X. Q. Shi

Analysis of different approaches to constructing perceptibility curves

ObjectivesTo construct and analyze perceptibility curves (PCs) according to two different approaches.Material and methodsA test object was used to determine the exposures and exposure differences between the total thickness of the test object and details consisting of holes of increasing depth. Two digital systems were employed to predict PCs according to the two different approaches. One approach defined exposures and exposure differences from dose-response functions, including secondary and scattered radiation. The other defined exposure and exposure differences as calculated transmitted radiation flux from the primary beam behind the test object, excluding secondary and scattered radiation. Integrals of the PCs and of the minuimum perceptible gray-level differences as functions of background gray levels were calculated. The validity of the different types of PCs was analyzed. Another test object was used to predict observer performance for the two systems.ResultsThe integrals of PCs obtained according to the above first-mentioned approach and integrals of gray-level differences as functions of background gray level were equal. The same integrals using the second approach were different. The second approach, however, successfully predicted observer performance for the two systems.ConclusionsOnly the first-mentioned approach gives PCs that are true representations of psychophysical properties. The second approach may, however, be employed to predict observer performance when different radiographic systems are employed.

Physical properties of a system for direct acquisition of digital intraoral radiographs

ObjectiveTo determine technical properties for a direct digital intraoral radiographic system, F1iOX (Fimet Oy, Moninkylä, Finland).MethodsA dose response function was calculated from seven radiographs exposed to a homogenous radiation field. The line spread function (LSF) and the modulation transfer function (MTF) were determined from a radiograph of a test object having a slit. Noise power spectra (NPSs) were determined at three exposures from radiographs exposed to a homogeneous radiation field. Noise equivalent quanta (NEQs) were calculated from NPSs and the MTF. Detective quantum efficiencies (DQEs) were determined from the NEQs and a representative value of the photon fluence. Signal-to-noise ratios (SNRs) were calculated from the NEQs and different signal contrasts.ResultsThe dose response function was linear and the system relatively sensitive. The maximum NPS was less than 10−5 mm2. NEQs indicate that the system captures a relatively high number of photons. At peaks of about 1 cycle/mm DQEs reached almost 35%. SNRs are relatively high.ConclusionThe technical properties found in this study indicate that the F1iOX system is suitable for intraoral dental radiography.To determine technical properties for a direct digital intraoral radiographic system, F1iOX (Fimet Oy, Moninkylä, Finland). A dose response function was calculated from seven radiographs exposed to a homogenous radiation field. The line spread function (LSF) and the modulation transfer function (MTF) were determined from a radiograph of a test object having a slit. Noise power spectra (NPSs) were determined at three exposures from radiographs exposed to a homogeneous radiation field. Noise equivalent quanta (NEQs) were calculated from NPSs and the MTF. Detective quantum efficiencies (DQEs) were determined from the NEQs and a representative value of the photon fluence. Signal-to-noise ratios (SNRs) were calculated from the NEQs and different signal contrasts. The dose response function was linear and the system relatively sensitive. The maximum NPS was less than 10−5 mm2. NEQs indicate that the system captures a relatively high number of photons. At peaks of about 1 cycle/mm DQEs reached almost 35%. SNRs are relatively high. The technical properties found in this study indicate that the F1iOX system is suitable for intraoral dental radiography.