N144 with connective tissue structures, lymph vessels, capillaries and nerves. This structure is not only a carrier of ions and other materials but also transfers energies and messages between the cells(Langevin and Yandow 2002, Fei et al 1998). It has been found that there is a high level of Ca in acupuncture points by proton-induced x-ray emission(PIXE)(Dang et al 1997, Chen et al 1998). Although Ca is predominantly a skeletal element, a small proportion is found inside the cells and in extracellular fluid acting as a chemical messenger between the cells, controlling motion and metabolism( Greenberg 1997, Theobald 2005). These researches inferred that acupuncture points were special areas where metastable Ca was conserved for se in emergencies. In this note, we investigated the chemical elements Ca, Fe, Cu and Zn in their vicinity by synch fl (SXRF) analysis 2. Methods and materials We measured the characteristic x-ray emissions of Ca, Fe, Cu and Zn at four different acupuncture points and in the surrounding tissues. The x-ray fluorescence analysis method (XRF)has been widely used for the study of human tissue samples (Theodorakou and Farquharson 2008, Geraki et al 2004, Borjesson et al 1998). PIXE and SXRF are two important methods of analysis of tissue composition(Eugene 1975, Ma and Yang 2000, Zhao et al 1989). PIXE uses high energy protons as a radiation source. It has been used to measure the Ca content of acupuncture points and it was found that it was much higher than in adjacent tissues. In this note, SXRF was employed for non-destructive microanalysis of several trace metal elements. SXRF is the emission of a characteristic secondary(or fluorescent) x-ray from a material that has been excited by synchrotron radiation(Valkovic and Moschini 1993 Lobinski et al 2006). When a material is exposed to radiation with the energy greater than its ionization energy of component atoms, the radiation can expel tightly-held electrons from the inner orbitals (lower energies) of the atom. The electrons in higher energy levels'fall into the lower level. At the same time, energy releases in the form of a photon, whose energy is equal to the energy difference of the two levels involved. Thus, the radiation has energy which is characteristic of the atoms present. That is to say, the synchrotron x-ray beam excites the secondary x-ray from the elements in the sample at characteristic wavelengths. It is well known that the synchrotron radiation has many advantages, such as high intensity and broad energy range. Therefore, SXRF is particularly advantageous for dete oncentrations of various trace elements with the characteristic fluorescence x-ray being in a wide spectrum range We analyzed the SXRF spectrum of the characteristic fluorescence of several elements within the area of tissue exposed to the synchrotron beam using software AXIL (Van Espen et al 1989), in which the integrated intensities from each element were calculated and should be proportional to their concentrations Ni= kioi Ci where Ni is the integrated intensity of the ith element, Qi is the fluorescent yield, Ci is the concentration of the ith element and ki is a constant depending on the experimental conditions. ince several elements were measured simultaneously, the parameter k; can be considered constant. Hence, Ci: Ci: Ck= Ni/Qi: Ni/Q;: Nk/Qk, where i,j and k denote different elements. Consequently, the ratios of different integrated intensities from the ith, jth and kth elements corrected for their fluorescent yields can be used to derive the relative ratios of the content of the corresponding elementN144 X Yan et al with connective tissue structures, lymph vessels, capillaries and nerves. This structure is not only a carrier of ions and other materials but also transfers energies and messages between the cells (Langevin and Yandow 2002, Fei et al 1998). It has been found that there is a high level of Ca in acupuncture points by proton-induced x-ray emission (PIXE) (Dang et al 1997, Chen et al 1998). Although Ca is predominantly a skeletal element, a small proportion is found inside the cells and in extracellular fluid, acting as a chemical messenger between the cells, controlling motion and metabolism (Greenberg 1997, Theobald 2005). These researches inferred that acupuncture points were special areas where metastable Ca was conserved for use in emergencies. In this note, we investigated the chemical elements Ca, Fe, Cu and Zn in acupuncture points and in their vicinity by synchrotron x-ray fluorescence (SXRF) analysis. 2. Methods and materials We measured the characteristic x-ray emissions of Ca, Fe, Cu and Zn at four different acupuncture points and in the surrounding tissues. The x-ray fluorescence analysis method (XRF) has been widely used for the study of human tissue samples (Theodorakou and Farquharson 2008, Geraki et al 2004, Borjesson ¨ et al 1998). PIXE and SXRF are two important methods of analysis of tissue composition (Eugene 1975, Ma and Yang 2000, Zhao et al 1989). PIXE uses high energy protons as a radiation source. It has been used to measure the Ca content of acupuncture points and it was found that it was much higher than in adjacent tissues. In this note, SXRF was employed for non-destructive microanalysis of several trace metal elements. SXRF is the emission of a characteristic secondary (or fluorescent) x-ray from a material that has been excited by synchrotron radiation (Valkovic and Moschini 1993, Lobinski et al 2006). When a material is exposed to radiation with the energy greater than its ionization energy of component atoms, the radiation can expel tightly-held electrons from the inner orbitals (lower energies) of the atom. The electrons in higher energy levels ‘fall’ into the lower level. At the same time, energy releases in the form of a photon, whose energy is equal to the energy difference of the two levels involved. Thus, the radiation has energy which is characteristic of the atoms present. That is to say, the synchrotron x-ray beam excites the secondary x-ray from the elements in the sample at characteristic wavelengths. It is well known that the synchrotron radiation has many advantages, such as high intensity and broad energy range. Therefore, SXRF is particularly advantageous for determining very low concentrations of various trace elements with the characteristic fluorescence x-ray being in a wide spectrum range. We analyzed the SXRF spectrum of the characteristic fluorescence of several elements within the area of tissue exposed to the synchrotron beam using software AXIL (Van Espen et al 1989), in which the integrated intensities from each element were calculated and should be proportional to their concentrations: Ni = kiQiCi, where Ni is the integrated intensity of the ith element, Qi is the fluorescent yield, Ci is the concentration of the ith element and ki is a constant depending on the experimental conditions. Since several elements were measured simultaneously, the parameter ki can be considered constant. Hence, Ci : Cj : Ck = Ni/Qi :Nj /Qj :Nk/Qk, where i, j and k denote different elements. Consequently, the ratios of different integrated intensities from the ith, jth and kth elements corrected for their fluorescent yields can be used to derive the relative ratios of the content of the corresponding element