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Modalities

CT

TermDefinition
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