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Physics
Ch 15
| Question | Answer |
|---|---|
| What is computed tomography (CT)? | A radiographic imaging method that uses x-rays and computer processing to produce cross-sectional images of the body. |
| What is a CT scanner composed of? | X-ray tube, detectors, patient table, gantry, and computer system. |
| What is the gantry in a CT scanner? | The circular frame that houses the x-ray tube and detectors and rotates around the patient. |
| What are the two main types of CT detectors? | Scintillation (indirect) and gas-filled ionization (older systems). |
| What is the purpose of a detector in CT? | To capture x-rays after passing through the patient and convert them into electrical signals. |
| What is a scintillator? | Material that converts x-ray photons into visible light for detection by photodiodes. |
| What is the difference between single-slice and multi-slice CT? | Single-slice acquires one slice per rotation; multi-slice acquires multiple slices simultaneously. |
| What is pitch in CT scanning? | The ratio of table movement per rotation to slice thickness. |
| How does pitch affect image quality and dose? | Higher pitch reduces dose and scanning time but may decrease image resolution. |
| What is slice thickness? | The thickness of the anatomical section imaged by the scanner. |
| How does slice thickness affect spatial resolution? | Thinner slices improve spatial resolution; thicker slices reduce detail. |
| What is matrix size in CT imaging? | Number of pixels in each row and column of the image (e.g., 512x512). |
| What is voxel in CT? | A three-dimensional volume element; includes slice thickness and pixel area. |
| What is Hounsfield Unit (HU)? | CT number representing tissue density relative to water (0 HU = water). |
| What is the HU of air? | Approximately -1000. |
| What is the HU of bone? | |
| What is window width in CT? | The range of Hounsfield Units displayed on the image; controls image contrast. |
| What is window level in CT? | The central HU value of the window; controls image brightness. |
| What is reconstruction in CT? | Processing raw detector data to produce cross-sectional images. |
| What is filtered back projection? | An algorithm used to reconstruct CT images from projection data. |
| What is iterative reconstruction? | A newer reconstruction method that reduces noise and allows lower radiation dose. |
| What is the purpose of automatic exposure control (AEC) in CT? | To adjust tube current to patient size and anatomy, optimizing dose and image quality. |
| What is mAs modulation in CT? | Adjusting tube current (mA) during rotation to reduce dose to low-attenuation regions. |
| What is beam collimation in CT? | Restricting the x-ray beam to desired slice thickness to improve image quality and reduce dose. |
| What is scatter correction in CT? | Techniques to reduce scattered radiation that can degrade image contrast. |
| What is a CT dose index (CTDI)? | A standardized measure of radiation dose output from a CT scanner. |
| What is dose-length product (DLP)? | CTDI multiplied by scan length; estimates total patient radiation dose. |
| What is the principle of ALARA in CT? | Minimize patient dose while obtaining diagnostically adequate images. |
| What is pitch >1 used for? | Faster scans with lower dose, often in screening or trauma. |
| What is pitch <1 used for? | Higher resolution scans, overlapping slices, higher dose. |
| What is multi-planar reconstruction (MPR)? | Reformatting CT data to produce images in sagittal, coronal, or oblique planes. |
| What is maximum intensity projection (MIP)? | Post-processing technique to visualize high-density structures like vessels. |
| What is volume rendering in CT? | 3D visualization of anatomy using all voxel data with shading and opacity. |
| What is helical (spiral) CT? | Continuous rotation of tube with moving patient table to acquire volumetric data. |
| What is the benefit of helical CT over axial CT? | Faster scan times and the ability to reconstruct images in any plane. |
| What is CT angiography (CTA)? | CT imaging technique to visualize blood vessels using contrast media. |
| What is contrast media used for in CT? | Enhances visualization of blood vessels, organs, and pathology. |
| What are common side effects of iodinated contrast? | Mild: warmth, metallic taste; Severe: allergic reaction, nephrotoxicity. |
| What is pre-contrast imaging in CT? | Scanning before contrast injection to identify baseline tissue densities. |
| What is post-contrast imaging in CT? | Scanning after contrast injection to visualize enhanced structures. |
| What is temporal resolution in CT? | Ability to capture rapid motion without blurring; important in cardiac CT. |
| What affects temporal resolution? | Rotation speed of gantry and number of detector rows. |
| What is spatial resolution in CT? | Ability to distinguish small structures in the image; determined by slice thickness, detector size, and pixel dimensions. |
| What is beam hardening artifact? | Streaks or dark bands caused by high-density structures like bone. |
| What is partial volume artifact? | Blurring or incorrect HU values when different tissues occupy the same voxel. |
| What is motion artifact? | Blurring or streaking due to patient movement during scan. |
| What is ring artifact? | Circular artifact caused by detector element malfunction. |
| What is CT number calibration? | Ensures HU values accurately represent tissue densities. |
| What is a scout or topogram in CT? | Preliminary 2D image used for planning the scan range. |
| What is patient centering importance in CT? | Reduces artifacts, ensures accurate AEC function, and optimizes image quality. |
| What is CT fluoroscopy? | Real-time CT imaging used to guide interventions such as biopsies or drain placements. |
| What is detector efficiency in CT? | Ability of detector to capture x-rays and convert them to signal (related to DQE). |
| What is CT table increment? | Distance the patient table moves between consecutive scans; affects pitch and slice overlap. |
| What is high-resolution CT (HRCT)? | Technique using thin slices and high spatial resolution for lung imaging. |
| What is iterative metal artifact reduction? | Software to reduce streak artifacts caused by metal implants. |
| What is a gantry tilt? | Tilting the CT gantry to align scan plane with anatomy. |
| What is z-axis resolution? | Resolution along the patient axis (slice thickness and spacing). |
| What is cone-beam artifact? | Distortion from divergent x-ray beams in multi-detector CT systems. |
| What is dual-energy CT? | Uses two different x-ray energies to differentiate tissue types. |
| What is CT number linearity test? | QC test to verify HU values correspond accurately to known densities. |
| What is slice sensitivity profile? | Distribution of slice sensitivity along z-axis; affects image sharpness. |
| What is CT reconstruction kernel? | Algorithm applied to raw data to emphasize contrast or spatial resolution. |
| What is the effect of a sharp kernel? | Improves edge detail but increases noise. |
| What is the effect of a soft kernel? | Reduces noise but decreases edge sharpness. |
| What is the purpose of phantom testing in CT? | Evaluates spatial resolution, contrast, noise, and artifacts for QA. |
| What is the typical matrix size in modern CT? | 512x512 or larger. |
| What is the typical slice thickness range in CT? | 0.5 mm to 5 mm, depending on anatomy and scan type. |
| What is the benefit of multi-slice CT in trauma? | Rapid acquisition of large volumes with thin slices for detailed assessment. |
| What is the effect of increasing kVp in CT? | Increases penetration and reduces contrast; can reduce patient dose in some situations. |
| What is the effect of increasing mAs in CT? | Reduces noise and improves image quality but increases patient dose. |
| What is gantry rotation time? | Time for one complete rotation of the x-ray tube around the patient. |
| What is the relationship between rotation time and temporal resolution? | Shorter rotation time improves temporal resolution. |
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