COMPUTED TOMOGRAPHY Flashcards
A scan of air in the gantry used to calibrate the scanner based on air density.
air calibration
Define “algorithm” in the context of CT imaging.
A mathematical formula for enhancing image features like soft tissue and edges.
Resolution where voxel dimensions differ along three axes.
anisotropic spatial resolution
What does “aperture” mean in a CT scanner?
The opening in the gantry where the patient passes during the scan.
Storing CT images on long-term devices like tapes or disks.
archiving
An image distortion unrelated to the subject being scanned.
artifact
What is “attenuation” in CT imaging?
The reduction of x-ray intensity by tissue density, resulting in CT numbers.
What plane does “axial” refer to in CT imaging?
The transverse plane.
What is a “bolus” in CT imaging?
Rapid IV injection of contrast media to enhance vascular imaging.
Rows of detector assemblies in the scanner.
channel
What is Computed Tomography (CT)?
A rotating x-ray tube and detector assembly creating cross-sectional images.
Volumetric imaging to construct 3D images of vascular structures.
CT angiography
How are CT numbers related to tissue density?
Higher CT numbers indicate denser tissues, and lower numbers indicate less dense tissues.
What is the CT number assigned to water?
0
What is the purpose of curved planar reformations in CT?
To create images in irregular or oblique planes using post-processing.
Converts analog signals to digital signals for CT image computation.
Data Acquisition System (DAS)
What materials are CT detectors commonly made of?
High-density photo-reactive crystals or pressurized stable gases.
A dose descriptor summarizing the radiation exposure over a scanned length.
dose-length product (DLP)
What is “dynamic scanning” in CT imaging?
Continuous raw data collection for later reconstruction, often used for high-flow vascular imaging.
What is the field of view (FOV) in CT?
The anatomical area displayed on the monitor, adjustable as needed.
What does the gantry in a CT scanner house?
X-ray tube, cooling system, detector assembly, and DAS.
What are the primary benefits of helical CT scanning?
Faster imaging with a continuous spiral data path and improved 3D reformation.
What are Hounsfield Units (HU)?
Numerical values indicating tissue density in a CT scan.
What is “image misregistration”?
Distortion caused by table movement or patient respiration during scans.
What is isotropic spatial resolution?
Voxel dimensions are equal along all three axes.
What is the CT matrix composed of?
Rows and columns of individual pixels containing numerical CT values.
What is the purpose of a Maximum Intensity Projection (MIP)?
To construct 3D images by displaying the brightest pixels from image stacks.
What is noise in a CT image?
Random CT number variations creating a grainy appearance.
Weighted averaging of densities in a voxel with multiple tissue types.
partial volume averaging
A single cell in the image matrix, representing a part of the scanned tissue.
pixel
A set of instructions for performing a CT scan, including slice thickness and table increments.
protocol
Noise from random variations in the number of detected x-ray photons.
quantum noise
Creating a digital image from raw scan data.
reconstruction
A specific area selected for analyzing tissue density.
region of interest” (ROI)
An electrical component allowing continuous gantry rotation.
slip ring
The ability to distinguish small, high-contrast objects in an image.
spatial resolution
What is the function of post-processing techniques in CT?
Enhancing images by applying special reconstruction algorithms.
The ability to capture motion within the shortest imaging time.
temporal resolution
What is the primary component of the CT imaging matrix?
A grid of pixels organized into rows and columns.
The CT number used to define structures in 3D reconstructions.
threshold value
What does voxel stand for?
Volume element, combining pixel area with slice thickness.
It controls the range of gray levels, affecting contrast.
window width
What is the historical significance of Godfrey Hounsfield?
He developed the first clinically viable CT scanner in 1970.
What are the key advantages of multi-detector CT (MDCT)?
Faster imaging, reduced motion artifacts, and better contrast resolution.
An increase in x-ray beam energy as it passes through denser objects.
beam hardening
What causes ring artifacts in third-generation CT scanners?
