Red-light excitation of protoporphyrin IX fluorescence for subsurface tumor detection

Abstract

OBJECTIVE The objective of this study was to detect 5-aminolevulinic acid (ALA)-induced tumor fluorescence from glioma below the surface of the surgical field by using red-light illumination. METHODS To overcome the shallow tissue penetration of blue light, which maximally excites the ALA-induced fluorophore protoporphyrin IX (PpIX) but is also strongly absorbed by hemoglobin and oxyhemoglobin, a system was developed to illuminate the surgical field with red light (620-640 nm) matching a secondary, smaller absorption peak of PpIX and detecting the fluorescence emission through a 650-nm longpass filter. This wide-field spectroscopic imaging system was used in conjunction with conventional blue-light fluorescence for comparison in 29 patients undergoing craniotomy for resection of high-grade glioma, low-grade glioma, meningioma, or metastasis. RESULTS Although, as expected, red-light excitation is less sensitive to PpIX in exposed tumor, it did reveal tumor at a depth up to 5 mm below the resection bed in 22 of 24 patients who also exhibited PpIX fluorescence under blue-light excitation during the course of surgery. CONCLUSIONS Red-light excitation of tumor-associated PpIX fluorescence below the surface of the surgical field can be achieved intraoperatively and enables detection of subsurface tumor that is not visualized under conventional blue-light excitation. Clinical trial registration no.: NCT02191488 (clinicaltrials.gov).

Fluorescence detection of deep intramucosal cancer excited by green light for photodynamic diagnosis using protoporphyrin IX induced by 5-aminolevulinic acid: an ex vivo study

“…22 So far, a clinical study reported ALA-PDD for brain tumor by red light excitation can be achieved to collect PpIX fluorescence associated with subsurface tumor at the depth up to around 5 mm. 19 On the other hand, thickness of gastric mucosa is 1.4 AE 0.3 mm and the volume of normal tissue related to the fluorescence background in the mucosa is smaller than the case for detecting subsurface tumor. Each excitation wavelengths have the same fluorescence ratio between tumor and normal tissues since because the fluorescence intensity is proportional to the concentration.…”

“…Roberts et al reported that the malignant brain tumor at the subsurface (up to the fluorophore depth of 5 mm from the surface) can be detected by fluorescence of PpIX with red-light excitation (the wavelength of 630 nm). 19 The attenuation rates in using red-light excitation were calculated for intramucosal gastric cancer as well as the case of the 405-and 505-nm wavelength light excitation. The attenuation rate with the wavelength of 630 nm was higher at the fluorophore depth of 1.2 mm or deeper region compared with the wavelength of 405 nm.…”

“…The PpIX fluorescence background for gastric cancer observation will provide less damage of the contrast than the clinical case. 19 Thus, although the PpIX fluorescence background damages the contrast of tumor detection, green light excitation will distinguish tumor lesion in normal gastric mucosa.…”

Preclinical evaluation of spatial frequency domain-enabled wide-field quantitative imaging for enhanced glioma resection

“…9 Finally, while the objective here was to enhance the accuracy of state-of-the-art PpIX FGR, which utilizes violet/blue light excitation, both qualitative PpIX FGR and SFD-qFI are limited to superficial tumors up to a depth of about 1 mm below the tissue surface. Our recent clinical implementation of PpIX FGR under red-light excitation 27 has shown additional benefit by identifying deep-seated tumors located up to 5 mm below the surface. Hence, we are currently investigating the use of SFDI using 625-nm excitation light to interrogate subsurface PpIX-rich tumors and recovering both the depth and the PpIX concentration at that depth.…”

Review of clinical trials in intraoperative molecular imaging during cancer surgery

“…In collaboration with his engineering colleagues, Dr. Roberts has been on the forefront of spectroscopic technologies, including quantitative approaches and spectrally resolved quantitative imaging even with multiple simultaneous fluorophores such as fluorescein and 5-ALA in the same patient. [10][11][12][13][14] Dr. Roberts emphasized the importance of the detection technology and the importance of collaboration with his engineering colleagues, with particular mention of Keith Paulsen, Pablo Valdes, and Brian Pogue.…”