Image Formation Flashcards
Who discovered X-rays?
Wilhelm Rontgen
Types of electromagnetic radiation
radiowaves, microwaves, infrared, visible light, ultraviolet light, X-rays and gamma rays
Shorter wavelengths have higher ___________, which results in __________ energy of the traveling photons.
Frequency, Increased
Range of electrovolts in X-rays
100 eV - 100 keV
Measure of change over a single period of time in a Sine Wave
Amplitude
The number of occurrences of a relating event per unit of time, expressed as cycles per unit of time
Frequency
Range of X-ray energy frequencies
30 petahertz to 30 exaherts
5 Forms of interaction w/ matter
- Coherent Scatter
- Compton Effect
- Photoelectric Effect
- Pair Production
- Photodisintegration
An x-ray photon interacts with the whole atom causing the atom as a whole to become excited, known as classical or thompson scatter. X-ray energy levels below 10 kiloelectrovots
Coherent Scatter
The minimum kVp setting on most CT scanners
80 kVp
X-ray photon interacts with an outer shell electron knocking it out of orbit
Compton Scattering
X-ray interacts with outer shell electron, knocking it out of orbit ionizing the atom producing a ___________
compton electron
Single projection image with large field of view
Localizer (scout, surview, tomogram, scanogram)
Used to specify perfectly transverse slices (abdomen, pelvis, chest)
AP Localizer
Used if the gantry needs to be at an angled to specify oblique slices (head and spine)
Lateral Localizer
Scan produced by the X-ray tube rotating around the stationary patient, then having the patient table move along the Z-axis at a specific distance before taking the next set of images.
Conventional Scan (axial scan, sequential scan, serial scan, step and shoot)
Type of scan that produces the best image quality.
Conventional Scan
Studies that still use Conventional Scanning
Neurological exams, Obese Patients, Cardiac Calcium Scoring
Scan mode used by having the X-ray tube rotate around the patient as the patient table moves at a specific speed determined the Pitch setting
Helical Scan (spiral scan, volumetric scan)
Advantages of Helical Scanning
Faster scan times
Made Coronary and Cardiac studies possible
More coverage in a single breath hold (less motion artifact)
Less contrast required
Arbitrary slice positioning
Ideal type of data for post-processing
2 factors that influence the path of the X-ray beam
Pre-patient collimation & Focal Spot
Speed of the patient table
Mathematical calculations used to divide the helical data into individual slice planes and placed in a raw data file.
Interpolation
Required to convert the helical path to transverse slices
Interpolation
What is a limiting factor with short scan that have high mA and quick rotation times?
Extreme Heat (causing scan delay)
