摘要:

An adaptive linear element (Adaline) was developed to estimate the two‐dimensional scatter exposure distribution in digital portable chest radiographs (DPCXR). DPCXRs and quantitative scatter exposure measurements at 64 locations throughout the chest were acquired for ten radiographically normal patients. The Adaline is an artificial neural network which has only a single node and linear thresholding. The Adaline was trained using DPCXR‐scatter measurement pairs from five patients. The spatially invariant network would take a portion of the image as its input and estimate the scatter content as output. The trained network was applied to the other five images, and errors were evaluated between estimated and measured scatter values. Performance was compared against a convolution scatter estimation algorithm. The network was evaluated as a function of network size, initial values, and duration of training. Network performance was evaluated qualitatively by the correlation of network weights to physical models, and quantitatively by training and evaluation errors. Using DPCXRs as input, the network learned to describe known scatter exposures accurately (7% error) and estimate scatter in new images (<8% error) slightly better than convolution methods. Regardless of size and initial shape, all networks adapted into radial exponentials with magnitude of 0.75, perhaps implying an ideal point spread function and average scatter fraction, respectively. To implement scatter compensation, the two‐dimensional scatter distribution estimated by the neural network is subtracted from the original DPCXR.

ISSN:0094-2405    

DOI:10.1118/1.596978

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In order to implement a computerized scheme for quantitative analysis of interstitial lung disease in chest radiographs in clinical situations, a fully automated method of selecting many square regions of interest (ROIs) in peripheral lung areas are developed. First, the peripheral lung regions are identified, based on the automated detection of lung apices, ribcage edges, and diaphragm. Then a large number of ROIs are selected sequentially by filling in the identified peripheral regions. Finally, those ROIs containing sharp edges are removed based on an edge gradient analysis, for which a gradient‐weighted edge orientation histogram is employed. Approximately 200–400 ROIs were automatically selected for each case with this method. The evaluation of using ROC analysis indicated that the automated ROI selection method was effective in quantitative analysis of lung textures in digital chest radiographs.

ISSN:0094-2405    

DOI:10.1118/1.596979

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

An automated method is developed for the detection and staging of skeletal changes due to hyperparathyroidism on digitized hand radiographs. Subperiosteal bony resorption, particularly along the radial margins of the middle and proximal phalanges, is among the earliest manifestations of secondary hyperparathyroidism. In order to quantify the severity of bone resorption in these regions, the computer method analyzes the roughness of the phalangeal margins, as projected on the radiograph. The regions of interest, which contain the phalanges, are obtained from the digitized hand radiographs by an image preprocessor. The radial margin of each phalanx is detected by a model‐guided boundary‐tracking scheme. The roughness of these boundaries is then quantified by the mean‐square variation and the first moment of the power spectrum. A receiver operating characteristic (ROC) study comparing the computer detection of hyperparathyroidism with the diagnosis by three experienced skeletal radiologists was performed by evaluating 84 hand images from 22 patients. Our present computer method can achieve a true‐positive rate of 94% and a true‐negative rate of 92%. Such a computer‐aided diagnosis system may assist radiologists in their assessment of primary and secondary hyperparathyroidism, since it is both accurate and not subject to either intra‐ or interobserver variations.

ISSN:0094-2405    

DOI:10.1118/1.596980

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A novel algorithm, histogram shifting (HS) is presented, which performs edge detection or edge enhancement with the choice of two parameters. The histogram of a region surrounding each pixel is found and translated toward the origin, resulting in the new pixel value. Images from a variety of medical imaging modalities were processed with HS to perform detection and enhancement of edges. Comparison with results obtained from conventional edge detection (e.g., Sobel) and with conventional edge‐enhancement algorithms is discussed. HS appears to perform the edge‐detection operation without introducing “double‐edge” effects often obtained with conventional edge‐detection algorithms. HS also appears to perform edge enhancement without introducing extensive noise artifacts, which may be noticeable with many edge‐enhancement algorithms.

