Diffusion MRI has an important role in research of the aging brain. Diffusion MRI can help elucidate the role of brain characteristics in the mechanisms supporting cognitive and motor health or leading to cognitive and motor decline in old age. Combining diffusion MRI with other imaging, clinical, neuropsychological, and most importantly neuropathologic information may provide invaluable insights towards the development of useful biomarkers of age-related diseases. To successfully accomplish the above, however, it is important to first realize the intricacies of conducting meaningful diffusion imaging investigations of the older adult brain.
The aging brain is an important neuroimaging research focus due to the significant negative impact of age-related cognitive and motor impairment on the quality of life of patients and caregivers, as well as on the health care system. Prevention, early detection and treatment of the causes that lead to cognitive and motor decline in aging are critical public health challenges. MRI is a critical tool in this fight as it contributes greatly towards our understanding of the complex role of brain characteristics in the mechanisms supporting cognitive and motor health or leading to cognitive and motor decline in old age. Multiple neuroimaging studies on older adults use MRI to a) establish the array of brain characteristics integral to cognitive and motor function in old age, b) uncover how these brain characteristics are influenced by genetic, demographic, lifestyle, neuropathologic and clinical factors, as well as interventions, and c) probe brain integrity in the preclinical stages of age-related diseases. Diffusion MRI can provide estimates of the structural integrity and connectivity of brain tissue, and therefore has a prominent role in neuroimaging research of aging.
Healthy aging has been linked to a number of changes in the brain. Gray and white matter atrophy, cortical thinning, expansion of the ventricles, demyelination, neuronal loss, white matter lesions, increased mineralization, micro infarcts, micro hemorrhages, are some of the changes that can be observed even in older adults with normal cognitive and motor function. Diffusion MRI is sensitive to age-related brain changes. Several diffusion MRI studies have shown that the diffusion anisotropy in white matter declines, and mean diffusivity increases, non-linearly with age in healthy older adults. These changes are independent of tissue loss and gender, they vary among brain structures, and are more substantial in frontal than posterior white matter. Age-related brain network changes have also been observed in older adults with normal cognitive and motor function, using structural connectivity based on diffusion imaging and tractography. In this presentation, we will provide an overview of the findings of diffusion MRI studies of healthy aging.
Dementia (such as Alzheimer’s disease, vascular dementia, dementia with Lewy bodies, Parkinson’s disease with dementia, frontotemporal dementia, etc.) is associated with brain changes above and beyond those seen in healthy aging. Diffusion imaging is sensitive to dementia-related brain abnormalities. However, since the vast majority of these brain changes are currently irreversible, early detection is crucial. Therefore, a number of studies have used diffusion imaging to characterize the early stages of disease that may lead to dementia. However, mixed neuropathologies are common in older adults and different age-related neuropathologies often have overlapping clinical manifestation. Therefore, combining diffusion imaging and neuropathologic assessment on the same older persons is crucial for the development of accurate biomarkers. In this talk, we will present diffusion imaging findings in dementia and early stages of disease, as well as efforts to link diffusion imaging and neuropathology.
Disease prevention is currently the best long-term strategy for reducing the burden of cognitive and motor impairment. Cognitive and motor reserve play a central role in prevention. The concept of reserve applies to many human physiologic systems that are highly redundant and show signs of disease only after considerable tissue damage has occurred. The nervous system has some type of reserve that can protect it from expressing pathology as cognitive and motor impairment. However, the concept of reserve is rather abstract and the exact brain characteristics that are responsible for maintaining normal cognitive and motor function in the presence of neuropathology are not well known. It is also not yet clear how various factors (e.g. lifestyle factors) that are known to enhance cognitive and motor reserve influence these brain characteristics. Diffusion imaging can be used to characterize the brain mechanisms involved in supporting and enhancing reserve.
Although diffusion imaging holds promise in research of aging, caution should be exercised and special considerations should be given to the diffusion imaging methods used to study the brain of older adults. Brain atrophy, white matter hyperintensities and other lesions typically absent from the young adult brain, can complicate voxel-wise and connectivity analyses and interpretation of results.
In conclusion, diffusion MRI has an important role in research of the aging brain. Diffusion MRI can help elucidate the role of brain characteristics in the mechanisms supporting cognitive and motor health or leading to cognitive and motor decline in old age. Combining diffusion MRI with other imaging, clinical, neuropsychological, and most importantly neuropathologic information may provide invaluable insights towards the development of useful biomarkers of age-related diseases. To successfully accomplish the above, however, it is important to first realize the intricacies of conducting meaningful diffusion imaging investigations of the older adult brain.