Physics us2010
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Transcript of Physics us2010
MFM cmu 2010
Physics & Principles
Basic Ultrasound20 October 2010
MFM cmu 2010
Physics & Principles
1. Ultrasound pulsesA. are poorly transmitted by liquidsB. are poorly transmitted by air gapsC. are partially reflected at interfaces between two liquid mediaD. are partially transmitted at interfaces between two solid media
MFM cmu 2010
Physics & Principles
2. The Fraunhofer zone is theA. Image planeB. Image focusC. Near fieldD. Far field
MFM cmu 2010
Physics & Principles
3. Diagnostic ultrasound intensity is often measured inA. mW/cm2
B. graysC. decibelsD. Hertz
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Physics & Principles
4. The propagation speed of sound through soft tissue isA. 1450 m/sB. 1650 m/sC. 1540 m/sD. 1230 m/s
MFM cmu 2010
Physics & Principles
5. Axial resolution can be improved byA. dampingB. increased spatial pulse lengthC. focusingD. increased bandwidth
MFM cmu 2010
Physics & Principles
6. Lateral resolution can be improved byA. focusingB. increased beam widthC. decreased bandwidthD. increased line density
MFM cmu 2010
Physics & Principles
7. The axial resolution of a transducer is primarily determined by A. sptial pulse lengthB. the transducer diameterC. the acoustic impedance of tissueD. focusing
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Physics & Principles
8. Crystals for ultrasound transducers are composed ofA. sodium iodideB. quartzC. barium titanateD. lead zirconate titanate
MFM cmu 2010
Physics & Principles
9. The TGC control compensates forA. focusingB. machine instabilityC. scan line densityD. attenuation
MFM cmu 2010
Physics & Principles
10. Phased array transducersA. have elements which emit ultrasound independentlyB. may be used to alter the beam directionC. are used only on real-time scannersD. have a variable frequency
MFM cmu 2010
Physics & Principles
Audible: 20 to 20,000 Hz Ultrasound: 1 to 30 MHz
Hertz: 1 cycle per second
Megahertz: 1,000,000 Hz
MFM cmu 2010
Physics & Principles
Diagnostic Imaging
0 20 Hz 20 kHz 1 MHz 30 MHz
Infrared Audible NDTSound Sound
Sound Spectra
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Physics & Principles
Time (1 sec.)
Sound WaveWavelength = 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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Physics & Principles
การเดิ�นทางผ่�านของเสี�ยง คลื่��นเสี�ยงไม่�สีาม่ารถเดิ�นทางในสี�ญญากาศไดิ�
ก�าซเป็ นตั"วน$าพาคลื่��นเสี�ยงท��ไม่�ดิ� คลื่��นเสี�ยงจะเดิ�นทางไดิ�ดิ�ข()นในตั"วกลื่างท��หนาแน�นข()น
Gas Liquid Solid
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Physics & Principles
- 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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Physics & Principles
Velocity
- Dependent on the medium and temperature- Relatively constant 1540 m/s in human body.
Velocity = Frequency * Wavelength ( )
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Physics & Principles
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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Physics & Principles
General Overview
Sea
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Physics & Principles
General Overview
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Physics & Principles
Am
plitu
de
Dept / Time
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Physics & Principles
Electric impulse Sound pulse
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Physics & Principles
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Physics & Principles
Matching Layer
TransducerCrystal
Tissue
Impedance Matching
TransducerCase
-To transmit as much power as possible from transducer to the tissue.
MFM cmu 2010
Physics & Principles
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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Physics & Principles
Ultrasound Beam
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Physics & Principles
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Physics & Principles
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Physics & Principles
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Physics & Principles
MFM cmu 2010
Physics & Principles
MFM cmu 2010
Physics & Principles
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.
MFM cmu 2010
Physics & Principles
MFM cmu 2010
Physics & Principles
Skin Level
Near Gain
Delay
Far GainKnee
Slope Rate
1cm/1Sec
2cm/2Sec
3cm/3Sec
4cm/4Sec
DGC or TGC or STC
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Physics & Principles
DGC or TGC or STC
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Physics & Principles
Spatial Resolution
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Physics & Principles
Spatial Resolution
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Physics & Principles
Lateral Resolution
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Physics & Principles
Lateral resolution is a function of the number of scan lines,
transducer elements and probe type and size.
Lateral Resolution
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Physics & Principles
Beam Profile & Focus
Focal Zone
Transducer
Electronic Focusing
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Physics & Principles
Axial Resolution
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Physics & Principles
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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Physics & Principles
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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Physics & Principles
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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Physics & Principles
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Physics & Principles
Temporal Resolution
Fast frame rates = Temporal Resolution = Anatomic Accuracy
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Physics & Principles
Frame Rates Depend on: PRF, Depth, Line density, Sector width
Frame Rates = PRF / Line number per frame
25 FramePer second Real Time
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Physics & Principles
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
MFM cmu 2010
Physics & Principles
1. Ultrasound pulsesA. are poorly transmitted by liquidsB. are poorly transmitted by air gapsC. are partially reflected at interfaces between two liquid mediaD. are partially transmitted at interfaces between two solid media
MFM cmu 2010
Physics & Principles
2. The Fraunhofer zone is theA. Image planeB. Image focusC. Near fieldD. Far field
MFM cmu 2010
Physics & Principles
3. Diagnostic ultrasound intensity is often measured inA. mW/cm2B. graysC. decibelsD. Hertz
MFM cmu 2010
Physics & Principles
4. The propagation speed of sound through soft tissue isA. 1450 m/sB. 1650 m/sC. 1540 m/sD. 1230 m/s
MFM cmu 2010
Physics & Principles
5. Axial resolution can be improved byA. dampingB. increased spatial pulse lengthC. focusingD. increased bandwidth
MFM cmu 2010
Physics & Principles
6. Lateral resolution can be improved byA. focusingB. increased beam widthC. decreased bandwidthD. increased line density
MFM cmu 2010
Physics & Principles
7. The axial resolution of a transducer is primarily determined by A. sptial pulse lengthB. the transducer diameterC. the acoustic impedance of tissueD. focusing
MFM cmu 2010
Physics & Principles
8. Crystals for ultrasound transducers are composed ofA. sodium iodideB. quartzC. barium titanateD. lead zirconate titanate
MFM cmu 2010
Physics & Principles
9. The TGC control compensates forA. focusingB. machine instabilityC. scan line densityD. attenuation
MFM cmu 2010
Physics & Principles
10. Phased array transducersA. have elements which emit ultrasound independentlyB. may be used to alter the beam directionC. are used only on real-time scannersD. have a variable frequency