Title: ECE 501 Introduction to BME
1ECE 501 Introduction to BME
Dr. Hang
ECE 501
2Part VI Medical Imaging Diagnostic
Ultrasound Imaging
Dr. Hang
ECE 501
3Introduction
- Physics of Ultrasound
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- Ultrasound Imaging System
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Dr. Hang
ECE 501
4Physics of Ultrasound
- What is Sound?
- Sound is a wave, i.e. traveling variations of
pressure. - It involves mechanical motion in the medium
through which it travels - Pressure variations cause particles of the
medium to vibrate due to increase and decrease of
density. -
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Dr. Hang
ECE 501
5Physics of Ultrasound
- What is Ultrasound?
- Pressure waves with frequencies higher than 20
KHz, higher than audible range of human beings. - Harmless unless very high intensities are used.
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Dr. Hang
ECE 501
6Physics of Ultrasound
- Pulsed Ultrasound
- Emitted from transducer
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Dr. Hang
ECE 501
7Physics of Ultrasound
- Resolution of Typical Ultrasound Scanner
- Center frequency f0 2-10 MHz
- Speed of sound in tissue C 1540m/s
- Wavelength ? C/f0
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Dr. Hang
ECE 501
8Physics of Ultrasound
- How to Get Positional Information?
- Range equation
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Dr. Hang
ECE 501
9Physics of Ultrasound
- Wave Propagation
- Absorption main factor that contributes to
attenuation -
- Reflection Scattering essential to create an
image but contribute little to -
attenuation. -
- Refraction
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Dr. Hang
ECE 501
10Physics of Ultrasound
Density of medium
Speed of sound in the medium
Dr. Hang
ECE 501
11Physics of Ultrasound
Reflection Factor
Transmission Factor
Dr. Hang
ECE 501
12Physics of Ultrasound
Dr. Hang
ECE 501
13Physics of Ultrasound
Specular scattering
Diffractive scattering
Diffusive scattering
Dr. Hang
ECE 501
14Physics of Ultrasound
- Attenuation
- Scattering 20
- Absorption (conversion of wave energy into
heat) 80 - Linear function of frequency high
frequencies are more attenuated - than low frequencies
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Dr. Hang
ECE 501
15Physics of Ultrasound
Doppler Effect
fD Doppler shift frequency f0 transducer
frequency v blood moving velocity c sound speed
Dr. Hang
ECE 501
16Ultrasound Imaging System
- Transducer
- An array of Piezoelectric crystal/ceramic
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- Deforms when a voltage is applied and transmits
acoustic waves - Electrical charge is created by the mechanical
of deformation
Dr. Hang
ECE 501
17Ultrasound Imaging System
Appropriately delayed pulses are transmitted from
an array of piezoelectric elements to achieve
steering and focusing at the point of interest.
The echoes returning are likewise delayed before
they are summed together to form a strong echo
signal from the region of interest.
Dr. Hang
ECE 501
18Ultrasound Imaging System
Dr. Hang
ECE 501
19Ultrasound Imaging System
Dr. Hang
ECE 501
20Ultrasound Imaging System
- TGC (Time Gain Compensation)
- amplifies the returned signal in proportion to
depth - or the time required for the signal to return
Dr. Hang
ECE 501
21Ultrasound Imaging System
- Demodulator
- Removes the carrier frequency
- Hilbert transform (for our project)
Dr. Hang
ECE 501
22Ultrasound Imaging System
- Echo processing
- Magnitude Envelope detection
- LOG Compress reduce the range from 12 bit to
8 bit
Dr. Hang
ECE 501
23Ultrasound Imaging System
- Scan conversion Interpolation
Dr. Hang
ECE 501
24Ultrasound Imaging System
- Spectral Doppler Short Time Fourier Transform
(spectrogram)
Dr. Hang
ECE 501