Section 3 Exam Flashcards
what percentage of the energy from the tube is released as heat and as x-rays?
99% heat, 1% x-rays
what spins in the x-ray tube?
anode
why does the tube have to be vacuum sealed?
so electrons don’t interact with air molecules and lose energy
Human body consists of six radiographic densities (listed least to most dense)
Gas or air
Fat
Water
Muscle
Bone
Tooth enamel
Metal
Cathode ____ __ to release _________ to hit spinning _____ to release x-ray
heats up, electrons, anode
Computed radiography makes use of?
photostimulable phosphor
X-ray beam collimation is used why?
pt dose is decreased, scatter dose is decreased, increases quality of image (all of the above)
focal spot is directly related to ______
detail
small focal spot =
sharper lines
Do grids help with detail?
yes it improves detail and absorbs scatter radiation
Greater SID =
increased detail
Lower OID =
reduced magnification
What studies the body using radio pharmaceuticals to evaluate?
PET scan
What is it called when sound is used to visualize internal?
sonography
What’s a portable fluoroscope called?
C-arm
Internal preparation would include?
contrast media or cleansing enema
Iodine contrast can result in:
hives, anaphylactic shock
You wouldn’t want to use barium if pt has a _____ ___________
Instead you would want to use a water soluble contrast like ___
bowel perforation, ISO
air used with contrast is called ______________
double-contrast
What is gradually replacing the barium enema?
CT and virtual colonoscopy
An x-ray study used to evaluated the patency of the oviduct?
hysterosalpingogram
Malfunctioning salivary glands may be examined during?
sialogram
What is it called if you have contrast studies of joints?
arthrogram
What does 90% of public exposure come from?
medical and dental x-rays
What does air kerma measure
ionizing radiation in the air
absorbed does by patient is measured in:
Gray (Gy)
What does the photoelectric effect have to do with?
inner electron shells transferring energy (all of the energy)
What does the compton effect have to do with?
outer electron shells (part of the energy)
Pair production has to do with:
radiation therapy
The law of bergonie and tribondeau implies that radiosensitivity is greatest in?
cells that are rapidly dividing
At which stage of life are you most sensitive to radiation?
fetus
Minimal total filtration must be _____ aluminum or equivalent
2.5mm
A unit used to measure a quantity called exposure.
This can only be used to describe an amount of gamma rays and x-rays, and only in air
roentgen (R)
A unit used to measure a quantity called absorbed dose.
This relates to the amount of energy actually absorbed in some material
radiation absorbed dose (rad)
A unit used to derive a quantity called equivalent dose.
This relates the absorbed dose in human tissue to the effective biological damage of the radiation
roentgen equivalent man (rem)
Effective Dose. Dose equivalent.
Biologic effect
sievert (Sv)
The _____ is a unit used to measure a
unit of radioactivity
curie (Ci)
equation for the inverse square law
I1 D2 ²
— = —
I2 D1
Primary items needed for production of x-rays:
Source of electrons
Means to accelerate electrons (Kinetic Energy)
Way to bring electrons to a sudden stop
* Kinetic Energy → X-Ray Energy
______ _____ is formed when x-rays pass through
the patient’s body and hit the image receptor
Latent image
Types of digital imaging:
computed radiography (CR)
direct digital radiography (DR)
Latent image is held on a phosphor plate.
Phosphor plate is encased in a cassette.
X-rays strike the plate and are trapped in high-energy state.
Computer processes the image by utilizing a laser beam
scanner.
Digitized
Creates visible image
computed radiography
Elements used are: cesium iodide, gadolinium
oxysulfide, and selenium.
Can be produced by direct and indirect
methods
digital radiography
X-rays interact directly with the element selenium creating an electric charge
direct digital radiography
X-rays first converted to light, then converted to an electrical signal
indirect digital radiography
subject density and thickness factors affecting the image
air, water, contrast, metal, pathologies
x-ray exposure factors
mAs, kVp, distance
Determines the wavelength of radiation, energy of the x-rays (penetration)
kilovoltage (kVp)
Exposure rate is directly proportional
Determines amount of x-rays per unit of time
milliamperage (mA)
As this distance decreases, detail decreases.
