Value of multiphoton microscopy in uro-oncology: a narrative review

Multi-photon microscopy (MPM) is a 3-dimension fluorescence imaging technique that combines the excitation of two low-energy photons, enabling less photo-bleaching and deeper penetration of the imaged tissue. Two signals are detected, autofluorescence (AF), from natural intracellular fluorophores [such as nicotinamide adenine dinucleotide phosphate (NADP) and flavine adenine dinucleotide (FAD) transformation], and second harmonic generation (SHG), a physical property of the laser enhancing non-centrosymmetric structures such as collagen fibers. MPM can give both visual and quantitative information of a fresh tissue (without the need of processing, cutting or staining the tissue), aiding in the progress towards optimizing a real-time imaging device. The objective of this review is to show the value and benefits of the use of MPM in uro-oncology.

A structured literature review was performed using PubMed and Web of Sciences, including all articles with the following keywords: "multiphoton microscopy", "two-photon microscopy", "non-linear microscopy", "second harmonic generation", "urology", "prostate", "bladder", "kidney", "upper tract", "oncology", "surgical margins", "frozen section". Articles were reviewed to summarize the use of this tool in performing biopsies, assessing surgical margins, staging and grading complementary tool, and real-time imaging.

A total of 476 articles were identified with these keywords, and later screened for inclusion. We finally included 47 publications that were relevant to our topic. The advantages of this technique have led to its application in the management of several cancers, allowing cellular description as well as quantitative measurements of AF or SHG and their correlation with clinical outcomes.

MPM has shown great improvement in providing a real time assessment of fresh tissue, giving oncologic diagnosis, performing in vivo imaging and quantitative analysis of the tissue as well as increasing precision of the diagnosis. This nonlinear optical technique has the potential of guiding both biopsy and surgery, as well as helping the surgeon with interesting additional tissue information intra-operatively.