PubMed Health⌕ Search

Biomedical subjects

M J Yaffe

Publications and source records attributed to M J Yaffe.

At least 19 recordsLinked to original sources
PubMed1997

X-ray detectors for digital radiography.

Digital radiography offers the potential of improved image quality as well as providing opportunities for advances in medical image management, computer-aided diagnosis and teleradiology. Image quality is intimately linked to the precise and accurate acquisition of information from the x-ray beam transmitted by the patient, i.e. to the performance of the x-ray detector. Detectors for digital radiography must meet the needs of the specific radiological procedure where they will be used. Key parameters are spatial resolution, uniformity of response, contrast sensitivity, dynamic range, acquisition speed and frame rate. The underlying physical considerations defining the performance of x-ray detectors for radiography will be reviewed. Some of the more promising existing and experimental detector technologies which may be suitable for digital radiography will be considered. Devices that can be employed in full-area detectors and also those more appropriate for scanning x-ray systems will be discussed. These include various approaches based on phosphor x-ray converters, where light quanta are produced as an intermediate stage, as well as direct x-ray-to-charge conversion materials such as zinc cadmium telluride, amorphous selenium and crystalline silicon.

Electrons↗
PubMed1997

Thickness-equalization processing for mammographic images.

A digital postprocessing technique was used to compensate for the limitations of laser film or cathode-ray-tube devices used to display digital mammograms. An algorithm identified and equalized for the large change in digital signal caused by the reduction in thickness at the margin of the compressed breast. The resulting images reflected only breast composition, and so the number of gray levels needed to display the processed image was greatly reduced, which facilitated presentation and analysis.

Female↗
PubMed1996

Variations in measured vessel diameters using coronary measurement system.

The Coronary Measurement System (CMS, MEDIS, Leiden, Netherlands) is a film-based QCA system that allows the user to vary the intensity of the light source which illuminates the film, thereby changing the brightness of the image viewed by the digitizing video camera. We found that significant variations in calibration factor (mm/pixel) and measured diameter can occur as a result of variations in either of these intensities. We calculated the variability of the measured diameters for a range of light intensities used for vessel measurement and for calibration. The root mean square deviations in estimated vessel diameter for simulated vessels having actual diameters of 2.03, 2.56, 3.03, and 3.55 mm were 0.13, 0.13, 0.13, and 0.11 mm, respectively, while the ranges (maximum-minimum estimates) were 0.47, 0.45, 0.47, and 0.36 mm, respectively. These results show that while mean errors due to changes in brightness are small, there is the potential for larger errors for certain combinations of light intensities.

Coronary Angiography↗
PubMed1996

Current status of digital mammography.

Some inherent limitations to further technical improvement in film-screen mammography exist. Many of these limitations can be overcome effectively with digital mammography, in which image acquisition, display, and storage are performed independently, thus allowing the optimization of each. Presented is a brief background of digital and analog imaging with emphasis on the features and drawbacks of digital mammography systems. Image storage, processing, and display, computer-aided detection and diagnosis, as well as telemammography are also discussed.

Diagnosis, Computer-Assisted↗
PubMed1996

Quantitative correlation of breast tissue parameters using magnetic resonance and X-ray mammography.

Previous investigators have shown that there is a strong association between the fraction of fibroglandular tissue within the breast as determined by X-ray mammography (per cent density) and breast cancer risk. In this study, the quantitative correlation between per cent density and two objective magnetic resonance (MR) parameters of breast tissue, relative water content and mean T2 relaxation time, as investigated for 42 asymptomatic subjects. Using newly developed, rapid techniques MR measurements were performed on a volume-of-interest incorporating equal, representative portions of both breasts. X-ray mammograms of each subject were digitised and analysed semiautomatically to determine per cent density. Relative water content showed a strong positive correlation with per cent density (Pearson correlation coefficient rp = 0.79, P < 0.0001) and mean T2 value showed a strong negative correlation with per cent density (rp = -0.61, P < 0.0001). The MR and X-ray parameters were also associated with sociodemographic and anthropometric risk factors for breast cancer (P < 0.05). The potential use of MR parameters to assess risk of breast cancer and to provide a frequent, non-hazardous monitor of breast parenchyma is discussed.

Adipose Tissue↗
PubMed1996

Analysis of signal propagation in optically coupled detectors for digital mammography: II. Lens and fibre optics.

An x-ray detector for digital x-ray mammography is under investigation, which consists of a phosphor screen coupled by a demagnifying fibre-optic taper to a time-delay integration mode, charge-coupled device (CCD) image array. The signal propagation through such a detector depends on the intensity and angular emission of light from the phosphor screen, the angular acceptance and transmission of light through the optics, and the spectral sensitivity of the CCD to the fluorescent light. The production of light by the phosphor screen was considered in a previous paper. Here, the issues related to the optics are examined. For phosphor screens coupled by lenses with limiting acceptance angles of less than 30 degrees, it was calculated that the coupling efficiency would be 10% greater than would be estimated under the assumption of a Lambertian source. These increases occur because a phosphor screen typically produces light which is more forward directed than a Lambertian source. Similar increases in efficiency are observed when a phosphor screen is coupled to a fibre-optic faceplate or taper. For fibre optics, exact estimation of the optical coupling efficiency requires knowledge of the angular-dependent transmission efficiency of the fibres.

Biophysical Phenomena↗
PubMed1996

Automated analysis of mammographic densities.

Information derived from mammographic parenchymal patterns provides one of the strongest indicators of the risk of developing breast cancer. To address several limitations of subjective classification of mammographic parenchyma into coarse density categories, we have been investigating more quantitative, objective methods of analysing the film-screen mammogram. These include measures of the skewness of the image brightness histogram, and of image texture characterized by the fractal dimension. Both measures were found to be strongly correlated with radiologists' subjective classifications of mammographic parenchyma (Spearman correlation coefficients, Rs = -0.88 and -0.76 for skewness and fractal dimension measurements, respectively). Further, neither measure was strongly dependent on simulated changes in mammographic technique. Correlation with subjective classification of mammographic density was better when both the skewness and fractal measures were used in combination than when either was used alone. This suggests that each feature provides some independent information.

Adult↗
PubMed1996

Computed tomography artifacts associated with craniofacial fixation devices: an experimental study.

This study compares the artifacts caused by eight different craniofacial fixation devices in computed tomography (CT) images. Using a Teflon CT phantom model, part I of this study involved the quantitative evaluation of the X-ray absorption properties of each fixation device. Part II utilized a human cadaveric model to determine the degree to which the artifact interfered with the visualization of anatomic structures. In part I, each fixation device was secured to the surface of the phantom and then scanned. All artifacts were compared on the basis of standard deviation in CT number. The severity of the artifact was related to the physical size of the fixation device and its composition. Vitallium devices generated a greater degree of CT artifacts than titanium devices of comparable size. In part II, fixation devices were secured to the orbital rims of human cadaveric heads and then scanned. Visualization of specified anatomic structures was graded independently. The results revealed that titanium fixation devices did not cause significant bone or soft-tissue image degradation, whereas all vitallium fixation devices, except micro mesh and micro (1.0 mm) straight plates, generated an artifact that resulted in some image degradation. The extent of image degradation was related to the fixation device size. Only the thickest vitallium fixation device, mini fragmentation (2.0 mm), resulted in bony image degradation. The degree of soft-tissue image degradation decreased as the size of vitallium fixation devices decreased such that micro fragmentation (0.8 mm) and pan fixation (1.3 mm) devices interfered with soft-tissue visualization only in the immediate vicinity of the plate. The results of this study confirm the previous work of Sullivan and colleagues and Fiala and associates. The data indicate that when postoperative imaging is an important clinical consideration: (1) the fewest number of internal fixation devices should be used to achieve rigid bony fixation, (2) the proximity of fixation devices to the regions of interest should be considered at the time of fixation, (3) titanium implants produce less artifacts than vitallium implants of comparable size, and (4) vitallium micro mesh and micro (1.0 mm) straight fixation devices do not produce artifacts resulting in significant image degradation.

Artifacts↗
PubMed1996

Symmetry of projection in the quantitative analysis of mammographic images.

Mammographic parenchymal patterns are among the strongest indicators of the risk of developing breast cancer. Risk evaluation through breast patterns may have an important role in studies of the aetiology of breast cancer and for monitoring changes in the breast in evaluating potential risk-modifying interventions. Typically, patterns are assessed by an experienced radiologist according to Wolfe grade, or on a coarse quantitative scale according to percent density. Parenchymal characterization methods, to overcome variability of classification by human observer, are under investigation. These include image segmentation using semi-automatic thresholding and automatic classification through textural and density measures. An important practical question relates to the extent to which information about mammographic pattern is carried by any one of the four views obtained in a typical examination. Specifically, variations of right-left breast symmetry and variations between the two standard views of each breast were tested. The mammograms of 30 premenopausal women, comprising 90 images [30 each of the right cranial-caudal (RCC), left cranial-caudal (LCC) and right medial-lateral oblique (RMLO)] were evaluated. Parameters included both subjective (radiologist classification and interactive image thresholding) and objective (fractal and skewness indices) quantitative measurements of parenchymal pattern. For the parameters tested, a high degree of correlations was observed for measurements on the RCC, LCC and RMLO views. Pearson correlation coefficients between 0.86-0.96 were found for the comparisons of quantitative parameters. The strong correlations suggest that, in the study and application of mammographic density classification, representative information is provided in a single view.

Adult↗
PubMed1996

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.

Biophysical Phenomena↗
PubMed1995

Quantitative classification of mammographic densities and breast cancer risk: results from the Canadian National Breast Screening Study.

BACKGROUND: The radiographic appearance of the female breast varies from woman to woman depending on the relative amounts of fat and connective and epithelial tissues present. Variations in the mammographic density of breast tissue are referred to as the parenchymal pattern of the breast. Fat is radiologically translucent or clear (darker appearance), and both connective and epithelial tissues are radiologically dense (lighter appearance). Previous studies have generally supported an association between parenchymal patterns and breast cancer risk (greater risk with increasing densities), but there has been considerable heterogeneity in risk estimates reported. PURPOSE: Our objective was to determine the level of breast cancer risk associated with varying mammographic densities by quantitatively classifying breast density with conventional radiological methods and novel computer-assisted methods. METHODS: From the medical records of a cohort of 45,000 women assigned to mammography in the Canadian National Breast Cancer Screening Study (NBSS), a multicenter, randomized trial, mammograms from 354 case subjects and 354 control subjects were identified. Case subjects were selected from those women in whom histologically verified invasive breast cancer had developed 12 months or more after entering the trial. Control subjects were selected from those of similar age who, after a similar period of observation, had not developed breast cancer. The mammogram taken at the beginning of the NBSS was the image used for measurements. Mammograms were classified into six categories of density, either by radiologists or by computer-assisted measurements. All radiological classification and computer-assisted measurements were made using one craniocaudal view from the breast contralateral to the cancer site in case subjects and the corresponding breast of control subjects. All P values represent two-sided tests of statistical significance. RESULTS: For all subjects, there was a 43% increase in the relative risk (RR) between the lower and the next higher category of density, as determined by radiologists, and there was a 32% increase as determined by the computer-assisted method. For all subjects, the RR in the most extensive category relative to the least was 6.05 (95% confidence interval [CI] = 2.82-12.97) for radiologists and 4.04 (95% CI = 2.12-7.69) for computer-assisted methods. Statistically significant increases in breast cancer risk associated with increasing mammographic density were found by both radiologists and computer-assisted methods for women in the age category 40-49 years (P = .005 for radiologists and P = .003 for computer-assisted measurements) and the age category 50-59 years (P = .002 for radiologists and P = .001 for computer-assisted measurements). CONCLUSION: These results show that increases in the level of breast tissue density as assessed by mammography are associated with increases in risk for breast cancer.

Adult↗
PubMed1995

Effects of non-linear flow and spatial orientation on technetium-99m hexamethylpropylene amine oxime single-photon emission tomography.

The effects of two post-acquisition corrections on the visual and quantitative analysis of technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomography (SPET) were determined. The corrections were for: (1) the improper spatial orientation of the patient data sets, and (2) the non-linear uptake of HMPAO across the blood-brain barrier. Reorienting the SPET image data sets removed observers' uncertainty in assessment caused by suspected head tilt; however, it increased their uncertainty due to perceived subtle perfusion deficits. Applying the correction to compensate for the decrease in uptake of HMPAO in high-flow regions resulted in an increase in the number of positive assessments. In a study involving 30 patient studies, intra-observer reliability increased from 62% to 83% (average of two observers) after applying both of the corrections, while inter-observer reliability improved from 62% to 81%. Quantitative methods of analysing the images are also affected by the corrections. In an ROI-based classification scheme, the quantitative assessments of more than one-half of the images are affected by the two corrections. These results need to be considered when comparing both quantitative and visual results from different studies in which the corrections may or may not have been applied.

Algorithms↗
PubMed1995

Analysis of signal propagation in optically coupled detectors for digital mammography: I. Phosphor screens.

