SPI Concepts-Red Book

How much is .000001?

10-6 or micro

What are acoustic propagation properties?

the effects of the medium upon the sound wave

What are biologic effects?

the effects of the sound wave upon the biologic tissue

What are the characteristics of period?

Def: time required to complete one cycleunits: microseconds or any unit of timeTV: .o6 to .5 microsecondDetermined by: sound sourceCBS: No

What intensity has the highest value?

SPTP- Spatial peak Temporal peak

What intensity is most relevant for thermal bioeffects?

SPTA- Spatial Peak Temporal Average

Which intensity has the lowest value?

SATA-Spatial Average Temporal Average

What are the three components of attenuation?

absorption (primary, sound converted into heat) , reflection, scattering

What is the oder of attenuation in different media?

Air>>Bone&Lung>>Soft Tissue>>Water**Attenuation in blood is less than that in soft tissue

What is specular reflection?

reflections from a smooth reflector (mirror) are specular and return in one direction

What is diffuse reflection or backscatter?

When a boundary is rough, reflected sound is disorganized and random

What is scattering?

The distribution of sound randomly in all directions*higher frequency sound scatters to a greater extent

What is Rayleigh Scatteirng?

If a reflector is much smaller than the wavelength of sound, sound is uniformly distributed in all directions*omnidirectional, red blood cell, frequency to the fourth power

What is the attenuation coefficient?

the amount of attenuation per centimeter. a way to report attenuation without dealing with how far sound travels, Units-dB/cm*in soft tissue it is 1/2 of the transducers frequency .5 dB/cm/MHz

What is impedance?

a number associated with a medium. Impedance is calculated not measured. represented by the letter Z*reflection of an ultrasound wave depends on different acoustic impedances of the media on either side of the boundary. Impedance= density x propagation speed

What is incident intensity?

~The intensity of the sound wave at the instant prior to striking a boundary (w/cm squared)

What is reflected intensity?

is the intensity that, AFTER striking a boundary, changes direction RETURNS BACK from where it came. (w/cm squared)

What is transmitted intensity?

intensity that, after striking a boundary, continues on in the same general direction that it was traveling

What is the reflection percentage in different biologic media?

soft tissue- air-99%soft tissue - bone -50%soft tissue - soft tissue - < 1%

What is reflection with normal incidence?

reflection occurs only if the two media at the boundary have different acoustic impedances

What is transmission with normal incidence?

these are simply reflection questions. whatever is not reflected must be transmitted.

What is refraction?

transmission with a bend*refraction is a change in direction as sound transmits from one medium to anotherRequires:1. oblique incidence2. different speeds *cannot occur with normal incidence or with identical prropagation speeds

How thick is the active element?

1/2 the wavelength thickalso called the ceramic, PZT or crystal

What is the purpose of the case?

~to protect the internal components from damage, and insulates the pt from electrical shock.**don't use a transducer with a cracked case due to the potential for electrical shock to the patient

Matching layer?

on-quarter wavelength thick, impedances: PZT > matching layer > gel > skin

Backing material/ damping element?

reduce ringing, short pulses create more accurate images short pulse length and durationlow sensitivitywide bandwidth (broadband)low Qdecreased output power

What is bandwidth?

the range of frequencies between the highest and lowest frequency emitted from the transducerbandwidth=highest frequency-lowest frequencysynonyms: the main frequency emitted by the transducer is called the center, resonant, primary or natural frequency

What is quality factor?

a unitless number related to extent of dampinglow q = damping and wide bandwidth, imaging (pulsed) transducershigh-q = no damping and narrow bandwidth, CW & therapeutic transducers

What determines the resonant frequency of a continuous wave transducer?

sound frequency = electrical frequency

What determines the resonant frequency of a pulsed transducer?

the main or center frequency of sound from a pulsed transducer is determined by 2 characteristics of the crystal:the thickness and propagation speed of the PZT material

For pulsed transducers, describe the crystal and PZT for higher and lower frequency.

Higher frequency:-thin crystal-fast PZTLower Frequency:-thick crystal-slow PZT**when a PZT crystal Is half as thick, the sound's frequency is twice as high

How is focal depth determined?

transducer diameter or aperturefrequency of the ultrasound

What characteristics create a shallow focus?

small diameterlow frequency

What elements create a deep focus?

large diameterhigh frequency

What are the characteristics of less divergance?

larger aperture or larger diameter active elementhigh frequency narrower beam in far fieldimproved lateral resolution in the far field

What are the characteristics of more divergance?

smaller aperture or smaller diameter active elementlow frequency wider beam in the far fielddegraded lateral resolution in the far field

What is frequency of a CW determined by?

electronic frequency

How is frequency of Pulsed Wave determeind?

thickness of ceramic and speed of sound in ceramic

How is focal length determeind?

aperture of active element and frequency of sound

How is divergence determined?

aperture of active element and frequency of sound

What is diffraction pattern?

v-shaped wave also called Huygen's wavelet.

Huygen's Principle

explains the hourglass shape of an imaging transducer's sound beameach tiny part of the surface of the large transducer face may be considered an individual tiny sound source creating a Huygen's wavelet

What is resolution?

the ability to image accurately

Describe axial resolution

the ability to distinguish two structures that are close together front to back, parallel to or along the beams main axis distance units-shorter pulses create better axial resolution---> short pulse means a short spatial pulse length or a short pulse durationcannot be changed by the sonographer-a new transducer is needed to change numerical value of AR is smaller, transducers are designed with backing material to have few cycles per pulse, so that the numerical axial resolution is low and the image accuracy is superior .05-.5 mm

Axial resolution equation

AR = spatial pulse length/ 2

What improves axial resolution?

less ringing-fewer cycles in pulse (fewer carrs in train)higher frequency, shorter wavelength,

Lateral resolution definition

minimum distance that two structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoesUnits-distance, mmLR = beam diameter, since beam diameter varies with depth, the LR also varies with depth. also called beam width variation or point spread artifactLR degrades at deeper depths (in the far zone)usually not as good as AR, because sound pulses are wider than they are short

What are special notes for high frequency pulsed ultrasound?

high frequency sound -improved AR in entire image-improved LR in the far far fieldBeam shape and divergence-in the far field, higher f pulsed sound has narrower beams compared to lower f in the far field

How does focusing alter beams?

narrower waist in the us beamshallower focussmaller focal zone

Where is focusing mainly effective?

in the near field and the focal zone

What are the two general types of focusing?

fixed-also called conventional or mechanicaladjustable by electronics also called phased array

What are the three methods of focusing?

lens-externalcurved PZT internal focusingElectronic focusing-adjustable, phased array technology provides dynamic, variable focusing orr multi-focusing

Single crystal transducers are always ______ focus.


Phased array transducers are said to have better what?

overall lateral resolution because the sonographer can move the focus to the anatomic region of clinical importance

What are the units of the acoustic variables?

pressure-pascalsdensity-kg/cm cubeddistance-distance, mm or cm

What are acoustic parameters?

describe the features of a particular sound wave

What waves are audible?

between 20 Hz and. 20,000 Hz, heard by man

What waves are ultrasound?

greater than 20,000. Hz, no frequency too high

What waves are infrasound?

less than 20 Hz, no. frequency, too low

What terms are associated with shallow imaging?

high PRFshort PRPhigh duty factor

What terms are associated with deep imaging?

low PFlong PRPlow duty factor