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RADT 411

CT Physics- unit 2

QuestionAnswer
What is the gantry enclosed in Metal
What is the anode made of Tungston-rhenium
What size focal spot can the x-ray tube in the gantry go up to 2 mm
Why is the x-ray anode in a CT gantry so much larger handles high heat dissipation
What is the purpose of the gantry filter it restricts passage of low-energy x-rays & allows passage of higher energy X-rays (lower patient dose)
What type of generator did the earlier CTs have 3-phase
What type of generators do later CTs have high frequency
What helps to determine patient dose pre-patient collimator
What helps to define slice thickness & reduces scatter radiation from entering the detectors post-patient collimator (pre-detector)
Another name for image receptor in CT gantry detector
What is DAS data acquisition system
What does the DAS do Amplifies the detector signal Converts analog to digital (ADC) Transmits the digital signal to the computer
Heavy patients make the table move _______, causing pitch to be off, which causes image quality to be worse slower
What are the three main differences between an x-ray tube and a CT tube CT tube is made of metal, as opposed to glass CT has a larger anode (heat dissipation) CT has a larger focal spot size (up to 2mm)
What restricts unwanted x-rays from entering the detectors assembly post-patient collimator
These physically block x-rays and are all automatic collimators
CT name for image receptor detector
What captures the beam from the patient and converts it into a signal that can be converted into a binary code detector
What is another name for a group of detectors detector array
Name the two types of detectors Xenon Gas Solid state (scintillating)
What type of detector can only detect x-rays entering along long axis xenon gas
What type of detector is 50%-60% efficient xenon gas (however textbook says 60%-87%)
What type of detector is packed closely together with no interspaces (1-1.5mm wide each) xenon gas
What is the most common type of detector used today Solid state (scintillating)
What type detector was used in 3rd generation CT scanners xenon gas
How efficient are solid state detectors 99%
t/f: Solid state detector are packed close together false
t/f: Solid state detectors have various widths and require a small gap between them true
t/f: Solid state detectors cannot accept x-rays at various angles false
What collects light and turns data to the DAS photodiode
What does scintillating mean in regards to CT detectors brief flashes of light
What is the order of CT image production x-ray tube->beam shaping filter->pre-patient collimator->fan x-ray beam->patient->
Raw data is also called scan data
Image data is also called digital data
take all of the data projections and compute & assign a CT # to each pixel to create an image image reconstruction
time from end of scanning to image display reconstruction time
finite set of steps performed to solve a solution algorithm
mathematical method of estimating the value of an unknown by using known values on either side (taking an average) interpolation
data from detectors that haven't been assigned an HU raw data, or scan data
processed data which has an HU image data
HU stands for Hounsfield unit
once reconstruction happens, what's next put it into a matrix
the process of taking attenuation profiles and inserting them into the matrix back projection
correlating beam measurements with the position they came from attenuation profile
t/f: Back projection results in a non-uniform image true:Difference between back projection and filtered back projection x-ray attenuation isn't uniform over the entire area it came from
different names for filtered back projection convolution filter Kernel Convolution
t/f: Filtered back projection has been used in every generation scanner false: it was used in all but the 7th generation
difference between back projection and filtered back projection Filtered back projection uses a correction filter to get a closer to exact representation of the object scanned
what is the benefit to filtered back projection it corrects for the fact the edges aren't properly filled out
True/False: Filtered back projection can only be done on raw data true
What is the latest (7th generation) way to reconstruct the CT image ASIR -- Adaptive Statistical Interactive Reconstruction
This occurs before filtered back projection in a spiral image interpolation
Data before convolution is called raw data or scan data
data that has just been filtered by a kernel during filtered back projection convoluted data
data that has been back projected and assigned an HU and displayed on a monitor image data
Going back to raw data and changing filters, slice thickness, FOV, etc... retrospective reconstruction
This uses only image data for multiplanar reconstruction, 3-D reconstruction, Maximum Intensity Projection (MIP) and quantitative measurements post processing, or image rendering (image reformation)
a post processing technique that uses new slices in a different orientation (sagittal, coronal, oblique) MPR (multi planar reconstruction)
The best sets of CT images comes from _____ slices thin
software program that will create a 2D image from a 3D image, used in angiography to separate superimposed vessels MIP (maximum intensity projection)
specialized software that can measure images to get info on volume, distance and diameter (used for pathology) quantitative measurements
the measurement of linear attenuation coefficient for a given tissue CT number
standard scale of CT numbers Hounsfield scale of Hounsfield Units (HU)
True/False: CT & HU are the same thing true
Can we change the attenuation of a specific tissue yes, by adding contrast
why are HU/CT numbers useful for pathologic diagnosis (seeing abnormal tissue within normal tissue)
changing the displayed contrast of an image post processed windowing
what is the window width the range of CT numbers
what does window width do for us allows us to see as many shades of gray as we want to
reducing WW ________ contrast increases
for bone tissue we want a _______ WW, which gives us _____ contrast & _____scale wide, low, long
for lung tissue we want a ______narrow WW, which gives us _____contrast & ______ scale narrow, high, short
changing the central value of the WW post processed window level
What is window level the center CT number
what does window level do for us allows us to set the center # wherever we want on the scale
t/f: Window level doesn't have to be at the center of WW false--window level is ALWAYS at the CENTER of window width
the area over width the CT scanner will collect data field of view (FOV)
determines the number of detectors collecting data for a particular scan scan field of view (SFOV)
Display field of view (FOV) is _________ than scan field of view (SFOV) smaller
Continuous acquisition scanning without table movement, primarily used for hearts (arterial contrast) Cine imaging
Created by: meechthebeech91