R A Couture1, C F Hildebolt. 1. Department of Radiology, Washington University, 510 South Kingshighway, St Louis, MO 63110, USA. couture@wuerl.wustl.edu
Abstract
OBJECTIVE: To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality. METHODS: Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source. RESULTS: The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential. CONCLUSIONS: The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.
OBJECTIVE: To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality. METHODS: Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source. RESULTS: The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential. CONCLUSIONS: The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.
Authors: M Nathalia Garcia; Charles F Hildebolt; D Douglas Miley; Debra A Dixon; Rex A Couture; Catherine L Anderson Spearie; Eric M Langenwalter; William D Shannon; Elena Deych; Cheryl Mueller; Roberto Civitelli Journal: J Periodontol Date: 2010-09-01 Impact factor: 6.993
Authors: Charles F Hildebolt; Rex Couture; Nathalia M Garcia; Debra Dixon; D Doug Miley; William Shannon; Cheryl Mueller; Eric Langenwalter; Cathy Anderson Spearie; R Civitelli Journal: Oral Surg Oral Med Oral Pathol Oral Radiol Endod Date: 2009-09
Authors: D Douglas Miley; M Nathalia Garcia; Charles F Hildebolt; William D Shannon; Rex A Couture; Catherine L Anderson Spearie; Debra A Dixon; Eric M Langenwalter; Cheryl Mueller; Roberto Civitelli Journal: J Periodontol Date: 2009-09 Impact factor: 6.993