羽石 秀昭

One of the challenging applications of PET is for in-beam PET, which is an in situ monitoring method for charged particle therapy. For this purpose, we have previously proposed an open-type PET scanner, OpenPET. The original OpenPET has a physically opened field-of-view (FOV) between two detector rings which irradiation beams pass through. This dual-ring OpenPET has a wide axial FOV including the gap. Therefore this geometry is not necessarily the most efficient when it is applied to in-beam PET in which only a limited FOV around the irradiation field is required. In this paper, we proposed new single-ring OpenPET geometry as more efficient geometry dedicated to in-beam PET. The detector ring of the proposed geometry is a cylinder both ends of which are cut by parallel aslant planes. The proposed geometry can be made compact so that the beam port can be placed close to the patient. © 2011 IEEE.

The use of circulant matrix as the sensing matrix in compressed sensing (CS) scheme has recently been proposed to overcome the limitation of random or partial Fourier matrices. Aside from reducing computational complexity, the use of circulant matrix for magnetic resonance (MR) image offers the feasibility in hardware implementations. This paper presents the simulation of compressed sensing for thoracic MR imaging with circulant matrix as the sensing matrix. The comparisons of reconstruction of three different type MR images using circulant matrix are investigated in term of number of samples, number of iteration and signal to noise ratio (SNR). The simulation results showed that circulant matrix works efficiently for encoding the MR image of respiratory organ, especially for smooth and sparse image in spatial domain. © 2012 Universitas Ahmad Dahlan.

The OpenPET and its real-time imaging capability have great potential for real-time tumor tracking in medical procedures such as biopsy and radiation therapy. For the real-time imaging system, we intend to use the one-pass list-mode dynamic row-action maximum likelihood algorithm (DRAMA) and implement it using general-purpose computing on graphics processing units (GPGPU) techniques. However, it is difficult to make consistent reconstructions in real-time because the amount of list-mode data acquired in PET scans may be large depending on the level of radioactivity, and the reconstruction speed depends on the amount of the list-mode data. In this study, we developed a system to control the data used in the reconstruction step while retaining quantitative performance. In the proposed system, the data transfer control system limits the event counts to be used in the reconstruction step according to the reconstruction speed, and the reconstructed images are properly intensified by using the ratio of the used counts to the total counts. We implemented the system on a small OpenPET prototype system and evaluated the performance in terms of the real-time tracking ability by displaying reconstructed images in which the intensity was compensated. The intensity of the displayed images correlated properly with the original count rate and a frame rate of 2 frames per second was achieved with average delay time of 2.1 s.

放射線治療のひとつである粒子線がん治療は深部のがんにも線量を集中させることができる.この粒子線がん治療の特徴を最大限に活かすために,治療計画通りの位置に照射できているかどうかをPET (Positron Emission Tomography)の方法を応用して画像化することが望まれている.放射線医学総合研究所ではがん診断・治療の融合を目的とした開放型PET装置「OpenPET」の開発を進めている.本研究では新たなOpenPET装置"Single-ring OpenPET"を提案する.Single-ring OpenPETは円筒を斜めに切断したような形状をしており,治療ビームが通過する開放領域を有する.特に装置を設計する際に長方形状の検出器ブロックの配置方法の検討が必要である.本研究では2つの配置方法を提案する.1つは検出器ブロックを楕円上に配置した検出器リングを斜めに並べる方法である.もう1つは従来PET装置と同様に検出器を円形リング状に並べ,各ブロックを体軸方向へ少しずつずらして配置する方法である.それぞれの配置方法でどのような再構成画像が得られるのか計算機シミュレーションで検討した結果,いずれの配置方法も良好な再構成画像を得ることができた.