Faulty or out-of-calibration detectors.
They restrict the x-ray beam, reducing patient dose and improving contrast.
collimators
Generation of CT Scan that eliminates ring artifacts due to stationary detectors.
fourth-generation
What is a major limitation of fifth-generation CT scanners?
High cost and limited availability.
The ratio of table movement per gantry rotation to the beam width.
pitch
What is the primary feature of sixth-generation CT scanners?
Continuous gantry rotation with slip ring technology for helical scans.
What distinguishes seventh-generation CT scanners?
They use multiple detector arrays, such as 64-slice configurations.
What are the main components of a CT scanner?
Gantry, operating console, and computer.
What materials are used for CT patient couches?
Low atomic number materials like carbon fiber.
What is the function of pre-patient collimators?
They limit the area of the patient exposed to the x-ray beam.
They equalize radiation intensity across the detector array.
bow-tie filter
What are common scan planes in CT?
Axial, coronal, sagittal, and oblique planes.
A preliminary image used for positioning and planning the scan.
scout view
Continuous data acquisition during table movement and gantry rotation.
spiral CT
They visualize high-intensity structures like blood vessels.
maximum intensity projection (MIP)
The ability to differentiate between tissues with small density differences.
contrast resolution
What determines slice thickness in CT?
The collimator settings and detector configuration.
They ensure accurate image data by correcting variations in detector response.
detector calibration
Distortion due to averaging different tissue densities within one voxel.
partial volume effect
What are the typical power requirements for CT x-ray tubes?
> 120 kVp and 400 mA.
They supply high-frequency power to the x-ray tube.
high-voltage generator
What does slice overlap achieve in CT imaging?
Improved resolution and reduced partial volume effects.
What does beam collimation improve in CT?
Image contrast and reduction of scatter radiation.
How does table speed affect pitch in CT?
Faster table speed increases pitch, reducing image resolution.
What is a voxel?
A 3D volume element representing tissue, defined by pixel size and slice thickness.
What factors influence CT image noise?
Tube current, pixel size, slice thickness, and patient dose.
What is the principle behind dual-source CT?
Using two x-ray tubes and detector arrays to reduce scan time.
What is modulation transfer function (MTF) in CT?
A measure of how accurately a scanner reproduces details at varying spatial frequencies.
What is the effect of using a higher kVp in CT?
Increased x-ray penetration and reduced image noise.
What is the role of scintillation detectors in CT?
Converting x-rays to light and then to electrical signals for image reconstruction.
What is the advantage of thin-slice imaging in CT?
Higher spatial resolution and reduced partial volume effects.
What is the primary advantage of helical CT scanners?
Faster acquisition of volumetric data during a single breath-hold.
What is CT dose index (CTDI)?
A measure of radiation exposure from a single CT scan.
What is “automatic tube current modulation” in CT?
A system adjusting tube current based on patient size and density.
What is a cone-beam artifact?
Distortion caused by the geometry of wide-beam CT acquisitions.
High-density objects like metal causing bright or dark streaks in images.
streak artifacts
It causes streaks or dark bands, particularly near dense structures.
beam hardening
How is patient positioning critical in CT?
To ensure all relevant anatomy is within the scan field and reduce artifacts.
What are the typical CT numbers for air and dense bone?
Air: -1000; Dense bone: +3000.
Amplifies weak signals from detectors for processing.
preamplifier
What is a significant limitation of spiral CT at higher pitches?
Reduced resolution along the z-axis.
What are the benefits of adaptive filtration in CT?
Improved image quality by reducing noise and artifacts.
What is the main advantage of curved detector arrays in CT?
Better alignment with the fan beam geometry for accurate detection.
What are the key advantages of a multislice CT detector array?
Faster scans and better coverage of anatomical regions.
A 3D rendering technique for visualizing surfaces of structures.
shaded surface display (SSD)
It represents 262,144 individual cells for detailed image representation.
