Basic Ultrasound Physics

موضوع: US basics الأربعاء يونيو 26, 2024 6:32 pm

Ultrasound is an important technique for tomographic imaging of soft tissues. It provides images in real time and so can also be used to interrogate the movement of structures such as cardiac valves and biopsy needles and, using Doppler, the patterns of blood flow in both large and small vessels. Contrast agents in the form of microbubbles are invaluable in cardiology and the liver, but images are generally obtained without them and thus are not dependent on organ function. Elastography adds information on tissue stiffness, an extension of manual palpation. Ultrasound at diagnostic intensities does not cause damage to tissues and, although complete safety is difficult to prove, it can be used for ovarian follicles and in the developing fetus.
Despite its very wide application in obstetrics, cardiology, abdominal and small parts imaging, the parts of the body that can be imaged with ultrasound are limited because ultrasound does not cross tissue–gas or tissue–bone boundaries so that structures lying deeper to them are obscured. Thus, ultrasound is not generally useful for the lungs and is difficult to use in the head—except in the neonate, as the open fontanelles provide an excellent ‘window’. In other areas, overcoming the barrier caused by the bony skeleton and gassy viscera requires technical expertise. Ultrasound is also subject to many artefactual signals, which complicate interpretation and add to the operator skills required.
Patient acceptance is high and preparation is minimal: bladder filling is required for pelvic imaging and fasting is helpful for the gallbladder. Mobile imaging systems for theatre and emergency point-of-care use are widely available and are being miniaturised while retaining their quality, so that in the future they may become used by all medical practitioners, though training will have to be made available.
Ultrasound is the ideal technique for biopsy and interventional guidance because it operates in real time. Real-time ultrasound can be fused with previously acquired 3D CT or MR data sets to improve the precision of biopsies and tumour ablation. A position sensor then adjusts the CT or MR image to match the ultrasound slice,
thus combining the strengths of each technique

اقتباس :: Ultrasound

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