Nixie
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X-ray resolution and sensors
I understand that resolution is limited by the focal size (cathode projection on anode) but how exactly? For one, the anode is at an angle, so at
least in one direction it would seem it would be squashed.
So for a medical rotating anode tube with one focal spot being 0.8 mm, what's the maximum resolution I can expect if used in cone-beam tomography?
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Looking at the desktop CT scanners that these guys make:
www.microphotonics.com
There's not much info on what kind of sensors they're using. I need some feedback on pitfalls of my idea to use a scintillation screen imaged by a
digital camera (camera being out of the beam path by means of a prism).
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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-jeffB
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| Quote: | Originally posted by Nixie
I understand that resolution is limited by the focal size (cathode projection on anode) but how exactly? For one, the anode is at an angle, so at
least in one direction it would seem it would be squashed.
So for a medical rotating anode tube with one focal spot being 0.8 mm, what's the maximum resolution I can expect if used in cone-beam tomography?
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"It depends."
Think about the geometry of your setup, and project rays from opposite edges of your 0.8mm spot through a point in your sample onto your detector. If
the point in your sample is 10x closer to the detector than the source, it'll cast a 0.08mm shadow, but you'll be getting a faint image because your
source is too far away. If the point in your sample is equidistant from the source and the detector, it'll cast a 0.8mm shadow. If your sample is
large relative to the source-detector distance, sample points nearest the source will cast fuzzier shadows, points nearest the detector will cast
sharper ones.
In X-ray work, you're effectively working with pinhole optics, and you're always starved for photons. This makes things simpler to analyze than
optical-lens systems, but I wouldn't call tomography "simple". I work with people who do micro-CT and other small-scale imaging; if I get a chance,
I'll ask after the spot size in our system, which uses a .05mm-pitch (20 pixels/linear mm) sensor and commonly generates images with 80-100 micron
resolution (voxel size). I'm not sure what our theoretical limit on resolution would be, but higher resolution implies poorer signal/noise
performance, which implies slower image acquisition or higher rad exposure -- it's a multi-faceted tradeoff, and you will weight the factors
differently than we do.
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Nixie
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Well, even 0.2 mm is sufficient resolution for me. I'm curious what kind of resolution and sensitivity I can expect from the scintillation screen
(one that is pretty standard from what the seller told me). Maybe aiming for a 512^3 is unrealistic (the camera would have to provide at least 9 bits
linear and noise free which means combining two exposures per projection if a regular consumer camera is used, and the scintillation screen's grain
resolution would have to be small enough). (Note: I'm obviously intending cone beam here; I'll use software freely available or just adapt the one I
wrote for optical tomography I did before)
Additionally, how much sensitivity is there of the 3D reconstruction to the monochromaticity (or lack thereof) of the X-ray beam? Filtering (Al
plate) helps, but there will still be significant spread in the photon energy I can get out of a system like the one I have, unless I find a way to
have fairly flat-topped pulses coming out of the power supply to generate uniform accelerating potential.
[Edited on 20-12-2007 by Nixie]
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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Texium
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Thread Moved
19-11-2023 at 12:14 |
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