Several studies reported that high b value DWI (b>1000 s/mm2) of prostate had potential to increase diffusion weighting, diminish T2 shine-through, and provide a higher contrast-to-noise ratio to improve the diagnostic performance of prostate cancer.^1,2 The disadvantages are increased motion and susceptibility artifacts, as well as decreased SNR.² Improved Zoomed Field of View DWI (iZOOM) was proposed with a 2D RF pulse applied on EPI DWI. A new algorithm of tilt was added to the RF pulse to excite the k-space.^3,4 It could reduce the FOV on the phase-encoding direction and has the possibility to overcome or alleviate problems caused by high b values by decreasing the echo train length and maintaining the RF sub-pulse bandwidth. Our aim was to assess the clinical feasibility of high b value (b=2000 s/mm2) iZOOM on prostate and to validate whether it is superior to regular DWI based on ss-EPI sequences at 3.0 T.

71 consecutive patients suspected of prostate cancer were included in our study. 13 patients who used to accept clinical therapy (endocrine therapy, radiotherapy, chemotherapy) or the DW images had severe distortion because of intestinal gas were excluded. Finally 58 patients (mean age 65.11 ± 10.45 years, range 31–84 years) were included in this study in total. Of them, 22 patients were diagnosed as noncancerous patients. And 36 patients were suspected to have prostate cancer and totally 50 lesions were got. This study was retrospective and was approved by local IRB. All the patients had no contraindications to enhanced MRI examination. Every patient was informed and signed the informed consent. A 3.0 T MRI scanner (Philips Achieva TX, Best, the Netherlands) with a 32-channel cardiac coil was adopted in the MRI examination. The MRI protocol included iZOOM and DWI, with the same b value of 2000s/mm2with parameters shown in Table 1.

The evaluation included three aspects: (1). The basic image quality: a). Geometric distortion b). Susceptibility artifacts c). Background of peripheral zone (PZ); (2). The display of lesions: a). Subjective: i. Contrast of lesion to background ii. Delineation of the lesion b) Objective: contrast-- the ratio of the ADC value difference between the lesion and the PZ background to that of PZ; (3). The comprehensive evaluation: comprehensive consideration of the former two aspects.

Regions of interest (ROIs) on ADC maps for measuring ADC value were manually drawn in areas of suspected lesions and normal PZ. Then we copied and pasted them to the other ADC map of the same patients. With these values we calculated the contrast of ADC. The statistical method for objective evaluation of contrast was repeated measures analysis of variance. Except the contrast of ADC value, all the other evaluations were subjective. Two radiologists carried out the subjective evaluation in consensus with a 5-point scoring system (from 1-point representing the best grade to 5-point representing the worst). Kruskal-Wallis test and Mann-Whitney U test (P<0.05 considered as significant difference) was used to evaluate the statistical significance of subjective evaluations by using IBM SPSS Statistics 20.0 (Armonk, New York, USA).

Representative case is shown in Figure 1(Figure1a and Figure 1b). For basic image quality assessment (see Table 2), iZOOM was better than regular DWI in aspects of artifact, distortion, which was statistically significant (p=0.000, < 0.05). There was no statistical difference of PZ background impression between IZOOM and DWI (p=0.433, >0.05). Although iZOOM showed relatively better scores, there was no statistically significant difference in subjective assessment of contrast (p=0.135, >0.05), delineation of lesion (p=0.052, >0.05), and objective assessment of contrast (p=0.324, >0.05, see Table 3). The comprehensive evaluation considering the basic image quality and the display of lesions demonstrated that there was statistical difference between iZOOM and regular DWI (p=0.000, <0.05, see Table 2), with a better overall image quality in iZoom.Our study shows that high b value (b=2000) iZOOM has better comprehensive image quality, less artifact and distortion yet similar contrast compared with regular high b value DWI. Further studies are still needed to correlate the pathology with imaging presentation.