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Chap 18 CT principle
Modalities. Chap 18. CT principles
| Question | Answer |
|---|---|
| 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 |
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Zoest35
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