  Immersive Colonography allows medical professionals to navigate inside the
intricate tubular geometries of subject-specific 3D colon images using Virtual
Reality displays. Typically, camera travel is performed via Fly-Through or
Fly-Over techniques that enable semi-automatic traveling through a constrained,
well-defined path at user-controlled speeds. However, Fly-Through is known to
limit the visibility of lesions located behind or inside haustral folds. At the
same time, Fly-Over requires splitting the entire colon visualization into two
specific halves. In this paper, we study the effect of immersive Fly-Through
and Fly-Over techniques on lesion detection and introduce a camera travel
technique that maintains a fixed camera orientation throughout the entire
medial axis path. While these techniques have been studied in non-VR desktop
environments, their performance is not well understood in VR setups. We
performed a comparative study to ascertain which camera travel technique is
more appropriate for constrained path navigation in Immersive Colonography and
validated our conclusions with two radiologists. To this end, we asked 18
participants to navigate inside a 3D colon to find specific marks. Our results
suggest that the Fly-Over technique may lead to enhanced lesion detection at
the cost of higher task completion times. Nevertheless, the Fly-Through method
may offer a more balanced trade-off between speed and effectiveness, whereas
the fixed camera orientation technique provided seemingly inferior performance
results. Our study further provides design guidelines and informs future work.
