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Wårdell K, Klint E, Milos P, Richter J. One-Insertion Stereotactic Brain Biopsy Using In Vivo Optical Guidance-A Case Study. Oper Neurosurg (Hagerstown) 2023; 25:176-182. [PMID: 37083519 PMCID: PMC10313274 DOI: 10.1227/ons.0000000000000722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 02/21/2023] [Indexed: 04/22/2023] Open
Abstract
BACKGROUND Stereotactic neurosurgical brain biopsies are afflicted with risks of inconclusive results and hemorrhage. Such complications can necessitate repeated trajectories and prolong surgical time. OBJECTIVE To develop and introduce a 1-insertion stereotactic biopsy kit with direct intraoperative optical feedback and to evaluate its applicability in 3 clinical cases. METHODS An in-house forward-looking probe with optical fibers was designed to fit the outer cannula of a side-cutting biopsy kit. A small aperture was made at the tip of the outer cannula and the edges aligned with the optical probe inside. Stereotactic biopsies were performed using the Leksell Stereotactic System. Optical signals were measured in millimeter steps along the preplanned trajectory during the insertion. At the region with the highest 5-aminolevulinic acid (5-ALA)-induced fluorescence, the probe was replaced by the inner cannula, and tissue samples were taken. The waiting time for pathology diagnosis was noted. RESULTS Measurements took 5 to 10 minutes, and the surgeon received direct visual feedback of intraoperative 5-ALA fluorescence, microcirculation, and tissue gray-whiteness. The 5-ALA fluorescence corroborated with the pathological findings which had waiting times of 45, 50, and 75 minutes. Because only 1 trajectory was required and the patient could be prepared for the end of surgery immediately after sampling, this shortened the total surgical time. CONCLUSION A 1-insertion stereotactic biopsy procedure with real-time optical guidance has been presented and successfully evaluated in 3 clinical cases. The method can be modified for frameless navigation and thus has great potential to improve safety and diagnostic yield for both frameless and frame-based neurosurgical biopsy procedures.
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Affiliation(s)
- Karin Wårdell
- Department of Biomedical Engineering, Linköping University, Linköping, Sweden
| | - Elisabeth Klint
- Department of Biomedical Engineering, Linköping University, Linköping, Sweden
| | - Peter Milos
- Department of Neurosurgery and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Johan Richter
- Department of Biomedical Engineering, Linköping University, Linköping, Sweden
- Department of Neurosurgery and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
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Liu Q, Contreras A, Afaq MS, Yang W, Hsu DK, Russell M, Lyeth B, Zanto TP, Zhao M. Intensity-dependent gamma electrical stimulation regulates microglial activation, reduces beta-amyloid load, and facilitates memory in a mouse model of Alzheimer's disease. Cell Biosci 2023; 13:138. [PMID: 37507776 PMCID: PMC10386209 DOI: 10.1186/s13578-023-01085-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 07/14/2023] [Indexed: 07/30/2023] Open
Abstract
BACKGROUND Gamma sensory stimulation may reduce AD-specific pathology. Yet, the efficacy of alternating electrical current stimulation in animal models of AD is unknown, and prior research has not addressed intensity-dependent effects. METHODS The intensity-dependent effect of gamma electrical stimulation (GES) with a sinusoidal alternating current at 40 Hz on Aβ clearance and microglia modulation were assessed in 5xFAD mouse hippocampus and cortex, as well as the behavioral performance of the animals with the Morris Water Maze. RESULTS One hour of epidural GES delivered over a month significantly (1) reduced Aβ load in the AD brain, (2) increased microglia cell counts, decreased cell body size, increased length of cellular processes of the Iba1 + cells, and (3) improved behavioral performance (learning & memory). All these effects were most pronounced when a higher stimulation current was applied. CONCLUSION The efficacy of GES on the reduction of AD pathology and the intensity-dependent feature provide guidance for the development of this promising therapeutic approach.
