摘要:

A light source for testing and setting up radiological television systems has been designed and built using green light emitting diodes and an optical integrating sphere. It is shown to have an optical spectrum similar to the green output phosphors used in x‐ray image intensifiers (XRII's). It can be made uniform in intensity across the output port and does not show the small scale granularity characteristic of phosphors. It has a Lambertian angular distribution which, by the addition of neutral density filters, can be made to mimic the angular distribution at the output of an XRII. It can easily and accurately be modulated or switched and a luminance comparable to that of an XRII output phosphor can be achieved.

ISSN:0094-2405    

DOI:10.1118/1.596392

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A cassette for simultaneously acquiring dual‐energy mammographic images is proposed and studied utilizing a theoretical noise analysis model. The cassette consists of a sandwich of two storage phosphor plates separated by a copper filter. The front, low atomic number, plate was assumed to be comprised of SrFBr and the rear, high atomic number, plate of commercially available BaFBr (98 mg/cm2coating weight). Assuming a constant x‐ray tube voltage of 50 kVp and a typical breast thickness, the theoretical model yielded a front SrFBr phosphor coating weight of ≊21 mg/cm2. The study indicates that a relatively large separation in the average x‐ray photon energies absorbed in the two plates can be obtained. It also indicates that both a high‐quality conventional (single energy) digital image and a tissue canceled digital image (i.e., a calcium image) can be obtained at dose levels comparable to those currently employed. The latter image could potentially improve the early detection of cancerous microcalcifications and also lends itself to computer aided diagnosis.

ISSN:0094-2405    

DOI:10.1118/1.596406

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

We investigated the effects of structured background noise on the detectability of stenotic lesions. Digital subtraction angiographic (DSA) images of stenotic blood vessels were simulated and superimposed onto uniform noise samples. Eighteen‐alternative forced choice (18‐AFC) experiments were employed to determine the detectability of the stenotic lesion in the structured‐noise background of a blood vessel. In this study, the dependence of detectability on lesion size, vessel size, and incident x‐ray exposure was examined. Our results indicate that the presence of structured noise in an image will reduce the detectability of a lesion. However, the relative performance of an observer when the lesion size and incident exposure were varied was the same with and without the presence of the structured background. Thus, conclusions obtained previously with regard to changes in the detectability of a lesion in the presence of uniform background noise can be applied directly to conditions in which simple structured anatomic background is present.

ISSN:0094-2405    

DOI:10.1118/1.596391

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A generalized formulation of the diffusion related nuclear magnetic resonance (NMR) signal is derived from a random walk model. Previous analyses performed in the NMR spectroscopy were the formulations of the diffusion related signal amplitude at a specific time, such as the spin echo formation time. They are, in general, not applicable to continuous time domain analyses. In this paper, we have extended the theory to the two‐dimensional imaging case and derived an analytical formula useful for the computation of the diffusion affected signal as a function of continuous time for a time variant gradient. This formulation will be useful in NMR imaging, especially in NMR microscopy where the diffusion associated signal attenuation is serious due to the strong gradient fields (100–1000 G/cm), and at the same time data are acquired continuously for the acquisition period. In addition to the loss of the resolution and signal‐to‐noise ratio due to the random phase fluctuation by diffusion, the variation of the intensity during the data acquisition period introduces a line broadening whose full width at half‐maximum is found to be much larger than the bandwidth‐limited resolution or diffusion related intrinsic resolution. This line spreading effect is integrated in a computer simulation and is evaluated as an integral part of the overall diffusion effects in μm resolution NMR imaging or NMR microscopy.

ISSN:0094-2405    

DOI:10.1118/1.596393

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A simple model has been developed for the generation of theoretical sensitivity and exposure profiles perpendicular to the tomographic plane in computed x‐ray tomography. The model incorporates the functional dependence on scanner geometry, focal spot size and shape, and detector sensitivity. The sensitivity and exposure profiles are best depicted as the convolution of functions, when appropriately scaled, describing the focal spot intensity distribution and the transmittance of the pre‐ and postpatient collimators. Predictions of the model agree well with experimental results on both sensitivity and exposure profiles for small and large nominal slice thicknesses from five different computed tomography (CT) x‐ray systems. The CT x‐ray systems selected represent both state of the art and older scanner models. Comparisons are also made on the degree of matching of the sensitivity and exposure profiles for each scanner which can be used as a measure of geometrical efficiency in the direction perpendicular to the tomographic plane.

