research papers 1030 # 2001 International Union of Crystallography  Printed in Great Britain ± all rights reserved J. Synchrotron Rad. (2001). 8, 1030±1034 Preliminary experiment of ¯uorescent X-ray computed tomography to detect dual agents for biological study Quanwen Yu, a,b Tohoru Takeda, a * Tetsuya Yuasa, b Yasuhiro Hasegawa, b Jin Wu, a Thet-Thet-Lwin, a Kazuyuki Hyodo, c F. Avraham Dilmanian, d Yuji Itai a and Takao Akatsuka b a Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan, b Faculty of Engineering, Yamagata University, Yonezawa, Yamagata 992-8510, Japan, c Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305, Japan, and d Medical Department, Brookhaven National Laboratory, Upton, NY 11973, USA. E-mail: ttakeda@md.tsukuba.ac.jp The simultaneous observation of various information, such as blood ¯ow, tissue metabolism and distribution of receptors, is quite important in order to understand the functional state of biomedical objects. The simultaneous detectability of contrast agents by ¯uorescent X-ray computed tomography (FXCT) with synchrotron radiation is examined in this study. The system consisted of a silicon (111) double-crystal monochromator, an X-ray slit system, a scanning table, a PIN diode, a highly puri®ed germanium detector and an X-ray charge-coupled device (CCD) camera. The monochromatic X-ray beam energy was adjusted to 37.0 keV and collimated into a pencil beam of 1  1 mm. The ¯uorescent spectra of the K lines for iodine and xenon were detected simultaneously. FXCT could image the distribution of both iodine and xenon agents in a phantom clearly and the contrast ratio was signi®cantly better than that of transmission X-ray computed tomography images. Keywords: ¯uorescent X-rays; computed tomography; iodine; xenon; multi-agents simultaneous detection. 1. Introduction In order to detect very low contents of nonradioactive speci®c materials without making slices of samples, ¯uorescent X-ray tomo- graphy (Cesareo & Mascarenhas, 1989; Takeda et al., 1995; Takeda, Maeda et al., 1996) and ¯uorescent X-ray computed tomography (FXCT) (Boisseau & Grodzins, 1987; Takeda, Akiba et al., 1996; Takeda et al., 1997, 1998, 1999) are being developed. The basic theoretical consideration of FXCT was presented by Hogan et al. (1991) and practical reconstruction methods of FXCT have been applied recently (Yuasa et al., 1997a; Rust & Weigelt, 1998). Using FXCT with synchrotron radiation, iodine contrast material ®lled in a phantom was clearly imaged (Takeda, Akiba et al., 1996; Takeda et al., 1997) as a result of the linear-polarized nature of synchrotron radiation (Iida & Gohshi, 1991). So, for living objects, FXCT is considered as an alternative approach to radioactive examinations with single photon emission computed tomography (SPECT). Thus there are two perspectives for the application of FXCT with synchrotron radiation, i.e. the imaging of living objects (Takeda, Akiba et al., 1996; Takeda et al., 1997; Akiba et al., 1997) and the micro-imaging of pathological objects (Takeda et al., 2000, 2001) and materials (Simionovici et al., 1999; Vincze et al. , 1999). In biomedical studies, various kinds of radionuclide agent are used to gather information about an organ, such as blood ¯ow, ischemic state, drug distribution, metabolism, receptor function and apotosis. For example, cerebral blood ¯ow and the density of cerebral cells can be evaluated quantitatively by using radioactive Xe-133 gas and I-123 Iomazenil (ethyl 5,6-dihydro-7-iodo-5-methyl-6-oxo-4H-imidazo[1,5- a][1,4]benzodiazepine-3-carboxylate), respectively. However, each type of information is usually obtained by a separate examination. In FXCT, images can be obtained from one examination by selecting the ¯uorescent K line of the elements, so that the simultaneous detec- tion of multi-agents is possible. In this paper, the possibility of simultaneous multi-agent detection by FXCT is examined using a phantom ®lled with nonradioactive xenon gas and iodine solution; the FXCT images are compared with transmission X-ray computer tomography (TXCT) images. 2. Materials and methods 2.1. Fluorescent X-ray computer tomography system with synchrotron radiation The FXCT system was constructed at the bending-magnet beam- line of BLNE-5A of the Tristan Accumulation Ring (6.5GeV, 10± 30 mA) of the High Energy Accelerator Research Organization, Tsukuba, Japan. The system consisted of a silicon (111) double- crystal monochromator, an X-ray slit system, a scanning table, a highly puri®ed germanium (HPGe) detector with a parallel colli- mator, a rotating X-ray shutter, an X-ray CCD camera, a PIN diode, and computer system (Fig. 1). Fluorescent X-rays were detected by the HPGe detector, whereas transmission X-rays were detected by the CCD camera. 2.1.1. X-ray energy selection and the formation of a pencil beam. The white X-ray beam was monochromated at 37.0 keV using a silicon double-crystal monochromator. The size of the incident monochro- matic X-ray beam was 65  3 mm (width and height, respectively). To make a pencil beam, the incident monochromatic X-ray was colli- mated into a 1.0  1.0 mm beam (horizontal and vertical directions, respectively) using a tantalum X-ray slit (Kohzu Ltd, Japan). 2.1.2. Fluorescent X-ray detector. The ¯uorescent X-rays were detected by a highly puri®ed germanium detector (LO-AXTH Series, EG&G Ortec Ltd, USA). It was operated in a photon-counting mode. The energy resolution was about 700 eV with a shaping time of 2 ms at 30 keV. The active area of detection of HPGe was 51.2 mm in diameter. The detected energy spectrum was digitized by a DSPEC spectrum master (EG&G Ortec Ltd, USA). 2.1.3. Transmission X-ray detector. The transmission X-ray detector was a ®bre-optically interfaced X-ray CCD camera cooled by a Peltier thermoelectric cooling device (238 K) (Princeton Instruments Ltd, USA). The X-ray CCD camera had 1240  1024 pixels with a pixel size of 22.5  22.5 mm. Data were digitized in a 16-bit analog-to- digital converter (ADC). The dynamic range of this detector was about 60000:1. An X-ray shutter was set in front of the X-ray CCD camera to prevent radiation damage. The CCD camera was driven by a controller (Princeton Instruments ST-138) and the data were read into a personal computer (PC) (Dimension, Dell Ltd, USA). The readout timings of the CCD camera and X-ray shutter were synchronized with the trigger pulses generated by the pulse motor controller. 2.1.4. PIN diode. The monochromatic X-ray intensity declined exponentially owing to the decrease of the ring current; hence the change of monochromatic X-ray intensity was measured by a PIN diode operated in the current-integration mode by a picoammeter