Accuracy assessment methods of tissue marker clip placement after 11-gauge vacuum-assisted stereotactic breast biopsy: comparison of measurements using direct and conventional methods

BACKGROUND:　 The objective of the study was to compare direct measurement with a conventional method for evaluation of clip placement in stereotactic vacuum-assisted breast biopsy (ST-VAB) and to evaluate the accuracy of clip placement using the direct method.　 METHODS:　 Accuracy of clip placement was assessed by measuring the distance from a residual calcification of a targeted calcification clustered to a clip on a mammogram after ST-VAB. Distances in the craniocaudal (CC) and mediolateral oblique (MLO) views were measured in 28 subjects with mammograms recorded twice or more after ST-VAB. The difference in the distance between the first and second measurements was defined as the reproducibility and was compared with that from a conventional method using a mask system with overlap of transparent film on the mammogram. The 3D clip-to-calcification distance was measured using the direct method in 71 subjects.　 RESULTS:　 The reproducibility of the direct method was higher than that of the conventional method in CC and MLO views (P = 0.002, P < 0.001). The median 3D clip-to-calcification distance was 2.8 mm, with an interquartile range of 2.0-4.8 mm and a range of 1.1-36.3 mm.　 CONCLUSION:　 The direct method used in this study was more accurate than the conventional method, and gave a median 3D distance of 2.8 mm between the calcification and clip.