click below
click below
Normal Size Small Size show me how
Modalities
CT
Term | Definition |
---|---|
Scout | Scanogram tomogram |
Formations of CT | data acquisition, image reconstructions, image display, manipulation, storage, record and communication |
Data acquisition | collection of x-ray transmission measurements from the patient |
pencil beam 1st generation | 1970 1 or 2 detectors, 4.5 minutes per slice only head imaging translate-rotate |
partial fan beam 2nd generation | 1972 15 seconds per slice, 10 minutes for 40 slides 30 or more detectors translate-rotate |
fan beam 3rd and 4th generation | 1976-1978 960 fixed detectors (4th gen) but tube spins Rotate 360 degrees |
Spiral scanning | continuous 360 rotation "Slinky" Multi-planar reconstruction |
32 slice | 320 slices per rotation |
multislice | 16 slices per rotation , 8 detector array |
advantages of multislice | shorter time, decreased amount of contrast, improved spatial resolution, improved image quality |
64 slice can acquire how many images per second? | 160 images |
Gantry | where the xray tube is in and detector The donut shape |
Aperature | hole in the middle |
computer | two types of software; operating system and applications |
table weight limit | 400 lbs |
up and down | y |
in and out | x |
back and forth | x |
step and shoot scanning | ct table moves to desired location, table remains stationary while the x-ray xray tube rotates within the gantry, slight pause in scanning as the table move to the next location (interscan delay) |
volume scanning | multi-phases, more coverage, isotropic viewing |
normal pitch | 1 |
less than 1 pitch | causes overlap of scan |
Hounsfield | figured how to measure attenuation |
how much water does the brain hold | 73% |
CT number | bone- +1000, water- 0, air-1000 |
DLP | dose length product |
Dose Metrics on Scanner | DI, DLP, MASAD, Effective dose DLP is most common |
CT dose index | single slice CTDI (fda, center, periphery and volume) |
Direct effect on dose | exposure tech factors, xray beam collimation, pitch, patients centering, number of detectors |
temple resolution | motion |
Exposure tech factors | kVp, mAs, AEC automatic tube current modulation |
effective mAs = | true mAs/pitch |
increase in # of detectors = | decrease in dose |
table index | where you center is 0 (if you go to the head its +) (if you go to the feet it is -) telling the table where to go |
pitch | # of scans scanning the body in a slinky type shape |
Dose optimization | ALARA, body size, tube current modulation, optimize tube voltage, longitudinal scan range, repeated scanning, scan modes, noise- reducing image reconstruction algorithms |
Exposure | quantity- amount of ionization produced in specific mass of air, C/kg SI |
Absorbed dose | amount of energy absorbed per unit mass, Gray (Gy) |
Effective dose | quantify the risk from partial body exposure |
Equivalent | Whole body exposure, Sv |
Image quality and Dose | spatial resolution, contrast resolution, noise , reduce noise by a factors of 2= increase dose, decrease slice thickness= increase in dose |
Affect dose factors | pitch radio (oversampling), thinner slices, # of slices obtained, kV, CT shields to reduce dose , pediatric protocol |
Voxels | volume elements and pixels |
Window Width | contrast, shades of grey |
Window Level | |
Small window width | SHORT GREY SCALE, high contrast |
window settings | lung, mediastinal, bone |
Multiplanar reconstruction | axial, sagittal, coronal |
specialized procedures | colonography, 3D reconstruction, enteroclysis coronal reconstruction, angiography, prtvutaneous drainage |
3D reconstruction techniques | MPR, volume rendering, maximum intesity projection, shaded surface display, colography, angiography, flouroscopy |
Questions for CT | Diabetic- Glucaphage, Kidney creatine .6-1.5 (2 is high and wont give contrast) SX, Ca |