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Akira Iwasaki

Publications and source records attributed to Akira Iwasaki.

16 recordsLinked to original sources
PubMed2006

[Two approximations to obtain the collimator scatter factor (Sc) for MLC irregular fields].

The collimator scatter factor (S(c)(MLC)) at MLC irregular fields for high-energy X-ray irradiation is generally assumed to be equal to the jaw collimator scatter factor (S(c)(jaw)) of the square field equivalent to the rectangular field produced using pairs of jaw collimators. However, this assumption becomes strained as the ratio of the MLC equivalent square field side to the jaw collimator equivalent square field side decreases. In this study, for 4 MV and 10 MV X-rays, the collimator scatter factor (S(c)(MLC)) for an MLC irregular field could be evaluated with a high degree of accuracy using the MLC irregular correction (F(MIC)) factor or the jaw collimator correction (F(JCC)) factor.

Phantoms, Imaging↗
PubMed2006

Characteristic features of a high-energy x-ray spectra estimation method based on the Waggener iterative perturbation principle.

We have redeveloped a high-energy x-ray spectra estimation method reported by Iwasaki et al. [A. Iwasaki, H. Matsutani, M. Kubota, A. Fujimori, K. Suzaki, and Y. Abe, Radiat. Phys. Chem. 67, 81-91 (2003)]. The method is based on the iterative perturbation principle to minimize differences between measured and calculated transmission curves, originally proposed by Waggener et al. [R. G. Waggener, M. M. Blough, J. A. Terry, D. Chen, N. E. Lee, S. Zhang, and W. D. McDavid, Med. Phys. 26, 1269-1278 (1999)]. The method can estimate spectra applicable for media at least from water to lead using only about ten energy bins. Estimating spectra of 4-15 MV x-ray beams from a linear accelerator, we describe characteristic features of the method with regard to parameters including the prespectrum, number of transmission measurements, number of energy bins, energy bin widths, and artifactual bipeaked spectrum production.

Algorithms↗
PubMed2005

Theoretical considerations for evaluating the degree of random-periodicity of radiographic noise.

Radiographic noise properties have been evaluated using the Wiener spectrum. However, this approach is not appropriate for periodic noise for two reasons. One is that it takes infinite values at the spatial frequencies of periodic noise. The other is that when adopting a numerical integration, it allows unstable values at each spatial frequency, depending on the integral region. Introducing three types of spectra (W(1), W(2), and W(3)) in connection with the Wiener spectrum, we propose a practical approach to evaluation of periodic noise. Radiographic images sometimes contain noise that is not totally random and not perfectly periodic. Therefore, using the Wiener spectrum and the W(1) spectrum, we also propose two factors for evaluation of the degree of random-periodicity of noise containing periodic signals.

Journal Article↗
PubMed2005

Sperm cryopreservation before cancer chemotherapy helps in the emotional battle against cancer.

BACKGROUND: Sperm cryopreservation before cancer chemotherapy is available for young patients with cancer. However, few patients bank their sperm. The authors evaluated by questionnaire the psychological impact of sperm cryopreservation. METHODS: The authors cryopreserved the sperm of 111 patients with cancer for free at the Yokohama City University (Yokohama, Japan). For the current study, questionnaires were mailed to 66 patients whose sperm had been cryopreserved. Fifty-one patients (77.3%) with testicular carcinomas (n = 24), leukemia or malignant lymphoma (n = 19), or other cancers (n = 8) answered the questionnaire. The average age at collection and the period of sperm cryopreservation were 30.1 +/- 6.0 (mean +/- standard deviation) and 3.3 +/- 2.2 years, respectively. RESULTS: Many patients were informed of the deleterious effects of cancer chemotherapy and worried about infertility in the future. However, only half of the patients banked their sperm on their own initiative. Other patients followed their physician's instruction. Eighty percent of patients replied that sperm cryopreservation helped in the battle against cancer. Sperm banking especially was found to encourage every patient who banked sperm on their own initiative. After cancer chemotherapy, 70% of patients wanted to have a child. However, 60% of patients were worried about infertility in spite of having their sperm cryopreserved. No patients wanted to use cryopreserved sperm for fathering children if their spermatogenesis was restored. Sperm cryopreservation invigorated many patients with cancer after cancer treatments. The majority of patients recommended sperm cryopreservation to other cancer patients. CONCLUSIONS: Sperm cryopreservation encouraged young patients with cancer during and after cancer treatment. It should be recommended for all young patients with cancer. However, sperm cryopreservation did not eliminate their fear of infertility.

Adult↗
PubMed2005

[Clinical study of unilateral intravaginal testicular torsion and anatomicalcomparative study of bilateral testes in orchiopexy].

