diagnostics Article Detection of Microcalcifications in Spiral Breast Computed Tomography with Photon-Counting Detector Is Feasible: A Specimen Study Matthias Wetzl 1, * , Evelyn Wenkel 1 , Eva Balbach 1 , Ebba Dethlefsen 2 , Arndt Hartmann 3 , Julius Emons 4 , Christiane Kuhl 2 , Matthias W. Beckmann 4 , Michael Uder 1 and Sabine Ohlmeyer 1   Citation: Wetzl, M.; Wenkel, E.; Balbach, E.; Dethlefsen, E.; Hartmann, A.; Emons, J.; Kuhl, C.; Beckmann, M.W.; Uder, M.; Ohlmeyer, S. Detection of Microcalcifications in Spiral Breast Computed Tomography with Photon-Counting Detector Is Feasible: A Specimen Study. Diagnostics 2021, 11, 848. https:// doi.org/10.3390/diagnostics11050848 Academic Editor: Katja Pinker-Domenig Received: 10 April 2021 Accepted: 6 May 2021 Published: 9 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Radiology, University Hospital Erlangen, Maximiliansplatz 3, 91054 Erlangen, Germany; evelyn.wenkel@uk-erlangen.de (E.W.); eva.balbach@uk-erlangen.de (E.B.); michael.uder@uk-erlangen.de (M.U.); sabine.ohlmeyer@uk-erlangen.de (S.O.) 2 Department of Diagnostic and Interventional Radiology, University Hospital Aachen, Pauwelsstraße 30, 52074 Aachen, Germany; edethlefsen@ukaachen.de (E.D.); ckuhl@ukaachen.de (C.K.) 3 Department of Pathology, University Hospital Erlangen, Krankenhausstraße 8-10, 91054 Erlangen, Germany; arndt.hartmann@uk-erlangen.de 4 Department of Gynecology and Obstetrics, University Hospital Erlangen, Universitätsstraße 21/23, 91054 Erlangen, Germany; julius.emons@uk-erlangen.de (J.E.); matthias.beckmann@uk-erlangen.de (M.W.B.) * Correspondence: Matthias.wetzl@uk-erlangen.de Abstract: The primary objective of the study was to compare a spiral breast computed tomography system (SBCT) to digital breast tomosynthesis (DBT) for the detection of microcalcifications (MCs) in breast specimens. The secondary objective was to compare various reconstruction modes in SBCT. In total, 54 breast biopsy specimens were examined with mammography as a standard reference, with DBT, and with a dedicated SBCT containing a photon-counting detector. Three different reconstruction modes were applied for SBCT datasets (Recon1 = voxel size (0.15 mm) 3 , smooth kernel; Recon2 = voxel size (0.05 mm) 3 , smooth kernel; Recon3 = voxel size (0.05 mm) 3 , sharp kernel). Sensitivity and specificity of DBT and SBCT for the detection of suspicious MCs were analyzed, and the McNemar test was used for comparisons. Diagnostic confidence of the two readers (Likert Scale 1 = not confident; 5 = completely confident) was analyzed with ANOVA. Regarding detection of MCs, reader 1 had a higher sensitivity for DBT (94.3%) and Recon2 (94.9%) compared to Recon1 (88.5%; p < 0.05), while sensitivity for Recon3 was 92.4%. Respectively, reader 2 had a higher sensitivity for DBT (93.0%), Recon2 (92.4%), and Recon3 (93.0%) compared to Recon1 (86.0%; p < 0.05). Specificities ranged from 84.7–94.9% for both readers (p > 0.05). The diagnostic confidence of reader 1 was better with SBCT than with DBT (DBT 4.48 ± 0.88, Recon1 4.77 ± 0.66, Recon2 4.89 ± 0.44, and Recon3 4.75 ± 0.72; DBT vs. Recon1/2/3: p < 0.05), while reader 2 found no differences. Sensitivity and specificity for the detection of MCs in breast specimens is equal for DBT and SBCT when a small voxel size of (0.05 mm) 3 is used with an equal or better diagnostic confidence for SBCT compared to DBT. Keywords: spiral breast CT; reconstruction modes; breast cancer; microcalcifications 1. Introduction Microcalcifications are small calcium-containing deposits in breast tissue with a maxi- mum size of 1 mm [1]. Their importance for the detection of malignant breast lesions is well known. In a review of the Swedish screening program, 74% of ductal carcinomas in situ (DCIS) and 30% of invasive breast cancers were associated with microcalcifications [2]. Furthermore, in 32% of cases, microcalcifications are the only imaging feature of invasive breast cancer or DCIS [3]. Four-view full-field digital mammography (FFDM) is the standard examination for the detection and classification of microcalcifications in screening and clinical breast exams [4]. Diagnostics 2021, 11, 848. https://doi.org/10.3390/diagnostics11050848 https://www.mdpi.com/journal/diagnostics