An omnidirectional viewing Laser Speckle Rheology (LSR) catheter has been developed by scientists at Harvard Medical School and Massachusetts General Hospital for mapping the mechanical properties of luminal (tubular) organs without the need for rotational motion.
The intraluminal LSR catheter incorporates illumination fibres, an optical fibre bundle, and a multi-faceted mirror, along with an externally mounted Mikrotron MC1310 1.3 MP CMOS camera interfaced to an imaging workstation via a BitFlow CameraLink frame grabber.
Laser Speckle Rheology has been successfully applied to image coronary plaques, blood coagulation, complex biofluids, tumours, and knee cartilage, among other conditions. However, in order to evaluate the mechanical properties of tissues within deep, inaccessible geometries, LSR must be conducted via a miniature endoscope or catheter.
To overcome this challenge, the scientists engineered the omnidirectional LSR using multiple single-mode fibres and a multifaceted pyramidal mirror to guide light to various circumferential locations on the lumen wall. Simultaneously it collects multiple laser speckle patterns, thus circumventing the need for mechanical rotation. Distal optics are optimized for a lumen of 3 mm diameter or about the size of a human coronary artery.
During imaging, a drive shaft containing the catheter assembly is pulled back through a transparent protective sheath in discrete steps over a maximum pullback distance of 20 cm. The Mikrotron camera will capture laser speckle patterns at frame rates of up to 2000 frames per second. The camera was directly housed on the motor drive unit with the proximal face of the optical fibre bundle imaged on the camera’s CMOS sensor using a 40X objective lens. The BitFlow frame grabber is designed for these types of situations where extremely high frame rates are required by acquiring up to 128 bits at 85 MHz pixel clock rate and DMA at data rates up to 2.0 GB/S.
Scientists believe that the omnidirectional viewing catheter may be useful for the biomechanical profiling of a number of pathological processes for several clinical and research applications. Its diameter is comparable in size to commercially available intravascular catheters and considerably smaller than several gastrointestinal endoscopes, opening the opportunity for evaluation in luminal organs or deep tissues via endoscopes, catheters, or needles.