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Physics > Chapter 24 > Flashcards

Chapter 24 Flashcards

1
Q

Bioeffects

A

the effects of the sound wave upon the biologic tissue through which it travels

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2
Q

Hydrophone

A

AKA: a microprobe
-needle like shaped with a tiny piece of PZT on the end
-A wire connects the PZT to an oscilloscope (readout meter)
-Pressure and amplitude (when calibrated) at specific locations is determined
-The needle can be moved within the beam, thus beam shape can be determined

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3
Q

Radiation Force Balance

A

-The sound beam strikes a float, or a ball
-measured force is communicated to a balance which determines the power in the beam
AKA: a feedback microbalance

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4
Q

Acousto-Optics

A

-Based on the interaction of sound and light
-Common instrument = Schlieren
-Is a shadowing system/camera that allows visualization of the shape of the sound beam in a medium
-Sound waves (beam profiles) appear as shadows

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5
Q

Calorimeter

A

-Like a thermos filled with absorbing material
-Sound beam is directed into the calorimeter and the total power is calculated by measuring the temperature rise and the time of heating
-Measures the power of the entire beam

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6
Q

Thermocouple

A

-A tiny electronic thermometer with a dab of absorbing material on it
-It is inserted into the sound beam and the temperature at that location is measured
-The temperature rise is related to the power or intensity of the sound beam at that particular location

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7
Q

Liquid Crystals

A

-Sound beam strikes the crystals, the sound energy is absorbed
-The change in crystal temperature causes a change in color, providing insight into the shape and strength of the sound beam

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8
Q

Risk-Benefit Relationship

A

Primary mandate of US, benefits to the patient must outweigh the risks of the exam

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9
Q

Therapeutic ultrasound

A

Controlled intensities can be used to create beneficial bioeffects

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10
Q

Therapeutic ultrasound

A

Controlled intensities can be used to create beneficial bioeffects

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11
Q

Dosimetry

A

measuring the “dosage” of ultrasound (or characteristics of the beam) likely to result in bioeffects

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12
Q

In vivo (“in living”)

A

studies are performed within the living body of a plant or animal

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13
Q

In vitro

A

-research is performed outside the living body; in an artificial environment
-These studies provide an opportunity to perform research that would be impossible with live human subjects
-The challenge is to meaningfully relate the results to the clinical setting

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14
Q

AIUM statement on In Vitro Bioeffects

A

-In vitro research is important
-In vitro bioeffects are real in the artifical environment and can initiate in vivo validation
-In vitro bioeffects which claim direct clinical significance without in vivo validation should be viewed with caution

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15
Q

Empirical Approach

A

-Is based on the acquisition and review of records from patients/animals exposed to US
-It seeks to establish a statistically significant exposure response relationship
-No mechanism is proposed

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16
Q

Mechanistic Approach

A

-Begins as a proposal that a specific mechanism has the potential to produce bioeffects
-Then a theoretical analysis/study is designed to test the mechanism i.e., the scope of the bioeffect at various exposure levels
-searches for a specific cause and effect

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17
Q

Thermal Bioeffects

A

Proposes that bioeffects result from temperature elevation

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18
Q

Thermal Index

A

a useful predictor of maximum temperature increase under most clinically relevant conditions

19
Q

Wp

A

is a power parameter calculated for output power and attenuation

20
Q

Wdeg

A

is the estimated power needed to increase tissue temp by 1ºC

21
Q

TIS

A

is the thermal index calculated assuming that the sound beam travels through soft tissue
first trimester (bone not mineralized)
-vascular, echo, abdominal

22
Q

TIB

A

is the thermal index calculated assuming that bone is at or near the beam’s focus, usually a higher number than the TIS
-second and third trimesters

23
Q

TIC

A

is the thermal index calculated assuming that cranial bone is in the sound beams near field
-Transcranial doppler

24
Q

Maximum heating of tissues is related to SPTA intensity

A

FDA limit is 720 mW/cm2 SPTA

25
Q

Thermal Findings

A

Tissue heating relates to:
1. Output power/temperature rise
2. Exposure time
3. Characteristics of tissue

26
Q

Temperature elevation becomes progressively greater in this order

A

2D – color – spectral doppler

27
Q

Nonthermal or Mechanical Bioeffects

A
  1. Cavitation
  2. Radiation Force
28
Q

Radiation Force

A

-Force in beam can deform structures
-Force can move fluid which creates shear (parallel) stress that deforms structures

29
Q

Lithotripsy = Therapeutic Ultrasound Example

A

-uses shock waves to break down stones in the kidney, gallbladder, or ureter.
-Intravascular lithotripsy is being proposed for coronary calcium prior to angioplasty

30
Q

Cavitation

A

-is the interaction of sound waves with microscopic, stabilized, gas bubbles in the tissues (gaseous nuclei); specifically Gaseous nuclei oscillate (expand and contract)

31
Q

Two forms of cavitation exist

A
  1. Stable
  2. Transient
32
Q

Stable: at lower MI levels, stable cavitation occurs

A

-Gaseous nuclei oscillate (expand and contract)
-They may double in size but do not burst
-Surrounding fluids micro stream
-Surrounding cells experience shear stress

33
Q

Transient Cavitation

A

-At higher MI levels gaseous nuclei burst
AKA: inertial or normal cavitation (TIN)
-The pressure threshold for transient cavitation is only 10% higher than that for stable cavitation

34
Q

Mechanical Index

A

is related to the likelihood of cavitational bioeffects

35
Q

Epidemiology (Population) Studies

A

-Is a branch of medicine that studies prevalence of disease in specific populations
-It is empirical: Seeks exposure response relationship

36
Q

Many epidemiologic studies deal with in utero fetal exposure to US and the response on

A

Birth weight
Length and Head Circumference
Apgar Scores
Congenital Abnormalities
Hearing
Infection

37
Q

Limitations of epidemiologic studies are

A

-Studies are retrospective, obtained form old medical records
-Ambiguities may exist in the data such as reason for exam, gestational age, # of scans, technique, and exposure time
-Risk factors other than US exposure may precipitate a bad outcome in the fetus (maternal age, smoking, environmental factors, alcohol, or drug abuse)

38
Q

The best epidemiologic studies are

A
  1. Prospective
  2. Randomized
39
Q

Prospective studies

A

are forward looking, a protocol is established, and specific information is systematically obtained

40
Q

Randomized studies

A

-create two groups of patients
-One group is exposed to US and the other is not
-The groups are otherwise similar taking other risk factors out of the equation

41
Q

Clinical Safety and Prudent Use

The conclusions of the AIUM include:

A

-No confirmed harmful bioeffects from exposure to diagnostic US has ever been reported
-It is possible that bioeffects may be identified in the future
-The benefit to the patient outweighs the risks
-It is appropriate to use diagnostic US prudently to provide benefit to the patient
-It is inappropriate to use diagnostic US in a non-medical setting for entertainment

42
Q

Training and Research

The conclusions of the AIUM include:

A

-No confirmed bioeffects on patients or sonographers have been found with the use of diagnostic US in research and training
-Research and training exams may differ from standard exams (longer research exams and greater exposure)
-The subject should be informed how the research study differs from standard diagnostic procedures

43
Q

Electrical Safety

A

-US systems present no special electrical safety hazard
-Basic precautions include:
>Proper grounding
>Routinely checked for proper condition
>Since transducer poses greatest risk, routinely check transducer housing for cracks

Physics (25 decks)

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