IMAGING

Correlation of proton MR spectroscopic imaging with Gleason score based on step-section pathologic analysis after radical prostatectomy
Zakian KL, Sircar K, Hricak H, Chen HN, Shukla-Dave A, Eberhardt S, Muruganandham M, Ebora L, Kattan MW, Reuter VE, Scardino PT, Koutcher JA
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
Radiology. 2005; 234: 804-14

• Purpose: To determine whether hydrogen 1 magnetic resonance (MR) spectroscopic imaging can be used to predict aggressiveness of prostate cancer.
• Materials and Methods: All patients gave informed consent according to an institutionally approved research protocol. A total of 123 patients (median age, 58 years; age range, 40-74 years) who underwent endorectal MR imaging and MR spectroscopic imaging between January 2000 and December 2002 were included. MR imaging and spectroscopy were performed by using combined pelvic phased-array and endorectal probe. Water and lipids were suppressed, and phase-encoded data were acquired with 6.2-mm resolution. Voxels in the peripheral zone were considered suspicious for cancer if (Cho + Cr)/Cit was at least two standard deviations above the normal level, where Cho represents choline-containing compounds, Cr represents creatine and phosphocreatine, and Cit represents citrate. Correlation between metabolite ratio and four Gleason score groups identified at step-section pathologic evaluation (3 + 3, 3 + 4, 4 + 3, and > or =4 + 4) was assessed with generalized estimating equations.
• Results: Data from 94 patients were included. Pathologic evaluation was used to identify 239 lesions. Overall sensitivity of MR spectroscopic imaging was 56% for tumor detection, increasing from 44% in lesions with Gleason score of 3 + 3 to 89% in lesions with Gleason score greater than or equal to 4 + 4. There was a trend toward increasing (Cho + Cr)/Cit with increasing Gleason score in lesions identified correctly with MR spectroscopic imaging. Tumor volume assessed with MR spectroscopic imaging increased with increasing Gleason score.
• Conclusion: MR spectroscopic imaging measurement of prostate tumor (Cho + Cr)/Cit and tumor volume correlate with pathologic Gleason score. There is overlap between MR spectroscopic imaging parameters at various Gleason score levels, which may reflect methodologic and physiologic variations. MR spectroscopic imaging has potential in noninvasive assessment of prostate cancer aggressiveness.
  
  
• Editorial Comment
  MR spectroscopic imaging of prostate provides metabolic data to the anatomical data obtained with conventional MR imaging. This technique has demonstrated an improvement in localizing cancer to a sextant of the prostate, estimating extracapsular extension, assessing the aggressiveness of prostate cancer and in localizing hidden suspicious areas of cancer in patients with rising PSA and negative prior biopsies. Specifically, MR spectra from regions of prostate cancer show a significant reduction or absence of citrate and polyamines, while choline is elevated relative to creatine resulting in significant changes in the (choline + creatine)/citrate ratio in regions of cancer . In this paper, the authors confirm previous study on the value of MR spectroscopic imaging as a noninvasive tool to assess prostate cancer aggressiveness. This is a very important contribution since prostate cancer aggressiveness is a key predictor of patient outcome. Several studies have shown that the biopsy results are limited in the determination of all cancer and Gleason grades. In the present study the authors’ shows that when compared with radical prostatectomy results, biopsy was used to correctly predict the pathologic Gleason score in only 64% of patients, 27 % were upgraded and 9 % downgraded. Another interesting observation was that the tumor volume, as defined by the number of MR spectroscopic imaging positive voxels, was positively correlated with Gleason score. In other words, MR spectroscopic imaging measurements of prostate tumor (Cho + Cr) / Cit and tumor volume correlate with pathologic Gleason score.
  In this study, they had a sub-optimal overall sensitivity of MR spectroscopic imaging for cancer Gleason 3+3. This results are very different from ours .We had a much higher sensitivity than 44% for the detection of tumor Gleason 3+3. One possible explanation is probably related to the fact that the authors used air in the endorectal coil. By switching the air to liquid perfluorocarbon, in the last 2 years, we were able to obtain much better MR spectra with superior metabolites discrimination and superior detection of tumor Gleason 3+3. Similarly to the authors we have found higher (Cho+Cr) / Cit ratios in patients with tumor with higher Gleason scores.

References
1. Kurhanewicz J, Vigneron DB, Nelson SJ: Three-dimensional magnetic resonance spectroscopic imaging of brain and prostate cancer. Neoplasia. 2000; 2: 166-189.
2. Prando A, Kurhanewicz J, Borges AP, Oliveira Jr EM, Figueiredo E: Prostatic biopsy directed by endorectal MR spectrocopic imaging in patients with elevated PSA and prior negative biopsies: Early experience. Radiology (in press).

Dr. Adilson Prando
Chief, Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil