Abstract
PurposeThe diffusion tensor image analysis along the perivascular space (DTI-ALPS) method was developed to evaluate the brain’s glymphatic function or interstitial fluid dynamics. This study aimed to evaluate the reproducibility of the DTI-ALPS method and the effect of modifications in the imaging method and data evaluation.Materials and methodsSeven healthy volunteers were enrolled in this study. Image acquisition was performed for this test–retest study using a fixed imaging sequence and modified imaging methods which included the placement of region of interest (ROI), imaging plane, head position, averaging, number of motion-proving gradients, echo time (TE), and a different scanner. The ALPS-index values were evaluated for the change of conditions listed above.ResultsThis test–retest study by a fixed imaging sequence showed very high reproducibility (intraclass coefficient = 0.828) for the ALPS-index value. The bilateral ROI placement showed higher reproducibility. The number of averaging and the difference of the scanner did not influence the ALPS-index values. However, modification of the imaging plane and head position impaired reproducibility, and the number of motion-proving gradients affected the ALPS-index value. The ALPS-index values from 12-axis DTI and 3-axis diffusion-weighted image (DWI) showed good correlation (r = 0.86). Also, a shorter TE resulted in a larger value of the ALPS-index.ConclusionALPS index was robust under the fixed imaging method even when different scanners were used. ALPS index was influenced by the imaging plane, the number of motion-proving gradient axes, and TE in the imaging sequence. These factors should be uniformed in the planning ALPS method studies. The possibility to develop a 3-axis DWI-ALPS method using three axes of the motion-proving gradient was also suggested.
Highlights
Since the introduction of the glymphatic system hypothesis by Illif et al [1], increasing number of studies have attempted to describe the fluid dynamics in the brain parenchyma [2,3,4,5,6]
As the impairment of neurofluid dynamics is closely associated with various pathologies, the concept of ‘central nervous system (CNS) interstitial fluidopathy’ has been proposed to indicate the pathologies caused by the abnormal neurofluid dynamics [9]
The follow-up tracer studies used the intrathecal administration of gadolinium-based contrast agent (GBCA) on MRI [32, 33]
Summary
Since the introduction of the glymphatic system hypothesis by Illif et al [1], increasing number of studies have attempted to describe the fluid dynamics in the brain parenchyma [2,3,4,5,6]. According to glymphatic system hypothesis, fluid movement in the brain’s interstitium causes the excretion of waste products within the brain. Japanese Journal of Radiology collective term for the fluids in which the central nervous system (CNS) is immersed, including the blood, cerebrospinal fluid, and interstitial fluid [8]. This concept helps explore and understand the fluid dynamics within the brain parenchyma. As the impairment of neurofluid dynamics is closely associated with various pathologies, the concept of ‘CNS interstitial fluidopathy’ has been proposed to indicate the pathologies caused by the abnormal neurofluid dynamics [9]
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