Clinical Application Of Readout-Segmented Echo-Planar Imaging For Diffusion-Weighted Imaging In Prostate

Part Ⅰ Readout-Segmented Echo-Planar Imaging for Diffusion-Weighted Imaging: Phantom Experiment and Preliminary Application in Normal ProstateObjective:Single-shot echo-planar imaging (SS-EPI) is currently the sequence used most routinely for clinical studies in DWI. However, susceptibility artifacts and image blur can be severe, particularly at3T, due to the long EPI readout and corresponding low bandwidth per pixel in the phase-encoding direction. Readout-segmented echo-planar imaging (RS-EPI) has been suggested as an alternative to SS-EPI for diffusion-weighted imaging (DWI) with reduced distortion. The purpose of the current study is to evaluate the performance of RS-EPI DWI in phantom experiment and compare it with the SS-EPI method in normal prostate.Materials and Methods:A MRI phantom called Magphan SMR100(Pat No:5165050) developed by U.S.A. phantom laboratory was tested. The phantom was scanned at3T with conventional SS-EPI, high resolution and RS-EPI. Imaging studies were evaluated for signal-to-noise ratio (SNR), spatial resolution, geometric distortion and contrast resolution. Qualitative and quantitative evaluation of image quality at3T in10healthy volunteers were obtained using above three different prostate DWI. quantitative assessment parameters include SNR and apparent diffusion coefficient (ADC) were also measured in peripheral zone and transition zone. A paired Wilcoxon rank sum test was used for statistical analysis in phantom experiment and in vivo prostate study.Results:In phantom experiment, SNR, spatial resolution, geometric distortion, and contrast resolution were rated significantly better by both readers for RS-EPI technique (P<0.05for all parameters). In the SS-EPI, as the matrix and scan time increasing, geometric distortion has not been suppressed. In vivo prostate study, RS-EPI reduced significantly geometric distortions and blurring, and improved image quality in the volunteers, compared to SS-EPI (P<0.05). There were no statistically significant difference in ADC and SNR between the two methods (P>0.05).Conclusion:RS-EPI DWI can effectively suppress magnetic susceptibility artifacts, reduce anatomical distortions. RS-EPI is a feasible technique in the normal prostate DWI for producing high-resolution DWI and subsequent in prostate disease lay theoretical foundation. Part Ⅱ Clinical Feasibility of Readout-Segmented Echo-Planar Imaging for Diffusion-Weighted Imaging in Prostate Disease at3TObjective:Conventional DW imaging speed is very fast, but in particular parts of the examination, such as the prostate, is affected by magnetic susceptibility artifacts. With increasing field strength, these effects are even more prominent. RS-EPI DWI can effectively suppress magnetic susceptibility artifacts and reduce anatomical distortion. However, the clinical application of this technology in prostate disease is rarely reported. The purpose of this study was to demonstrate the feasibility of the RS-EPI technique in DWI of the prostate disease and to compare the image quality of RS-EPI DWI of the prostate with conventional SS-EPI diffusion images on a3T clinical scanner.Materials and Methods:A total of478adult patients apply for prostate MRI examination in our hospital between May2013and January2015. After rigorous screening,252cases of primary prostate disease patients underwent conventional MRI, and a plus DWI scans, including conventional SS-EPI and RS-EPI in two ways. Two genitourinary observers (blinded to which sequence was reviewed) evaluated the DW images acquired on the252patients by using RS-EPI and conventional SS-EPI, scoring them in terms of sharpness, distortion level, lesion contrast, lesion conspicuity, detailed anatomical visualization and overall image quality on a5-point Likert scale (1, nondiagnostic;5, excellent). Lesion contrast noise ratio (CNR) and ADC values were calculated. Agreement between two readers was assessed with weighted κ and exact Bowker test of symmetry. Differences in image quality and image parameters between conventional SS-EPI and RS-EPI were compared using the Wilcoxon rank sum test or paired t test.Results:The κ value were0.76,0.79,0.52,0.55,0.63,0.65for image sharpness, anatomical distortion, imaging contrast, lesion conspicuity, detailed anatomical visualization and overall image quality (all P<0.05), indicating moderate to substantial agreement between the two observers. Bowker test of