Digital tomosynthesis in breast imaging

Digital x-ray tomosynthesis: current state of the art and clinical potential

Digital x-ray tomosynthesis is a technique for producing slice images using conventional x-ray systems. It is a refinement of conventional geometric tomography, which has been known since the 1930s. In conventional geometric tomography, the x-ray tube and image receptor move in synchrony on opposite sides of the patient to produce a plane of structures in sharp focus at the plane containing the fulcrum of the motion; all other structures above and below the fulcrum plane are blurred and thus less visible in the resulting image. Tomosynthesis improves upon conventional geometric tomography in that it allows an arbitrary number of in-focus planes to be generated retrospectively from a sequence of projection radiographs that are acquired during a single motion of the x-ray tube. By shifting and adding these projection radiographs, specific planes may be reconstructed. This topical review describes the various reconstruction algorithms used to produce tomosynthesis images, as well as approaches used to minimize the residual blur from out-of-plane structures. Historical background and mathematical details are given for the various approaches described. Approaches for optimizing the tomosynthesis image are given. Applications of tomosynthesis to various clinical tasks, including angiography, chest imaging, mammography, dental imaging and orthopaedic imaging, are also described.

Breast tomography with synchrotron radiation: preliminary results

A system for in vivo breast imaging with monochromatic x-rays has been designed and built at the synchrotron radiation facility Elettra in Trieste (Italy) and will be operational in 2004. The system design involves the possibility of performing both planar mammography and breast tomography. In the present work, the first results obtained with a test set-up for breast tomography are shown and discussed. Tomographic images of in vitro breasts were acquired using monochromatic x-ray beams in the energy range 20-28 keV and a linear array silicon pixel detector. Tomograms were reconstructed using standard filtered backprojection algorithms; the effect of different filters was evaluated. The attenuation coefficients of fibroglandular and adipose tissue were measured, and a quantitative comparison of images acquired at different energies was performed by calculating the differential signal-to-noise ratio of fibroglandular details in adipose tissue. All images required a dose comparable to the dose delivered in clinical, conventional mammography and showed a high resolution of the breast structures without the overlapping effects that limit the visibility of the structures in 2D mammography. A quantitative evaluation of the images proves that the image quality at a given dose increases in the considered energy range and for the considered breast sizes.

The current status of digital mammography

Digital imaging has shown rapid advances in recent years. Various different digital mammography systems are now available for clinical use. Digital mammography does have clear advantages over traditional screen film mammography, but this is yet to convincingly translate into improved cancer detection rates. This review aims to describe the different technologies, introduce concepts related to image quality and review the current evidence for the use of digital mammography systems in clinical practice. Advanced applications of digital mammography such as computer-aided detection (CAD) are also discussed.

Tomographic optical breast imaging guided by three-dimensional mammography

We introduce a modified Tikhonov regularization method to include three-dimensional x-ray mammography as a prior in the diffuse optical tomography reconstruction. With simulations we show that the optical image reconstruction resolution and contrast are improved by implementing this x-ray-guided spatial constraint. We suggest an approach to find the optimal regularization parameters. The presented preliminary clinical result indicates the utility of the method.

Contrast-enhanced digital mammography: initial clinical experience

PURPOSE

To investigate the potential of using intravenous contrast material with full-field digital mammography to facilitate the detection and characterization of lesions in the breast.

MATERIALS AND METHODS

Twenty-two women scheduled for biopsy because they were suspected of having abnormalities at breast imaging underwent imaging with contrast material-enhanced digital mammography. Six sequential images of the affected breast were obtained, with a contrast agent injected intravenously between the time the first and second images were obtained. Image processing included registration and logarithmic subtraction. Lesions were evaluated for the presence, morphology, and kinetics of enhancement. Lesion type, size, and pathologic findings were correlated with the findings at contrast-enhanced digital mammography.

RESULTS

At contrast-enhanced digital mammography, enhancement was observed in eight of 10 patients with biopsy-proved cancers. In one case of ductal carcinoma in situ and one case of invasive ductal carcinoma, enhancement was not observed. No enhancement was seen in seven of 12 cases in which lesions were suspected of being malignant at initial imaging but were benign. Morphology generally correlated with the pathologic diagnosis. The kinetics of lesion enhancement showed similarity to that seen with gadolinium-enhanced magnetic resonance imaging but was not consistent.

CONCLUSION

The results of this preliminary study suggest that contrast-enhanced digital mammography potentially may be useful in identification of lesions in the mammographically dense breast. Further investigation of contrast-enhanced digital mammography as a diagnostic tool for breast cancer is warranted.

Circular tomosynthesis: potential in imaging of breast and upper cervical spine--preliminary phantom and in vitro study

Phantom and in vitro studies were performed to evaluate the potential application of digital circular tomosynthesis in imaging of the breast and upper cervical spine. A prototype volumetric x-ray system was used to image a mammographic phantom, a fresh mastectomy specimen, and a head phantom containing the upper cervical spine. Results show that breast tissue visualization is improved by the ability to produce sectional images that blur overlying structures and yield three-dimensional information about calcification clusters. In upper cervical spine imaging, digital circular tomosynthesis effectively blurs overlying jaw and skull structures so that C1 and C2 can be visualized in a standard anteroposterior view.

Why should breast tumour detection go three dimensional?

Although x-ray mammography is widely developed for breast tumour detection, it suffers from spatial superposition in its two-dimensional (2D) representation of a three-dimensional (3D) breast structure. Accordingly, 3D breast imaging, such as cone-beam computed tomography (CT), arises at the historic moment. In this paper, we theoretically elucidate the spatial superposition effect associated with x-ray mammography on breast tumour detection. This explanation is based on the line integral of x-ray traversing a composite breast model. As a result, we can characterize the difficulty of detecting small tumours in terms of local intensity contrast in x-ray images. In comparison, we also introduce cone-beam CT breast imaging for 3D breast volume representation, which offers advantages for breast mass segmentation and measurement. The discussion is demonstrated with an experiment with a breast surgical specimen. In conclusion, we strongly believe that 3D volumetric representation allows for more accurate breast tumour detection.

Tomographic mammography using a limited number of low-dose cone-beam projection images

A method is described for using a limited number (typically 10-50) of low-dose radiographs to reconstruct the three-dimensional (3D) distribution of x-ray attenuation in the breast. The method uses x-ray cone-beam imaging, an electronic digital detector, and constrained nonlinear iterative computational techniques. Images are reconstructed with high resolution in two dimensions and lower resolution in the third dimension. The 3D distribution of attenuation that is projected into one image in conventional mammography can be separated into many layers (typically 30-80 1-mm-thick layers, depending on breast thickness), increasing the conspicuity of features that are often obscured by overlapping structure in a single-projection view. Schemes that record breast images at nonuniform angular increments, nonuniform image exposure, and nonuniform detector resolution are investigated in order to reduce the total x-ray exposure necessary to obtain diagnostically useful 3D reconstructions, and to improve the quality of the reconstructed images for a given exposure. The total patient radiation dose can be comparable to that used for a standard two-view mammogram. The method is illustrated with images from mastectomy specimens, a phantom, and human volunteers. The results show how image quality is affected by various data-collection protocols.

The effects of stereo shift angle, geometric magnification and display zoom on depth measurements in digital stereomammography

We are developing virtual three-dimensional (3-D) cursors for measuring depths in digital stereomammograms. We performed a study to investigate the effects of stereo shift angle, geometric magnification, and display zoom on the accuracy of depth measurements made with a virtual 3-D cursor. A phantom containing 50 low contrast fibrils at depths ranging from 1 to 11 mm was imaged with a full-field digital mammography system. Left- and right-eye images were generated at stereo shift angles of +/-3 degrees and +/-6 degrees, using either contact or 1.8x geometric magnification geometry. The images were viewed on a high-resolution stereoscopic display system in normal and 2x zoom mode. Observers viewed the images with stereo glasses and adjusted the depth of a cross-shaped virtual cursor to best match the perceived depth of each fibril. The results for two trained observers with excellent stereo acuity were nearly identical when viewing the same images. The average root mean square errors for the two observers were 1.2 mm (+/-3 degrees contact, no zoom), 1.3 mm (+/-3 degrees contact zoom), 0.8 mm (+/-6 degrees contact, no zoom), 0.6 mm (+/-6 degrees contact, zoom), 0.8 mm (+/-3 magnification, no zoom), 0.7 mm (+/-3 degrees magnification, zoom), and 0.2 mm (+/-6 degrees magnification, no zoom). One observer repeated the entire study for two additional fibril phantom configurations. Combining all the results, we found that for the contact geometry increasing the stereo shift angle from +/-3 degrees to +/-6 degrees improved the depth measurement accuracy by factors of about 1.2-4.0. Zooming did not provide observable improvement in the depth measurement accuracy; sometimes having no effect, sometimes improving the accuracy, and other times reducing the accuracy, with no general trends. Its effect is likely within experimental errors. However, the stereo effect was more readily visualized in the zoom mode. Geometric magnification improved the depth measurement accuracy. The best accuracy among all cases was about 0.2 mm, obtained with geometric magnification using a stereo angle of +/-6 degrees. This is the mode we recommend for obtaining accurate depth measurements with virtual cursors in stereomammograms.

Microcalcification detectability for four mammographic detectors: flat-panel, CCD, CR, and screen/film)

Amorphous silicon/cesium iodide (a-Si:H/CsI:Tl) flat-panel (FP)-based full-field digital mammography systems have recently become commercially available for clinical use. Some investigations on physical properties and imaging characteristics of these types of detectors have been conducted and reported. In this perception study, a phantom containing simulated microcalcifications (microCs) of various sizes was imaged with four detector systems: a FP system, a small field-of-view charge coupled device (CCD) system, a high resolution computed radiography (CR) system, and a conventional mammography screen/film (SF) system. The images were reviewed by mammographers as well as nonradiologist participants. Scores reflecting confidence ratings were given and recorded for each detection task. The results were used to determine the average confidence-rating scores for the four imaging systems. Receiver operating characteristics (ROC) analysis was also performed to evaluate and compare the overall detection accuracy for the four detector systems. For calcifications of 125-140 microm in size, the FP system was found to have the best performance with the highest confidence-rating scores and the greatest detection accuracy (Az = 0.9) in the ROC analysis. The SF system was ranked second while the CCD system outperformed the CR system. The p values obtained by applying a Student t-test to the results of the ROC analysis indicate that the differences between any two systems are statistically significant (p<0.005). Differences in microC detectability for the large (150-160 microm) and small (112-125 microm) size microC groups showed a wider range of p values (not all p values are smaller than 0.005, ranging from 0.6 to <0.001) compared to the p values obtained for the medium (125-140 microm) size microC group. Using the p values to assess the statistical significance, the use of the average confidence-rating scores was not as significant as the use of the ROC analysis p value for p value.

Mammogram synthesis using a 3D simulation. I. Breast tissue model and image acquisition simulation

A method is proposed for generating synthetic mammograms based upon simulations of breast tissue and the mammographic imaging process. A computer breast model has been designed with a realistic distribution of large and medium scale tissue structures. Parameters controlling the size and placement of simulated structures (adipose compartments and ducts) provide a method for consistently modeling images of the same simulated breast with modified position or acquisition parameters. The mammographic imaging process is simulated using a compression model and a model of the x-ray image acquisition process. The compression model estimates breast deformation using tissue elasticity parameters found in the literature and clinical force values. The synthetic mammograms were generated by a mammogram acquisition model using a monoenergetic parallel beam approximation applied to the synthetically compressed breast phantom.

A calibration approach to glandular tissue composition estimation in digital mammography

The healthy breast is almost entirely composed of a mixture of fatty, epithelial, and stromal tissues which can be grouped into two distinctly attenuating tissue types: fatty and glandular. Further, the amount of glandular tissue is linked to breast cancer risk, so an objective quantitative analysis of glandular tissue can aid in risk estimation. Highnam and Brady have measured glandular tissue composition objectively. However, they argue that their work should only be used for "relative" tissue measurements unless a careful calibration has been performed. In this work, we perform such a "careful calibration" on a digital mammography system and use it to estimate breast tissue composition of patient breasts. We imaged 0%, 50%, and 100% glandular-equivalent phantoms of varying thicknesses for a number of clinically relevant x-ray techniques on a digital mammography system. From these images, we extracted mean signal and noise levels and computed calibration curves that can be used for quantitative tissue composition estimation. In this way, we calculate the percent glandular composition of a patient breast on a pixelwise basis. This tissue composition estimation method was applied to 23 digital mammograms. We estimated the quantitative impact of different error sources on the estimates of tissue composition. These error sources include compressed breast height estimation error, residual scattered radiation, quantum noise, and beam hardening. Errors in the compressed breast height estimate contribute the most error in tissue composition--on the order of +/-7% for a 4 cm compressed breast height: The spatially varying scattered radiation will contribute quantitatively less error overall, but may be significant in regions near the skinline. It is calculated that for a 4 cm compressed breast height, a residual scatter signal error is mitigated by approximately sixfold in the composition estimate. The error in composition due to the quantum noise, which is the limiting noise source in the system, is shown to be less than 1% glandular for most breasts.

New modalities in breast imaging: digital mammography, positron emission tomography, and sestamibi scintimammography

Digital mammography, PET, and sestamibi scintimammography are three new modalities in breast imaging. DM has advantages over film-screen mammography in image storage, retrieval, and processing and may lower the recall rate. Computer-aided detection may increase the sensitivity of mammographic screening without a substantial reduction in specificity. Whereas PET and sestambi scintimammography are not useful in breast cancer screening, PET may play a role in detecting nodal metastases and monitoring treatment response, and sestamibi scintimammography in selected cases may serve as an adjunct to conventional imaging. The cost-effectiveness of these new modalities remains to be evaluated, but all have the potential to significantly advance the diagnosis and management of women with breast cancer.

Normalized glandular dose (DgN) coefficients for arbitrary X-ray spectra in mammography: computer-fit values of Monte Carlo derived data

Normalized glandular dose (DgN) values have been reported by several investigators for specific spectra, however for unconventional or unanticipated x-ray spectra considered for use in mammography, practical methods are not available for DgN computation. In this study, the previously validated SIERRA Monte Carlo code was used to compute the normalized glandular dose coefficients for monoenergetic energies from 8 keV to 50 keV. The overall mammography geometry used was a 65 cm source to image distance, a 1.2 cm air gap between the breast and the detector, and breast thicknesses ranging from 2 to 9 cm. A 4 mm layer of skin was also modeled, and semicircular breast radii of 8.5 cm and 10.0 cm were studied. Breast compositions of 0% glandular, 50% glandular, and 100% glandular were evaluated. The Monte Carlo derived DgN results demonstrated coefficients of variation less than 0.3%. The monoenergetic DgN values, DgN(E), were computer fit using commercial software and the best fit equations are reported. All fits resulted in r2 values of 0.9999 or better. The computer fit equations, along with easy to use spectral modeling routines, are available electronically on the web.

Dedicated breast CT: radiation dose and image quality evaluation

PURPOSE

To evaluate the feasibility of breast computed tomography (CT) in terms of radiation dose and image quality.

MATERIALS AND METHODS

Validated Monte Carlo simulation techniques were used to estimate the average glandular dose (AGD). The calculated photon fluence at the detector for high-quality abdominal CT (120 kVp, 300 mAs, 5-mm section thickness) was the benchmark for assessing the milliampere seconds and corresponding radiation dose necessary for breast CT. Image noise was measured by using a 10-cm-diameter cylinder imaged with a clinical CT scanner at 10-300 mAs for 80, 100, and 120 kVp. A cadaveric breast was imaged in the coronal plane to approximate the acquisition geometry of a proposed breast CT scanner.

RESULTS

The AGD for 80-kVp breast CT was comparable to that for two-view mammography of 5-cm breasts (compressed breast thickness). For thicker breasts, the breast CT dose was about one-third less than that for two-view mammography. The maximum dose at mammography assessed in 1-mm(3) voxels was far higher (20.0 mGy) than that at breast CT (5.4 mGy) for a typical 5-cm 50% glandular breast. CT images of an 8-cm cadaveric breast (AGD, 6.3 mGy) were subjectively superior to digital mammograms (AGD, 10.1 mGy) of the same specimen.

CONCLUSION

The potential of high signal-to-noise ratio images with low anatomic noise, which are obtainable at dose levels comparable to those for mammography, suggests that dedicated breast CT should be studied further for its potential in breast cancer screening and diagnosis.

Effect of angular disparity of basis images and projection geometry on caries detection using tuned-aperture computed tomography

OBJECTIVE

The purpose of this study was to determine whether projection geometry and angular disparity of basis images used for tuned-aperture computed tomography (TACT) slice generation influence observer performance in caries detection.

STUDY DESIGN

Four sets of 8 projections of each of 40 teeth were acquired by using a digital sensor. Each set was radially distributed and subtended angular disparities of 10 degrees, 20 degrees, 30 degrees, and 40 degrees, representing strict projection geometries. A fifth set of images was acquired by using unconstrained geometry. TACT slices were generated from all experimental conditions and presented to 8 observers who viewed the images on a high-resolution monitor. Observers scored the presence/absence of caries with a 5-point confidence scale. Ground truth was achieved by histologic examination of tooth sections. Receiver operating characteristic curves measured observers' diagnostic performance. Analysis of variance was used to test for significant differences among observers and between experimental conditions.

RESULTS

No statistically significant difference between angular disparities was found for the detection of either occlusal (P =.105) or proximal (P =.052) caries. No statistically significant difference between unconstrained and stringent projection geometries was found for the detection of either occlusal (P =.879) or proximal (P =.130) caries.

CONCLUSIONS

Angular disparities ranging from 10 degrees to 40 degrees provide comparable performance in caries detection with TACT. Both unconstrained and stringent projection geometries may be used when reconstructing TACT slices for caries detection tasks.

Perspective on digital mammography

Digital mammography, particularly through its advanced applications, holds great promise for improved diagnostic accuracy, but the display of the images is not ideal at present. Clinical softcopy workstations are somewhat unwieldy to use, and image processing has not yet been optimized for each machine or for each clinical task. In addition, the cost-effectiveness and accuracy of the technology warrant careful study before digital mammography becomes widely disseminated and potentially replaces screen-film mammography, a technology that has been well documented to reduce breast cancer mortality.

Alignment of a volumetric tomography system

A test-bed system has been developed for imaging phantoms with tomosynthesis and volumetric computed tomography. This system incorporates an amorphous silicon flat panel detector on a movable gantry and a computer-controlled rotational positioning stage. In this paper, an analysis of the sensitivity of reconstructed images to geometrical misalignment is presented. Application of this method to circular digital tomosynthesis is examined, with spatial resolution in the focal plane as the criterion for evaluating the effect of misalignment. A software-based method is presented for correcting data for imperfect system alignment prior to image reconstruction. Experimental results yield reconstructed images with spatial resolution approaching the theoretical limit based on detector pixel size and accounting for data interpolation.

What every surgical oncologist should know about digital mammography

This article reviews the available information on digital mammography for surgeons who care for patients with breast cancer. The limitations of the current film-based technology and why digital mammography promises to improve breast cancer detection and breast lesion diagnosis are described. The basics of digital imaging technology are reviewed, including a description of image contrast and spatial resolution and its variance from currently available clinical digital mammography systems. The results of clinical trials completed to date are reported. An upcoming large screening trial for digital mammography, sponsored by the National Cancer Institute, is described. Future technological developments, including improvements in softcopy display, image processing, computer-aided detection and diagnosis (CADD), tomosynthesis, and digital subtraction mammography (DSM), are briefly discussed.

Evaluation of linear and nonlinear tomosynthetic reconstruction methods in digital mammography

RATIONALE AND OBJECTIVES

The purpose of this study was to comparatively evaluate digital planar mammography and both linear and nonlinear tomosynthetic reconstruction methods.

MATERIALS AND METHODS

A "disk" (ie, target) identification study was conducted to compare planar and reconstruction methods. Projective data using a composite phantom with circular disks were acquired in both planar and tomographic modes by using a full-field, digital mammographic system. Two-dimensional projections were reconstructed with both linear (ie, backprojection) and nonlinear (ie, maximization and minimization) tuned-aperture computed tomographic (TACT) methods to produce three-dimensional data sets. Four board-certified radiologists and one 4th-year radiology resident participated as observers. All images were compared by these observers in terms of the number of disks identified.

RESULTS

Significant differences (P < .05, Bonferroni adjusted) were observed between all reconstruction and planar methods. No significant difference, however, was observed between the planar methods, and only a marginally significant difference (P < .054, Bonferroni adjusted) was observed between TACT-backprojection and TACT-minimization.

CONCLUSION

A combination of linear and nonlinear reconstruction schemes may have potential implications in terms of enhancing image visualization to provide radiologists with valuable diagnostic information.

Filtered backprojection for modifying the impulse response of circular tomosynthesis

A filtering technique has been developed to modify the three-dimensional impulse response of circular motion tomosynthesis to allow the generation of images whose appearance is like those of some other imaging geometries. In particular, this technique can reconstruct images with a blurring function which is more homogeneous for off-focal plane objects than that from circular tomosynthesis. In this paper, we describe the filtering process, and demonstrate the ability to alter the impulse response in circular motion tomosynthesis from a ring to a disk. This filtering may be desirable because the blurred out-of-plane objects appear less structured.

Comparison of tomosynthesis methods used with digital mammography

RATIONALE AND OBJECTIVES

The authors performed this study to investigate the potential applicability of tomosynthesis to digital mammography. Four methods of tomosynthesis-tuned aperture computed tomography (TACT)-backprojection, TACT-iterative restoration, iterative reconstruction with expectation maximization, and Bayesian smoothing-were compared to planar mammography and analyzed in terms of their contrast-detail characteristics. Specific comparisons between the tomosynthesis methods were not attempted in this study.

MATERIALS AND METHODS

A full-field, amorphous, silicon-based, flat-panel digital mammographic system was used to obtain planar and tomosynthesis projection images. A composite tomosynthesis phantom with a centrally located contrast-detail insert was used as the object of interest. The total exposure for multiple views with tomosynthesis was always equal to or less than that for the planar technique. Algorithms were used to reconstruct the object from the acquired projections.

RESULTS

Threshold contrast characteristics with all tomosynthesis reconstruction methods were significantly better than those with planar mammography, even when planar mammography was performed at more than twice the exposure level. Reduction of out-of-plane structural components was observed in all the tomosynthesis methods analyzed.

CONCLUSION

The contrast-detail trends of all the tomosynthesis methods analyzed in this study were better than those of planar mammography. Further optimization of the algorithms could lead to better image reconstruction, which would improve visualization of valuable diagnostic information.

Breast imaging using an amorphous silicon-based full-field digital mammographic system: stability of a clinical prototype

An amorphous silicon-based full-breast imager for digital mammography was evaluated for detector stability over a period of 1 year. This imager uses a structured CsI:TI scintillator coupled to an amorphous silicon layer with a 100-micron pixel pitch and read out by special purpose electronics. The stability of the system was characterized using the following quantifiable metrics: conversion factor (mean number of electrons generated per incident x-ray), presampling modulation transfer function (MTF), detector linearity and sensitivity, detector signal-to-noise ratio (SNR), and American College of Radiology (ACR) accreditation phantom scores. Qualitative metrics such as flat field uniformity, geometric distortion, and Society of Motion Picture and Television Engineers (SMPTE) test pattern image quality were also used to study the stability of the system. Observations made over this 1-year period indicated that the maximum variation from the average of the measurements were less than 0.5% for conversion factor, 3% for presampling MTF over all spatial frequencies, 5% for signal response, linearity and sensitivity, 12% for SNR over seven locations for all 3 target-filter combinations, and 0% for ACR accreditation phantom scores. ACR mammographic accreditation phantom images indicated the ability to resolve 5 fibers, 4 speck groups, and 5 masses at a mean glandular dose of 1.23 mGy. The SMPTE pattern image quality test for the display monitors used for image viewing indicated ability to discern all contrast steps and ability to distinguish line-pair images at the center and corners of the image. No bleeding effects were observed in the image. Flat field uniformity for all 3 target-filter combinations displayed no artifacts such as gridlines, bad detector rows or columns, horizontal or vertical streaks, or bad pixels. Wire mesh screen images indicated uniform resolution and no geometric distortion.

Mammographic imaging with a small format CCD-based digital cassette: physical characteristics of a clinical system

The physical characteristics of a clinical charge coupled device (CCD)-based imager (Senovision, GE Medical Systems, Milwaukee, WI) for small-field digital mammography have been investigated. The imager employs a MinR 2000 (Eastman Kodak Company, Rochester, NY) scintillator coupled by a 1:1 optical fiber to a front-illuminated 61 x 61 mm CCD operating at a pixel pitch of 30 microns. Objective criteria such as modulation transfer function (MTF), noise power spectrum (NPS), detective quantum efficiency (DQE), and noise equivalent quanta (NEQ) were employed for this evaluation. The results demonstrated a limiting spatial resolution (10% MTF) of 10 cy/mm. The measured DQE of the current prototype utilizing a 28 kVp, Mo-Mo spectrum beam hardened with 4.5 cm Lucite is approximately 40% at close to zero spatial frequency at an exposure of 8.2 mR, and decreases to approximately 28% at a low exposure of 1.1 mR. Detector element nonuniformity and electronic gain variations were not significant after appropriate calibration and software corrections. The response of the imager was linear and did not exhibit signal saturation under tested exposure conditions.

Digital mammography, sestamibi breast scintigraphy, and positron emission tomography breast imaging

Digital mammography allows for the separate optimization of image acquisition and display. Through this technology, and the application of image processing and computer aided diagnosis, breast cancer detection and breast lesion diagnosis might be improved. Besides the obvious data storage, retrieval, and transmission advantages that digital mammography will allow, additional advances such as tomosynthesis, dual energy mammography and digital subtraction mammography are in development. The possible future utility of Sestamibi breast scintigraphy and breast imaging with positron emission tomography is also discussed.

Comparative value of 99mTc-sestamibi scintimammography and sonography in the diagnostic workup of breast masses

OBJECTIVE

This study was conducted to assess the relative roles of 99mTc-sestamibi scintimammography and sonography in the evaluation of breast lesions that are indeterminate or suspicious on mammography or clinical examination.

SUBJECTS AND METHODS

Twenty-five patients with 33 biopsy-proven breast lesions underwent both scintimammography and sonography. Lesions were categorized as benign or requiring biopsy on the basis of the absence or presence of a focus of increased activity on scintimammography and the shape, orientation, and echogenicity of the lesion on sonography.

RESULTS

Sensitivity and specificity in detecting breast cancer were 92% and 95%, respectively, for scintimammography and 100% and 48%, respectively, for sonography. The higher specificity of scintimammography was statistically significant (p < 0.01).

CONCLUSION

Although the overall accuracy of 99mTc-sestamibi scintimammography in the diagnosis of breast cancer was high, it has several disadvantages in comparison with sonography. Scintimammography has a slightly higher false-negative rate for breast cancer, is unable to reveal cysts, is more expensive, takes longer to perform, and involves ionizing radiation. For these reasons, scintimammography with 99mTc-sestamibi is unlikely to either replace sonography or be frequently used in addition to sonography.

Full breast digital mammography with an amorphous silicon-based flat panel detector: physical characteristics of a clinical prototype

The physical characteristics of a clinical prototype amorphous silicon-based flat panel imager for full-breast digital mammography have been investigated. The imager employs a thin thallium doped CsI scintillator on an amorphous silicon matrix of detector elements with a pixel pitch of 100 microm. Objective criteria such as modulation transfer function (MTF), noise power spectrum, detective quantum efficiency (DQE), and noise equivalent quanta were employed for this evaluation. The presampling MTF was found to be 0.73, 0.42, and 0.28 at 2, 4, and 5 cycles/mm, respectively. The measured DQE of the current prototype utilizing a 28 kVp, Mo-Mo spectrum beam hardened with 4.5 cm Lucite is approximately 55% at close to zero spatial frequency at an exposure of 32.8 mR, and decreases to approximately 40% at a low exposure of 1.3 mR. Detector element nonuniformity and electronic gain variations were not significant after appropriate calibration and software corrections. The response of the imager was linear and did not exhibit signal saturation under tested exposure conditions.

