Basic Principles and Techniques

Ultrasonography depends on the presence of sonographic "windows," which allow sound wave propagation and detection of echo signals. These signals form the basic sonographic units for image generation. Therefore, as a general rule, US is indicated when visualization of the target object is not blocked by intervening bone or air, such as calvarium or bowel gas. This limitation does not completely negate the use of US in the evaluation of adult brain disorders, as discussed later. The usefulness of US as an imaging tool in pediatrics is particularly appealing owing to its inherent lack of ionizing radiation.

Carotid US consists of gray scale imaging to assess location and extent of plaque and Doppler to measure flow velocities and degree of stenosis. Color may be added to the Doppler to improve visualization of the flow lumen and optimize the Doppler angle. The term carotid duplex, currently in vogue, represents the union of these entities. Measurements of peak systolic velocity (PSV) and end-diastolic velocity (EDV) are made in the distal common carotid artery, carotid bulb, and cervical internal carotid artery. Color information enhances the ability of carotid duplex in the identification of maximal flow velocity points and further is useful in allowing precise transducer placement in patients when high-flow jets are encountered.

The bony calvarium severely inhibits sound propagation, which has limited the ability of US to directly image the brain in adults. However, research led to the development of transducers capable of measuring intracranial flow velocities of key vascular structures despite the presence of intervening bone. This technology resulted in the development of TCD, the study of the intracranial arteries using the spectral analysis of blood flow velocity. The technique

generally employs a 2-MHz pulsed Doppler transducer. Vessel identification is based on the cranial window utilized, transducer position, and depth of sample volume. The direction and velocity of blood flow is recorded, noting the relationship to the terminal internal carotid and response to common carotid artery compression. 'd , y Unfortunately, TCD may be limited by the thickness of the calvarium, which simply may not allow the measurement of intracranial Doppler signals.

Alcohol No More

Alcohol No More

Do you love a drink from time to time? A lot of us do, often when socializing with acquaintances and loved ones. Drinking may be beneficial or harmful, depending upon your age and health status, and, naturally, how much you drink.

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