Ultrasound is a non-invasive imaging modality in which image of the internal anatomical structure is obtained in the form of dotted structures with the help of frequency of 2-20MHz which is beyond the audible range of human being. Because of high frequency the penetration power of ultrasonic waves is very high and it can penetrate into deeper body parts.
These high frequency sound waves are produced by transducer. This transducer acts as both transmitter and a receiver of sound waves. They have piezo electric crystals which are align in proximal and distal rows.
Piezo electric crystals: Piezo electric crystals are those substances which vibrate vigorously when electric current is supplied to them. When electricity applied to the transduced the Piezo electric crystals start vibrating in this way the electrical energy is converted into mechanical energy. Due to vibration high frequency sound waves are produced. Therefore, converting the mechanical energy in sound waves passes through the different interfaces of internal anatomical structure and absorbed/scattered according to the density of the organ and then these sound waves are again reflected back in the form of echoes which are align receive by the same transducer. This transducer converts the sound energy into electrical signals in term are converted into digital convertor and these digital signals are displayed on oscilloscope in the form of dotted anatomical structures.
Ultrasound is a non-invasive imaging mortality and does not shows any adverse biological effect of its clinical applications and therefore it can be safely used for all age groups and also for fetal evolution and neo-natal neuron’s studies it gives excellent soft tissues contrast, resolutions and has wide clinical applications in gynecology, obstetrics, pediatrics and cardiac imaging.
Wave length: The distance between two crest and trough of a sound wave particularly between two points is known as wavelength. Wavelength is a very specific characteristic sound as it determines the rate of propagation of sound waves through a medium. Smaller the wavelength larger the frequency of the sound waves and therefore greater is the intensity or the penetration power of the sound energy.
Frequency: Number of cycle per second repeated by the sound waves is known as frequency both wavelength and frequency of the sound wave determines the velocity of sound along the medium of propagation.
Acoustic impedance: Acoustic impedance is a very common terminology used in ultrasound in common term it is defined as the opposition or resistance offered by the system or the system medium through which the sound waves are travelling. It results in production of an acoustic pressure in the system.
Acoustic enhancement: It is also known as posterior enhancement and it refers to the increased echoes deep to the structure that transmit the sound waves exceptionally well. This is the most common phenomenon in case of body structures filled with fluid like gall bladder, hydrated cyst, urinary bladder etc.
Resolution: In general term resolution is the ability of an imaging mortality to differentiate between the adjacent body structures. In ultrasonography it is commonly reflexed depth or linear resolution and it is parallel to the direction of the ultrasound beam and therefore it is not affected by the depth of scanning.
Generally there are three modes of ultrasound which used in clinical application. These are as follows:
Transducers are the most important component of ultrasound unit and therefore selection of the appropriate transducer according to the demand of scanning is very important for better image quality and proper diagnosis. Apart from selection acute angle of application of the transducer on body of the patient also plays an important role. Various types of transducer in ultrasonography depending upon different parameters like shape of the transducer, field of view, alignment of piezo electric crystals, frequency range and size of the transducer. Based on these following categories of ultrasound transducer are available.
Apart from the above major categories there are some other types of probes for specific use like:
Some special kind of transducers is also used for surgical interventions like laparoscopy and Doppler imaging.
Focal zone: The area where the ultrasound beams width is narrowest.
Near field: The area between the actual surface of the transducer or beam point and focal zone.
The phased array transducer can also be used for abdominal and brain scanning.
Apart from the above transducer there are certain transducers especially designed for specific purposes like laparoscopic transducers used in laparoscopic surgery and biopsy transducer which are used in ultrasound guided biopsies.