Two years of neurosurgical intraoperative MRI in Sweden - evaluation of use and costs.

BACKGROUND: The current shortage of radiology staff in healthcare provides a challenge for departments all over the world. This leads to more evaluation of how the radiology resources are used and a demand to use them in the most efficient way. Intraoperative MRI is one of many recent advancements in radiological practice. If radiology staff is performing intraoperative MRI at the operation ward, they may be impeded from performing other examinations at the radiology department, creating costs in terms of exams not being performed. Since this is a kind of cost whose importance is likely to increase, we have studied the practice of intraoperative MRI in Sweden. METHODS: The study includes data from the first four hospitals in Sweden that installed MRI scanners adjacent to the operating theaters. In addition, we included data from Karolinska University Hospital in Solna where intraoperative MRI is carried out at the radiology department. RESULTS: Scanners that were moved into the operation theater and doing no or few other scans were used 11-12% of the days. Stationary scanners adjacent to the operation room were used 35-41% of the days. For scanners situated at the radiology department doing intraoperative scans interspersed among all other scans, the proportion was 92%. CONCLUSION: Our study suggests that performing exams at the radiology department rather than at several locations throughout the hospital may be an efficient approach to tackle the simultaneous trends of increasing demands for imaging and increasing staff shortages at radiology departments.

Foundations of Bayesian Learning in Clinical Neuroscience.

There is an increasing interest in using prediction models to forecast clinical outcomes within the fields of neurosurgery and clinical neuroscience. The present chapter outlines the foundations of Bayesian learning and introduces Bayes theorem and its use in machine learning methodology. The use of Bayesian networks to structure and define associations between outcome predictors and final outcomes is highlighted and Naïve Bayes classifiers are outlined for use in predicting neurosurgical outcomes, where the understanding of underlying causes is less important. The present work aims to orient researchers in Bayesian machine learning methods and when and how to use them. When used correctly, these tools have the potential to improve the understanding of factors influencing neurosurgical outcomes, aid in structuring the relationships between them, and provide reliable machine learning classification models for predicting neurosurgical outcomes.

Feasibility and Accuracy of Thoracolumbar Pedicle Screw Placement Using an Augmented Reality Head Mounted Device.

BACKGROUND: To investigate the accuracy of augmented reality (AR) navigation using the Magic Leap head mounted device (HMD), pedicle screws were minimally invasively placed in four spine phantoms. METHODS: AR navigation provided by a combination of a conventional navigation system integrated with the Magic Leap head mounted device (AR-HMD) was used. Forty-eight screws were planned and inserted into Th11-L4 of the phantoms using the AR-HMD and navigated instruments. Postprocedural CT scans were used to grade the technical (deviation from the plan) and clinical (Gertzbein grade) accuracy of the screws. The time for each screw placement was recorded. RESULTS: The mean deviation between navigation plan and screw position was 1.9 ± 0.7 mm (1.9 [0.3-4.1] mm) at the entry point and 1.4 ± 0.8 mm (1.2 [0.1-3.9] mm) at the screw tip. The angular deviation was 3.0 ± 1.4° (2.7 [0.4-6.2]°) and the mean time for screw placement was 130 ± 55 s (108 [58-437] s). The clinical accuracy was 94% according to the Gertzbein grading scale. CONCLUSION: The combination of an AR-HMD with a conventional navigation system for accurate minimally invasive screw placement is feasible and can exploit the benefits of AR in the perspective of the surgeon with the reliability of a conventional navigation system.

Fluoroscopy-Assisted C1-C2 Posterior Fixation for Atlantoaxial Instability: A Single-Center Case Series of 78 Patients.

