The information on the frictional resistance of a self-propelled robotic capsule endoscope moving inside the body is very important for the design and the performance enhancement of such parameters of the capsule endoscope as power consumption, motion control and positioning accuracy. Based on this motivation, the ultimate goal of this research was to develop an analytical model that can predict the frictional resistance of the capsule endoscope moving inside the living body. In this work, experimental investigations of the fundamental frictional characteristics and the viscoelastic behaviors of the small intestine were performed by using custom-built testers and various capsule dummies. The small intestine of a pig was used for the experiments. Experimental results showed that the average frictional force was 10-50 mN and higher moving speed of the capsule dummy resulted in larger frictional resistance of the capsule. In addition, the friction coefficient did not change significantly with respect to the apparent area of contact between the capsule dummy and the intestine, and also the friction coefficients decreased with an increase in the normal load and varied from 0.08 to 0.2. Such frictional behaviors could be explained by the lubrication characteristics of the intestine surface and typical viscoelastic characteristics of the small intestine material. Also, based on the experimental results, a viscoelasticity model for the stress relaxation of the small intestine could be derived.KEY WORDS: biotribology, capsule endoscope, small intestine, stress relaxation, viscoelasticity Nomenclature F Friction force (N) l Friction coefficient N Normal force applied to the capsule (N) r(t) Stress applied to the small intestine (Pa, N/m 2 ) 0Strain applied to the small intestine t Time

clinicaltrials.gov, NCT01004497.

In vivo pre-clinical single-photon emission computed tomography (SPECT) is a valuable tool for functional small animal imaging, but several physical factors, such as scatter radiation, limit the quantitative accuracy of conventional scintillation crystal-based SPECT. Semiconductor detectors such as CZT overcome these deficiencies through superior energy resolution. To our knowledge, little scientific information exists regarding the accuracy of quantitative analysis in CZT-based pre-clinical SPECT systems for different isotopes. The aim of this study was to assess the quantitative accuracy of CZT-based pre-clinical SPECT for four isotopes: 201 Tl, 99m Tc, 123 I, and 111 In. The quantitative accuracy of the CZT-based Triumph X-SPECT (Gamma-Medica Ideas, Northridge, CA, U.S.A.) was compared with that of a conventional SPECT using GATE simulation. Quantitative errors due to the attenuation and scatter effects were evaluated for all four isotopes with energy windows of 5%, 10%, and 20%. A spherical source containing the isotope was placed at the center of the air-or-water-filled mouse-sized cylinder phantom. The CZT-based pre-clinical SPECT was more accurate than the conventional SPECT. For example, in the conventional SPECT with an energy window of 10%, scatter effects degraded quantitative accuracy by up to 11.52%, 5.10%, 2.88%, and 1.84% for 201 Tl, 99m Tc, 123 I, and 111 In, respectively. However, with the CZT-based pre-clinical SPECT, the degradations were only 9.67%, 5.45%, 2.36%, and 1.24% for 201 Tl, 99m Tc, 123 I, and 111 In, respectively. As the energy window was increased, the quantitative errors increased in both SPECT systems. Additionally, the isotopes with lower energy of photon emissions had greater quantitative error. Our results demonstrated that the CZT-based pre-clinical SPECT had lower overall quantitative errors due to reduced scatter and high detection efficiency. Furthermore, the results of this systematic assessment quantifying the accuracy of these SPECT for various isotopes will provide valuable reference information for the design of CZT-based preclinical SPECT system imaging protocols.

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