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Affiliation(s)
- Qian Liu
- Institute for Regenerative Cures, Department of Ophthalmology & Vision Science, Department of Dermatology, University of California Davis, Sacramento, CA, 95817, USA
- Institute of Biomedical and Health Engineering, Shenzhen Institutes of Advanced Technology (SIAT), Chinese Academy of Sciences, Shenzhen, China
| | - Adam Contreras
- Institute for Regenerative Cures, Department of Ophthalmology & Vision Science, Department of Dermatology, University of California Davis, Sacramento, CA, 95817, USA
| | - Muhammad Shan Afaq
- Institute for Regenerative Cures, Department of Ophthalmology & Vision Science, Department of Dermatology, University of California Davis, Sacramento, CA, 95817, USA
| | - Weijian Yang
- Department of Electrical and Computer Engineering, University of California, Davis, CA, 95616, USA
| | - Daniel K Hsu
- Institute for Regenerative Cures, Department of Ophthalmology & Vision Science, Department of Dermatology, University of California Davis, Sacramento, CA, 95817, USA
| | - Michael Russell
- Institute for Regenerative Cures, Department of Ophthalmology & Vision Science, Department of Dermatology, University of California Davis, Sacramento, CA, 95817, USA
| | - Bruce Lyeth
- Department of Neurological Surgery, University of California, Davis, CA, 95616, USA
| | - Theodore P Zanto
- Neuroscape, Department of Neurology, University of California San Francisco, San Francisco, CA, 94158, USA.
| | - Min Zhao
- Institute for Regenerative Cures, Department of Ophthalmology & Vision Science, Department of Dermatology, University of California Davis, Sacramento, CA, 95817, USA.
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Klint E, Richter J, Wårdell K. Combined Use of Frameless Neuronavigation and In Situ Optical Guidance in Brain Tumor Needle Biopsies. Brain Sci 2023; 13:brainsci13050809. [PMID: 37239281 DOI: 10.3390/brainsci13050809] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 05/10/2023] [Accepted: 05/13/2023] [Indexed: 05/28/2023] Open
Abstract
Brain tumor needle biopsies are performed to retrieve tissue samples for neuropathological analysis. Although preoperative images guide the procedure, there are risks of hemorrhage and sampling of non-tumor tissue. This study aimed to develop and evaluate a method for frameless one-insertion needle biopsies with in situ optical guidance and present a processing pipeline for combined postoperative analysis of optical, MRI, and neuropathological data. An optical system for quantified feedback on tissue microcirculation, gray-whiteness, and the presence of a tumor (protoporphyrin IX (PpIX) accumulation) with a one-insertion optical probe was integrated into a needle biopsy kit that was used for frameless neuronavigation. In Python, a pipeline for signal processing, image registration, and coordinate transformation was set up. The Euclidian distances between the pre- and postoperative coordinates were calculated. The proposed workflow was evaluated on static references, a phantom, and three patients with suspected high-grade gliomas. In total, six biopsy samples that overlapped with the region of the highest PpIX peak without increased microcirculation were taken. The samples were confirmed as being tumorous and postoperative imaging was used to define the biopsy locations. A 2.5 ± 1.2 mm difference between the pre- and postoperative coordinates was found. Optical guidance in frameless brain tumor biopsies could offer benefits such as quantified in situ indication of high-grade tumor tissue and indications of increased blood flow along the needle trajectory before the tissue is removed. Additionally, postoperative visualization enables the combined analysis of MRI, optical, and neuropathological data.
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Affiliation(s)
- Elisabeth Klint
- Department of Biomedical Engineering, Linköping University, 581 85 Linköping, Sweden
| | - Johan Richter
- Department of Biomedical Engineering, Linköping University, 581 85 Linköping, Sweden
- Department of Neurosurgery, Linköping University Hospital, 581 85 Linköping, Sweden
| | - Karin Wårdell
- Department of Biomedical Engineering, Linköping University, 581 85 Linköping, Sweden
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Mauritzon S, Ginstman F, Hillman J, Wårdell K. Analysis of laser Doppler flowmetry long-term recordings for investigation of cerebral microcirculation during neurointensive care. Front Neurosci 2022; 16:1030805. [PMID: 36408392 PMCID: PMC9671599 DOI: 10.3389/fnins.2022.1030805] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 10/18/2022] [Indexed: 11/19/2023] Open
Abstract
Cerebral blood flow is monitored in the neurointensive care unit (NICU) to avoid further brain damage caused by secondary insults following subarachnoid hemorrhage and brain trauma. Current techniques are mainly snap-shot based and focus on larger vessels. However, continuous monitoring of the smaller vessels may help detect the onset of secondary insults at an earlier stage. In this study, long-term measurements of brain microcirculation with laser Doppler flowmetry (LDF) were performed and evaluated. The aim was to identify and describe physiological signal variations and separate these from movement artifacts. Fiberoptic probes for subcortical LDF recordings of perfusion and total light intensity (TLI) were implanted in three patients with subarachnoid hemorrhage. Data were successfully collected and visualized in real-time over 4 days, resulting in 34, 12, and 8.5 h per patient. Visual observation, wavelet transforms, moving medians, and peak envelopes were used to identify and describe movement artifacts and physiological changes. Artifacts occurred in <5% of the total recording time and could be identified through signal processing. Identified physiological signal patterns included a slowly increasing perfusion trend over hours, vasomotion mainly at 2 cycles/min both in the perfusion and the TLI, and rapid, synchronized changes in the TLI and the perfusion on 38 occasions. Continuous LDF recordings indicating changes in the microvascular blood flow can increase the understanding of the microcirculation in the injured brain. In the long run, this may become a complement for the detection of secondary insults at an earlier stage than possible with today's techniques.
