摘要:

Previous attempts to use time subtraction intravenous digital subtraction angiography for ventricular imaging have been hampered by artifacts due to cardiac and respiratory motion. We have previously reported a motion‐immune dual‐energy technique in which kVp is switched between 60 and 120, at 300–500 mA, 30 times/s. In order to quantitate parameters such as ejection fraction and left ventricular volume, it is necessary to correct for scatter and veiling glare (SVG), which are the major sources of nonlinearities in videodensitometric digital subtraction angiography (DSA). In this report, a convolution filtering method has been investigated to estimate SVG in DSA images. In the first step, a grey level transformation of the detected image is utilized to get an estimated SVG image. In the second step this image is convolved to produce an image with appropriate spatial frequency content. Estimates of SVG in several Humanoid chest phantom images were obtained using Gaussian convolution kernels with a full width at half‐maximum (FWHM) of 51–125 pixels. The root‐mean‐square (rms) percentage error of these estimates was obtained by comparison with direct SVG measurement. A convolution kernel with a FWHM of 75 pixels in each dimension applied to 16 Humanoid phantom images with various projections, thicknesses, and beam energies resulted in an average rms percentage error of 9.7% in the SVG estimate, for the 16 cases studied. The SVG estimation consisting of grey scale‐to‐SVG fraction lookup table (LUT) is made based on previous measurements. The x‐ray settings required for each patient are utilized to alter the LUT in order to account for patient thickness variations. The technique is easy to implement and can be performed within a few seconds, without any additional patient exposure.

ISSN:0269-3127    

DOI:10.1118/1.596277

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Many mammography units now have microfocal spots ranging in size from 0.09 to 0.4 mm for magnification radiography. On site measurements of these focal spots are not possible without invasive procedures if National Equipment Manufacturers Association (NEMA) specifications are to be followed. This paper describes a method to perform such measurements expeditiously (1.5 h) and noninvasively. We describe how this method differs from NEMA test specifications, and report the test results of 22 units from ten manufacturers. Six of the focal spots were larger than the manufacturer's specifications which were based on current NEMA standards. Emphasis is placed on the need for verifiable standards for mammography x‐ray systems.

ISSN:0269-3127    

DOI:10.1118/1.596264

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A parametric spectral model based on the work of Birch and Marshall is used to characterize the x‐ray spectra of a specific x‐ray system. Using least‐squares comparison between measured and calculated attenuation data, an equivalent spectrum (EQSPEC) is iteratively found which very closely matches the measured attenuation characteristics of the x‐ray system. The resulting parametric spectrum is a function of the anode angle (θ), equivalent kilovoltage (kVeq), and the equivalent aluminum filtration (Aleq), and these three parameters can serve as very concise yet very accurate indices of beam quality. The utility of the EQSPEC for characterization and reporting of x‐ray spectra (and thus beam quality) may have numerous applications in diagnostic imaging procedures where spectral quality is an important consideration.

ISSN:0269-3127    

DOI:10.1118/1.596223

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

We are developing an automated method for determining physical measures of lung textures in digital chest radiographs in order to detect and characterize interstitial lung disease. With this method, the underlying background density variations caused by the gross lung and chest wall anatomy are corrected for in order to isolate the fluctuating patterns of the underlying lung texture for subsequent computer analysis. The power spectrum of lung texture, which is obtained from the two‐dimensional Fourier transform, is filtered by the visual system response of the human observer. The magnitude and coarseness (or fineness) of the lung textures are then quantified by the root‐mean‐square (rms) variation and the first moment of the power spectrum, respectively. Preliminary results indicate that the rms variations and/or the first moments of the texture of abnormal lungs with various interstitial diseases are clearly different from those of normal lungs. Our results suggest strongly that quantitative texture measures calculated from digital chest images may be useful to radiologists in their assessment of interstitial disease.

ISSN:0269-3127    

DOI:10.1118/1.596224

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Three‐dimensional (3‐D) surface reconstructions provide a method to view complex anatomy contained in a set of computed tomography (CT), magnetic resonance imaging (MRI), or single photon emission computed tomography tomograms. Existing methods of 3‐D display generate images based on the distance from an imaginary observation point to a patch on the surface and on the surface normal of the patch. We believe that the normalized gradient of the original values in the CT or MRI tomograms provides a better estimate for the surface normal and hence results in higher quality 3‐D images. Then two algorithms that generate 3‐D surface models are presented. The new methods use polygon and point primitives to interface with computer‐aided design equipment. Finally, several 3‐D images of both bony and soft tissue show the skull, spine, internal air cavities of the head and abdomen, and the abdominal aorta in detail.

