gms | German Medical Science

Objective: Transcranial Doppler sonography (TCD) is widely used for bedside detection and monitoring of cerebral vasospasm in the setting of intensive care unit (ICU). Because of a missing imaging modality, its accuracy and reliability highly depends on users examination experience. The combination of both TCD and neuronavigation allows anatomical orientation and rapid re-examinations during the period of vasospasm-risk.

Methods: The virtual instrument-offset of a neuronavigation System (Kolibri™, Brainlab, Germany) was used to navigate the ultrasound beam of a TCD probe (MultiDop T digital, DWL, Germany). A CT-Angiography (CT-A), which was previously performed for reasons of SAH diagnosis, was used to track the patient's head. Instead of an invasive Mayfield-clamp a flexible Headband with a mounted reference star and anatomical landmarks were used to perform the registration. After image-guided (IG) detection of each vessel, trajectories with an entry- (adequate US-window) and a target-point (point of optimal flow-signal) were acquired for MCA, carotid-T and BA-tip to allow rapid and reliable serial examinations. Distances between the site of the CT-correlated vessel-center and the point of an optimal Doppler-signal in the initial as well as in the following serial nTCD examinations were recorded.

Results: IG detection (without Doppler-feedback) of pre-planned vessel targets led to a positive signal in all cases for MCA (n = 29), in 81% for carotid-T (n = 27) and in 90% for basilar-tip (BA) (n = 29). Mean distance between pre-planned target and point of optimal signal was 2.64 mm (SD ± 1.15 mm, n = 94). During serial re-examinations average of distances between sides of an optimal signal in each investigation was 2.75 mm (SD ± 1.20 mm, n = 56). There was no evidence that either time between CT-A study and nTCD investigation or examination duration itself influences the accuracy of non-invasive nTCD.

Conclusions: Because of its high accuracy and low spatial deviation (less than 3 mm), image-guidance can help to reduce inter- and intra-investigator variations and standardize the procedure. It is applicable to sedated or awake patients and since it provides 3D anatomical orientation, it allows secure detection as well as differentiation of certain vessel-segments, especially for users with little hands-on experience. Due to this navigated bedside TCD can help to monitor vasospasm after SAH non-invasively and more reliably, even in very circumscribed cerebral vessel segments and under conditions of the ICU.