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A PHOTON DOSE DISTRIBUTION MODEL EMPLOYING CONVOLUTION CALCULATIONS

MEDICAL PHYSICS 1985年第2期12卷 169-177页

作者： BOYER, A MOK, E CANC THERAPY & RES CTR SAN ANTONIO TX 78229 USA

A 3-dimensional photon beam calculation is described which models the primary, first-scatter, and multiple-scatter dose components from first principles. Three key features of the model are a multiple-scatter calculation based on diffusion theory;the demonstration of the modulation transfer function of the radiation dose transport process;and the use of the finite fast Fourier transform to perform the required convolutions. The results of calculations for cobalt-60 in a homogeneous phantom are used to verify the accuracy of the model.

关键词： Dosimetry/exposure assessment PHANTOMS RADIATION DOSE DISTRIBUTIONS COBALT 60 GAMMA DOSIMETRY SCATTERING MATHEMATICAL MODELS Photons Transport processes Diffusion Fourier transforms modulation transfer functions

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EFFECT OF FINITE PHOSPHOR THICKNESS ON DETECTIVE QUANTUM EFFICIENCY

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MEDICAL PHYSICS 1989年第5期16卷 773-780页

作者： NISHIKAWA, RM YAFFE, MJ HOLMES, RB ONTARIO CANC INST DIV PHYS TORONTO M4X 1K9 ONTARIO CANADA UNIV TORONTO TORONTO GEN HOSP RADIOL RES LABS TORONTO M5G 1L7 ONTARIO CANADA

In this paper we describe theoretically the relationship between the finite thickness of a phosphor screen and its spatial-frequency-dependent detective quantum efficiency DQE (f). The finite thickness of the screen causes a variation in both the total number of light quanta emitted from the screen in a burst from a given x-ray interaction and in the spatial distribution of the quanta within the light burst [i.e., shape or point spread function (PSF) of the light burst]. The variation in magnitude of the burst gives rise to a spatial-frequency-independent reduction in DQE, characterized by the scintillation efficiency AS. The variation in PSF causes a roll off in DQE with increasing spatial frequency which we have characterized by the function RC (f). Both AS and RC (f) can be determined from the moments of the distribution of the spatial Fourier spectrum of light bursts emitted from the phosphor and thus they are related: AS is a scaling factor for RC (f). Our theory predicts that it is necessary for all light bursts which appear at the output to have the same magnitude to maximize AS and the same shape to maximize RC (f). These requirements can lead to the result that the fluorescent screen with the highest modulation transfer function will not necessarily have the highest DQE (f) even at high spatial frequencies.

关键词： Computed tomography Radiography PHOSPHORS THICKNESS QUANTUM EFFICIENCY SCREENS FLUOROSCOPY SPATIAL FREQUENCY transfer functions X−RAY RADIOGRAPHY 87.56.1.f Phosphors Quantum effects modulation transfer functions Emission spectra Visible spectra Spatial scaling

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NUCLEAR-MEDICINE IMAGING WITH PRESSURIZED MULTIWIRE PROPORTIONAL CHAMBERS

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OPTICAL ENGINEERING 1974年第2期13卷 126-129页

作者： KAUFMAN, L BLUMIN, L CAVALIER.R PEREZMEN.V STOKER, G UNIV CALIF SAN FRANCISCO CA 94122 USA VET ADM HOSP SAN FRANCISCO CA USA LAWRENCE BERKELEY LAB BERKELEY CA USA