ISSN:0094-2405    

DOI:10.1118/1.596981

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In this paper, it is demonstrated that obtaining OTF's for only two directions, parallel and perpendicular to the x‐ray tube axis, is insufficient to completely describe the performance of nonisotropic radiographic systems. By performing experiments with three radiological systems in which slit images were obtained for ten different directions, we confirmed that OTF's vary in a nonlinear fashion for directions that are intermediate to the parallel and perpendicular ones. Moreover, we have also identified for each system a range of field orientations—referred to as “Optimum Region”—where sharper images can be obtained. These experimental results can be accounted for by the transfer functions theory.

ISSN:0094-2405    

DOI:10.1118/1.597146

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Noninvasive analysis of heavy elements in external tissues by diagnostic‐x‐ray spectrometry (DXS) is presented. Pt can be detected accurately with sensitivity below 1 μg/g wet weight of tissue. In the present paper the possibility to monitor Pt accumulation and clearance in the external tissues of cancer patients treated with cisplatin [Cis‐diamminedichloro‐platinum (II)‐cDDP] chemotherapy is reported. The DXS method is based on x‐ray fluorescence analysis. Heavy elements in the small skin area of interest are analyzed by their excitation with a monochromatic soft x‐ray beam of 14.6 KeV. Spectral L lines of heavy metals such as Pt are detected with minimum interference by other elements in the tissues. Skin Pt levels up to about 6 μg/g were observed following several courses of cDDP treatment. The Pt seemed to be homogeneously distributed in different skin areas with similar levels in the dermis and epidermis. The rate of clearance of Pt from the skin (50% in about 30 days) was slower by three orders of magnitude than its clearance from plasma. Further studies may use DXS to establish the accurate kinetics of Pt deposition and clearance in tissues of cDDP treated patients, as well as the exact relation between tissue Pt levels and the development of the drug related late complications.

ISSN:0094-2405    

DOI:10.1118/1.596997

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The image information transfer properties of a number of x‐ray fluorescent screens have been measured for x‐ray energies from 17 to 320 keV. The detective quantum efficiency of the screens at each x‐ray energy has been determined by separate measurements of the x‐ray absorption efficiency and the statistical factor associated with the emission of optical photons upon absorption of an incident x ray. Data have been recorded for both rare‐earth phosphor screens and calcium tungstate screens. The value of the statistical factor for optical photon emission tends toward a constant value as the incident energy increases. Comparisons of the image information transfer properties are presented for several screens, which have been measured over a ten year interval. The utility of the screens for high‐energy radiography is discussed.

ISSN:0094-2405    

DOI:10.1118/1.596998

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

This paper proposes a radiographic sensitivity attenuation curve for screen‐films systems. This curve expresses the relative inverse value of mAs value needed to give the same photographic density. This curve decreases more slowly with increasing object thickness than the exposure attenuation curve generally used hitherto. By using the radiographic sensitivity attenuation curve and the exposure attenuation curve, the voltage‐ripple dependence of mAs values and patient dose for the same photographic density was obtained. As predicted theoretically in a previous paper [Med. Phys.18, 921 (1991)], it was verified quantitatively the reverse order that larger ripple values resulted in lower patient dose and lower mAs value for the unsaturating current mode at large ripple. This reverse order clearly appeared in two‐pulse units. These phenomena were experimentally verified. As a result it was found that in radiographing with a two‐pulse unit, larger mA value results in lower patient dose.

ISSN:0094-2405    

DOI:10.1118/1.596999

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In x‐ray spectral measurement using a semiconductor detector system, accurate positioning of the detector in front of the anode is very important. This needs accurate determination of the focal spot position on the target in an x‐ray tube. We present a simple technique to determine the focal spot position accurately. Using a pinhole technique, the focal image made by x rays is overlapped on the target image made by visible rays emitted when filament heating takes places. Both images are made in the same geometry with the tube diaphragm and filter removed.

ISSN:0094-2405    

DOI:10.1118/1.597122

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

ISSN:0094-2405    

DOI:10.1118/1.597000

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY