Figure 9.

A challenging scenario in which BB markers are eclipsed by interventional devices. (a) Projection images showing one BB marker traversing the length of a transpedicle needle in consecutive projections. (b) The resulting sinograms exhibit gaps in which BB detections are lost when traversing the needles; however, the segmentation algorithm in the Free-Form automatic method is capable of recovering detection, since it continues to predict the projected location of search windows and finds the BBs when they emerge from the shadow of highly attenuating implants.