Radiology basics

Quiz #1

What are the American College of Radiology (ACR) Appropriateness Criteria?

evidence based guidelines that assists healthcare providers in determining the type of imaging most appropriate for a clinical condition

What are the Ottawa Foot Rules?

clinical guidelines used to help determine whether a patient with a foot/ankle injury requires imaging; includes specific criteria to be assessed including the presence of bone tenderness at the base of the fifth metatarsal, bone tenderness at the navicular, or the inability to bear weight both immediately and in the ED for four steps

What are the required components of the radiograph?

1. X-ray beam source

2. patient

3. image receptor

On a radiograph, why do bones appear white while air appears black?

bones absorb x-ray photons so fewer photons reach the detector & appear white (radiopaque); air absorbs very few x-ray photons so most photons reach the detector & appear black (radiolucent)

How does ionizing radiation cause tissue damage?

• ionizing radiation changes the chemical properties of molecules after exposure

• radiation changes water molecule to a free radical (highly reactive molecules)

• free radicals damage cellular components (DNA) and result in cell dysfunction or cell death

What is attenuation in radiography?

reduction in the intensity of an X-ray beam as it passes through tissue due to absorption and scattering of X-ray photons

What is high attenuation in radiography?

tissue absorbs many x-ray photons so fewer photons reach the detector; appears white on radiograph; bone

What is low attenuation in radiography?

tissue absorbs few x-ray photons so more photons reach the detector; appears black or dark gray on radiograph; air

How does tissue density affect appearance on a radiograph?

denser tissues absorb more x-ray photons (higher attenuation) and appear white; less dense tissues absorb fewer x-ray photons (lower attenuation) and appear black

What are the main methods used to capture X-ray images?

1. film/screen

2. fluoroscopy

3. computed radiography (CR)

4. digital radiography (DR)

What is a fluoroscopy?

uses continuous / pulses x-rays; produces real-time moving images; allows visualization of motion

What is a computed radiography (CR)

uses a special imaging plate instead of film (phosphor screen); plate is scanned by a computer after exposure; converts image into digial format

What is a digital radiography (DR)?

uses electronic digital detectors; uses an x-ray sensitive semiconductor material to produce images immediately on computer

What is radiodensity?

the physical property of a tissue or object that determines how much X-ray it absorbs (attenuates); high radiodense objects appear lighter and low radiodense objects appear darker

What does radiopaque mean?

not easily penetrated by x-ray (i.e., the lead shield)

What does radiolucent mean?

easily penetrated by x-ray (i.e., air)

What are the four basic radiographic densities of human tissue (from darkest to lightest)?

1. air (black)

2. fat (dark gray)

3. water (light gray)

4. bone (white)

What is contrast media?

substances placed in the body to improve the visibility of structures on images; appears bright white outlined; ex: barium used for GI study

What is an arthrography?

a contrast-enhanced imaging study of a joint; contrast media injected into joint space and used to evaluate structures (cartilage, ligaments, labrum, joint capsule)

What is a myelography?

a contrast-enhanced imaging study of the spinal cord; contrast media injected into the subarachnoid space surrounding the spinal cord and used to evaluate structures (spinal cord, nerve roots, etc)

Why are multiple projection angles needed in radiography?

• a radiography is a 2D image instead of 3D

• a single view may miss/hide fractures, dislocations, or other abnormalities

• multiple projections provide a more complete understanding of the anatomy

What does the phrase, “one view is no view” mean?

a single radiograph only provides the length and width; at least two views should be taken at different angles to allow the viewer to create an image with length, width, and depth

What is a projection in radiography?

the path of the X-ray beam through the body to the detector; different proejctions create different views of the same structure;

• anteroposterior (AP), posteroanterior (PA), lateral, and oblique

What are common patient positions used for radiographs?

upright (erect), seated, supine, prone, recumbent, Trendelenburg, and decubitus

What is the erect position?

the patient is in the upright / vertical position (standing or sitting)

What is the recumbent position?

the patient is lying down (supine, prone, or side-lying)

What is the Trendelenburg position?

patient lies on their back with the head lower than the feet

What is the decubitus position?

the patient is lying on their side with the x-ray beam horizontal

What are the possible outcomes of a routine standard radiograph exam?

1. positive or negative for a suspected clinical diagnosis

2. negative for suspected diagnosis, but raises the index of suspicion for a different condition

3. inconclusive (image does not provide enough information to make a definitive diagnosis; additional imaging needed)

4. wrong (initial clinician diagnosis incorrect or study performed not appropriate for condition; additional imaging needed)