Physics of Ultrasound Ultrasound Imaging and Artifacts

103 Pages·2017·4.8 MB·English

Physics of Ultrasound
Ultrasound Imaging and Artifacts
รศ.นพ.เดโช จกั ราพานิชกุล
สาขาหทยั วทิ ยา, ภาควชิ าอายรุ ศาสตร์ คณะแพทยศาสตรศ์ ริ ริ าชพยาบาล
Diagnosis
‐TTE
‐ TEE
‐ ICE
‐3D
‐ 4D 
Evaluation of Hemodynamic
Cardiac Anatomy
Assessment
Multidimensional Echocardiography
Ultrasound Physics
Wave Motion VS Circular Motion
Ultrasound Waves
• Diagnostic medical ultrasound typically uses transducers with a
frequency between 1-20 MHz
• Humans can hear sound waves with frequencies between 20 Hz and 20 KHz
• Adult echocardiogram: 2-4 MHz
• Pediatric echocardiogram: 4-8 MHz
Frequency
One hertz (Hz) = One cycle per second
Frequency (f)time = number of cycles
Frequency (f) 1 period = 1 cycle
1 cycle
Period ()
Time
1
=
Frequency (f)
period
Wavelength
Wavelength (λ) times frequency (f) equals the propagation velocity (c):
c    f
 Propagation velocity in the heart is 1540 m/s, the wavelength for any
transducer frequency can be calculated as
1.54
 (mm) 
f (MHz)

Interaction with Tissue:
Speed of Sound
Compressed Compressed
Expanded Expanded
(high pressure) (high pressure)
Distance
• As sound travels through tissue it compresses and expands the tissue. 
• Where the tissue is compressed, the speed of sound is higher.
Nonlinear Propagation
Compressed Compressed
Expanded Expanded
(high pressure) (hightpressure)
Higher‐pressure portions
of the wave travel faster
Distance
• As the wave passes through tissue, the top of the waveform gets pulled forward to be non‐sinusoidal shape.
• Propagation in which speed depends on pressure and the wave shape changes is called “nonlinear 
propagation”. 
• Harmonic frequency is generated from this nonlinear propagation.