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MFM cmu 2010
Physics & Principles
Basic Ultrasound
20 October 2010

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1. Ultrasound pulses
A. are poorly transmitted by liquids
B. are poorly transmitted by air gaps
C. are partially reflected at interfaces
between two liquid media
D. are partially transmitted at interfaces
between two solid media

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2. The Fraunhofer zone is the
A. Image plane
B. Image focus
C. Near field
D. Far field

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3. Diagnostic ultrasound intensity is often
measured in
A. mW/cm2
B. grays
C. decibels
D. Hertz

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4. The propagation speed of sound through
soft tissue is
A. 1450 m/s
B. 1650 m/s
C. 1540 m/s
D. 1230 m/s

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5. Axial resolution can be improved by
A. damping
B. increased spatial pulse length
C. focusing
D. increased bandwidth

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6. Lateral resolution can be improved by
A. focusing
B. increased beam width
C. decreased bandwidth
D. increased line density

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7. The axial resolution of a transducer is
primarily determined by
A. sptial pulse length
B. the transducer diameter
C. the acoustic impedance of tissue
D. focusing

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8. Crystals for ultrasound transducers are
composed of
A. sodium iodide
B. quartz
C. barium titanate
D. lead zirconate titanate

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9. The TGC control compensates for
A. focusing
B. machine instability
C. scan line density
D. attenuation

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10. Phased array transducers
A. have elements which emit ultrasound
independently
B. may be used to alter the beam direction
C. are used only on real-time scanners
D. have a variable frequency

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 Audible: 20 to 20,000 Hz
 Ultrasound: 1 to 30 MHz
 Hertz: 1 cycle per second
 Megahertz: 1,000,000 Hz

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Diagnostic
Imaging
0 20 Hz 20 kHz 1 MHz 30 MHz
Infrared Audible NDT
Sound Sound
Sound Spectra

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Time (1 sec.)
Sound Wave
Wavelength = Distance a wave travels is a single cycle
As frequency increase wavelength become smaller
Amplitude
(dB)
Frequency = number of times wave is repeated per second

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การเดินทางผ่านของเสียง
 คลื่นเสียงไม่สามารถเดินทางในสูญญา
กาศได้
 ก็าซเป็นตัวนำาพาคลื่นเสียงที่ไม่ดี
 คลื่นเสียงจะเดินทางได้ดีขึ้นในตัวกลาง
ที่หนาแน่นขึ้น
Gas Liquid Solid

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- Mechanical vibration or wave
- With frequencies above the range of human
ear which is greater than 20 kHz. For medical
diagnosis, typically ranging from 1 to 30 MHz.
The Nature of Ultrasound
Compressive Wave

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Velocity
- Dependent on the medium and temperature
- Relatively constant 1540 m/s in human body.
Velocity = Frequency * Wavelength ( λ )

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Approximate velocities of sound in human medium
Medium Velocity (m/s)
Blood 1570
Brain 1540
Fat 1450
Kidney 1560
Muscle 1590
Distilled Water 1540

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General Overview
Sea

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General Overview

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Amplitude
Dept / Time

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Electric impulse Sound pulse

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Matching Layer
Transducer
Crystal
Tissue
Impedance Matching
Transducer
Case
-To transmit as much power as possible from transducer to the tissue.

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Acoustic Output
 Acoustic Output increases or decreases the system
power during transmit. Always adjust gain before
adjusting acoustic output.
 Acoustic Output optimizes the image quality thereby
minimizing exposure time to the patient while
maximizing the penetration and echo return.

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Ultrasound Beam

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Attenuation
Attenuation of ultrasound wave occurs when it is propagating
through the medium. Loss of propagating energy will be in the
form of heat absorbed by the tissue, approximately 1 dB/cm/MHz,
or caused by wavefront dispersion or wave scattering.

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Skin Level
Near
Gain
Delay
Far Gain
Knee
Slope Rate
1cm
/1Sec
2cm
/2Sec
3cm
/3Sec
4cm
/4Sec
DGC or TGC or STC

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DGC or TGC or STC

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Spatial Resolution

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Lateral Resolution

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Lateral resolution is a function of the number of scan lines,
transducer elements and probe type and size.
Lateral Resolution

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Beam Profile & Focus
Focal Zone
Transducer
Electronic
Focusing

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Axial Resolution

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Spatial Resolution
Frequency Low High
Resolution Better
Penetration Better

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Transducer Frequency

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Contrast Resolution
• Contrast resolution is the ability to distinguish
subtle differences in similar tissues.
• Grayscale maps depicting 256 shades of gray
are used to display contrast.

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Dynamic Range and Contrast
256 dBNarrow Wide
Which photo gives a better representation of the baby?
Which photo gives enough sensitivity to detect a tear on the baby’s face?

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Dynamic Range
 Dynamic Range controls how echo intensities are
converted to shades of gray, thereby creating a range of
gray scale that can be adjusted.
 Dynamic Range is useful for optimizing tissue texture to
differentiate between echo levels that are close
together.

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Temporal Resolution
Fast frame rates = Temporal Resolution = Anatomic Accuracy

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Frame Rates Depend on: PRF, Depth, Line density, Sector width
Frame Rates = PRF / Line number per frame
25 Frame
Per second
Real Time

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Depth or Field of View
organ
15 cm FOV
5
10
15
organ
10 cm FOV
5
10
Display all of the relevant area appropriately. Zoom can help

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10. Phased array transducers
A. have elements which emit ultrasound
independently
B. may be used to alter the beam
direction
C. are used only on real-time scanners
D. have a variable frequency

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