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Questions and Answers
What is the primary function of the prepatient collimation in a single-detector row system?
What is the advantage of MDCT scanners compared to single-detector row systems?
How is the total distance from the first slice to the last slice affected by the slice increment?
What is the result of using a 7-mm slice increment in a CT scan?
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What is the purpose of the AP localizer image in CT scan planning?
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What is the result of opening the collimators to their maximum in a single-detector row system?
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How do MDCT scanners acquire multiple slices in a single rotation?
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What is the relationship between the slice thickness and the slice increment in a CT scan?
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What is the benefit of using contiguous slices in a CT scan?
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How many detector elements can be used in parallel rows in MDCT scanners?
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Study Notes
Parameters for Efficiency
- Initially setting DFOV (Display Field of View) and image center enhances department efficiency.
- Correct placement and sizing of lines over localizer images define DFOV and indicate image center via x, y coordinates.
- A second localizer scan at 90° provides more accurate selection of DFOV and image center.
Role of Localizer Scans
- Post-study, localizer scans serve as a reference, displaying the location of cross-sectional images.
- Scout images included in procedures help in accurately cross-referencing the localizer lines.
Single-Detector Row Systems
- Until the 1990s, commercial scanners featured many detector elements in a single row.
- Third-generation systems had around 700 detector elements arranged in an arc.
- Fourth-generation systems increased this to 4,800 detectors in a complete ring.
- Variable-width detector rows improve scanning flexibility, being thinner in the center and wider at the edges.
Multidetector Row Systems (MDCT)
- MDCT systems can acquire four simultaneous slices through multiple parallel rows of detector elements, as thin as 1 mm.
- This arrangement provides a fourfold increase in data volume during a single rotation compared with Single-Detector Row CT (SDCT).
- Systems designed with more than four parallel rows of detectors enable scanning with varied slice thicknesses.
Example of Multidetector Usage
- The GE Lightspeed QX/I scanner has 16 detector rows, each 1.25 mm wide, allowing various groupings to achieve contiguous slices.
- For abdominal scans, setting a 5 mm collimator opening results in a requirement of 40 images for a 200 mm z distance.
- If utilizing a 7 mm slice increment (skipping 2 mm), total scanned distance increases to 280 mm, illustrating the impact of slice increment choices.
Collimation and Slice Thickness
- Adjusting prepatient collimation alters slice thickness: maximum opening produces the widest slices, while partial closure creates thinner slices.
- Understanding collimation mechanics is essential for tailored imaging results.
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Description
Learn how to set the Department Field of View (DFOV) and image center correctly in Magnetic Resonance Imaging (MRI) to improve department efficiency. Understand the importance of localizer lines and their placement in determining DFOV and image center.
