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CT Imaging

Overview

[wikipedia]

A Computed Tomography (CT) machine acquires xray images from different angles around the head-to-toe axis of the patient.

The machine provides a stack of 2D axial xray "slices" of the patient, giving a 3D view of the internals.

Pre-operative applications are in diagnosis, modelling, and planning.

Intraoperative CT (iCT) can be used for tool guidance (e.g. brachytherapy and biopsy), but out-of-plane tool tracking is difficult as only a slice of the tool appears.

Some facts:

CT Machine

The CT is an xray machine that spins around the patient.

Below, T is the xray tube, X are the xrays, D is the detector, and R is the direction of rotation.

[radiopaedia.org]

CT machines have gone through several generations of development:

[radiologykey.com]

Sinograms

The raw output for one CT slice is a 2D "sinogram", g(θ,ρ):

Angles range in only [0,180] degrees because the rays at angles θ and θ+180 have almost the same attenuation. (Why not the same?)

[ humanhealth.iaea.org/HHW/MedicalPhysics/NuclearMedicine/ImageAnalysis/3Dimagereconstruction ]

The value in the sinogram at (θ,ρ) is the total xray attenuation along the corresponding ray, or

μ(t)dt ,

where the integral is taken betweeen the xray source and detector.

Recall the Beer-Lambert law:

Iout=Iineμ(t)dt

Then the total xray attenuation stored in the sinogram is

μ(t)dt=lnIinlnIout

Iin is the known energy of the emitted xray.

Iout is the detected energy at the detector element.

Question: What does the sinogram of an isolated fiducial look like?

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