انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة

Ultrasound in Medicine

الكلية كلية طب حمورابي     القسم الكلية ذات القسم الواحد     المرحلة 1
أستاذ المادة نادية حسين صاحب طاهر       22/05/2017 16:38:10
Lecture: Ultrasound in Medicine
Introduction:
Human ears respond to sound in the frequency range of about 20 to 20000 Hz, medical engineers developed techniques for using ultrasound for diagnosis. Basically, an ultrasound source sends a beam of pulses of 1 to 5 MHz sound into the body. The time required for the sound pulses to be reflected gives information on the distances to the various structures or organs in the path of the ultrasound beam.
There are several methods of generating ultrasound. The most important for medical applications involves the piezoelectric effect. Many crystals can be cut so that on oscillating voltage across the crystals will produce a similar vibration of the crystal, thus generating a sound wave.
Pulses of ultrasound are transmitted into the body placing the vibrating crystal in close contact with the skin, using water or a jelly past to element the air. This gives a good coupling at the skin and greatly increases the transmission of ultrasound into the body and of the echoes back to the detector. The vibration of the crystal produced by the echoes generate a voltage a cross it- the signals are displayed on an oscilloscope.
Many of applications of ultrasound in medicine are based on the principles of sonar. In sonar a sound wave pulse is sent out and is reflected from an object, from the time required to receive the echo and the known velocity of sound in water. This procedure is called the A- scan method of ultrasound diagnosis; pulses for A- scan work are typically a few microseconds long. They are usually emitted at 400 to 1000 pulse/s.
A device that converts electrical energy to mechanical energy or vice versa is called transducer. Each transducer has a natural resonant frequency of vibration. The thinner the crystal, the higher the frequency at which it will oscillate. For a quartz crystal cut long a certain axis (X- cut), a thickness of 2.85 mm gives a resonant frequency of about 1 MHz Typical frequencies for medical work are in the 1 to 5 MHz range.

In general, structure smaller than the wavelength ? cannot be resolved.
? = V/f
Where V is the velocity of sound and f is the frequency, the high frequency sound has shorter wavelengths and allows better resolution than low frequency sound; since the absorption increases as the frequency increases.


المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .