Temporal performance of amorphous selenium mammography detectors.

We investigated temporal performance of amorphous selenium (a-Se) detectors specifically designed for mammographic imaging. Our goal is to quantify the inherent lag and ghosting of a-Se photoconductor as a function of imaging conditions. Two small area electroded a-Se samples, one positively and the other negatively biased on the entrance side of x rays, were used in the experiments. The study of lag and ghosting was performed by delivering a number of raw exposures as experienced in screening mammography to the samples at different electric field strength E(Se) while measuring the current through the a-Se sample. Ghosting at different operational conditions was quantified as the percentage x-ray sensitivity (x-ray generated photocurrent measured from the sample) reduction compared to before irradiation. Lag was determined by measuring the residual current of a-Se at a given time after the end of each x-ray exposure. Both lag and ghosting were measured as a function of E(Se) and cumulative exposure. The values of E(Se) used in our experiments ranged from 1 to 20 V/microm. It was found that ghosting increases with exposure and decreases with E(Se) for both samples because of the dominant effect of recombination between trapped electrons and x-ray generated holes. Lag on the other hand has different dependence on E(Se) and cumulative exposure. At E(Se) < or = 10 V/microm, the first frame lag for both samples changed slowly with cumulative exposure, with a range of 0.2%-1.7% for the positively biased sample and 0.5%-8% for the negatively biased sample. Overall the positively biased sample has better temporal performance than the negatively biased sample due to the lower density of trapped electrons. The impact of time interval between exposures on the temporal performance was also investigated. Recovery of ghosting with longer time interval was observed, which was attributed to the neutralization of trapped electrons by injected holes through dark current.

Cassette-based digital mammography.

Over the past several years, digital mammography systems have been installed clinically across North America in small but growing numbers. A photostimulable phosphor-based full-field digital mammography image was evaluated in this investigation. Commonly known as computed radiography (CR), its use closely mimics the screen-film mammography paradigm. System performance using modulation transfer function (MTF) and detective quantum efficiency (DQE) metrics show MTF(2.5 mm(-1)) = 0.5, DQE(2.5 mm(-1)) = 0.3, and MTF(5.0 mm(-1)) = 0.2, DQE(5.0 mm(-1)) = 0.05, for a 26 kVp beam, 0.03 mm molybdenum tube filtration, 4.5 cm tissue attenuation, and 15 mR incident exposure to the detector. Slightly higher DQE values were measured at 32 kVp with 0.025 mm rhodium tube filtration. CR mammography advantages include the ability to use existing mammography machines, where multiple rooms can be converted to "digital" operation, which allows overall cost savings compared to integrated digital mammography systems. Chief disadvantages include the labor-intensive handling of the cassettes prior to and after the imaging exam, lack of a direct interface to the x-ray system for recording technique parameters, and relatively slow processing time. Clinical experience in an IRB-approved research trial has suggested that digital mammography with photostimulable storage phosphors and a dedicated CR reader is a viable alternative to conventional screen-film mammography.

[Experimental studies on image quality in conventional film screen system, digital phosphor storage plate mammography in mangnification technique and digital mammography in CCD-technique]. / Experimentelle Untersuchungen zur Bildgüte konventioneller Film-Folien-Mammographie, digitaler Mammographie mit Speicherfolien in Vergrösserungstechnik und voll digitaler Mammographie in CCD-Technik.

UNLABELLED: Comparison of image quality between conventional film screen system, digital phosphor storage plate mammography in magnification technique and digital mammography in CCD-technique. MATERIALS AND METHODS: Radiograms of a RMI-mammography phantom were acquired using a conventional film screen system, two digital storage plate systems and two digital systems in CCD-technique. Additionally, the radiograms of one digital phosphor storage plate system were postprocessed emphasizing contrast and included in the comparison. RESULTS: The detectability of details was the best with the digital mammography in CCD-technique in comparison with the conventional film screen technique resp. digital phosphor storage plate in magnification technique. CONCLUSIONS: Based on these results there is the possibility to replace the conventional film screen system by further studies--this has to be confirmed.

X-ray imaging with amorphous selenium: optimal spectra for digital mammography.

The optimum x-ray spectra for acquisition of digital mammographic images using an amorphous selenium (a-Se) photoconductor are investigated. The recorded images consist of latent charge distributions on the surface of an a-Se plate, which are then read out using two methods, laser discharge, or flat panel recharge. The investigation is based on a model of the breast previously developed for a phosphor-based digital readout system, and has been extended to include the effects specific to the use of photoconductors. The effects of plate thickness, x-ray scatter, readout noise, dose, and the kind of breast tissue on the nature of the optimum spectrum are explored for the two readout methods. The results indicate that use of a kilovoltage setting in the current mammographic range, and a molybdenum target spectrum is appropriate for digital readout of a-Se detectors. This conclusion contrasts with the appreciably higher kilovoltages traditionally used with the xerographic (toner) readout of latent charge images on a-Se.

[Imaging methods in diagnosis and differential diagnosis of breast cancer]. / Bildgebende Verfahren zur Diagnostik und Differentialdiagnostik des Mammakarzinoms.

The diagnosis of breast cancer is primarily based on X-ray mammography. Under optimal conditions, a sensitivity of approximately 90% can be achieved. When strict criteria of indication are observed for the additional use of ultrasound or contrast-enhanced MRI, the sensitivity can be increased to about 98%. In addition, the differential diagnosis between benign and malignant lesions can be improved and the rate of biopsies due to false-positive mammograms can be reduced. However, further investigation with ultrasound or MRI of dense or mastopathic breasts that are clinically asymptomatic is not indicated, since it reduces specificity without significant gain of sensitivity.

X-ray imaging using amorphous selenium: a photoinduced discharge readout method for digital mammography.

A new digital image readout method for electrostatic charge images on photoconductive plates is described. The method can be used to read out images on selenium plates similar to those used in xeromammography. The readout method, called the air-gap photoinduced discharge method (PID), discharges the latent image pixel by pixel and measures the charge. The PID readout method, like electrometer methods, is linear. However, the PID method permits much better resolution than scanning electrometers while maintaining quantum limited performance at high radiation exposure levels. Thus the air-gap PID method appears to be uniquely superior for high-resolution digital imaging tasks such as mammography.

CT scanning of the breast in problem cases.

This is a report of the experience with 200 patients who during 1981 to 1984 underwent breast scanning on a conventional body scanner. Pre- and post-contrast scans of the breast were obtained. A postcontrast enhancement of 50 HU and more turned out to be specific for malignant lesions. Radiation dose to the breast was in the same range as with high filtration xeromammography and high resolution film-screen mammography with additional grid. Breast scanning is recommended in cases in which mammography alone is of limited value, including dense fibrocystic breasts in women at high risk, follow-up in breast cancer patients after breast conserving therapy, in patients with silastic implants and in the follow-up of breasts with huge scars due to multiple biopsies.

Factitious microcalcifications in breast biopsy material: laboratory-induced error by use of tattoo powder for specimen mammography.

A xeromammogram led to the surgical excision of a calcified breast lesion on a 66-year-old female. Before specimen mammography was performed, the excised tissue was oriented with tattoo pigment. The specimen mammogram then revealed multiple calcifications caused by unsuspected radio-opaque material in the tattoo pigment, and the original calcifications were obscured. This case demonstrates the hazards involved utilizing tattoo powders for orienting xeromammographically discovered specimens.

Breast specimen radiography: evaluation of a compression device.

The irregular shape and uneven tissue thickness of excised breast specimens makes radiographic evaluation difficult, especially when calcifications are not present. Xeroradiographs before and after compression of 20 separate excised breast specimens were compared, and 17 of the same specimens were compared after compression combined with immersion in water. Specimen compression improved visibility of the lesion on average in 88% of cases, and visibility was equal in 12%. Combined compression/immersion further improved visibility of the lesion on average in 37% of cases. More significantly, evaluation of the compressed specimen led to a change in interpretation of the radiographs in 45% of cases. Compression of the specimen in specimen radiography is recommended in all cases in which pre-biopsy localization is performed.

[Clinical dosimetry in xeromammography using the low dose system]. / Dosimetria clinica in xeromammografia con sistema "low dose".

