(a) Electroencephalogram (EEG) may show normal or non-specific diffuse slow waves, slowed alpha wave rhythm, low amplitude, or even disappear when the disease is severe. Generally, there is a correlation between the degree of EEG changes and the degree of intellectual impairment of the patient. (b) Brain CT mainly shows brain atrophy. General atrophy of the gray matter of the brain is manifested by increased and deepened sulci and widened fissures in both cerebral hemispheres, and atrophy of the temporal lobe (mainly the middle temporal gyrus) is manifested by increased and deepened sulci, narrowing of the middle temporal gyrus, widening of the suprasellar and circumferential pools, and enlargement of the temporal horn of the lateral ventricle. (iii) Magnetic resonance imaging (MRI) has the highest soft tissue contrast resolution of all medical imaging modalities and can clearly distinguish the gray and white matter of the brain. The brain atrophy or ventricular enlargement shown is clearer and more sensitive than CT, and the ability to measure the volume of the entire temporal lobe or structures such as the hippocampus and amygdala is important for the early diagnosis of AD. (d) Single photon emission tomography (SPECT) is a medical imaging technique combining radionuclide imaging and computer technology, which can show the local cerebral blood perfusion and thus reflect the functional changes in the brain; the decrease in cerebral blood flow in the temporoparietal cortex of AD patients is more pronounced in the posterior temporoparietal lobe, showing hypoperfusion or perfusion deficit areas, and the degree of decreased blood perfusion can be similar or significantly different between the left and right sides. The degree of decreased perfusion can be similar or significantly different between the left and right sides. (v) Positron emission tomography (PET) is a nuclear medicine tool for obtaining information on cellular activity or metabolism with the aid of scanning the movement of radioactive tracers in the body and for imaging, and is a method for displaying brain energy metabolism in three dimensions for purposes related only to the brain. It can show reduced glucose metabolism in the parietal temporal cortex, manifesting as a hypometabolic area or metabolic deficit area. The metabolism detected during quiet time reflects the degree of morphological damage, the metabolic rate in the active state reflects the potential ability of the brain to respond to functional tests, and the metabolism of AD is more severely involved during activity than during quiet time.