3863

An Innovative MRI phantom Allowing Evaluation of the Influence of Fat Fraction on the Measurement of ADC under Different Glass Bead Densities
Jo-Hua Peng1, Chun-Jung Juan1,2,3, Yi-Jui Liu4, Ruey-Hwang Chou5, Hing-Chiu Chang6, Chang-Hsien Liou2,7, Szu-Hsien Chou1,2, Yen-Ting Wu1,2, Bai-Wen Wu2, and Hsu-Hsia Peng1
1Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, 2Department of Medical Imaging, China Medical University Hsinchu Hospital, Hsinchu, Taiwan, 3Department of Radiology, School of Medicine, China Medical University, Taichung, Taiwan, 4Department of Automatic Control Engineering, Feng Chia University, Taichung, Taiwan, 5Institute of Cancer Biology, China Medical University, Taichung, Taiwan, 6Department of Biomedical Engineering, Chinese University of Hong Kong, Sha Tin, Hong Kong, 7Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu, Taiwan

Synopsis

Although a single-function phantom for either ADC or fat content is popular, it is crucial to develop a multiple-function phantom to simulate the real situation of human tissue in vivo. The aim of our study was to design a novel phantom containing different fat fractions and cellularity to evaluate the effect of fat content on ADC measurement in vivo as in human tissue environment. In conclusion, the influence of fat contents and glass beads density on ADC values was examined in our dual-function phantom, which can be helpful to improve the accuracy of ADC quantification in clinical practice.

Introduction

By measuring tissue characteristics in addition to anatomic information, MRI has provided some imaging biomarkers1 quantifying brain volume2, tumor volume3, functional network connectivity4, fat fraction5 and diffusion of tissue water6. Diffusion-weighted imaging (DWI) can measure proton diffusion information (i.e., apparent diffusion coefficient, ADC)6, while IDEAL IQ sequence allows us to measure the fat fraction of tissue7. In order to increase the reliability and comparability of data gathered from MR biomarkers, standardization of imaging protocols and calibration of measures using MR phantoms are necessary to validate the accuracy of these measures in vivo8. For example, diffusion phantom and water-fat phantom have been designed for measuring ADC9 and fat fraction10, respectively. Clinically, the ADC measurement in fatty tissue, such as breast11 and parotid gland12, has been shown to be influenced by the fat content. Although a single-function phantom for either ADC or fat content is popular, it is crucial to develop a multiple-function phantom to simulate the real situation of human tissue in vivo. The aim of our study was to design a novel phantom containing different fat fractions and cellularity to evaluate the effect of fat content on ADC measurement in vivo as in human tissue environment.

Materials and Methods

Phantom design: An ensemble of phantoms consisting of six different fat fractions (FF, 0%, 10%, 20%, 30%, 40%, and 50%) and five different glass bead densities (GBD, 0, 0.1, 0.25, 0.5 and 1.0 g/50cc.) was created using mixtures of soybean oil, glass particles (#K37,3M microspheres, Easy Composites Ltd.)9, and water together with an emulsifying agent (Trion X-100)13 and a coagulant (agarose)14. MRI scans: All images were performed by a 1.5 Tesla MR scanner (GE Signa MR450w, GE Healthcare). IDEAL IQ sequence was applied to quantify the fat fraction of phantom8. The IDEAL IQ method was a three-dimensional fast spoiled gradient-echo (3D-FSPGR) sequence employing a six-echo acquisition (1.1ms-6.38ms) with imaging parameters including TR of 19.6ms, FOV of 210×210 mm2, matrix size of 128×128, bandwidth of 90.91 kHz, flip angle of 5, and slice thickness of 10mm. DWI was performed using single-shot echo planar imaging with water excitation and the scanning parameters of TR of 4000 ms, TE of 78.1 ms, b values of 0 and 1000 $$$s/mm^{2}$$$, FOV of 210×210 mm2, slice thickness of 10 mm, matrix size of 128×128, and bandwidth of 250 kHz. Data processing: Proton density fat fraction (PDFF) maps were automatically produced by the MRI scanner. ADC maps were generated via pixel-by-pixel computation from b0 and b1000 images based on the Stejskal–Tanner relationship：$$$ADC=ln[S_{b=1000}/S_{b=0}]/(-b)$$$. A slice containing the largest cross-sectional area of the phantom was chosen for ROI selection to circle whole tube in every DWI and IDEAL IQ scans. Then the values of mean and standard deviations (SD) were calculated for analysis. Linear regression analysis was used to evaluate the relationship among the fat, GBD, and ADC measures.

Result

Five cylinders containing solidified agarose-based emulsions with FF of 10%, 20%, 30%, 40%, and 50% from left to right, respectively, were demonstrated (Fig.1a). Microscopic images of 10% (right column) and 50% (left column) FF tubes with GBD of 0 (upper row), 0.1 g/50cc (middle row), and 0.5 g/50cc (lower row) were illustrated (Fig. 1b), showing the distribution and arrangement of fat droplets, glass beads, and water in the emulsion. Scatter plots show high linearity (slope 1~1.05) and small bias (-0.17%~2.04%) of FF between PDFF maps and phantoms at different GBDs (Fig. 2). Fig. 3 displays the relationship between ADC and FF without glass beads (GBD=0). Fig. 4 displays the relationship between ADC and GBD without fat content (FF=0). Fig. 5 displays the relationship between ADCs and FF at different GBDs.

Discussion and Conclusion

In this study, an innovative, dual-function phantom was designed for the quantitative measurement of ADC and fat fraction. Results showed the high accuracy of fat fraction in our phantom (Fig. 2) irrelevant to glass particles. In the diffusion phantom, the ADC decreased as the density of glass beads increased because of the reduction in diffusion space of proton, which is similar to a previous study9. However, our results that ADC in phantom with GBD of 0 is negatively proportional to the fat fraction of phantom due to the characteristic of tiny diffusion in oil15 and that ADC decreased by effects from both fat fraction and glass density are unique. In conclusion, the influence of fat contents and glass beads density on ADC values was examined in our dual-function phantom, which can be helpful to improve the accuracy of ADC quantification in clinical practice.

Acknowledgements

No acknowledgement found.

References

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Figures

Figure 1. (a) A fat fraction phantom was constructed to simulate human tissue. (b) Photomicrographs (40×) of phantom with 10% FF and 50% FF.

Figure 2. (a) PDFF maps of IDEAL IQ in 10%, 20%, 30%, 40%, and 50% FF (top to down), and in 0, 0.1, 0.25, and 0.5 g/50c.c. PD (left to right) . (b) FF distribution with different PD in between fat fraction map and fat fraction of phantom.

Figure 3. (a) DWI (b0 and b1000) and ADC with FF 10%, 30%, and 50%. (b) The scatter plot showing the relationship in the phantom (0 between ADC (mean and SD) and phantom FF.

Figure 4. (a) DWI (b0 and b1000) and ADC with DB 0, 0.5, and 1 g/cc. (b)The linear relation of the mean and SD of ADC measured along with different density of beads.

Figure 5. (a) DWI (b0 and b1000) and ADC in BD 0.5 g/cc with FF 10%, 30%, and 50%. (b) ADCs at different BD (0, 0.1, 0.25, 0.5 and 1.0 g/50cc.) with respect to different phantom FF (0%, 10%, 20%, 30%, 40%, and 50%)

Proc. Intl. Soc. Mag. Reson. Med. 30 (2022)
3863
DOI: https://doi.org/10.58530/2022/3863