Synchrotron radiation phase-contrast X-ray CT imaging igures 4a(1) and (2)are two of the IL-XPCt areas are higher than those in the surrounding tissues, and reconstruction slices of sample A and reveal some the vascular density(Aa Gg%)is also much higher than interesting findings. The first, supported by what can be that in the surrounding tissues, indicating that there is an seen in the tomographic image slices, is the contrast accumulation of microvessels in these two acupuncture between the various tissue distributions through the points areas differences of the tissue's absorptivity. Although such differentiation is usually impossible to observe based on 2D scans, our methods easily clarify these small Conclusions differences in the sample. The second observa hich can be seen from the comparison of two IL- In summary, 3D imaging of acupuncture points was XPCT reconstructed slices, is that the diameters of the successfully performed by using IL-XPCT with synchrotron blood vessels (the white dots denoted by arrows are radiation. The 3D structures of acupuncture points have surely the cross sections of vessels) are different and the been shown with a spacial resolution of about 15 um. The distribution of them is irregular in these two slices, but accumulation of microvessels in acupuncture point regions the details are not explicit in this figure and will be is a clear characteristic, which cannot be seen in the discussed below surrounding tissues. Figures 4a(3)and b(3) show 3D renderings of the reconstructed volume data set of sample A and the non- Acknowledgements This work ported by the National Basic acupuncture point sample B for comparison. Most of the Research Program of China(no 2006CB504509)and the Project of structures, which cannot be seen in the slice images, are the State Key Program of the National Science Foundation of China ( Grant no. 10635060). We also would like to thank the staff of SSRF visible in the IL-XPCT images, including very thin hairs. BL13W for technical support and their help in treatment of IL-XPCT For example, some long blood vessels surrounded by lots images of fine branches in sample A can be seen(Fig 4a(3). The largest blood vessel, with a diameter of about 50 um (denoted by the black arrow), is the artery. The fine branches vessels, whose diameter varies from approximate- References ly 15 to 40 um, are the venule or the microvessels(denoted by the white arrow). But in the non-acupuncture point area 1. Zhang Y, Yan XH, Liu CL et al(2006)Photoluminescence of ( Fig. 4b (3)), there are only some big blood vessels(pointed acupuncture pointWaiqiu'"in human superficial fascia. J Lumin out by the black arrows) with a few microvessels(pointed 19-120:969 out by the white arrow) 2. Yan XH, Zhang XY, Liu CL et al (2009)Do acupuncture points exist? Phys Med Biol 54(9): N143-N150 Figures 4c and d show the 3D IL-XPCT images of 3. Andrew CA, Min P, Jessica RS et al(2010) Electrical impedance another sample ST36 and corresponding compared sur- of acupuncture meridians: the relevance of subcutaneous collag- rounding tissues. As shown in Figs. 4a and milar enous bands. PLoS ONE 5(7): e11907 accumulations of microvessels can be seen 4. Langevin HM, Yandow JA (2002)Relationship of acupuncture points and meridians to connective tissue planes. Anat Rec 269 diameter also varies by several tens of microns. (6):257-265 In order to quantitatively determine the vascular 5. Fitzgerald R(2000) Phase-sensitive x-ray imaging. Phys Today accumulation in the acupuncture point regions and the 53:23-27 surrounding tissues, the comparative vascular distribution 6. Momose A(2005)Recent advances in x-ray phase imaging. Jpn J Appl Phys 44: 6355-6359 area(Aa%)and comparative average gray-scalee value 7. Mosose A(1995) Demonstration of phase-contrast X-ray com- (Gg%) of Fig. 3 were calculated by computer image puted tomography using an X-ray interferometer. Nucl Instrum analysis. The ratio of the vascular area to acupuncture Methods Phys Res A 352(3): 622-628 point area represents the comparative vascular distribution 8. Dilmanian FA, Zhong Z, Ren B et al (2000) Computed tomography of x-ray index of refraction using the diffraction area,and the ratio of the vascular area average gray-scale enhanced imaging method. Phys Med Biol 45(4): 933-946 value to acupuncture point area average gray-scale value 9. Pfeiffer F, Kottler C, Bunk O, David C(2007) Hard X-ray phase represents the comparative average gray-scale value. tomography with low-brilliance sources. Phys Rev Lett 98 we used 10 l08105 Raven C, Snigirev A, Snigireva I et al (1996)Phase-contrast Aa Gg% to represent the vascular 8].The microtomography with coherent high-energy synchrotron x rays. calculated results are collected in 物时 1. and the Appl Phys Lett 69(13): 1826-1828 uncertainties are also given I1. Spanne P, Raven C, Snigireva I, Snigirev A (1999) 由bh From Table 1, we can clearly see that both holography and phase-contrast microtomography wit ergy x-rays. Phys Med Biol 44: 741 omparative distribution area(Aa%)and comparative 12. Shen XY, Wang H(1999) Acupuncture and Moxibustion. People's average gray-scale value(Gg%)in the acupuncture point Medical Publishing House, Beijing, p 311 and 372 SpringFigures 4a(1) and (2) are two of the IL-XPCT reconstruction slices of