0.1 - X-ray Basics Flashcards
What is an X-ray?
- X-rays are a form of electromagnetic radiation
- It is an ionizing radiation
What is the wavelength and intensity of X-rays?
- wavelength = 0.01-10nm
- photon energy = 100 eV - 100 keV
wavelength is inversely proportional to the intensity of the X-ray (rate of penetration and beam hardness)
How are X-rays produced?
A direct current, hot cathode releases electrons that are accelerated in a vacuum tube by high-voltage. The accelerated high velocity electrons collide with a metal anode to create X-rays.
The current and voltage of the X-ray machine determines the properties of the X-ray beam
What are the main properties of X-rays?
- electromagnetic radiation
- traverse thick objects without much absorption or scattering
- ionizes atoms and disrupts molecular bonds
- higher atomic number materials attenuate a greater percentage of the beam than lower atomic number materials
- induces variable chemical changes in film emulsion
- certain materials can convert X-ray into visible light (fluoroscopy)
Magnification of X-rays
- X-ray beams diverge in straight lines from the source causing magnification and distortion
- structures closer to the X-ray source and magnified
- structures closer to the X-ray detector appear more realistic in size
- magnification/distortion is not an issue multislice modalities (PET/MR/CT)
What are common examples of static X-ray images?
- chest X-ray
- bone X-ray
- abdominal X-ray
- mammography
- bowel follow-through study
What are examples of common fluoroscopy studies?
- cholangiography
- catheterisation of hepatic artery
- urogram of transplanted kidney
- GI studies with barium contrast agent
- placement of medical devices
- angiograms
- orthopedic surgeries
- placement of medical devices
What is fluoroscopy?
- dynamic/functional imaging (X-ray movie)
- continuous X-ray radiation is used to examine movement of structures and contrast agents
- higher radiation dose than in X-ray images
What does the attenuation of X-ray depend on?
atomic number, density and thickness of the material
What appears bright on X-rays?
- described as radiopaque or decreased transparency
- denser structures
- structures that attenuate large amounts of X-rays
- higher atomic number materials
- ie. bone, calcification, contrast agents
What appears dark on X-rays?
- described as radiolucent or increased transparency
- more transparent structures
- structures that are less attenuating
- ie. air, fat
Brightness in fluoroscopy imaging
- reversed compared to X-ray
- dense structures appear dark
- more transparent structures appear brighter
What are the major X-ray densities?
- air
- fat
- soft tissue (water)
- bone
- metal
How is the resolution of X-ray?
X-ray has excellent spatial resolution but poor soft tissue resolution
What is the benefit of X-ray in lateral decubitus position?
patients in poor condition benefit from taking abdominal X-rays in lateral decubitus position to detect air-fluid levels and free peritoneal air
Detecting breast malignancy in mammography
it is easier to detect microcalcifications in adipose breast tissue than dense breasts, thus malignancy can easily go unnoticed in denser breasts
What should be considered in case of posterior fat pad in elbow joint?
- appearance of lucent crescent of fat in the olecranon fossa (true lateral view)
- indicates trauma
- consider supracondylar fracture or intra-articular fracture (ie. lateral condyle fracture)
How to diagnose pleural effusion on X-ray?
- homogenous decreased transparency
- costophrenic angle is not visible
What is the anatomy of bowels in abdominal X-ray?
- colon: more meteoristic than small bowels
- small bowels: minimal gas content, located more centrally
What are the advantages and disadvantages of X-ray imaging for bone?
- the higher attenuation of calcification in bones makes it easier to be visualised in contrast to surrounding tissue
- sclerotic bone tissue can be visualised but there isn’t much information on the bone marrow
- X-ray has great linear resolution so it is great for fractures, at least two projections are always required
- X-ray does not detect soft-tissue injuries well
The use of barium as a contrast agent in radiography
- barium coats the gastro-intestinal mucosa in a thin layer so it is useful for GI studies
- if contraindicated iodine-based contrast agent is used
- barium causes severe peritonitis and mediastinitis if it gets into contact with the peritoneum or pleura
- contraindications of barium: GI postoperative setting, perforation, anastomosis insufficiency, aspiration
What is a small bowel follow-through exam?
- non-contrast X-ray image is taken
- patient drinks iodine-based contrast agent
- image is taken every 30-60 minutes to follow the advancement of the contrast agent through the bowels
- contrast agent appears in the colon usually 30-120 minutes later (normal small bowel transit time)
When is X-ray not indicated?
- nephrolithiasis: gold standard is low-dose non-enhanced abdominal CT
- head trauma: non-enhanced head CT is recommended
- acute sinusitis: clinical diagnosis is sufficient
- chronic/recurrent sinusitis, polyposis, fungal infections, surgical planning: non-enhanced CT
- back pain with neurological symptoms: non-enhanced MRI
- lung cancer screening: low-dose non-enhanced CT
What are the advantages of radiography?
- excellent spatial resolution
- easily accessible
- quick
- available as portable devices
- contrast agents
- fluoroscopy is a dynamic, functional imaging modality
- specific signs are seen for a few diseases
