Introduction: Distinguishing neoplasm from normal brain parenchyma in real time is critical for the neurosurgeon. Near-infrared (NIR) fluorescence-guided-surgery has demonstrated superior sensitivity for detecting neoplasm intraoperatively. To prepare for the increasing number of NIR fluorophores in future molecular imaging trials, we chose to compare a state-of-the-art neurosurgical microscope (System1) to one of the commercially available NIR-visualization exoscope platforms (System2).
Methods: System1 had a xenon light source with a filter for 820-860nm. System2 had an 805nm laser light source and a camera for 820-860nm. Serial dilutions of ICG from 0.47 – 1007µg/L were imaged with both systems under the same conditions and NIR signal for each concentration was recorded. In addition, 12 patients with intracranial tumors received 5mg/kg of intravenous ICG infusion approximately 24 hours prior to surgery. In the operating room, NIR signal-to-background-ratios (SBR) for the tumors were measured with both systems at various points along the surgery.
Results: In-vitro, System2 demonstrated greater ICG sensitivity and detection range (System1: 1.5–251 µg/L with maximum SBR 3.25; System2: 0.99–503µg/L with maximum SBR 12). In-vivo, 26 intraoperative NIR images were taken with System1 and 24 with System2 in 12 patients. Prior to dura opening, System1 did not reliably detect ICG fluorescence, with SBR 1.2±0.15, while System2 easily detected NIR fluorescence from the tumor with SBR 2.0±0.69 (p-value=0.0168). Similarly, after dura opening, System1 and System2 detected NIR fluorescence with SBRs of 1.4±0.23 and 4.6±1.8, respectively (p-value<0.001). Finally, with the tumor in direct line of sight, System1 and System2 detected NIR fluorescence with SBRs of 1.6±0.30 and 6.8±1.9, respectively (p-value <0.001).
Conclusions: Dedicated NIR imaging platforms can outperform conventional surgical microscopes in intraoperative NIR detection, with significantly greater sensitivity and detection range. Future microscopes that incorporate this enhanced sensitivity into the neurosurgery operative workflow may enhance the use of intraoperative NIR fluorescence to detect neoplasm and improve patient outcome.
Patient Care: Recently, intraoperative fluorescence for distinguishing areas of neoplasm from normal brain has been described. While much of the research focus is on the specific types of dyes, another factor that heavily influences the experience is the type of imaging system used. Our research systemically compares two representative systems from each category in order to provide objective data for neurosurgeons to understand the different available imaging modalities.
Learning Objectives: By the conclusion of this session, participants should be able to
1) Understand that options for intraoperative fluorescence imaging exist beyond the traditional surgical microscopes
2) Describe the main advantages and disadvantages of the two systems
3) Identify a system that suits their own operative workflow