sample A and reveal some interesting findings. The first, supported by what can be seen in the tomographic image slices, is the contrast between the various tissue distributions through the differences of the tissue’s absorptivity. Although such differentiation is usually impossible to observe based on X-ray 2D scans, our methods easily clarify these small density differences in the sample. The second observa￾tion, which can be seen from the comparison of two IL￾XPCT reconstructed slices, is that the diameters of the blood vessels (the white dots denoted by arrows are surely the cross sections of vessels) are different and the distribution of them is irregular in these two slices, but the details are not explicit in this figure and will be discussed below. Figures 4a(3) and b(3) show 3D renderings of the reconstructed volume data set of sample A and the non￾acupuncture point sample B for comparison. Most of the structures, which cannot be seen in the slice images, are visible in the IL-XPCT images, including very thin hairs. For example, some long blood vessels surrounded by lots of fine branches in sample A can be seen (Fig. 4a(3)). The largest blood vessel, with a diameter of about 50 μm (denoted by the black arrow), is the artery. The fine branches vessels, whose diameter varies from approximate￾ly 15 to 40 μm, are the venule or the microvessels (denoted by the white arrow). But in the non-acupuncture point area (Fig. 4b(3)), there are only some big blood vessels (pointed out by the black arrows) with a few microvessels (pointed out by the white arrow). Figures 4c and d show the 3D IL-XPCT images of another sample ST36 and corresponding compared sur￾rounding tissues. As shown in Figs. 4a and b, similar accumulations of microvessels can be seen and their diameter also varies by several tens of microns. In order to quantitatively determine the vascular accumulation in the acupuncture point regions and the surrounding tissues, the comparative vascular distribution area (Aa%) and comparative average gray-scalee value (Gg%) of Fig. 3 were calculated by computer image analysis. The ratio of the vascular area to acupuncture point area represents the comparative vascular distribution area, and the ratio of the vascular area average gray-scale value to acupuncture point area average gray-scale value represents the comparative average gray-scale value. Taking both Aa% and Gg% into account, we used Aa Gg% to represent the vascular density [18]. The calculated results are collected in Table 1, and the uncertainties are also given. From Table 1, we can clearly see that both the vascular comparative distribution area (Aa%) and comparative average gray-scale value (Gg%) in the acupuncture point areas are higher than those in the surrounding tissues, and the vascular density (Aa Gg%) is also much higher than that in the surrounding tissues, indicating that there is an accumulation of microvessels in these two acupuncture points areas. Conclusions In summary, 3D imaging of acupuncture points was successfully performed by using IL-XPCT with synchrotron radiation. The 3D structures of acupuncture points have been shown with a spacial resolution of about 15 μm. The accumulation of microvessels in acupuncture point regions is a clear characteristic, which cannot be seen in the surrounding tissues. Acknowledgements This work was supported by the National Basic Research Program of China (no. 2006CB504509) and the Project of the State Key Program of the National Science Foundation of China (Grant no. 10635060). We also would like to thank the staff of SSRF BL13W for technical support and their help in treatment of IL-XPCT images. References 1. Zhang Y, Yan XH, Liu CL et al (2006) Photoluminescence of acupuncture point “Waiqiu” in human superficial fascia. J Lumin 119–120:96–99 2. Yan XH, Zhang XY, Liu CL et al (2009) Do acupuncture points exist? Phys Med Biol 54(9):N143–N150 3. Andrew CA, Min P, Jessica RS et al (2010) Electrical impedance of acupuncture meridians: the relevance of subcutaneous collag￾enous bands. PLoS ONE 5(7):e11907 4. Langevin HM, Yandow JA (2002) Relationship of acupuncture points and meridians to connective tissue planes. Anat Rec 269 (6):257–265 5. Fitzgerald R (2000) Phase-sensitive x-ray imaging. Phys Today 53:23–27 6. Momose A (2005) Recent advances in x-ray phase imaging. Jpn J Appl Phys 44:6355–6359 7. Mosose A (1995) Demonstration of phase-contrast X-ray com￾puted tomography using an X-ray interferometer. Nucl Instrum Methods Phys Res A 352(3):622–628 8. Dilmanian FA, Zhong Z, Ren B et al (2000) Computed tomography of x-ray index of refraction using the diffraction enhanced imaging method. Phys Med Biol 45(4):933–946 9. Pfeiffer F, Kottler C, Bunk O, David C (2007) Hard X-ray phase tomography with low-brilliance sources. Phys Rev Lett 98: 108105 10. Raven C, Snigirev A, Snigireva I et al (1996) Phase-contrast microtomography with coherent high-energy synchrotron x rays. Appl Phys Lett 69(13):1826–1828 11. Spanne P, Raven C, Snigireva I, Snigirev A (1999) In-line holography and phase-contrast microtomography with high energy x-rays. Phys Med Biol 44:741 12. Shen XY, Wang H (1999) Acupuncture and Moxibustion. People’s Medical Publishing House, Beijing, p 311 and 372 Synchrotron radiation phase-contrast X-ray CT imaging