The world's first open type PET, named OpenPET, is being developed at the National Institute Radiological Sciences. We are aiming to employ the OpenPET in radiotherapy and to track the respiratory motion of a tumor in the thoracoabdominal region of a patient. By using PET images, we expect that the tumor itself can be directly visualized without using radio-opaque markers, but this goal has not been achieved yet. Our demonstration results using a small prototype OpenPET system showed that the system can output reconstructed images at about 2 frames per second with about a 2 s delay this delay is mainly due to the reconstruction calculation time. In this study, we developed a time delay correction method for tumor tracking for the OpenPET. Since it is difficult to correct the time delay using only the tumor location 2 s before, we introduced another sensor to acquire the respiration phase for correction. In the proposed method, the relationship between tumor motion and the additional sensor output signal was calculated by support vector regression (SVR) and the time delay was corrected by using the regression line which represents the relationship. We simulated this time delay correction method with computer-generated PET images which had practical respiration motions obtained from clinical MRI. As a result, we could track the tumor within almost 1.5 mm mean error when we assumed the use of a belt type respiratory motion sensor. We also found from the simulation that disturbance of the relationship can be detected by gates. Thus we could avoid the tracking errors which are caused by disturbance of the correlation. © 2012 IEEE.

The world's first open type PET, named OpenPET, is being developed at the National Institute Radiological Sciences. We are aiming to employ the OpenPET in radiotherapy and to track the respiratory motion of a tumor in the thoracoabdominal region of a patient. By using PET images, we expect that the tumor itself can be directly visualized without using radio-opaque markers, but this goal has not been achieved yet. Our demonstration results using a small prototype OpenPET system showed that the system can output reconstructed images at about 2 frames per second with about a 2 s delay this delay is mainly due to the reconstruction calculation time. In this study, we developed a time delay correction method for tumor tracking for the OpenPET. Since it is difficult to correct the time delay using only the tumor location 2 s before, we introduced another sensor to acquire the respiration phase for correction. In the proposed method, the relationship between tumor motion and the additional sensor output signal was calculated by support vector regression (SVR) and the time delay was corrected by using the regression line which represents the relationship. We simulated this time delay correction method with computer-generated PET images which had practical respiration motions obtained from clinical MRI. As a result, we could track the tumor within almost 1.5 mm mean error when we assumed the use of a belt type respiratory motion sensor. We also found from the simulation that disturbance of the relationship can be detected by gates. Thus we could avoid the tracking errors which are caused by disturbance of the correlation. © 2012 IEEE.

We propose a VR based injection training system using Standardized Patient (SP) with an original haptic needle which can represent a haptic expression. SP is trained to realistically portray a real patient. In the proposed system, trainee can virtually puncture the SP using the haptic needle. In addition, the haptic needle can represent a haptic expression of needle insertion of the virtual anatomical model. By using the proposed system, trainee can feel virtual puncture as well as operating for real patient. © 2012 The authors and IOS Press. All rights reserved.

Lung motion due to respiration causes image degradation in medical imaging, especially in nuclear medicine which requires long acquisition time. We have developed a method for image correction between the respiration-gated (RG) PET images in different respiration phases or breath-hold (BH) PET images in inconsistent respiration phase. In the method, the RG or BH PET images in different respiration phase are deformed under two criteria similarity of image density distribution and smoothness of estimated motion vector field (MVF). However, only these criteria may cause un-natural motion estimation of lung. In this paper, assuming the use of a PET-CT scanner, we add another criterion that is the similarity to the motion direction estimated from inhalation and exhalation CT images. The proposed method was applied to XCAT phantom image data and seven patients' BH-PET image data. Successful registration results were obtained by the proposed method. © 2011 IEEE.

We propose a VR-based injection training system using Simulated Patient (SP) with an original haptic needle which can represent a haptic expression. SP is trained to realistically portray a real patient. In order to increase a realistic sensation and effect of training, it is important to train with real human. Therefore we propose a new training system which fuse SP and virtual training system. In the proposed system, trainee can virtually puncture the SP using the haptic needle. In addition, the haptic needle can represent a haptic expression of needle insertion of the virtual anatomical model. We developed the haptic needle which can represent a reaction force of puncturing. A reaction force of needle insertion is generated by clipping needle by using computer-controlled electromagnet and permanent magnet, and then a friction force is accrued. By using the proposed system, trainee can feel virtual puncture as well as operating for real patient.

