with pointers Flashcards
(35 cards)
- is the result of averaging the linear
attenuation coefficient in a voxel that is heterogeneous in composition. - increases with increasing pixel size and
section thickness.
Partial volume artifact
- also known as cupping artifacts
- caused by polychromatic nature of x-ray beam
- as the lower-energy photons are absorbed, the beam becomes more penetrating, causing an underestimation of attenuation coefficient (HU)
- marked at high-contrast interfaces, such as between dense bone in the skull and brain
beam hardening artifacts
result of 0.5 to 2 second scan times which allow both involuntary (cardiac) and voluntary patient motion
- structures move from one voxel to another during data acquisition, introducing errors in the reconstruction, -random or unpredictable motion
- produces streak artifact
motion artifacts
- may arise in third-generation systems if one or more detectors are faulty or miscalibrated
ring artifacts
- A larger BLANK reduces spatial resolution
- Thicker BLANK use more photons, increasing contrast resolution
slice thickness
- is a measure of the effective section thickness
- The pitch ratio is the most important factor that affects the slice-BLANK
- more accurate descriptor of slice thickness
Slice sensitivity profile
- Measure the radiation dose to the patient within the primary beam of the scanner
- increases with tube voltage
Computed tomography dose index (CTDI)
represents the average dose a patient receives during an examination
Multiple scan average dose (MSAD)
the ability of the CT scanner to reproduce a high contrast edge with accuracy and is expressed mathematically
Edge-response function (ERF)
- the larger the BLANK, the lower the subject contrast, the poorer the spatial resolution
- smallest 2D unit in CT image; representing an area within the slice
pixel
a 3D unit representing tissue volume; combines pixel area and slice thickness
voxel
in CT scan the size of the matrix and FOV determines the BLANK
Spatial resolution
number of pixel used to reconstruct the CT image has ad direct effect on spatial resolution
Pixel matrix
- influences the physical dimension of each pixel
- Smaller BLANK produces an image with less tissue per voxel, which in turn provides high resolution and larger image of a smaller area of interest
field of view (FOV)
it is produced in the direction of motion
streak artifact
signal overlap between adjacent detector channel that can reduce resolution
crosstalk
what are the 2 patient dose in ct scan
- ctdi
- msad
ct noise can be reduced by increasing the BLANK
scan time
the time the computer takes to process raw data into an image
reconstruction time
the term BLANK refers to mathematical function rather than aluminum or metal
filter
type of filter to achieve the best spatial resolution
detail reconstruction filter
- bone filters have the best spatial resolution
- Soft tissue filters have lower spatial resolution
reconstruction kernel/filter
The projections acquired by each detector during CT are stored in the computers memory
image reconstruction
-CT image has 250,000 equations
- Is defined as the ability to distinguish one soft tissue from another without regard for size or shape. This is an area in which CT excels.
- Is the difference in the HU values between tissues
CONTRAST RESOLUTION
