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Imaging > Cone Beam CT > Flashcards

Cone Beam CT Flashcards

1
Q

what is cone beam for

A

it is for use in the OR to perofm testing then

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2
Q

what kind of detector does cone beam CT

A

It uses a flat panel detector for decreased dose and better resolution and contrast

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3
Q

what is data aquisition for CBCT

A

it is rotation without table translation

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4
Q

is cone axial or helical

A

it is axial only

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5
Q

what is FDK reconstruction

A

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

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6
Q

what happens to the FOV during this

A

it is increasing volume coverage from the non-cylindrical nature of it

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7
Q

what are cone beam artifacts and why do they happen

A

they are more severe as the angle increases. These are often streaking artifacts

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8
Q

compare cone beam to noraml

A

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

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9
Q

why is dentist office good for CBCT

A

it is great for planning and can lower radiation dose and have a seated position

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10
Q

why is CBCT good for intervential

A

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

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11
Q

why is it good for breast

A

breast hanges through the table, so decreased dose to sensitive tissue and then limits the exposure overall

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12
Q

why is CBCT used in radiation therapy

A

image guided radiation therapy to improve the accuracy of the radiation field placedment and to resuce the exposure of healthy tissue

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13
Q

what is offline calibration

A

assume source trajectory is reproducible in a short time. Measure phantoms with known positions and estimate source and detector geometry based on the pjantom.

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14
Q

what is data truncation

A

it is due to limited detector size and the beam is not wide enough to cover the whole patient in the scan

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15
Q

asymmetric cone beam CT

A

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

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16
Q

what is the image reconstruction for asymmetric cone beam

A

it is filtered backprojection. FBPD/BPF

17
Q

what is the main form of scatter in the cone beam CT

A

compon is fairly isotropic at angles above 10 degrees which produces a uniform fog over the image

18
Q

what are some of the artifacts from scatter

A

scatter degrades imae quality and leads to cupping srtifacts, streak artifacts, lower CNR

19
Q

what happens to scatter as cone angle increases

A

it increases as cone angle increases

20
Q

what is scatter correction for and how to scatter remove

A

analytical scatter field estimation, mote carlo bases, measurement based, primary beam modulation not included

21
Q

what are fixed blockers

A

pre-measure and used in following scans

22
Q

what are moving blockers

A

scatter measurement during scans

23
Q

what is temporal resolution

A

CBCT has a much longer rotation time and this means that the resolution is much worse

24
Q

what is a 4D cone beam CT

A

in 4D CBCT projections are gated into several groups (respiratory phases) based on phase.amplitude information

25
Q

what can improve the artifacts from cone beam

A

streak coming from high contrast objects and estimate streaking from bones to start. Using iterative reconstruction and combine with prior knowledge.

26
Q

what is detector lag

A

it is defined as signal present in frames following the frame in which it was generated.

27
Q

what can detector lag cause

A

it can lead to image artifacts such as streaking, blurring, and severe shading artifacts

28
Q

what kind of dose measurment tool do we use for cone beam and regular CT

A

cone beam is a point chamber while a pencil chamber is used for normal because you integrate over the length

Imaging (19 decks)

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