Currently Available Neuroimaging Approaches in Alzheimer Disease (AD) Early Diagnosis

Abstract

Computerized Tomography (CT)Nowadays CT is not considered a standard technique for diagnosing AD, least of all in early stages. Its main usefulness is in differential diagnosis since it is less expensive, faster and more widely available than MRI. CT allows ruling out some clinical situations which lead to MEGMeasures magnetic fields and, indirectly, yields rather precise information about brain electrical activity CT = computerized tomography; MRI = magnetic resonance imaging; fMRI = functional magnetic resonance imaging; DTI = diffusion tensor imaging; SPECT = single-photon emission computed tomography; PET = positron emission tomography; MEG = magnetoencephalography; BOLD = blood oxygen level-dependent; NAA = N-acetyl aspartate; Cr = Creatinine; AD = Alzheimer's disease Table 1. Typical findings of different brain imaging methods used in AD and MCI diagnosis Magnetic Resonance Imaging (MRI) 1.2.1 Structural MRIThis technique provides the best possible spatial resolution. Given the fact the most robust neuroimaging finding in AD is the atrophy of mesial temporal structures, structural MRI is the most widely used approach. Hippocampal atrophy is another well known finding, but atrophy within other brain areas has also been described in entorrhinal cortex, amygdala, basal ganglia (nucleus basalis of Meynert), thalamus and bilateral parietal cortex. It is relevant to mention here that in terms of early diagnosis some consider the entorrhinal cortex as the earliest area affected by AD. Other researchers have stated that the nucleus basalis of Meynert is a key structure in AD early diagnosis (Herholz et al, 2004;Grothe et al, 2010). Functional MRI (fMRI)fMRI provides signal intensities images associated with a relative cerebral blood flow during cognitive tasks. Resting and activation functional MRI studies have showed a lesser coordinated activity in the hippocampus, inferior parietal lobes -both bilaterally-and cingulate cortex in patients with AD. This neuroimaging technique is nowadays used to monitor AD patients' treatment. Combining genetic risk with functional MRI memory task paradigms has shown to be a very accurate pre-symptomatic predictor of cognitive decline. Diffusion Tensor Imaging (DTI)DTI allows visualizing neuronal connectivity or, more precisely, local fiber orientation and white matter tracts integrity. Patients with AD show decreased fiber density in temporal white matter, probably related to the medial temporal grey matter atrophy, as well as in the splenium of the corpus callosum. www.intechopen.com Currently Available Neuroimaging Approaches in Alzheimer Disease (AD) Early Diagnosis 149In mild cognitive impairment (MCI), however, this decreased fiber density has been located in the anterior part of the corpus callosum. SpectroscopyIt provides information on tissue substrate or metabolite concentrations. Specifically the Nacetyl aspartate (NAA) has been used as a biomarker of neuronal death, and it has been demonstrated that in patients with MCI and AD is significantly reduced compared to hea...

New Frontiers in Alzheimer's Disease Diagnosis

“…Based on the low tissue contrast in comparison to magnetic resonance imgaging (MRI), CT serves well in the diagnostic classification of dementia syndromes. Advantages compared to MRI include a shorter time of investigation, low costs and a broad distribution [44]. In addition, CT allows an uncomplicated monitoring of critically ill patients.…”

“…These can predominamtly be located in the medial temporal lobe, in the hippocampus and the gyrus parahippocampalis. Also, the entorhinal cortex, the amygdala, basal ganglia as well as thalamus and the parietal cortex can be involved [44]. An important role in the early detection of AD plays the Nucleus basalis Meynert.…”

“…Due to the inherent magnetic properties of blood, represented by hemoglobin and deoxyhemoglobin, different patterns of activiation are visible [44].…”