Image-guided transcranial Doppler sonography for monitoring of defined segments of intracranial arteries

Surface Point Cloud Ultrasound with Transcranial Doppler: Coregistration of Surface Point Cloud Ultrasound with Magnetic Resonance Angiography for Improved Reproducibility, Visualization, and Navigation in Transcranial Doppler Ultrasound

Transcranial Doppler (TCD) ultrasound is a standard tool used in the setting of recent sub-arachnoid hemorrhage (SAH). By tracking velocity in the circle-of-Willis vessels, vasospasm can be detected as interval velocity increase. For this disease process, repeated TCD velocity measurements over many days is the basis for its usefulness. However, a key limitation to TCD is its user dependence, which is itself largely due to the fact that exact information about probe positioning is lost between subsequent scans. Surface point cloud ultrasound (SPC-US) was recently introduced as a general approach combining ultrasound and three-dimensional surface imaging of patient + probe. In the present proof-of-principle demonstration, we have applied SPC-US to TCD and co-registered the skin surface with that from MRA images to provide a roadmap of the vasculature in 3D space for better speed, accuracy, reproducibility, and potential semi-automation of TCD. Collating the acronyms, we call the combined approach SPC-US-TCD. TCD of the M1 was obtained while three-dimensional photographic images were obtained with the Structure Sensor camera. MRA imaging was also obtained. SPC-US-TCD and corresponding MRA 3D reconstruction images were co-registered in MeshMixer using the skin surfaces for alignment. A cylinder the width of the TCD probe was placed over the fused images and aligned with the direction and orientation of the TCD probe to demonstrate the acoustic beam. In the fused images, the acoustic beam intersects the right M1 segment of the middle cerebral artery (MCA). The angle of insonation is well demonstrated and measurable in various planes. Distance measurements made in Blender localized the TCD probe position based on three skin surface landmarks, and tabulated orientation based on three angles along the corresponding directions. SPC-US-TCD provides valuable information that is otherwise not present in TCD studies. By co-registering SPC-US-TCD data with that from cross sectional vessel imaging, precise probe location relative to external skin surface landmarks as well as 3D vessel location relative to TCD probe placement offers the potential to provide a roadmap that improves exam reproducibility, speed of acquisition, and accuracy. The goal of future work is to demonstrate this improvement statistically by application to multiple patients and scans.

Image-Guided Transcranial Doppler Ultrasound for Monitoring Posthemorrhagic Vasospasms of Infratentorial Arteries: A Feasibility Study

BACKGROUND

A considerable number of patients with subarachnoid hemorrhage (SAH) develop vasospasms of the infratentorial arteries. Transcranial Doppler sonography (TCD) is used to screen for vasospasm. In this study, we used a technical modification that combines TCD with an image guidance device that the operator can use to navigate to the ultrasonic window and to predefined intracranial vascular targets. Our aim was to analyze the feasibility, spatial precision, and spatial reproducibility of serial image-guided TCD of infratentorial and-for comparison-supratentorial arteries in the clinical setting of monitoring for vasospasm after SAH.

METHODS

The study included 10 SAH patients, who each received 5 serial image-guided TCD examinations. Using computed tomography angiography data, trajectories to the infratentorial and supratentorial cerebral arteries were planned and loaded into an image guidance device tracking the Doppler probe. As a measure of spatial precision and spatial reproducibility, we analyzed the distances between the positions of preplanned vascular targets and optimal Doppler signals.

RESULTS

The mean distance between preplanned and optimal target points was 4.8 ± 2.1 mm (first exam), indicating high spatial precision. The spatial precision decreased with increasing depth of the vascular target. In all patients, image-guided TCD detected all predefined supratentorial and infratentorial vascular segments. There were no significant changes in spatial precision in serial exams, indicating high reproducibility.

CONCLUSIONS

Image-guided TCD is feasible for supratentorial and infratentorial arteries. It shows high spatial precision and reproducibility. This study provides a basis for future clinical studies on image-guided TCD for post-SAH vasospasm screening.

Volumetric analysis of intracranial vessels: a novel tool for evaluation of cerebral vasospasm

PURPOSE

Together with other diagnostic modalities, computed tomography angiography (CTA) is commonly used to indicate endovascular vasospasm treatment after subarachnoid hemorrhage (SAH), despite the fact that objective, user-independent parameters for evaluation of CTA are lacking. This exploratory study was designed to investigate whether quantification of vasospasm by automated volumetric analysis of the middle cerebral artery M1 segment from CTA data could be used as an objective parameter to indicate endovascular vasospasm treatment.

METHODS

We retrospectively identified SAH patients who underwent transcranial Doppler sonography (TCD), CTA, and CT perfusion (CTP), with or without subsequent endovascular treatment. We determined vessel volume/vessel length of the M1 segments from CTA data and used receiver operating characteristic curve analysis to determine the optimal threshold of vessel volume to predict vasospasm requiring endovascular treatment. In addition, blinded investigators independently analyzed TCD, CTA, and CTP data.

RESULTS

Of 45 CTA examinations with corresponding CTP and TCD examinations (24 SAH patients), nine indicated the need for endovascular vasospasm treatment during examination. In our patients, vessel volume < 5.8 µL/mm was moderately sensitive but fairly specific to detect vasospasm requiring endovascular treatment (sensitivity, 67%; specificity, 78%; negative predictive value (NPV), 89%; positive predictive value (PPV), 46%). For CTA, CTP, and TCD, we found NPVs of 96%, 92%, and 89%, PPVs of 40%, 35%, and 35%, sensitivities of 89%, 78%, and 67%, and specificities of 67%, 64%, and 69%, respectively.

