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
Synopsis
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.Purpose:
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.
Conclusion:
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.
Acknowledgements
No acknowledgement found.References
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