Introduction: The use of 5-aminolevulinic acid-induced (ALA) protoporphyrin IX (PpIX) fluorescence has been shown to be a powerful tool for surgical guidance, but current technologies demonstrate low sensitivity, leaving tumor tissue undetected. We have previously shown a single-point quantitative fluorescence approach that can significantly improve the diagnostic accuracy of PpIX. We hypothesized that an imaging technique that provides full field-of-view, spectrally-resolved attenuation correction and fluorescence detection, would allow the surgeon to make quantitative assessments of PpIX fluorescence across the full surgical field-of-view and in near-real time, thus providing the improved detection benefits of quantitative fluorescence in imaging mode (QFI).
Methods: A microscope-integrated device for spectrally-resolved acquisition across the full field-of-view in near-real time was built, and validated in tissue simulating phantoms and CNS-1 glioma Lewis rats to assess system performance. We then performed a feasibility study on 5 patients with glioma (2 glioblastoma, 1 anaplastic astrocytoma, 1 anapastic mixed oligo-astrocytoma, 1 mixed oligo-astrocytoma) to test our QFI technique.
Results: In tissue phantoms, our QFI technique, compared to standard fluorescence, accurately quantified PpIX (linear regression analysis, R2 = 0.89 vs R2 = 0.27), demonstrated highly sensitive detection (limit of detection, 40 ng/ml vs 1000 ng/ml), and improved contrast (normalized contrast analysis, >1 order of magnitude) with a spatial resolution of 0.25 mm (contrast transfer function analysis). Validation of QFI-derived PpIX measurements with our established probe in rodents showed no significant difference (p<0.001) and a high correlation (r = 0.80, p<0.001). Clinical deployment successfully quantified PpIX fluorescence in both visually fluorescent and non-visually fluorescent regions.
Conclusions: These findings demonstrate the feasibility of performing quantitative fluorescence imaging with no disruption to the surgical workflow, using an imaging device that integrates with the surgical microscope. This technique opens the door to performing highly sensitive and quantitative assessments of PpIX to identify infiltrative tumor margins.
Patient Care: This work is aimed at improving current technologies in fluorescence guided neurosurgery, which in turn will help improve surgical guidance and extent of resection.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Understand the principles of spectrally resolved, quantitative fluorescence imaging; 2) Discuss, in small groups, how to carry out and implement the QFI technique; 3) Understand the major factors that impact detection of intraoperative fluorescence.
References: 1. Stummer W, Pichlmeier U, Meinel T, Wiestler OD, Zanella F, Reulen HJ. Fluorescence-guided surgery with 5-aminolevulinic acid for resection of malignant glioma: a randomised controlled multicentre phase III trial. Lancet Oncol. May 2006;7(5):392-401.
2. Roberts DW, Valdes PA, Harris BT, et al. Coregistered fluorescence-enhanced tumor resection of malignant glioma: relationships between delta-aminolevulinic acid-induced protoporphyrin IX fluorescence, magnetic resonance imaging enhancement, and neuropathological parameters. J Neurosurg. Mar 2011;114(3):595-603.
3. Valdes PA, Leblond F, Kim A, et al. Quantitative fluorescence in intracranial tumor: implications for ALA-induced PpIX as an intraoperative biomarker. J Neurosurg. Jul 2011;115(1):11-17.
4. Valdes PA, Kim A, Leblond F, et al. Combined fluorescence and reflectance spectroscopy for in vivo quantification of cancer biomarkers in low- and high-grade glioma surgery. J Biomed Opt. Nov 2011;16(11):116007.