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21 Cards in this Set

  • Front
  • Back
What does the term volume coverage speed performance refer to?
The capability of rapidly scanning a large longitudinal (z)colume with high longitudinal (z axis) resolution with low artifacts.
What is poor geometric efficency?
When the xray beam is highly collimated to the size of the detectors and only a small percentage of the xrays emitted are used in the imaging process.
What are dual slice CT scanners?
Dual slice scan geometry includes a fan beam of xrays falling on two rows of detectors.
Introduced in 1998
What is the overall goal of multislice detectors?
To improve the volume covered and the increase the speed at which it is acquired
What are the two mechanisms that affect image quality in CT?
1. Data Acquisition
2. Image Reconstruction
What are some of the diffeneces between single slice and multislice scanners in regaurds to Collimation?
Single slice- Pre and Postcollimator widths are equal, the beam may or may not be collimated to the detector array, width of precollimator determines slice thickness,

Multislice Scanners- The beam is collimated to fall on the entire multirow detector,
What is the BW? and where is it measured?
- Beam width
- Measured in the z axis at the center of rotation, defined by the precollimator width
What are some of the diffeneces between single slice and multislice scanners in regaurds to Beam Geometry?
Single slice- small fan / parallel fan-beam geometry

Multislice Scanners- as the number of detector rows increases the fan angle beam becomes wider, resulting in a large cone beam creating more beam divergence
What are some of the diffeneces between single slice and multislice scanners in regaurds to Pitch
Single slice- the ratio of the distance the table translates per gantry rotation to the beam width

Multislice Scanners- pitch + table movement per rotation/detector row collimation (spacing)
What are some of the diffeneces between single slice and multislice scanners in regaurds to Slice thickness?
Single slice- the slice thickness is determined by the pitch and width of the precollimator

Multislice Scanners- the slice thickness is determined by the beam width, the pitch and other factors such as the shape and width of the reconstruction filter in the z axis
What are some of the diffeneces between single slice and multislice scanners in regaurds to Image Reconstruction?
Single slice- requires interpolation (360 and 180 degrees LI) because not all rays pass through the image plane

Multislice Scanners- New algorithms in conjuction with the 360 and 180 degrees L Interpolation allow for image reconstruction.
What are the three algorithms developed for multipslice image reconstruction?
1. Spiral/Helical scanning by interlaced sampling- smaller z-gatps are pbtained by changing pitch to separate date

2. Longitudinal interpolation by z-filtering- flexiable pitch, sll data is processed by wieghted summation, filtering in the longitudinal (z) direction. The filter can control spatial resolution, noise and quality.

3. Fan-Beam reconstruction- Used if there are a small number of detector rows, multiple parallel beams to mock the cone beam, and using the MUSCOT- multislice cone-beam tomography reconstruction method
What is the xray generator?
A high frequency generator that provides a stable high voltage to the xray tube, to ensure efficient xray production. 60 kW
What is the xray tube?
A rotating anode tube capable of high heat storage capacity with high anode and tube housing cooling rates.
What are the multislice detectors?
Solid state scintillation detecors , they consist of segments of varying sizes, where each section can be turned on or off to change the slice thickness.
What is the data acquisition system (DAS)?
Which is the detector electronics that are responsible for digitizing the signals from the detectors before they are sent to the computer.
What is spatial resolution?
The ability of the scanner to image fine detail and is measured in line pairs/cm.
What is contrast resolution?
The ability of the scanner to discriminate small differences in tissue contrast.
What is noise?
A fluctuation of CT numbers throughout a uniform material, it degrades image quality and decreases detail.
What are the 5 major advantages of multislice CT?
1. Increase speed and volume coverage.
2. Improved spatial resolution, thinner slices, Isotropic imaging / resoultion
3. Efficient use of xray beam
4. Reduced radiation exsposure by 40%.
5. Improved CT flouro = better needle placement.
What is isoropic resolution?
Where all sides of the voxels in the slice are equal.