Bioeffects, New Developments, and QA Safety

UT 200 Quiz 9

bioeffects

change to biological tissues as ultrasound beam travels through tissue

types of bioeffects

• thermal

• non-thermal

dosimetry

science of identifying and measuring characteristics if an ultrasound beam relevant to its potential for producing biological effects

dosimetric quantities that are measured

• acoustic pressure

• acoustic power

• acoustic intensity

• radiation force

acoustic pressure

• acoustic variable

• formula: force/unit area

• units: Newton/m² (Pascal) or Newton/cm²

• peak pressures in an acoustic field are measured

compressions

areas of peak positive pressures

rarefactions

areas of peak negative pressures

acoustic power

• AKA output or transmit power

• rate at which work is performed

• formula: acoustic energy/time

• units: Joule/sec → Watt or mWatt

acoustic intensity

• formula: acoustic power/beam area

• units: Watt/cm² or mWatt/cm²

• not uniform over space or time

• ex: think of a light bulb in a small room vs. a big room

the conversion of sound energy to heat is measured using the following instruments

• calorimeter

• thermocouple

• liquid crystal

calorimeter

measures the total power in a sound beam through absorption (power of the entire beam)

thermocouple

measures the sound beam’s power at a particular location in the beam

liquid crystal

measures the change in temperature because the crystals change color to indicate different temperatures

hydrophone

• measures acoustic pressures at a specific location

• can also measure the period, PRP, PRF, and PD

• two types are used to measure acoustic pressure or intensity (output power)

  • hydrophone probes

  • membrane hydrophones

grayscale imaging has the ___ output power, while PW doppler has the ___ output power

lowest; highest

hydrophone probes

• have a tiny piezoelectric element

• looks like a needle

membrane hydrophones

membrane is made of polyvinylidene fluoride

radiation force balance

• the force that is exerted when an ultrasound wave hits a target that absorbs, scatters, or reflects energy

• the target is a balance or a float, the measured force is related to the sound beam power

  • measured radiation force relates to the intensity or power of the sound beam

• shear stresses and streaming of fluids can distort or disturb biological structures

acousto-optics

• based on the interaction of sound and light

• shows the hourglass beam shape

• uses a shadowing system called Schlieren imaging to view the shape of an ultrasound beam in a medium

what does this picture show?

Schlieren image of a focused beam from a TDR with broken crystals

methods for measuring intensity

1. spatial peak - temporal peak (SPTP)

2. spatial average - temporal peak (SATP)

3. spatial peak - temporal average (SPTA)

4. spatial average - temporal average (SATA)

5. spatial average - pulse average (SAPA)

6. spatial peak - pulse average (SPPA)

___ is the most relevant intensity with respect to tissue heating because we are concerned about the highest energy over the on/ring time

SPTA

because peak measurements are larger than average measurements, ___ intensity has the highest value and ___ has the lowest value

SPTP; SATA

spatial distribution

• refers to how the beam energy is distributed over physical space in the body

• determined by the beam parameters

temporal distribution

refers to how the energy is distributed over time

1

peak compression

2

peak rarefaction

3

temporal peak (TP)

4

pulse average (PA)

5

temporal average (TA)

6

spatial peak (SP)

7

spatial average

8

beam intensity profile

the amount of acoustic energy a patient is exposed to can be limited using the ___ principle

ALARA

ALARA means

as low as reasonably achievable

as medical professionals, it is our job to make sure

• exams are medically justified

• exams are not prolonged unless medically justified

• patient exposure is minimized

___ acoustic intensities can cause damage to biological tissues

high

how to minimize patient exposure

use high receiver gain and low output power

thermal bioeffects

• tissue temperature elevation

• related to the output characteristics of the TDR and tissue properties

• temperature and exposure time determine the likelihood of bioeffects

T/F: maximal heating is related to the beam’s SPTA intensity

true

SPTA should not exceed ___ for an unfocused beam

100 mW/cm²

SPTA should not exceed ___ for a focused beam

1W/cm²

there are no confirmed bioeffects for up to ___ elevation above normal and exposure time up to 50 hours

