Melvin P. Siedband

Optimal x-ray spectra for screen-film mammography.

Theoretical and experimental techniques have been used to study optimal x-ray for screen-film mammography. A simple model of mammographic imaging predicts optimum x-ray energies which are significantly higher than the K-characteristic energies of Mo. A subjective comparison of x-ray spectra from Mo-anode and W-anode tubes indicates that spectra produced by a W-anode tube filtered with materials of atomic number just above that of Mo are more suitable for screen-film mammography than spectra produced by the Mo-anode/Mo-filter system. The imaging performance of K-edge filtered, W-anode tube spectra was compared to the performance of Mo-anode spectra using phantom measurements and mastectomy specimen radiography. It was shown that optimal W-anode spectra can produce equal contrast with an exposure reduction of a factor of two to three, a dose reduction of a factor of two, and equal or reducing tube loading, compared to Mo-anode spectra. A computer simulation was carried out to extend the initial, monoenergetic theory to the case of real, polychromatic sources. The effects of varying filter material and thickness, tube operating potential, and breast thickness were all studied. Since W-anode x-ray tubes are considered to be better for Xerox mammography than Mo-anode tubes, this study has shown that both Xerox and screen-film techniques can be performed optimally with a single, properly designed, W-anode x-ray tube.

Test cassette for measuring peak tube potential of diagnostic x‐ray machines

A test cassette employing a modification of the Ardran-Crooks attenuation technique for measuring peak tube potential (and half-value layer) is described. The technique employs a radiographic intensifying screen which is exposed to a hardened x-ray beam. Copper penetrameters are used to determine the attenuator thickness which reduces the light output from the screen to that transmitted by an optical attenuator over an adjacent area of the screen. The test cassette was calibrated by using x-ray machines whose high voltages were measured electrically. The test cassette has a measurement precision of +/- 1 kVp and an accuracy of +/- 3 kVp or better in the range 50-130 kVp for x-ray generators with the same voltage waveform.

Applying a PC accelerator board for medical imaging

An AT-compatible computer was used to expand X-ray images that had been compressed and stored on optical data cards. Initially, execution time for expansion of a single X-ray image was 25 min. The requirements were for an expansion time of under 10 s and costs of under

X-Ray Beam Filtration For Mammography

1000 for computing hardware. This meant a computational speed increase of over 150 times was needed. Tests showed that incorporating an 80287 coprocessor would only give a speed increase of five times. The DSP32-PC-160 floating-point accelerator board was selected as a cost-effective solution to the need for more computing power. This board provided adequate processor speed, onboard memory, and data bus width; floating-point math precision; and a high-level language compiler for code development.<<ETX>>

X-ray doses from radar received by Belgian professional military radar operators.

The characteristic lines of molybdenum-anode x-ray tubes yield high contrast images on film of thin breasts. For thicker breasts, the higher spectral energies are transmitted and the lower energies are mostly absorbed, resulting in higher patient exposure and reduced contrast. However, filters from rhodium (Z=45) to tin (Z=50) can be used to shape the energy distribution of tungsten-anode tubes to improve contrast and reduce patient exposure. Measured spectra and phantom test data are described.

Block truncation image compression with bit‐map compensation

Possible causes of excess rates of hemolymphatic cancers among Belgian military “Hawk” radar operators have been debated, with some authors favoring electromagnetic (microwave) radiation, while the authors of the original study (Degrave et al.) maintaining that ionizing radiation cannot be excluded. While serving as experts for military plaintiffs seeking damages for X-ray exposures from the Hawk and other types of radar units, we made individualized dose calculations for radar operators and supervising personnel. These estimates were based on fits (e.g., Fig. 1) to dose rate measurements at 5 cm above “PAR” and “HPIR” radar equipment, made retrospectively by the German Radar Commission, along with exposure time and distance distributions obtained from interviews with radar personnel, and judgments based on our collective experience with historical exposure reconstruction (JB, BF), radar tube performance and radar design (MS), and service on the German Radar Commission (BF). The actual dose calculation involves computing the product of terms shown in Eq. (1) and averaging over the component distributions using Monte Carlo methods.

Differential Energy Absorption X-Ray Cassette

A modification to the block truncation coding technique is described in which images are improved by using the bit map to increase contrast gradients. In the image, amplitude values are functions of the ‘‘1’s’’ and ‘‘0’s’’ in the bit map and a weighting factor is determined by spatially convolving each pixel of the bit map. The effect is a general improvement in the appearance and a reduction of the ‘‘blockiness’’ of the image.

Choosing And Setting Up TV Systems For Fluoroscopy

A special cassette was designed to enhance radiographic image contrast using two intensifying screens which preferentially absorb in different regions of the x-ray energy spectrum, and which expose corresponding emulsions. The emulsions are developed in subtractive colors to display the structure of interest as variations in both intensity and hue. Theoretical expressions for contrast enhancement available with various screen combinations were made. Preliminary phantom color radiographs show the potential of this technique for contrast enchancement.

Optical data card for medical imaging

Closed circuit television systems are now in use in most fluoroscopy rooms for a variety of reasons: 1) Obviation of dark adaptation 2) Simultaneous viewing of the images by many observers 3) Convenient positioning of the images 4) Image processing by electronic means 5) Recording by tape, disc, storage tube

Independent viewer for optical data cards

Stimulable phosphor cassettes, personal computers, optical discs and optical data cards permit the design of a filmiess radiographic system. X-ray cassettes are read by a laser scanner and images are displayed and stored at the small computer. More than 100 images can be stored on the computer hard disk and recalled by the radiologist for interpretation. Four high resolution monitors permit the system to be used in the same way as a radiographic alternator (multiple viewer). A report can be prepared, the images annotated and the results stored on an optical disc used by the clinic/hospital as a permanent archive. Individual records and images can be copied to credit card-size optical data cards for use by the referring physician or surgeon. The data cards can be displayed on an inexpensive independent viewer. The computer can be coupled to external medical imaging systems, CT, MRI, etc., via an Ethernet port or an ACRINEMA interface. The first system is being developed for the US Army Medical Research and Development Command under Contract DAMD17-88C-8058.