512x512 matrix
They ensure even x-ray exposure across the detector array, reducing artifacts.
bow-tie filter
What are examples of post-processing techniques in CT?
MIP, SSD, and MPR (Multiplanar Reformation).
What is an example of an MSCT (Multi-Slice CT) advantage?
Reduced scan times for larger anatomical coverage.
What is an artifact commonly associated with patient movement?
Motion artifacts, appearing as blurring or double images.
How does pixel size affect spatial resolution in CT?
Smaller pixels improve spatial resolution.
What are the two types of collimators in CT?
Pre-patient and post-patient collimators.
What is the function of a scintillator in CT detectors?
To convert x-rays into light for further signal processing.
What is a characteristic of third-generation CT scanners?
Rotating x-ray tube and detector array with a wide fan beam.
What does “anisotropic voxel” mean?
A voxel with unequal dimensions along its axes.
What are streak artifacts caused by?
High-density objects, such as metal implants or dense bone.
What is the effect of thick slices in CT imaging?
Reduced spatial resolution but potentially lower noise.
It reduces aliasing and enhances edge clarity.
oversampling
What is the effect of increased pitch in spiral CT?
Faster scanning but reduced z-axis resolution.
Estimating values between known data points for smoother images.
interpolation
How is scatter radiation reduced in CT?
Through the use of collimators and high-efficiency detectors.
What is a typical reconstruction algorithm in CT?
Filtered back projection or iterative reconstruction
What are common CT contrast agents?
Iodinated compounds and sometimes barium for specific studies.
What is a primary limitation of dual-source CT?
Increased complexity and cost of the scanner.
What is a key advantage of electron beam CT?
High-speed imaging, often used for cardiac studies.
What is the purpose of a histogram in CT image analysis?
To evaluate pixel value distribution and image uniformity.
It represents a 3D tissue volume in the scanned area.
voxel
The fraction of incident x-rays absorbed and converted to usable signals.
quantum efficiency
What is a major advantage of iterative reconstruction in CT?
Improved image quality with lower noise and radiation dose.
What is the difference between axial and spiral CT scanning?
Axial scans are step-by-step, while spiral scans involve continuous rotation and table movement.
ensure accuracy in image data and reduce system noise.
calibration
What is a cone-beam CT scanner typically used for?
Dental imaging and certain orthopedic studies.
The time taken by the computer to create images from raw data.
reconstruction time
It serves as the primary interface between the operator and system components.
host computer
What is the advantage of high-speed rotors in CT x-ray tubes?
They dissipate heat efficiently, enabling prolonged imaging sessions.
The distance the table moves between each scan acquisition.
table increment
How does gantry tilting benefit certain CT scans?
It helps to avoid artifacts and improve visualization of specific anatomical planes.
What is the benefit of using thinner slices in CT imaging?
Better resolution and reduced partial volume artifacts.
The range between the smallest and largest detectable signals.
dynamic range
To emit x-rays for capturing internal body structures.
x-ray tube
Software to adjust for artifacts caused by x-ray energy changes.
beam hardening correction software
How does CT achieve high temporal resolution?
By reducing gantry rotation time and using dual-source technology.
Gradual deviation of CT numbers due to variations in data capture.
shading
Reducing scatter radiation to improve image quality.
scatter suppression
What is the effect of slice thickness on noise in CT images?
Thicker slices reduce noise but decrease spatial resolution.
The inherent variability in CT numbers for a uniform object.
“system noise”
What is a shaded volume display (SVD) used for in CT?
Creating 3D images sensitive to operator-selected pixel ranges.
The ability to process and display data immediately during acquisition.
real-time reconstruction
limit scatter reaching the detector and improve contrast resolution.
pre-detector collimators
It minimizes artifacts like beam hardening and motion streaks.
artifact correction
What is the principal use of CT angiography (CTA)?
Visualizing blood vessels in 3D for diagnostic purposes.
What is the function of the integrator in CT data acquisition systems?
To sum the signals received from detectors.
What is the typical range of CT numbers for fat and muscle?
