Rotary Encoder For Medical Research Applications

The MR318 MRI-compatible fibre-optic rotary encoder from Micronor is ideal for functional-MRI (fMRI) research and related medical applications, as well as military and industrial. The MR318 is a non-metallic rotary position sensor that can operate with complete 'transparency' in extreme electromagnetic fields. Prior to the MR318, engineers had no commercial solution for measuring continuous position within an MRI chamber.

Motors or actuators could be hydraulic or pneumatic but no commercial, non-metallic position sensor existed, according to Micronor. A homemade fibre-optic proximity/limit switch was the best solution, but this was awkward to design, package and could only provide position information at discrete points. The MR318 enables fully functional motion control apparatus with closed-loop feedback. The MR318's product development combined Micronor's passive fibre-optic encoder technology with material engineering that flowed down to the smallest component.

For interchangability and compatibility with existing products, the MRI encoder would use the same industry standard size 58mm form factor and pair with the same MR310 interface module. The MRI environment-specific material requirements represented the greatest challenges. Anything (patient or equipment) placed in the MRI chamber must be devoid of metallic or ferrous materials that might disrupt the MRI machine's electromagnetic field and operation. It became more that a part-for-part conversion of the existing MR312 encoder's design.

Special attention had to be paid to the choice and machinability of materials chosen for the housing, shaft, bearings, encoder wheel and optical assembly. The optical fibre and optical components (filter and mirror) were the only original components that did not require redesign. The MR318 rotary encoder has become an enabler for fMRI research and related medical applications. The device allows medical researchers and radiologists to develop MRI-compatible test and diagnostic apparatus where measuring position, angle or speed is required.

It became possible to monitor the brain activity of stroke and other impaired patients while engaged in various locomotor activities (pedalling, lifting, limb movement and so on). For example, monitoring brain activity at discrete pedal positions allows the researcher to observe how the brain and body adjusts to therapy as well as evaluate new rehabilitation techniques. The encoder also enables the development of more sophisticated MRI phantoms for machine calibration, teaching and training.

Non-medical applications - especially military and industrial - also exist for the MR318. The RF 'transparency' of the encoder is ideal for designing embedded servo loop systems for equipment designed for EW (electronic warfare), DEW (directed energy weapons) and EMC (electromagnetic compatibility). There are test apparatus applications within anechoic chambers as well as electromagnetic-based industrial separation processes. As an example, the MR318 encoder provides X/Y position feedback for a prototype electromagnetic sensor array.

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