In September, 2011 an important question was raised in an online Urology News posting by Medscapei. Author Greg Freiherr examined the implications of using a powerful noninvasive diagnostic imaging technique called proton MR spectroscopy, or MRS, to distinguish cancerous tissue from healthy tissue. This topic is of interest within the prostate cancer community, as some patients believe that the MRS replaces the more invasive prostate needle biopsy. Essentially, Freiherr confronted this issue, asking if an imaging tool can both identify cancerous cells AND adequately characterize them.
The author points out that certain types of cancer manifest unique "fingerprints" or biochemical signatures. The cancer cells have cellular metabolites that show up in MRS images as "spectral peaks" that can be compared to the way nearby healthy tissues show up. With the proper technology, this type of analysis adds less than 15 minutes to a standard MRI (Magnetic Resonance Imaging) exam.
MRS is promising in diagnosing prostate cancer, which has a "distinct signature of reduced citrate and elevated choline," writes Freiherr. In fact, an 8-center clinical trial correlated MRS images with tissue from surgically removed prostates, validating that the MRS images had correctly distinguished between cancerous and noncancerous tissuesii.
distinct signature of reduced citrate and elevated cholineFreiherr
However, there are several challenges that must be addressed before MRS is acceptable as an alternative to prostate biopsy. An obvious hurdle is the exclusion of reimbursement by Medicare/Medicaid and private third-party payers. Equally crucial is the lack of standardization in the protocol, and the technology requires improvements that would eliminate inconclusive or ambiguous diagnostic spectra. Finally, today there is no true substitute for the kinds of genetic or molecular examination that can be accomplished with the actual cells extracted by needle biopsy. For physicians and patients interested in focal ablation procedures, laboratory analysis of cell lines yields greater knowledge and therefore a higher degree of confidence regarding appropriate treatment choices.
Freiherr concludes, "...MRS use is far from becoming standard. Even staunch advocates agree that it must be used in conjunction with other modalities and techniques. MRS is increasingly referred to as a 'virtual biopsy'; however, MRS is not a candidate to replace the biopsy needle, at least not in the near term."
ihttp://www.medscape.com/viewarticle/750176_print
iiScheenen T, Fütterer J, et al. Discriminating cancer from noncancer tissue in the prostate by 3-dimensional proton magnetic resonance spectroscopic imaging: a prospective multicenter validation study. Invest Radiol. 2011;46:25-33.