Abstract
In clinical practice as well as in many volumetric studies we use different reorientations of the brain position towards x and y axis on the magnetic resonance imaging (MRI) scans. In order to find out whether it has an overall effect on the resulting 2D data, manual hippocampal area measurements and rotation variability of the brain (in two reoriented axes) and the skull were performed in 23 Alzheimer's disease patients and 31 healthy controls. After the MRI scanning, native brain scans (nat) were reoriented into the two different artificial planes (anterior commissure – posterior commissure axis (AC-PC) and hippocampal horizontal long axis (hipp)). Hippocampal area and temporal horn of the lateral ventricle was measured manually using freeware Image J program. We found that 1) hippocampal area of nat images is larger compared to hipp images, area of the nat images is equal to the AC-PC images and area of the hipp images is smaller compared to AC-PC images, 2) hippocampal area together with the area of the temporal horn for nat images is larger compared to hipp images, area of the hipp images is smaller compared to the AC-PC images and area of the nat images is smaller compared to the AC-PC images. The conclusion is that the measured area of the hippocampus in the native MRI is almost the same as the area of MRI reoriented only into the AC-PC axis. Therefore, when performing 2D area studies of the hippocampus or in the clinical practice we recommend usage of not-reoriented MRI images or to reorient them into the AC-PC axis. Surprising finding was that rotation of both AC-PC and hipp line towards x-axis among patients varies up to 35° and the same is true for the skull rotation so that it is not only a matter of the brain position.
Highlights
Visualization of the medial temporal structures, especially the hippocampus, plays an important role in the clinical evaluation of the Alzheimer’s disease (AD) [1, 2]
The area of the hippocampal cross-section was measured in 54 subjects (31 controls and 23 AD patients of heterogeneous age category) in three types of brain rotation so that for each brain rotation (3x) we accounted 216 area measurements (26108 - left and right together)
In order to quantify the effect of 3 different brain positions on the hippocampal area measurement, we rotated the brain manually in the MRIcro program prior to the area measurements of the hippocampus alone and hippocampus with the temporal horn of the lateral ventricle
Summary
Visualization of the medial temporal structures, especially the hippocampus, plays an important role in the clinical evaluation of the Alzheimer’s disease (AD) [1, 2]. Most of them utilize frontal sections of the hippocampus. In order to evaluate hippocampal atrophy in neurological practice, we often look at the transition from the hippocampal alveus into the hippocampal body which we call optimal section. At this section we can observe the area of both hippocampus as well as temporal horn of the lateral ventricle in its prime (other more frontal or dorsal sections does not fully cover structure). The absolute position of the brain structures commonly used for evaluation, such as anterior and posterior commissure and the hippocampus may vary for example due to cellular changes accompanying aging process [4]
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