The OpenPET geometry is our new idea to visualize a physically opened space between two detector rings. In this paper, we developed the first small prototype to show a proof-of-concept of OpenPET imaging. Two detector rings of 110 mm diameter and 42 mm axial length were placed with a gap of 42 mm. The basic imaging performance was confirmed through phantom studies; the open imaging was realized at the cost of slight loss of axial resolution and 24% loss of sensitivity. For a proof-of-concept of PET image-guided radiation therapy, we carried out the in-beam tests with C-11 radioactive beam irradiation in the heavy ion medical accelerator in Chiba to visualize in situ distribution of primary particles stopped in a phantom. We showed that PET images corresponding to dose distribution were obtained. For an initial proof-of-concept of real-time multimodal imaging, we measured a tumor-inoculated mouse with F-18-FDG, and an optical image of the mouse body surface was taken during the PET measurement by inserting a digital camera in the ring gap. We confirmed that the tumor in the gap was clearly visualized. The result also showed the extension effect of an axial field-of-view (FOV); a large axial FOV of 126 mm was obtained with the detectors that originally covered only an 84 mm axial FOV. In conclusion, our initial imaging studies showed promising performance of the OpenPET.

X'tal cube is a next generation DOI detector for PET with high resolution and sensitivity that we are developing. It is constructed from a cubic scintillation crystal and silicon photomultipliers (SiPMs) coupled on various positions of six surfaces of the cube. A laser processing technique is applied to produce 3D optical boundaries composed of micro-cracks inside a monolithic scintillator crystal. In this paper, in order to design optical characteristics properly, we developed a Monte Carlo simulator which is able to arrange laser-processed optical boundaries (LPB) arbitrarily. Optical characteristics of LPB were measured using a set of laser and photo-diode and then modeled for simulator. Effectiveness of the simulator was confirmed from a comparison with the experiment using a cubic LYSO monolithic crystal with 6 x 6 x 6 segments. Furthermore, the simulator was accelerated by parallel computing with a general purpose GPU (GPGPU). Calculation speed with GPGPU was 350 to 430 times faster than that with only CPU. © 2011 IEEE.

The X'tal cube is our new PET detector which is composed of a segmented crystal block and multi-pixel photon counters (MPPCs). It detects scintillation photons in three dimensions by arranging MPPCs on multiple surfaces of the crystal block. It is possible to collect scintillation photons efficiently for higher energy, spatial, and timing resolution. We have previously reported that 3 mm isotropic spatial resolution was obtained using the X'tal cube. In this study, we achieved 1 mm isotropic spatial resolution. The developed X'tal cube detector was composed of 1.0 1.0 1.0 mm3 LYSO crystals, which were structured into 16 16 16 arrays. Each surface of the crystal block was covered with 44 MPPCs with 3.0 mm 3.0 mm sensitive area. We evaluated crystal identification and energy performance, and the results showed that the X'tal cube has the expected 1 mm isotropic spatial resolution. © 2010 IEEE.

In diagnosis and treatment of knee joint diseases, it is effective to study the three-dimensional (3D) motion of the patient's knee joint involving the femur, tibia, and patella. A 2D/3D registration method with use of fluoroscopy and CT images is promising for this purpose. However, there is no report showing whether the dynamic 3D motion of the patella can be obtained. In this study, we tried to examine dynamic 3D motion of the knee joint which included the patella. First, in order to investigate the accuracy of the position estimation, we conducted an experiment on a pig knee joint which had several fiducial markers placed on it, and we found that errors in the estimation of rotation and translation were less than 1 mm and 1 deg. We then carried out an image-acquisition experiment with healthy knee joints of three volunteers and confirmed that 3D motions of the femur, tibia, and patella were successfully obtained for all cases. © 2010 Japanese Society of Radiological Technology and Japan Society of Medical Physics.

