Dose

Question 1

What are different types of radiation dose?

Answer 1

1. Absorbed dose
2. Equivalent dose
3. Effective dose

Question 2

What is absorbed dose?

Answer 2

Total amount of radiation absorbed by any part of tissue

mGy

Question 3

What is equivalent dose?

Answer 3

Takes into account the type of radiation and its effect on the body

mSv

Question 4

What is the formula for equivalent dose?

Answer 4

Equivalent dose = absorbed dose x radiation weighting factor

Question 5

What is effective dose?

Answer 5

Specific to the type of radiation and sensitivities of specific affected areas/organs

mSv

Question 6

What is the formula of effective dose?

Answer 6

Effective dose = equivalent dose x tissue weighting factor

Question 7

What is CTDI?

Answer 7

Computed Tomography Dose Index

Question 8

What are the types of CTDI?

Answer 8

CTDI₁₀₀ (mGy)

CTDI_w

CTDI_vol

DLP

Question 9

What is CTDI₁₀₀?

Answer 9

Absorbed dose in the centre of a 100 mm scan range

Question 10

What is CTDI_W?

Answer 10

Calculation including centre and peripheral dose of a head or body phantom

CTDI_W = 1/3 CTDI_100,centre + 2/3 CTDI_100,edge

Question 11

What is CTDI_vol?

Answer 11

Relative to pitch

Question 12

What is DLP?

Answer 12

DLP (mGy*cm) = CTDI_vol x scan length

Question 13

How does slice thickness affect images?

Answer 13

Thicker slice = better image quality. = less detail/info

Question 14

What are methods to reduce dose?

Answer 14

1. Dose modulation - different mA at different parts of same body depending on what is required by thickness
2. Bismuth shielding - used on radio sensitive organs (i.e. breast, thyroid), placed directly on body part
3. Bow tie pre-filter - between tube and patient, shapes tube so thinner in middle (higher dose) and thicker outer
4. Iterative reconstruction - post imaging to compare raw data to what image should resemble
5. Patient position/prep - tech can position super dense parts out of field and position differently to include or exclude whatever