Week 5 - Acquisition Flashcards
-Determines the area within the gantry from which the raw data is acquired
-determines the number of detector cells collecting data
*isocentering crucial
*should come close to just encompassing the patient
Scan field of view (SFOV)
T/F
Anything outside the SFOV is not imaged
True
Artifacts from outside the FOV
Out of field artifacts
Ex. Arms on abdomen scan
-determines how much of the collected raw data is used to create the image
-acts like a digital zoom on a camera
-affects image quality by changing the pixel size
*cannot be larger than SFOV
Display field of view (DFOV)
T/F
DFOV is always smaller than SFOV
True
What are the 2 methods of data acquisition?
Slice by slice - axial
Volume - spiral/helical
What 3 steps contribute to interscan delay in slice by slice CT scan?
- Tube and detectors accelerate to a constant speed
2. - Tube and detectors slow down and come to a stop
- Table and patient indexed to the next scanning position
What is an advantage of step and shoot scanning? (Slice by slice)
-When breathing movement is not seen, image quality is slightly superior to that of helical scanning
-slices are axial in nature
What are some limitations of slice by slice scanning? (Axial)
-longer exam times because of start-stop action, table indexing, cable unwinding
T/F
A limitation of axial scanning is certain portions of anatomy are omitted because patient respiration phase may not be consistent each time
True
Why does axial (slice by slice) acquisition misregistration occur?
Occurs because of different breathing patterns between scans
What causes a “steplike” contour appearance in 3D images in axial (slice by slice) scanning?
Inconsistent levels of inspiration
What are the applications of volume scanning, and could not be done without it?
- CT fluoroscopy
- CT perfusion
- 3D imaging
- CT angiography
- CT endoscopy: Virtual reality
- Cardiac CT imaging
- Artificial Intelligence in CT
T/F
The 7 applications of volume scanning could not be done with axial scanning
True
T/F
Not all CT are done supine
True
-allows for reconstruction and display of images in real time with variable frame rates
-used when doing CT biopsies
CT fluoroscopy
What 3 advantages is CT fluoroscopy based on?
- Fast, continuous scanning made possible by spiral/helical scanning
- Fast image reconstruction made possible by special hardware performing quick calculations and a new image reconstruction algorithm
- Continuous image display by use of cine mode at frame rates of 2-8 images per second
Used to evaluate strokes, vasospasms, neurovascular disorders
Determined the extent of irreversible infarcted brain tissue
Generates map of the cerebral blood flow, cerebral blood volume, and mean transit time
CT perfusions
What needs to be performed before a CT perfusion?
CT angiogram
Used in radiation treatment planning, cranial imaging, surgical planning, and orthopaedics
Transforms transaxial CT data into simulated 3D images
3D imaging
CT imaging of blood vessels pacified by contrast media
CT angiography
The creation of inner views of tubular structures is called virtual endoscopy
CT virtual reality
To image the beating heart with the goal of reducing motion artifacts and a loss of both spatial and contrast resolution
CT cardiac imaging
*ECG is used when doing cardiac scanning
What is the goal of DLR (deep learning reconstruction) (artificial intelligence in CT)
- Provide improved image quality
- Dose performance
- Reconstruction speed
What are the requirements for volume scanning?
-continuously rotating scanner based on slip ring technology
-continuous table movement
-increased heat loading (min. 200mA per revolution)
-increased cooling capacity of xray tube
-spiral/helical weighing algorithm
-mass memory to store the vast amount of data collected
What is the first step in data acquisition?
Scanning
Why is holding the breath required in a volume scan?
Eliminates artifacts, misregistration, motion
T/F
There is no defined slice in volume scanning, so localization of a particular slice is difficult
True
(Not a true perpendicular slice)
T/F
Volume scanning uses non planar geometry, meaning the slices are not true parallel as in slice by slice
True
T/F
Axial scanning uses planar geometry (parallel slices)
True
T/F
Effective slice thickness increases in volume scanning because it is influenced by the width of the fan beam and the speed of the table
True
T/F
When inconsistent projection data is used with standard reconstruction process, streak artifacts akin to motion artifacts are clearly apparent on the image
True
What post processing technique is used to solve the problems of volume scanning?
Interpolation
What algorithm is used in the reconstruction of images?
Filtered back-projection algorithm
How is motion eliminated in volume scanning?
- Calculation (interpolation) of planar dataset from the tissue volume data set for every image
- Reconstruction of images similar to conventional CT by use of the filtered back-projection algorithm
T/F
Contrast resolution is improved with thicker slices
True
-2 xray tubes and 2 corresponding detectors positioned 90 degrees from eachother
-temporal resolution improved
-increased scan speed is useful in cardiac imaging
DSCT
Dual source
-acquisition of data using 2 different kvp settings simultaneously
-can be performed using DSCT or SSCT
DECT
Dual energy
Used when doing CT biopsies
CT fluoroscopy
-the planar slice is interpolated by using points that are 360 degrees apart
-degrades image quality
360 degree linear interpolation algorithm -SSCT
-LI algorithm improves image quality by using points that are closer to the planar slice to be interpolated
-a second spiral is calculated from the measured spiral/helical and offset by 180 degrees
180 degree linear interpolation algorithm
*higher/better interpolation
*detail is improved, but produces more noise
T/F
In SSCT scanners, a higher pitch ratio degrades image quality and produces artifacts
True
In MSCT, as beam width increases, scatter also increases. Postpatient collimators are used to remove scatter
True
