Assessing the Changes of Cortical Thickness in Alzheimer Disease With MRI Using Freesurfer Software.

Introduction: In this study, we intend to determine the correlation between the thickness of the cerebral cortex and the severity of the cognitive disorder in Alzheimer disease (AD).

Methods: A total of 20 (14 women and 6 men) patients diagnosed with AD with a Mean age of 72.95 years, and 10 (7 women and 3 men) cognitively normal (CN) subjects with a Mean age of 70.50 years were included in the study. Of the AD patient and CN subjects, 70% were female, and 30% were male. All individuals underwent 1.5 T Magnetic resonance imaging (MRI). The MRI scanning protocol included 3D MPRAGE (3D-T1W) sequence. All images were analyzed using Freesurfer v5.3, and then the brain cortical thickness in 7 cortical areas (inferior temporal, middle temporal, superior temporal, parahippocampal, pars triangularis, rostral middle frontal, and superior frontal) was calculated.

Results: The analysis of covariance (ANCOVA) was conducted to compare the mean thickness of each region between the patient and the control group. There was a significant difference in the mean cortical thickness in all regions. In all cases, the mean cortical thickness in CN subjects was greater than in AD patients. However, the mean thickness of pars triangularis left hand in CN subjects was not significantly greater than that in AD patients. The receiver operating characteristic system (ROC) was designed to evaluate the predictive power of the patients and the healthy people. We have selected a thousand cut-off points from 1.5 to 3.5 mm for cortical thickness. When the cut-off points were within 2.276878-2.299680 mm in the left hemisphere, Youden's index was maximum. The sensitivity and specificity, in this case, were 80%. Also, when the cut-off points were within the range of 2.263278-2.282278 mm in the right hemisphere, the sensitivity and specificity were 90% and 80%, respectively.

Conclusion: This study demonstrates the importance of quantifying the cortical thickness changes in the early diagnosis of AD. In addition, examining the pattern of changes and quantifying the reduction in the thickness of the cortex is a crucial tool for displaying the local and global atrophy of the brain. Also, this pattern can be used as an alternative marker for the diagnosis of dementia. Finally, to the best of our knowledge, our study is the first to report finding on the cortical thickness that would help the clinician have a better differential diagnosis. Also, this study has checked the possibility of early diagnosis of the disease.

Highlights: The correlation between the thickness of cerebral cortex and the severity of cognitive disorder in Alzheimer's disease was determined.The cortical thickness change is an important factor in early diagnosis of Alzheimers disease.The pattern of reduction in the thickness changes is a crucial tool for displaying the local and global atrophy of the brain.

Plain Language Summary: The neurodegenerative disorder Alzheimer's disease (AD) is a fast-growing epidemic in aging populations worldwide. In 2050, one new case of AD is estimated to increase up to every 33 seconds. So the diagnosis of AD in the early stage considerably decreases the progress of dementia and helps identify a correct treatment approach. The cortical thickness measured by structural neuroimaging has received a significant surrogate biomarker that could provide powerful tools for the early diagnosis of AD. Since the sensitivity and specificity of MRI are higher, it offers essential advantages for identifying brain atrophy patterns. The manual cortical thickness measurement methods are time-consuming and require experienced anatomists compared with automated methods. In this regard, Freesurfer software, which is a freely available program and provides information for quantifying the functional and structural features of the brain, is used. The current study demonstrates examining the pattern of changes and quantifying the reduction in the thickness of the cortex. This can also be used as an alternative marker for the early diagnosis of dementia using cortical thickness measurment that would help the physicians.