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ECE 501 Introduction to BME

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ECE 501 Introduction to BME Dr. Hang ECE 501 Part VI Medical Imaging Diagnostic Ultrasound Imaging ECE 501 Introduction to BME Part VI Medical Imaging ... – PowerPoint PPT presentation

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Title: ECE 501 Introduction to BME


1
ECE 501 Introduction to BME
Dr. Hang
ECE 501
2
Part VI Medical Imaging Diagnostic
Ultrasound Imaging
Dr. Hang
ECE 501
3
Introduction
  • Physics of Ultrasound
  • Ultrasound Imaging System

Dr. Hang
ECE 501
4
Physics 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.

Dr. Hang
ECE 501
5
Physics 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.

Dr. Hang
ECE 501
6
Physics of Ultrasound
  • Pulsed Ultrasound
  • Emitted from transducer

Dr. Hang
ECE 501
7
Physics of Ultrasound
  • Resolution of Typical Ultrasound Scanner
  • Center frequency f0 2-10 MHz
  • Speed of sound in tissue C 1540m/s
  • Wavelength ? C/f0

Dr. Hang
ECE 501
8
Physics of Ultrasound
  • How to Get Positional Information?
  • Range equation

Dr. Hang
ECE 501
9
Physics of Ultrasound
  • Wave Propagation
  • Absorption main factor that contributes to
    attenuation
  • Reflection Scattering essential to create an
    image but contribute little to

  • attenuation.
  • Refraction

Dr. Hang
ECE 501
10
Physics of Ultrasound
  • Acoustic Impendence

Density of medium
Speed of sound in the medium
Dr. Hang
ECE 501
11
Physics of Ultrasound
  • Reflection

Reflection Factor
Transmission Factor
Dr. Hang
ECE 501
12
Physics of Ultrasound
  • Oblique Incidence

Dr. Hang
ECE 501
13
Physics of Ultrasound
  • Scattering

Specular scattering
Diffractive scattering
Diffusive scattering
Dr. Hang
ECE 501
14
Physics 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

Dr. Hang
ECE 501
15
Physics of Ultrasound
Doppler Effect
fD Doppler shift frequency f0 transducer
frequency v blood moving velocity c sound speed
Dr. Hang
ECE 501
16
Ultrasound Imaging System
  • Transducer
  • An array of Piezoelectric crystal/ceramic
  • Deforms when a voltage is applied and transmits
    acoustic waves
  • Electrical charge is created by the mechanical
    of deformation

Dr. Hang
ECE 501
17
Ultrasound Imaging System
  • Transducer

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
18
Ultrasound Imaging System
  • Transducer

Dr. Hang
ECE 501
19
Ultrasound Imaging System
  • System Diagram

Dr. Hang
ECE 501
20
Ultrasound 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
21
Ultrasound Imaging System
  • Demodulator
  • Removes the carrier frequency
  • Hilbert transform (for our project)

Dr. Hang
ECE 501
22
Ultrasound Imaging System
  • Echo processing
  • Magnitude Envelope detection
  • LOG Compress reduce the range from 12 bit to
    8 bit

Dr. Hang
ECE 501
23
Ultrasound Imaging System
  • Scan conversion Interpolation

Dr. Hang
ECE 501
24
Ultrasound Imaging System
  • Spectral Doppler Short Time Fourier Transform
    (spectrogram)

Dr. Hang
ECE 501
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