The pressurized xenon-filled multi-wire proportional chamber (MWPC) is an imaging detector with high intrinsic spatial resolution and good uniformity of response. We describe the design and operation of a 20 x 20 cm2 MWPC with a mass of 0.14 g/cm2 of xenon, maintained at 60 psi absolute. Electromagnetic delay-lines are used to obtain position information. Imaging studies have been performed using a Nuclear Chicago low-energy high-resolution collimator. The intrinsic resolution of the system was determined for 60 keV and 140 keV photons using bar phantoms, and was found to be 1 mm and 2 mm respectively. The modulation transfer Function for 140 keV is down to 70 percent response at 1.4 cycles per cm. Stopping-power is about 65 percent for 1-125 and 10 percent for Tc-99m. The distribution of thyroid hormones in the rat was clearly demonstrated. Picker thyroid phantoms filled with 1-125 and TC-99m were imaged with good detail. Preliminary 1-125 thyroid studies in humans have shown a promising potential. Other studies in rats have included liver/spleen imaging with Tc-99m-sulfur colloid and skeletal imaging with Tc-99m-polyphosphate. The excellent spatial resolution of the detector, together with the addition of higher efficiency collimators and operation at higher pressures realize a system with characteristics that are adequate for clinical use. These components are now being incorporated in a 30 x 30 cm2 MWPC.

关键词： Nuclear medicine Collimators Sensors Spatial resolution Surgery Electromagnetism Image sensors modulation transfer functions Photons Xenon

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Experimental validation of the Wigner distributions theory of phase-contrast imaging

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MEDICAL PHYSICS 2005年第4期32卷 928-931页

作者： Donnelly, EF Price, RR Pickens, DR Vanderbilt Univ Med Ctr Dept Radiol & Radiol Sci Nashville TN 37232 USA

Recently, a new theory of phase-contrast imaging has been proposed by Wu and Liu [Med. Phys. 31, 2378-2384 (2004)]. This theory, based upon Wigner distributions, provides a much stronger foundation for the evaluation of phase-contrast imaging systems than did the prior theories based upon Fresnel-Kirchhoff diffraction theory. In this paper, we compare results of measurements made in our laboratory of phase contrast for different geometries and tube voltages to the predictions of the Wu and Liu model. In our previous publications, we have used an empirical measurement (the edge enhancement index) to parametrize the degree of phase-contrast effects in an image. While the Wu and Liu model itself does not predict image contrast, it does measure the degree of phase contrast that the system can image for a given spatial frequency. We have found that our previously published experimental results relating phase-contrast effects to geometry and x-ray tube voltage are consistent with the predictions of the Wu and Liu model. (c) 2005 American Association of Physicists in Medicine.

关键词： Radiography Distribution theory and Monte Carlo studies X-ray imaging Wigner distribution Medical imaging Medical image contrast Medical X-ray imaging X-ray detectors modulation transfer functions X-ray optics Radiography Image sensors X-ray effects Diffraction theory

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GRATING DETECTABILITY - METHOD TO EVALUATE ABERRATION EFFECTS IN VISUAL INSTRUMENTS

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OPTICAL ENGINEERING 1979年第1期18卷 33-38页

作者： GILES, MK White Sands Missile Range. (United States)

The theory of signal detectability is used to evaluate the effects of instrument aberrations on a total visual optical system with the human eye included. A quantitative measure of grating detectability is obtained using a single-stimulus, random-presentation procedure, with multiple-rating responses. The results indicate that the detectability of square-wave gratings, viewed through a telescope, decreases as aberrations are introduced in the instrument. The amount of degradation is determined for each of six aberration conditions. This degradation index can be used to obtain the degraded modulation transfer function of the total system for each aberration condition.

关键词： Visualization Signal detection Detection theory Eye modulation transfer functions Telescopes Visual optics

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IMAGING PERFORMANCE OF A DIGITAL STORAGE PHOSPHOR SYSTEM

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MEDICAL PHYSICS 1987年第5期14卷 744-751页

作者： HILLEN, W SCHIEBEL, U ZAENGEL, T Philips GmbH Research Laboratory Aachen P. O. Box 1980 D-5100 Aachen West Germany Philips GmbH Research Laboratory Aachen P. O. Box 1980 D-5100 Aachen West Germany Philips GmbH Research Laboratory Aachen P. O. Box 1980 D-5100 Aachen West Germany

