Prog Med Phys.  2019 Dec;30(4):139-149. 10.14316/pmp.2019.30.4.139.

Assessment of the Cerebrospinal Fluid Effect on the Chemical Exchange Saturation Transfer Map Obtained from the Full Z-Spectrum in the Elderly Human Brain

Affiliations
  • 1Department of Radiology, Kyung Hee University Hospital at Gangdong, College of Medicine, Kyung Hee University, Seoul, Korea. ghjahng@gmail.com
  • 2Department of Biomedical Engineering, Kyung Hee University, Yongin, Korea.

Abstract

PURPOSE
With neurodegeneration, the signal intensity of the cerebrospinal fluid (CSF) in the brain increases. The objective of this study was to evaluate chemical exchange saturation transfer (CEST) signals with and without the contribution of CSF signals in elderly human brains using two different 3T magnetic resonance imaging (MRI) sequences.
METHODS
Full CEST signals were acquired in ten subjects (Group I) with a three-dimensional (3D)-segmented gradient-echo echo-planar imaging (EPI) sequence and in ten other subjects (Group II) with a 3D gradient and spin-echo (GRASE) sequence using two different 3T MRI systems. The segmented tissue compartments of gray and white matter were used to mask the CSF signals in the full CEST images. Two sets of magnetization transfer ratio asymmetry (MTR(asym)) maps were obtained for each offset frequency in each subject with and without masking the CSF signals (masked and unmasked conditions, respectively) and later compared using paired t-tests.
RESULTS
The region-of-interest (ROI)-based analyses showed that the MTR(asym) values for both the 3D-segmented gradient-echo EPI and 3D GRASE sequences were altered under the masked condition compared with the unmasked condition at several ROIs and offset frequencies.
CONCLUSIONS
Depending on the imaging sequence, the MTR(asym) values can be overestimated for some areas of the elderly human brain when CSF signals are unmasked. Therefore, it is necessary to develop a method to minimize this overestimation in the case of elderly patients.

Keyword

CEST; Cerebrospinal fluid signal; MTR asymmetry; Sequence type; Brain-tissue degeneration
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