This distance should be kept at a maximal practical
level to keep images sharp and detailed
focal-object distance
As SID increases, level of detail ________
increases
Cross-sectional views
Eliminates need for exploratory surgery
Computer reconstructs information into an image
Computed Tomography (CT)
Also cross-sectional views
Utilizes manipulation of magnetic field and radio waves (no
radiation)
Magnetic Resonance Imaging (MRI)
Radiopharmaceutical agent injection
Physiologic condition or function
Cross-sectional images
Positron Emission Tomography (PET)
Radioactive materials introduced
into the body
Images of major organs
Nuclear Medicine (NM)
Brings digital imaging together with hospital and radiology information systems.
Total management of patient’s case
Digital network can be accessed in a variety of authorized stations
Picture Archiving and Communication System (PACS)
has high-atomic number, shows up white on radiographic procedures
Commonly introduced intravenously to visualize blood vessels and organs
Adverse Reactions
Non-ionic contrast reduces occurrence of reactions
iodine-based contrast media
Similar contrast qualities as iodine.
Cannot be absorbed by the body
Great for gastrointestinal studies
Allergic reactions are rare
barium-based contrast media
Chest Radiography
Used with barium or iodine studies to produce a “double-contrast”
air contrast media
Early measurement used
to measure the amount of radiation to turn the skin red
Erythema dose
Ionizing radiation that
produces ions in 1 cubic centimeter of air
Air Kerma
Becquerel:
Activity
dose limit for radiation workers
50 mSv per year (annual effective dose - whole body)
dose limit for general public (frequent exposure)
1 mSv rems per year
dose limit for general public (infrequent exposure)
5 mSv rems per year
dose limit for embryo or fetus
0.5 mSv per month during gestation
dose limit for embryo or fetus
5 mSv total for gestation
Three main types of photon interactions that are important in radiology:
Photoelectric Effect
Compton Scatter
Pair Production
Most common
Knocks out inner-shell electron and transfers all energy.
Usually occurs with low- energy photons.
Photoelectric Effect interaction
▸ Incoming photon interacts with orbital
electron.
▸ Portion of energy is transferred.
▸ Classic (or unmodified) Scattering
▸ Entering photon changes direction
but does not transfer energy.
▸ Modified Scattering
▸ Collision occurs and partial energy is
transferred by photon
Compton Scatter interaction
▸ Photon of extremely high energy approaches the nucleus.
▸ Both positive electron (positron) and negative electron formed.
▸ Both positron and electron ionize other atoms.
▸ Annihilation reaction
▸ Positron reacts with orbital electron and both particles disappear and create two photons that move in the opposite direction.
▸ Does not occur in diagnostic radiography (may occur in Radiation Therapy)
Pair Production interaction
Cells for reproduction
germ cells
cells that perform all other body functions
somatic cells
When radiation hits a cell, there are 4 possible results:
▸ Pass through without any damage
▸ Temporary damage, but cell regains normal functions.
▸ Damage cell without cell recovering.
▸ Kill the cell
Ionizing radiation interacts directly with the DNA molecule and breaks in the “rung” of the DNA “ladder” occur
Direct-hit theory
Cells are most sensitive to ionizing radiation when they are
rapidly dividing
Time between initial radiation and occurrence of any biological change
latent period
Occurs within minutes, hours, days, or weeks (short term)
Large dose is received by the entire body over a short period of time (larger than 1 Gy)
acute radiation syndrome
Somatic-General body cells
Cancer, cataracts, life-span shortening
long-term effects
Germ cells-sexual reproduction
Transmitted to future generations and therefore not evident to the individual that was exposed
genetic
Measurement of radiation
dose to an individual
Dosimetry
