D. Zhang et al. imaging methods [8], grating-based phase contrast imaging where E is the IL-XPCT slices reconstruction filtered factor. methods [9], and in-line XPCT (IL-XPCT) methods [10]. In Figure 1 shows our experimental arrangement. It consists of this work, IL-XPCT is mainly used. It is also known as the specimen on a rotation stage, a monochromator, and a propagation-based phase contrast CT. Because the synchrotron detector. beam is sufficiently spatially coherent during the experiment, the setup of IL-XPCT is extremely simple and needs no Sample preparation djustment except for the sample-to-detector distance. All samples investigated were provided by the Anatomy Teaching and Research Section of the Second Military Medical Methods and materials University, Shanghai, China. We used New Zealand white rabbits to prepare our samples. After the adult rabbits were Principle of IL-XPCT and experimental setup killed by a large dose of anesthetic, we injected 5% sodium citrate saline into the abdominal aorta for anticoagulation and to The principles of IL-XPCT, which were described in detail help empty the blood vessels. Then contrast agent comprising a elsewhere [ll, are briefly reviewed here. When parallel mixed solution of barium sulfate and latex particles(their coherent light with wavelength A irradiates samples diameter is about several hundred nanometers)was injected into perpendicularly, in accordance with Fresnel diffraction the abdominal aorta to make the blood vessels more highlighted theory, the plane wave goes through the samples, and the in CT images. About 15 min later, samples were dissected from intensity distribution of the disturbed wave at the down- the rabbits and immersed in formalin for fixation. stream distance z can be written as Two acupuncture points RN3 and ST36 were studied in this work. The Chinese name of RN3 is Zhongji, and that of ST36 (x,y)=|hz°Ub (1) is Zusanli. They are frequently used in acupuncture, and the acupuncture at these points shows distinct clinical effects. Their where the symbol represents convolution, 0 is the locations are well known RN3 is located in the abdomen at different IL-XPCT rotation angles, UE is the light complex 1/13 of the distance from the pubic symphysis joint to the joint amplitude distribution after the sample when the rotation of the chest and abdomen, and ST36 is located at about 0.3 cm angle is 0, and h, is the Fresnel transmission factor, which below the tibial tuberosity, on the dorsolateral side of the can be written as hindlimb [12, 13]. The effective diameter of these acupuncture points in rabbits is about 5 mm(should be about 10 mm for hi(r,y)=[exp(ikz)/iz] exp[ir(x+y2)/az] (2) numans). Two samples were cut from RN3 and ST36 regions respectively. Each sample comprises a solid cylinder, with a height of approximately 1.2 cm and a diameter of 4.5 mm to Byrotating samples, we collect the IL-XPCT projection ensure that the samples are in the acupuncture point area. The data for every rotation angle 0 between 0o and 180. Then cut from the rN3 area is called sample A, and the we can use the filtered back-projection method to recon- cut from ST36 is called sample C. Samples without struct all IL-XPCT slices. Finally an internal structure any acupuncture point were taken at about 3 cm away from nage with edge enhancement of the sample obtained. Let f(x1, x2, x3) be the distribution function of RN3 and ST36. They are called sample B and sample D, respectively. Samples A, B, C, and D had almost the same he sample, and it can be written as size. All operative procedures related to animal care strictly conformed to the guidelines of the Chinese govemmer f(x,x2,x3)=/*ad (3) the intemational ethical guidelines for biomedical re were also abided by in our study Fig. 1 Layouts of the IL-XPCT system of the BL13W l80° rotation xperimental station, Shanghai Monochromator Synchrotron Radiation Facility (SSRF) springerimaging methods [8], grating-based phase contrast imaging methods [9], and in-line XPCT (IL-XPCT) methods [10]. In this work, IL-XPCT is mainly used. It is also known as propagation-based phase contrast CT. Because the synchrotron beam is sufficiently spatially coherent during the experiment, the setup of IL-XPCT is extremely simple and needs no adjustment except for the sample-to-detector distance. Methods and materials Principle of IL-XPCT and experimental setup The principles of IL-XPCT, which were described in detail elsewhere [11], are briefly reviewed here. When parallel coherent light with wavelength λ irradiates samples perpendicularly, in accordance with Fresnel diffraction theory, the plane wave goes through the samples, and the intensity distribution of the disturbed wave at the down￾stream distance Z can be written as IZ q ð Þ¼ x; y hZ»UZ q



; ð1Þ where the symbol * represents convolution, θ is the different IL-XPCT rotation angles, Uz q is the light complex amplitude distribution after the sample when the rotation angle is θ, and hz is the Fresnel transmission factor, which can be written as hzð Þ¼ x; y ½ expð Þ ikz =ilz exp ip x2 þ y2 =lz  : ð2Þ By rotating samples, we collect the IL-XPCT projection data for every rotation angle θ between 0° and 180°. Then we can use the filtered back-projection method to recon￾struct all IL-XPCT slices. Finally an internal structure image with edge enhancement of the sample can be obtained. Let f(x1, x2, x3) be the distribution function of the sample, and it can be written as f xð Þ¼ 1; x2; x3 Z p 0 I Z q » "dq; ð3Þ where ε is the IL-XPCT slices reconstruction filtered factor. Figure 1 shows our experimental arrangement. It consists of the specimen on a rotation stage, a monochromator, and a detector. Sample preparation All samples investigated were provided by the Anatomy Teaching and Research Section of the Second Military Medical University, Shanghai, China. We used New Zealand white rabbits to prepare our samples. After the adult rabbits were killed by a large dose of anesthetic, we injected 5% sodium citrate saline into the abdominal aorta for anticoagulation and to help empty the blood vessels. Then contrast agent comprising a mixed solution of barium sulfate and latex particles (their diameter is about several hundred nanometers) was injected into the abdominal aorta to make the blood vessels more highlighted in CT images. About 15 min later, samples were dissected from the rabbits and immersed in formalin for fixation. Two acupuncture points RN3 and ST36 were studied in this work. The Chinese name of RN3 is Zhongji, and that of ST36 is Zusanli. They are frequently used in acupuncture, and the acupuncture at these points shows distinct clinical effects. Their locations are well known. RN3 is located in the abdomen at 1/13 of the distance from the pubic symphysis joint to the joint of the chest and abdomen, and ST36 is located at about 0.3 cm below the tibial tuberosity, on the dorsolateral side of the hindlimb [12, 13]. The effective diameter of these acupuncture points in rabbits is about 5 mm (should be about 10 mm for humans). Two samples were cut from RN3 and ST36 regions respectively. Each sample comprises a solid cylinder, with a height of approximately 1.2 cm and a diameter of 4.5 mm to ensure that the samples are in the acupuncture point area. The sample cut from the RN3 area is called sample A, and the sample cut from ST36 is called sample C. Samples without any acupuncture point were taken at about 3 cm away from RN3 and ST36. They are called sample B and sample D, respectively. Samples A, B, C, and D had almost the same size. All operative procedures related to animal care strictly conformed to the guidelines of the Chinese Government and the international ethical guidelines for biomedical research were also abided by in our study. Fig. 1 Layouts of the IL-XPCT system of the BL13W experimental station, Shanghai Synchrotron Radiation Facility (SSRF) D. Zhang et al.