ULTRASONOGRAPHY

BioSonar
120 KHZ - bats, okras, dolphins: Ultrasound gives sight to these "blind
seers".

Types of Waves
1. transverse and 2.longitudinal US belongs to the latter class.

Forms of US
1. pulsed and 2. continuous
Pulsed is the most commonly used form.
Terms: Pulse repetition rate, pulse repetition period, duty factor, pulse
duration, spatial pulse length

Analogies between image and sound

Velocity of ultrasound
It depends on density and compressibility of the medium.
velocity in soft tissue =5 times the velocity in air
velocity in bone = twice the velocity in soft tissue

Resolution
High frequency means better resolution and small frequency means
worse resolution. But frequency is not the only criterion. It will lead to shallow penetrability.

Ophtalmic probes: to view the superficial topographic features of the
cornea at 15 MHz

Intensity and Loudness of Sound
The unit is decibel.
Threshold of human hearing has been assigned 0 Db.

Scattering
Secular Reflection and back-scattered reflection

The piezoelectric Effect
Whenever an alternating potential is applied on the opposite faces of
the piezoelectric crystal, a pressure wave is generated.
If the applied frequency is in the ultrasoubd range >20 KHz, teh
pressure wave will also be ultrasound.

Standing Waves

The efficiency of the ransducer will be maximum when the thickness of
the probe is an integral multiple of half the wavelength.

The conversion factor
1 cm = 13 microseconds

Operational Modes
Static: 1. Amplitude (A) mode 2. Brightness (B) mode
Dynamic: 1. Compund B Mode 2. Motion (M) Mode 3. Doppler mode

Doppler Ultrasound
1. Ultrasonic stethoscope
2. Digital Sphygmomanometer

Acoustic Shadowing
Case example of a patient suffering from coliolithoisis