Abstract
We present a system capable of real-time delivery and monitoring of laser therapy by imaging with optical coherence tomography (OCT) through a double-clad fiber (DCF). A double-clad fiber coupler is used to inject and collect OCT light into the core of a DCF and inject the therapy light into its larger inner cladding, allowing for both imaging and therapy to be perfectly coregistered. Monitoring of treatment depth is achieved by calculating the speckle intensity decorrelation occurring during tissue coagulation. Furthermore, an analytical noise correction was used on the correlation to extend the maximum monitoring depth. We also present a method for correcting motion-induced decorrelation using a lookup table. Using the value of the noise- and motion-corrected correlation coefficient in a novel approach, our system is capable of identifying the depth of thermal coagulation in real time and automatically shut the therapy laser off when the targeted depth is reached. The process is demonstrated ex vivo in rat tongue and abdominal muscles for depths ranging from 500 µm to 1000 µm with induced motion in real time.
Highlights
Laser therapy allows for targeted removal or thermal coagulation of tissues through light absorption by various absorbers in the tissue, such as water, hemoglobin and other macromolecules [1,2,3]
In this work we presented a new laser therapy monitoring technique that allowed us to monitor the progression of thermal coagulation of excised animal tissue
A 532 nm therapy laser was used with optical coherence tomography (OCT) imaging through a single double-clad fiber compatible with endoscopic use
Summary
Laser therapy allows for targeted removal or thermal coagulation of tissues through light absorption by various absorbers in the tissue, such as water, hemoglobin and other macromolecules [1,2,3] It is used in the treatment of epithelial cancerous and pre-cancerous lesions such as Barrett’s esophagus [4,5,6], in eye diseases such as diabetic retinopathy [7,8,9,10] and retinal vein occlusion [11,12] and in respiratory papillomatosis, a viral-induced disease in the upper airway [13,14]. Under-treatment requires repeat visits with the associated cost, while overtreatment generally causes complications requiring surgical treatment [15,16,17]. Such precise monitoring requires real-time imaging techniques capable of resolving the thin epithelial layers (generally a few hundred microns) under treatment. When the target zone is small and presents mostly subsurface features for guidance, properly targeting the therapy can prove challenging unless treatment is guided by cross-sectional imaging
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