2°C

any exam causing temperature elevation greater than ___ could potentially harm a fetus

41°C

fetal tissues are ___ tolerant of tissue heating than adult tissues

less

T/F: fetal defects resulting from temperature elevation have not been documented

false

thermal index (TI)

• used to predict an increase in temperature

• there are 3 different thermal indices used for different imaging applications: TIS, TIB, and TIC

TIS

thermal index in soft tissue

TIB

thermal index in bone

TIC

thermal index in cranial bone

___ modalities have a greater risk of thermal bioeffects than ___ because the ultrasound beam is transmitted in the same direction (causing heat to build up)

non-scanned; scanned

scanned modalities

• acquires information over a plane which allows time for the heat to dissipate

• 2-D (B-Mode) and color doppler

non-scanned modalities

• ultrasound beam is transmitted in the same direction which causes heat to build up

• CW doppler PW doppler, M-mode, and A-mode

mechanical (non-thermal) bioeffects

• damage caused by the actual oscillation of the sound wave on tissue

• as the sound wave propagates through tissues, there are areas of compressions and rarefactions

• can cause the formation of gas bubbles in tissues

types of mechanical bioeffects

• radiation force

• cavitation

• streaming

cavitation

• worrisome because bubbles generated can get larger, and the bubbles can rupture

• 2 types of cavitation: stable or transient (inertial)

stable cavitation

produces bubbles that oscillate in a stable manner and do not rupture

transient cavitation

• potential to cause the most bioeffects

• larger bubbles are produced and rupture

• results in an increase in tissue temperature

• can cause cell death in the affected area

the risk of mechanical bioeffects can be measured using the

mechanical index (MI)

as the TDR frequency increases, MI ___

decreases

acoustic power and microbubble responses

radiation force is another type of ___

MI

microstreaming

• occurrence of shear stresses by the fluid surrounding the cells

• useful with therapeutic ultrasound

  • promotes fluid mixing and targeted drug delivery (DNA, drugs, macromolecules into a cell)

bioeffects research may be conducted

in vivo or in vitro

in vivo research

performed within the living body of an animal or plant

in vitro research

• “in glass”

• performed outside the living body in an artificial environment

• gives the opportunity to perform experiments that would be unethical or impossible to do in humans

in vitro ultrasound research

• a computer model estimates the temperature elevation of tissues during exposure to ultrasound

• previous study demonstrated that very high ultrasound intensities can cause genetic damage and cell death

epidemiology

branch of medicine associated with population studies

empirical studies provide an exposure response using

clinical surveys

many epidemiologic studies deal with ___ fetal exposure to ultrasound

in-utero

the best epidemiologic studies are

• prospective

• randomized

prospective studies

• are forward-looking

• provide a complete and accurate compilation of meaningful information from medical records

retrospective studies

• are from the past

• less desirable because data is from the past, less accurate, or incomplete

randomized studies

• create 2 groups of patients

  • one group is exposed to ultrasound

  • one group is not exposed to ultrasound

• risk factors that affect fetal outcome are present in both groups and are accounted for

limitations of studies

• data can be inaccurate because indications, GA, MI, TI, and the required # of scans be inconsistent between patients

• other risk factors other than exposure to ultrasound can affect fetal growth or lead to abnormality

  • maternal age

  • environmental factors

  • poor nutrition

  • smoking

  • alcohol

  • drug use

skipped slide 32

come back if needed

electrical and mechanical hazards

• instruments should be checked for proper condition

• inspected to ensure proper physical status

• transducers have the greatest risk because it is in contact with the patient

  • check for electrical shock from a cracked transducer housing

  • image quality is compromised when cracked

advancements in imaging architecture

• virtual beamforming

• big data

• enhanced digital signal processing (eDSP)