ISSN:0094-2405    

DOI:10.1118/1.596394

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In order to detect and characterize interstitial disease in the lungs, we are developing an automated method for the determination of physical texture measures, which assess the magnitude and coarseness (or fineness) of lung texture in digital chest radiographs. This method is based on an analysis of the power spectrum of lung texture. We now describe an automated classification method for distinction between normal and abnormal lungs with interstitial disease, in which we employ these texture measures and their data base. This computerized method includes three independent tests, one for a definitely abnormal focal pattern, one for a relatively localized abnormal pattern, and one for a diffuse abnormal pattern. The performance of this computerized classification scheme is compared with that of radiologists by means of receiver operating characteristic (ROC) analysis. Our results indicate that this computerized method can be a valuable aid to radiologists in their assessment of interstitial infiltrates.

ISSN:0094-2405    

DOI:10.1118/1.596412

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A novel method allows the determination of three‐dimensional object structure from two projection images that are obtained at arbitrary, unknown orientations. Only minimal prior information concerning the imaging system is required. First, the image coordinates of eight or more object points that can be identified unambiguously in both views are used to determine the relative geometry of the two projections. Subsequently, the three‐dimensional coordinates of the identified object points are determined, to within a scale factor, from the image coordinates of the points and the calculated imaging system geometry. A theoretical description of the overall method is provided, along with techniques for the reduction of effects of experimental errors and numerical errors thay may arise in the course of the calculations. Methods to retrieve the absolute scale of the object are discussed also.

ISSN:0094-2405    

DOI:10.1118/1.596401

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

We measured the characteristic curve, modulation transfer function (MTF), and the Wiener spectrum of a commercially available computed radiographic (CR) system with photostimulable phosphor plate (imaging plate, IP). The characteristic curve (system response) obtained by an inverse‐square x‐ray sensitometry showed a wide dynamic range (order of 103in maximum). The slit technique was employed to determine the MTF's, such as IP MTF, presampling MTF including the unsharpness of the detector (IP) and the blurring effect of the sampling aperture, and laser‐printer MTF. It was found that the MTF of the standard type of IP was comparable to that of medium‐speed screen/film systems. The noticeable degradation of resolution in our CR system, however, occurred at the stage of image data sampling: the presampling MTF was inferior to the IP MTF due to the effect of the scattering and resultant spreading of the incident laser beam and the emitted luminescence. The noise was characterized by means of digital Wiener spectrum using uniformly exposed noise data. Exposure ranges could be separated into different sections depending upon the noise sources, such as quantum mottle at low exposure and system structure noise at high exposure.

ISSN:0094-2405    

DOI:10.1118/1.596402

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Diaphanography, also known as transillumination, is a breast diagnostic technique based on differences in the diffuse transmittance of visible or near‐infrared radiation. Previous papers by the authors reported on investigations of the effect of tumor size, depth at which the tumor is located, the thickness of the breast, and the effect of using photons of different wavelengths. The results from the study reported here indicate that absorption of light in hemoglobin is the basis for the luminance contrast, and shift in the infrared to red transmission ratio, in the diaphanographic image. Evidence is based on known extinction coefficients for oxyhemoglobin and deoxyhemoglobin as a function of wavelength, measurements of the transmitted spectrum in specimens,invivodual wavelength transillumination imaging of lesions containing different amounts of blood (bloody and clear cysts, hematomas, veins, fibroadenomas, and carcinomas), and comparison of preoperative diaphanographic images to blood vessel volumes measured by microscopic analysis of surgical specimens. Oxygenation affects the relative proportions of infrared and red light transmitted, but does not influence the diagnosis based on luminance contrast.

ISSN:0094-2405    

DOI:10.1118/1.596403

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In the context of radioimmunotherapy of cancer, there is a need for continued improvement of dosimetry of radionuclides localized in tumors. Current methods assume uniform distribution of radionuclides in the tumor despite experimental evidence indicating nonuniformity. We have developed a model in which nonuniform distribution of radioactivity in the tumor is taken into account. Spherically symmetric radionuclide distributions, depending linearly and exponentially on the radial position, are considered. Dose rate profiles in the tumor are calculated for potentially useful beta‐emitting radionuclides, including32P,67Cu,90Y,111Ag,131I, and188Re, and for193mPt, an emitter of conversion electrons and low‐energy Auger electrons. For the radionuclide distributions investigated, high‐energy beta emitters, such as90Y, are most effective in treating large tumors (diameter,d≳1 cm), whereas for small tumors (d∼1 mm), medium energy beta emitters such as67Cu are better suited. Very small tumors (d<1 mm), and micrometastases are best handled with low‐energy electron emitters such as193mPt.

ISSN:0094-2405    

DOI:10.1118/1.596404

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY