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Biomedical subjects

M J Yaffe

Publications and source records attributed to M J Yaffe.

At least 19 recordsLinked to original sources
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

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↗
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↗
PubMed1994

Optimization of spectral shape in digital mammography: dependence on anode material, breast thickness, and lesion type.

It has been proposed that breast cancer detection can be improved through the use of digital mammography. It is hypothesized that the choice of proper shape of the x-ray spectrum incident upon the breast can yield an improved image signal-to-noise ratio (SNR) for a given dose. To test this hypothesis, an energy transport model incorporating measured breast tissue attenuation coefficients and published exposure-to-dose conversion values was developed to describe the image acquisition process. The choice of applied kilovoltage and filter for Mo and W target x-ray sources has been optimized with respect to SNR and absorbed dose for detectors based on a Gd2O2S scintillating screen under the conditions of perfect coupling of light between the screen and a solid state photodetector. For the W spectra, the optimum filter-kVp combinations could provide 41%, 13%, and 42% improvements in SNR for 2-cm, 6-cm and 8-cm breasts, respectively, over the conventional Mo filtration, for a practical imaging time of 1.0 s. W and Mo spectra produce similar SNR values for a given filter thickness except for the 4-cm breast. Given the limitations of current technology, however, the W spectra produce the optimum SNRs in a shorter imaging time for breast thicknesses greater than and less than 4 cm. The maximum SNR for imaging both infiltrating ductal carcinoma and calcifications is provided by the same filter-kVp combination, allowing optimization based on breast thickness and composition only. The model can now be used to compare and improve upon novel detector designs.

Breast↗
PubMed1994

Binary vascular reconstruction from a limited number of cone beam projections.

This paper describes a method to perform reconstruction of vascular cross-sectional images from a limited number of x-ray angiographic cone-beam projections. It is assumed that the projection data can be simplified by identifying blood vessels in each angiogram and removing signals due to other structures. Under these conditions, the x-ray attenuation coefficient, mu, can be modeled as a binary variable having a value mu 0 within the vessel and "0" outside. The reconstruction is performed by minimizing a cost function using the method of simulated annealing. In this paper, we demonstrate that the introduction of a priori information allows one to reconstruct a sphere and a simulated branched vessel from three views with, respectively, 97% and 93% of voxels having correct values. The addition of a continuity constraint for the reconstruction of the branched vessel resulted in further reduction in the percentage of misplaced voxels. Calculations require from one to six hours of CPU time on a Sun SparcStation 2 computer for the cases investigated here. The effect of noise, "cooling" schedule, and number of views on the reconstruction are examined using simulated vessel projections. Modifications to our approach to accelerate the reconstruction are also discussed.

Angiography↗
PubMed1994

Performance of glass fiber antiscatter devices at mammographic energies.

Using fiber optic manufacturing techniques, it is possible to produce a radiographic grid that discriminates against scattered radiation in two dimensions. Such grids consist of septa composed of glass with a high lead content; the interspace material is air, so that approximately 80% of the grid area is open. In this way, effective high ratio grids can be produced with relatively low Bucky factors. The performance of samples of such grid material is characterized in terms of both scatter rejection and dose efficiency for application in digital mammography in both slot-beam and area-beam geometry. For area beams, five- to tenfold improved scatter rejection relative to conventional grids was observed. In slot configurations, such grids could provide improved SNR/dose performance and more effective utilization of the heat loading capability of the x-ray source.

Fiber Optic Technology↗
PubMed1994

Analysis of the spatial-frequency-dependent DQE of optically coupled digital mammography detectors.

The effect of optical coupling efficiency on the spatial-frequency-dependent propagation of signal and noise is considered for x-ray image detectors for digital mammography in which a phosphor screen is optically coupled to a charge-coupled device (CCD) image array. For experimental purposes, optical coupling between a Gd2O2S:Tb phosphor screen and a CCD image array was provided by relay lenses. Neutral density filters were inserted between the lenses to vary the optical coupling efficiency without altering the inherent spatial resolution. The total coupling efficiency, defined as the number of electrons (e-) recorded in the CCD per x-ray interaction in the phosphor, was calculated in each case. The modulation transfer function, and the contributions to the total noise power spectrum (NPS) of x-ray quantum noise, secondary quantum noise, and inherent detector noise were measured as a function of coupling efficiency. These data were used to calculate the spatial-frequency-dependent detective quantum efficiency [DQE(f)]. The NPS due to x-ray quantum noise had a significant spatial-frequency dependence for coupling efficiencies of more than 9 e- per x-ray interaction, but little spatial-frequency dependence for coupling efficiencies of less than 2 e- per x-ray interaction. These results indicate that to preserve high spatial-frequency values of DQE(f), and to ensure that images are x-ray quantum-noise limited at high spatial frequencies, a coupling efficiency on the order of 10 e- per x-ray interaction is required.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrons↗
PubMed1994

A model for optimization of spectral shape in digital mammography.

X-ray mammography is the most sensitive imaging modality available for the detection of breast cancer. The highest performance can only be achieved, however, if the complete imaging system is optimized. The development of digital mammography offers an opportunity to obtain improved sensitivity in mammography. In such systems, the decoupling of the recording and display processes allows each component of the imaging system to be optimized separately. In this paper we describe a method for optimizing the recording process for digital mammographic techniques. Our method uses an energy transport model of the propagation of signal and noise through the imaging system. The computations make use of experimentally determined data wherever possible so that the number of assumptions in the model can be minimized. The model predicts the signal-to-noise ratio for a constant dose to the breast, and therefore allows comparison and optimization both for different x-ray spectra and for different imaging tasks. The major energy-dependent components of the model have been verified, and good agreement is demonstrated between predictions by the model of both contrast and SNR and experimentally measured values. Calculations for a particular imaging task, detection of a 200-microns cubic calcification in a 6-cm, 50% adipose-50% glandular breast, illustrate application of the model for optimization of spectral shape.

Breast Neoplasms↗
PubMed1994

Determination of thresholds for detection of cerebellar blood flow deficits in brain SPECT images.

UNLABELLED: Two observer studies were performed to determine the threshold (i.e., ratio of the counts in a lesion area to the counts in the corresponding contralateral region) at which two experienced observers diagnosed blood flow deficits in the cerebellum in 99mTc-HMPAO SPECT scans to be clinically significant, and investigate the effect of the intensity mapping scale on the detectability of lesions. METHODS: Lesions representing blood flow deficits varying from no decrease to a 12.5% decrease were simulated in 300 patient images. The first study, a receiver-operator characteristics (ROC) experiment, used two observers to compare the detectability of lesions with three intensity mapping scales: two pseudocolor scales, and a linear gray scale. A second "threshold-criterion" study was done to estimate the threshold at which observers determine deficits to be clinically significant. RESULTS: In the ROC study, the observers were more accurate in detecting lesions displayed in pseudocolor than in gray scale. In the threshold-criterion study, the threshold at which observers assessed clinically significant deficits was found to range between 0.900 and 0.950 (corresponding to a 5%-10% decrease in counts), depending on the observer, and the intensity mapping scale. For both observers, the detection threshold was higher (i.e., closer to 1.0) with the pseudocolor scale than with the gray scale. CONCLUSION: The definition of a threshold value for use in quantitative techniques is dependent on both the observer and the intensity mapping scale. Observers were more accurate with the pseudocolor scales.

Cerebellum↗
PubMed1994

Are physicians meeting the needs of family caregivers of the frail elderly?

OBJECTIVE: To explore expressed needs, both formal and informal, of family caregivers of frail elderly. To evaluate roles of physicians. DESIGN: Questionnaire survey of members of the Montreal Jewish community providing care for frail elderly family members. SETTING: Jewish community of Montreal. PARTICIPANTS: Volunteer caregivers who were caring for a family member or friend 60 years or older, who had greatest responsibility for providing physical or emotional support to an elderly person, who saw themselves as caregivers, and who could speak English or French were studied. Of 118 volunteers, 32 were excluded because they withdrew for personal reasons or because they did not meet study criteria. MAIN OUTCOME MEASURES: Demographic variables, functional status of the care receiver, use of home care services, and needs assessment to identify additional services. RESULTS: An average of 75.4% respondents did not use formal support services. Just under half of caregivers were dissatisfied with the attention they received from the health care system, and more than one third expressed feelings of stress, depression, guilt, and isolation. CONCLUSIONS: Hypotheses for this discontent are presented. Physicians may be uninterested in helping caregivers; even if they were receptive to counseling caregivers, they could be poorly remunerated for the types of counseling sessions that are usual for caregivers; and being a professional caregiver to family caregivers is demanding in itself.

Activities of Daily Living↗
PubMed1994

Diagnosing and treating lateral epicondylitis.

Lateral epicondylitis is often encountered in primary care. Although its diagnosis can be fairly straightforward, its treatment is often difficult. This review examines the epidemiology, pathophysiology, and clinical presentation of tennis elbow. Management options are discussed.

Humans↗