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IACC > US safety > Flashcards

US safety Flashcards

1
Q

Is ultrasound safe?

A

Widely used for years without obvious adverse effect
Subtle long term effects not ruled out
Use ALARA principle

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2
Q

What are the main hazards associated with ultrasound exposure?

A

Heating
Acoustic cavitation - growth then collapse of bubbles => shockwaves
Gas-body effects - complete reflection causes doubling of amplitude
Radiation pressure - streaming in fluids, shear stress at beam edges

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3
Q

How does heating affect the unborn fetus?

A

Heat is a teratogen; fetal exposure during pregnancy causes abnormality

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4
Q

What is the formula for MI?

A

MI = pr(0.3) / \sqrt(f)

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5
Q

What are the three different categories of TI?

A

TIS soft tissue
TIB bone
TIC cranial bone

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6
Q

How does frequency affect heating?

A

heating is directly proportional to frequency

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7
Q

How does frequency affect risk of acoustic cavitation?

A

MI is used to quantify the risk of acoustic cavitation risk and is proportional to 1/sqrt(f)

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8
Q

SAR is measured in [W/kg] What is the analogous equivalent for US?

A

Acoustic dose rate = mu * I_ta / rho_0

mu: absorption coefficient
I_ta: time averaged intensity
rho_0: density

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9
Q

What are the IEC surface temperature limits in air?

A

T max: 50 degree C
dT max: 27 degree C

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10
Q

What are the IEC surface temperature limits for external tissue?

A

T max: 43 degree C
dT max: 10 degree C

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11
Q

What are the IEC surface temperature limits for internal tissue?

A

T max: 43 degree C
dT max: 6 degree C

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12
Q

Which TI should I use for fetal scanning?

A

TIS for first 10 weeks post last menstrual period
TIB thereafter

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13
Q

How can I calculate the initial rate of temperature rise during scanning?

A

Q=mcdT

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14
Q

Which two parts of the anatomy are high risk for gas body effects?

A

lung and intestine

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15
Q

Which scanning mode is associated with highest TI and why? (two things)

A

PW Doppler
non-scanned mode
long pulses

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16
Q

What is the purpose of the derating factor in the equation for MI?

A

Convert value measured in water to that which might be measured in tissue, according to attenuation properties of tissue.

17
Q

Under which circumstances are risk of acoustic cavitation highest?

A

presence of microbubble contrast agent + high MI

18
Q

What can acoustic cavitation do to kidney?

A

capillary haemorrhage

19
Q

How can I prevent infection hazard associated with endo-cavity scanning? (two things)

A

use disposable probe covers
high level disinfection

20
Q

What is the guidance on 1st trimester Doppler in obstetrics?

A

WFUMB: No routine Doppler in 1st trimester
Can use to e.g. refine trisomy risks.

21
Q

What is the safety guidance on echocardiography?

A

WFUMB: High MI can induce premature ventricular contractions, so avoid if acute coronary syndrome.

22
Q

What temperature rise is potentially hazardous to the fetus and which mode can achieve this?

A

BMUS advise that a rise of 4+ degrees is potentially hazardous to fetus.

Doppler modes can achieve this at/near bone.

23
Q

What is the upper limit of TI for general scanning?

A

6.0

24
Q

What is the upper limit of TI for obstetric scanning?

A

3.0

25
Q

What is the recommended range of TI for general scanning?

A

<1.0

26
Q

What is the recommended range for TI for obstetric scanning?

A

<0.7

27
Q

At which MI should you exercise caution with microbubble contrast agents in general scanning?

A

> 0.7

28
Q

At which MI is it possible to damage neonatal lung and intestine?

A

MI>0.3

29
Q

What is BMUS stance on souvenir scanning?

A

Not encouraged

30
Q

IEC 60601-2-37 contents?

A

Based on the Output Display Standard.

Says when TI and MI must be displayed.

Also contains temperature limits for probes.

31
Q

IEC 60601-2-37 requirement for display of temperature TOE probes applied above what temperature?

A

41 deg C

32
Q

What is Track 3 for FDA?

A

Scanners that conform to the ODS.

Must display MI and TI.

Must publish max MI and TI in manuals.

Must have a safety education program.

33
Q

FDA Track 3 derated Ispta limits?

A

720 mW/cm^2
50 mW/cm^2 opthalmic

34
Q

FDA Track 3 derated Isppa limits?

A

190 W/cm^2

35
Q

FDA max MI?

A

1.9
0.23 opthalmic

36
Q

FDA max TI

A

6.0
1.0 opthalmic

37
Q

What does IEC 62359 tell us?

A

How to measure MI and TI

38
Q

Equation for TIS and TIB for scanned modes?

A

TI=W_01*fc/ 210

IACC (7 decks)

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