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CT/MR Physics Test 2
Notecards for CT/MRI Test 2
| Question | Answer |
|---|---|
| What is the gantry enclosed in | Metal |
| What is the anode made of | Tungston-rhenium, put on with a chemical vapor process |
| 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 | to handle 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% |
| True/False: Solid state detector are packed close together | False |
| True/False: Solid state detectors have various widths and require a small gap between them | True |
| True/False: 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 |
| True/False: Back projection results in a non-uniform image | True-- x-ray attenuation isn't uniform over the entire area it came from |
| different names for filtered back projection | Convolution filter Kernel Convolution |
| True/False: 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 |
| True/False: 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 whish 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:
cleotaylor
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