Angulated needle placement in CT guided percutaneous needle biopsy of the thorax

Computed tomography (CT)-guided percutaneous needle biopsy is often necessary to evaluate small intrathoracic lesions. Not infrequently, an overlying structure such as a rib or vessel precludes insertion of the biopsy needle within the CT slice containing the lesion. Insertion and angulation of the needle at a site within an adjacent CT slice is then required. In order to determine the optimal skin-entry site and degree of angulation for biopsy needle insertion, we analyzed the geometric relationship between lesion depth, needle length, and needle angulation.