Investigated regional apparent diffusion coefficient values of the morphologically normal feline brain

Abstract

Objectives: Diffusion-weighted imaging (DWI) MRI is increasingly available in veterinary medicine for investigation of the brain. However, apparent diffusion coefficient (ADC) values have only been reported in a small number of cats or in research settings. The aim of this study was to investigate the ADC values of different anatomical regions of the morphologically normal brain in a feline patient population. Additionally, we aimed to assess the possible influence on the ADC values of different patient-related factors, such as sex, body weight, age, imaging of the left and right side of the cerebral hemispheres and white vs grey matter regions.

Methods: This retrospective study included cats undergoing an MRI (3T) examination with DWI sequences of the head at the Vetsuisse Faculty of the University Zurich between 2015 and 2021. Only cats with morphologically normal brains were included. On the ADC maps, 10 regions of interest (ROIs) were manually drawn on the following anatomical regions: caudate nucleus; internal capsule (two locations); piriform lobe; thalamus; hippocampus; cortex cerebri (two locations); cerebellar hemisphere; and one ROI in the centre of the cerebellar vermis. Except for the ROI at the cerebellar vermis, each ROI was drawn in the left and right hemisphere. The ADC values were calculated by the software and recorded.

Results: A total of 129 cats were included in this study. The ADC varied in the different ROIs, with the highest mean ADC value in the hippocampus and the lowest in the cerebellar hemisphere. ADC was significantly lower in the white cerebral matter compared with the grey matter. ADC values were not influenced by age, with the exception of the hippocampus and the cingulate gyrus.

Conclusion and relevance: ADC values of different anatomical regions of the morphologically normal feline brain in a patient population of 129 cats in a clinical setting are reported for the first time.

Keywords: ADC; DWI; MRI; Magnetic resonance imaging; apparent diffusion coefficient.

Figure 1

Transverse apparent diffusion coefficient (ADC) maps showing the region of interest (ROI) drawn on: (a) the right caudate nucleus and left rostral internal capsule; (b) right piriform lobe and left caudal internal capsule; (c) left thalamus and right hippocampus; (d) cingulate gyrus; (e) frontal lobe; and (f) right cerebellar hemisphere and cerebellar vermis. Except for the cerebellar vermis, all the ROIs were drawn on the right and on the left side. Note the limited spatial resolution of the ADC map. The left side is on the right side of the image. Border ROI thickness has been increased for representative purposes. Typically, the ROIs were drawn as follows: on the head of the caudate nucleus; on the rostral and caudal internal capsule (rostral at the level of the head of the caudate nucleus or one slice caudally; and caudal, one slice apart from the rostral localisation); on the piriform lobe in the area of its best definition and largest extent; on the thalamus hemisphere as published; on the ventral hippocampus (at the level of the ROI on the thalamus or one slice caudally); on the cortex cerebri at the level of the cingulate gyrus and of the frontal lobe; on the cerebellar hemispheres at the level of the their best definition and largest extent; and sagittal on the cerebellar vermis where most clearly identified

Figure 2

Boxplot of the mean apparent diffusion coefficient (ADC) in the different anatomical regions (× 10^–3 mm²/s). Light blue boxes: white matter; grey boxes: grey matter; dark blue boxes: grey and white matter combined. For each plot, the box represents the 25th to 75th percentiles, the horizontal line represents the median and the cross represents the mean. Whiskers represent the highest value within 1.5-times the interquartile range (IQR) and the lowest value within 1.5-times the IQR. Circles represent the outliers