ISSN:0269-3127    

DOI:10.1118/1.596225

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In order to calculate the doses received by the organs of 530 children treated by radiation for cancer between 1945 and 1969 at the G. Roussy Institute, we have developed a computer program for organ location calculation. To calculate the location of each child's organs of interest at the time of the treatment, only two parameters are necessary; sex and height or sex and age when the height at the time of the treatment is unknown. The algorithm is based on the metric studies of growth known as auxology. Each organ is located by one point representing its center. The model has been checked on 100 healthy children.

ISSN:0269-3127    

DOI:10.1118/1.596226

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Image restoration methods have been shown to increase the contrast of nuclear medicine images by decreasing the effects of scatter and septal penetration. Image restoration can also reduce the high‐frequency noise in the image. This study applies constrained least‐squares (CLS) restoration to the projection images of single photon emission computed tomography (SPECT). In a previous study, it was noted that CLS restoration has the potential advantage of automatically adapting to the blurred object. This potential is confirmed using planar images. CLS restoration is then modified to improve its performance when applied to SPECT projection image sets. The modification was necessary because the Poisson noise in low count SPECT images causes considerable variation in the CLS filter. On phantom studies, count‐dependent Metz restoration was slightly better than the modified CLS restoration method, according to measures of contrast and noise. However, CLS restoration was generally judged as yielding the best results when applied to clinical studies, apparently because of its ability to adapt to the image being restored.

ISSN:0269-3127    

DOI:10.1118/1.596227

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Microdosimetric investigations were performed in a solidTEphantom at the DT‐neutron generator at Hamburg–Eppendorf. Event size spectra were measured at different depths on the axis of a 10×10 cm2field and at different lateral positions at a constant depth. Additionally, the microdosimetric spectrum of a60Co source was determined. From radiobiological measurements the relative biological effectiveness (RBE) of crypt stem cells of mice was estimated as a function of lineal energy. The measured microdosimetric spectra are folded with this RBE function so that RBE values at different positions in the phantom were obtained. The predicted change of the RBE inside and outside the useful beam of a 10×10 cm2field is shown. Contributions to the RBE dose from the various charged particle components are analyzed separately.

ISSN:0269-3127    

DOI:10.1118/1.596228

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A polynomial formula, deduced from the data published by Millset al. [Med. Phys.12, 473 (1985)], in predicting the relative electron beam output factors, is presented in this report. This formula contains four parameters. By choosing four measured output factors, from four field sizes normalized at the field size of (10,10), the values of these parameters can be determined. A comparison of the factors predicted with this formula and the values measured by Millset al. shows that the differences between the field sizes of (4,4) to (30,30) are 0.5% or less in 31 out of 35 field sizes. All the 35 field sizes are within 1% for an electron beam of 20 MeV. With 6‐MeV electron beams, the differences are 0.5% or less in 26 out of 35 field sizes, and 1% or less in 31 out of 35 field sizes. Those having differences greater than 1% have either a small field size (5 cm) or a large field size (20 cm). Considering that this formula requires only four accurately measured relative output factors, one can predict the factors of any field within an acceptable accuracy. The calculation is easy with a scientific hand calculator. This formula provides major improvement over the other methods which require many mesurements to be taken in order to interpolate with acceptable accuracy.

ISSN:0269-3127    

DOI:10.1118/1.596229

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

An improved electron multiple‐scattering distribution is presented in the form of a composite function which combines three expressions valid over different scattering angle regions: a modified relativistic Mott single‐scattering term for large angle scattering, a modified Moliere Gaussian term for small angle scattering, and an exponential term for the intermediate angle scattering region. The exponential term has two adjustable parameters which make possible the smooth transition from the large to the small scattering angle regions. The proposed distribution exhibits better agreement with experiment than other multiple‐scattering distributions commonly used in Monte Carlo electron transport codes, is amenable to direct sampling over a continuous range of electron energies and step sizes, can be used for elements of any atomic number, and is particularly suitable for use on small memory computers.

ISSN:0269-3127    

DOI:10.1118/1.596230

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY