CT scanner components, slice acquisition concepts, and windowing basics tested on radiologic technology certification exams.
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- What does the acronym CT stand for in medical imaging?
- Computed Tomography
- What is the gantry in a CT scanner?
- The ring-shaped housing that contains the x-ray tube, detector array, and related components, through which the patient passes
- What does slip ring technology allow a CT gantry to do?
- Rotate continuously in one direction without cables twisting, enabling helical (spiral) scanning
- Water has a Hounsfield Unit (HU) value of ____.
- 0
- Air has a Hounsfield Unit (HU) value of approximately ____.
- -1000
- What is the approximate Hounsfield Unit range for fat?
- About -100 to -60 HU
- What is the approximate Hounsfield Unit range for dense compact bone?
- About +1000 to +3000 HU
- What does window width (WW) control in a CT image?
- The range of CT numbers (HU) displayed across the grayscale, which determines image contrast
- What does window level (WL) represent in a CT image?
- The midpoint HU value of the window width, centering the grayscale on a tissue of interest
- A narrow window width produces what kind of image contrast?
- High contrast, with fewer shades of gray spread over a small HU range
- A wide window width produces what kind of image contrast?
- Low contrast, with many shades of gray spread over a large HU range
- What is pitch in helical (spiral) CT?
- The ratio of table travel per gantry rotation to the slice (beam) thickness
- What does a pitch of 1 mean in helical CT?
- The table moves a distance equal to one slice thickness during each gantry rotation
- What is the function of the detector array in a CT scanner?
- It converts transmitted x-ray photons that pass through the patient into electrical signals
- What does the Data Acquisition System (DAS) do in CT?
- Converts the analog electrical signal from the detectors into digital data for image reconstruction