CT Principle 1 Flashcards
Unlike X-rays, CT reconstructs ____ of internal structures according to ____ for almost every region in the body
cross sectional images; x-ray attenuation coefficients (tissue density)
CT was previously known as
Computed Axial Tomography (CAT Scan)
What imaging technique was used to visualize the brain before the invention of CT?
radiography
Which mathematician introduced the transformation operator that laid the foundation for tomographic reconstruction?
Johann Radon
After the injection of air in pneumoencephalography, the patient was rotated, somersaulted or placed in a ___________ position to depicts the entire ventricular system and subarachnoid spaces
Decubitus
Who validated Allan Cormack’s work by building the first prototype CT scanner?
Sir Godfrey Hounsfield
which gen uses pencil beam
1st Gen
which gen uses narrow fan beam
2nd Gen
which gen uses wide fan beam
3rd, 4th, 6th
which gen uses electron gun firing beam
5th
which gen uses cone beam
7th
which gen uses translate-rotate
1st, 2nd
which gen uses rotate-fixed
4th
which gen uses rotate-rotate
3rd, 6th, 7th
which gen uses stationary-stationary electron beam
5th
which gen uses rotate-rotate (helical/spiral)
6th, 7th
which gen uses slip ring technology
3rd, 6th, 7th
What is the main advantage of CT over conventional radiography?
Elimination of superimposition of structures
The first generation of CT scanners used which motion for scanning?
Translate – rotate
In CT, what does the term ‘voxel’ refer to?
A volume element in 3D space
pre-patient collimators is place between
filter & patient
post-patient collimators is placed
on top of detector
purpose of pre-patient collimators
lowers dose & over beaming
purpose of post-patient collimators
reduces scatter, penumbra
defines slice thickness
what are slip rings
alternatives to cabling system; power & control signals comms via rotating frame through slip ring
what is the main benefit of slip rings
Allow scan frame to rotate continuously with no need to stop between rotations to rewind system cables
CT Detector Image Formation Process
- x-rays generates radiation
- x-rays penetrate body & attenuated by tissue
- attenuated x-rays processed by detector
- detector converts radiation into electrical signals
- converts digital data into high res images
GOS
Gadolinium Oxysulfide
Pr
Praesodynium-doped
UFC
ultra fast ceramic
CsI
Cesium Iodide
Solid scintillator layer converts ___
x-ray photons to light photons
photodiode converts __
light photons to electrical signals
properties of solid state detectors
- high detection
- high geometry
- small size of DELs
DELs are important for
spatial resolution
high detection & high geometry are important for
radiation dose
what does beam shaping filtering do
Hardens x-ray by removing low energy x rays that do not contribute to image formation but increase patient dose
as the x-ray energies become narrower, the beam becomes more ___
monochromatic
what is the common beam filter used
bow-tie filter
what happens if the iso-centering is off
off iso-centering > need to increase x-ray output due to filtering mismatch > increases dose
what is related to couch top speed
pitch
sequential scans are when the patient moves ___
gradually layer-by-layer through gantry during scan
spiral scans are when the patient moves ___
continuously through gantry during scan
advantages of multi-row detectors against single row detectors
- reduced scan time (more coverage + faster scans)
- shorter breath holds
- fewer motion artifacts
- allows for multiphase contrast enhanced scanning
- reduced dose
- more efficient use of x-rays with increasing slices
how many images are created per rotation when using single slice detectors
1 per rotation
how many images are created per rotation when using multi slice detectors
hundred per rotation
what controls slice thickness along z-axis for single slice detectors
collimation
what controls slice thickness along z-axis for multi slice detectors
activating diff combo of detector rows along z-axis; by detector size
detector pitch definition
distance table travels in 1 360 degrees gantry rotation divided by beam collimation / x-ray beam width
pitch detector ranges from
0.75 to 1.5
choice of pitch influences __
image quality + dose
the higher the pitch, the ___ the dose & image quality
lower
the lower the pitch, the ___ the dose & image quality
higher
what does pitch fundamentally influence
- dose
- image quality
- scan time
