ABSTRACT
Versatile programmable materials have long been envisioned that can reconfigure themselves to adapt to changing use cases in adaptive infrastructure, space exploration, disaster response, and more. We introduce a robotic structural system as an implementation of programmable matter, with mechanical performance and scale on par with conventional high-performance materials and truss systems. Fiber-reinforced composite truss-like building blocks form strong, stiff, and lightweight lattice structures as mechanical metamaterials. Two types of mobile robots operate over the exterior surface and through the interior of the system, performing transport, placement, and reversible fastening using the intrinsic lattice periodicity for indexing and metrology. Leveraging programmable matter algorithms to achieve scalability in size and complexity, this system design enables robust collective automated assembly and reconfiguration of large structures with simple robots. We describe the system design and experimental results from a 256-unit cell assembly demonstration and lattice mechanical testing, as well as a demonstration of disassembly and reconfiguration. The assembled structural lattice material exhibits ultralight mass density (0.0103 grams per cubic centimeter) with high strength and stiffness for its weight ( 11.38 kilopascals and 1.1129 megapascals, respectively), a material performance realm appropriate for applications like space structures. With simple robots and structure, high mass-specific structural performance, and competitive throughput, this system demonstrates the potential for self-reconfiguring autonomous metamaterials for diverse applications.
ABSTRACT
PURPOSE: To investigate the effects of increasing source-to-image distance (SID) on radiation dose and image quality for digital radiography examinations of the pelvis. METHODS: Using a Carestream DirectView DR 7500 unit, anteroposterior pelvic images were obtained on 97 consecutive patients at a standard 115-cm SID (group 1). Ninety-nine patients were examined using the same equipment and acquisition parameters but with the maximum achievable SID (group 2). For each examination, tube potential, milliampere seconds, SID, and source-to-skin distances were recorded. This facilitated the calculation of entrance surface dose, including backscatter, and effective dose using Quality Assurance Dose Data System software. The resultant images were independently assessed for image quality by 3 blinded observers-2 reporting radiographers and 1 consultant radiologist. Image quality was graded using an established scoring system, which assessed image quality at multiple anatomical locations. RESULTS: For group 1, median (interquartile range [IQR]; the median value is presented with the corresponding interquartile range in parentheses) entrance surface dose with backscatter was 1.95 mGy (1.23 mGy-3.10 mGy), which was lower by 1.15 mGy (0.78 mGy-2.22 mGy) for the increased SID group (22 patients at 135 cm, 77 patients at 144 cm) (Mann-Whitney U test, P < .001). Effective dose calculations generated a median (IQR) of 0.32 mSv (0.13 mSv-0.52 mSv) for group 1 and a lower median of 0.19 mSv (0.13 mSv-0.37 mSv) for group 2 (P < .001). No observers (intraclass correlation coefficient = 0.675) found a significant change in image quality by increasing SID (group 1, 2.0 ± 1.8; group 2, 1.6 ± 1.4; P > .05) when comparing the difference in image quality scores with the maximum score available. DISCUSSION: Our results demonstrate a reduction in entrance surface dose, including backscatter and effective dose, of 39% and 41%, respectively, when operating at extended SIDs. Results were generated from a clinically based study and included a wide spectrum of patients. Multiple regression confirmed that increasing the SID contributes to a dose reduction. Increasing SID is a simple and cost-effective method for reducing radiation dose and can be applied to all patients by all radiographers and with all commercially available digital radiography units. CONCLUSION: For digital pelvic radiography, increasing SID is a potential method for reducing entrance surface and effective radiation doses without compromising image quality.
