Diffuse optical imaging (DOI) providing functional information of tissues has drawn great attention for the last two decades [1]. Near infrared (NIR) DOI systems composed of scanning equipment, opt-electrical measuring module, system control, and data processing and image reconstruction schemes are developed for the screening and diagnosis of breast tumors. Mostly, the scanning equipment belonging to fixed source-and-detector configuration limits computed image resolution to an extent [2–4].To cope with the issue, a flexible ring-scanning mechanism design has been investigated and analyzed in order to obtain the most probable effectiveness and efficiency while retaining acceptable scanning time. Before the detail design of ring-scanning equipment was conducted, finite-element-based image reconstruction schemes were performed to obtain tomographical images through changing source-and-detection arrangement of the ring-scanning mechanism. From the simulation [5], the 2Z3S or 3Z3S configuration was found an apparently better design for the ring-scanning mechanism in terms of both the resolution of reconstructed optical-property images and the scanning time of equipment. Following the previous study, this technical brief demonstrates the design, fabrication, and test of the prototype ring-scanning equipment.Prostrate ring-scanning-based architecture in the developed NIR DOI system is considered for the screening and diagnosis of breast tumors, as shown in Fig. 1, the schematic diagram of the system. The ideas and concepts of design are based on the following considerations:The circular scanning module is divided into m zones, and each zone includes n NIR sources and l detection fibers. Due to the space limitation and the physical dimension of source-and-detection-fiber heads, 36 source-and-detection channels are adopted, and 10 deg separation between each two heads is arranged.The radial movement of a single optical channel set functions through a radial guiding slot and an optical channel bracket. A bracket makes an optical channel set fixed, as shown in Fig. 2. A single optical channel set (Fig. 3) is composed of an illumination fiber or a liquid light guide for detection, a light guide unit with two fixers, a linear guideway incorporated with a seat driven by a stepping motor, a link, and a bearing. To drive the whole 36 optical source-and-detector channels, Fig. 4 shows the mechanism that mainly includes a rotating disk, a belt tension pulley, a V-belt pulley, and a V-belt for the purpose of a radial movement.Figure 5 demonstrates the angular-movement mechanism of optical source-and-detector channels, mainly including a stepping motor and a speed-reduction gearbox with bevel gears.In a radial-movement mode to drive each optical channel bracket, it was realized by the link moving in the guiding slot, where a bearing is mounted at the other end of link to allow the link rotating with the inner race. The rotating disk was driven by a stepper motor and a V-belt set for speed reduction, as shown in Fig. 4.In a circular-movement mode to achieve ring scanning, Fig. 5 shows a stepper motor installed beneath the scanning platform connects to a bevel gearbox with a speed reduction ratio 2 for a smooth drive. The ring-scanning angle can be as high as 360 deg, which is dependent on the source-and-detector configuration used; for instance, the scanning angle is 150 deg for the configuration 2Z3S. Here *Z#S denotes all optical channels set into * zones, and # illumination channels in a single zone. Therefore, six illumination channels and 30 detection channels in total are in the design of configuration 2Z3S associated with 36 optical channels.In this prostrate equipment for NIR diffuse optical imaging, our experimental scenario is designated as below.Based on the synthesized design with acceptable scanning time and simulated imaging quality [5], the prototype equipment was machined and assembled, as shown in Fig. 6. The experiments to acquire NIR data and reconstruct images for verification will be performed in the near future. To illustrate probable image reconstruction through the proposed prostrate ring-scanning equipment, a computational case study was synthesized. Figure 7 illustrates two sets of reconstructed μa and μs′ images for the design of configuration 2Z3S associated with 18 and 36 optical channels, respectively. In the simulation case, a 10 mm-diameeter tumor in a 100 mm-diameter background tissue is assumed. The original cross section image was obtained with slicing a 3D breast MRI from Taipei Medical University Hospital.The proposed *Z#S design is rather cost-effective than the fixed optical-channel one. As to the performance of image reconstruction, Figs. 7(c) and 7(e) are still competitive to their counterparts, Figs. 7(b) and 7(d), respectively.The study was partially supported by the grant NCU-LSH-102-A-013.
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Apr 1, 2016
I V Kovalev + 5