Background and Objectives: Posterior C1-C2 fixation, with trans-articular screws (TAS) or screw-rod-construct (SRC), is the main surgical technique for atlantoaxial instability, and can be performed with a fluoroscopy-assisted free-handed technique or 3D navigation. This study aimed to evaluate complications, radiological and functional outcome in patients treated with a fluoroscopy-assisted technique. Materials and Methods: A single-center consecutive cohort study was conducted of all adult patients who underwent posterior C1-C2 fixation, using TAS or CRS, between 2005-2019. Results: Seventy-eight patients were included, with a median follow-up time of 6.8 years. Trauma was the most common injury mechanism (64%), and cervicalgia the predominant preoperative symptom (88%). TAS was used in 33%, and SRC in 67% of cases. Surgery was associated with a significant reduction in cervicalgia (from 88% to 26%, p < 0.001). The most common complications were vertebral artery injury (n = 2, 2.6%), and screw malposition (n = 5, 6.7%, of which 2 were TAS and 3 were SRC). No patients deteriorated in their functional status following surgery. Conclusions: Fluoroscopy-assisted C1-C2 fixation with TAS or SRC is a safe and effective treatment for atlantoaxial instability, with a low complication rate, few surgical revisions, and pain relief in the majority of the cases.

Intraoperative cone beam computed tomography is as reliable as conventional computed tomography for identification of pedicle screw breach in thoracolumbar spine surgery.

OBJECTIVES: To test the hypothesis that intraoperative cone beam computed tomography (CBCT) using the Allura augmented reality surgical navigation (ARSN) system in a dedicated hybrid operating room (OR) matches computed tomography (CT) for identification of pedicle screw breach during spine surgery. METHODS: Twenty patients treated with spinal fixation surgery (260 screws) underwent intraoperative CBCT as well as conventional postoperative CT scans (median 12 months after surgery) to identify and grade the degree of pedicle screw breach on both scan types, according to the Gertzbein grading scale. Blinded assessments were performed by three independent spine surgeons and the CT served as the standard of reference. Screws graded as Gertzbein 0 or 1 were considered clinically accurate while grades 2 or 3 were considered inaccurate. Sensitivity, specificity, and negative predictive value were the primary metrics of diagnostic performance. RESULTS: For this patient group, the negative predictive value of an intraoperative CBCT to rule out pedicle screw breach was 99.6% (CI 97.75-99.99%). Among 10 screws graded as inaccurate on CT, 9 were graded as such on the CBCT, giving a sensitivity of 90.0% (CI 55.5-99.75%). Among the 250 screws graded as accurate on CT, 244 were graded as such on the CBCT, giving a specificity of 97.6% (CI 94.85-99.11%). CONCLUSIONS: CBCT, performed intraoperatively with the Allura ARSN system, is comparable and non-inferior to a conventional postoperative CT scan for ruling out misplaced pedicle screws in spinal deformity cases, eliminating the need for a postoperative CT. KEY POINTS: • Intraoperative cone beam computed tomography (CT) using the Allura ARSN is comparable with conventional CT for ruling out pedicle screw breaches after spinal fixation surgery. • Intraoperative cone beam computed tomography can be used to assess need for revisions of pedicle screws making routine postoperative CT scans unnecessary. • Using cone beam computed tomography, the specificity was 97.6% and the sensitivity was 90% for detecting pedicle screw breaches and the negative predictive value for ruling out a pedicle screw breach was 99.6%.

Multi-view 3D skin feature recognition and localization for patient tracking in spinal surgery applications.

BACKGROUND: Minimally invasive spine surgery is dependent on accurate navigation. Computer-assisted navigation is increasingly used in minimally invasive surgery (MIS), but current solutions require the use of reference markers in the surgical field for both patient and instruments tracking. PURPOSE: To improve reliability and facilitate clinical workflow, this study proposes a new marker-free tracking framework based on skin feature recognition. METHODS: Maximally Stable Extremal Regions (MSER) and Speeded Up Robust Feature (SURF) algorithms are applied for skin feature detection. The proposed tracking framework is based on a multi-camera setup for obtaining multi-view acquisitions of the surgical area. Features can then be accurately detected using MSER and SURF and afterward localized by triangulation. The triangulation error is used for assessing the localization quality in 3D. RESULTS: The framework was tested on a cadaver dataset and in eight clinical cases. The detected features for the entire patient datasets were found to have an overall triangulation error of 0.207 mm for MSER and 0.204 mm for SURF. The localization accuracy was compared to a system with conventional markers, serving as a ground truth. An average accuracy of 0.627 and 0.622 mm was achieved for MSER and SURF, respectively. CONCLUSIONS: This study demonstrates that skin feature localization for patient tracking in a surgical setting is feasible. The technology shows promising results in terms of detected features and localization accuracy. In the future, the framework may be further improved by exploiting extended feature processing using modern optical imaging techniques for clinical applications where patient tracking is crucial.