Fat: -100; Muscle: 50.
control imaging parameters and monitor scan progress.
operating console
How is field of view (FOV) related to matrix size?
Larger FOV increases pixel size for the same matrix.
What is a slip-ring technology advantage in CT?
It allows continuous rotation of the gantry for faster scans.
What is the purpose of a patient couch in CT?
To position the patient accurately for imaging.
The automated movement of the patient table between scans.
“couch indexing”
Enhancements like 3D reconstructions and multiplanar reformation.
post-processing
What are the benefits of multislice CT (MSCT)?
Faster acquisition, greater coverage, and higher resolution imaging.
The ratio of table movement per rotation to beam width.
pitch
limit x-ray exposure to the area of interest, reducing scatter.
beam collimation
A preliminary image used to position the patient before scanning.
scout image
A circular artifact caused by a faulty or miscalibrated detector.
ring artifact
What is the principle of CT reconstruction?
Converting raw data into cross-sectional images using algorithms.
a measure of radiation dose in a single scan slice.
CT Dose Index (CTDI)
What is the impact of increased detector rows in CT?
Faster scan times and better anatomical coverage.
enhances image quality and reduce patient radiation dose.
iterative reconstruction
What is “volume imaging” in CT?
Capturing a continuous 3D data set instead of individual slices.
What is “temporal resolution” in CT?
The scanner’s ability to image moving objects clearly.
What are common post-processing techniques in CT?
MIP, MPR, SSD, and volume rendering.
An artifact caused by insufficient x-ray photons reaching the detector.
photon starvation
What are the key factors affecting spatial resolution in CT?
Pixel size, slice thickness, and detector size.
What is “contrast enhancement” in CT imaging?
Using contrast agents to improve the visualization of structures.
What is the significance of the matrix size in CT imaging?
Larger matrix sizes provide better image detail.
The longitudinal distance the patient table moves per gantry rotation.
table speed
An image where pixel values are represented as varying shades of gray.
gray-scale image
What is the impact of high kVp settings in CT?
Increased penetration with reduced noise and beam hardening artifacts.
What is “detector efficiency” in CT?
The ability of a detector to capture and convert x-rays to signals.
Software or techniques to minimize artifacts from energy shifts in the x-ray beam.
beam-hardening correction
What does “data interpolation” achieve in CT?
Filling in missing data points to create smoother images.
It determines resolution and influences partial volume effects.
slice thickness
A 3D imaging technique using the entire voxel data for visualization.
volume rendering
What is “effective dose” in CT radiation measurements?
The total radiation risk considering tissue sensitivity.
What is a “pixel” in CT imaging?
smallest 2D element in the imaging matrix.
performs calculations and logical operations for image reconstruction.
central processing unit
What is “maximum intensity projection” (MIP)?
A technique to display the highest-intensity pixels along viewing lines.
Bright or dark lines caused by high-density objects or beam hardening.
streak artifacts
What is a major advantage of dual-energy CT?
Differentiating materials based on their energy-dependent attenuation properties.
Techniques to minimize random variations in pixel values.
noise reduction
What is “isotropic resolution” in CT imaging?
Equal spatial resolution in all dimensions (x, y, z).
Filtering techniques to enhance image quality by reducing noise.
adaptive filtration
What is the benefit of “overlapping slices” in CT?
Improved z-axis resolution and reduced artifacts.
To measure x-rays after they pass through the patient and convert them into signals.
detectors
What is the impact of low pitch values in CT scanning?
Increased resolution but higher patient dose.
What is “partial volume effect”?
Misrepresentation of tissue density due to averaging within a voxel.
How is “slice thickness” related to image noise?
Thicker slices reduce noise levels in the image.
Adjusting for distortions like beam hardening and motion artifacts.
artifact correction
What is the purpose of “gantry tilt” in CT imaging?
To align the scan plane with the anatomy or avoid certain structures.
What is “table increment” in CT?
The distance the patient table moves between consecutive scans.