A controlled evaluation of tuned-aperture computed tomography applied to digital spot mammography

The purpose of this work was to compare the detection accuracy of 3-dimensional (3D) modalities of tuned-aperture computed tomography (TACT) with that of conventional 2-dimensional (2D) digital spot mammograms. A standardized mammographic phantom was placed beneath cadaveric breast tissues of varying densities. Five radiologists were asked to detect as many objects (specks, fibers, and low-contrast masses) as possible from 90 displays in a controlled and factorially balanced multivariate experiment. Radiographic exposure was varied systematically, and projections were averaged to ensure stochastic comparability. Scores were weighted to eliminate task-specific bias and were analyzed by multivariate analyses of variance. All display modalities based on the linear application of the 3D TACT reconstruction method yielded significantly higher detection scores for all tasks than did conventional 2D digital spot mammography, which served as the scientific control modality. This effect was found to be statistically significant (P < .001) in spite of significant variations between tissues (P < .001), observers (P < .001), and exposures (P < .01). TACT may be a promising alternative or enhancement to conventional 2D digital mammography for tasks well simulated by this experimental design.

Development of a time-domain optical mammograph and first in vivo applications

We have developed a laser-pulse mammograph capable of recording optical mammograms within approximately 3 min by measuring time-resolved transmittance at each of typically 1500 scan positions, 2.5 mm apart. As a first application two patients who have tumors were investigated successfully. From measured distributions of times of flight of photons corrected for edge effects we derived (1) characteristic quantities, such as photon counts in selected time windows, to generate optical mammograms; (2) effective transport scattering and absorption coefficients of breast tissue at each scan position, assuming the breast to be homogeneous; and (3) optical properties of a selected tumor by applying the theory of diffraction of photon density waves by spherical inhomogeneity. Mammograms recorded at different lateral offsets between source and detector fiber were used to estimate the depth of inhomogeneities.

What's new in mammography

Early diagnosis of breast cancer plays the leading role in reducing mortality rates and improving the patients' prognosis: mammography is the most sensitive technique currently available for the detection of nonpalpable lesions and therefore the method of choice. However, mammography has some limitations and the technique must be improved with technological devices without affecting image quality. This could be the target to increase diagnostic accuracy. Mammography sensitivity and specificity are now improved with the digital computer assisted technique, teleradiology, digital tomosynthesis or digital angiography--used to study microvascularization--3D imaging or synchrotron light, and laser mammography. Such other technological devices as Mammospot reduce breast thickness and provide better breast compression. Digital mammography can be carried out with film or direct digitization. The advantages of the digital technique are a shorter examination time, less storage space, electronic image recording, with image 'adjustments' made by the radiologist, and especially computerized analysis. The computer aided diagnosis can be defined as the diagnosis made by the radiologist who considers the results of computerized analysis as a 'second opinion'. In this way incidental mistakes made by radiologists, can be corrected by the computer analysis. Computers are a basic element also in teleradiology, which needs immediate and simultaneous admittance to the patient's history and permits radiology optimization in rural areas too. As for tomosynthesis, it permits to study a single slice of the breast without glandular tissue overlapping, which is useful in dense breasts where the diagnosis can be made with a lower X-ray dose. Moreover, this method fits the current mammographic systems easily. 3D imaging is still a work in progress. Synchrotron mammography is used only on surgery specimens, where it exhibits high resolution and contrast, depicting structures and details missed by conventional mammography. Breast DSA allows the study of vessels < 0.20 mm in diameter and of fine microvascular details; it can also demonstrate neoangiogenesis. Laser mammography permits bilateral examinations of the breast in 10-15 mins and is currently used also for breast cancer therapy, although only in animal trials. To conclude, after reviewing new techniques and evaluating the real cost/benefit ratio for each of them, conventional mammography remains the most sensitive tool for breast cancer diagnosis.