INFRARED 800
28Pages

INFRARED BOO Video Angiography A practical guide for the surgeon University Clinic for Neurosurgery Bern University Hospital E-mail: andreas.raabe@insel.ch

© Prof. Dr. A. Raabe 3rd edition, August 2010

1 Introduction The goals of surgical treatment of intracranial vascular malformations are to occlude or to excise the lesion and to maintain blood flow in parent, branching, and perforating vessels. These goals, however, are not always achieved. There are numerous publications showing that postopera­ tive imaging often demonstrates unexpected and incomplete treatment as well as compromise of normal vessels, neither of which is diagnosed by visual inspection during the surgery. The logical consequence was therefore to develop or adopt techniques that assist the surgeon during intraoperative...

The intraoperative fluorescence technology is fully integrated into the surgical microscope. The operative field is illuminated by a light source from the microscope with a wavelength that covers part of the indocyanine green (ICG) dye absorption band (700-850 nm, maximum 805 nm). A specially designed dielectric filter transmits an excitation light to generate fluorescence and simultaneously provides UV and thermal protection from the light source. Light passing through this filter in the near-infrared wavelength fits exactly to the absorption band of the injected ICG. In the observation...

3.1 Pharmacokinetics Within 1 to 2 seconds of intravenous injection, ICG is bound mainly to globulins (alpha-1 lipoproteins). It remains intravascular with normal vascular permeability. ICG is not metabolized in the body and is excreted exclusively by the liver. 3.2 Side-effects Indocyanine green can cause adverse reactions due to sodium iodine (drug contains 5%) or the molecule itself. The dye has been used widely in medical imaging, and it has been proven to be a relatively safe drug (3). Adverse reactions, however, can occur, ranging from mild to severe, including rare cases of death....

4 Implementation of INFRARED 800 angiography during surgery The INFRARED 800 technique is designed to perform infrared angiography without interrup­ tion to the surgical procedure. This technique involves full microscope integration (Fig. 3A) enabling clear visualization of the surgical situs during the angiography. The surgeon maintains his microscope view and can move structures out of sight with the use of suction or any surgical (A) instrument to focus on the structure of interest. Thus, the setup permits easy-to-use angiography procedure without interference with the surgical workflow....

4.2 Microscope preparation and workflow Set up the microscope for INFRARED 800 use before surgery (Fig. 4). The user should be familiar with the set-up menu of the microscope which can be found under the configuration menu in the fluorescence option. It is important to decide where on the configur­ able handgrip the INFRARED 800 mode will be activated (Fig. 5). Other parameters such as length of short and long review loops and number of repetitions, Picture-in-Picture mode or signal for external monitors are already predefined, but can also be adjusted according to the surgeon’s preference....

An initial press of a button on the handgrip sets up the system automatically. User guid­ ance ensures optimum settings for zoom and focus. Pressing the button again activates the synchronous video recording of white light and the infrared view. The brightness of the infrared image is automatically adjusted to the respective application. After recording, the automatic re­ eat p function for the first seconds of the flow phase is activated. During playback, INFRARED 800 recognizes the start of the inflow on the video and jumps directly to this sequence, skipping over the blank recording. The...

4.3 Patient preparation There is no special preparation necessary, except 4.4 Dye preparation and administration The surgeon usually announces the need for INFRARED 800 a few minutes ahead of time, enabling the anesthesiologist to prepare the fluorescence dye (25 mg per injection). The final command to inject the dye is given by the surgeon after he has started INFRARED 800 (Fig. 5), adjusted the zoom and focus (Fig. 6A and 6B), activated recording and has ensured that the monitor is in the INFRARED 800 mode by seeing the black INFRARED 800 screen. The anesthesiologist must ensure that the...

I IRSflQ ZOOM odjui Lirciit 11 rcici immttlr J 1 Si] •oasi ^gpf Fig. 6A: A message is displayed when the actual zoom (in this case 6.4x) exceeds the recom- mended zoom (less than 5.0). It can easily be adjusted on the touchscreen if necessary. IRSflG FOOJi idjuaJntenl n i«(nnni«ided [HW inn] Fig. 6B: A message is displayed when the actual focus (in this case 457mm) exceeds the recommended focus distance (less than 300mm). In this case the microscope should be brought closer to the surgical field.

4.5 Optimizing fluorescence image quality intraoperatively Optimum image quality depends on several factors such as light intensity, zoom, focus, iris, cardiocirculatory factors, depth and width of the surgical field and avoidance of bleeding or cerebrospinal fluid (CSF) accumulation around the structures of interest. Many factors can be influenced and the surgical microscope OPMI Pentero supports the user by providing an intelligent AutoGain function for optimum brightness as well as fluorescence detection and automatic iris adjustment. Image contrast is increased with a shorter focus...

5 Image interpretation Fig. 7-9: Three phases of dye inflow into brain vessels consisting of an arterial, a capillary and a combined arteriovenous phase. (Fig. 7) (Fig. 8) INFRARED 800 angiography provides a real-time video of dye inflow in brain vessels consisting of an arterial (Fig. 7), a capillary (Fig. 8) and a combined arteriovenous phase (Fig. 9). This mixed arteriovenous image is generated by the recirculating dye. The most important phases are: 1) the first inflow (early arterial phase) for identifying delay or cessation of flow in branching vessels or perforators suggesting vessel...