Augmented reality navigation for cranial biopsy and external ventricular drain insertion.

OBJECTIVE: The aim of this study was to evaluate the accuracy (deviation from the target or intended path) and efficacy (insertion time) of an augmented reality surgical navigation (ARSN) system for insertion of biopsy needles and external ventricular drains (EVDs), two common neurosurgical procedures that require high precision. METHODS: The hybrid operating room-based ARSN system, comprising a robotic C-arm with intraoperative cone-beam CT (CBCT) and integrated video tracking of the patient and instruments using nonobtrusive adhesive optical markers, was used. A 3D-printed skull phantom with a realistic gelatinous brain model containing air-filled ventricles and 2-mm spherical biopsy targets was obtained. After initial CBCT acquisition for target registration and planning, ARSN was used for 30 cranial biopsies and 10 EVD insertions. Needle positions were verified by CBCT. RESULTS: The mean accuracy of the biopsy needle insertions (n = 30) was 0.8 mm ± 0.43 mm. The median path length was 39 mm (range 16-104 mm) and did not correlate to accuracy (p = 0.15). The median device insertion time was 149 seconds (range 87-233 seconds). The mean accuracy for the EVD insertions (n = 10) was 2.9 mm ± 0.8 mm at the tip with a 0.7° ± 0.5° angular deviation compared with the planned path, and the median insertion time was 188 seconds (range 135-400 seconds). CONCLUSIONS: This study demonstrated that ARSN can be used for navigation of percutaneous cranial biopsies and EVDs with high accuracy and efficacy.

Augmented reality navigation in spine surgery: a systematic review.

BACKGROUND: Conventional spinal navigation solutions have been criticized for having a negative impact on time in the operating room and workflow. AR navigation could potentially alleviate some of these concerns while retaining the benefits of navigated spine surgery. The objective of this study is to summarize the current evidence for using augmented reality (AR) navigation in spine surgery. METHODS: We performed a systematic review to explore the current evidence for using AR navigation in spine surgery. PubMed and Web of Science were searched from database inception to November 27, 2020, for data on the AR navigation solutions; the reported efficacy of the systems; and their impact on workflow, radiation, and cost-benefit relationships. RESULTS: In this systematic review, 28 studies were included in the final analysis. The main findings were superior workflow and non-inferior accuracy when comparing AR to free-hand (FH) or conventional surgical navigation techniques. A limited number of studies indicated decreased use of radiation. There were no studies reporting mortality, morbidity, or cost-benefit relationships. CONCLUSIONS: AR provides a meaningful addition to FH surgery and traditional navigation methods for spine surgery. However, the current evidence base is limited and prospective studies on clinical outcomes and cost-benefit relationships are needed.

Diffuse reflectance spectroscopy for breach detection during pedicle screw placement: a first in vivo investigation in a porcine model.