The angular emission of light from turbid phosphor screens has been measured and modelled. As a first approximation, turbid phosphor screens have traditionally been modelled as Lambertian sources; however, Giakoumakis et al have previously shown that light emission from turbid phosphor screens is in fact more forward peaked. In this article, we extend the theory of Giakoumakis to include turbid phosphor screens that incorporate a transparent overcoat. The refractive index of the optical coupling medium in contact with the overcoat is shown to have a direct effect on both light output and angular emission from the screen. It was found that simple laws of refraction adequately describe this phenomenon. To model the angular emission of light from such phosphor screens, a term was included to describe the refraction from the overcoat into the adjacent coupling medium. The data obtained are required to calculate the propagation of the signal in a digital mammography detector in which a phosphor screen is optically coupled to a charge-coupled device (CCD) image array.

Biophysical Phenomena↗
PubMed1995

X-ray imaging with amorphous selenium: detective quantum efficiency of photoconductive receptors for digital mammography.

Factors affecting the zero spatial frequency detective quantum efficiency of photoconductor-based x-ray detectors operating in the mammographic energy range are modeled for monoenergetic incident x rays. The problem is separated into two sections: the calculation of the x-ray absorption and the Swank factor. X-ray absorption in this energy range, for most practical photoconductors, is dominated by the photoelectric effect. The Swank factor has four components: fluorescence escape, stochastic variations in gain, variations of gain due to incomplete coupling of charge from the photoconductive layer to the detector electrode, and the nonlinear discharge arising from the field-dependent x-ray gain, an effect that is unique to photoconductors. Calculations are performed for selenium, which is currently the most technologically advanced photoconductor available for digital x-ray imaging. For thicknesses of selenium exceeding 50 microns and for energies between 12 and 50 keV, the detective quantum efficiency of this photoconductor is found to exceed that of a conventional Gd2O2S-based mammographic phosphor screen.

Efficiency↗
PubMed1995

Recommended specifications for new mammography equipment: report of the ACR-CDC Focus Group on mammography equipment.

The American College of Radiology has published a report that describes desirable features for new mammography x-ray units that will contribute to high-quality imaging. It encompasses all aspects of x-ray equipment performance including mechanical considerations, the x-ray tube focal spot and spectrum, generator performance, collimation, scatter rejection, and the automatic exposure control. The report is intended to provide guidance to equipment manufacturers and to purchasers of mammography systems with regard to basic performance levels that should be expected.

Female↗
PubMed1995

Digital mammography, computer-aided diagnosis, and telemammography.

Film-screen x-ray mammography is an effective tool for the detection and diagnosis of breast cancer. Several limitations of current mammographic technology have been identified, and there is now good evidence that improved image quality and possibly reduced radiation dose could be achieved if mammograms are acquired directly in digital form. In this article, the rationale for digital mammography is presented and various approaches to the design of a digital mammography system are described. Current challenges in developing a practical, clinically acceptable digital mammography system are discussed and applications of digital mammography to computer-aided diagnosis, telemammography, and quantitative imaging are suggested.

Artifacts↗
PubMed1994

Physician characteristics and the recognition of depression and anxiety in primary care.

We examined physician characteristics associated with the recognition of depression and anxiety in primary care. Fifty-five physicians treating a total of 600 patients completed measures of psychosocial orientation, psychological mindedness, self-rating of sensitivity to hidden emotions, and a video test of sensitivity to nonverbal communication. Patients were classified as cases of psychiatric distress based on the CES-D scale and the Diagnostic Interview Schedule. Physician recognition was determined by notation of any psychosocial diagnosis in the medical charts over the ensuing 12 months. Of 192 patients scoring 16 or above on the CES-D, 44% (83) were recognized as psychiatrically distressed. Three findings were central to this study: 1) Physicians who are more sensitive to nonverbal expressions of emotion made more psychiatric or psychosocial assessment of their patients and appeared to be over-inclusive in their judgments of psychosocial problems; 2) Physicians who tended to blame depressed patients for causing, exaggerating, or prolonging their depression made fewer psychosocial assessments and were less accurate in detecting psychiatric distress; 3) False positive labeling of patients who had no evidence of psychiatric distress was rare. Surprisingly, more severe medical illness increased the likelihood of labeling and accurate recognition. Physician factors that increased recognition may indicate a greater willingness to formulate a psychiatric diagnosis and an ability notice nonverbal signs of distress.

Adult↗