Masayoshi Akisada

Irradiation synchronized with respiration gate

A respiratory gating technique was developed for radiotherapy of tumors unable to remain stable due to respiration. Irradiation was started and stopped with a microwave oscillator of a linear accelerator controlled by gating signals at specific points in the respiratory cycle. This technique was tested in a phantom specially designed to simulate a patient with lung cancer and in clinical therapy for lung tumors of seven patients. A mask was used to check ventilation in the phantom and airbags were used to measure thoracoabdominal pressure in patients and in the phantom; this enabled us to detect the excursion of the tumors. Low sensitivity film for verification demonstrated the efficacy of this technique. The gated irradiation was proved to ensure more precise radiotherapy for tumors located close to the diaphragm.

Filarial Chyluria in Japan

The clinical manifestations of bancroftian filariasis may be roughly classified into three stages: subclinical, acute, and chronic. Filaria bancrofti has a special predilection for the lymphatic system. After a long period of so-called “incubation,” the symptoms of the acute stage appear, e.g., repeated fever attacks, called “Kusafurui,” often associated with lymphangioadenitis. The chronic complications, occurring from five to twenty years after the primary infestation, are represented by various conditions, such as elephantiasis of the leg, hydrocele testis, chyluria, or permanent swelling of the lymph nodes. A survey of filariasis among 7,766 people in Okinawa by Saigo (1) showed an incidence of 14.24 per cent for microfilaremia, 1.07 per cent for chyluria, and 1.94 per cent for elephantiasis. Sassa (2) found a microfilaremia incidence of 10.76 per cent in 22,698 people in the Amami-Oshima and Okierabu Islands. These islands are far south of Japan and just north of Okinawa. Since lymphographic demonstr...

N-isopropyl-p-[123I]iodoamphetamine SPECT in MELAS syndrome: comparison with CT and MR imaging.

Regional cerebral perfusion was studied in three patients with the mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome, using single photon emission computed tomography (SPECT) with N-isopropyl-p-[123I]iodoamphetamine (IMP). Accumulation of the tracer was relatively decreased in the parietooccipital regions and also in the frontotemporal regions after stroke-like episodes. However, quantitative regional cerebral blood flow (rCBF) measurement showed that rCBF was relatively well preserved even at these sites, and a hyperemic state was observed at the sites of normal accumulation. IMP SPECT may be useful in the diagnosis and assessment of the progress of the MELAS syndrome.

The Role of Preoperative Radiotherapy for Invasive Thymoma

Six patients with large invasive thymomas were treated by preoperative irradiation with 12 to 20 Gy before total or partial resection of the tumor. The responses of these 6 thymomas were estimated on the chest radiograms as follows; complete response in 2 patients, partial response in 3 and no response in one. Although the clinical responses varied, the surgical specimens of all the tumors pronounced severe fibrosis, probably not related to irradiation, and necrotic foci with a few viable tumor cells. Total resection of the thymoma was performed in 3 patients and subtotal resection in 3. Adhered or involved surrounding tissues such as the pericardium, pleura and/or veins were also resected in most patients. Preoperative radiotherapy facilitated total or subtotal resection of the invasive thymoma mass by reducing the tumor volume.

Effect of strength training on the relationship between magnetic resonance relaxation time and muscle fibre composition

SummaryThe effect of muscle hypertrophy on the relationship between magnetic resonance (MR) relaxation time and muscle fibre composition was investigated. Relaxation time and muscle fibre composition were measured in five subjects before and after a 20-week period of strength training. Muscle fibre composition in all subjects exhibited a significant shift to a predominance of fast-twitch (FT) fibres as a result of 20-week strength training (% area FT fibres: mean values from 49.8%, SD 17.9% to 57%, SD 5.6%; P<0.05). Longitudinal relaxation time (T1) and transverse relaxation time (T2) were prolonged significantly after strength training (T1 mean values from 334.9 ms, SD 13.6 to 359.0 ms, SD 9.0, P<0.001; T2 from 27.5 ms, SD 0.9 to 30.8 ms, SD 2.3, P<0.05). A constant relationship was observed in changes caused by strength training in muscle fibre composition (% area FT) and relaxation time, with a high correlation obtained between both parameters. These results indicate that MR relaxation time can be used for non-invasive estimation of muscle fibre composition.

Real time K‐edge subtraction x‐ray imaging

This paper describes an x‐ray K‐edge subtraction television system for noninvasive angiography utilizing synchrotron radiation. The phantom, including contrast material (iodine), is irradiated by monochromatized dual‐energy x‐ray flux, alternately, using a high speed monochromator. The monochromator consists of a silicon crystal plate vibrating at 15 Hz so that the phantom is irradiated by the x‐ray flux of 150 eV above and below the K‐edge photon energy of iodine, 15 times per second. As an x‐ray detector, TV cameras optically coupled to an x‐ray image intensifier are used and the video signal is processed to display the subtraction image of pairs of successive images in real time. This system was fully implemented and moving phantoms were examined. Both the time interval between the energy change and the exposure time of each image has been shortened to 2 ms.

