Computed tomography of the breast (BCT) has been a topic of interest for about two decades. It was proposed and evaluated in different designs by a number of groups as a potential alternative method for breast imaging. So far efforts have shown success with respect to soft tissue imaging but suffer from limited spatial resolution. We designed and evaluated a BCT scanner aiming for three-dimensional (3D) spatial resolution of better that 100 µm to provide means for improved assessment of 3D micro-calcification clusters.
METHOD AND MATERIALSThe concept of the scanner is built on fast spiral CT using directly converting cadmium telluride detector technology with 100 µm pixel pitch; it was evaluated and confirmed previously by simulations. Here we assessed spatial resolution on a prototype setup by measuring the modulation transfer function (MTF) using a 10 µm diameter tungsten wire. High precision Ruby beads immersed in a plastic breast-mimicking setup and 10 surgically resected breast specimens were measured in direct comparison to full field digital mammography (FFDM). The same 60 kV scan protocol was used for all BCT measurements; standard clinical settings were used for FFDM imaging. Micro-CT at 30 µm resolution was employed as reference standard for judging the specimen results.
RESULTSBCT exposures were kept at a level corresponding to below 6 mGy average glandular dose related to exposure of a tissue-equivalent cylinder of 14 cm diameter. Spatial resolution characterized by the MTF's 10% value was measured as 64 lp/cm. Ruby beads were clearly visible in BCT exams down to 130 µm, the smallest size available; FFDM revealed beads down to 160 µm. Specimen examinations confirmed these results qualitatively. For specimens, BCT showed micro-calcifications down to 100 µm; it was vastly superior in separating structures in different layers by virtue of its slice imaging nature.
CONCLUSIONHigh-resolution BCT allows improving the assessment of 3D micro-calcification clusters and avoids erroneous superimposition effects, which may pretend fictitious lesions in projection imaging.
CLINICAL RELEVANCE/APPLICATIONBreast CT offering high resolution in all three dimensions shall enable improved analysis and diagnostics of micro-calcifications.