Cerebral blood flow (CBF) is of paramount importance to human brain function, as the brain relies on a continuous blood supply to meet its energy needs. Blockage of a cerebral blood vessel during neurosurgery, even if transient and short-lived, may result in irreversible brain tissue damage (i.e. stroke) and loss of cortical function, if not identified quickly enough.

Laser speckle contrast imaging (LSCI) has been demonstrated to provide the ability to visualize flow in vessels in real time and continuously without the need for contrast agents. In LSCI, the tissue of interest is illuminated with low power laser light at red or near infrared wavelengths and the light reflected from the tissue surface is imaged onto a camera. The resulting images are laser speckle patterns and a computer processes the images to produce speckle contrast images, which are images of the motion within the field of view (ie, blood flow).

The purpose of this clinical investigation is to assess the usefulness and accuracy of LSCI compared to ICGA and/or FA during neurovascular surgery. LSCI videos will be recorded automatically intraoperatively in each patient before, during, and after ICGA and/or FA in the same surgical field of view to guarantee comparability of the methods.

Cerebral blood flow (CBF) is of paramount importance to human brain function, as the brain relies on a continuous blood supply to meet its energy needs. Blockage of a cerebral blood vessel during neurosurgery, even if transient and short-lived, may result in irreversible brain tissue damage (i.e. stroke) and loss of cortical function, if not identified quickly enough.

Neurosurgery involves the treatment of blood-vessel related pathologies within the brain, like intracranial aneurysms, arteriovenous malformations and dural arteriovenous fistulas, but also the handling of vessels during brain tumor resections. For these operations, assessment of flow in vessels is of paramount importance. So far, the surgeon can not "see" blood flowing inside the artery or vein. Real-time flow visualization during surgery could help neurosurgeons better understand the consequences of vascular occlusion events during surgery, recognize potential adverse complications, and thus prompt timely intervention to reduce the risk of stroke. The current standard for visualizing flow in arteries during surgery is indocyanine green angiography (ICGA) and fluorescein angiography (FA), which involves administering a bolus of fluorescent dye intravenously and imaging the wash-in of the dye to determine which vessels are perfused. Both ICGA and FA provide only a punctual view of perfusion over several seconds, being far away from a continuous assessment.

Laser speckle contrast imaging (LSCI) has been demonstrated to provide the ability to visualize flow in vessels in real time and continuously without the need for contrast agents. In LSCI, the tissue of interest is illuminated with low power laser light at red or near infrared wavelengths and the light reflected from the tissue surface is imaged onto a camera. The resulting images are laser speckle patterns and a computer processes the images to produce speckle contrast images, which are images of the motion within the field of view (ie, blood flow).

With these properties LSCI has the potential to deliver for the first time continuous visualisation of blood flow in large and small vessels and to overcome limitations of ICGA and FA. LSCI is an established technique for studies of CBF and has predominantly been used to study microcirculation of the cerebral cortex during neurosurgical procedures. However, the spatial resolution in the clinical setting and its accuracy compared to ICGA and FA are unclear.

The purpose of this clinical investigation is to assess the usefulness and accuracy of LSCI compared to ICGA and/or FA during neurovascular surgery. LSCI videos will be recorded automatically intraoperatively in each patient before, during, and after ICGA and/or FA in the same surgical field of view to guarantee comparability of the methods.

Inclusion Criteria:

• Vascular pathology of the brain or brain tumors requiring elective microsurgical treatment (e.g., aneurysm, arteriovenous malformation, dural arteriovenous fistula, glioma, meningioma, metastasis)
• Adults (18 years or older)
• Informed consent signed by the subject

Exclusion Criteria:

• Patients lacking capacity to consent