Stereotaxy is widely used for breast biopsy and needle localization of mammographically detected lesions. If a lesion shift occurs during stereotaxy, corrections (even though possible with vacuum biopsy) is difficult due to the difficult assessment of the exact 3D shift. In this study we investigated the correlation between lesion shift (in up to three dimensions) and its visualisation on the stereotactic images (0 degree, -15 degrees, +15 degrees). The study was performed on a Fischer prone table (Fischer Imaging Europe, Vejle, Denmark) using a 3.8-mm steel ball (as lesion) and a 20-G needle. The 17 major malpositions of the ball with respect to the needle were imitated and imaged. A simple rule is suggested as to how the deviation in all three dimensions can be detected from the scout and the two stereotactic views. The rule proved to be a valuable tool to correctly assess lesion shifts.
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