BACKGROUND: The safe and accurate placement of pedicle screws remains a critical step in open and minimally invasive spine surgery, emphasizing the need for intraoperative guidance techniques. Diffuse reflectance spectroscopy (DRS) is an optical sensing technology that may provide intraoperative guidance in pedicle screw placement. PURPOSE: The study presents the first in vivo minimally invasive procedure using DRS sensing at the tip of a Jamshidi needle with an integrated optical K-wire. We investigate the effect of tissue perfusion and probe-handling conditions on the reliability of fat fraction measurements for breach detection in vivo. METHODS: A Jamshidi needle with an integrated fiber-optic K-wire was gradually inserted into the vertebrae under intraoperative image guidance. The fiber-optic K-wire consisted of two optical fibers with a fiber-to-fiber distance of 1.024 mm. DRS spectra in the wavelength range of 450 to 1600 nm were acquired at several positions along the path inside the vertebrae. Probe-handling conditions were varied by changing the amount of pressure exerted on the probe within the vertebrae. Continuous spectra were recorded as the probe was placed in the center of the vertebral body while the porcine specimen was sacrificed via a lethal injection. RESULTS: A typical insertion of the fiber-optic K-wire showed a drop in fat fraction during an anterior breach as the probe transitioned from cancellous to cortical bone. Fat fraction measurements were found to be similar irrespective of the amount of pressure exerted on the probe (p = 0.65). The 95% confidence interval of fat fraction determination was found in the narrow range of 1.5-3.6% under various probe-handling conditions. The fat fraction measurements remained stable during 70 min of decreased blood flow after the animal was sacrificed. DISCUSSIONS: These findings indicate that changes in tissue perfusion and probe-handling conditions have a relatively low measureable effect on the DRS signal quality and thereby on the determination of fat fraction as a breach detection signal. CONCLUSIONS: Fat fraction quantification for intraoperative pedicle screw breach detection is reliable, irrespective of changes in tissue perfusion and probe-handling conditions.

Incidence and predictors of kyphotic deformity following resection of cervical intradural tumors in adults: a population-based cohort study.

BACKGROUND: The first line of treatment for most cervical intradural tumors is surgical resection through laminotomy or laminectomy. This may cause a loss of posterior pulling force leading to kyphosis, which is associated with decreased functional outcome. However, the incidence and predictors of kyphosis in these patients are poorly understood. OBJECT: To assess the incidence of posterior fixation (PF), as well as predictors of radiological kyphosis, following resection of cervical intradural tumors in adults. METHODS: A population-based cohort study was conducted on adult patients who underwent intradural tumor resection via cervical laminectomy with or without laminoplasty between 2005 and 2017. Primary outcome was kyphosis requiring PF. Secondary outcome was radiological kyphotic increase, measured by the change in the C2-C7 Cobb angle between pre- and postoperative magnetic resonance images. RESULTS: Eighty-four patients were included. Twenty-four percent of the tumors were intramedullary, and the most common diagnosis was meningioma. The mean laminectomy range was 2.4 levels, and laminoplasty was performed in 40% of cases. No prophylactic PF was performed. During a mean follow-up of 4.4 years, two patients (2.4%) required delayed PF. The mean radiological kyphotic increase after surgery was 3.0°, which was significantly associated with laminectomy of C2 and C3. Of these, C3 laminectomy demonstrated independent risk association. CONCLUSIONS: There was a low incidence of delayed PF following cervical intradural tumor resection, supporting the practice of not performing prophylactic PF. Kyphotic increase was associated with C2 and C3 laminectomy, which could help identify at-risk patients were targeted follow-up is indicated.

Towards Optical Imaging for Spine Tracking without Markers in Navigated Spine Surgery.

Surgical navigation systems are increasingly used for complex spine procedures to avoid neurovascular injuries and minimize the risk for reoperations. Accurate patient tracking is one of the prerequisites for optimal motion compensation and navigation. Most current optical tracking systems use dynamic reference frames (DRFs) attached to the spine, for patient movement tracking. However, the spine itself is subject to intrinsic movements which can impact the accuracy of the navigation system. In this study, we aimed to detect the actual patient spine features in different image views captured by optical cameras, in an augmented reality surgical navigation (ARSN) system. Using optical images from open spinal surgery cases, acquired by two gray-scale cameras, spinal landmarks were identified and matched in different camera views. A computer vision framework was created for preprocessing of the spine images, detecting and matching local invariant image regions. We compared four feature detection algorithms, Speeded Up Robust Feature (SURF), Maximal Stable Extremal Region (MSER), Features from Accelerated Segment Test (FAST), and Oriented FAST and Rotated BRIEF (ORB) to elucidate the best approach. The framework was validated in 23 patients and the 3D triangulation error of the matched features was < 0 . 5 mm. Thus, the findings indicate that spine feature detection can be used for accurate tracking in navigated surgery.

Management of perineural (Tarlov) cysts: a population-based cohort study and algorithm for the selection of surgical candidates.