CONCLUSION

Vessel volumes could provide a new objective parameter for the interpretation of CTA data and could thereby improve multimodal assessment of vasospasm in SAH patients.

Image-guided transcranial Doppler sonography for monitoring of vasospasm after subarachnoid hemorrhage

OBJECTIVES

Transcranial Doppler ultrasound (TCD) is a standard method for bedside vasospasm monitoring after subarachnoid hemorrhage (SAH). Image guidance has previously been shown to reduce intra- and interobserver variability of this method. The aim of the present study was to compare image-guided and conventional TCD in vasospasm monitoring after SAH.

PATIENTS AND METHODS

418 TCD exams of 24 consecutive SAH patients registered in a database were evaluated. Of these, 130 image-guided exams were identified which had been performed on the same day as conventional Doppler exams. These matched pairs were taken for statistical analysis. Data were tested statistically using the sign test applied at patient level to aggregated data.

RESULTS

The rate of complete exams (both M1, A1, P1 segments) was significantly higher in image-guided exams (92% vs. 74%, p<0.001), and the superiority of image-guided exams was significantly related to smaller sizes of the temporal bone window. There were more exams with Doppler sonographic vasospasm (mean flow velocity>120cm/s) in image-guided exams (38% vs. 33%) which, however, did not reach statistical significance.

CONCLUSION

Image-guidance leads to a standardization of serial TCD exams, which resulted in significantly more complete exams, most prominent in patients with poor temporal bone windows, and a higher detection rate of Doppler sonographic vasospasms. Image-guided TCD therefore has the capability to improve bedside vasospasm monitoring after SAH.

Neuroanesthesiology update

We review topics pertinent to the perioperative care of patients with neurological disorders. Our review addresses topics not only in the anesthesiology literature, but also in basic neurosciences, critical care medicine, neurology, neurosurgery, radiology, and internal medicine literature. We include literature published or available online up through December 8, 2013. As our review is not able to include all manuscripts, we focus on recurring themes and unique and pivotal investigations. We address the broad topics of general neuroanesthesia, stroke, traumatic brain injury, anesthetic neurotoxicity, neuroprotection, pharmacology, physiology, and nervous system monitoring.

Image-guided implantation of pre-calibrated catheters in the ICU: a feasibility study

BACKGROUND

Image-guided implantation of intracranial catheters is a routine procedure. Although time for surgery is short, transport from the intensive care unit (ICU) to the operation room (OR) is time-consuming and endangers patients in vulnerable intracranial pressure phases. Unfortunately, technical aspects of image guidance have so far required surgery to be performed in the operation room. In this observational study we investigated the feasibility of image-guided catheter placement in the ICU using a pre-calibrated stylet for implantation of intracranial catheters for a variety of indications and compare the results of procedures performed in the OR.

METHODS

Twenty-three patients received implantation of 31 image-guided intracranial catheters or external ventricular drains using a pre-calibrated stylet in the ICU or in the OR. The times required for navigation planning, transport and surgery were assessed. Pre-operative trajectory planning, intra-operative screenshots of the navigation system and postoperative computed tomography (CT) scans were compared.

RESULTS

Eleven external ventricular drains and nine intracranial catheters for fibrinolytic therapy of intracerebral haemorrhage were implanted in the OR, whereas ten external ventricular drains and one catheter for fibrinolytic therapy were implanted in the ICU. All catheters implanted on the ICU, 81.8 % of external ventricular drains and 88.8 % of lysis catheters placed in the OR had an optimal position to function.

CONCLUSION

A pre-calibrated stylet in combination with the flexible headband equipped with reference arrays allows the application of image guidance in the ICU. It reduced time expended for patients and employees, and avoided the risks of ICU transport to the OR.

Image guidance to improve reliability and data integrity of transcranial Doppler sonography

BACKGROUND

Principles and accuracy of image-guided transcranial Doppler (IG TCD) sonography have been published recently. However, it remains open whether combination of image guidance and TCD offers an additional clinical advantage. This study scores the accuracy of conventional TCD examinations and investigates the potential improvement of TCD data integrity and reliability regarding the additional use of IG.

METHODS

Conventional TCD was performed by a group of experienced investigators, who were blinded to images of a navigation system tracking the Doppler probe, whereas an independent observer documented the TCD findings, acquired by the investigators, due to saving spatial data of the TCD sample volume using IG for subsequent analysis. In a second set of experiments, image guidance was available to investigators without any previous TCD experience.

RESULTS

The analysis of 3D data of vessels (n=173) labeled by experienced investigators in conventional TCD, revealed a rate of 37% misinterpreted Doppler signals regarding the target vessel. Correctness of labeling was comparable between the different vascular segments. The rate of correct labeling was higher for right- (69%) than for left-sided vessels (57%). In comparison, by using IG, TCD investigators without any previous TCD experience achieved a significantly lower rate of 10% (n=39) mislabeled vessels.

CONCLUSIONS

Our data suggest, that misinterpretation of the vascular source of the Doppler signal is a common source of errors in conventional TCD. Visualization of the vascular anatomy by image guidance offers improved accuracy and reliability of TCD results and may positively influence the learning curve for inexperienced investigators.