symmetry P values were greater than0.05. The mean Likert scores for conventional SS-EPI and RS-EPI were as follows:image sharpness,2.88±0.62and4.24±0.80; distortion level,2.94±0.62and4.38±0.64; contrast,3.32±0.79and3.72±0.73; lesion conspicuity,3.02±0.71and3.96±0.61; detailed anatomical visualization,3.08±0.53and4.20±0.76; and overall image quality,3.12±0.72and4.16±0.68, respectively. RS-EPI DWI requires significantly better image quality and reduces susceptibility artifacts than conventional SS-EPI (all P<0.05). The conventional SS-EPI was superior to RS-EPI in CNR (P<0.05), whereas there were no significant differences in ADC between SS-EPI and RS-EPI (P>0.05).Conclusion:RS-EPI is a feasible technique in the prostate for producing high-resolution DW images with reduced geometric distortion and reduced blurring and offers potentially superior image quality compared to conventional SS-EPI technique at3T. This technique could provide reliable imaging evidence for future accurate prostatic disease-pathology control studies, should be vigorously publicity and promotion. Part Ⅲ Clinical Application of Readout-Segmented Echo-Planar Imaging for Diffusion-Weighted Imaging in Prostate Cancer at3TObjective:DWI is based on the random motion characteristics of water molecules and it enables investigation of the architecture of the biological environment. In the prostate study, DWI is widely used for differentiating malignant from benign prostatic tissues, and assessing cancer staging, biological potential, treatment planning, therapy response and local recurrence. As a new imaging technology, RS-EPI can effectively suppress DWI susceptibility artifacts produced by conventional SS-EPI to obtain high-resolution images without distortion. The purpose of this study was to implement RS-EPI DWI on a clinical scanner at3.0T for prostate cancer imaging and to explore its impact on the image quality and quantitative measurement parameters.Materials and Methods:A total of252clinical patients underwent3.0T prostate MRI examination in our hospital between May2013and January2015. Fifty-eight patients with prostate cancer which were confirmed by biopsy or surgery (radical or TURP) pathology were retrospectively analyzed. Pathological findings were obtained within one month after the MRI examination. All patients had not received any treatment for prostate cancer (i.e., androgen ablation, radiotherapy, chemotherapy, radical surgery, cryosurgery). Images were obtained using RS-EPI and high resolution SS-EPI with an identical scanning time, acceleration factor, target resolution, and image post-processing procedure. Two genitourinary observers (blinded to which sequence was reviewed) evaluated the DW images acquired on the58patients by using RS-EPI and high resolution SS-EPI, scoring them in terms of sharpness, distortion level, lesion contrast, lesion conspicuity, detailed anatomical visualization and overall image quality on a5-point Likert scale (1, nondiagnostic;5, excellent). SNR, contrast, CNR and ADC values of tumors were calculated. Image quality differences were compared between two different DWI techniques in prostate cancer clinical scanning. Differences in image quality and image parameters between conventional SS-EPI and RS-EPI were compared using the Wilcoxon rank sum test. The relationship between parameters measured in two different DWI methods was analyzed by the method of Pearson correlation test.Results:RS-EPI was superior to high resolution SS-EPI in distortion level, lesion contrast, visibility and overall image quality(all P<0.05), whereas there were no significant differences in sharpness and anatomical details between RS-EPI and high resolution SS-EPI (P>0.05). There were significant differences in SNR and contrast between the two DWI techniques (P<0.05), but no differences in CNR and ADC (P>0.05). The comparison of SNR, lesion contrast, CNR and ADC between the two DWI techniques showed a positive correlation (r=0.712,0.823,0.625,0.872), were statistically significant (P<0.05).Conclusion:RS-EPI diffusion imaging is superior to the high-resolution SS-EPI in the aspect of overall image quality in prostate cancer DW MR imaging. This technology can effectively reduce prostate DWI image distortion and blurring, increase the rate of small lesions display. RS-EPI DWI is a robust tool to delineate the lesion contour and may accurately define the target for biopsy, has a higher significance application prospects for the early diagnosis and identification of prostate cancer.