• bit by bit frame creation

conventional beamforming

• beamformer generates the voltage that drives the transducer and determines the PRF and intensity

• amplify returning echoes and compensate for attenuation

• with a conventional beamformer, pulses are fired separately and returned separately and must be sorted out

limitations of conventional beamforming

• spatial resolution vs. frame rate are traded for image optimization

• some relevant data can be lost during the process

virtual beamforming utilizes

graphic processing units (GPUs)

graphic processing units (GPUs)

• specialized processor originally designed to accelerate graphics rendering

• can process many pieces of data simultaneously, making them useful for machine learning, video editing, and gaming applications

• determines the echo received from each pixel location

GPUs overcome the limitations of conventional beamforming, which are

• beam divergence

• slice thickness

• beam breakage

• lobe artifacts

benefits of virtual beamforming

• detail resolution

• contrast resolution

• temporal resolution

• increased sensitivity

• increased penetration

• artifact reduction

• improved doppler operation

  • simultaneous grayscale, color, and spectral doppler

• big data

• eDSP

• bit-by-bit frame creation

which image uses virtual beamforming?

• the image on the left uses conventional beamforming

• the image on the right uses virtual beamforming

big data

the ability to acquire, transfer, process, and store massive volumes of digital data received through virtual beamforming

in ultrasound applications, ___ ___ represents the interaction of acoustic energy with human soft tissue and provides the potential for a new generation of diagnostic possibilities

big data

the four V’s of big data

• volume (amount)

• variety (type and sources)

• veracity (quality and trust)

• velocity (speed)

enhanced digital signal processing (eDSP)

• analyzes the enormous size and diversity of the acoustic data generated by virtual beamforming

• further processes the big data

• software algorithms identify, separate, and group acoustic information into digital “siloes”

• this process provides a thin ultrasound beam image

benefits of eDSP

• improved temporal resolution

• automated sound speed compensation

• enhanced B-mode tissue characterization

• tissue transparency

• automated radiofrequency-generated B-mode measurements

• attenuation imaging

bit-by-bit frame creation

• data populated by the “big data” is processed into individual pixels in the back end using bit-by-bit frame creation

• after creation, additional digital signal processing software algorithms can be applied before the frame is presented for operator interpretation

___ sonographic imaging platforms utilize a line-by-line frame method

conventional

the use of bit-by-bit frame creation allows for

• speckle tracking

• contrast enhanced ultrasound

• vector flow imaging

• hemodynamic imaging

• temporal resolution transparent exceeds 1000 frames/sec

synthetic spatial compounding

• conventional imaging integrates data from 3 different angles of insonation to produce a single frame

• spatial compounding uses data received from eDSP whereby reducing frame time

quality assurance (QA)

• routine and period evaluation of all ultrasound systems to guarantee optimal image quality

• required for all diagnostic labs

  • needed to obtain and maintain lab accreditation

  • equipment performance testing and statistical analysis of lab results

QA includes

• assessment of systems components

• repairs and record keeping

  • inspection, evaluation, and calibration

• preventative maintenance

• patient tracking

• peer review

• QA meetings

• evaluation of oversights and errors

• develop protocols that are consistent and methodological to minimize the number and severity of errors

five goals of QA

1. proper operation of the system

2. detects gradual changes in image quality

3. minimize downtime

4. reduce the number of non-diagnostic exams

5. reduce the number of repeat scans

QA device categories

• tissue equivalent phantom

• doppler phantom

• beam profile/slice thickness

performance measurements during QA

• axial resolution

• lateral resolution

• depth calibration (vertical distance)

• horizontal distance calibration

• system sensitivity

• registration accuracy

• dead zone

• image uniformity (tissue texture)

• lesion detection (anechoic cyst and mass resolution)

• grayscale contrast resolution (displayed dynamic range)

• focal zone

• depth of penetration

sensitivity

ability of a system to display low-level echoes