Is voxel-based apparent diffusion coefficient reproducible?
Masamitsu Hatakenaka1, Koichi Onodera1, Naomi Koyama1, and Mitsuhiro Nakanishi2

1Diagnostic Radiology, Sapporo Medical University, Sapporo, Japan, 2Division of Radiology, Sapporo Medical University Hospital, Sapporo, Japan

Synopsis

To evaluate reproducibility of voxel-based ADC, voxel-based ADC of the phantom was measured using clinical 3T MRI system. The direction of motion probing gradient affected the voxel-based ADC significantly in both echo planar imaging and turbo spin echo diffusion-weighted imaging. Also voxel-based ADC differed both between identical positioning examinations and between slightly different positioning examinations. Voxel-based ADC could not be reproduced sufficiently even in a phantom study. It would be recommended to pay enough attention when performing voxel-based ADC study like histogram analysis for tumor ADC.

Purpose

To evaluate reproducibility of voxel-based apparent diffusion coefficient (ADC).

Materials and Methods

ADC of the phantom containing 0.2 mM gadolinium and 80% polyvinyl alcohol (Nikkofines (90-401 type), Tokyo, Japan) was measured in a whole-body 3T clinical MRI system (Ingenia, Philips Medical Systems, Best, The Netherland). The measurements were performed three times for diffusion weighted imaging with both single shot echo planar imaging (DWI-EPI) (Fig. 1) and multi-shot turbo spin echo (DWI-TSE) (Fig. 2) . 1st and 2nd examinations were performed at an identical positioning and 3rd examination was done at a slightly different positioning. The sequence parameters were as follows: field of view=220 mm, matrix size=112x112, number of averages=4, slice thickness=4 mm, SENS factor=2, repetition time=3000 ms, echo time=81.1 ms for DWI-EPI and 87.6 ms for DWI-TSE, b-factor=0 and 1000 s/mm2, three orthogonal motion proving gradients (MPG). Each voxel ADC was calculated by fitting signal intensity change within the region of interest containing 197 voxels into mono-exponential curve. ADCs measured by DWI-EPI and DWI-TSE with right-to-left, anterior-to-posterior, foot-to-head motion probing gradients, and three synthesized imaging were described as ADC-EPI-RL, ADC-EPI-AP, ADC-EPI-FH, ADC-EPI-ISO, ADC-TSE-RL, ADC-TSE-AP, ADC-TSE-FH, and ADC-TSE-ISO, respectively. And ADCs from 1st, 2nd, and 3rd examinations were differentiated by adding 1, 2, and 3 at the end, for example ADC-EPI-RL1 means ADC calculated by 1st DWI-EPI with right-to-left MPG. The voxel-based ADCs measured by several sequences were compared using paired t-test and t-test for evaluating MPG direction effect (ADC-EPI-RL vs. ADC-EPI-AP vs. ADC-EPI-FH, and ADC-TSE-RL vs. ADC-TSE-AP vs. ADC-TSE-FH) and reproducibility using both identical (1st ADC-EPI vs. 2nd ADC-EPI, and 1st ADC-TSE vs. 2nd ADC-TSE) and not identical positioning (1st ADC-EPI vs. 3rd ADC-EPI, and 1st ADC-TSE vs. 3rd ADC-TSE). p<0.05 was considered statistically significant.

Results

Regarding effect of different MPG directions (Fig. 3), significant difference was observed between ADC-EPI-RL1 and ADC-EPI-AP1, between ADC-EPI-AP1 and ADC-EPI-FH1, between ADC-TSE-RL1 and ADC-TSE-AP1, and between ADC-TSE-RL1 and ADC-TSE-FH1. Regarding reproducibility for identical positioning (Fig. 4), significant difference was observed between ADC-EPI-RL1 and ADC-EPI-RL2, between ADC-EPI-ISO1 and ADC-EPI-ISO2, and between ADC-TSE-FH1 and ADC-TSE-FH2. Regarding reproducibility for different positioning (Fig. 5), significant difference was observed in all DWI-EPI and DWI-TSE comparisons between 1st and 3rd examinations except between ADC-TSE-AP1 and ADC-TSE-AP3.

Discussion

The present study demonstrated that voxel-based ADC could not be reproduced using even phantom. Many studies have been reported regarding histogram analysis based on voxel-based ADC distribution1-4. We consider enough attention should be payed when analyzing voxel-based ADC distribution.

Voxel-based ADC values differed among different MPG directions in both DWI-EPI and DWI-TSE. As phantom was considered having no anisotropy, these differences could be originated in the difference of MPG strength and/or image distortion. Voxel-based ADC values differed between 1st and 2nd identical position examinations. As DWI-EPI showed significant difference in 2 comparisons, between ADC-EPI-RL1 and ADC-EPI-RL2 and between ADC-EPI-ISO1 and ADC-EPI-ISO2 but DWI-TSE showed significance in only between ADC-TSE-FH1 and ADC-TSE-FH2, this difference may be due to strong distortion artifact in DWI-EPI and/or low signal-to noise ratio of DWI-TSE. Voxel-based ADC values differed between 1st and 3rd slightly different position examinations even in synthesized images. We consider this result should be kept in mind when analyzing sequential voxel-based ADC histogram changes of tumor, e.g. pre- and post-chemoradiotherapy.

Conclusion

The reproducibility of voxel-based ADC is not high enough even in a phantom study. It would be recommended to pay enough attention when performing voxel-based ADC study like histogram analysis for tumor ADC.

Acknowledgements

No acknowledgement found.

References

1. Donati OF, Mazaheri Y, Afaq A, et al. Prostate cancer aggressiveness: assessment with whole-lesion histogram analysis of the apparent diffusion coefficient. Radiology 2014;271(1):143-152.

2. Liang HY, Huang YQ, Yang ZX, Ying D, Zeng MS, Rao SX. Potential of MR histogram analyses for prediction of response to chemotherapy in patients with colorectal hepatic metastases. European radiology 2015.

3. Lin Y, Li H, Chen Z, et al. Correlation of histogram analysis of apparent diffusion coefficient with uterine cervical pathologic finding. AJR American journal of roentgenology 2015;204(5):1125-1131.

4. Rodriguez Gutierrez D, Manita M, Jaspan T, Dineen RA, Grundy RG, Auer DP. Serial MR diffusion to predict treatment response in high-grade pediatric brain tumors: a comparison of regional and voxel-based diffusion change metrics. Neuro-oncology 2013;15(8):981-989.

Figures

Figure 1: DWI-EPI(1st examination)

A: DWI-EPI at b=0, B: DWI-EPI at b=1000 s/mm2 with RL MPG, C: signal intensity of each voxel of A, D: signal intensity of each voxel of B


Figure 2: DWI-TSE (1st examination)

A: DWI-TSE at b=0, B: DWI-TSE at b=1000 s/mm2 with RL MPG, C: signal intensity of each voxel of A, D: signal intensity of each voxel of B


Figure 3: Comparison of ADC-EPI among different MPG derections

Figure 4: Comparison of ADC-EPI between identical positioning

Figure 5: Comparison of ADC-EPI between different positioning



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