We have previously developed a method that combines a mini gamma camera with an optical camera to synthesize the two kinds of images and help surgeons to easily identify sentinel lymph nodes on the gastric surface in cancer resection surgery. Since we assumed in this method that the object surface is flat, its application was limited. In this article, we extend this method so as to estimate the three-dimensional shape of the object from stereo optical cameras. A prototype system with a mini gamma camera and two optical cameras was constructed and a preliminary experiment with a rigid machine-made phantom was performed. From comparison with results obtained by the previous method, we confirmed the effectiveness of using the three-dimensional shape.

胸部の3次元動態を解析することは、慢性閉塞性肺疾患など呼吸機能に深くかかわる疾患の診断や治療に有用である。そこで我々は以前、MRIを用いた胸腹部の立体画像の時系列データ、すなわち4次元画像の構築法を考案した。本論文では、4次元MR画像を用いた呼吸に伴う胸部動態の解析方法として、横隔膜機能画像の生成について示す。具体的には、呼吸による動きがもっとも大きく、呼吸の特徴が顕著に現れる横隔膜に注目し、4次元MR画像から横隔膜を抽出して、横隔膜の変位量と変位スピードを可視化する手法を提案する。横隔膜表面の抽出は、はじめに時系列第1フレームの3次元画像についてマニュアルで行い、次にこの表面を正規化相互相関を用いて時系列に追跡していく。また可視化は、横隔膜の体軸方向の変位量と変位スピードを疑似カラーマップ化することによって行う。健常者、患者を含む6例のデータに適用したところ、被験者間、また部位ごとの相違を視覚的に確認することができ、その有用性が示唆された。(著者抄録)

今年度よりスタートした文科省・科研費・新学術領域「計算解剖学」の達成目標や期待される成果について、領域のメンバーおよび領域メンバー以外の研究者により討論を行う。

A method is proposed in which the locations and electric current vectors of multiple biomagnetic current dipoles can be estimated without a priori information regarding the exact number of dipoles. In this method, an additional constraint is used in the cost function in conjunction with a constraint regarding degree of matching between estimated dipole parameters and a measured magnetic field. Two constraints, a constraint on the sum of current magnitude and that on the sum of each dipole's contribution on measured data, are proposed as the additional constraint in this paper. Computer simulation clearly shows that either constraint can be effectively used to suppress the ambiguity caused by the lack of information regarding the exact number of dipoles. Since the cost function becomes highly nonlinear, the simulated annealing algorithm 1, 2 is essential to search for the minimum of the cost function. © 2010 SPIE-The International Society for Optical Engineering.

The video capture of surgery is becoming widely used but the colors reproduced by conventional RGB-based video systems differ from the original. In this work, 6-band multispectral video was applied to the open surgery for highfidelity color reproduction, and medical doctors visually evaluated the reproduced image quality. As a result, 1) the 6- band video system was rated significantly higher in "color reproducibility," "fidelity," and "material appearance." 2) The perceived color differences between 6-band/RGB and 6-band/3-band were significant. 3) Color videos from 6-band data were transmitted via network, and approximately enough quality was obtained with 15Mbps bit rate. These results show the potential of multispectral technology for the improvement of surgical video quality. © 2010 Copyright SPIE - The International Society for Optical Engineering.

A breath-hold (BH) acquisition method is easy of operation and recently studied actively. In the method, a patient is asked to hold his/her breath for 10 to 30 s as the image acquisition is performed. This is repeated several times and the obtained images are summed. In practice, however, a patient cannot necessarily hold his/her breath at the same timing of breathing. In such a case, the summed images still has a blur. In this paper, we propose to apply our image registration method developed before for respiratory-gated images to BH images. The BH images are nonlinearly motion-corrected so as to match a reference BH image and summed. Through the experiment with ten patient BH image data, we confirmed that the proposed method is effective in obtaining a non-blurred image. © 2010 IEEE.