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Affiliation(s)
- Stina Mauritzon
- Neuroengineering Lab, Department of Biomedical Engineering, Linköping University, Linköping, Sweden
| | - Fredrik Ginstman
- Department of Neurosurgery and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Jan Hillman
- Department of Neurosurgery and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Karin Wårdell
- Neuroengineering Lab, Department of Biomedical Engineering, Linköping University, Linköping, Sweden
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Wårdell K, Nordin T, Vogel D, Zsigmond P, Westin CF, Hariz M, Hemm S. Deep Brain Stimulation: Emerging Tools for Simulation, Data Analysis, and Visualization. Front Neurosci 2022; 16:834026. [PMID: 35478842 PMCID: PMC9036439 DOI: 10.3389/fnins.2022.834026] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2021] [Accepted: 03/01/2022] [Indexed: 01/10/2023] Open
Abstract
Deep brain stimulation (DBS) is a well-established neurosurgical procedure for movement disorders that is also being explored for treatment-resistant psychiatric conditions. This review highlights important consideration for DBS simulation and data analysis. The literature on DBS has expanded considerably in recent years, and this article aims to identify important trends in the field. During DBS planning, surgery, and follow up sessions, several large data sets are created for each patient, and it becomes clear that any group analysis of such data is a big data analysis problem and has to be handled with care. The aim of this review is to provide an update and overview from a neuroengineering perspective of the current DBS techniques, technical aids, and emerging tools with the focus on patient-specific electric field (EF) simulations, group analysis, and visualization in the DBS domain. Examples are given from the state-of-the-art literature including our own research. This work reviews different analysis methods for EF simulations, tractography, deep brain anatomical templates, and group analysis. Our analysis highlights that group analysis in DBS is a complex multi-level problem and selected parameters will highly influence the result. DBS analysis can only provide clinically relevant information if the EF simulations, tractography results, and derived brain atlases are based on as much patient-specific data as possible. A trend in DBS research is creation of more advanced and intuitive visualization of the complex analysis results suitable for the clinical environment.
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Affiliation(s)
- Karin Wårdell
- Neuroengineering Lab, Department of Biomedical Engineering, Linköping University, Linköping, Sweden
| | - Teresa Nordin
- Neuroengineering Lab, Department of Biomedical Engineering, Linköping University, Linköping, Sweden
| | - Dorian Vogel
- Neuroengineering Lab, Department of Biomedical Engineering, Linköping University, Linköping, Sweden
- Institute for Medical Engineering and Medical Informatics, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland
| | - Peter Zsigmond
- Department of Neurosurgery and Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Carl-Fredrik Westin
- Neuroengineering Lab, Department of Biomedical Engineering, Linköping University, Linköping, Sweden
- Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Marwan Hariz
- Unit of Functional Neurosurgery, UCL Queen Square Institute of Neurology, London, United Kingdom
- Department of Clinical Sciences, Neuroscience, Ume University, Umeå, Sweden
| | - Simone Hemm
- Neuroengineering Lab, Department of Biomedical Engineering, Linköping University, Linköping, Sweden
- Institute for Medical Engineering and Medical Informatics, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland
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Zsigmond P, Wårdell K. Optical Measurements during Asleep Deep Brain Stimulation Surgery along Vim-Zi Trajectories. Stereotact Funct Neurosurg 2020; 98:55-61. [PMID: 32079023 DOI: 10.1159/000505708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Accepted: 12/31/2019] [Indexed: 11/19/2022]
Abstract
BACKGROUND Optics can be used for guidance in deep brain stimulation (DBS) surgery. The aim was to use laser Doppler flowmetry (LDF) to investigate the intraoperative optical trajectory along the ventral intermediate nucleus (VIM) and zona incerta (Zi) regions in patients with essential tremor during asleep DBS surgery, and whether the Zi region could be identified. METHODS A forward-looking LDF guide was used for creation of the trajectory for the DBS lead, and the microcirculation and tissue greyness, i.e., total light intensity (TLI) was measured along 13 trajectories. TLI trajectories and the number of high-perfusion spots were investigated at 0.5-mm resolution in the last 25 mm from the targets. RESULTS All implantations were done without complications and with significant improvement of tremor (p < 0.01). Out of 798 measurements, 12 tissue spots showed high blood flow. The blood flow was significantly higher in VIM than in Zi (p < 0.001). The normalized mean TLI curve showed a significant (p < 0.001) lower TLI in the VIM region than in the Zi region. CONCLUSION Zi DBS performed asleep appears to be safe and effective. LDF monitoring provides direct in vivomeasurement of the microvascular blood flow in front of the probe, which can help reduce the risk of hemorrhage. LDF can differentiate between the grey substance in the thalamus and the transmission border entering the posterior subthalamic area where the tissue consists of more white matter tracts.
