The terms Ultrasonography and Sonography are used interchangeably. This diagnostic technique makes use of high frequency sound waves, aimed at areas in the body in order to produce visual images of anatomical structures. Ultrasonography is also known as diagnostic sonography and echocardiography when used in imaging the heart.
Ultrasonography makes use of generated sound waves to produces visible images of soft body tissues. Sonic waves, as a form of energy, are known as longitudinal pressure waves. These waves result when molecules are pushed together, becoming less dense (rarified). As a wave passes through molecules, they are not transported by the wave but merely vibrate back and forth (around a neutral position). A molecule will be moved through the compression and rarification cycle a specific number of times per second and this is called the frequency of the wave. The unit of measurement for sound wave frequency is termed Hertz (Hz). The human ear is capable of detecting frequencies ranging between 20Hz and 20,000Hz. (The greater the frequency, the higher the audible sound of the wave). Frequencies beyond 20,000Hz are inaudible to the human ear and are called ultrasonic. Ultrasonography utilizes sound waves between one million and 15 million Hz.
Typically, an ultrasound machine comprises of four major components: Transducer (allows for the machine to body interface); Electronic signal processing unit (controls the power output to the transducer); Display unit (normally a computer monitor screen); and some device for recording and storing the images produced (usually video or film equipment).
Ultrasonography has wide application in the field of medical diagnostics. It is best suited for obtaining images of solid, or uniform soft tissue and fluid-filled tissue. Performance is limited when imaging calcified structures (like bone) or air-filled objects (like the bowel). Ultrasonography is most commonly used for imaging fetus development during pregnancy, gallbladder disease diagnosis, certain forms of cancer, scrotum and prostate abnormality evaluation, heart and thyroid examination as well as breast examinations. Doppler imaging sonography is a technique developed to view the flow of blood in blood vessels as well as to guide needles through bodily structures when obtaining biopsy specimens. Detailed images of the fetus in the uterus may be viewed using three-dimensional ultrasounds.
Most ultrasonic examinations are performed externally by moving a transducer over the skin surface. Normally, a gel would be applied to the skin. This allows the transducer to glide smoothly as well as to eliminate the formation of air pockets between the skin and transducer (this would interfere with the imaging obtained). Where necessary, a probe is inserted into a bodily orifice. Examples are: Trans-esophogal cardiogram, which requires a specialiized transducer placed in the esophogus to obtain a clearer image of the heart; Trans-rectal examinations require a transducer to be inserted into a male patient’s rectum in order to obtain images of the prostate; Trans-vaginal ultrasound examinations are used to obtain images of the ovaries and uterus and of the fetus during the early weeks of pregnancy.
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