Korean J Radiol.  2015 Apr;16(2):297-303. 10.3348/kjr.2015.16.2.297.

Effects of MR Parameter Changes on the Quantification of Diffusion Anisotropy and Apparent Diffusion Coefficient in Diffusion Tensor Imaging: Evaluation Using a Diffusional Anisotropic Phantom

• Kim SJ
• Choi CG
• Kim JK
• Yun SC
• Jahng GH
• Jeong HK
• Kim EJ

• KMID: 2070173
• DOI: http://doi.org/10.3348/kjr.2015.16.2.297

Abstract

OBJECTIVE
To validate the usefulness of a diffusional anisotropic capillary array phantom and to investigate the effects of diffusion tensor imaging (DTI) parameter changes on diffusion fractional anisotropy (FA) and apparent diffusion coefficient (ADC) using the phantom.
MATERIALS AND METHODS
Diffusion tensor imaging of a capillary array phantom was performed with imaging parameter changes, including voxel size, number of sensitivity encoding (SENSE) factor, echo time (TE), number of signal acquisitions, b-value, and number of diffusion gradient directions (NDGD), one-at-a-time in a stepwise-incremental fashion. We repeated the entire series of DTI scans thrice. The coefficients of variation (CoV) were evaluated for FA and ADC, and the correlation between each MR imaging parameter and the corresponding FA and ADC was evaluated using Spearman's correlation analysis.
RESULTS
The capillary array phantom CoVs of FA and ADC were 7.1% and 2.4%, respectively. There were significant correlations between FA and SENSE factor, TE, b-value, and NDGD, as well as significant correlations between ADC and SENSE factor, TE, and b-value.
CONCLUSION
A capillary array phantom enables repeated measurements of FA and ADC. Both FA and ADC can vary when certain parameters are changed during diffusion experiments. We suggest that the capillary array phantom can be used for quality control in longitudinal or multicenter clinical studies.

Keyword

Diffusion tensor imaging; Fractional anisotropy; Apparent diffusion coefficient; Phantom study; Magnetic resonance imaging

MeSH Terms

Anisotropy
Diffusion Magnetic Resonance Imaging/*instrumentation/*methods
Diffusion Tensor Imaging/*instrumentation/*methods
Humans
*Phantoms, Imaging
Research Design
Signal-To-Noise Ratio

Figure

• 

  Fig. 1 Photographs of phantom and phantom installed in head coil. A. Capillary array phantom, measuring 1 cm in length and 1 cm in diameter. B. Capillary array phantom (arrow) is attached to water-filled bottle and installed in 8-channel head coil. Phantom is securely placed in syringe tube filled with distilled water and air bubble is meticulously removed.

• 

  Fig. 2 B0 (A), ADC (B), FA (C), and color-coded FA (D) images of phantom generated by post processing of DTI source images on workstation. Water-filled bottle was cropped in figures. ADC = apparent diffusion coefficient, DTI = diffusion tensor imaging, FA = fractional anisotropy

• 

  Fig. 3 SNR measurement. Signal intensity was measured on b0 images of water-filled bottle (A). ROI of 100 mm3 was placed in center of bottle (arrow). Noise image was obtained simultaneously with DTI and noise was measured in corresponding area of b0 images (B, arrow). Noise image was used to measure noise, as it is very difficult to measure noise directly in images when using parallel imaging. SNR was calculated using following equation: SNR = 1.253 × mean of object (ROI in b0 image) / mean of noise image (ROI in noise image). Factor of 1.253 is fixed factor expressing mean of noise image to standard deviation of object with signal at same location. DTI = diffusion tensor imaging, ROI = region-of-interest, SNR = signal-to-noise ratio

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