ct unit 3 test Flashcards
Determines the quantity of the x-ray energy and this choice of parameter is more flexible and forgiving.
mAs
Determines how much and what section of the collected raw data are to be used to create or display an image.
Changing this factor changes image quality by changing pixel size
Display Field of View
When a CT technologist selects a smaller inappropriately size of this parameter it will cause a reduction in pixel size therfore increasing in image noise.
If selected too small will reduce voxel size
Slice Thickness
The comparison of the image to the actual object being scanned for the means of providing useful information or a diagnosis.
Image Quality
Determines the quality of the beam and determines the beams ability to penetrate a thick dense anatomical part.
Main feature of image quality that can be manipulated.
kVp
A volume element that is determined by height, length, and width.
Voxel
Determines how the data are filtered in the reconstruction process.
Raw data is filtered
Reconstruction algorithm
The CT component that the technologist programs in protocols and scan parameters.
Operator’s console
The distance the table travels between slices during the actual scanning of the patient.
Translation or Rotation
A ratio of the distance the table travels per 360 degree rotation to the total collimated x-ray beam width.
Is usually 1-2 only referred to in helical scanning
Pitch
Determines the area within the gantry for which raw data area is acquired therefore gantry isocenter is very crucial.
Isocenter crucial determines within gantry for which raw data is acquired
Scan Field of View
The ability to differentiate a structure that varies only slightly in density from surrounding structures. CT has superior advantage verses conventional radiography with this ability to distinguish .5 percent paramater variation.
Contrast Resolution
The system’s ablity to resolve, as separate forms, small objects placed together
Isocenter is very crucial for spatial resolution
Spatial Resolution
How rapid the data is acquired and this parameter is controlled by the gantry rotation speed, the number of detector channels in the system and the speed with which the system can record changing signals.
The speed
Temporal Resolution
Occurs in digital imaging and refers to the fact that the relationship between radiation dose and the image quality is less direct than in film screen imaging.
In digital you really can’t see if your image is over or under exposed
Uncoupling effect
Spatial Resolution is also termed as
Detail Resolution
- What operations can the CT Technologist perform at the Operator’s Console?
• Starting or ending, changing of normal protocol scanning parameters, thickness and table increments, windowing and leveling of images as it appears on CRT
- ? Identify the maximum ranges for the kVp and the mA settings.
120-140 kVp
20-800 mAs
- How does the matrix size and display field of view have an effect on pixel size?
When DFOV is kept constant and matrix size is increased, pixel size is reduced
- Identify the common matrix size used in CT.
512x512
- Identify the affects of increasing or decreasing field of view has on the size of the pixel.
How to convert pixel size.
If you decrease the DFOV it improves spatial resolution
(d)= FOV/matrix
How does matrix size effect spatial resolution?
Matrix Size: increased matrix size, improves spatial resolution
How does pixel size effect spatial resolution?
Pixel Size: reduced pixel size = improved spatial resolution
How does focal spot size effect spatial resolution?
) Focal Spot Size: smaller focal spot size= increases spatial resolution
How does pitch effect spatial resolution?
) Pitch: increasing the pitch reduces spatial resolution
How does patient motion effect spatial resolution?
) Patient Motion: reduces spatial resolution
How does slice thickness effect spatial resolution?
) Slice Thickness: thinner slices increase spatial resolution
What is Spatial Resolution?
The ability to resolve as separate forms small objects that are close together
How does mAs/dose effect contrast resolution?
) mAs/Dose: increase mAs- increases contrast resolution- increases patient dose
How does pixel size effect contrast resolution?
) Pixel Size: reduce pixel size decreases contrast resolution
How does slice thickness effect contrast resolution?
) Slice Thickness: thicker slices allow more photons reducing noise (increase contrast)
How does patient size effect contrast resolution?
) Patient Size: larger patients require more photons but increase attenuation factor creating noise (decrease contrast resolution)
- In reference to the quality of a CT image, temporal resolution is controlled by what scanning parameters?