Heterogeneity of Muscle Energetics in Human Muscle Fiber Type Using 31P Nuclear Magnetic Resonance

AbstractTo evaluate the association between muscular phosphate metabolites or intracellular pH at rest and muscle fiber composition of musculus vastus lateralis in human, we measured phosphorus nuclear magnetic resonance (31P NMR) spectra and performed muscle biopsy in 30 subjects. The intracellular pH tended to be higher in cases with a higher percentage of fast-twitch fibers (% FT fibers). On the other hand, no relationship was observed between phosphocreatine (PCr)/inorganic phosphate (Pi) and percent FT fibers. This is inconsistent with previously reported results of 31P NMR studies in animals. These results suggest that PCr concentration is the same for the two major fiber types (FT and slow-twitch [ST] fibers) of human skeletal muscle. Knowledge of which relationship between muscle fiber composition and intracellular pH accounts for our results awaits further investigation.

Two-dimensional intravenous coronary arteriography using above-K-edge monochromatic synchrotron x-ray

RATIONALE AND OBJECTIVES For intravenous (i.v.) coronary arteriography, a real-time two-dimensional (2D) imaging system is being developed using above-K-edge monochromatic X-rays alone. The potential diagnostic value of this system was examined in the current study. METHODS The angiographic system consisted of an asymmetric silicon (311) monocrystal, an image intensifier, and a charged-coupled device camera. It was constructed at the beam line of the Tristan Accumulation Ring. Monochromatic X-rays of 33.32 keV were used, and each image was recorded over 2 msec. RESULTS Ventricular wall motion and the anatomy of the coronary arteries could be seen in dogs by sequential images obtained without subtraction. The left anterior descending coronary artery, left circumflex coronary artery, and right coronary artery and the branches of these vessels were observed. The parts of the coronary arteries overlapping the aorta and left ventricle were revealed somewhat during washout of the contrast material. CONCLUSION For a 2D imaging system, monochromatic i.v. coronary angiography using an energy above the iodine K-edge might be able to image the coronary arteries without subtraction. However, the image quality needs to be improved by increasing the X-ray flux, decreasing background radiation scatter from the object, and decreasing contamination with 99-keV X-rays.

Iodine K-edge dual-energy imaging for subtraction angiography using synchrotron radiation and a 2-dimensional detector

Abstract A 2-dimensional energy-subtraction imaging system using synchrotron radiation has been improved in a number of ways; especially the energy-switching mechanism in which a monochromator crystal is oscillated trapezoidally has been improved. These improvements have led to real-time imaging of the right coronary artery in a rabbit after an intravenous injection of a contrast agent. This artery has a diameter of about 0.5 mm. However, this system has limitations concerning the energy difference between two component exposures and the total time of acquiring two images. We have tested a new method. Since the crystal was too heavy to oscillate quickly, the next step was to make the energy switching faster than in the previous method by the use of lighter moving parts. An iodine filter is used in the new method. Filter-chopping of the X-ray beam switches the dual-energy imaging energies, because the iodine filter selectively absorbs high-energy X-rays rather than K-edge energy X-ray. Moreover, by the use of the iodine filter, the energy difference between two exposures can be decreased to less than half of that in the previous method. Preliminary studies on the new method were performed in rats.

Phosphorus-31 nuclear magnetic resonance study on the effects of endurance training in rat skeletal muscle

SummaryTo evaluate changes in muscle energetics following endurance training, we measured phosphorus-31 nuclear magnetic resonance (31P NMR) spectra on rat muscle in vivo before and after training in the same animals. The endurance training lasted for 3 months. The31P NMR spectra were obtained serially at rest, during exercise by electrical stimulation, and during recovery. Intramuscular phosphocreatine (PCr), inorganic phosphate (Pi, adenosine 5′-triphosphate (ATP) and pH were determined from the NMR spectra. The ratio of PCr : (PCr + Pi) at rest showed no difference between the trained and control groups even after 3 months of training. During exercise, however, this ratio was significantly higher in the trained group than in the control group. The ratio also recovered more rapidly after exercise in the trained group. The intramuscular pH decreased slightly by approximately 0.1 pH unit during exercise but did not show a significant difference between the groups. These results indicated that endurance training of 3 months duration improved the ATP supply system in the muscle. They also demonstrated that31P NMR is a potent method for evaluating the effects of training in the same individuals.