Ultrasound Physics

Question 1

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

Answer 1

COMPRESSION

Question 2

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.

Answer 2

RAREFACTION

Question 3

Distance compressions or rarefactions.

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

Answer 3

WAVELENGTH

Determined by the frequency and speed of sound.

Question 4

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

Answer 4

FREQUENCY

Question 5

Infrasound is

Answer 5

Less than 15Hz

Question 6

Audible acoustic spectrum

Answer 6

15Hz to 20kHz (20,000Hz)

Question 7

Ultrasound spectrum is

Answer 7

Above 20kHz

Diagnostic ultrasound uses 2-10MHz

Question 8

Time duration of one wave cycle

Answer 8

PERIOD

Question 9

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

Answer 9

Difference in the speed of sound at tissue boundaries

Question 10

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

Answer 10

PRESSURE AMPLITUDE

Pascal (Pa) - Newton per square meter

Question 11

Thickness that reduces the ultrasound intensity by 3dB

Answer 11

HVT (HALF VALUE THICKNESS)

Question 12

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)

Answer 12

SCATTERING

Question 13

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

Answer 13

REFRACTION

Question 14

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

Answer 14

Reflection

Question 15

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

Answer 15

Absorption

Question 16

The si unit for acoustic impedance

Answer 16

R a y l

is equal to 1 kg per meter squared second

Question 17

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

Answer 17

Smooth interface

Question 18

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

Answer 18

Angle of refraction

Question 19

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

Answer 19

Hyperechoic

Hypo- lower scatter amplitude

Question 20

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

Answer 20

Piezoelectric material

Question 21

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.

Answer 21

Electrical dipoles

Question 22

Most common synthetic piezoelectric ceramic material

Answer 22

Led zirconate titanate (PZT)

Question 23

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

Answer 23

Damping block

Question 24

This is the primary use of acoustic coupling gel

Answer 24

Removing air pockets which could attenuate and reflect sound beams

Acoustic impedance is similar to soft tissue

Question 25

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

Answer 25

Harmonic imaging

Question 26

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

Answer 26

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

Question 27

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

Answer 27

Fresnel zone

Question 28

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

Answer 28

Side lobes and grating lobes

Question 29

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

Answer 29

Axial resolution

Question 30

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

Answer 30

Lateral resolution

Question 31

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

Answer 31

Shadowing

Question 32

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

Answer 32

Enhancement

Question 33

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

Answer 33

Ring-down artifacts

Question 34

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

Answer 34

Grating lobes

Question 35

Pseudosludge is an example of _____

Answer 35

Side lobe

Question 36

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

Answer 36

Ambiguity

Question 37

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

Answer 37

Twinkling artifact May be used to identify small renal stones

Question 38

Rate of energy production absorption or flow

Answer 38

Power SI unit: Watts (1Joule per second)

Question 39

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

Answer 39

acoustic intensity

Question 40

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

Answer 40

Thermal index

Question 41

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

Answer 41

Mechanical index

Question 42

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

Answer 42

Heat deposition