Both nonspecific and specific cancer-targeted fluorescent agents are currently being used for in vivo cancer detection.
Fluorescence endoscopy is becoming increasingly important in many medical diagnostic tests. Based on the molecular absorption of light, this technique works by revealing tissue abnormalities that are hidden from view under normal white light. Already, fluorescence endoscopy can improve the endoscopic detection of non-visible malignant lesions or tumors, for example. Sensitizers, which accumulate in these lesions, induce tissue fluorescence in response to light of certain wavelengths. In the field of gastroenterology, this ability to reveal and visualize lesions holds promise for the early detection of dysplasia and cancers. Similarly, near-infrared (NIR) fluorescence rigid endoscopic imaging systems are emerging as a critical tool in some brain surgeries.
Fluorescence endoscopy, which is gaining ground in these and other medical applications compared to traditional white light endoscopic techniques, places some unique requirements on optical lenses. For example, a lens with the right combination of high resolution, anti-reflective coatings and minimal focus shift can enable better fluorescence imaging across the visible and NIR range, which includes wavelengths between 400 and 850 nanometers.
To explore this topic further, this white paper will discuss various lens design considerations, including optical filters and anti-reflective coatings, that can further optimize the performance of NIR fluorescence endoscopy in medical and life science applications.
Compared to visible light fluorescence imaging, NIR fluorescence imaging exhibits superior tissue penetration and causes less autofluorescence in adjacent tissue. For these reasons, the technique is becoming increasingly important in many medical applications:
Recent advancements in coating and thin-filter optical technologies are finding more uses in the medical and life science industries and can optimize NIR fluorescence endoscopic techniques. One such advancement, called the Extended Bandwidth and Angular Dependency (eBAND) lens coating, deploys a nano-structured layer with an ultra-low refractive index, the dimensions of which are smaller than the wavelengths of visible light. This nano-structured layer, coupled with the sophisticated multi-layer coatings underneath, yields significant anti-reflection properties. By suppressing tangential reflection, this coating also reduces undesired flare and ghosting to deliver sharp, crisp images even in very poor lighting conditions.
Compared to other anti-reflective coatings, eBAND is suitable for wavelengths from 400 to 1,700 nanometers, which includes the visible to near-infrared range. Thanks to this capability, eBAND enables deeper examinations using indocyanine green (ICG), a medical dye frequently used in tests that involve the heart and liver, as well as certain parts of the eye. Another coating technology is the Broad-Band Anti-Reflective (BBAR) coating. Like eBAND, this coating suppresses the surface reflections that lead to ghosting and flare to deliver clearer images.
Modulation transfer function (MTF) is a reference value that enables optical designers to quantify the overall imaging performance of a system in terms of its resolution and contrast. Designers often refer to MTF data in applications like fluorescence endoscopy that depend on imaging accuracy for success. Although a helpful value to know, MTF does not always reflect the real-world performance of the lens. Nonetheless, understanding the MTF curves of the lens and other parts within an optical system allows designers to select and optimize the components for a particular resolution. To this end, one of our strengths at Tamron is our ability to manufacture optical products with real-world values that very closely resemble their design values.