X-Ray Physics Final Exam Review

stochastic effects

stochastic effects

probability or frequency of the biologic response to radiation dose

non-threshold- any dose is damaging

usually a low dose of radiation exposure in a long period of time and a late response

long term: takes months or years

non-stochastic effects

aka deterministic effects

radiation response increases in severity with increasing radiation dose

has a threshold dose

usually a high dose of radiation exposure in a short period of time and an early response

short term: takes hours or days

non-threshold dose

there is no safe amount/dose of radiation

threshold dose

first evidence of biologic effects does not occur until a certain minimum dose is achieved- like sunburn

unobservable effects may occur

genetic effects

effect that is passed down genetically from person who was radiated

somatic effects

occurs only in the person who was radiated

factors that may influence the amount of effect from radiation

size of dose

rate of dose

part of body exposed

age of person

type of radiation involved

law of bergonie and tribondeau

the most radiosensitive cells are immature cells that are highly proliferative, have a high growth rate, and are poorly differentiated

younger the tissue the more sensitive

tissues with high metabolic rate have higher sensitivity

what are the cardinal principles of radiation saftey

time, distance, shielding

patient shielding

was used to shield reproductive regions but no longer used because they had caused too many retakes that resulted in more exposure

what does ALARA stand for

as low as reasonably achievable

primary barrier

wall that central ray is directed at

behind where bucky is

secondary barrier

barriers designed to protect from scatter and leakage

less thick than primary barrier, rarely require lead

what are two types of radiation monitoring devices

film badges and thermoluminescent dosimeters

maximum permissable dose (MPD)

doses below the MPD should not result in somatic or genetic effects

what is the MPD based on

a linear non-threshold dose response relationship

the more radiation, the more chance of ill effect

what is the whole body occupational MPD per year

5 REM/year

what is whole body occupational MPD for pregnant women

0.5 REM/year

what is whole body non-occupational MPD

0.1 REM/year

MPD for lens of eye

15 REM/year

MPD for skin

50 REM/year

new formula for calculating MPD

1 x patients age

linearity

different mA and time that result in same mAs

all images should look the exact same

reproducability

using the same settings on the console

images should be the exact same

what is the unit for intensity of x-rays in the air in classical

Roentgen (R)

what is the unit for absorbed dose in classical

RAD

what is the unit for occupational exposure in classical

REM

when should x-rays of a female be taken

0-10 days from the onset of menstruation

start of period to day 10 of cycle

conventional radiography

plain film x-ray

requires chemical processing narrow film latitude

what are two types of digital radiography

computed radiography

direct to digital radiography

computed radiography

uses a cassette and PSP plate

PSP plate is read and sent to computer

easier to update because it can fit older equipment better

direct to digital radiography

no cassette requited

images sent directly from machine to computer

able to do post processing

wider film latitude

what is the best way to reduce scatter

grid

when should you use a grid

with kVp over 60 and when body parts are over 10 cm

grid ratio

height of the lead strip divided by the interspace width

grid ratio relationships

higher grid ratio, less scatter

higher grid ratio, increased contrast

higher grid ratio, decreased density

higher grid ratio, more patient exposure

intensifying screens

used inside a conventional cassette and intensifies the light so you need less x-ray photons

contains rare earth elements/crystals

lowers patient dose

what are the geometric properties

magnification and penumbra

what affects magnification and penumbra

SID: decreased SID, more magnification vice versa

OID: increase OID, more magnification vice versa

what are photographic factors

density and contrast

what affects density

SID: shorter SID, more density

OID: shorter OID, more density

amount of scatter

mAs

what affects contrast

OID: longer OID, more contrast

amount of scatter

kVp

what is fog

gray on an image (scatter)

what is quantum mottle

graininess

what are the three interactions with matter

absorption, transmission, scatter

absorption

white or lightness on an image

photon disappears

transmission

black or darkness on an image

photon goes straight through and hits image receptor

scatter

shades of gray on image

photon changes energy and direction

what determines the type of interaction that occurs

the energy of the photon

what occurs at 0-10 kVp

classical scatter

does not contribute to image, photon just gets excited

what occurs at 10-60 kVp

photoelectric effect (absorption)

what occurs at 60-125 kVp

Compton scatter

what is the process of producing x-rays

electrons are boiled off at the cathode and are sent to the anode and create x-rays at the focal spot and then are delivered to the patient

what is the main controlling factor of density

mAs

what is the main controlling factor of contrast

kVp

what is the purpose of the developer when processing film x-rays

to convert exposed silver halide crystals to black metallic silver

what are the four basic steps of developing film

developing: produces visible image from latent image

fixing: removes remaining silver halide and hardens gelatin

washing: removes excess chemicals

drying: removes water and prepares image for viewing

where should digital x-rays be stored

PACs system

steps for CR

cassette with PSP plate loaded and exposure taken

cassette placed in CR reader for image to be read

scanner sends image to computer within 25-90 seconds and then erases PSP plate

how many images can be converted at a time using CR

one

steps for DDR

exposure taken

look at computer screen

how often should film badges be sent in

every month

how often should TLD badges be sent in

every three months

what parts of the x-ray machine are designed for protection

protective tube housing, control panel, SID, Collimation, beam alignment, filtration

what is the controlled area

where you take the x-rays

what is the maximum exposure rate for controlled area

less than 100 mR/year

what is the uncontrolled area

other areas in the office such as waiting rooms

what is the maximum exposure rate of uncontrolled area

less than 10 mR/year

when is it necessary to wear a dosometer

when you might receive 10% MPD

what should you do with the control badge

keep away from radiation area- place in a drawer or cabinet

measures background radiation and is sent back with other badges

direct effect

single or double DNA strand break

indirect effect

free radical is formed from a water molecule

effects of stochastic effect

leukemia

cancers: bone, lung, thyroid, breast

local tissue damage: skin, gonads, eyes

shortened life span

genetic damage

effects of deterministic effect

acute radiation syndrome: hemolytic, GI, CNS

local tissue damage: skin, gonads, extremities

hematologic depression

genetic damage

what can increase patient dose

high frequency grid ratio, increasing mAs, longer exposure time, larger field size, ect.