Rad Bio Quiz 2

4 basic types of quantities measured in medicine

Radiation exposure, radiation dose, dose equivalent, effective dose

Narrowly defined as the intensity of radiation incident upon the surface of object

Exposure

Exposure is best detected as ___ events in the air just above the surface

Ionization

The intensity of radiation entering through the surface into the body, (Not the amount absorbed by the body)

Entrance Skin Exposure (ESE)

The intensity of radiation incident upon the surface of the body, be it a human or an ion chamber

Radiation exposure

What is the only way to count xray photons before some of them are absorbed by the object

Measuring the ionizations they are causing in the air just above the surface

Unit for exposure

Coulomb per Kilogram C/Kg

Air kerma unit

Gray

The effect of radiation on the human body as a whole also depends on ___

How much was absorbed

Exposure Area Product (EAP) expresses the difference by multiplying what

The exposure by the collimated area of tissue

What is the unit for EAP

Gy-cm²

What units do we use

SI units

What 2 things describe the amount of actual biological harm

Dose equivalent or effective dose

The intensity of radiation incident upon the surface of a body

Radiation exposure

How do you count the xray photons that go across an area before they are absorbed by an object

Extrapolate their number from the ionizations they are causing in air molecules near the surface being exposed.

Ionization in air molecules creates a __ in surrounding air

Electrical charge

Electrons that are freed from their atoms by ionization can then be attracted to the positive __ of a detection device

Anode

The unit for electrical charge

Coulomb

1 Coulomb= how many electrons

6.3 × 10¹⁸

The international standard unit for radiation exposure is

C/kg (Coulomb per kilogram)

The quantity __ has largely replaces the quantity, exposure for expressing the co0ncentration of radiation at the bodys surface

Air kerma

Unit for air kerma

Gray

The unit Gray for air kerma applies to __ energy rather than electrical charge generated

Absorbed

What unit is now widely used to describe the Entrance Skin Exposure (ESE)

Gray

The concept of exposure expresses the concentration of radiation delivered to a particular

Location

The effect of radiation exposure on the human body as a whole depends on what

How much of the body was exposed to the radiation

__ is the product of the exposure multiplied by the collimated area of tissue that was exposed

Exposure Area Product (EAP)

What is the unit for EAP

Gy-cm²

If a 20 mGy exposure is delivered to a 24 × 30 cm area of the abdomen, the exposed tissue area is __, and what is the EAP?

Exposed tissue area: 24 × 30 = 720 cm²

EAP: 20 × 720 = 14,400 mGy-cm²

In terms of radiation effect on a patient, what is more pertinent? EAP unit or the exposure alone

EAP unit

For the best indication of the overall effect of the procedure on the patient, we add what

The EAPs of all individually exposed areas together

The sum of all EAPs is called what

The surface integral exposure (SIE)

The unit for measuring the concentration of radiant energy deposited in a specific body tissue is

Gray

The milligray is __ of a gray

One thousandth

The microgray is __ of a gray

One millionth

1 Gy= __ J/kg

1

Soft tissue has a physical density nearly identical to what

Water

What do we use to measure the portion of energy absorbed internally

Kerma

What does Kerma stand for

Kinetic Energy Released per MAss

__ is radiation dose absorbed in tissue, with the unit Gray

Kerma

__ is the radiation exposure at the surface of the body, also with the unit Gray

Air kerma

Kerma unit

Gy

Air kerma unit

Gy_a

Body tissue is how many times denser than air

1000 times

1 Gray of air Kerma results in approx. how many Gray of tissue dose

1

The unit of dose

Gray

A technique of 100 kVp and 30 mAs delivers a dose of 3 microgray. The same technique is used for 2 different patients, one using an 18 × 24 cm collimated field and the other using a 24 × 30 cm collimated field.

Which patient will receive more dose?

Which patient will receive more harm?

Dose: Both receive the same dose because the same technique was used

Harm: Find the Dose Area Product (DAP)

A) 3 × 18 × 24 = 3 × 432 = 1,296

B 3 × 24 × 30 = 3 × 720 = 2,160

Patient B received the greatest harm

The concentration of deposited energy describes

Dose

What is the most practical quantity for monitoring the radiation delivered to patients

Dose Area Product (DAP)

Air kerma is reported as what

The skin entrance dose (SED)

__ dose is the radiation quantity that describes the total energy absorbed by the body for a radiographic procedure

Integral dose

How to find integral dose for a CT scan

Dose concentration of each slice times the number of slices taken

Unti for integral dose

Joule

The total energy absorbed by the body in Joules defines

Integral dose

The weighting factor __ refers to the relative harmfulness of the type of radiation being used compared to that of an xray beam at 250 kV

W_r

W_r for neutrons

10

W_r for alpha particles

20

W_r for xrays, gamma rays, beta particles, and positrons

1

When the absorbed dose in Grays is multiplied by W_r, we obtain the __ __, a true measurement of biological harm/effectiveness

Dose equivalent

The unit for dose equivalent

Sievert

The __ is the most appropriate unit for conveying the effects of medical radiation exposure on patients and personnel

Sievert

How much biological harm is done by a 4 mGy dose of alpha particles? (finding dose equivalent)

4 mGy x 20 W_r = 80 mSv

The weighting factor __ is used to find the relative sensitivity of the particular tissue or organ being exposed compared to other tissues

W_t

If a pelvis exposure delivered a dose of 600 microgray to the gonads (W_t = .20), what would the effective dose be

600 × 0.20 = 120 microgray

A total body effective dose can be found by what

Summing the effective doses for each exposed area

Most of a radiographers occupational dose comes from what

Fluoroscopy

The occupational total body effective dose for radiographers is generally assumed to be __ of their monitor reading for a dosimeter worn outside of a lead apron

1/10

In nature, what unit describes energy deposited per mass of substance

Gray

What 2 are true biological units describing the harm done to an organism

Dose equivalent and effective dose

One mrem is equal to __ mSv

0.01

To convert mrem to microsieverts, simply multiply by what

10

Unit for radioactivity

Becquerel

The __ unit is a simple count of the number of decay events, or emissions of any wave or particle from a radioactive object each second

Becquerel

One becquerel is how many decay events per second

One

Unit for energy absorbed in air (J/kg)

Gray

Unit for energy absorbed in tissue (J/jk)

Gray

Unit for biological harm

Sievert