14-05-2011, 10:10 AM
Presented by:
Ahmed Hamed
[attachment=13873]
Physics of diagnostic ultrasound
Sound :is amechanical energy transmitted by pressure waves in amaterial medium #sound categories: Infrasonic: less than 20 HZ Audible sound: from 20 HZ to 20 KHZ ultrasound:from 20 KHZ to 30 MHZ #source of motion :any vibrating object
#The source of sound waves in medical ultrasound is apiezoelectric transducer
Wave motion :
Wave: is acoordinated disturbance moving at afixed speed through amedium and it doesn't include an actual passage of medium particles
Wave shape:
1- longitudinal wave
2- transverse wave
Our application sound is longitudinal wave
Acoustic pressure : to quantify the wave strength
For the sound wave:
Frequency : No. of vibrations per second made by the sound source
Period: time it takes for the disturbance repeat itself
F=1/T
Speed of the sound:
C =
B: is bulk’s modelus
Ro:is the density
The average sound speed in soft tissue=
1540 M/S
The wavelength : is the distance between any two peaks
(Attention)
Reflection and transmission at interfaces
Acoustic impedance:
Z=R*C rayls
Reflection:
Specular reflector: is a large flat smooth reflector.
Say we have a perpendicular incidence of ultrasound beam on aspecular reflector
Amplitude reflection coefficient:
R=(z2-z1)/(z2+z1)
#coupling material
For the nonperpendicular incidence:
Diffuse reflection:
Scattering echo depend on:
1- No. of scatters per unit volume.
2-the acoustic impedance changes at the scatter interface.
3-the scatters size.
4-the ultrasound frequency.
#Rayleigh scatters
#the Decibel notation: provides acomparison of two signal level .
dB=10 log i2/i1
#Attenuation: it is a reduction of the amplitude of the ultrasound beam as a function of the distance
#Sources of Attenuation:
1-Reflections and scatter interfaces.
2-Absorbtion.
Frequency dependences:
1-Sound speed.
2-spatial resolution.
3-scattering.
4-attenuation.
Wave Interferance:
#constructive interferance
# Destructive interferance
Ahmed Hamed
[attachment=13873]
Physics of diagnostic ultrasound
Sound :is amechanical energy transmitted by pressure waves in amaterial medium #sound categories: Infrasonic: less than 20 HZ Audible sound: from 20 HZ to 20 KHZ ultrasound:from 20 KHZ to 30 MHZ #source of motion :any vibrating object
#The source of sound waves in medical ultrasound is apiezoelectric transducer
Wave motion :
Wave: is acoordinated disturbance moving at afixed speed through amedium and it doesn't include an actual passage of medium particles
Wave shape:
1- longitudinal wave
2- transverse wave
Our application sound is longitudinal wave
Acoustic pressure : to quantify the wave strength
For the sound wave:
Frequency : No. of vibrations per second made by the sound source
Period: time it takes for the disturbance repeat itself
F=1/T
Speed of the sound:
C =
B: is bulk’s modelus
Ro:is the density
The average sound speed in soft tissue=
1540 M/S
The wavelength : is the distance between any two peaks
(Attention)
Reflection and transmission at interfaces
Acoustic impedance:
Z=R*C rayls
Reflection:
Specular reflector: is a large flat smooth reflector.
Say we have a perpendicular incidence of ultrasound beam on aspecular reflector
Amplitude reflection coefficient:
R=(z2-z1)/(z2+z1)
#coupling material
For the nonperpendicular incidence:
Diffuse reflection:
Scattering echo depend on:
1- No. of scatters per unit volume.
2-the acoustic impedance changes at the scatter interface.
3-the scatters size.
4-the ultrasound frequency.
#Rayleigh scatters
#the Decibel notation: provides acomparison of two signal level .
dB=10 log i2/i1
#Attenuation: it is a reduction of the amplitude of the ultrasound beam as a function of the distance
#Sources of Attenuation:
1-Reflections and scatter interfaces.
2-Absorbtion.
Frequency dependences:
1-Sound speed.
2-spatial resolution.
3-scattering.
4-attenuation.
Wave Interferance:
#constructive interferance
# Destructive interferance