White et al. reported on preliminary findings using a novel intra-operative brain-shift monitor using shear-mode transcranial ultrasound [16]. Despite the advantages of ultrasound in an intra-operative setting compared to other imaging methods [9], such as high temporal resolution, AZD6244 cost portability, and non-ionizing mode of radiation, the application of commercially available TCS systems for intra-operative monitoring of DBS electrode placement has been reported only rarely so far. One early study applied a former-generation TCS system (Sonoline Elegra, Siemens; Erlangen, Germany) during implantation of DBS electrodes into the targeted subthalamic nucleus

(STN) in patients with Parkinson’s disease [17]. The authors reported an easy visualization of the 0.8 mm thick electrode. The position of the imaging artefact of the tip of the DBS electrode appeared to be within in the anatomic region of substantia nigra that usually is of high echogenicity in patients with Parkinson’s disease. Additionally, PTC124 the segment of the laterally

running posterior cerebral artery at the corresponding level could also be displayed. The authors found the appearing correct position of the DBS electrode tip on TCS at a place just touching the echo-signals of the substantia nigra. The results of this pilot study were limited by the poorer lateral image resolution of the TCS system applied compared to contemporary TCS systems [7], and the missing estimation of the exact size of the electrode imaging artifacts which caused some uncertainty with regard to the exact electrode tip position. In a more recent study, a contemporary

TCS system (Acuson Antares, Siemens; Erlangen, Germany) was applied intra-operatively to monitor the placement of DBS electrode into the GPI in patients with idiopathic dystonia [8]. In this study not only the visualization of the final DBS electrodes was possible but also the simultaneous visualization of 2–5 closely located microelectrodes used for detection of the optimal trajectory of the final electrode (Fig. 2A). Another advantage of the intra-operative TCS monitoring was that the distance of the DBS electrode tip to the artery at the anatomic GNA12 target (penetrating branch of the posterior communicating artery) could be assessed (Fig. 2B). This was possible since the extent of the imaging artefact of the electrode had been estimated in advance for the referring TCS system and implant [8]. This even enabled intra-operatively the decision to insert the final DBS electrode somewhat deeper than it would have been done using only the pre-operatively planned navigation data [8]. Simultaneous visualization of the artery at the anatomic target prevented hemorrhages at the target site.