Normal and neoplastic breast tissues have been characterised in terms of x-ray attenuation. Samples of normal fat and fibrous tissue were obtained from reduction mammoplasty and autopsy, and infiltrating duct carcinoma specimens from mastectomy and lumpectomy. A high-purity germanium spectroscopy system and a beam of 120 kV constant potential x-rays were used to determine the linear attenuation coefficient from 18 to 110 keV. Densities were determined from buoyancy measurements and were used to obtain mass attenuation coefficients. Infiltrating duct carcinomas and fat are well distinguished by x-ray attenuation. For photon energies used for film-screen mammography, infiltrating duct carcinomas are more attenuating than fibrous tissue. Above 31 keV, the ranges of attenuation of the two tissue types overlap. The attenuation coefficients of tissues have been concisely represented by equivalent thicknesses of lucite and aluminium. Analysis based on the average attenuation properties of tissues indicates that dual-energy mammography, using an ideal imaging system, would require 0.06 cGy to provide images in which 1 cm infiltrating duct carcinomas are displayed with a signal to noise ratio of 5 against a background over which the fat/fibrous contrast has been suppressed. This dose is similar to that currently used in conventional film-screen mammography.

https://iopscience.iop.org/article/10.1088/0031-9155/32/6/002/pdf

X-ray characterisation of normal and neoplastic breast tissues.

Methods for patient dosimetry of x rays used in medical imaging have not been previously dealt with by the ICRU. Whereas some of the dosimetric concepts and techniques used in radiotherapy have been successfully employed for medical imaging using x rays, additional dosimetric quantities and measurement methods are required for patient dosimetry for procedures such as radiography, fluoroscopy and CT. This report presents specification of x-ray beams and quantities and units for dose measurement and calculation in medical x-ray imaging, including application specific quantities and new symbols. It addresses measurement methods for normalization quantities and for quantities recommended for the establishment and use of diagnostic reference levels. It presents methods of determining organ and tissue doses as well as doses in localized regions of organs and tissues, including detailed information on dose conversion coefficients. ___________ * Tentative Abstract of a forthcoming ICRU Report expected for the end of 2004.

Patient Dosimetry for x rays used in medical imaging

The interpretation of dental radiographs for the diagnosis of periodontal disease conditions poses several difficulties. These include the inability to adequately reproduce the projection geometry and optical density of the exposures. In order to improve the ability to extract accurate quantitative information from a radiographic survey of periodontal status, a method was developed which provided for consistent reproduction of both geometric and densitometric exposure parameters. This technique employed vertical bitewing projections in holders customized to individual segments of the dentition. A copper stepwedge was designed to provide densitometric standardization, and wire markers were included to permit measurement of angular variation. In a series of 53 paired radiographs, measurement of alveolar crest heights was found to be reproducible within approximately 0.1 mm. This method provided a full mouth radiographic survey using seven films, each complete with internal standards suitable for computer-based image processing.

A method for the geometric and densitometric standardization of intraoral radiographs.

A review of breast imaging has already appeared in 1982 in this journal. Consequently, the present article concentrates on a discussion of only those developments of a more recent nature. Although the emphasis is placed on the physical aspects of the different imaging methods concerned, the essential factors relating to the clinical background and the associated radiation risk are also outlined. The completeness of detail depends on the present clinical importance of the method under discussion. X-ray mammography, which is still the most important breast imaging technique and has proved to be an effective method for breast cancer screening, is therefore treated in greater detail. Since the early 1980s, ultrasound B-mode scanning has evolved to an indispensable adjunct to x-ray mammography. For Doppler sonography, diaphanography, contrast-enhanced MRI, CT and DSA, the visualization of a tumour depends essentially on the enhanced vascularity of the lesion. Whether this will prove to be a reliable indicator for malignancy remains to be shown in controlled clinical studies. Common to all imaging systems is the increasing use of digital methods for signal processing, which also offers the possibility of computer-aided diagnosis by texture analysis and pattern recognition.

http://iopscience.iop.org/article/10.1088/0031-9155/41/3/001/pdf

Recent developments in breast imaging.

The comparative performance of mammographic X-ray systems that use different anode/filter combinations has been assessed for screen-film and digital imaging. Monte Carlo techniques have been used to calculate average glandular dose as well as contrast and signal-to-noise ratio for imaging two test details. Five anode/filter combinations have been studied to establish the potential for dose saving or image quality improvement. For screen-film mammography, it was found that little benefit is gained by changing from a standard 28 kV molybdenum/molybdenum spectrum for breasts up to 6 cm thick. For thicker breasts, where the tube potential for the standard technique might be increased, 20% improvement in contrast can be achieved without dose penalty using molybdenum/rhodium or rhodium/rhodium spectra, whereas dose savings of more than 50% can be attained whilst maintaining contrast using tungsten/rhodium or rhodium/aluminium spectra. In digital mammography, a molybdenum/molybdenum spectrum delivers the lowest dose for a 2 cm breast, but gives the highest dose for thicker breasts. Tungsten/rhodium or rhodium/aluminium spectra provide the lowest doses at greater thicknesses. It is concluded that for screen-film mammography, molybdenum/molybdenum is the spectrum of choice for all but the thickest or most glandular breasts. In digital mammography, an alternative spectrum is preferable for breasts thicker than 2 cm.

Influence of anode/filter material and tube potential on contrast, signal-to-noise ratio and average absorbed dose in mammography: a Monte Carlo study.

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.

Optimal x-ray spectra for screen-film mammography.

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. (AIP)

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

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.

X-Ray Beam Filtration For Mammography

A series of tests is described which can be used to determine whether image intensifier systems are operating properly. These methods minimize the amount of dis-mantling so that systems may be evaluated with minimum interruption of their regular use. New systems may be specified in terms of these tests to assure that minimum standards of performance are met at the time of system installation and acceptance. Suggestions are also given which describe the operating features of system components.

How The User May Specify And Measure The Performance Of Image Intensifier Systems

Small computers incorporating hard disc memory, multiple high resolution monitors and the small computer systems interface (SCSI) can be used for low-cost filmless radiography. A system has been constructed which can perform all of the functions required of a small clinic or field hospital including scheduling, reporting, image acquisition and display, image annotation, image storage and transmission, and control of peripheral devices. The peripheral devices include an optical card reader/writer, an optical disc reader/writer, a SCSI to DIN/PACS port, an Ethernet port and a SCSI to a long distance telephone/computer port, the Integrated Services Digital Network (ISDN) port. Individual patient optical data cards may be prepared, all images and reports may be archived in a small optical disc in the computer, other image sources may be coupled to the system via the DIN/PACS port, data may be exchanged with the local DIN via the Ethernet port and with distant sites via the ISDN port. The small optical data cards, about the size of a credit card, are used for individual patient images and reports. An independent viewer may be used to display the contents of the cards. The result is a complete "filmless and paperless" medical imaging system. The system was developed on Contract DAMD17-88C-8058 with the US Army Medical Research and Development Command.

Melvin P. Siedband

Papers

Optimal x-ray spectra for screen-film mammography.

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

X-Ray Beam Filtration For Mammography

How The User May Specify And Measure The Performance Of Image Intensifier Systems

Filmless Radiographic System For Army Field Hospitals