Utility of Transcranial Ultrasound in Predicting Alzheimer's Disease Risk

Abstract

Alzheimer's disease (AD) is a progressive, neurodegenerative disease characterized by an increasing incidence. One of the pathologic processes that underlie this disorder is impairment of brain microvasculature. Transcranial ultrasound is a non-invasive examination of cerebral blood flow that can be employed as a simple and useful screening tool for assessing the vascular status of brain circulation in preclinical and clinical stages of AD. The objective of this review is to explore the utility of using a transcranial ultrasound to diagnose AD. With transcranial ultrasound, the most frequently studied parameters are cerebral blood flow velocities and pulsatility indices, cerebrovascular reserve capacity, and cerebral microembolization. On the basis of current knowledge, we recommend using as a transcranial Doppler sonography screening method of choice the assessment of cerebrovascular reserve capacity with breath-holding test.

On the early diagnosis of Alzheimer's Disease from multimodal signals: A survey

“…The parameters of these patterns allow to compute the direction and speed of the blood flow. The experience of the operator and the indirect parameters like the depth of the sample volume, the position of the transducer and the direction of the flow allow to assign the received Doppler signal to a specific artery [180].…”

“…A higher degree of carotid atherosclerosis has been found to be correlated the same way with the disease and a higher risk of developing it [184]. The total CBF is also decreased in AD patients [185,186], as well as the cerebrovascular reserve capacity (CVRC) and the mean flow velocity (MFV) [176,180,187,188]. CVRC "is a parameter of cerebrovascular autoregulation describing the ability for vasodilation of cerebral arterioles in setting of low cerebral perfusion pressure" [180].…”

“…The total CBF is also decreased in AD patients [185,186], as well as the cerebrovascular reserve capacity (CVRC) and the mean flow velocity (MFV) [176,180,187,188]. CVRC "is a parameter of cerebrovascular autoregulation describing the ability for vasodilation of cerebral arterioles in setting of low cerebral perfusion pressure" [180]. Decreased CVRC or middle cerebral artery flow velocity could also reveal a higher risk for developing a dementia [189].…”

“…Unfortunately, ultrasonography has also some drawbacks. Mistakes can be done in the identification of individual vessels and in the estimation of blood velocity due to the angle between the vessel and the ultrasonic beam [180]. Nowadays, colour-coded duplex ultrasonography might overcome some of these drawbacks, but it offers lower performance for long monitoring.…”

Cerebral Hemodynamics in Mild Cognitive Impairment: A Systematic Review

“…Until recently, vascular pathology as a mechanism in dementia was thought to be confined to vascular dementia, but it is becoming increasingly understood that impaired vascular structure and function are important in the development of AD [6][7][8][9]. The two-hit hypothesis combines both the vascular and amyloid cascade hypotheses, acknowledging that vascular dysfunction (first hit), is likely to result in amyloid beta deposition (second hit), and ultimately neurodegeneration and cognitive decline [10,11].…”