- If this episode doesn't fascinate you, I don't know what will!!
- Radiographs
- Ionizing radiation hits a photosensitive film to produce an image
- Digital radiography: photosensitive plate processed by electronic reader to be stored digitally
- PACS system: picture archiving, communications, and storage system
- Plain films = X-ray = radiograph = without contrast material
- Advantages: availability, less expensive
- Disadvantages: limited detail, uses radiation (caution in pregnancy)
- Uses: chest x-ray, abdomen x-ray, bone visualization
- Densities
- Air is black (absorbs the least), bone is white (calcium), metal appears whitest, fat and soft tissues appear in between as gray
- CT scanners
- Uses x-ray machine that rotates around patient to create different planes and produce a large series of 2D images slices
- Important to understand positioning of patient from image (you're look up from the bottom of their feet, with patient's right on the left of the screen)
- Hounsfield units: -1000 to +1000, water is zero, air is -1000, bone is +400-600, fat is -40 to -100, soft tissues is 20-100
- Windowing: range of densities to most optimally view certain structures
- Advantages: greater detail
- Disadvantages: more radiation, more expensive
- Uses: non-contrast head CT for stroke, traumas, 3D reformats
- Ultrasound
- Uses high frequency sound waves emitted from a probe
- Advantages: less expensive, availability, no ionizing radiation
- Disadvantages: operator dependent, low resolution
- Uses: great for pregnancy, gallstones, breast masses, thyroid nodules
- Doppler flow: red towards probe, blue away from probe
- MRI
- Uses magnetic fields and radio waves to affect hydrogen items
- Advantages: great resolution, no radiation
- Disadvantages: expensive, time-consuming, special precautions (pacemakers)
- Uses: brain imaging (MS), soft tissues like muscles, tendons, ligaments, herniated discs, spinal cord pathologies
- Fluoroscopy
- Uses ionizing radiation in real-time
- Can give barium to a patient which will show up black
- Uses: esophagrams, voiding cystourethrograms, interventional radiology (angiography)
- Advantages: mobile, procedure guidance, dynamic
- Disadvantages: higher dose of radiation
- Nuclear medicine
- Uses radioactive substances (elements that emit radiation as they decay) and couples them with drugs that will accumulate in certain tissues
- Different types of scans: positron emission tomography (PET) scans use radioactive glucose (fluorodeoxyglucose, FDG), single photon emission computed tomography (SPECT) uses a gamma camera to acquire images from many angles to create a 3D map
- Different organs use different substances; the brain loves glucose and the thyroid loves iodine
- Uses: cancer imaging, assessing for metastases
- Less radiation than CT scans, but must use caution with radiation exposure via shielding and appropriate timing
References: Herring's Learning Radiology, Radiopaedia, Mandell's CORE Radiology