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Mosby's Exam Review > Radiation Protection > Flashcards

Radiation Protection Flashcards

1
Q

what is the main concept to follow for radiation protection in CT?

A

ALARA

as low as reasonably achievable

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2
Q

what three principles should encompass radiation protection in CT?

A

strict clinical indication
protocol optimization
shielding

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3
Q

What three scenarios would limiting CT scanning benefit in saving radiation dose?

A

limiting ct to strict indications
limit scan lengths to clinically indicated areas
minimize multi-phase exams

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4
Q

What determines an optimized protocol?

A

One that acquires images with acceptable noise levels at low possible dose, while still delivering images of diagnostic quality

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5
Q

What 4 things need to be considered when making changes to scanning parameters?

A

examination indication, regions of interest, patient’s body habitus and age

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6
Q

What is the process of adjusting parameters such as mA/kVp, slice thickness and pitch for the purpose of reducing patient radiation dose while maintaining adequate image quality?

A

protocol optimization

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7
Q

What relationship lies between mA setting, scan time and patient dose?

A

directly proportional

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8
Q

If mAs is doubled, what happens to radiation dose?

A

doubled

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9
Q

what relationship is between kVp and radiation dose?

A

direct and exponential

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10
Q

What will happen as result of decreasing only kVp? (mas, scan time and pitch stay the same)

A

significant decrease in quantity of x-radiation produced by CT tube and subsequent decrease in patient dose

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11
Q

What two situations can a decrease in kvp be applied without a loss in image quality?

A

pediatric imaging and CT angiography exams

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12
Q

What is the section of the patient being scanned referred to in CT data acquisition?

A

dose profile

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13
Q

What controls the dimension of the longitudinal (z-axis) of the dose profile and the measurement of it at the isocenter?

A

collimation

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14
Q

With what type of scan will an increase in collimation result in a decrease in patient radiation dose?

A

single slice

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15
Q

What happens to slice thickness when collimation is increased?

A

thinner slice width

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16
Q

How is collimation proportionately related to radiation dose?

A

indirectly

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17
Q

How does an increase in collimation affect image noise?

A

increases

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18
Q

although not usually necessary, what is typically adjusted to accommodate for the increased noise from thin sections?

A

increase in mAs

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19
Q

What type of collimation is used in MDCT and also improves dose efficiency because less overbeaming occurs?

A

wide collimation

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20
Q

What type of beam width increases overbeaming while reducing dose efficiency?

A

narrow beam width

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21
Q

reconstructed algorithms and windowing settings have what type of controlling factor with patient dose?

A

indirect

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22
Q

What are noise levels in CT a function of?

A

dose

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23
Q

How does a decrease in dose affect image noise?

A

increases

24
Q

How can noise be reduced after image is displayed?

A

appropriate reconstruction algorithm or correct window settings

25
Q

What is a factor that image noise is directly related to?

A

patient size

26
Q

What happens to image noise when patient size decreases?

A

decreases

27
Q

What is a protocol optimization for making adjustments for noise and patient size?

A

size-based dose (mAs) adjustments

28
Q

Should the clinical indication be considered in attempt to reduce radiation dose?

A

yes

29
Q

What is an example of a clinical indication and scan that can be imaged with less dose and tolerate more noise for a diagnosis?

A

CT Abdomen and Pelvis for renal stones

30
Q

Why can a scan for kidney stones be acquired with less dose and still obtain diagnostic quality images?

A

the kidney stones absorb radiation due to high density structures, creating high contrast pathology

31
Q

during SSCT, pitch greater than what value can allow for the acquisition of a given scan volume in a shorter time and reduce patient dose?

A

greater than 1

32
Q

What does an increase in pitch in MDCT result in?

A

image noise

33
Q

What technical factor is considered when increasing pitch in order to reduce noise and obtain diagnostic image quality?

A

increase in mA

34
Q

What feature has been added to the scanner to manage patient radiation dose on the basis of size, density and overall attenuation of the part being imaged?

A

AEC - automatic exposure control

35
Q

What two types of automatic tube current modulation exist?

A

Angular and Longitudinal

36
Q

This type of ATCM runs along the x- and y- axis and automatically adjusts mA settings according to slice thickness of the part as the tube rotates from AP to LAT position

A

angular ATCM

37
Q

When using the angular option of ATCM, which plane attenuates the least radiation as the tube moves from AP to LAT?

A

AP position

38
Q

This type of ATCM runs along the z- axis and adjusts the mA setting based on attenuation differences of the patient as the scan moves longitudinally down the z-axis

A

longitudinal ATCM

39
Q

What type of gating is used during MDCT cardiac studies in order to reduce patient exposure?

A

prospective

40
Q

What feature in prospective gating allows for pulses of x-radiation rather than continuous exposure to be used?

A

ECG- triggered tube current modulation

41
Q

What is reduced during the cardiac phase that is not utilized for image reconstruction?

A

tube current

42
Q

The radiation dose savings gained with ECG-triggered tube current modulation depend on the patient’s what?

A

heart rate

43
Q

What happens to radiation dose savings when a patient’s heart rate increases?

A

decreases

44
Q

What setting is available on some scanners that adjust tube kilovoltage according to varying patient attenuation during CT acquisition?

A

automated tube voltage selection

45
Q

what object can be utilized during CT to reduce scatter radiation dose to sensitive tissues that lie outside of the scan acquisition range?

A

out-of-plane lead or contact shielding

46
Q

What are two examples of radiosensitive organs that should be shielded?

A

breast tissue and gonads

47
Q

Where on the patient should contact shields be placed in order to maximize dose reduction as best as possible?

A

both above and below the patient

48
Q

Where does the lead shield need to be located on the patient when using ATCM while scanning?

A

outside the scan range

49
Q

what will occur if a lead shield is placed within the anatomy being scanned with ATCM?

A

increase in radiation exposure to patient

50
Q

What type of shielding can be utilized in the orbits, thyroid and breast tissue to reduce effective radiation dose?

A

in-plane bismuth shield

51
Q

what other material can be added to bismuth shield to reduce dose?

A

rubber

52
Q

What is a disadvantage of bismuth shielding that may occur on the image?

A

streak artifact

53
Q

What can be placed between the patient and the bismuth shield to reduce scatter artifact?

A

thin foam spacer

54
Q

What organization recommends against the use of bismuth shielding in favor of more comprehensive dose reduction techniques?

A

AAPM- American Association of Physicists in Medicine

55
Q

What personnel evaluates the room shielding requirements?

A

qualified radiologic health physicist

56
Q

What are four considerations taken when evaluating room shielding requirements?

A

exam workload, scanner position, construction of doors and windows

Mosby's Exam Review (18 decks)

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