The imaging performance of a storage phosphor system (SPS) for digital projection radiography is studied in which the x-ray image is temporarily stored in a light-stimulable phosphor plate which is subsequently read out by a scanning laser beam. The imaging performance of this system has been analyzed for two types of imaging plates. The spatial resolution is described by the modulation transfer function and the signal-to-noise (S/N) ratios of the recorded image data are measured in terms of noise-equivalent quanta and detective quantum efficiency. Their dependence on detector entrance dose and spatial frequency is discussed. A detailed analysis of the different sources of image noise is given to outline the intrinsic features and limits of the system. Finally, the S/N behavior of the SPS is compared with published data of screen-film systems.

关键词： Medical imaging Non‐ionizing radiation equipment and techniques Biomedical imaging X‐ and γ‐ray instruments PERFORMANCE DIGITAL SYSTEMS X−RAY RADIOGRAPHY BIOMEDICAL RADIOGRAPHY IMAGE STORAGE TUBES PHOSPHORS SPATIAL RESOLUTION SIGNAL−TO−NOISE RATIO IMAGE PROCESSING Phosphors Image analysis Laser beams Digital radiography Image sensors Spatial resolution Radiography modulation transfer functions Laser efficiency Quantum measurement theory

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Influence of sound pressure level on the processing of amplitude modulations by auditory neurons of the locust

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JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY 2008年第3期194卷 255-265页

作者： Weschke, Gerroth Ronacher, Bernhard Humboldt Univ Inst Biol Abt Verhaltenphysiol D-10099 Berlin Germany

Typical features of natural sounds are amplitude changes at different time scales. In many species, amplitude modulations constitute decisive cues to recognize communication signals. Since these signals should be recognizable over a broad intensity range, we investigated how the encoding of amplitude modulations by auditory neurons depends on sound pressure level. Identified neurons that represent different processing stages in the locusts' auditory pathway were stimulated with sinusoidal modulations of a broad band noise carrier, at different intensities, and characteristic parameters of modulation transfer functions (MTFs) were determined. The corner frequencies of temporal MTFs turned out to be independent of intensity for all neurons except one. Furthermore, for none of the neurons investigated corner frequencies were significantly correlated with spike rate, indicating a remarkable intensity invariance of the upper limits of temporal resolution. The shape of the tMTFs changed with increasing intensity from a low-pass to a band-pass for receptors and local neurons, while no consistent change was observed for ascending neurons. The best modulation frequency depended on intensity and spike rate, especially for receptors and local neurons. Remarkably, the adaptation state of some neurons turned out to be independent of the spike rate during the modulation part of the stimulus.

关键词： modulation transfer functions temporal resolution intensity invariance adaptation grasshoppers

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REDUCTION OF ALIASING IN modulation transfer-FUNCTION MEASUREMENTS

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MEDICAL PHYSICS 1986年第5期13卷 658-662页

作者： EHRHARDT, JC Department of Radiology University of Iowa Hospitals and Clinics Iowa City Iowa 52242

The images formed by many radiological system are difficult to sample at spatial intervals small enough to avoid aliasing in the calculation of the system''s modulation transfer function. However, is a system''s response can be assumed to be symmetrical, this assumption can be used to effectively double the sampling density and to double the frequency limit before aliasing occurs. To accomplish this, a more complex algorithm is required. In this work, the formula for the calculation of the modulation transfer function from a symmetrical, one-dimensional line spread function is derived and a similar result for a symmetrical, two-dimensional point spread function is presented. The effect of noisy data and errors in the estimation of the offset of the center of the line spread function from a sampling point are investigated by simulation studies. For low noise (relative standard deviation of 1%) and an offset error of no more than 2% of 3% of a sampling interval, reasonably precision is obtained. These conditions appear to be achievable, especially when the noise is Poisson distributed.

