Development and validation of a triple-LED surgical loupe device for fluorescence-guided resections with 5-ALA

Second-Generation Wide-Field Visualization Devices for 5-ALA-Induced Fluorescence and Concepts for Validation in Neurosurgery-A Systematic Review

BACKGROUND AND OBJECTIVES

Fluorescence-guided resection (FGR) of malignant gliomas with five-aminolevulinic acid (5-ALA) is an established method using surgical microscopes equipped with filter systems for observing fluorescence. Over the past decade, new technologies have been introduced for the same purpose, with available publications evaluating their clinical efficacy based on varying criteria. This study aims to review technologies and concepts of validation in the context of 5-ALA-mediated FGR.

METHODS

A systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement was performed to identify devices capable of detecting 5-ALA-induced fluorescence. Articles found eligible for this review were analyzed, focusing on the methods of validation used for novel devices. A qualitative analysis is presented.

RESULTS

Using predefined eligibility criteria, 22 studies were analyzed. Publications on the following visualization devices were reviewed: FL400 (Leica Microsystems), Aeos (Aesculap), BLUE400 and BLUE400 AR Filter System (Carl Zeiss Meditec AG), Endoscope with D-Light C (Karl Storz), Fiberscope N-4L (Machida), ORBEYE 4K 3D Digital Video Microscope (Olympus), and several customized surgical loupe systems. In many cases, validation seemed unstandardized, with inherent biases and limited reproducibility.

CONCLUSION

This review illustrates the significance of device validation within the framework of FGR. It emphasizes the criticality of validating devices in accordance with established standard, i.e. the BLUE400 filter system, which was employed in the approval studies of 5-ALA. Furthermore, standardized concepts of validation are required to assess whether new devices are, in fact, a reliable or superior alternative in the field of FGR. Published guidelines should be considered when performing future studies.

Intraoperative Imaging and Optical Visualization Techniques for Brain Tumor Resection: A Narrative Review

Advancements in intraoperative visualization and imaging techniques are increasingly central to the success and safety of brain tumor surgery, leading to transformative improvements in patient outcomes. This comprehensive review intricately describes the evolution of conventional and emerging technologies for intraoperative imaging, encompassing the surgical microscope, exoscope, Raman spectroscopy, confocal microscopy, fluorescence-guided surgery, intraoperative ultrasound, magnetic resonance imaging, and computed tomography. We detail how each of these imaging modalities contributes uniquely to the precision, safety, and efficacy of neurosurgical procedures. Despite their substantial benefits, these technologies share common challenges, including difficulties in image interpretation and steep learning curves. Looking forward, innovations in this field are poised to incorporate artificial intelligence, integrated multimodal imaging approaches, and augmented and virtual reality technologies. This rapidly evolving landscape represents fertile ground for future research and technological development, aiming to further elevate surgical precision, safety, and, most critically, patient outcomes in the management of brain tumors.

Comparison of minimal detectable protoporphyrin IX concentrations with a loupe device and conventional 5-ALA fluorescence microscopy: an experimental study

Significance

The 5-aminolevulinic acid (5-ALA) fluorescence technique is now widely applied for intraoperative visualization of specific central nervous system (CNS) tumors. Previous technical implementations of this technique have relied on specifically modified surgical microscopes to visualize intratumoral fluorescent protoporphyrin (PpIX). While this approach evidently allows for reliable intraoperative tumor visualization, it requires the availability of specifically modified surgical microscopes and their use even in cases where the operating neurosurgeon would prefer to use surgical loupes. Recently, a novel loupe device was introduced that is also capable of visualizing 5-ALA fluorescence.

Aim

The aim of this study was therefore to compare the detected PpIX concentrations between the conventional fluorescence microscope and the novel loupe device.

Approach

We used fluorescence phantoms of different PpIX concentrations for comparison between a conventional fluorescence microscope and the novel loupe device. For this purpose, we created fluorescence images using the excitation light sources of the conventional fluorescence microscope and the loupe device with both available background illumination modes (low and high). Subsequently, the minimal detectable PpIX concentrations according to each technique were determined by five independent neurosurgeons.

Results

Using the conventional fluorescence microscope, the median minimal detectable PpIX concentration was 0.16    μ g / ml (range: 0.15 to 0.17    μ g / ml ). By the loupe device, the median minimal detectable PpIX concentration was 0.12    μ g / ml (range: 0.10 to 0.12    μ g / ml ) and 0.08    μ g / ml (range: 0.07 to 0.08    μ g / ml ) for the high- and low-modes, respectively. Altogether, the minimal detectable PpIX concentrations were significantly lower using the loupe device compared to the conventional fluorescence microscope (p = 0.007 ).

Conclusions

Our data indicate that the novel loupe device is able to visualize 5-ALA fluorescence with high sensitivity and thus might serve as a powerful tool for visualization of specific CNS tumors in the future.

The NXDC-MEN-301 Study on 5-ALA for Meningiomas Surgery: An Innovative Study Design for the Assessing the Benefit of Intra-Operative Fluorescence Imaging

BACKGROUND

5-aminolevulinic acid (5-ALA; Gleolan^TM, NX Development Corps., Lexington, USA) is approved for fluorescence-guided resections of suspected malignant gliomas. Experience has demonstrated that meningiomas also show fluorescence, which may be a useful surgical adjunct. We present an innovative design for a multi-center, prospective study to determine the clinical safety and potential benefit of fluorescence-guided resection of meningiomas with utmost bias reduction.

METHODS

All patients with suspected meningioma (all grades) receive Gleolan^TM 20 mg/kg 2-4 h prior to surgery supported by fluorescence excitation from a blue light source (Blue400, Zeiss Meditech, Oberkochen, Germany; FL400, Leica Microsystems, Heerbrugg, Switzerland). Surgeons are asked whether a residual tumor can be observed to fluoresce under blue light (BL) after the tumor is no longer recognizable using conventional illumination at the end of surgery. In addition, when faced with tissues of uncertain tissue type (so-called "indeterminate" tissue), this study records how often surgeons make a correct decision based on fluorescence and how this influences surgical strategy. The primary endpoint is the percentage of patients in whom one of these two benefits are observed. Other endpoints include the diagnostic accuracy of fluorescence compared to white light (WL) versus correlative histology. For bias reduction, pertinent data are derived from surgical videos reviewed by independent reviewers blinded to surgeons' assessments of tissue type and fluorescence status. Data will be included from approximately 100 study participants completing the study at approximately 15 centers in the United States, Germany, and Austria.

RESULTS

As of May 2022, 88 patients have completed the study. No adverse safety signal has been detected.

CONCLUSIONS

Preliminary data confirm the feasibility of our study design. Accrual is targeted for completion in the third quarter of 2022.