The results obtained by utilizing low-dose plates in xeromammography are reported. Phantom experimental examinations and dosimetric measurements were made before using these plates. The new exposition data were then compared to those obtained with the old plates. Findings prove low-dose plates to be more sensitive--thus granting very good iconographic results with reduction of skin dose (about 30%) at FFD of 110 cm. The skin dose has been compared to that obtained with the most modern mammographs.

Mammographic needle localization of lesions seen in only one view.

A new xeromammographic needle localization technique for occult breast lesions seen on only one view is described, which permitted successful localization of an occult lesion visible only on mediolateral projection. To test its accuracy, the method was also applied to 15 other cases (16 lesions) where the lesion was seen in two views, but localization was performed as if it were seen in one view only. The technique takes advantage of the geometry of x-ray beam angulation and triangulation.

[Clinical advantage of xeroradiography in the diagnosis of breast cancer].

Xeroradiography is an excellent method of visualizing soft tissue structures in mammography. A feature of xeroradiography is the edge effect and wide recording latitude, which permit visualization of variety of tissue densities. Recent advancement in film mammography using molybdenum anode and film-screen system appears to exceed xeroradiography in spatial resolution and sensitivity. In the large breast, however, the characteristic lower energy radiation of molybdenum anode is almost absorbed by the glandular tissue, resulting in a loss of image quality and reduced diagnostic accuracy. Xeroradiography can maintain the good contrast resolution even in such a case.

Breast imaging.

The majority of information available today indicates that the most efficient and accurate method of screening women to detect early-stage breast cancer is an aggressive program of patient self-examination, physical examination by well-trained, motivated personnel, and high-quality x-ray mammography. There are two important factors in the implementation of mammographic screening. The first is the availability of facilities to perform high-quality, low-dose mammography, which is directly related to the second factor: the expense to society for support of this large-scale effort. Cost-benefit analysis is beyond the scope of this review. In 1979 Moskowitz and Fox attempted to address this issue, using data from the Breast Cancer Detection Demonstration Project in Cincinnati, but additional analysis is required. The cost for each "curable" cancer that is detected must be compared with the psychological, social, and personal losses that accrue, as well as the numerous medical expenses incurred, in a frequently protracted death from breast cancer. All other imaging techniques that have been reviewed should be regarded as adjuncts to rather than replacements for mammographic screening (Table 1). Ultrasound and computerized tomography are helpful when the physical examination and mammogram are equivocal. Other techniques, such as transillumination, thermography, and magnetic-resonance imaging, should be considered experimental. In patients with clinically evident lesions, x-ray mammography is helpful to evaluate the suspicious area, as well as to "screen" the remaining tissue in both breasts and to search for multicentric or bilateral lesions. Mammography is the only imaging technique that has been proved effective for screening. The low doses required by present-day mammographic technology pose a possible risk that is so small it is not measurable. The image quality has improved considerably over the past decade, and data supporting the benefits of mammography are increasing. As a result, the American Cancer Society has recently modified its recommendations to include mammographic screening of asymptomatic women beginning at the age of 40 years (Table 2). Before any new system can be considered a replacement for mammographic screening, carefully executed trials are necessary to prove efficacy beyond anecdotal claims.

Mammographic detectability of breast microcalcifications.

Controlled in vitro studies of breast microcalcification detectability were done comparing a wide variety of standard and state-of-the-art mammography techniques (conventional and microfocal spot x-ray tubes, screen-film and xeroradiographic recording systems, contact and magnification techniques). Results confirmed previous observations that geometric unsharpness is the limiting factor in microcalcification detectability for most conventional mammography systems. Results also indicated superior microcalcification detection for: xeroradiographic over screen-film recording systems, positive-mode over negative-mode xeroradiography, microfocal spot contact over conventional contact techniques, and microfocal spot magnification over all contact techniques. No differences were found between a standard screen-film technique and a screen-film technique requiring about one-half the radiation exposure. On the other hand, although there was no differences between standard xeroradiography and a modest-added-filtration (reduced-dose) xeroradiographic technique, standard xeroradiography demonstrated superior microcalcification detection over a reduced-dose technique that used large amounts of added beam filtration. The clinical applicability of these findings is discussed.