Carr-Purcell-Meiboom-Gill imaging of prostate cancer: quantitative T2 values for cancer discrimination

Abstract

Quantitative, apparent T(2) values of suspected prostate cancer and healthy peripheral zone tissue in men with prostate cancer were measured using a Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence in order to assess the cancer discrimination potential of tissue T(2) values. The CPMG imaging sequence was used to image the prostates of 18 men with biopsy-proven prostate cancer. Whole gland coverage with nominal voxel volumes of 0.54 x 1.1 x 4 mm(3) was obtained in 10.7 min, resulting in data sets suitable for generating high-quality images with variable T(2)-weighting and for evaluating quantitative T(2) values on a pixel-by-pixel basis. Region-of-interest analysis of suspected healthy peripheral zone tissue and suspected cancer, identified on the basis of both T(1)- and T(2)-weighted signal intensities and available histopathology reports, yielded significantly (P<.0001) longer apparent T(2) values in suspected healthy tissue (193+/-49 ms) vs. suspected cancer (100+/-26 ms), suggesting potential utility of this method as a tissue specific discrimination index for prostate cancer. We conclude that CPMG imaging of the prostate can be performed in reasonable scan times and can provide advantages over T(2)-weighted fast spin echo (FSE) imaging alone, including quantitative T(2) values for cancer discrimination as well as proton density maps without the point spread function degradation associated with short effective echo time FSE sequences.

Figure 1

Axial images of a 63-year old man with biopsy proven prostate adenocarcinoma of the right lobe (Gleason 3+3=6, 5% of 1/3 cores) and left lobe (Gleason 4+3=7, 80%, 20%, and 5% of 3/4 cores) and PSA 7.9 who subsequently underwent radical prostatectomy that showed Gleason 3+4=7 involving the posterior right quadrant and Gleason 3+4=7 involving anterior and posterior left quadrants. Geometric mean images generated from the 1^st (A), 2^nd (B), 3^rd (C), and 4^th (D) group of TEs. D is derived from the last 4 TEs (182, 196, 210, 224 ms) and demonstrates a band of hypointense signal in the posterior right and left midgland but with no evidence of extracapsular penetration (stage T2c). ROI placements for SH (blue) and SC (red) are shown. E. Corresponding T2 map. T2 values for SH and SC were 215ms and 94ms respectively. F. Corresponding PD map..

Figure 2

Coronal images of a 43-year old male with prostate adenocarcinoma of the right lobe (Gleason 4+4=8, 100% and 80% of 2/6 cores) and left lobe (Gleason 4+5=9, 100%, 100%, 100%, and 90% of 6/6 cores) and PSA 41.0 who subsequently underwent neoadjuvant chemotherapy with bevacizumab plus docetaxel prior to radical prostatectomy. Geometric mean images from the 1^st – 4^th group of TEs (A–D, respectively). A focal hypointense nodule is noted in the left base that extends beyond the capsule into the left seminal vesicle (stage T3b). ROI placements for SH (blue) and SC (red) are shown. E. Corresponding T2 map. T2 values for SH and SC were 195ms and 74ms respectively F. Corresponding PD map.

Figure 3

Apparent T2 values for all suspected healthy (SH) tissue and suspected cancer (SC) peripheral zone ROIs sampled in this study. Three cases in which the patient underwent prostatectomy without first undergoing neoadjuvant therapy are circled. Significant differences were measured between the apparent T2 values of suspected healthy tissue and suspected cancer with μ±σ of 193±49 and 100±26 ms, respectively. (p < 0.0001)

Figure 4

Typical T2 decay curves with fits to echoes 2 through 12 using mono- and biexponential fits. Note the noise floor is well below the signal remaining in the 12 th echo even for the more quickly decaying SC ROI.