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21 Cards in this Set
- Front
- Back
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What does the term volume coverage speed performance refer to?
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The capability of rapidly scanning a large longitudinal (z)colume with high longitudinal (z axis) resolution with low artifacts.
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What is poor geometric efficency?
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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.
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What are dual slice CT scanners?
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Dual slice scan geometry includes a fan beam of xrays falling on two rows of detectors.
Introduced in 1998 |
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What is the overall goal of multislice detectors?
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To improve the volume covered and the increase the speed at which it is acquired
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What are the two mechanisms that affect image quality in CT?
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1. Data Acquisition
2. Image Reconstruction |
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What are some of the diffeneces between single slice and multislice scanners in regaurds to Collimation?
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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, |
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What is the BW? and where is it measured?
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- Beam width
- Measured in the z axis at the center of rotation, defined by the precollimator width |
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What are some of the diffeneces between single slice and multislice scanners in regaurds to Beam Geometry?
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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 |
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What are some of the diffeneces between single slice and multislice scanners in regaurds to Pitch
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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) |
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What are some of the diffeneces between single slice and multislice scanners in regaurds to Slice thickness?
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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 |
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What are some of the diffeneces between single slice and multislice scanners in regaurds to Image Reconstruction?
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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. |
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What are the three algorithms developed for multipslice image reconstruction?
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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 |
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What is the xray generator?
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A high frequency generator that provides a stable high voltage to the xray tube, to ensure efficient xray production. 60 kW
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What is the xray tube?
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A rotating anode tube capable of high heat storage capacity with high anode and tube housing cooling rates.
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What are the multislice detectors?
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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.
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What is the data acquisition system (DAS)?
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Which is the detector electronics that are responsible for digitizing the signals from the detectors before they are sent to the computer.
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What is spatial resolution?
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The ability of the scanner to image fine detail and is measured in line pairs/cm.
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What is contrast resolution?
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The ability of the scanner to discriminate small differences in tissue contrast.
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What is noise?
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A fluctuation of CT numbers throughout a uniform material, it degrades image quality and decreases detail.
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What are the 5 major advantages of multislice CT?
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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. |
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What is isoropic resolution?
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Where all sides of the voxels in the slice are equal.
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