Corresponding author: ass prof Fahrudin Smajlovic, MD, PhD. Faculty of health sciences. University of Sarajevo. Sarajevo, Bolnicka 25.
Received 2011 Jun 1; Accepted 2011 Aug 4. Copyright © 2011 AVICENAThis is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Ultrasound device, essentially, consists of a transducer, transmitter pulse generator, compensating amplifiers, the control unit for focusing, digital processors and systems for display. It is used in cases of: abdominal, cardiac, maternity, gynecological, urological and cerebrovascular examination, breast examination, and small pieces of tissue as well as in pediatric and operational review.
Key words: medicine, ultrasound.In physics the term “ultrasound” applies to all acoustic energy with a frequency above human hearing (20,000 hertz or 20 kilohertz). Typical diagnostic sonographic scanners operate in the frequency range of 2 to 18 megahertz, hundreds of times greater than the limit of human hearing. Higher frequencies have a correspondingly smaller wavelength, and can be used to make sonograms with smaller details. Diagnostic sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Sonography is effective for imaging soft tissues of the body. Sonographers typically use a hand-held probe (called a transducer) that is placed directly on and moved over the patient. A water-based gel is used to couple the ultrasound between the transducer and patient (1, 2).
Although discovered 12 years before the X-ray ray (1883.), the ultrasound is a much later found application in medicine. The first practical application of ultrasound is recorded during the World War I in detecting of submarines. The application of ultrasound in medicine began in fifties of last century. First was introduced in the obstetrics, and after that in all the fields of the medicine (the general abdominal diagnostics, the diagnostics in the field of the pelvis, cardiology, ophthalmology and orthopedics and so on) (3). From the clinical aspect the ultrasound possesses the priceless significance because of its noninvasive, good visualization characteristics and relatively easy management (4,5). From the introducing of the processing of the signals of gray scale in 1974 B-mode of the sonography became the widely accepted method. The progress in the forming of the transducers has led to better space resolution and the imaging of very small structures in the abdomen (0.5-1 cm). The development of real-time system led to, even, to the possibility of the continued visualization or the ultrasound fluoroscopy (1). In the ultrasound diagnostics can be differed two techniques (2): transmission and reflection
Transmission technology is based on distinguishing the tissues with different absorbance of ultrasound. Due to uneven absorption of ultrasound images provides internal structure that consists of a mosaic of lighter and darker places. This technology is now abandoned (6,1).
Reflection technology (echo) registers the pulse is reflected from the boundary of two tissues with different acoustic resistance. The technique is based on principle of functioning sonar (“Sonar Navigation and Ranging”). A sound wave is typically produced by a piezoelectric transducer encased in a probe. Strong, short electrical pulses from the ultrasound machine make the transducer ring at the desired frequency. The frequencies can be anywhere between 2 and 18 MHz’s The sound is focused either by the shape of the transducer, a lens in front of the transducer, or a complex set of control pulses from the ultrasound scanner machine. This focusing produces an arc-shaped sound wave from the face of the transducer. The wave travels into the body and comes into focus at a desired depth. Newer technology transducers use phased array techniques to enable the sonographic machine to change the direction and depth of focus. Almost all piezoelectric transducers are made of ceramic (1).
To generate a 2 D-image, the ultrasonic beam is swept. A transducer may be swept mechanically by rotating or swinging. Or a 1D phased array transducer may be use to sweep the beam electronically. The received data is processed and used to construct the image. The image is then a 2D representation of the slice into the body. 3D images can be generated by acquiring a series of adjacent 2D images. Commonly a specialized probe that mechanically scans a conventional 2Dimage transducer is used. However, since the mechanical scanning is slow, it is difficult to make 3D images of moving tissues. Recently, 2D phased array transducers that can sweep the beam in 3D have been developed. These can image faster and can even be used to make live 3D images of a beating heart.
Four different modes of ultrasound are used in medical imaging (1, 3).
A-mode: A-mode is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth. Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy.
B-mode: In B-mode ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen.
M-mode: M stands for motion. In m-mode a rapid sequence of B-mode scans whose images follow each other in sequence on screen enables doctors to see and measure range of motion, as the organ boundaries that produce reflections move relative to the probe.
Doppler mode: This mode makes use of the Doppler effect in measuring and visualizing blood flow. Doppler sonography play important role in medicine. Sonography can be enhanced with Doppler measurements, which employ the Doppler effect to assess whether structures (usually blood) are moving towards or away from the probe, and its relative velocity. By calculating the frequency shift of a particular sample volume, for example a jet of blood flow over a heart valve, its speed and direction can be determined and visualized. This is particularly useful in cardiovascular studies (sonography of the vasculature system and heart) and essential in many areas such as determining reverse blood flow in the liver vasculature in portal hypertension (6,7). The Doppler information is displayed graphically using spectral Doppler, or as an image using color Doppler (directional Doppler) or power Doppler (non directional Doppler). This Doppler shift falls in the audible range and is often presented audibly using stereo speakers: this produces a very distinctive, although synthetic, pulsing sound (8).
The transoesophageal echo cardiography (TEE) opened the window in the diagnostic imaging in the field of the cardiography, card surgery and anesthesia. Using TEE in 2-D mode, the anesthesiologist can monitor the heart movements, and cardiac surgeon will become the valuable information about the heart condition after the critical surgical procedure.
Ultrasonic waves are waves of frequency above the audible frequencies the human ear. In medical diagnostics are used ultrasound frequencies between 3 and 10 MHz.
The most important parameters describing the wave are (1):