Ultrasound Waves and Their Application in Medicine

Radiation Physics-2 Al-Mustaqbal University College 3rd 1 Assistant lecturer: Assistant lecturer: AnsamFadil AnsamFadil Ali Ali Showard Showard

Introduction Energy can exist in many forms, and in some forms has the ability to move from one place to another. When energy moves as a wave through a medium, this is known as radiation. Sound is a physical phenomenon that carries energy from one point to another. In this respect is similar to radiation, but differs from the radiation that does not pass through the vacuum and that means it needs to matter in order to transfers from one place to another. This is because the sound waves are actually vibrations that pass through the material. If there is any substance, nothing can vibrate and sound cannot exist.

**One of the most important features in the sound is frequency, defined as the number of cycles per unit time ( sec 1) introduced into the medium each second is referred to as the frequency of the wave, expressed in units of hertz, kilohertz, or megahertz, and defines the hertz as one vibration, or cycle, per second that is V =1/T *The maximum height of the wave cycle is the amplitude of the ultrasound wave. *The distance covered by one cycle is the wavelength ( ) of the ultrasound wave. *The product of the frequency ( ) and the wavelength ( ) is the velocity of the wave

Unlike light and x-ray, sound requires a medium which propagate through it such as water or soft tissue and it consists of longitudinal vibrations in much the same way as a compression can be seen to travel along the length of a spring as shown in figure 2.

There is a specific extent of the frequencies in the human ear can hear or respond to them. The human ear in young adults can hear the frequency extent from 20 Hz to 20,000 Hz. The extent of frequencies greater than this limit is called ultrasonic frequencies (Ultrasound). Frequencies in the extent of 2 MHz (million cycles per second) to 20 MHz are used in diagnostic ultrasound which is too high for the human ear can hear.

Ultrasound Ultrasound is a mechanical disturbance that moves as a pressure wave through a medium. When the medium is a patient, the wavelike disturbance is the basis for use of ultrasound as a diagnostic tool. Appreciation of the characteristics of ultrasound waves and their behavior in various media is essential to understanding the use of diagnostic ultrasound in clinical medicine Definition Ultrasound Physical Definition; Ultrasound (ultrasonic) is the term used to describe sound of frequencies above 20 000 Hertz (Hz), beyond the range of human hearing. The term "ultrasonic" applied to sound refers to anything above the frequencies of audible sound. Medical Definition; Diagnostic Medical Ultrasound is the use of high frequency sound to aid in the diagnosis and treatment of patients and the frequency ranges used in medical ultrasound imaging are 2 - 15 MHz.

Features of Ultrasound Diagnostic ultrasound offers advantages over other imaging modalities, the feature of ultrasound: 1. Safe in pregnancy 2. Has no known side effects 3. Inexpensive 4. Portable 5. Minimal preparation of patients 6. Painless 7. Gives direct vision for biopsie Some problems with ultrasound imaging are that the diagnostic images sometimes cannot be obtained because of the size of the patient, or because the ultrasound beam cannot traverse the areas of air-filled or bone in such cases, the cross-sectional imaging with CT or MRI can be used instead.

Basic Principle of Ultrasound Sound waves are generated by what is known as the piezoelectric effect . The pressure waves of an echo distort crystals, causing them to emit an electrical impulse. Ultrasound images are generated not by X-rays but by sound waves that are sent by a transducer into the human body . In abdominal ultrasound, the frequencies used generally are between 2.5 and 5.0 (MHz). Send the ultrasound pulses when electrical pulses are applied to it. A short time later, receives the echoing waves when the transducer is pressed against the skin and converted back into electrical pulses that are then processed by the system and formed into an image.

The transducer (probe) is the small hand-held component of the ultrasound imaging equipment that resembles a microphone and it performs several functions as will be described in detail later. A transducer includes many such crystals. Depending on the impulse applied, they can produce sound waves of various frequencies specified in megahertz (MHz). In fact, such a transducer may emit sound wave frequencies between, for example, 2 and 6 MHz.