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Affiliation(s)
- Peter Zsigmond
- Departments of Neurosurgery and Clinical and Experimental Medicine, Linköping University, Linköping, Sweden,
| | - Karin Wårdell
- Department of Biomedical Engineering, Linköping University, Linköping, Sweden
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Akshulakov SK, Kerimbayev TT, Biryuchkov MY, Urunbayev YA, Farhadi DS, Byvaltsev VA. Current Trends for Improving Safety of Stereotactic Brain Biopsies: Advanced Optical Methods for Vessel Avoidance and Tumor Detection. Front Oncol 2019; 9:947. [PMID: 31632903 PMCID: PMC6783564 DOI: 10.3389/fonc.2019.00947] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 09/09/2019] [Indexed: 01/06/2023] Open
Abstract
Stereotactic brain needle biopsies are indicated for deep-seated or multiple brain lesions and for patients with poor prognosis in whom the risks of resection outweigh the potential outcome benefits. The main goal of such procedures is not to improve the resection extent but to safely acquire viable tissue representative of the lesion for further comprehensive histological, immunohistochemical, and molecular analyses. Herein, we review advanced optical techniques for improvement of safety and efficacy of stereotactic needle biopsy procedures. These technologies are aimed at three main areas of improvement: (1) avoidance of vessel injury, (2) guidance for biopsy acquisition of the viable diagnostic tissue, and (3) methods for rapid intraoperative assessment of stereotactic biopsy specimens. The recent technological developments in stereotactic biopsy probe design include the incorporation of fluorescence imaging, spectroscopy, and label-free imaging techniques. The future advancements of stereotactic biopsy procedures in neuro-oncology include the incorporation of optical probes for real-time vessel detection along and around the biopsy needle trajectory and in vivo confirmation of the diagnostic tumor tissue prior to sample acquisition.
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Affiliation(s)
- Serik K Akshulakov
- Department of Neurosurgery, JSC "National Center for Neurosurgery", Nur-Sultan, Kazakhstan
| | - Talgat T Kerimbayev
- Department of Neurosurgery, JSC "National Center for Neurosurgery", Nur-Sultan, Kazakhstan
| | - Michael Y Biryuchkov
- Department of Neurosurgery and Traumatology, West Kazakhstan Marat Ospanov State Medical University, Aktobe, Kazakhstan
| | - Yermek A Urunbayev
- Department of Neurosurgery, JSC "National Center for Neurosurgery", Nur-Sultan, Kazakhstan
| | - Dara S Farhadi
- University of Arizona College of Medicine, Phoenix, AZ, United States
| | - Vadim A Byvaltsev
- Department of Neurosurgery, JSC "National Center for Neurosurgery", Nur-Sultan, Kazakhstan.,Department of Neurosurgery and Innovative Medicine, Irkutsk State Medical University, Irkutsk, Russia
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Zsigmond P, Hemm-Ode S, Wårdell K. Optical Measurements during Deep Brain Stimulation Lead Implantation: Safety Aspects. Stereotact Funct Neurosurg 2018; 95:392-399. [DOI: 10.1159/000484944] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 11/01/2017] [Indexed: 11/19/2022]
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Rejmstad P, Haj-Hosseini N, Åneman O, Wårdell K. Optical monitoring of cerebral microcirculation in neurointensive care. Med Biol Eng Comput 2017; 56:1201-1210. [PMID: 29218511 PMCID: PMC6013533 DOI: 10.1007/s11517-017-1725-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Accepted: 09/14/2017] [Indexed: 11/29/2022]
Abstract
Continuous optical monitoring of local cerebral microcirculation could benefit neurointensive care patients treated for subarachnoid hemorrhage (SAH). The aim of the study was to evaluate laser Doppler flowmetry (LDF) and diffuse reflectance spectroscopy (DRS) for long-term monitoring of brain microcirculation and oxygen saturation (SO2) in the neurointensive care unit (NICU). A fiber optic probe was designed for intraparenchymal use and connected to LDF and DRS for assessment of the local blood flow (perfusion and tissue reflectance (TLI)) and SO2 in the brain. The optically monitored parameters were compared with conventional NICU monitors and Xe-CT. The LDF signals were low with median and 25 to 75% interquartiles of perfusion = 70 (59 to 83) a.u. and TLI = 2.0 (1.0 to 2.4) a.u. and showed correlation with the NICU monitors in terms of heart rate. Median and interquartiles of SO2 were 17.4 (15.7 to 19.8) %. The lack of correlation between local perfusion and cerebral perfusion pressure indicated intact cerebral autoregulation. The systems were capable of monitoring both local perfusion and SO2 with stable signals in the NICU over 4 days. Further clinical studies are required to evaluate the optical systems’ potential for assessing the onset of secondary brain injury.
