of prostate volume or biopsy location.
Targeted biopsies were more likely to reveal cancer than non-targeted biopsies. When highly suspicious areas were targeted, a 33 percent positive rate was demonstrated, compared with 7 percent for untargeted biopsies.
Overall, 30 men were diagnosed with prostate cancer, nine using systematic biopsy only, six with MRI fusion-guided biopsy only and 16 using both protocols.
The authors added that after a “proper targeting technique” was established, 12 of the last 22 patients undergoing targeted biopsy were found to have prostate cancer. Three of these patients were diagnosed with systematic biopsy alone, four with targeted biopsy alone and five using both protocols.
The most common reasons for failure of 3D guidance included difficulties in positioning the tracking arm, software issues and poor patient compliance. The researchers converted to freehand biopsies in these cases.
“Use of 3D tracking and image fusion has the potential to transform MRI into a clinical tool to aid biopsy and improve current methods for diagnosis and follow-up of [prostate cancer],” Natarajan and co-authors stated. They cautioned, however, that, “While promising, these early experiences have not yet conclusively shown the benefit of tracking and targeted biopsy with MR fusion.”