439 Research Article Received: 20 January 2009 Revised: 2 April 2009 Accepted: 19 April 2009 Published online in Wiley Interscience: 28 May 2009 (www.interscience.com) DOI 10.1002/xrs.1190 First experimental result with fluorescent X-ray CT based on sheet-beam geometry Qingkai Huo, a* Hidenori Sato, a Tetsuya Yuasa, a Takao Akatsuka, a Jin Wu, b Thet-Thet Lwin, b Tohoru Takeda b and Kazuyuki Hyodo c Fluorescent X-ray computed tomography (FXCT) enables us to reveal the cross-sectional distribution of very low concentration of specific elements, e.g. I, Gd, or Au, in biomedical samples at a spatial resolution of several hundred micrometers, and it has been used to evaluate the states of cerebral perfusion and fatty acid metabolic function of small animals in vivo and ex vivo. However, since the current system employs the data-acquisition scheme of the first-generation type of CT, it requires a huge amount of time to obtain a whole set of projections. In order to overcome the problem, we propose a novel imaging geometry using a sheet incident beam. We performed a proof-of-concept experiment using a preliminary imaging system constructed at beam line BLNE-5A, KEK. The efficacy of the proposed method is demonstrated by the reconstructed images of a physical phantom containing various concentrations of iodine solution and a mouse brain that is extracted after intravenous injection of 127 I-IMP for observing the cerebral perfusion and then fixed with formalin. Copyright c  2009 John Wiley & Sons, Ltd. Introduction In recent biomedical research, nuclear imaging techniques such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) are very important tools to investigate the cause, diagnosis and therapy of diseases from the molecular viewpoint. [1–4] However, these techniques suffer from insufficient spatial resolution. Therefore, the invention of novel molecular imaging techniques with high contrast and high spatial resolutions has been eagerly awaited. X-ray fluorescence analysis (XRF) is a physicochemical analysis method to identify trace elements with high sensitivity by detecting the fluorescent X-rays emitted from them. Use of synchrotron X-rays as the light source empowers it to detect trace elements with much higher sensitivity, because synchrotron X-rays have some excellent properties for XRF. [5–8] In addition, combining XRF with the computed tomography technique enables us to establish a low-invasive or nondestructive cross-sectional imaging method for biomedical use at high sensitivity and high spatial resolution. [8 – 16] So far, we have developed the first generation of fluorescent X-ray computed tomography(FXCT) imaging system to collect fluorescent photons emitted from iodine using a thin incident beam. [17 – 25] A schematic diagram of the experimental setup is shown in Fig. 1. A white X-ray beam from a source is monochromatized using a Si-plate monochromator and is collimated into a thin beam using slits in front of the sample. The thin incident beam impinges on a sample placed on translational and rotational stages. Fluorescent X-ray photons are emitted isotropically from the iodine atoms along the incident beam, with intensity proportional to the product of the iodine concentration and the incident X-ray flux rate. The fluorescent photons are acquired with an energy- resolving detector such as a high-purity germanium solid-state detector (HPGe SSD), which is positioned perpendicular to the incident monochromatic X-ray beam for maximally reducing the Compton-scattered photons. Projection data for CT are generated by summing the net photon counts in an energy window of about 2 keV in width, whose center corresponds to the iodine Kα fluorescent line of 28.3 keV. For acquiring a single projection, the sample is translationally scanned at constant steps. Afterwards, the sample is rotated at constant angular steps. The data collection is repeated over 180 ◦ . That is, the data acquisition scheme follows the scanning protocol of the first generation of CT. So far, we have successfully imaged various kinds of biological samples both ex vivo and in vivo. [17 – 27] As for in vivo imaging, FXCT has a problem: the conventional FXCT takes a huge amount of measurement time to acquire a single tomographic image because it adopts the sequential data collection scheme with a pencil beam, which is the first generation of data acquisition scheme in CT. Although it is desirable to collect as much data as possible for a high-quality image, the whole measurement must be completed under anesthesia and then the number of data points is severely restricted. Therefore, we have not yet attained the potential spatial resolution for in vivo imaging. In this paper, in order to solve the problem of measurement time, we propose a parallel data collection method using a sheet- beam geometry with a linear array of detectors. We performed a proof-of-concept experiment using a preliminary imaging system. The efficacy of the proposed method is demonstrated by the reconstructed images of a physical phantom and an extracted mouse brain. ∗ Correspondence to: Qingkai Huo, Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Japan. E-mail: qingkai@post.kek.jp a Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Japan b Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tenoudai, Tsukuba, Japan c High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Japan X-Ray Spectrom. 2009, 38, 439–445 Copyright c  2009 John Wiley & Sons, Ltd.