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Chap 18 CT principle

Modalities. Chap 18. CT principles

CAT stands for what? why isn't this term acceptable? computerized axial tomography, because CT images are routinely reconstructed in sagittal and coronal planes as well as in obliques
_______ gen scanners used a pencil thin beam with one detector first
What gen were capable of head CT only? first
How long did first gen scanners take per slice? second gen? 4.5 minutes per slice, 15 seconds per slice
how many detectors did second gen have? 30 or more
Third gen scanners had up to how many detectors? 960, opposite the tube so together they rotated around the patient in a complete 360
Difference between 3rd and 4th gen scanners? When were they developed? Both developed during 1980s, 4th gen posses a fixed ring of 4800 or more detectors which completely surround the patient in the gantry.
_____ replaced the high-tension cables and allowed for continuous rotation of the x-ray tube, which when combined with movement of the table, acquired data in a _____/____ fashion. slip rings, helical/spiral
General term to describe helical and spiral scanning acquisition? (because helical and spiral are vendor specific...) Volume CT scanners. (also capable of single slice)
3 advantages of volume scanning over single slice? Multiplanar reconstruction (MPR... data can be 3D, coronal, etc.), Shorter scan times (shorter because patient moves continuously through gantry), Artifacts reduced (no patient motion reduces artifacts)
Scanners developed before 1992 were capable of what kind of scanning only? What changed by 1998? Single slice, one slice at a time. Multi-slice technology, capable of 4 slices simultaneously. (now can do up to 320 slices per tube rotation)
Multislice CT offers (4) advantages over single slice or volume CT scanners: Shorter acquisition time. Decreased amount of contrast needed (because of the increased acquisition time). Improved spatial resolution (submillimeter slice thickness possible). Improved image quality (Thinner slices)
3 major components of CT scanner Gantry, computer, operator console
Gantry consists of what 3 things tube, detector array, collimators
Typical gantry can be angled how many degrees? 30
Central opening of the gantry is called aperature
Current gen CT scanners generally use ____ collimator/s, prepatient. one
CT computer requires two types of software, What are they and what does each manage? one for the operating system, manages hardware. One for applications, manages pre and post processing, image recon.
kV, milliamps, pitch, FOV, slice thickness, table indexing, recon algorithms, display windows are all ways to control the parameters of an exam. AKA _______, which the operator controls from where? protocols, from the console
The depth of a voxel is determined by what slice thickness
CT has better _______ resolution contrast
After the computer determines the degree of attenuation (linear attenuation coefficient) for each voxel, these values are converted to another numeric scale called CT numbers (used to be Hounsfield units)
The baseline for CT numbers is ____________ which is assigned the CT number value of _____. water, 0.
Dense cortical bone has a value of ______-_______, and air (least amount of attenuation) has a value of _______. +1000 to +3000, air is -1000
Window Width controls the displayed image ________. contrast
Wide WW will result in __________, Narrow WW will result in ________. Wide= low contrast (chest). Narrow= high contrast (cranial imaging).
Window Level controls the image _______ brightness.
The amount of anatomy covered during a scan is determined by the ______. pitch
Pitch is a ratio that reflects the relationship between _____ and _____. table speed and slice thickness
What is the formula for pitch? pitch = couch movement (mm/sec) per 360 degree rotation of tube / collimation
A 1:1 pitch indicates what? The table speed and slice thickness are equal.
a 2:1 pitch would be over or under sampling? undersampling.
A .5:1 pitch ratio would increase or decrease dose? over or under sampling? increase dose, oversampling.
Conventional radiography can display tissues that have at least 10% difference in density, CT can detect differences of ___% or less. 1%
Axial scans are views as though the viewer were facing the patient, looking at the scan from the _____ end of the pt. foot. (bottom up?)
contrast media for CT (Iodinated) is commonly followed by a saline bolus injection. Why? Increased duration of contrast enhancement, also may allow for a reduction in amount of contrast used.
Lower pitch and thinner slices result in _____ dose more
What is dose modulation? Allows the min dose required per slice to be determined by the scanogram, each slice is then obtained with the use of optimal mAs
What is Image Gently? Program for Pediatric scanning
Contrast enhancement is or isnt necessary for all suspected neoplasia because of possible breakdown of the normal blood brain barrier. is
Subderal hematoma is a blood clot that forms between dura mater and surface of brain
Cerebrovascular accident may be caused by a rupture or occlusion of an artery in the brain. The rupture of an artery leads to a/an _______ stroke. The occlusion of an artery can result in a/an ______ stroke hemorrhagic stroke, ischemic stroke
Hydrocephalus referes to an increase in the volume of CSF within the brain.
Hydrocephalus leads to the enlargement of the ventricles and subsequent compression of surrounding brain structures
CT angiography is a general term for a CT exam that provides 3D images of vascular structures in axial, coronal, sagittal planes.
In CT flouroscopy, the same ___ is used as in conventional imaging, however, a lower ___ is used. kV, mA.
Voxels are _________. This means they have the same value of a property in all directions. isotropic.
MPR is what recon images from axial to coronal and sag
Created by: Zoest35