Scalp fiducials

Fiducial markers or fiducials are objects placed in the field of view of an imaging system which appear in the produced images, for use as points of reference or a measure. They are mostly used to register the imaging space to the surgical space in image guided surgery (IGS). Frameless navigated neurosurgical operations can be considered as the most common example.

The user must select a minimum of tree fiducials on both the neuro-radiological images and on the real surgical space, so that a rigid registration (6 degree of freedom) can be computed by the IGS system. Fiducial markers can be invasively fixed to the skull (bone fiducials) or non invasively to the skin (adhesive scalp fiducials). The latter are more commonly used but the inherent problem of scalp deformation must be faced. Bone fiducials are more accurate but the cost of some degree of invasiveness must be paid. Alternatively, markerless registration can be obtained tracing the scalp with a pointer and computing a surface registration.