Gantry rotation speed, number of detectors channels in the system
- When should a technologist be concerned with obtaining the highest temporal resolution possible during their scanning of:
When imaging moving structures and for dynamic moving iodinated CM studies
when there is more than one type of tissue is contained within a voxel
Partial Volume Artifact:
artifacts from the pt appear as shading, streaking, blurring, or ghosting
Voluntary & involuntary
Motion:
when the scan contains metal objects in the SFOV that will create streak artifacts
Metallic Artifact
by anatomy that extends outside of the selected SFOV
Will give a streaky appearance
Out-of Field Artifact
caused by imperfect detector elements which appear as a ring or concentric ring
3rd generation
Ring Artifact:
Interruption in electricity/electrical surge
Storms
Tube arching
What factors affect beam hardening artifacts
Filtration low energy parts of the beam before it goes through the patient. Calibration of equipment. Beam hardening software.
Filtration, calibrating, beam hardening software
-relate to petrous ridges because of density
- What are some strategies in which the CT technologist should do to reduce or eliminate motion artifacts?
Prep the patient for the exam fully explaining the procedure and what they need to do. Use breathing instructions. Sedation. Immobilization.
Short scan time to compensate for involuntary motion.
Communication is number one way to prevent movement
- What is the difference between image reconstruction and image reformation for CT imaging?
) Image Reconstruction: Raw data or manipulated to create pixels that are then used to create an image. Images are digitized using an algorithm in which the images was already received by a computer
) Image Reformation: When image data are assembled to produce images in different planes or to produce 3D images. Software allows additional information to be obtained that were not originally scanned
: Raw data or manipulated to create pixels that are then used to create an image. Images are digitized using an algorithm in which the images was already received by a computer
Image Reconstruction
When image data are assembled to produce images in different planes or to produce 3D images. Software allows additional information to be obtained that were not originally scanned
Image Reformation
What are three things that cause artifacts
⚫️equipment
⚫️pt
⚫️physics
- Explain how the following factors degrade a reformatted image?
) Segmentation Errors:
) Image Noise:
) Artifact:.
Segmentation Errors: when a vessel or structure has been subtracted out of edited out
Image Noise: if noise is sufficient enough it will have a big effect on image equality
Artifact: makes it difficult for an accurate reading or diagnosis and can leave gaps.
: when a vessel or structure has been subtracted out of edited out
Segmentation Errors
: if noise is sufficient enough it will have a big effect on image equality
Image Noise
: makes it difficult for an accurate reading or diagnosis and can leave gaps.
Artifact
- What is the term used for the collection, classification, storage, retrieval, and dissemination of recorded information for the imaging department?
Informatics
Describe the two key elements in the information infrastructure for imaging network:
Radiology Information System (RIS): Used for scheduling patients, storing reports, patient tracking, protocoling examinations, and billing
) Picture Archive and Communication System (PACS): Technologies necessary for the storage, retrieval, distribution, and display of images
Used for scheduling patients, storing reports, patient tracking, protocoling examinations, and billing
Strictly for the radiology department
Radiology Information System (RIS):
Technologies necessary for the storage, retrieval, distribution, and display of images
The information must be in digital form. The more information coming to the radiologist the more volume/work flow. You don’t store raw data, just the image data.
Picture Archive and Communication System (PACS)
- Why has the PACS system become so important to the imaging world?
PACS allows the integration of image acquisition devices display work stations, and storage systems. This technology has made a big impact on the work flow of radiologists and technologist, as well as referring physicians since it allows easy remote access to the images of pts.
- Why is an optical storage disk the most preferred data storage devices rather than hard copy films?
They can be used for long term data storage. CD/DVD has a greater storage capacity. The CD/DVD can hold more information and in a smaller space than actual hard films.
Requires the use of a large pixel size
Contrast resolution
Requires the use of a small focal spot size
Spatial resolution
Requires the thinner slice thickness
Spatial resolution
Requires the use of a smaller pixel size
Spatial resolution
Best is patient is of smaller size
Contrast resolution
Requires the use of a large matrix size
Spatial resolution
Requires the use of a larger slice thickness
Contrast resolution
Requires the use of a smaller matrix size
Contrast resolution
This parameter has direct influence with mAs
Contrast resolution
Prefers the use of a 1 to 2 pitch
Spatial resolution
Less patient motion during the scanning
Spatial And contrast
This factor depends on the quality of raw data and the reconstruction method as a means of being determined
Spatial resolution
Least amount of noise is very detrimental to this type of resolution
Contrast resolution
A higher mAs could be used to offset the signal to image noise but increasing the patient dose will result
Contrast resolution
The use of reconstruction algorithm can increase and decrease this resolution pending on removing an artifact or fine detail of bone
Spatial resolution
