Computed Tomography Flashcards
Computed Tomography (CT)
non-invasive x-ray technology with a computer
What does it provide?
detailed, digital, cross-sectional images of the body in any plane = “slices”
True or False: A CT is relatively free from superimposition of different tissues.
True
What are the two components necessary to take a CT?
- high intensity x-ray tube
- x-ray imaging detectors
What houses the components necessary to take a CT image?
the gantry
What function does the motorized patient table play during a CT?
moves the patient through the circular opening in the CT machine continually during the examination
True or False: The process to obtaining a CT is similar to obtaining a radiograph.
true
Describe “the science” behind a CT.
- during the rotation, x-ray source produces a fan-shaped beam of x-rays
- attenuation occurs
- imaging detectors create a snapshot
- many snapshots at different angles are collected in one rotation
- snapshots sent to computer
- computer reconstructs snapshots into cross-sectional images of the tissues
True or False: Radiographs carry a higher radiation dose than a CT scan.
false - CT scans have a higher radiation dose than radiographs.
What is the issue with ordering a CT on a child?
larger window for opportunity for expression of radiation damage due to children being more sensitive to radiation than adults
How can we accommodate pediatric patients that absolutely need a CT?
change the settings on the CT to adjust radiation dose to a smaller body size
What is key when considering ordering a CT for a pediatric patient?
order ONLY IF NECESSARY!
2 to 3 CT head scans equals how many mGy to the brain?
50-60
Children with a greater exposure reported a ______________ increase in risk of brain tumor or leukemia than those with 5mGy exposure.
threefold
Do the same principles of radiodensity and radiographic density that we utilize with x-rays apply to CT scans?
yes
What are the two characteristics of object radiodensity?
atomic #
Thickness
Relative radiodensity are displayed based on the average values of what scale?
hounsfield scale
how does the computer apply average values to display overlapping tissues?
overlapping tissues are displayed in one shade of grey
radiodensity represents sum of ____________ & ____________ tissues
osseous & tendinous
Hyperdense represents __________ and appears ________.
bone, white
Isodense represents __________ and appears _________.
brain matter/muscle tissue, grey
Hypodense represents _________ and appears __________.
fluid/fat/air, grey-black or black
How may metals impede image interpretation?
metals lead to streaking artifacts
In a CT, how is an axial view read?
anatomic position from the feet up
In a CT, how is a sagittal view read?
from left to right
In a CT, how is a front view read?
anatomic position facing the viewer
When would you choose to obtain a CT for a musculoskeletal concern?
- subtle fx
- complex fx
- when MRI is contraindicated
- infectious processes
What is the preferred imaging method for a suspected spinal fx?
CT
What are the ABC’S when viewing a CT?
Alignment
Bone density
Cartilage joint or canal spaces
Soft tissues
Where should cortical bone be more dense?
along the margins
What are upper extremity indications for a CT?
- shoulder complex fx
- elbow complex fx
- wrist/hand complex fx
When would you choose to obtain a CT for a neurological concern?
- acute trauma to the brain (bleeding & hemorrhaging)
- tumor, cysts, abscesses
- spinal cord eval when MRI is contraindicated
In the brain, how does grey and white matter appear?
grey matter appears lighter than white matter
What occurs in the grey matter?
where the processing happens (cell bodies, dendrites, axon terminals)
What occurs in the white matter?
communication (axons)
In an acute hemorrhage, how does blood appear on a CT?
bright white (hyperdense)
In a subacute hemorrhage, how does blood appear on a CT?
fades to grey (isodense)
In a chronic hemorrhage, how does blood appear on a CT?
fades to darker grey/black (hypodense)
Can a chronic hemorrhage or ischemic stroke be seen on an MRI?
no
CT arthrography
intravenous injection that is specific to a joint
CT myelogram
CT imaging + myelography
injection of water-soluble contrast medium into posterior subarachnoid space, then performing a CT scan
A CT myelogram enhances the ability to visualize abnormalities affecting the -
spinal cord, spinal canal, spinal nerve roots & blood vessels of the spinal cord
Is a CT myelogram commonly used?
no - not since the invention of the MRI.
it is an invasive examination w/increased risk
When is CT myelogram indicated over MRI?
contraindication to MRI
