Physics of Diagnostic Radiology Week 4

What are the 3 types of x-ray filter?

Primary

Secondary

Compensating

What is the AKA of primary filter?

HVL / half value layer

What type of x-rays does the primary filter remove?

x-rays with energy less than 50 kV (AKA "soft x-rays")

T or F: The primary filter softens the x-ray beam

False (hardens the beam)

What % doe she primary filter reduce the strength of the beam?

50%

What unit is used to measurethe primary filter?

mm of aluminum

What is the value of filtration in the inherent/primary filter?

2.5 mm

What is the total mm of aluminum in the primary filter with the collimator?

3.5 mm

What is the term for A permanent filter that hardens the beam even further?

Secondary filter

What type of imaging uses a secondary filter?

Mammography

What is the term for a filter that Accommodates the thickness variation of the anatomical part?

Compensating filter

Which filter Allows for more uniform optical density?

Compensating filter

Which end of the compensating filter attenuates more x-rays?

Thicker end

Why is a compensating filter needed in an AP thoracic?

The lungs are air density and require less x-rays

T or F: A beam-restriction device can alter the field of view

False

What limits x-ray beams to required size?

X-ray beam restriction-collimation

What shape would the x-ray beam be if there was no collimation?

Cone-shaped (circular x-ray)

T or F: X-ray beam restriction often exceeds the film size

False (need to show evidence of collimation on 3 sides)

What are the functions of x-ray beam restriction?

Limits patient radiation dose

Decrease scatter radiation reaching the film

What is the most common beam-restricting device?

Variable-aperture collimator

T or F: The center of the receptor should be aligned to the center of collimation

True

What is the term for where the x-ray beam comes out of?

X-ray focus

What are the AKAs of focal film distance?

TID (tube image distance)

SID (source image distance)

What FFD are most films taken at?

40"

What views are taken at 72" FFD?

Lateral cervical (N,F,E)

Cervical obliques

Chest

What is the AKA of Object Film Distance (OFD)?

OID (object image distance)

T or F: Larger OFD is less desirable because it has more magnification

True

What is the AKA for Film-object distance?

Source object distance (SOD)

What is the unit for Exposure?

Roentgen (R)

What is the unit for absorbed dose?

RAD (rad)

What is the international unit for absorbed dose?

Gray (Gy)

What is the unit for equivalent dose?

REM (rem)

What is the international unit for equivalent dose?

Sievert (Sv)

What is the unit of radioactivity?

Curie (ci)

What is the international unit of radioactivity?

Becquerel (Bq)

What describes radiation intensity through air?

Exposure

What types of radiation does exposure apply to?

x-rays and gamma rays interaction with air

What is the typical unit of exposure?

milliroentgen (mR)

What is used to measure exposure?

dosimeter

What describes the quantity of radiation received by the patient?

RAD: Radiation absorbed Dose (GY)

What is the conversion of 1 gray to rad?

1 gray = 100 rad

What Describes quantity of radiation received by radiation workers and populations?

REM: Radiation equivalent Man (SV)

What measures REM?

Occupational radiation monitoring devices

What is the conversion of 1 sievert to rem?

1 sievert = 100 rem

What are the 5 interactions that x-rays can have with matter?

Classical (coherent, thompson)

Compton

Photoelectric effect

Pair production

Photodisintegration

Which interactions of x-rays with matter are most important clinically?

Absorption

Scatter

Penetration

Which 3 interactions of x-rays with matter occur in radiology?

Classical (coherent, thompson)

Compton

Photoelectric effect

What is the order of increasing energy of interactions of x-rays with matter?

Classical (coherent, thompson)

Compton

Photoelectric effect

Pair production

Photodisintegration

What voltage does the classical / Coherent effect occur at?

10 volts or less

What is the term for directional change of an x-ray?

Scatter

T or F: Classical interactions deposit energy into material

False (deposits no energy)

T or F: Classical scatter ionizes atoms

False

What is the term for when an Incident x-ray interacts with an outer-shell electron and ejects it from the atom?

Compton effect/compton scatter

What is the term for X-ray scatted back in the direction of the incident x-ray?

Backscatter radiation

What is the source of most of the occupational radiation exposure received by x-ray techs

Compton effect/compton scatter

T or F: Compton effect/compton scatter is ionizing

True

T or F: Scatter increases image contrast

False (reduces)

What is the term for when the Incident x-ray is totally absorbed during ionization of inner shell electron?

Photoelectric effect

Which electron is ejected from the K shell with the photoelectric effect?

The photoelectron

What does the photoelectric effect occur?

When there is use of contrast materials, such as barium

T or F: The photoelectric effect causes ionization

True

What is the term for when x-rays and nuclear electric fields cause the x-ray to disappear and cause 2 electrons to appear (1 positive and 1 negative)?

Pair production

Why doesn't pair production occur in diagnostic radiation?

It doesn't occur below 1.02 MeV of energy

What type of imaging will pair production occur in?

PET

What is the term for an x-ray space interaction with electrons where they are absorbed by the nucleus?

Photodisintegration

What type of particle is ejected in photo disintegration?

Nucleon

T or F: Photodisintegration is found in diagnostic radiology

False

T or F: Electrons change directions with the photoelectric effect

False

What type of x-rays are desirable to hit the receptor?

Transmitted x-rays

What type of x-rays are undesirable to hit the receptor?

Scattered x-rays

What are the two sources of scatter?

Classical and compton scatter

What type of scatter is more common?

Compton

T or F: A photon hitting the receptor darkens it, thus the reason why scatter reduced contrast

True

T or F: There is a linear relationship between amount of scatter and reduction of contrast

false (exponential)

What is the solution for scatter?

Grid

What size body parts should the grid be used for?

Greater than 8-10 cm in dimension

What is the function of the grid?

Improves image contrast and resolution (by removing scatter radiation)

Who invented the grid?

Gustave Bucky

When was the grid invented?

1913

What are grids made of?

Lead strips

What is the term for vertical lines seen throughout the image when using grid technique?

Grid lines

Who improved the grid by invention of the Bucky diaphragm to remove grid line artifacts?

Hollis E. Potter

What is the equation for grid ratio?

h/D (h = height of lead strips, D = distance between strips)

What is the equation for grid frequency?

1 / (t + D) (t = height of the lead strips, D = distance between strips)

T or F: Diverging lead strips are focused while parallel lead strips are unfocused

False

T or F: Higher grid ratio = more effect in removing scatter

True

T or F: Increased grid ratio increases patient radiation dose

True

What is the term for the number of lead strips per inch or centimeter?

Grid frequency

To or F: Higher grid frequency increases patient radiation dose?

True

What is the recommendation for grid ratio?

8:1, 10:1, or 12:1

What is the recommendation for grid frequency?

100-120 lines per inch