OBJECTIVE: Perineural cysts, also known as Tarlov cysts, are cerebrospinal fluid-filled growths that develop at the intersection of a dorsal root ganglion and posterior nerve root. They are typically an asymptomatic and incidental finding during routine spine imaging. For symptomatic perineural cysts, there is little evidence on which treatment is most effective or when it is indicated. The aim of this study was to review our experience from a population-based cohort of patients with symptomatic perineural cysts and to propose an algorithm that could be used in the selection of surgical candidates. METHODS: A retrospective review was conducted of all adult (≥ 15 years) patients with symptomatic perineural cysts who were referred to Karolinska University Hospital between 2002 and 2018. RESULTS: Thirty-nine patients were included. The most common symptom was sciatica (n = 22). Cyst aspiration was performed in 28 patients, 24 of whom showed clinical improvement and were offered surgery. Microsurgical cyst fenestration was performed in 17 patients, 16 of whom showed clinical improvement at long-term follow-up. There were no surgical complications. Ten of the patients who were offered surgery chose to be treated conservatively instead, four of whom showed progression of symptoms at long-term follow-up. CONCLUSIONS: Microsurgical cyst fenestration seems to be a safe and effective option for symptomatic relief in patients with perineural cysts. Based on the results from our series and those of others, we propose an algorithm for the selection of surgical candidates.

Long-Term Functional Outcomes Following Surgical Treatment of Spinal Schwannomas: A Population-Based Cohort Study.

Spinal schwannomas are the second most common form of primary intradural spinal tumor. Despite being benign, they may cause spinal cord compression and subsequently acute or chronic neurological dysfunction. The primary treatment is surgical resection. The aim of this study was to identify pre- and postoperative predictors of favorable outcomes after surgical treatment for spinal schwannoma. All adult patients surgically treated for spinal schwannoma between 2006 and 2020 were eligible for inclusion. Medical records and imaging data were retrospectively reviewed. The primary outcome measures were neurological improvement according to the modified McCormick Scale (mMC) and changes in motor deficit, sensory deficit, gait disturbance, bladder dysfunction, and pain at long-term follow-up. In total, 180 patients with a median follow-up time of 4.4 years were included. Pain was the most common presenting symptom (87%). The median time between symptom presentation and surgery was 12 months, while the median time between diagnosis (first MRI) and surgery was 3 months. Gross total resection (GTR) was achieved in 150 (83%) patients and the nerve root could be preserved in 133 (74%) patients. A postoperative complication occurred in 10 patients (5.6%). There were significant postoperative improvements in terms of motor, sensory, gait, and bladder functions, as well as pain (p < 0.001). Of these symptoms, bladder dysfunction was the one most often improved, with complete symptom resolution in all cases. However, no other predictors of improvement could be identified. There were three cases of recurrence after GTR and nine cases of regrowth after STR. Reoperation was performed in six (3.3%) cases. GTR was associated with a significant improvement in neurological status at long-term follow-up and increased the chance of progression-free survival.

Pedicle Screw Placement Using an Augmented Reality Head-Mounted Display in a Porcine Model.

This protocol helps assess the accuracy and workflow of an augmented reality (AR) hybrid navigation system using the Magic Leap head-mounted display (HMD) for minimally invasive pedicle screw placement. The cadaveric porcine specimens were placed on a surgical table and draped with sterile covers. The levels of interest were identified using fluoroscopy, and a dynamic reference frame was attached to the spinous process of a vertebra in the region of interest. Cone beam computerized tomography (CBCT) was performed, and a 3D rendering was automatically generated, which was used for the subsequent planning of the pedicle screw placements. Each surgeon was fitted with an HMD that was individually eye-calibrated and connected to the spinal navigation system. Navigated instruments, tracked by the navigation system and displayed in 2D and 3D in the HMD, were used for 33 pedicle cannulations, each with a diameter of 4.5 mm. Postprocedural CBCT scans were assessed by an independent reviewer to measure the technical (deviation from the planned path) and clinical (Gertzbein grade) accuracy of each cannulation. The navigation time for each cannulation was measured. The technical accuracy was 1.0 mm ± 0.5 mm at the entry point and 0.8 mm ± 0.1 mm at the target. The angular deviation was 1.5° ± 0.6°, and the mean insertion time per cannulation was 141 s ± 71 s. The clinical accuracy was 100% according to the Gertzbein grading scale (32 grade 0; 1 grade 1). When used for minimally invasive pedicle cannulations in a porcine model, submillimeter technical accuracy and 100% clinical accuracy could be achieved with this protocol.

