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MIDS 139 (Core Exam) > Ch 15 Safety + Bioeffects > Flashcards

Ch 15 Safety + Bioeffects Flashcards

1
Q

What studies on bioeffects of u/s have been done?

A

Plant studies: used primarily for understanding cavitational effects in living tissue

Animal studies: allowed determination of conditions under which thermal + non-thermal bioeffects occur

Human studies (epidemiology): studies long-term effects on fetus’s or people with a history of previous sonograms (shows no known risks)

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2
Q

In the low MHz frequency range, were there confirmed adverse effects?

A

Nope

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3
Q

SPTA intensities should be below what?

A

Unfocused beam: <100 mW/cm^2
Focused beam: <1 W/cm^2

(temp increases to <1.5 degrees C)

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4
Q

What should peak rarefactional pressure be?

A

<0.4 Mpa (MI < 0.4) in tissues with natural gas bodies + with contrast enhanced diagnostic u/s

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5
Q

What should the MI be for tissue with gas + tissue w/o gas?

A

With gas: < 0.4
W/o gas: < 1.9

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6
Q

List 2 mechanisms by which u/s could produce biologic effects?

A

-Heating: thermal
-Mechanical: non thermal

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7
Q

Explain heating with u/s?

A

-U/s produces a temp rise as it propagates through tissues
-The temp rise depends on several factors

(factors: intensity, frequency, amount of beam focusing, tissue perfusion, time spent scanning, type of tissue scanned + scanned vs non-scanned modality)

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8
Q

When would tissue damage occur from heating?

A

If critical time temperature values were exceeded

(if temp rises over 1.5 degrees C = now considered significant)

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9
Q

The temperature should not rise above how many degrees C?

A

1.5

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10
Q

Approx. 80 known biological effects are due to what?

A

Hyperthermia

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11
Q

An excessive temperature increase can result in what?

A

Toxic effects

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12
Q

No significant adverse biological effects have been observed with a temperature of what?

A

< 1.5 degrees C (and in exposures up to 50 hours)

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13
Q

Are adult, fetal or neonatal tissues more tolerant of heat?

A

Adult

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14
Q

What are thermal indices (TI)?

A

-Provides a real time display of the probability that an u/s could induce thermal injury
-It is a guide for the sonographer regarding the magnitude of the temperature increase

(TI of 1: means approx temp rise of 1 degree C after a long exposure)

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15
Q

Differentiate TIS, TIB + TIC thermal index presets on the u/s machines?

A

TIS:
-for soft tissue
-suitable for 1st trimester

TIB:
-for bone
-suitable for 2nd/3rd trimester

TIC:
-for cranial bone
-suitable for neonatal, pediatric + adult scanning

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16
Q

List the TI that will not present a bioeffect + the TI that will cause a bioeffect to the embryo?

A

TI < 1.5 = no bioeffect

TI > 4 for 5 mins = bioeffect

17
Q

List the TI recommendations for pre-natal exams?

A

TI < 0.5:
-most preferred setting
-suitable for 1st trimester
-used for extended scanning time

TI > 0.5-1:
-scan time must be less than 30 min

TI > 2.5:
-scan time must be less than 1 min

18
Q

List the TI recommendations for post-natal exams?

A

TI < 2 = used for extended scanning time

TI 2-6 = scan time must be less than 30 min

TI > 6 = scan time must be less than 1 min

19
Q

Mechanical mechanisms of interaction include what 3 things?

A

-Radiation force (think force by sound beam)
-Streaming (think stress on cells)
-Cavitation (think bubbles)

20
Q

What are the 2 types of cavitation?

A

Stable:
-bubbles already present in the medium expand + contract during each cycle in response to the applied pressure
-bubbles expand under low pressure + contract under high pressure
-cavitation in tissues occurs under CW + high intensity conditions

Transient (worse form):
-bubbles are so large that they collapse + produce shock waves
-occurs in extremely high temps
-potential for significant destructive effects

21
Q

Bubble related effects depend on what?

A

Peak rarefactional pressure

(rarefaction = regions of low pressure)

22
Q

Cavitation can occur in tissues containing what?

A

-Gas bubbles with sufficient amplitude + frequency conditions

(contrast agents introduce an additional consideration regarding cavitation effects)

23
Q

Is TI or MI formulated to assist users in evaluating the likelihood of cavitation?

A

MI

24
Q

What is a mechanical index (MI)?

A

It assists users in evaluating the likelihood of cavitation related adverse biologic effects

25
Q

Biologic effects have been confirmed with an MI above what?

A

MI > 0.4 with a gas body contrast

26
Q

List the MI recommendations for pre-natal exams?

A

MI < 0.4 = if gas bodies are present

(if no gas bodies the MI can be increased, but should still remain low for bioeffects not related to gas bodies)

27
Q

List the MI recommendations for post-natal exams?

A

MI < 0.4 = if gas bodies are present
MI < 1.9 = if no gas bodies

(MI should be much lower for neonatal studies than adult studies)

28
Q

Explain the intensity in regards to time with mechanical + thermal bioeffects?

A

Mechanical: high intensity for short period time

Thermal: low intensity for long period time

29
Q

What is the mechanical bioeffect + what is the safe limit to prevent it?

A

Bioeffect: cavitation
(when the sound beam reaches highest intensity in a physical space over a short period of time)

Safe limit to prevent cavitation: <190 W/cm^2

30
Q

What is the thermal bioeffect + what is the safe limit to prevent it?

A

Bioeffect: heating
(when the sound beam reaches highest intensity in a physical space over a long period of time)

Safe limit to prevent cavitation: <720 W/cm^2

31
Q

Differentiate the thermal bioeffect risks with scanned vs non-scanned modalities?

A

Scanned:
-2D B-mode, CD, power doppler, 3D imaging
-lower risk of bioeffects
(b/c energy is distributed line by line over a wide area, allowing time for heat to dissipate)

Non-scanned:
-CW, PW, M-mode
-higher risk for bioeffects
(b/c energy is constantly transmitted in same direction, decreasing time for heat to dissipate)

32
Q

List 5 factors that affect the amount of heat produced during an u/s?

A

-Beam intensity (power + spatial distribution)
-PD + PRP
-Absorption rate of tissues
-Ability of the tissue to conduct heat away
-Scanning time

33
Q

Put 2D B-mode, CD, CW, PW + M-mode in order from the highest thermal risk to lowest?

A
  1. PW
  2. CW
  3. CD
  4. M-mode
  5. 2D B-mode
34
Q

Put 2D B-mode, CD, CW, PW + M-mode in order from the highest mechanical risk for cavitation to the lowest?

A
  1. 2D B-mode
  2. M-mode
  3. CD
  4. PW
  5. CW
35
Q

What is the ALARA principle?

A

As low as reasonably achievable!!!

It means:
-exposure time + acoustic output should be kept at a min
-used only when medically indicated

MIDS 139 (Core Exam) (16 decks)

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