The Optimization of Zoomed Field of View DWI (iZOOM) with Echo Planar Imaging (EPI) Sequence Excited by a Two Dimensional Radiofrequency Pulse (2D RF) on Prostate at 3.0 T
Kangjie Xu1, Xiaodong Zhang1, Chengyan Wang2, Hongxia Sun1, Yu Zhang3, Zhigang Wu4, and Xiaoying Wang1

1The Department of Radiology, Peking University First Hospital, Beijing, China, People's Republic of, 2Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China, People's Republic of, 3Philips Healthcare, Beijing, China, People's Republic of, 4Philips Healthcare (Suzhou) Co., Ltd, Suzhou, China, People's Republic of


This study aims to demonstrate the feasibility of iZOOM using a 2D RF pulse EPI sequence in the application of prostate DWI and the optimization of iZOOM at 3.0 T MRI. 58 patients took prostate MRI examination with 3 iZOOM sequences (1. b=1000, resolution: 1.4×1.4mm; 2. b=1000, resolution: 1.0×1.0mm; 3. b=2000, resolution: 1.4×1.4mm). Images were evaluated with the basic image quality, the display of lesions and overall image quality. The result shows iZOOM is feasible on prostate DWI. High b value and high resolution iZOOM are both favored by radiologists.


According to PIRADS v2 published by ACR 2014, DWI is the dominant technique in the diagnosis of prostate cancer (PCa) in peripheral zone (PZ) and an important sequence for cancer in central gland (CG). Currently, DWI is mainly based on single shot EPI (ss-EPI) sequence. For the low bandwidth on phase encoding direction in 3.0T MRI, ss-EPI sequence usually produces severe distortion and signal absence in areas of inhomogeneous magnetic field. And temporal resolution is restricted for the smaller k-space used in ss-EPI to reduce image blurring.1 By exciting a small region of interest (ROI), 2D RF could realize zoomed imaging for specific ROI, which might help in acquiring high resolution imaging, easing distortion with reduced EPI echo train length, and reducing image blurring and other artifacts from non-interesting areas.2,3 For prostate is a small organ in deep pelvis, zoomed FOV DWI (iZOOM) mentioned above is appropriate for prostate in the detection and diagnosis of PCa. The aim of our study is to demonstrate the feasibility of iZOOM using a 2D RF pulse EPI sequence in the application of prostate DWI and the optimization of iZOOM at 3.0 T MRI.

Materials and Methods:

The retrospective study was approved by IRB. 68 consecutive patients who were suspected of PCa without contraindications to MRI or MRI contrast agents were included in this study. 10 patients were out of group because of accepted therapy (radiotherapy, endocrine therapy, chemotherapy) or severe distortion caused by gas in rectum. At last totally 58 patients (mean age 65.11 ± 10.45 years, range 31–84 years) were included. MRI examinations were performed with a 3.0T MRI scanner (Philips Achieva TX, the Netherlands) using a 32-channel cardiac coil. Beside T1-weighted imaging, T2-weighted imaging, regular DWI (b=800, resolution: 3×3mm) and DCE imaging, the MRI protocol included 3 iZOOM sequences: Sequence 1. b=1000, resolution: 1.4×1.4mm; Sequence 2. b=1000, resolution: 1.0×1.0mm; Sequence 3. b=2000, resolution: 1.4×1.4mm. Other parameters for iZOOM were set as follows: FOV: 160×72×96mm, Matrix: 116×51, SENSE=1, NSA: 2×6 (b=1000)/2×10 (b=2000), TR/TE: 8075.8ms/ 56.2ms, BW:735kHz, Slice thickness: 4mm, number of slices: 22. Two experienced radiologists rated the iZOOM images (with score from 1-5: 1-point represents the best grade and 5-point represents the worst) in consensus from 3 aspects. The first is evaluation on the basic image quality included geometric distortion, susceptibility artifacts, background of PZ. The second is based on the display of lesions including delineation of the lesion and contrast between lesion and background. The third, overall image evaluation and option of the most favorite sequence(s) were made. The objective evaluation of contrast ratio was about ADC value difference of lesion and PZ to ADC value of PZ. For subjective evaluation, the statistical analysis was performed with Kruskal-Wallis test and Mann-Whitney U test (p<0.05 considered as significant difference). For objective evaluation, repeated measures analysis of variance was performed.

Results & Discussion:

The results of basic image quality, display of lesion, and overall image evaluation of 58 patients are summerized in table 1. There was no significant difference in distortion and other artifacts and the delineation of lesion among the three sequences (all p>0.05, see table 1). Sequence 3 had the best PZ background impression with statistical significance (p=0.000, <0.05, see table 1), while there was no significant difference between Sequence 1 and 2 (p=0.368, >0.05). Statistically significant differences were found in contrast between Sequence 1 and 3 both subjectively and objectively, while there was no significant difference of contrast between Sequence 2 and 3. The difference of contrast between Sequence 1 and 2 was not in accordance between subjective and objective evaluation (see table 1). The total impression showed statistically significant difference between Sequence 1 and 3, while no statistical difference between Sequence 1 and 2, Sequence 2 and 3 (p>0.05, see table 1). The results of option of favorite sequences are shown in table 2, it reflects that Sequence 2 and 3 were more preferred, especially the latter one. Further study would be done to correlate the radiographic imaging to pathology results and also the optimization the parameters of iZOOM need to be carried out as soon as possible.


Our results show that iZOOM is feasible on prostate DWI, and also demonstrates higher overall image quality with high b value (b=2000). High resolution iZOOM and high b value iZOOM are both favored by radiologists, with high b value iZOOM leading ahead, which might help in detection and staging of PCa.


No acknowledgement found.


1. Chilla G S, Cher Heng T, Chenjie X, et al. Diffusion weighted magnetic resonance imaging and its recent trend—a survey. Quant Imaging Med Surg 2015;5(3):407-422. 2. Ma C, Dan X, Kevin F, et al. Reduced FOV Excitation Using Second-Order Gradients and Spatial-Spectral RF Pulses. Magn Reson Imaging. 2013;69(2):503-508. 3. Riffel P, Henrik J M, John N M, et al. Zoomed EPI-DWI of the Pancreas Using Two-Dimensional Spatially-Selective Radiofrequency Excitation Pulses. PLoS One. 2014;9(3): e89468.


Figure1. a. b=1000s/mm2, resolution: 1.4×1.4mm; b. b=1000s/mm2, resolution: 1.0×1.0mm; c. b=2000s/mm2, resolution: 1.4×1.4mm. iZOOM demonstrates higher overall image quality with b value of 2000s/mm2.

Table 1. The overall image quality and display of lesion

Table 2. The option of sequences

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)