Automatic image registration on intraoperative CBCT compared to Surface Matching registration on preoperative CT for spinal navigation: accuracy and workflow.

INTRODUCTION: Spinal navigation solutions have been slower to develop compared to cranial ones. To facilitate greater adoption and use of spinal navigation, the relatively cumbersome registration processes need to be improved upon. This study aims to validate a new solution for automatic image registration and compare it to a traditional Surface Matching method. METHOD: Adult patients undergoing spinal surgery requiring navigation were enrolled after providing consent. A registration matrix-Universal AIR (= Automatic Image Registration)-was placed in the surgical field and used for automatic registration based on intraoperative 3D imaging. A standard Surface Matching method was used for comparison. Accuracy measurements were obtained by comparing planned and acquired coordinates on the vertebrae. RESULTS: Thirty-nine patients with 42 datasets were included. The mean accuracy of Universal AIR registration was 1.20 ± 0.42 mm, while the mean accuracy of Surface Matching registration was 1.94 ± 0.64 mm. Universal AIR registration was non-inferior to Surface Matching registration. Post hoc analysis showed a significantly greater accuracy for Universal AIR registration. In Surface Matching, but not automatic registration, user-related errors such as incorrect identification of the vertebral level were seen. CONCLUSION: Automatic image registration for spinal navigation using Universal AIR and intraoperative 3D imaging provided improved accuracy compared to Surface Matching registration. In addition, it minimizes user errors and offers a standardized workflow, making it a reliable registration method for navigated spinal procedures.

Optical Methods for Brain Tumor Detection: A Systematic Review.

Background: In brain tumor surgery, maximal tumor resection is typically desired. This is complicated by infiltrative tumor cells which cannot be visually distinguished from healthy brain tissue. Optical methods are an emerging field that can potentially revolutionize brain tumor surgery through intraoperative differentiation between healthy and tumor tissues. Methods: This study aimed to systematically explore and summarize the existing literature on the use of Raman Spectroscopy (RS), Hyperspectral Imaging (HSI), Optical Coherence Tomography (OCT), and Diffuse Reflectance Spectroscopy (DRS) for brain tumor detection. MEDLINE, Embase, and Web of Science were searched for studies evaluating the accuracy of these systems for brain tumor detection. Outcome measures included accuracy, sensitivity, and specificity. Results: In total, 44 studies were included, covering a range of tumor types and technologies. Accuracy metrics in the studies ranged between 54 and 100% for RS, 69 and 99% for HSI, 82 and 99% for OCT, and 42 and 100% for DRS. Conclusions: This review provides insightful evidence on the use of optical methods in distinguishing tumor from healthy brain tissue.

Current knowledge on spinal meningiomas: a systematic review protocol.

INTRODUCTION: Meningiomas are primary central nervous system tumours that arise from both cranial and spinal meninges. Spinal meningiomas occur less frequently than their cranial counterparts and are consequently given less attention in the literature. Therefore, systematic studies are needed to summarise the current knowledge on spinal meningiomas, providing a solid evidence base for treatment strategies. This systematic review of the literature will therefore assess studies describing spinal meningiomas, their epidemiology, diagnostics, treatment and outcomes. METHODS AND ANALYSIS: Electronic databases, including PubMed, Web of Science and Embase, will be searched using the keywords "spinal" and "meningioma". The search will be set to provide only English studies published after 2000 to avoid any conflicts regarding terminology and classification, as well as to reflect the current status. Case reports, editorials, letters and reviews will also be excluded. Reference lists of relevant records will also be searched. Identified studies will be screened for inclusion, by one reviewer in a first step and then three in the next step to decrease the risk of bias. The results will be categorised to allow for a structured summary of the outcomes and their evidence grade conforming to the Grading of Recommendations, Assessment, Development and Evaluation approach. Categories may include: epidemiology, histopathology, radiological diagnostics, surgery, complications, non-surgical or adjuvant treatments, disease outcomes and predictors, and lastly recurrence. This review will summarise the current knowledge on spinal meningiomas to allow for a better understanding of the disease and contribute to improve its management. For clinicians, the systematic collection and grading of available evidence may aid in decision making and for those seeking to further the scientific field, this review may help to identify areas where knowledge is currently lacking. ETHICS AND DISSEMINATION: Ethics approval was not required for our systematic review as it is based on existing publications. The results will be disseminated via submission for publication in a peer-reviewed journal.

