Cone Beam CT Flashcards
what is cone beam for
it is for use in the OR to perofm testing then
what kind of detector does cone beam CT
It uses a flat panel detector for decreased dose and better resolution and contrast
what is data aquisition for CBCT
it is rotation without table translation
is cone axial or helical
it is axial only
what is FDK reconstruction
it is projecting measured sata along each row to the central row. Filter the projected data smiliarly as 2D fan beam and conduct 3D backprojection. Extra weighting factors for a short scan
what happens to the FOV during this
it is increasing volume coverage from the non-cylindrical nature of it
what are cone beam artifacts and why do they happen
they are more severe as the angle increases. These are often streaking artifacts
compare cone beam to noraml
geometry- normal is close while cone has open gantry, the source is pulsed in cone beam while the source is continuous for the nomral. the detector for cone beam is so much larger .rotation tiem is also longer for cone beam. There is only axial for CBCT
why is dentist office good for CBCT
it is great for planning and can lower radiation dose and have a seated position
why is CBCT good for intervential
it is good for 3D imaging during the procedure. This can be invluded in the set up wit hfluoro, and it can be a good roadmap for it. DSA is limited by vasculatity of lesions
why is it good for breast
breast hanges through the table, so decreased dose to sensitive tissue and then limits the exposure overall
why is CBCT used in radiation therapy
image guided radiation therapy to improve the accuracy of the radiation field placedment and to resuce the exposure of healthy tissue
what is offline calibration
assume source trajectory is reproducible in a short time. Measure phantoms with known positions and estimate source and detector geometry based on the pjantom.
what is data truncation
it is due to limited detector size and the beam is not wide enough to cover the whole patient in the scan
asymmetric cone beam CT
to enlarge scanning field of view, detector is shifted towards one end. Asymmetric detector covers more than 1/2 of the imaging object at given view. Sufficient data are acquired in a full rotation
what is the image reconstruction for asymmetric cone beam
it is filtered backprojection. FBPD/BPF
what is the main form of scatter in the cone beam CT
compon is fairly isotropic at angles above 10 degrees which produces a uniform fog over the image
what are some of the artifacts from scatter
scatter degrades imae quality and leads to cupping srtifacts, streak artifacts, lower CNR
what happens to scatter as cone angle increases
it increases as cone angle increases
what is scatter correction for and how to scatter remove
analytical scatter field estimation, mote carlo bases, measurement based, primary beam modulation not included
what are fixed blockers
pre-measure and used in following scans
what are moving blockers
scatter measurement during scans
what is temporal resolution
CBCT has a much longer rotation time and this means that the resolution is much worse
what is a 4D cone beam CT
in 4D CBCT projections are gated into several groups (respiratory phases) based on phase.amplitude information
what can improve the artifacts from cone beam
streak coming from high contrast objects and estimate streaking from bones to start. Using iterative reconstruction and combine with prior knowledge.
what is detector lag
it is defined as signal present in frames following the frame in which it was generated.
what can detector lag cause
it can lead to image artifacts such as streaking, blurring, and severe shading artifacts
what kind of dose measurment tool do we use for cone beam and regular CT
cone beam is a point chamber while a pencil chamber is used for normal because you integrate over the length