High-fidelity color imaging technology that incorporates spectrum-based color reproduction system, called "natural vision" (NV) is applied to the field experiment of telemedicine. The experiment comprises mainly two parts 1) High-fidelity color video of open surgery was captured by the six-band multispectral camera, and the image quality was visually evaluated by medical doctors, 2) Video-based teleconsultation experiment between a regional general hospital and a clinic in an island near the hospital, was conducted with using the natural vision system. Copyright 2009 ACM.

When a color video system with highly accurate color reproduction is designed, a good measure for evaluating the image quality including the color reproduction is required. Especially, in codec of motion pictures a good measure is strongly desired to determine a proper compression rate (bit rate). In this paper, we focus on the image quality of motion pictures compressed by H.264/AVC codec which is receiving increased attention. In this study, we investigated the usefulness of S-CIELAB. At first, S-CIELAB color difference calculation was applied to the frames of motion pictures after H.264/AVC codec. The performance was better than CIELAB color difference but not satisfactory. We then limited the region of calculation of ClELAB color difference to the smooth regions where compression error tends to attract attention of observers. Experimental results showing that the modification is promising are obtained.

We have previously developed a method that combines a mini gamma camera with an optical camera to synthesize the two kinds of images and help surgeons to easily identify sentinel lymph nodes on the gastric surface in the cancer resection surgery. Since it is assumed in this method that the object surface is flat, the application is limited. In this article, we extend this method so as to estimate the three-dimensional shape of the object from stereo optical cameras. A prototype system with a mini gamma camera and two optical cameras was constructed and a preliminary experiment was performed. © 2008 IEEE.

A four-layer depth-of-interaction (DOI) detector was proposed from and developed at the research project at the National Institute of Radiological Sciences in Japan, with the aim of achieving high resolution and high spatial sensitivity. Previously, we had developed a Monte Carlo simulation for a DOI detector with 2 x 2 x 4 crystal elements. In this study, in order to simulate the final version of the DOI detector of the project, which uses a larger number of crystal elements, we have developed a much faster and simpler simulator. In this paper the algorithm of the simplified simulator as well as the previously proposed Monte Carlo method is presented and the validation of the simplified simulator through comparisons with the full Monte Carlo simulation and with some experimental results is described.

This article presents a comprehensive study on the spectrum-based color reproduction system, called Natural Vision (NV), which aims to break through the limitation of red-green-blue (RGB) three-primary schemes. After a basic discussion on the motivation for color imaging technology beyond RGB, the method for systematizing the multispectral and multiprimary color imaging technologies, including image capture, processing, storage, printing, and display, is presented. Then experimental multispectral systems for both still image and video are introduced, and the following features of spectrum-based scheme are revealed: a) highly accurate color reproduction is possible even under different illumination environment, b) an expanded color gamut can be reproduced by multiprimary color displays, c) the influence of observer metamerism can be reduced by the spectral color reproduction, and d) the quantitative spectral attributes of an object, useful for its analysis or recognition, can be captured and preserved. Finally, the effectiveness of the system is also demonstrated through experiments in fields of application, such as medicine, digital archives, color printing, electronic commerce, and computer graphics. (C) 2008 Society for Imaging Science and Technology.

We have developed a method that combines a small semiconductor gamma camera with an optical camera to synthesize the two respective kinds of images and help surgeons to easily identify sentinel lymph nodes in various cancer surgery. The proposed method includes some key techniques such as distortion correction of the optical camera image, distance estimation between the camera head and the object surface using a laser and the optical camera, and perspective transformation of the gamma camera image to fuse with the optical camera image. The method, along with preliminary experimental results with a prototype setup are presented here.

