a,b,c Examples of the sagittal view of the right hippocampus on the MRI in one native and two reoriented axis.

<p>MRI sections were selected according to the best visibility of the of the hippocampus on the sagittal sections (its long or dorsoventral axis), a) position of the hippocampus on the “native” MRI scan, b) reorientation of the “native” MRI scan into the hipo-axis axis (where long axis of the hippocampus is parallel to the horizontal axis), c) reorientation of the “native” MRI scan into the CA-CP. White lines represent long axis of the hippocampus.</p

Hippocampal Spatial Position Evaluation on MRI for Research and Clinical Practice

<div><p>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, <i>native brain scans</i> (nat) were reoriented into the two different artificial planes (<i>anterior commissure – posterior commissure</i> axis (AC-PC) and <i>hippocampal horizontal long axis</i> (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.</p></div

Effects of the brains rotations on the area measurements of the hippocampus on the MRI.

<p>Three groups are presented on the x-axis – nat (as the unaltered MRI scans were exported for 2D area analysis), hipp (x-axis is parallel to the long axis of the hippocampus) and AC-PC (x axis is parallel to the line connecting <i>anterior</i> and <i>posterior commissure</i>). On the y-axis, 2D area values of the hippocampi in mm² are presented. Results are presented as median ± min-max.</p

Skull rotation variability in MRI.

<p>Skull dorsal and ventral skull rotation expressed as Frankfurt plane angles in decimal degree on x-axis (- counter clockwise rotation or dorsal and + clockwise rotation or ventral).</p

Example of manual anatomical delineation of the hippocampus (white line with grey area inside) and temporal horn of the lateral ventricle (white line with black area inside) on the left and right side.

<p>Coronal sections of the MRI are located at the transition from the <i>alveus</i> of the hippocampus into the hippocampal body.</p

Relationship between brain and skull rotation.

<p>The brain rotation in AC-PC axis and the skull rotation (Frankfurt plane) exhibit a similar degree of variability (- counter clockwise or dorsal). AC-PC axis, Mean  = -8.57°, SE = 9.2°. Frankfurt (auriculo-orbital) plane, Mean  = −16.3°, SE = 8.02°.</p

Brain rotation variability of AC-PC vs nat on MRI.

<p>The extent of the brain rotation in AC-PC vs nat is shown in decimal degrees on x-axis (– counter clockwise and + clockwise rotation) (p<0.05).</p

Brain rotation variability of hipp vs nat on MRI.

<p>Data showing difference between left and right hipp axes (in the left and right hemisphere). There is a significant difference between left hipp axis rotation in the AD patients compared to the controls (p = 0.008). The right hipp axis rotation in the AD patients compared to the controls are not significant (p = 0.08). ANOVA F (2, 51)  = 2.54.</p