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Adv. Mod Unit 3
CT
| Question | Answer |
|---|---|
| Which plane divides the body into inferior (caudal) & superior (cranial) portions? | transverse (axial) plane |
| which plane divides the body into right and left portions? | sagittal |
| which plane divides the body into anterior & posterior portions? | coronal |
| What plane is the orthogonal plane? | oblique |
| What are the major developments in xray beam and detector geometry called? | generations |
| Which generation CT scanner used a pencil-wide xray beam & single detector? | first |
| Which generation CT scanner used a wide fan beam that eliminated the need for translation? | third |
| Which CT scanner generations have curved detector array? | third and fourth |
| T/F: In fourth generation, the tube and detectors both move. | false; the tube rotates but the detector don't |
| What are volume CT scanners? | continous rotation of the xray tube while patient moves through the gantry. |
| Which scanners can slice up to 320 slices per tube rotation? | multislice scanners |
| What are some advantages to multislice CT scanners? | *shorter acquistion time *decreased amount of contrast medium *improved spatial resolution *improved image quality |
| What is the opening of a CT scanner called? | aperture |
| What is the mounted framework that surrounds the patient called? | gantry |
| What part of the CT scanner is made up of photodiodes coupled with scintillation crystal materials? | detector array |
| How is a digital signal made from a CT scanner? | xrays are converted into light, light is converted into electrical energy and then into digital signal |
| On multidetector units, what determines the slice thickness? | the size of the detector row used |
| kv, mAs, pitch, field of view, slice thickness, table indexing, reconstruction algorithms, display windows are settings that are adjusted based on what? | each patient |
| What does each pixel in a CT matrix represent? | CT number |
| What is a voxel? | 3D or volumetric picture element that represents the attenuation characteristics of the anantomy found in the voxel |
| What is another name for a CT #? | hounsfield unit |
| What Hounsfield unit is water? | 0 |
| How is a Hounsfield unit/CT # created? | by using a formula relating the attenuation coefficient of the tissue being imaged to that of water. |
| What is the mathematical unit that describes the shade of gray that is related to the attenuation characteristic in the voxel? | CT #/ Hounsfield unit |
| What color does bone show up on CT? | white |
| What is the hounsfield unit for air? | -1000 |
| As WW (window width) increases, what happens to the contrast? | contrast decreases |
| As WW is narrower, what happens to the contrast? | contrast increases |
| Pixels with CT numbers of -200 or lower are what color? | black |
| Pixels with CT numbers of 600 or higher are what color? | white |
| What does setting the window level determine? | the midpoint of the range of CT numbers to be displayed |
| What does setting the window width determine? | adjusts how many CT number are visible in the range |
| What range should the WL be for soft tissue anatomy? | 30-60 |
| As WL (window level) increases, what happens to the image display? | the image gets dimmer |
| As WW decreases, what happens to the contrast? | contrast increases |
| As WL decreases from +248 to -106, the image appears how? | whiter |
| As WW decreases from 603 to 95, the contrast does what? | increases |
| What is another name for scout? | scanogram |
| What is a scanogram used for? | used to select the range of the CT scan |
| What determines the amount of anatomy covered during a scan? | pitch |
| What is the pitch to be considered undersampling? | 2:1 a pitch higher than 1 |
| What is the pitch to be considered oversampling? | .05:1 a pitch lower than 1 |
| What does it mean if the pitch is 1? | table speed and slice thickness are equal; when the tube makes one complete rotation the distance that the table moves is the same measurement as the beam width. |
| Which image reformatting setting demonstrates contrast filled structures? | maximum intensity projection |
| Which image reformatting demonstrates the outline of outer shell of the structures? | surface shaded rendering |
| Name some specialized procedures done in CT. | 3D reconstruction, CT virtual endoscopy, CT enteroclysis, CT angiography |
| What is the contrast media used in CT? | iodinated, nonionic |
| What is checked before contrast is administrated? | for possible poor renal function (creatinine) |
| In the lung windows, what kind of window is used? wide? narrow? | wide |
| How do patients lay on the table for a Chest CT? | supine with arms elevated above head |
| What is different when doing a Chest CT when the patient has possible cancer and a patient who doesn't? | Patients who have a history of cancer, you want to scan thru the adrenal glands. For patient who don't have a cancer history, scan to the lung bases. |
| T/F: For cardiac studies and pulmonary embolism protocols, IV iodinated contrast is administered. | true |
| For abdomen CT, what are your parameters to scan? | diaphragm to iliac crests |
| For a pelvis CT what are the parameters? | iliac crest to symphysis pubis |
| For a routine abdomen or pelvis study what are your mm per slice? | 5-7mm |
| When you increase pitch, what happens to pt. dose? | pt. dose decreases |
| thinner CT slices does what to pt. dose? | increases pt. dose |
| T/F: the primary difference between each generation of CT scanners was the speed of the system. | false; the difference was the number and arrangement of detectors |
| What are the three primary components of a computed tomographic system? | *gantry *computer *operator console |
| What do the detectors measure in a CT system? | attenuation of radiated tissue |
| The depth of the voxel is determined by what? | slice thickness |
| CT numbers are a numerical scale that represent tissue _________. | densities |
| The general CT number for white brain matter is_____. | +45 |
| The general CT number for blood is ____. | +20 |
| The general CT number for lung tissue is _____. | -200 |
| Which medium serves as a baseline for CT numbers? | water (0). |
| Window width controls what? | displayed image contrast |
| window level controls what? | image brightness |
| Pitch is the relationship between _________ & ________. | table speed; slice thickness |
| How must the intravenous contrast media be adminstered during a multislice CT scan? | hand, bolus injection |
| T/F: Patient dose is higher for a CT scan of the head as compared with a routine skull series. | true |
| T/F: the higher the pitch ratio during a volume CT scan, the greater the patient dose. | false; the lower the pitch ratio = greater patient dose |
| Trauma to the skull may lead to a collection of blood accumulating under the dura mater is called what? | subdural hematoma |
| What is the most common slice thickness range for a routine CT study of the chest? | 5mm |
| Which CT generation scanner contains a bank of up to 960 detectors? | third |
| Which CT generation scanner has 4800 or more detectors on a fixed ring? | fourth |
| Which CT generation scanner was the first scanner with fan-shaped beam and 30 or more detectors? | second |
Created by:
mokapis
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