Dependence of apparent diffusion coefficient on slice position in magnetic resonance diffusion imaging

Yasuo Takatsu; Masafumi Nakamura; Yuichi Suzuki; Tosiaki Miyati

doi:10.1016/j.mri.2023.01.009

Dependence of apparent diffusion coefficient on slice position in magnetic resonance diffusion imaging

Magn Reson Imaging. 2023 Jun:99:41-47. doi: 10.1016/j.mri.2023.01.009. Epub 2023 Jan 20.

Authors

Yasuo Takatsu¹, Masafumi Nakamura², Yuichi Suzuki³, Tosiaki Miyati⁴

Affiliations

¹ Molecular Imaging, School of Medical Sciences, Fujita Health University, 1-98, Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan; Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan. Electronic address: yasuo.takatsu@fujita-hu.ac.jp.
² Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan; Department of Radiology, Otsu City Hospital, 2-9-9, Motomiya, Otsu-City, Shiga 520-0804, Japan. Electronic address: nakamura-xx@leto.eonet.ne.jp.
³ Department of Radiology, The University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
⁴ Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan. Electronic address: ramiyati@mhs.mp.kanazawa-u.ac.jp.

PMID: 36682397
DOI: 10.1016/j.mri.2023.01.009

Abstract

Purpose: The position dependence of the apparent diffusion coefficient (ADC) in magnetic resonance imaging (MRI) by echo-planar imaging (EPI)- and turbo spin echo (TSE)-diffusion-weighted imaging (DWI) was assessed using phantoms.

Methods: Six pure water-filled containers were placed parallel to the direction of the static magnetic field from the center of the magnetic field to the foot direction (five containers) and the head direction (one container). Six slice positions were set, and a cross-section image was scanned at the center of each container using a 1.5-T MRI scanner. Diffusion times for both EPI- and TSE-DWI were matched as much as possible. The slice thickness was adjusted to match the signal-to-noise ratio (SNR) at the center of the magnetic field for both sequences. A B₁ map was analyzed. The ADC and SNR at each position of both sequences were tested using the Wilcoxon signed-rank test (P = 0.05) and compared using Friedman and Steel-Dwass multiple comparison tests (P = 0.05). Pearson correlation coefficients between ADC and SNR and between ADC and flip angle (FA) were calculated.

Results: ADC decreased significantly with distance from the center of the magnetic field for both EPI-DWI and TSE-DWI (P < 0.05). TSE-ADC was significantly higher than EPI-ADC for all combinations (P < 0.01). Based on the Friedman test, the SNR of EPI- and TSE-DWI was significantly different and depended on the slice position (P < 0.01). The Pearson correlation coefficient between ADC and SNR was 0.78 in EPI-DWI and 0.60 in TSE-DWI, whereas that between ADC and FA was 0.97 in EPI-DWI and 0.94 in TSE-DWI. The FA decreased by 0.048 and 0.047° per mm from the center of the magnetic field to head and foot directions, respectively.

Conclusion: ADC depends on the slice position and decreases with an increase in distance from the magnetic field center. Caution should be taken when comparing and quantitatively evaluating the ADC at sites shifted in the long-axis direction.

Keywords: Apparent diffusion coefficient; Diffusion-weighted image; Magnetic resonance imaging; Signal-to-noise ratio; Turbo spin echo.

MeSH terms

Diffusion Magnetic Resonance Imaging* / methods
Echo-Planar Imaging / methods
Magnetic Resonance Imaging* / methods
Magnetic Resonance Spectroscopy
Reproducibility of Results
Signal-To-Noise Ratio