CT P1 Flashcards
What is CT
an imaging procedure that uses X-ray equipment and computer processed measurements taken from different angles to produce cross sectional images
Name two CT limitations
1: superimposed structures
2: different structures with low contrast
what is the function of a CT detector?
conversions of X-ray into electrical signal
what are the CT detector characteristics?
- small in size because better spatial resolution
- allows many detectors to be connected to form an array
- high dictation efficiency and high sensitivity to capture a wide dynamic range
- fast response
- high stability to function under the high speeds of rotating granty
what are the main functions of an Xray tube?
they have longer faster continues exposure times at higher KV and mAS
They have larger and thicker anode to absorb and dissipate large amounts
what are the advantages of metal cermaic tubes
1.higher tube loading
2. longer tube life
3.spiral groove bearing uses Liquid Metal alloy as lubricant
what does Stratton xray tube do?
allows the entire tube body to rotate rather than just the anode
what is a slip ring
a slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure.
how many CT scanner generations are there
3
what’s the 5th generation
its a developed specifically for cardiac scanning , this is known as electron beam scanners
what’s the 6th generation
spiral / he
what is the 7th generation?
multi detector array CT
what is attenuation?
attenuation is how easily a material can be penetrated by an xray beam.
what is attenuation coefficient?
a fraction of a beam of X-rays that absorbed or scattered per unit thickness of the absorber
what is the attenuation coeffiecient equation
It= I0e-ux
I0= incident beam
It= transmitted beam
u-attentuation coeffieinct
X= thickness of body part imaged
e= mathematical constant
how is an image produced?
CT uses a reconstruction algorithm called black projection
what is black projection?
screens are designed to enhance contrast by absorbing ambient light
what is filtered back projection
its used to fix the problem caused by black projection: this type of filtration picks up sharp edges within the projection and subtracts out extra smearing caused by black projection
what is image filtering?
reduces x-ray intensity, but not the maximum energy of the x-ray beam spectrum.
what is iterative reconstruction
Iterative reconstruction refers to an image reconstruction algorithm used in CT that begins with an image assumption, and compares it to real time measured values while making constant adjustments until the two are in agreement
what is image matrix
this consist of square Matrix of picture elements which each one represents a voxel of the tissue of the patient
What is CT windowing
this is when the CT image grayscale component of an image is manipulated via the CT numbers, this changes the appearance of the picture to highlight the particular structures
what is window width (WW)
an images contrast
what is WL
the brigthness of an image
What is a pitch
speed of the table movement through the gantry defines helical pitch
what is interpolation?
an estimate of a value at a certain position using known data from nearby points
what are CT detectors and their functions?
- small in size so its better for spatial resolution
- allows for multiple detectors too be combined
what is the attenuation coefficient?
it describes the fraction of a beam or xray that is absorbed or scattered per unit thickness of the absorber
what is image reconstruction?
