Stereotactic localization of breast lesions: how it works and methods to improve accuracy

A computer simulation of stereotactic breast biopsy was developed that paralleled the geometric configuration of a currently available breast biopsy system. This model was developed to define and improve the targeting of breast lesions with stereotactic biopsy techniques. Lesions must be clearly identified and accurately targeted on both views for successful localization. Nonvisualization of a lesion may result from overlying tissue or from the geometric configuration of the imaging system. Familiarity with the geometric configuration of the biopsy unit, especially the location of the reference point and center of rotation, facilitates understanding of apparent changes in lesion position (parallax shift). Inaccuracy in lesion targeting on one or both views will manifest predominantly as an error in the calculated z value (depth). The magnitude and direction of this error are largely determined by the direction of the targeting error. Compensatory strategies include use of a long-throw core biopsy gun or directional vacuum-assisted biopsy device and additional sampling along the z axis and should be accompanied by critical evaluation of both pre- and postfire images. Understanding geometric considerations as well as how targeting accuracy affects accuracy in lesion localization should lead to greater success in sampling even challenging breast lesions at stereotactic biopsy.

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.

A novel approach to microcalcification detection using fuzzy logic technique

Breast cancer continues to be a significant public health problem in the United States. Approximately, 182,000 new cases of breast cancer are diagnosed and 46,000 women die of breast cancer each year. Even more disturbing is the fact that one out of eight women in the United States will develop breast cancer at some point during her lifetime. Since the cause of breast cancer remains unknown, primary prevention becomes impossible. Computer-aided mammography is an important and challenging task in automated diagnosis. It has great potential over traditional interpretation of film-screen mammography in terms of efficiency and accuracy. Microcalcifications are the earliest sign of breast carcinomas and their detection is one of the key issues for breast cancer control. In this study, a novel approach to microcalcification detection based on fuzzy logic technique is presented. Microcalcifications are first enhanced based on their brightness and nonuniformity. Then, the irrelevant breast structures are excluded by a curve detector. Finally, microcalcifications are located using an iterative threshold selection method. The shapes of microcalcifications are reconstructed and the isolated pixels are removed by employing the mathematical morphology technique. The essential idea of the proposed approach is to apply a fuzzified image of a mammogram to locate the suspicious regions and to interact the fuzzified image with the original image to preserve fidelity. The major advantage of the proposed method is its ability to detect microcalcifications even in very dense breast mammograms. A series of clinical mammograms are employed to test the proposed algorithm and the performance is evaluated by the free-response receiver operating characteristic curve. The experiments aptly show that the microcalcifications can be accurately detected even in very dense mammograms using the proposed approach.

Appraising pulmonary edema using supine chest roentgenograms in ventilated patients

The role of portable, anteroposterior, supine chest X-rays (CXRs) in distinguishing hydrostatic pulmonary edema (HPE) from permeability pulmonary edema (PPE) in mechanically ventilated patients is controversial. We prospectively obtained and evaluated such CXRs in 33 supine, mechanically ventilated intensive-care-unit patients with pulmonary artery catheters. Three chest radiologists independently reviewed CXRs without clinical information and recorded the cardiothoracic (CT) ratio, vascular pedicle width (VPW), and other radiographic features commonly used to evaluate pulmonary edema. Hydrostatic pulmonary edema was associated with a larger CT ratio (p < 0.001), subjective impressions of cardiomegaly (p < 0.01), and increased VPW (p = 0.02). There was a significant correlation between the pulmonary artery occlusion pressure and the VPW (r = 0.45, p = 0.0076) and CT ratio (r = 0.52, p = 0.0016), as well as between the VPW and CT ratio (r = 0.49, p = 0.0032). Despite this detailed evaluation of the CXRs, the mean accuracy of the radiologists' clinical diagnosis of HPE versus PPE was 41%, and 15 of 19 (79%) of PPE patients showed one or more roentgenographic signs of volume overload. Receiver-operating-characteristic curves were constructed to determine optimum cut-off values of VPW and CT ratio associated with HPE. Hydrostatic pulmonary edema was found to correlate best using a VPW > 63 mm coupled to a CT ratio > 0.52 (p = 0.027). With this combination of objective criteria, radiologists' diagnostic accuracy could have been increased to 73%. We therefore conclude that measurements of CT ratio and VPW correlate with pulmonary artery occlusion pressure in supine, mechanically ventilated patients. Distinction of hydrostatic from permeability pulmonary edema is difficult using portable, supine CXRs, but readily assessed radiologic signs may contribute to the correct diagnosis.

Chest X-ray changes in air space disease are associated with parameters of mechanical ventilation in ICU patients

To assess relationships between parameters of mechanical ventilation (MV) and portable chest X-ray (CXR) measurements of lung length (LL) and severity of air space disease, a prospective, randomized, blinded comparison of 102 adults in a university hospital was performed. Each patient received two portable, supine CXRs on different MV breaths within 5 min of one another. Ventilator parameters were recorded. All 204 CXRs were randomly assorted and read independently by three radiologists. Air space disease was considered more severe with pressure support ventilation (PSV) breaths than with intermittent mandatory ventilation (IMV) breaths (p = 0.0003), and its extent correlated inversely with static compliance (p = 0.0001, r = -0.40). Among patients having CXRs on both IMV and PSV breaths, 15 of 67 (22%) had their overall degree of air space disease read differently by one category (mild, moderate, or severe). Increases in LL between the two CXRs were associated with increasing peak (p = 0.0038) or mean (p = 0.0065) airway pressure, tidal volume (VT) (p = 0.022), and VT per kilogram (p = 0.006). We conclude that lung volume changes during MV, typically not noted nor controlled for during portable chest radiography, may substantially alter the interpretation of air space disease and LL. Physicians monitoring intensive care unit (ICU) patients with daily CXRs should be aware of the variables influencing interpretation of portable CXRs of ICU patients.