关键词： Medical imaging Non-ionizing radiation equipment and techniques Biomedical imaging BIOMEDICAL RADIOGRAPHY IMAGE PROCESSING SPATIAL RESOLUTION DIAGNOSTIC TECHNIQUES SAMPLING 87.56.1 modulation transfer functions Poisson's equation Medical imaging

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A total-imaging-system generalized performance comparison of an x-ray image intensifier and a microangiographic system in neurovascular angiography: Effect of focal spot and scatter

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MEDICAL PHYSICS 2005年第6期32卷 2080-2081页

作者： Yadava, G Rudin, S Bednarek, D Hoffmann, K Kyprianou, I SUNY Buffalo Toshiba Stroke Res Ctr Dept Phys Buffalo NY 14260 USA US FDA NIBIB Lab Assessment Med Imaging Syst Rockville MD 20857 USA

Purpose: To quantify the total-system performance of an x-ray image intensifier and compare it with a microangiographic system in terms of the generalized metrics of GMTF, GNNPS, GNEQ, and GDQE which include the effect of geometric-unsharpness, scatter from the patient, as well as the detector characteristics. This presentation expands on our previous work with generalized imaging-system metrics to include a detailed study of the effect of varying the focal-spot. Method and Materials: A commercial x-ray image intensifier (XII) C-arm unit and a high-resolution ROI microangiographic detector were evaluated with reference to their performance in neurovascular angiographic studies. The study was performed using clinically relevant spectra and conditions specific for each system. A uniform head-equivalent phantom was used, and images were acquired for 60 to 100 kVp at a source-to-image distance of 100 cm for the XII and 75 cm for the microangiographic system. The detector, focal-spot, and scatter unsharpness were quantified in terms of their respective MTF's, and the scatter fraction was determined. These were combined to express a Generalized MTF (GMTF) with spatial frequencies referenced to the object plane. The effect of varying field-size, air-gap and focal-spot size (0.3 mm and 0.6 mm nominal) was studied. A detailed total-system evaluation of the two systems was carried out in terms of the generalized performance metrics of GMTF, GNNPS, GNEQ, and GDQE. Results: The results of the GMTF and GDQE comparison of the two systems indicate that the microangiographic system performs substantially better than the II at higher spatial frequencies, as needed in image-guided, neuro-interventional procedures. Use of a smaller focal spot further improves its high frequency behavior. Conclusion: This generalized approach can provide a more realistic evaluation of total-system performance leading to improved system designs tailored to the specific imaging task. (Partial support fro

关键词： Medical imaging Image sensors Image intensifiers Image detection systems Angiography modulation transfer functions

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Special historical reprint: An assortment of image quality indexes for radiographic film-screen combinations-can they be resolved?

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JOURNAL OF MEDICAL IMAGING 2014年第3期1卷 031013页

作者： Myers, Kyle Chen, Weijie US FDA Rockville MD 20857 USA

Robert F. Wagner wrote his first SPIE paper(1) in 1972, within the first year of his joining the Bureau of Radiological Health, the precursor to the FDA's Center for Devices and Radiological Health. He had been hired to build a laboratory and develop methodologies for assessing the performance of diagnostic x-ray systems, in support of the passage of the Radiation Control for Health and Safety Act. In that first year, Bob met with leading scientists in medical imaging as well as other specialties including vision, communications, and television. He formulated a risk-benefit approach to his work, recognizing that the patient exposure associated with the creation of a medical image needed to be considered in light of the usefulness of that image. Bob's manuscript, reprinted in this special section of the Journal of Medical Imaging, provided an insightful review of the image quantification field, including modulation transfer functions, Wiener spectra, and the basis for receiver operating characteristic curves, along with a bold statement that laid the foundation for the entire field of medical imaging assessment to follow, that image quality "must be defined in terms of the task that the image is destined to perform." (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).

关键词： Medical imaging Image quality Control systems Diagnostics modulation transfer functions Receivers Safety Televisions X-rays

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