الفهرس 
Physical principles of ultrasound.Only 14 pages are availabe for public view
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Abstract
Ultrasonography as a tool for exploring the body has a rich history. Sonar (sound navigation and ranging) is the technique of sending sound waves and detecting the returning echoes to discover hidden objects. The creation of an image from sound is achieved in three steps; producing a sound wave, receiving echoes, and interpreting those echoes.
Ultrasound guidance is rapidly becoming the gold standard for regional anaesthesia. Regional anaesthesia has benefits over general anaesthesia, such as decreased morbidity and mortality, superior postoperative analgesia, cost-effectiveness, decreased postoperative complications and an improved postoperative course.
Ultrasound imaging is noninvasive and is easy to use, does not involve exposure to radiation, and is not affected by the type of anesthesia administered. Ultrasound allows the anesthesiologist to visualize the target nerves and surround structures in real time during block placement, which is particularly advantageous in children because the majority of regional anesthetic procedures in this age group are performed under general anesthesia.
The use of ultrasound in the perioperative setting has extended the way anesthesiologists practice clinically. The ultrasound already has been widely accepted clinically for regional anesthesia and central catheter placement as well as for diagnostic purposes like the Focused Assessment with Sonography for Trauma (FAST) examination and the use of transesophageal echocardiography has exploded as a hemodynamic monitor during surgery.
Now, with the availability of bedside ultrasound, we can ”see” more of the anatomical structures and technique has become much less blind. Perhaps, it is appropriate to say that the ”art” is giving way to the technology.
Ultrasound is very useful for peripheral nerve block in the upper limbs as it allows the anesthetist to minimize the dose of local anaesthetic and advance the needle to the nerve safely.
Ultrasound can also be a useful aid to locate arteries, mark the skin for unguided blocks or as a real-time guide of needle or catheter position related to the nerve or related blood vessels, and can be used to define the spread of local anaesthetic.