Objective This study evaluated the respiratory motion of lungs using a nonlinear motion correction technique for respiratory-gated single photon emission computed tomography (SPECT) images. Methods The motion correction technique corrects the respiratory motion of the lungs nonlinearly between two-phase images obtained by respiratory-gated SPECT. The displacement vectors resulting from respiration can be computed at every location of the lungs. Respiratory lung motion analysis is carried out by calculating the mean value of the body axis component of the displacement vector in each of the 12 small regions into which the lungs were divided. In order to enable inter-patient comparison, the 12 mean values were normalized by the length of the lung region along the direction of the body axis. Results This method was applied to 25 Technetium (Tc)-99m-macroaggregated albumin (MAA) perfusion SPECT images, and motion analysis results were compared with the diagnostic results. It was confirmed that the respiratory lung motion reflects the ventilation function. A statistically significant difference in the amount of the respiratory lung motion was observed between the obstructive pulmonary diseases and other conditions, based on an impaired Student's t test (P < 0.0001). Conclusions A difference in the motion between normal lungs and lungs with a ventilation obstruction was detected by the proposed method. This method is effective for evaluating obstructive pulmonary diseases such as pulmonary emphysema and diffuse panbronchiolitis.

Computational fluid dynamics (CFD) simulation was carried out for an oscillatory flow in a 3-D realistic model of the human central airways, and the effect of airway geometry on the oscillatory flow structure was revealed. The computational model of multi-branching airways was prepared from X-ray CT images. Airway diameter ranges from approx. 2 to 14 mm. The flow in the airway model was simulated using CFD software : Fluent. The resultant flow showed differences compared with that observed in a simplified planar multi-branching model. The inspiratory flow patterns were relatively similar to the patterns observed in a simplified airway model, but the expiratory flow patterns strongly depended on the realistic airway geometry and showed more complicated secondary flow structures. Secondary flow velocities were higher in the realistic airway model than in the simplified airway model in both the inspiratory and expiratory flows. Performing Lagrangian fluid particle tracking, we discussed the convective dispersion due to asymmetric inspiratory and expiratory velocity profiles.

Surface reflectances are metameric for a colour input device if they induce identical response under one light source and induce a set of distinct responses under a second light source. Depending on the device sensitivities, metamerism will be different in structure (which reflectances form metamer sets), cardinality (the number of reflectances in each set) and their perceptual magnitude (e.g. the colour mismatch region of a metamer set under a change of illuminant). In this paper we propose measures to quantify the differences in colour input devices from the point of view of metamerism. Specifically, three quantitative correlates are proposed: the proportion of potentially metameric reflectances (reflectances that give identical response under a canonical illuminant), the proportion of metameric reflectances (potentially metameric reflectances that result in a colour mismatch under any of the test illuminants), the magnitude of the colour mismatch (CIE Delta E's of metameric reflectances under all relevant illuminants). In addition we introduce frequency images that visualise the extent of metamerism for a particular set of spectral sensitivities and a multi-spectral image of interest. Our aim in this study is twofold. firstly, to provide a means for the study of colour input devices from the point of view of their degree of metamerism; secondly, to expose the relationship between the accuracy of reflectance estimation and the extent of metamerism of a particular device. To illustrate our approach we compare several devices of various spectral sensitivities (trichromatic and multispectral) as well as series of synthetic sensitivities designed to study two particular aspects: the number of sensors and their shape.

