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Multivoxel Magnetic Resonance Spectroscopy of Prostate

Author(s): Mahyar Ghafoori

Journal: Iranian Journal of Radiology
ISSN 1735-1065

Volume: 6;
Issue: S1;
Start page: 74;
Date: 2009;
Original page

"nProstate cancer continues to be diagnosed with increasing frequency. MRI has an important role in the diagnosis, staging and follow-up of prostate cancer. The advent of the endorectal coil for high-resolution imaging of the prostate was hailed as a major achievement in prostate cancer imaging. MR spectroscopy (MRS) is a valuable tool that significantly increases the detection rate of prostate cancer and helps to make correct diagnosis of equivocal lesions in MRI. In MRS, magnetic resonance signals of small molecular-weight metabolites that reside in tissues are revealed. The metabolites visualized in MRS are identified by their resonance frequency, which is based on the chemical environment of hydrogen atoms. Each metabolite resonates at a different frequency, often referred to as chemical shift, which is measured in parts per million (ppm). In prostate MRS, several key metabolic resonances are identifiable. Principle among these is that of citrate, a metabolite found in relatively high concentrations in the prostate tissue owing to its presence in prostatic secretions. The citrate resonance is found at 2.6 ppm. Other resonances of interest are creatine and choline, the latter being a metabolite that is often elevated in malignant tissue. These metabolites resonate at 3.0 and 3.2 ppm, respectively. Depending on the quality of the prostate MRS examination, these resonance peaks may overlap partially. "nAs such, distinct choline and creatine resonances may merge and may be hard to identify as separate peaks in the MR spectra. In MRS, the location of the spectrum or spectra in question is usually identified by a box or grid overlaid on an anatomic image. MRS can be performed as a single voxel over a specified lesion, or it can be performed to obtain multiple spectra from a two-dimensional or three-dimensional grid. A three-dimensional MRS grid is the best method of prostate MRS to encompass the entire prostate. MRS of the prostate allows the reader to obtain metabolic information from distinct regions of the prostate gland. Because normal and cancerous prostate tissue contains distinct MR spectral signatures, the information from MRS can be used to supplement that of MRI to identify areas of tumor involvement in the prostate. MRS in conjunction with conventional MRI increase the number of detected cancers compared to standard MRI alone. Using MRS as a supplement to conventional T2W MRI may improve the overall tumor depiction, which in turn improves the reader’s confidence in identifying the foci of the extracapsular disease associated with smaller tumors that may have been missed on conventional T2W imaging alone. Thus, incorporation of MRS with MRI improves the overall staging by distinguishing between organ-confined and extracapsular spread of disease. In this presentation I will demonstrate the results of prostate spectroscopy of 67 patients performed during the last 6 months.   
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