NDLI: Simultaneous, maximum-likelihood determination of focal length and source position for point-source experiments with pinhole collimation

Content Provider	IEEE Xplore Digital Library
Author	Metzler, S.D. Patil, N.H. Accorsi, R.
Copyright Year	2004
Description	Author affiliation: Dept. of Radiol., Duke Univ. Med. Center, Durham, NC, USA (Metzler, S.D.; Patil, N.H.)
Abstract	Experimental measurements with a point source provide a valuable tool for characterizing the point-spread function and sensitivity of pinhole collimation. These results may test new theoretical formulas or provide calibrations for reconstructing data. Extracting results from point-source data is also more tenable than from more complex phantoms. However, one limiting factor with point-source measurements for high-precision tests is the determination of the position of the point source relative to the aperture. A maximum-likelihood fit may be used to determine simultaneously the position of the point source and the collimator's focal length. In this study, a robotic 1D linear stage was mounted on a box collimator to change the angle of the point source with respect to the aperture's axis of symmetry; the perpendicular height above the aperture, y, was unchanged by this stage. A second stage controlled y. A total of 66 projections (11 angle; 6 y) were acquired for each of three different focal lengths. The projections' centroids were fit to equations predicting their value as a function of focal length, point-source position, and electronic read-out. The differences in focal length from a reference were -6.2, 7.6, and 12.8 mm. The focal length to the reference was 176.1 mm. Measured focal lengths in each case agreed well with micrometer measurements. Differences in focal length and y also agreed well with micrometer measurements. Standard deviations of focal length and y were about 0.5 mm. In conclusion, this method can determine point-source position during experiment setup and measure focal length to within a millimeter.
Starting Page	3569
Ending Page	3573
File Size	1029583
Page Count	5
File Format	PDF
ISBN	0780387007
ISSN	10823654
e-ISBN	0780387015
DOI	10.1109/NSSMIC.2004.1466656
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2004-10-16
Publisher Place	Italy
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Collimators Length measurement Apertures Testing Position measurement Calibration Data mining Imaging phantoms Robots Equations
Content Type	Text
Resource Type	Article

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