Fourty-eight patients were operated on for unilateral intravaginal testicular torsion at Yokohama Red Cross Hospital during the period between July 1976 and December 2001. Orchiopexy was carried out on 20 out of 48 patients. Only 8 patients could receive orchiopexy within 8 hours after the onset of symptoms. Although, 24 of the 48 patients had visited a medical doctor within 8 hours after the onset. Therefore, the less the testes might be sacrificed if these patients could be immediately sent to a clinic with an urologic speciality. The contralateral uninvolved testis has been said to require orchiopexy because it has an anatomical structure similar to the testis with torsion. However, the contralateral testes in 5 out of 20 patients with ipsilateral orchiopexy turned out to have a normal anatomical structure according to our classification of intravaginal testicular torsion. This suggests that no orchiopexy is necessary if the contralateral uninvolved testis has a normal anatomical structure from the standpoint of torsion type.

Adult↗
PubMed2005

[Theoretical considerations for evaluating the degree of random-periodicity of graphic noise.].

Graphic noise properties are usually evaluated using the Wiener spectrum. However, this approach is not appropriate for periodic noise for two reasons. One is that it takes infinite values at the spatial frequencies of periodic noise. The other is that when adopting a numerical integration, it allows unstable values at each spatial frequency, depending on the integral region. Introducing three types of spectra (W(1), W(2), and W(3)) in connection with the Wiener spectrum, we propose a practical approach to evaluation of periodic noise. Graphic images sometimes contain noise that is not totally random and not perfectly periodic. Therefore, using the Wiener spectrum and the W(1) spectrum, we also propose two factors for evaluation of the degree of random-periodicity of noise containing periodic signals.

Humans↗
PubMed2004

Microgravity experiments on phase change of self-rewetting fluids.

A series of microgravity experiments on self-rewetting fluids has been conducted at the 10-second drop shaft of the Japan Microgravity Center (JAMIC). In all the experiments, 1.5 wt% of 1-butanol aqueous solution were employed as a self-rewetting fluid. The objective of the first experiment was to observe the boiling behavior of two-dimensional adjacent dual vapor bubbles with the aid of a two-wavelength interferometer and tracer particles. A significant difference was observed between a self-rewetting fluid and a normal fluid (CFC-113 in this experiment) in bubble interaction and flow developed along vapor/bubble interface. The second experiment focused on the flow at the bubble/heater contact area and around the three-phase interline, visualized with tracer particles. Differing behavior among three fluids, 1-butanol aqueous solution, CFC-113, and ethanol aqueous solution, was observed. The last microgravity experiment was a demonstration of wickless heat pipes containing three different fluids as a working fluid, 1-butanol aqueous solution, water, and ethanol aqueous solution. The temperature variation of working fluid in the heat pipe was monitored, and the liquid flow returning from the condensation region to the evaporation region was visualized by tracer particles. In addition to microgravity experiments, the performance of conventional heat pipes with 1-butanol aqueous solution was evaluated on the ground, and compared with water heat pipes. Our preliminary results are presented.

1-Butanol↗
PubMed2004

[Method of estimating 10 MV X-ray irregular field dose using the collimator scatter factor (Sc) and phantom scatter factor (Sp)].

It has been found that in general 10 MV X-ray dose calculation can be made accurately for multi-leaf collimator irregular fields by using the total scatter factor (S(cp)), collimator scatter factor (S(c)), and phantom scatter factor (S(p)) proposed by Khan et al. With respect to the collimator scatter factor (S(c)), we used the field-mapping method of Kim et al. to obtain equivalent square fields of irregular fields (the collimator reverse effect can be accurately dissolved using the field-mapping method). Even for extremely small multi-leaf fields compared with the main collimator opening, X-ray output calculations could be made accurately by introducing the small segment correction (SSC) factor. With respect to the phantom scatter factor (S(p)), highly accurate calculations could be made for irregular field irradiation by applying an F(MLC) (MLC radiation leakage) factor to the equivalent square field (in cases in which the ratio of the multi-leaf equivalent square field side to the main collimator equivalent square field side is less than 0.6). However, it has been found that highly accurate dose calculations can, in general, be performed when the main collimator is limited just at the opening determined by the multi-leaf collimator field.

Phantoms, Imaging↗
PubMed2004

[Method for estimating 4 MV X-ray irregular field dose using the collimator scatter factor (Sc) and phantom scatter factor (Sp)].

Calculation of in-air or in-water dose for 4 MV X-ray irregular fields could be accurately performed using the collimator scatter factor (S(c)) and phantom scatter factor (S(p)) concepts. It has been revealed that the equivalent square field for a multi-leaf collimator (MLC) irregular field can be evaluated accurately by using the S(p)-Clarkson or S(c)-Clarkson integration method; however, the S(c)-Clarkson integration method is more straightforward because the S(c) factor expresses the in-air X-ray output factor. It has been found that when the MLC field is relatively much smaller than the main collimator field, the Sc factor can be accurately evaluated by introducing the small segment correction (SSC) factor (except for the case in which the MLC field is less than 1 x 1 cm(2)). It has also been found that both the S(p) factor and the tissue-phantom ratio (TPR) can be precisely evaluated by introducing the F(MLC) factor in cases in which the ratio of the MLC equivalent square field side to the main collimator equivalent square field side is less than about 0.7.

