gms | German Medical Science

Objective: For the specification of position, sensor-based navigation procedures use: a) a signal emitter that induces a fixed, defined electromagnetic field in the area of the operation site and b) small sensor pulses that detect the position of various operating instruments in the electromagnetic field. Because of the lack of clinical data and long-term studies, electromagnetic systems have been viewed for a long time as prone to malfunctioning, temperamental and imprecise. Now for the first time DC pulsed measuring techniques are thought to be secure against external ferromagnetic and electrostatic influences.

Methods: In the first five-year analysis of this kind on the routine usage of a DC pulsed navigation systems, the precision achieved (FLE-Fiducial Localization Error, FRE-Fiducial Registration Error, TRE-Target Registration Error, and PE-Positional Error) was investigated in 207 cranial operations. Various external influences and technical limits were analyzed as sources of possible errors.

Results: The operational areas were: (E1) 86/207 cases (41.5%) for specification of the target point and the entry trajectory, (E2) 19/207 cases (9.2%) for specification of the amount of resection, (E3) 11/207 cases (5.3%) for transnasal and transsphenoidal access, (E4) 20/207 cases (9.7%) for operations on the skull base and on the neurocranium, and (E5) 71/207 cases (34.4%) for functional navigation. The mean FRE was: 1.78 mm (±0.72) for operational area E1, 1.63 mm (±0.61) for E2, 1.34 mm (±0.57) for E3, 1.39 (±0.43) for E4, and 1.70 (±0.64) for E5. The mean TRE centroid was 1.45 (±0.58); the mean TRE target was 1.65 (±0.70). The mean intraoperative position error between the beginning of the OP and the end of the OP (t mean 164.7 min) was PE=0.74 mm (±0.52).

Conclusions: Navigation systems have established themselves as helpful instruments in cranial neurosurgery. With the development of the pulsed DC technique now, precision levels can also be reached that are comparable to those of the already established optical and mechanical measuring procedures. It must be noted that the influence on the measuring precision within the operating field decreases with a decreasing iron component and magnetizability of the various metals (low alloy metals > high allow metals > aluminum > titanium). The continual specification of the position error of a fixed reference point is recommended for the estimation of this degree of error.