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Affiliation(s)
- Peter Rejmstad
- Department of Biomedical Engineering, Linköping University, Linköping, Sweden.
| | - Neda Haj-Hosseini
- Department of Biomedical Engineering, Linköping University, Linköping, Sweden
| | - Oscar Åneman
- Department of Neurosurgery, Linköping University Hospital, Linköping, Sweden.,Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | - Karin Wårdell
- Department of Biomedical Engineering, Linköping University, Linköping, Sweden
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Wårdell K, Hemm-Ode S, Rejmstad P, Zsigmond P. High-Resolution Laser Doppler Measurements of Microcirculation in the Deep Brain Structures: A Method for Potential Vessel Tracking. Stereotact Funct Neurosurg 2016; 94:1-9. [PMID: 26795207 DOI: 10.1159/000442894] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 11/30/2015] [Indexed: 11/19/2022]
Abstract
BACKGROUND Laser Doppler flowmetry (LDF) can be used to measure cerebral microcirculation in relation to stereotactic deep brain stimulation (DBS) implantations. OBJECTIVE To investigate the microcirculation and total light intensity (TLI) corresponding to tissue grayness in DBS target regions with high-resolution LDF recordings, and to define a resolution which enables detection of small vessels. METHODS Stereotactic LDF measurements were made prior to DBS implantation with 0.5-mm steps in the vicinity to 4 deep brain targets (STN, GPi, Vim, Zi) along 20 trajectories. The Mann-Whitney U test was used to compare the microcirculation and TLI between targets, and the measurement resolution (0.5 vs. 1 mm). The numbers of high blood flow spots along the trajectories were calculated. RESULTS There was a significant difference (p < 0.05) in microcirculation between the targets. High blood flow spots were present at 15 out of 510 positions, 7 along Vim and GPi trajectories, respectively. There was no statistical difference between resolutions even though both local blood flow and TLI peaks could appear at 0.5-mm steps. CONCLUSIONS LDF can be used for online tracking of critical regions presenting blood flow and TLI peaks, possibly relating to vessel structures and thin laminas along stereotactic trajectories.
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Affiliation(s)
- Karin Wårdell
- Department of Biomedical Engineering, Linkx00F6;ping University, Linkx00F6;ping, Sweden
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A laser Doppler system for monitoring cerebral microcirculation: implementation and evaluation during neurosurgery. Med Biol Eng Comput 2015; 54:123-31. [PMID: 26105147 DOI: 10.1007/s11517-015-1332-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Accepted: 06/11/2015] [Indexed: 01/12/2023]
Abstract
The aim of this study was to adapt and evaluate laser Doppler perfusion monitoring (LDPM) together with custom-designed brain probes and software for continuous recording of cerebral microcirculation in patients undergoing neurosurgery. The LDPM system was used to record perfusion and backscattered light (TLI). These parameters were displayed together with the extracted heart rate (HR), pulsatility index (PI) and signal trends from adjustable time intervals. Technical evaluation was done on skin during thermal provocation. Clinical measurements were performed on ten patients undergoing brain tumour surgery. Data from 76 tissue sites were captured with a length varying between 10 s to 15 min. Statistical comparisons were done using Mann-Whitney tests. Grey and tumour tissue could be separated from white matter using the TLI signal (p < 0.05). The perfusion was significantly higher in grey and tumour tissue compared to white matter (p < 0.005). LDPM was successfully used as an intraoperative tool for monitoring local blood flow and additional parameters linked to cerebral microcirculation (perfusion, TLI, HR and PI) during tumour resection. The systems stability opens up for studies in the postoperative care of patients with, for example, traumatic brain injury or subarachnoid haemorrhage.
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