Two fields of radiology, medical imaging and radiation therapy, are coded separately in medical fee system, and the health care statistics of 2003 shows that expenditure on the former was 5.2% of the whole medical cost and the latter 0.28%.
Introduction of DPC, an abbreviation of Diagnostic Procedure Combination, was carried out in 2003, which was an essential reform of medical fee payment system that have been managed on fee-for-service base throughout, and 22% of beds for acute patients care are under the control of DPC payment in 2006. As medical imaging procedures are basically classified in inclusive payment in DPC system, their accurate statistics cannot be figured out because of the lack of description of individual procedures in DPC bills. Policy-making of medical economics will suffer a great loss from the deficiency of detailed data in published statistics.
Important role in clinical diagnoses of CT a nd MR results an increase of fee paid for them up to more than half of total expenditure on medical imaging. So, dominant reduction of examination fee has been done for MR imaging, especially in 2002, to reduce the total cost of medical imaging.
Follows could be featured as m ajor topics of medical imaging in health insurance system, (a) fee is newly assigned for electronic handling of CT-and-MR images, and nuclear medicine, and (b) there is still a mismatch between actual payment and quality of medical facilities. As matters related to medical imaging, the followings should be stressed; (a) numbers of CT and MR units per population are dominantly high among OECD countries, but, those controlled by qualified radiologists are at the average level of those countries, (b) there is a big difference of MR examination quality among medical facilities, and (c) 76% of newly-installed high-end MR units are supplied by foreign industries.
Hopefully, there will be an increase in the concern to medical fee payment system and health care cost because they possibly influence patient care, personnel affairs in clinical facilities, technological development of medical devices, and so on.

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In inverse planning of IMRT, optimum intensity maps are generated using an optimization algorithm. In this paper, impacts of two different optimization algorithms on the intensity map in IMRT treatment planning were evaluated. These were from the steepest descent (SD) and simulated annealing (SA) methods. The following five patterns were compared: [1] SD with calculation time of 5 min; [2] SD with the terminal criterion based on cost function; [3] SA with calculation time of 5 min; [4] SA with the terminal criterion; and [5] SA with the terminal criterion using a smoothing filter. Differences of D95%fo r the planning target volume, V70Gfyo r the rectum wall and the bladder wall were up to 0.5,1.8 and 3.2 %, respectively in all patterns. The dosimetric impact was negligible. In contrast, generated intensity maps were sensitive to the algorithms. Intensity maps generated by SA tended to have much fluctuation due to numerical artifacts compared to those generated by SD. The difference in the profile was over 7 % between the algorithms. The smoothing filter decreased the fluctuation in intensity maps of SA. In conclusion, it is important to understand impacts of optimization algorithms on the intensity map and the dose distribution.

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We investigated the performance of model observers (the channelized Hotelling observer (CHO), channelized non-prewhitening observer (CNPWO) and non-prewhitening observer (NPWO)) for lesion detection in single photon emission computed tomography (SPECT) imaging. Methods: Using a simulation tool, we generated the numerical phantom with a hot lesion for cases having various contrasts and sizes and projection data including photon attenuation, scatter and distance-dependent collimatordetector response. The SPECT images were reconstructed using the filtered back-projection method and the ordered-subsets expectation-maximization method. Fifty lesion-absent and lesion-present images were generated and the detectability indices derived from CHO (dCHO)C, NPWO (dCNPWO) and NPWO (dNPWO) were calculated from a total of 100 images. These procedures were repeated 5 times for each condition. The relationships among these detectability indices were investigated for various projection counts, lesion contrasts and lesion sizes. Results: All detectability indices increased with increases of projection count, lesion contrast and lesion size. Although there were good correlations among them, the relationships between dcHo and dNpwo and between dCNPWO and dNPWO were not linear. The coefficient of variation of dCHO tended to be significantly greater than that of doipwo and dNpwo. Conclusion: This study will be useful for understanding the performance of model observers when evaluating lesion detection in SPECT imaging.

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New PET scanners utilize depth-of-interaction (DOI) information to improve image resolution, particularly at the edge of field-of-view while maintaining high detector sensitivity. However, the inter-crystal scatter (ICS) effect cannot be neglected in DOI scanners due to the use of smaller crystals. ICS is the phenomenon wherein there are multiple scintillations for irradiation of a gamma photon due to Compton scatter in detecting crystals. In the case of ICS, only one scintillation position is approximated for detectors with Anger-type logic calculation. This causes an error in position detection and ICS worsens the image contrast, particularly for smaller hotspots. In this study, we propose to model an ICS probability by using a Monte Carlo simulator. The probability is given as a statistical relationship between the gamma photon first interaction crystal pair and the detected crystal pair. It is then used to improve the system matrix of a statistical image reconstruction algorithm, such as ML-EM in order to correct for the position error caused by ICS. We apply the proposed method to simulated data of the jPET-D4, which is a four-layer DOI PET being developed at the National Institute of Radiological Sciences. Our computer simulations show that image contrast is recovered successfully by the proposed method.

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PET scanners are an important component in functional brain imaging devices. Several PET scanners have been developed during the last two decades for brain research studies. We are developing a high-performance brain PET scanner, jPET-D4. This scanner is designed to achieve not only high spatial resolution but also high sensitivity using four-layered depth-of-interaction (DOI) detectors. The scanner has five block detector rings with the ring diameter of 390 mm and each block detector ring consists of 24 DOI detectors. In previous work, we have demonstrated that 3 mm FWHM uniform spatial resolution within the field-of-view could be realized. In this paper, we describe the jPET-D4 system and evaluate its performance. The average energy resolution for 120 DOI detectors is optimized to 16 % ± 1.0 %. The scatter fraction for this system is 40 % with an energy window of 400 600 keV. The sensitivity for the point source is 102 kcps/MBq (10.2 %) with a 400 keV LLD. Maximum noise equivalent count rate (NECR) is 154 kcps at 11 kBq/ml with a 10 ns coincidence time window. We evaluated scatter fraction and NECR following procedures based on NEMA NU2-1994. These first evaluation measurements indicate the jPET-D4 has good performance.

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