Clot composition characterization using diffuse reflectance spectroscopy in acute ischemic stroke.

Acute ischemic stroke caused by large vessel occlusion is treated with endovascular thrombectomy, but treatment failure may occur when clot composition and thrombectomy technique mismatch. In this proof-of-concept study, diffuse reflectance spectroscopy (DRS) is evaluated for identification of clot composition ex vivo. DRS spectra and histology were acquired from 45 clot units retrieved from 29 stroke patients. DRS spectra correlated to clot RBC content, R= 81, p < .001, and could discriminate between RBC-rich and fibrin-rich clots, p < 0.001. Sensitivity and specificity for detection of RBC-rich clots were 0.722 and 0.846 respectively. Applied in an intravascular device, DRS could potentially provide intraprocedural information on clot composition that could increase endovascular thrombectomy efficiency.

Identifying clot composition using intravascular diffuse reflectance spectroscopy in a porcine model of endovascular thrombectomy.

BACKGROUND: Endovascular thrombectomy has revolutionized the management of acute ischemic stroke and proven superior to stand-alone intravenous thrombolysis for large vessel occlusions. However, failed or delayed revascularization may occur as a result of a mismatch between removal technique and clot composition. Determination of clot composition before thrombectomy provides the possibility to adapt the technique to improve clot removal efficacy. We evaluated the application of diffuse reflectance spectroscopy (DRS) for intravascular determination of clot composition in vivo. METHODS: Three clot types, enriched in red blood cells or fibrin or with a mixed content, were prepared from porcine blood and injected into the external carotids of a domestic pig. A guidewire-like DRS probe was used to investigate the optical spectra of clots, blood and vessel wall. Measurement positions were confirmed with angiography. Spectra were analyzed by fitting an optical model to derive physiological parameters. To evaluate the method's accuracy, photon scattering and blood and methemoglobin contents were included in a decision tree model and a random forest classification. RESULTS: DRS could differentiate between the three different clot types, blood and vessel wall in vivo (p<0.0001). The sensitivity and specificity for detection was 73.8% and 98.8% for red blood cell clots, 80.6% and 97.8% for fibrin clots, and 100% and 100% for mixed clots, respectively. CONCLUSION: Intravascular DRS applied via a custom guidewire can be used for reliable determination of clot composition in vivo. This novel approach has the potential to increase efficacy of thrombectomy procedures in ischemic stroke.

Diffuse reflectance spectroscopy sensor to differentiate between glial tumor and healthy brain tissue: a proof-of-concept study.

Glial tumors grow diffusely in the brain. Survival is correlated to the extent of tumor removal, but tumor borders are often invisible. Resection beyond the borders as defined by conventional methods may further improve prognosis. In this proof-of-concept study, we evaluate diffuse reflectance spectroscopy (DRS) for discrimination between glial tumors and normal brain ex vivo. DRS spectra and histology were acquired from 22 tumor samples and nine brain tissue samples retrieved from 30 patients. The content of biological chromophores and scattering features were estimated by fitting a model derived from diffusion theory to the DRS spectra. DRS parameters differed significantly between tumor and normal brain tissue. Classification using random forest yielded a sensitivity and specificity for the detection of low-grade gliomas of 82.0% and 82.7%, respectively, and the area under curve (AUC) was 0.91. Applied in a hand-held probe or biopsy needle, DRS has the potential to provide intra-operative tissue analysis.