Physics us2010

MFM cmu 2010

Physics & Principles

Basic Ultrasound20 October 2010

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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

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2. The Fraunhofer zone is theA. Image planeB. Image focusC. Near fieldD. Far field

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3. Diagnostic ultrasound intensity is often measured inA. mW/cm2

B. graysC. decibelsD. Hertz

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4. The propagation speed of sound through soft tissue isA. 1450 m/sB. 1650 m/sC. 1540 m/sD. 1230 m/s

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5. Axial resolution can be improved byA. dampingB. increased spatial pulse lengthC. focusingD. increased bandwidth

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6. Lateral resolution can be improved byA. focusingB. increased beam widthC. decreased bandwidthD. increased line density

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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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8. Crystals for ultrasound transducers are composed ofA. sodium iodideB. quartzC. barium titanateD. lead zirconate titanate

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9. The TGC control compensates forA. focusingB. machine instabilityC. scan line densityD. attenuation

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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

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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 NDTSound Sound

Sound Spectra

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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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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 ( )

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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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Am

plitu

de

Dept / Time

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Electric impulse Sound pulse

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Matching Layer

TransducerCrystal

Tissue

Impedance Matching

TransducerCase

-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 GainKnee

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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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 FramePer 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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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


2. The Fraunhofer zone is theA. Image planeB. Image focusC. Near fieldD. Far field

MFM cmu 2010


3. Diagnostic ultrasound intensity is often measured inA. mW/cm2B. graysC. decibelsD. Hertz

MFM cmu 2010


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


5. Axial resolution can be improved byA. dampingB. increased spatial pulse lengthC. focusingD. increased bandwidth

MFM cmu 2010


6. Lateral resolution can be improved byA. focusingB. increased beam widthC. decreased bandwidthD. increased line density

MFM cmu 2010


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


8. Crystals for ultrasound transducers are composed ofA. sodium iodideB. quartzC. barium titanateD. lead zirconate titanate

MFM cmu 2010


9. The TGC control compensates forA. focusingB. machine instabilityC. scan line densityD. attenuation

MFM cmu 2010


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

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