Improving medical, bioscience device performance

Advanced optics deliver high-resolution images so diagnostic instruments can uncover hard-to-identify tissue abnormalities earlier, and they guide users of surgical instruments with greater precision. The growing field of fluorescence endoscopy can reveal certain tumors or lesions that otherwise can’t be detected using traditional white light endoscopy. In designing medical and life science instruments that involve lasers, fluorescence, and other optical disciplines, image quality relies on lens quality.

Distortions due to electromagnetic waves can adversely affect results in fluorescence endoscopy, Raman spectroscopy instruments, and other critical equipment, so lenses must be optimized to eliminate undesirable light and contamination. Here’s how optical filters and coatings ensure optimal lens performance with exceptionally low distortion.

Block unwanted light

To achieve optimal optical performance, medtech equipment requires tight control of the wavelength. Notch filters are effective in ensuring precise wavelength control and image integrity. These optical filters reject wavelength transmission across a defined range of the electromagnetic spectrum and allow high transmission outside that range. Notch filter performance is based on its ability to block an unwanted frequency – optical density (OD) – and the rate at which it transmits other wavelengths. Medical and life science devices are typically sensitive to light transmission and demand high-OD notch filters. A high OD indicates a low transmission percentage. For example, OD1 energy transmission is 10%, whereas OD6 – a very desirable OD figure for medtech devices that demand high sensitivity – is 0.0001%. For many optical component vendors, OD6 is often a design barrier. Tamron designs and manufactures notch filters that achieve blocking OD of 6 or more within a specific wavelength range from 400nm, visible to 1,700nm, near-infrared (NIR). These notch filters incorporate thin coatings that help lenses achieve various effects, make certain functions possible, and provide greater surface protection, optimizing overall optical performance. Due to continuous developments in thin film coatings, medtech device designers can satisfy specific requirements and expand optical capabilities in new fields. Technical experts can also customize an ideal notch filter and coating combination that best meets needs.

When specifying a notch filter, make sure it’s manufactured to deliver the consistent performance that medical and bioscience equipment demand. An ideal notch filter specialist will have an ISO-certified manufacturing facility and maintain strict controls and batch inspections throughout production. These attributes ensure filter surfaces without imperfections and irregularities, so each unit achieves OD6 every time. Tamron backs up its quality controls with an inspection certificate confirming it meets specifications; customers receive high-precision notch filters with minimal differences between design and manufacturing variables.

Notch filters are well-suited as an integral part of a comprehensive optical system in a range of equipment in medical and bioscience disciplines, including:

Raman spectroscopy – Devices used for analyzing lithium-ion batteries, electronic component fabrication, and food and medicine production

Fluorescence imaging – Cameras that support fluorescence-guided surgeries

Solve filter-lens alignment issues

When setting up an off-the-shelf external optical filter with a lens unit, it can be difficult to get the components into precise alignment. If the optical components aren’t aligned, the filter won’t achieve the correct angle of incidence (AOI). Even the best-performing filter can’t reach its full optical potential unless it’s used at the proper AOI. Sometimes device designers don’t know how to achieve the right AOI, which is why it pays to work with a partner that specializes in optical design.

For example, a custom-designed lens unit and filter combination can eliminate time and expense aligning the individual components. Using advanced mechanical simulation processes and software, a lens manufacturer specializing in optical design can place a band pass filter at the correct AOI without affecting the accuracy of the lens unit and filter. The graphs in Figure 3 illustrate the modular transfer function (MTF) – a reference value in quantifying a system’s resolution and contrast performance – of an improperly aligned lens unit and bandpass filter versus a combined lens unit and bandpass filter. As the graphs indicate, the improperly aligned lens unit and bandpass filter exhibits lesser-quality preservation of spatial detail versus an all-in-one custom lens unit with internal band pass filter.

In addition to having expertise in designing notch and bandpass filters, Tamron also designs and produces lens units, including cemented prisms with sensor relative error of 1µm or less that maintain high performance at temperatures up to ~140°C.

Work with your optical component supplier

When an instrument design calls for high-quality lenses or lens assemblies, not all optical component suppliers are the same. In selecting optical lenses or filters for a medical or bioscience device, be sure to communicate the application requirements as well as the lens specifications.

While many vendors can produce lenses and filters, few suppliers can optimize products to meet exact requirements. The right optical component specialist will take the information provided and incorporate those specifications into the lens or filter design. And, if there’s an existing design, they can use advanced mechanical simulation technology to make modifications in-house to ensure the lens, filter, or lens assembly achieves optimal optical performance. With quality products together with engineering assistance and custom capabilities, Tamron is a single source for advanced optical components for demanding medical or bioscience instruments.

About the author: Kota Yamamoto is section manager, medical device development department for Tamron.