Korean J Radiol.  2019 Jul;20(7):1138-1145. 10.3348/kjr.2018.0899.

Analysis of Apparent Diffusion Coefficients of the Brain in Healthy Controls: A Comparison Study between Single-Shot Echo-Planar Imaging and Read-out-Segmented Echo-Planar Imaging

• Choi Y
• Hwang EJ
• Nam Y
• Choi HS
• Jang J
• Jung SL
• Ahn KJ
• Kim BS

• KMID: 2467024
• DOI: http://doi.org/10.3348/kjr.2018.0899

Abstract

OBJECTIVE
To compare apparent diffusion coefficients (ADCs) of brain segments by using two diffusion-weighted imaging acquisition modes, single-shot echo-planar imaging (ss-EPI) and read-out-segmented echo-planar imaging (rs-EPI), and to assess their correlation and agreement in healthy controls.
MATERIALS AND METHODS
T2-weighted (T2W) images, rs-EPI, and ss-EPI of 30 healthy subjects were acquired using a 3T magnetic resonance scanner. The T2W images were co-registered to the rs-EPI and ss-EPI, which were then segmented into the gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) to generate masking templates. ADC maps of rs-EPI and ss-EPI were also segmented into the GM, WM, and CSF by using the generated templates. ADCs of rs-EPI and ss-EPI were compared using Student's t tests and correlated using Pearson's correlation coefficients. Bland-Altman plots were used to assess the agreement between acquisitions.
RESULTS
ADCs of rs-EPI and ss-EPI were significantly different in the GM (p < 0.001) and WM (p < 0.001). ADCs showed high agreement and correlation in the whole brain and CSF (r > 0.988; p < 0.001). ADC of the WM showed the least correlation (r = 0.894; p < 0.001), and ADCs of the WM and GM showed poor agreement. Pearson's correlation equations for each brain segment were y = 1.1x - 59.4 (GM), y = 1.45x - 255 (WM), and y = 0.98x - 63.5 (CSF), where x and y indicated ADCs of rs-EPI and ss-EPI, respectively.
CONCLUSION
While ADCs of rs-EPI and ss-EPI showed high correlation and agreement in the whole brain and CSF, ADCs of the WM and GM showed significant differences and large variability, reflecting brain parenchymal inhomogeneity due to different regional microenvironments. ADCs of different acquisition methods should be interpreted carefully, especially in intra-individual comparisons.

Keyword

Apparent diffusion coefficient; Diffusion-weighted imaging; Single-shot echo-planar imaging; Read-out-segmented echo-planar imaging; Magnetic resonance imaging

MeSH Terms

Brain*
Cerebrospinal Fluid
Diffusion*
Echo-Planar Imaging*
Gray Matter
Healthy Volunteers
Magnetic Resonance Imaging
Masks
White Matter

Figure

• 

  Fig. 1 Representative images of 55-year-old healthy subject.A, B. rs-EPI at b = 0 and b = 1000. D, E. ss-EPI at b = 0 and b = 1000. ADC map of whole brain calculated using rs-EPI (C) and ss-EPI (F). G. Mask template of WM, GM, and CSF. ADC = apparent diffusion coefficient, CSF = cerebrospinal fluid, GM = gray matter, rs-EPI = read-outsegmented echo-planar imaging, ss-EPI = single-shot echo-planar imaging, WM = white matter

• 

  Fig. 2 Box plots for ADCs of rs-EPI and ss-EPI in whole brain (A), GM (B), WM (C), and CSF (D).Corresponding p values between two ADCs are shown in upper left corners.

• 

  Fig. 3 Scatter plots with estimated Pearson's correlation lines and 95% confidence intervals of whole brain (A), GM (B), WM (C), and CSF (D).

• 

  Fig. 4 Bland-Altman plots show variability in ADCs between rs-EPI and ss-EPI of whole brain (A), GM (B), WM (C), and CSF (D).Mean ADC differences and limits of agreements (1.96 times standard deviation) are displayed; all units are in 10−6 mm2/s.

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