ULTRASOUND IMAGING : TRANSDUCERS

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 Ultrasound transducer



A typical source of ultrasound is a transducer, which works on the principle of piezoelectric effect.
Transducer is a device which convert energy from one form to another..
In transducer the piezoelectric crystal like quartz converts electrical energy into US energy and vise versa.

Piezoelectric material or crystal



Piezoelectric means pressure electricity.
Piezoelectric materials have molecular dipoles containing + & - electric charges, and the net charges is zero.

If electrical voltage is applied across the crystal, the dipole orientation changes, resulting in variation of crystal thickness.
The crystal undergoes compression and expression, and ultrasound waves are produce.

Natural piezoelectric material is quartz crystal and synthetic ceremic material is most commonly used as crystal e.g. lead zirconate titanate (PZT) or polyvinylidene difluoride.

Transducer design



US transducer consist five main components 
1.Piezoelectric crystal
2. Matching layer
3.Backing block
4.Housing
5.Co axial cable

(1) piezoelectric crystal

Usually lead zirconate titanate (PZT) is used.
Crystal thickness is determined by what resonance frequency is desired.

(2) Matching layer

The matching layer minimize the acoustic impedance differences between transducer and the patient's skin.
It improves the transmission efficiency of US into the patient .
Its thickness must be equal to 1/4 of the wavelength of sound, which is called quarter wave matching.

(3)backing block

The backing block is on the back side of the crystal, made up of tungsten particles or rubber suspended in epoxy resin.
It determines the purity of sound and the length of time a sound persists.

(4)transducer housing

Provide Electrical insulation and protection to crystal.
Include a plastic case, metal shield and acoustic absorber.

(5) Co axial cable

Provide connectivity to crystal to monitor.


Clinical Transducer type



Different- different probes used in different - different regions.
The clinical probes are as follows :
Endovaginal - used in pelvic region
Endorectal - prostate
Transesophageal - used in heart 
Intravascular - blood vessels

Sources -
Wikipedia, basic radiolgical physics by K thylan,
Sk bhargav





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