Fundamentals of CT-Midterm Flashcards
what is the axial CT
it is feet up so looking through the body in circular slices
what is a coronal CT
it is one where you see the outline of the front of the body and pass through it
what is a saggital CT
it is from the side and seeing through that direction
name the CT planes
sagital, coronal, axial
what plane is a chest Xray
coronnal
is CT spatial resolution better or worse than xray
CT has a ten times reduction in spatial resolution
is CT contrast resolution better or worse than xray
CT has increased contrast resolution
why does CT have increased contrast resolution
decreased scatter because of scatter rejection, detectors have higher signal to noise ratios and linear response over wide dynamic range. \
CT does not have overlapping anatomy as well
what is radon transform
it is mathmatical reconstruction of internal structure from multiple external projections.
what is Cormack contribution to CT
created a calculation from radiation transmission
where was the first CT scanner
London
what is the EMI mark 1 scanner
it is the first CT scanner at Mayupo. It rotated around the patient and the x-ray tube would go across one degree at a time which created six images
as CT improves, what is the general thing that is changing
it is getting more contrast and it is faster so better resolution and better contrast
what are the basics of CT
x-ray tubes comes out in thin spaces then absorbs the dose by detector and spins so lots of x-rays at different angles
what is the width of a CT detector in real life
it is everything with magnification and focal spot stays the same
what is a voxel
it is a pixel with volume
which is the pair of materials with constant CT number values for different X-ray tube voltages
air and water
what is CT number and the formula
CT (u-uwater)/uwater x1000»»> it is hounsfeld units. Normalize for water so that it is equal to zero. Scale it to make it more readable. EMI=500 sealing, but 1000 now.
what is the CT number for air
-1000
what is the CT number range
tissue/material is the basis
if the CT number is negative what does it mean
its probably fat
what is a CT number for bone
1000
what would be a good estimate for liver
142
what is window width
of CT number mapped to total number of shades of grey which are 64 overall.
display window level
CT number in the center of the window
Display window what do you do to optimize it
wide window, so full range (all numbers) but if want more detail, map narrower range (whatever is too high to get the most ranges)
what is the interaction in CT for bone and oter
it is photoelectric effect and compton scattering
What does Compton do during CT
:it is based on density effect: electrons/volume
what does photoelectric effect do for CT
strong Z and E effects formula is Z3/E3
draw an x-ray spectra for CT
draw it
what filter is used for CT
titanium and aluminum filter so it absorbs lower energy x-rays
what anode is used for CT
tungsten
CT signal reflects differences in rho, rho e, and Z
chart off page 11
which generation of CT has made it
Generation III
what does the electron beam CT do
electron beam swept around tungsten ring so super fast
what is fifth generation used for
built for cardiac imaging. Could get through jore area faster. Fundamental dose is insufficient it is fifth generation CT
what is the single slice axial scan
the table moves, it is step and shoot, it spins around the patient then moves and then does it again. The cables were the limitation at this point. Volume coverage was very slow
what is a helical scan
it added the slippage technique where the signal could hop across the tube so it can move around the patient better. It is continuous spin while there is the patient moving. Uniform longitudinal sampling density, arbitrary slice thickness for reconstruction
what is the difference between single slice and multi slice
single slice is the patient moving through the plane spiral path. and multislice is more coverage per rotation so thinner slices and shorter scan times. More detectors and less gaps between the data points
what is dual source CT
it has double sources so that you dont have to make a wider beam
cone beam CT is
it is more for ENT and dental and innervention. It is slower rotation time and inferior image quality as compared to diagnositic CT.
what are the components of a CT scanner
tube, generator, collimators, filters, detectors, data aquisition system, gantry and slip ring, p[atient table and alignment lights operator console, image reconstruction system
what is differnt about the x0-ray tube
it is higher generator power, higher anode heat capacity, faster spin so makes more electrons overall, the anode and cathode are parallel to xz-axis to prevent heal effect. Nomal focal spot, and the tube has a life of 200,000 exoisure
what is the collimation for the CT
there are pre-patient collimator- so there is beam shaping and reduces dose, adn there is post patient colimators for the scatter rejection
what is a bowtie filter
it is shaped to get less patient dose on teh sides, but it can crack leading to artifact
what type of detector is used in CT
it is a scintillator with titanium scintilates light and light stays and localits hit in between reflextors. Light hits the phtoelectrode to create electrons for the electronic signal
what is the energy integrating detector
higher energy of phton leaves a higher enery of signal. Iodine is used a lot but it can swamp lowe energy leading to missed information
what is the effect of detector apperature
digital detector has width of a and under sample necause it is not sampling two its a width so it roolls it off to prevent aliasing?
flying focxal spot and how it is used
it has lots of asliasing so it wobbles so the flying focal spot helps to fit it into the Nyquist criteia
what does flying focal spot do
it increases sampling
what effects data aquisition system performance
it is influence by dark current. signal cross talk, linearity, electronic noise, dynamic range, thermal stability, and quantization accuracy
what is dark current
it is signal residue when there’s no light so interferes with low current
slip ing is what
eliminates need to rewind the gantry. Mandatory for helial aquisition of data. Passes detector data to the computer
gantry is what
it is the spinner. It spinds fast and one rotation in a quarter of a second. Acquires quickly
patient table weight limit
400-600 pound weight limit
image reconstruction what is it
it is a parallel processing sys
what are the functions of image reconstruction
it is pre-processing (calibration, data correction), image reconstruction, and some post processing. THere is parallel computing, iterative reconstruction requires more computational power
what are the things in a CT scanner that can both improve image quality adn reduce dose
bow tie filter and Al/Cu filter
what is topogram or scout image
tube stays and point moves so that can figure out where to go
scan more that is axial
it is sequential and step and shoot
what is cine scanning is
continuous scanning that is axial with no table movement
can you choose different slice widths for this
yes
what is the formula for pitch
it is pitch=table translation per rotation/deterction colimation
what is pitch
space between slices
effetve mAs
mAs/pitch
image thickness is
nominal width o fimage secotion sensitivit yprofile: line spread function
patial volume
get by with no increase dose but better images is that softness of edge is ebcause image changes slightly in the z diretion
what happens with slimmer slices
more noisey but better resolution
what happens with thicker slices
it is less noisey- it is for general imaging better.
