Radiographic Detectability Of Breast Microcalcifications: In Vitro Studies Using A Wide Variety Of Mammography Techniques

AbstractControlled in vitro studies of breast microcalcification detectability were accomplishedusing a wide variety of standard and state -of- the -art mammography techniques (conventionaland microfocal spot x -ray tubes, screen -film and xeroradiographic recording systems,contact and magnification techniques). Results confirm previous observations thatgeometric unsharpness is the limiting factor in microcalcification detectability for mostconventional mammography systems. Results also indicate superior microcalcificationdetection for: xeroradiographic > screen -film recording systems, positive -mode > negative -mode xeroradiography, microfocal spot contact > conventional contact techniques,microfocal spot magnification > contact techniques, and 2X magnification > 1.5Xmagnification techniques. Clinical applications of these findings are discussed.IntroductionRadiographic detection of breast microcalcifications having characteristic shape anddistribution is often crucial to the early diagnosis of breast carcinoma(1 -3). However,conventional mammography demonstrates microcalcifications in only 30 -50% of breastcancers(4 -6), while 60 -80% of these cancers can be shown to have calcifications bysubsequent histological examination(7,8). Clearly, many breast cancers containmicrocalcifications that are smaller than the limits of resolution of conventionalmammography.The recent development of microfocal spot x -ray tubes adapted for mammographic usepromises to allow for increased microcalcification detectability; laboratory and clinicalstudies with such equipment have shown it to produce sharper, more detailed images of thebreast(9'10). This study involves in vitro comparisons of microcalcification detectabilityusing both conventional mammography apparatus and a wide variety of microfocal spottechniques (different recording systems, degrees of magnification, exposure parameters), inorder to demonstrate the ability of the various techniques to portray the fine detailnecessary for early breast cancer detection.Materials and MethodsA total of 13 radiographic techniques were evaluated, using three different x --ray tubes,three different recording systems, and various degrees of magnification (Table 1). Breastmicrocalcifications were simulated by a graded series of aluminum oxide specks of knownsize (Radiation Measurements, Inc., Middleton, WI), embedded in whole human breastspecimens. Specks ranged from 0.15 mm to 0.91 mm in size, as measured by a calibrated 10Xocular lupe. Specks were arranged randomly using 4 -12 particles of each of eight sizes.They then were sealed in place between two pieces of transparent tape. A differenttransparent -tape strip of specks was used for each breast specimen. The number, location,and distribution of specks of each size were recorded both visually and radiographicallyfor each of the strips of specks, to provide a baseline for comparison with subsequentobservations made from the radiographs under study.It is important to carry out a study of breast calcification detectability using actualhuman breast tissue, since the elemental composition, x -ray scattering properties, andcomplexity of anatomic structure of the human breast is not approximated in anyexperimental animal or in breast phantoms. We used ten whole, fresh (unfixed) breastspecimens from adult female cadavers and four whole surgical mastectomy specimens for thispurpose. These specimens were radiographed under conditions of uniform compression similarin degree to those employed clinically; the average compressed thickness of our 14specimens was 5.2 cm. For each specimen, the strip of aluminum oxide specks was positionedin a plane perpendicular to the central ray, alternatively on top of the specimen at mid -breast level, and at the bottom of the specimen. Precise measurements were made of focus -film distance and speck -film distance (object -film distance) so that the degree of speckmagnification could be calculated for each image.* American Cancer Society Junior Faculty Clinical Fellow.