Rad Bio: Unit 6 Exam

Exposure SI unit

Colomb (C/kg)

Exposure

Radiation intensity in air/tube output

Absorbed Dose & Air Kerma SI unit

Gray (Gy)

Absorbed Dose/Air Kerma

Biological effects/quantity patient received

Equivalent & Effective Dose SI unit

Sievert (Sv)

Equivalent/Effective Dose

Occupational workers exposure

Radioactivity SI unit

Bequerel (Bq)

Radioactivity

Quantity of radioactive material

What does low SNR cause?

Noise

What does high SNR cause?

Burnout

Low patient dose technique

High kVp, low mAs

Exposure Indicator

Numerical value for receptor exposure; derived from the median pixel value in the VOI

AAPM Task Group 116

Sets deviation index

K_IND

Indicated equivalent air kerma; indicator of detected air kerma

K_TGT

Target equivalent air kerma; optimal exposure for each body part

Beam Restriction

Limiting the primary beam to a smaller area to decrease exposure to tissue irradiated and reduce scatter production

What are types of beam restricting devices?

• Collimators/shutters

• Aperture diaphragms

• Cones/cylinders

Increased beam restriction = __________ patient dose

Decreased

Filtration

Hardens the beam by cleaning up the low energy x-rays increasing the average energy of the beam

Inherent Filtration

Glass envelope, insulating oils, window and mirror

Added Filtration

Sheets of Al outside of the glass window

Total filtration built into the housing is _______ mm Al equivalent for units operating above 70 kVp

2.5

How to reduce patient exposure in fluoroscopy:

• Last image hold

• Timer

• Pulsed fluoro

• Beam restriction

• Decrease mag mode

• ABC

• II on top

Primary Radiation

Primary beam

Secondary Radiation

Scatter and leakage radiation

What contributes the most to occupational exposure?

Scatter

Cardinal Rules

Time, distance and shielding

Increase beam restriction = _________ scatter

Decrease

What effects scatter production?

Amount of tissue irradiated, collimation and kVp

What effects scatter cleanup?

Grids, air gap technique

What is the scatter beam intensity?

1/1000 at a 90 degree angle 1 meter from the patient

Radiation must scatter _______ before reaching behind console.

2x

For mobile protection where should you stand?

6 ft (2 m) 90 degrees from the patient/path of the beam

Where should the II be located?

On top

For the c-arm, who should the II be angled towards?

The operator

Primary Protective Barrier

Any wall the beam can be directly aimed at, perpendicular to the primary beam; 1/16 Pb equivalent extending 7ft from the floor

Secondary Protective Barrier

Protects against leakage and scatter (walls you cannot aim beam directly at), parallel to the beam, 1/32 Pb equivalent and must overlap ½. inch of the primary barrier

Lead aprons, thyroid shields

0.5 mm lead

Lead gloves

0.25 mm lead

Lead eyeglasses

0.35 mm lead

Leakage radiation can not excess _____ mGy per hour 1 meter from the housing

1

Bucky slot cover and protective drape/curtain

0.25 mm lead

When does the audible timer go off in fluoro?

After 5 minutes

What is the best method of protection when taking exposures in fluoro?

Use the remote or operate from behind the console

Fixed fluoroscopy SSD

15 in (38 cm)

Mobile fluoroscopy SSD

12 in (30 cm)

Normal fluoro rate

88 mGy/min

High level fluoro rate

176 mGy/min

With tube below table, where is air kerma rate measured?

1 cm above tabletop

With tube above table, where is air kerma rate measured?

30 mm above tabletop

Where should personal dosimeters be worn?

Collar level

Where should pregnant personal dosimeters be worn?

Waist level

What dosimeter gives an immediate readout?

Pocket ionization chamber

OSL badge

Aluminum oxide, tin, copper - laser released (most popular, most sensitive)

TLD dosimeter

Lithium fluoride - heat released (read only once, can fade in heat and light)

Control Badges

Used to calculate monthly doses; badge is kept in a distant room to look at background radiation being recieved, is then subtracted from occupational dose

What are dose reports measured in?

mrem or mSv

What are dose reports broken down into?

Deep dose, shallow dose, and eye dose

Occupational Effective Dose

50 mSv (5,000 mrem)

Lens of eye annual occupational dose

150 mSv (15,000 mrem)

Extremity annual occupational dose

500 mSv (50,000 mrem)

Public annual frequently exposed dose

1 mSv

Public annual infrequently exposed dose

5 mSv

Public annual lens of eye and extremity dose

50 mSv

Embryo/fetus dose for entire gestation

5 mSv

Embryo/fetus dose for 1 month

0.5 mSv

What are campaigns for radiation safety?

Image Gently and Image Wisely