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Radiology Physics > Ultrasound Physics > Flashcards

Ultrasound Physics Flashcards

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1
Q

____ is caused by a mechanical deformation induced by an external force with a resultant increase in the pressure of the medium

A

COMPRESSION

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2
Q

This occurs following the compression event - as the backward motion of piston reverses the force, the compressed particles transfer their energy to adjacent particles with a subsequent reduction in the local pressure amplitude.

A

RAREFACTION

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3
Q

Distance compressions or rarefactions.

Distance between any two points that repeat on the sinusoidal wave of pressure amplitude.

A

WAVELENGTH

Determined by the frequency and speed of sound.

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4
Q

Number of times the wave oscillates through one cycle each second.

A

FREQUENCY

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5
Q

Infrasound is

A

Less than 15Hz

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6
Q

Audible acoustic spectrum

A

15Hz to 20kHz (20,000Hz)

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7
Q

Ultrasound spectrum is

A

Above 20kHz

Diagnostic ultrasound uses 2-10MHz

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8
Q

Time duration of one wave cycle

A

PERIOD

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9
Q

Fundamental property that generates echoes (and contrast) in an ultrasound image.

A

Difference in the speed of sound at tissue boundaries

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10
Q

Defined as the peak maximum or peak minimum value from the average pressure on the medium in the absence of a sound wave

A

PRESSURE AMPLITUDE

Pascal (Pa) - Newton per square meter

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11
Q

Thickness that reduces the ultrasound intensity by 3dB

A

HVT (HALF VALUE THICKNESS)

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12
Q

Occurs by reflection or refraction usually by small particles within the tissue medium, causing the beam to diffuse in many directions (which gives rise to characteristic texture and gray scale in the acoustic image)

A

SCATTERING

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13
Q

Describes the change in direction of the transmitted ultrasound energy with non perpendicular incidence.

A

REFRACTION

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14
Q

This occurs at tissue boundaries where there is a difference in the acoustic impedance of adjacent materials.

A

Reflection

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15
Q

Is the process whereby acoustic energy is converted to heat energy whereby sound energy is lost and cannot be recovered

A

Absorption

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16
Q

The si unit for acoustic impedance

A

R a y l

is equal to 1 kg per meter squared second

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17
Q

When the wavelength of ultrasound beam is much greater than structural variations of the boundary

A

Smooth interface

18
Q

Determined by the speed of sound change that occurs at a boundary

A

Angle of refraction

19
Q

Term used for describing scatter characteristics where in higher scatter amplitude is seen

A

Hyperechoic

Hypo- lower scatter amplitude

20
Q

It converts electrical energy into mechanical energy by physical deformation of the crystal structure

A

Piezoelectric material

21
Q

These are molecular entities containing positive and negative electric charges that have an overall neutral charge. When mechanically compressed by an externally applied pressure the alignment of the dipose is disturbed from the equilibrium position to cause an imbalance of the charge distribution.

A

Electrical dipoles

22
Q

Most common synthetic piezoelectric ceramic material

A

Led zirconate titanate (PZT)

23
Q

Layered on the back of the piezo electric element this material absorbs the backward directed ultrasound energy and attenuates three ultrasound signals from housing.

A

Damping block

24
Q

This is the primary use of acoustic coupling gel

A

Removing air pockets which could attenuate and reflect sound beams

Acoustic impedance is similar to soft tissue

25
Q

Lower frequency ultrasound is transmitted into the patient and the higher frequency harmonics created from the interaction with contrast agents and tissues are received as echoes

A

Harmonic imaging

26
Q

What are the basic elements of a CMUT (capacitive micromachined ultrasound transducers)?

A

Capacitor cell with a fixed electrode (backplate)
Free electrode (membrane)

27
Q

The near field is a jason to the transducer phase and has a converging beam profile, also known as

A

Fresnel zone

28
Q

These are unwanted emissions of ultrasound energy directed away from the main pulse caused by the radial expansion and contraction of the transducer element during thickness contraction and expansion

A

Side lobes and grating lobes

29
Q

Refers to the ability to discern two closely spaced objects in the direction of the beam

A

Axial resolution

30
Q

Also known as azimuthal resolution refers to the ability to discern as separate two closely space objects perpendicular to the beam direction

A

Lateral resolution

31
Q

Hypo intense signal area distal to an object or interface and is caused by objects with high attenuation or reflection of the incident beam without the return of echoes

A

Shadowing

32
Q

This occurs distal to objects having very low ultrasound attenuation such as fluid field cavities arise from increase transmission of sound by these structures

A

Enhancement

33
Q

Displayed as a series of parallel bonds extending posterior to a collection of gas

A

Ring-down artifacts

34
Q

This occurs with multi elementary transducers and result from the division of a smooth transducer surface in the a large number of small elements

A

Grating lobes

35
Q

Pseudosludge is an example of _____

A

Side lobe

36
Q

Created when a high prf limits the amount of time spent listening for echoes during the prp

A

Ambiguity

37
Q

Represented as a rapidly changing mixture of colors typically seen distal to a strong reflector such as a calculus and is often mistaken for aneurysm when evaluating vessels

A

Twinkling artifact

May be used to identify small renal stones

38
Q

Rate of energy production absorption or flow

A

Power

SI unit: Watts (1Joule per second)

39
Q

The rate at which sound energy flows through a unit area and is usually expressed in watt per square centimeter

A

acoustic intensity

40
Q

This is the ratio of the acoustical power produced by the transducer to the power required to raise tissue in the beam area by 1° c

A

Thermal index

41
Q

Cavitation is a consequence of negative pressures that induce bubble formation from extraction of result gases in the medium. While ___ is a value that estimates the likelihood of cavitation by the ultra sound beam

A

Mechanical index

42
Q

Determined by the average ultrasound intensity in the focal zone and the absorption coefficient of the tissue

A

Heat deposition

Radiology Physics (6 decks)

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