Many, historically or archeologically valuable paintings such as wall paintings in ancient tombs or Buddhist paintings in Japan or the other Asian countries have been drawn with natural mineral pigments (NMP). The digital archive of those paintings, the identification of pigments used in the paintings and the retrieval of color fading are strongly desired. Multispectral image acquisition of those paintings is very useful for both archive and analysis purposes. In this paper, we focus on the segmentation by pigment from multispectral images in the visible range. Here the kernel based nonlinear subspace method (KNS) is applied to the pigment-based segmentation of multispectral images of the paintings. At first, 55 NMP patches were made and the spectral reflectances were measured. Next, multispectral image acquisition of the color patch array and a Buddha painting drawn with those pigments were performed. Using the training sets of color patches, the segmentation of those images was performed. For comparison, image segmentation from three-band image and a conventional linear subspace method called CLAFIC were tested. It was found that the KNS method with multispectral images worked best than the other methods. Quantitative evaluation with color patches was carried out and the visual evaluation for the segmentation result of the Buddha painting was also performed.

Common, tri-chromatic, RGB colour-acquisition devices capture spectral signals by a coarse sampling through three broad colour filters. Due to metamerism, a single response from a RGB device corresponds to an infinite set of possible surface spectral reflectances. In order to acquire higher quality surface colour descriptors that reduce metamerism in the acquisition process, multi-spectral imaging devices are used. These sample the spectral signals more finely through > 3 colour filters, enabling better estimation of surface spectral reflectance and consequently mitigating the problem of metamerism. In this paper the performance of a 6-channel digital video camera is evaluated in terms of it's accuracy to capture surface spectral reflectances. A. number of known techniques to estimate reflectance from device response are examined, such as linear least squares, the Wiener estimation technique, Tikhonov regularised estimation as well as the Metamer Set Maximum Likelihood method. The performance of each algorithm is compared under different training and testing conditions. The experiments show that there estimation accuracy is significantly increased by using multi-spectral acquisition and furthermore that there is benefit in using more advanced estimation techniques still.

The color reproduction accuracy of a multispectral video system was visually evaluated by expert dermatologists to investigate the feasibility of the system in telemedicine applications. The erythema produced by a skin prick test was used as a substitution of real skin lesion, and the dermatologists performed a color matching experiment, in which the color chips were compared with the reproduced images and the real skins. As a result, the mutisperctral video system, consisting of 6-band HDTV camera, 6-primary display and spectrum-based color reproduction, decreased the perceptual color difference between the reproduced image and the real object, as compared with a conventional 3-band HDTV system. It was also shown that the oversights of skin lesions could be reduced in 6-band video reproduction. Through the experiments including multispectral video transmission between the remote hospitals in addition to above skin color matching, dermatologists rated that the natural color reproduction realized by multispectral video is almost satisfactory for the diagnosis of skin disorders. Copyright 2006 Society for Imaging Science and Technology.

We described a method of CG rendering that uses spectral reflectance and multispectral data obtained using different types of measurement systems. This method can be used to synthesize CG and live-action pictures with different numbers of bands. We experimentally created a short movie using multispectral CG and live-action pictures and demonstrated that we can generate natural and accurate color images.

Multiband cameras have been studied and developed for accurate color reproduction. On the other hand, high dynamic range image acquisition is also strongly desired in many applications. Multiband cameras can potentially meet both needs if their sensitivities are properly controlled. In this article, a method for expansion of the dynamic range that uses a six-band camera consisting of three high-sensitivity bands and three low-sensitivity bands is introduced. Experimental results demonstrating the effectiveness of the method are also shown. © 2006 Wiley Periodicals, Inc.

We are developing a high-performance brain PET scanner, jPET-D4, which provides 4-layer depth-of-interaction (DOI) information. The scanner is designed to achieve not only high spatial resolution but also high scanner sensitivity with the DOI information obtained from multi-layered thin crystals. The scanner has 5 rings of 24 detector blocks each, and each block consists of 1024 GSO crystals of 2.9 mm x 2.9 mm x 7.5 mm, which are arranged in 4 layers of 16 x 16 arrays. At this stage, a pair of detector blocks and a coincidence circuit have been assembled into an experimental prototype gantry. In this paper, as a preliminary experiment, we investigated the performance of the jPET-D4's spatial resolution using the prototype system. First, spatial resolution was measured from a filtered backprojection reconstructed image. To avoid systematic error and reduce computational cost in image reconstruction, we applied the DOI compression (DOIC) method followed by maximum likelihood expectation maximization that we had previously proposed. Trade-off characteristics between background noise and resolution were investigated because improved spatial resolution is possible only when enhanced noise is avoided. Experimental results showed that the jPET-D4 achieves better than 3mm spatial resolution over the field-of-view.

