Object. Application of sensitive infrared imaging is ideally suited to observe blood vessels and blood flow in exposed organs, including the brain. Temporary vascular occlusion is an important part of neurosurgery, but the capacity to monitor the effects of these occlusions in real time is limited. In surgical procedures that require vascular manipulation, such as those involving aneurysms, arteriovenous malformations (AVMs), or tumors, the ability to visualize blood flow in vessels and their distribution beds would be beneficial. The authors recount their experience in the use of a sensitive (0.02°C), high-resolution (up to 50 µm/pixel) infrared camera with a rapid shutter speed (up to 2 msec/frame) for localizing cortical function intraoperatively. They observed high-resolution images of cerebral arteries and veins.
The authors hypothesized that infrared imaging of cerebral arteries, performed using a sensitive, high-resolution camera during surgery, would permit changes in arterial flow to be be seen immediately, thus providing real-time assessment of brain perfusion in the involved vascular territory.
Methods. Cynomolgus monkeys underwent extensive craniectomies, exposing the frontal, parietal, and temporal lobes. Temporary occlusions of the internal carotid artery and middle cerebral artery branches (30 events) were performed serially and were visualized with the aid of an infrared camera.
Arteries and veins of the monkey brain were clearly visualized due to cooling of the exposed brain, which contrasted with blood within the vessels that remained at core temperature. Blood flow changes in vessels were seen immediately (< 1 second) in real time during occlusion and reopening of the vessels, regardless of the duration of the occlusion. Areas of decreased cortical blood flow rapidly cooled (−0.3 to 1.3°C) and reheated in response to reperfusion. Rewarming occurred faster in arteries than in the cortex (for a 20-minute occlusion, the change in temperature per second was 2 × 10−2°C in the artery and 7 × 10−3°C in the brain). Collateral flow could be evaluated by intraoperative observations and data processing.
Conclusions. Use of high-resolution, digital infrared imaging permits real-time visualization of arterial flow. It has the potential to provide the surgeon with a means to assess collateral flow during temporary vessel occlusion and to visualize directly the flow in parent arteries or persistent filling of an aneurysm after clipping. During surgery for AVMs, the technique may provide a new way to assess arterial inflow, venous outflow, results of embolization, collateral flow, steal, and normal perfusion pressure breakthrough.
On the Origins of the Cerebral IVIM Signal