In memoriam of Dr. Eiichi Tanaka who passed away on August 21, 2021, I review his achievement in the research of tomographic image reconstruction. Tomographic image reconstruction is an important research area which has wide applications including X-ray CT, nuclear medicine imaging such as PET and SPECT, and electron microscopy. Since 1970’s, Dr. Tanaka has worked on numerous important topics in tomographic reconstruction fields aiming at using them in image reconstruction for PET and SPECT. Among them, in this paper, I will introduce his research on Filtered BackProjection (FBP) method, analytical attenuation correction in SPECT, image reconstruction in Time-of-Flight PET, image reconstruction for 3-D PET imaging, and iterative image reconstruction method called Dynamic Row-Action Maximum Likelihood Algorithm (DRAMA).

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This article gives dominant research contributions of the late Dr. Eiichi Tanaka in the field of very weak radioactivity measurements with a new type of an extremely low background β-ray scintillation spectrometer, which consists of a large plastic scintillator and a gas-flow GM counter located in the small hollow in the bottom part of the plastic scintillator. The pulse signals from plastic scintillator are coincidence-gated by the pulses from the GM counter. Dominant background signals due to the energetic muons still appear in the higher region than 3.5 MeV even with coincidence gating mode, but extreme reduction of background can be attained in the 0～3 MeV region which is essentially important in the β-ray spectrometry for most of radionuclides.

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The present status of progress in methods of assessment of the Pu lung burden is reviewed, and is given a disscussion on the difficulties encountered in the assessment e.g. those which are inherent to high-sensitivity counting of low energy X-rays, those due to the differences in the isotopic composition of various Pu isotopes and Am which are encountered in the calibration of the detection efficiency for low energy X-rays.

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進行したステージの筋ジストロフィーでは, 運動機能障害が重度なために, 身の回りのことや, 趣味活動への参加が少なくなっていく.作業療法では, 患者が求める活動に必要な運動と環境要素を分析し, 活動に挑戦し易い環境調整を支援する. また, 作業療法士は, 環境への適応を促す過程を通して, 患者の興味を掘りおこし, 患者自身の問題解決能力を育む.

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It is known that the multiple jets issued parallel from a number of two-dimensional nozzles, interfere with each other.
In this report, the flow patterns of the three and four two-dimensional parallel jets were investigated experimentally.
In the three and four jets, the two outside jets set up a dual jet flow with an associated reverse flow. When the inside jets are introduced, the flow field of the three and four jets are largely affected by the ratios of the inside jet velocity to the outside one. In order to examine the effect of varying the ratio of the velocities in the inside and outside jets on the flow pattern, measurement of the flow by a tandem type hot-wire anemometer and flow visualization by oil film were carried out.

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厚い隔壁を有する高エネルギー用コリメータにより発生する偽像を除去するために, ガンマカメラの位置信号X, Yを周期的に変化する三角波に乗せることによって, 電気的に位置信号を振らせる方法について検討した。ガンマカメラの解像力の劣化をできるだけおさえ, しかも偽像を最少にするために位置信号の至適な振動幅の調整は, 位置信号を処理することによって得られたline spread functionの空間周波数特性を, 計算によって求められたコリメータを含むガンマカメラの総合解像力を半値幅にもつガウス分布の空間周波数特性に近づくように三角波の振幅と周波数を試行錯誤的に変えて行った。ファントム実験から偽像除去に関しほぼ満足すべき結果を得た。

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The vortx shedding from a circular cylinder in oscillatory flow in a pipe is visualized by smoke-wire method. It has been observed that patterns of vortex shedding varies with the oscillatory amplitude under a constant Reynolds number and oscillation frequency. Two characteristic flow patterns are observed; one is that two symmetric vortices are shed simultaneously during one period of the flow oscillation, and the other is that two symmetric vortices and single one are shed alternately.

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Further investigation on a practical applications of the Karman vortex flow meter were studied. In this experiments, the effects of a distance between two parallel side plates of a Karman vortex shedding from cylinders with three shapes of cross-sections were investigated. The three types of cross-section were (1) circular type, (2) semi-circular type and (3) semicircular with plate which is effective to stabilize the vortex shedding.
Within the limits of this experiment, the shedding frequency of the vortex were reduced by the groth of the boundary layers of each side plate, and a characteristic flow patterns were observed by the flow visualizations.

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大型シンチカメラは直径38.7cmのNaI結晶を有するAnger型カメラである。使用開始以来1年9か月間に1, 200症例のシンチグラフィが行なわれ, これにより臨床的得失が明らかにされた。ファントム実験の結果では, 有効検出直径は34cmであり, これは一般に使用している標準型カメラより約70%広いことを意味する。また, 解像力はコリメータより5および10cm距離において6.3mmのバーを解像し, 標準型に劣らなかった。感度の均一性については, 不規則な不均一像が認められ調整が必要であった。臨床利用の結果では, 肺, 肝, 骨, 腎のシンチグラムについては大型カメラの有利性が示されたが, 脳, 脳槽ではかえって不利であった。

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The purpose of this article is to introduce achievement and philosophy on studies of SPECT reconstruction algorithms which Dr. Eiichi Tanaka dedicated himself to carrying out. The method that Dr. Tanaka suggested first (in 1974) was to reconstruct analytically a section image from the projection data convoluted the correction functions. The correction functions were optimized to yield a maximum ‘signal-to-noise ratio’. In 1983 and 1984, two image reconstruction algorithms, WBP and RPC were suggested assuming a uniform attenuation in the object. Dr. Tanaka understood intuitively that these methods had few noise and distortions in reconstructed images. WBP was an approximate solution, but three type analytically methods were reported by Tretiak O, et al., Bellini S, et al., and Inoyue T, et al. In 1995, Metz CE, et al. and Kudo H, et al. succeeded independently each other in finishing a general theory of the analytic absorption Radon Conversion by using parameter “n”. The relations among the above three analytically methods and WBP were explained, beautifully. The important thing in the study is a flexible idea such as catching a problem as the issue of black box or reverse and the result to be concise and elegant.

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