We propose a method for correcting the motion of the lungs between different phase images obtained by respiratory-gated single photon emission computed tomography (SPECT). This method is applied to SPECT images that show a preserved activity distribution in the lungs such as 99m-Tc macro aggregated albumin (99m-Tc-MAA) perfusion images and 99m-Tc-Technegas ventilation images. In the proposed method, an objective function, which consists of both the degree of similarity between a reference image and a deformed image, and the smoothness of deformation is defined and optimized using a simulated annealing algorithm. For the degree of similarity term in the objective function, an expansion ratio, defined as the ratio of change in local volume due to deformation, is introduced to preserve the total activity during the motion correction process. This method was applied to data simulated from computer phantoms, data acquired from a physical phantom, and 17 sets of clinical data. In all cases, the motion correction between inspiration and expiration phase images was successfully achieved. © 2006 IEEE.

Many of old Asian paintings have been drawn with natural mineral pigments. The digital archive of those paintings, the identification of pigments used in the paintings and the retrieval of color fading are strongly desired. The multispectral image acquisition of those paintings allows the digital archive of accurate color information of objects. Moreover, it has a potential of identification of used pigments and leads to the possibility of the retrieval of color fading. This paper describes our first trial of statistical analysis of the reflectance spectra of natural mineral pigments, image acquisition of those paintings by a multispectral camera and the construction of the GUI based segmentation tool for the aid of analysis of paintings.

Acquisition and analysis of three-dimensional movement of knee joint is desired in orthopedic surgery. We have developed two methods to obtain dynamic volume images of knee joint. One is a 2D/3D registration method combining a bi-plane dynamic X-ray fluoroscopy and a static three-dimensional CT, the other is a method using so-called 4D-CT that uses a cone-beam and a wide 2D detector. In this paper, we present two analyses of knee joint movement obtained by these methods: (1) transition of the nearest points between femur and tibia (2) principal component analysis (PCA) of six parameters representing the three dimensional movement of knee. As a preprocessing for the analysis, at first the femur and tibia regions are extracted from volume data at each time frame and then the registration of the tibia between different frames by an affine transformation consisting of rotation and translation are performed. The same transformation is applied femur as well. Using those image data, the movement of femur relative to tibia can be analyzed. Six movement parameters of femur consisting of three translation parameters and three rotation parameters are obtained from those images. In the analysis (1), axis of each bone is first found and then the flexion angle of the knee joint is calculated. For each flexion angle, the minimum distance between femur and tibia and the location giving the minimum distance are found in both lateral condyle and medial condyle. As a result, it was observed that the movement of lateral condyle is larger than medial condyle. In the analysis (2), it was found that the movement of the knee can be represented by the first three principal components with precision of 99.58% and those three components seem to strongly relate to three major movements of femur in the knee bend known in orthopedic surgery.

In addition to the great advancement of high-resolution and large-screen imaging technology, the issue of color is now receiving considerable attention as another aspect than the image resolution. It is difficult to reproduce the original color of subject in conventional imaging systems, and that obstructs the applications of visual communication systems in telemedicine, electronic commerce, and digital museum. To breakthrough the limitation of conventional RGB 3-primary systems, "Natural Vision" project aims at an innovative video and still-image communication technology with high-fidelity color reproduction capability, based on spectral information. This paper summarizes the results of NV project including the development of multispectral and multiprimary imaging technologies and the experimental investigations on the applications to medicine, digital archives, electronic commerce, and computer graphics.