Phantoms, Imaging↗
PubMed2003

Semen cryopreservation for patients with malignant or non-malignant disease: our experience for 10 years.

PURPOSE: We report our experience in 10 years of sperm cryopreservation to reveal the present state of the cryopreservation project. MATERIALS AND METHODS: 42 germ cell tumor, 110 non-germ cell tumor and 2 non-malignant disease patients who visited our clinic for semen cryopreservation were retrospectively analyzed. RESULTS: Only 7 (20%) out of 35 unilateral testicular tumor patients who had received no chemotherapy met the WHO criteria for sperm concentration and motility. However, there were no patients with azoospermia. Three testicular tumor patients with previous chemotherapy and 4 retroperitoneal germ cell tumor patients had poor sperm concentrations and motilities. Twenty (52%) out of 38 non-germ cell tumor patients without previous chemotherapy met the WHO criteria. In contrast, only 9 patients (13%) met the WHO criteria among 72 patients with previous chemotherapy. Twenty-nine patients (40%) with chemotherapy were azoospermia. Totally, 74 (96%) of 77 tumor patients' semen without chemotherapy and 34 (45%) of 75 with chemotherapy were cryopreserved. Sperm from a patient with testicular torsion were cryopreserved. CONCLUSION: Most cancer patients without previous chemotherapy, regardless of underlying disease, had abundant motile sperm. However, half of the patients who had received chemotherapy did not have suitable sperm for freezing. It is important to inform young cancer patients of the cryopreservation project immediately after the diagnosis is made.

Adolescent↗
PubMed2003

[Two cases of 46,XX male with chief complaint of infertility].

We report two cases of XX male with chief complaints of infertility. Physical examination of both patients aged 42 and 29 demonstrated normal male habitus except for small testes. Semen analyses demonstrated no spermatozoa. Endocrinological examinations showed hypergonadotrophic hypogonadism. Vesiculograms demonstrated normal seminal tracts. Histological examination of their testes did not reveal germ cells; one case lacked seminiferous tubules and there was hyalinization in the seminiferous tubule in another case. Chromosomal analyses of peripheral blood demonstrated 46,XX. The sex-determining region Y gene was positive and DAZ (deleted in azoospermia) gene was negative in both cases.

Adult↗
PubMed2002

[The effect of high concentration of sodium and potassium ion on motility of human sperm preserved in electrolyte-free solution].

PURPOSE: To assess the effect of high concentration of sodium and potassium ion on the motilities of human sperm following the preservation in electrolyte-free solution. PATIENT: Semen samples were obtained from patients attending our infertility clinic. The motilities of their sperm were more than 40%. METHOD: Ejaculated sperm were washed by using the electrolyte-free Percoll gradient and then preserved in electrolyte-free solution at 4 degrees C for a week. The preserved sperm was incubated and analyzed after the addition of electrolyte solutions under acid or alkaline condition. The sperm were continuously preserved for a day at room temperature and analyzed. RESULT: The sperm was by the addition of 35-135 mM Na+ or 5-135 mM K+ in acid solutions. Under the alkaline conditions, sperm were reactivated without Na+ or K+. However, the addition of 135 mM Na+ or K+ significantly decreased in sperm motilities. The some sperm in the solution containing low concentration of Na+ or K+ ions maintained their motilities for a day at room temperature. However, all sperm lost their motilities in the 135 mM Na+ or K+ solutions. CONCLUSION: The high concentration of Na+ or K+ ions had detrimental effects on motilities of sperm following the preservation in electrolyte-free solution.

Humans↗
PubMed2002

[Comments on evaluation method for equivalent square fields to the collimator scatter factors of rectangular fields].

In the measurement of 4 MV and 10 MV X-ray collimator scatter factors (S(c)), the method of using an acrylic mini-phantom showed no significant differences between cases in which the chamber axis was either parallel or perpendicular to the beam axis. Chamber readings with an aluminum or acrylic build-up cap were not reflected by contaminant electrons when the chamber axis was parallel to the beam axis. On the basis of the data on 4 MV and 10 MV X-ray collimator Sc measured using an acrylic mini-phantom, we examined three methods of obtaining square fields equivalent to rectangular fields, and reached the following conclusions: (1) The A/P method was not accurate because it did not take into account the structure of the radiation head. (2) Regarding the geometrical weight factor (k) used in the field-mapping method, more accurate k values were obtained when using the geometrical places of the flattening filter (or the second source, taken from the concept of extra-focal radiation), the upper and lower collimators, and the chamber, rather than when using the geometrical places of the source, the upper and lower collimators, and the chamber. (3) The most accurate k values could, in general, be obtained when determined on the basis of measured S(c) data.

Phantoms, Imaging↗
PubMed2001

[Comments on the primary and scatter dose-spread kernels used for convolution methods]

The basic primary and scatter dose-spread kernels used for convolution methods are usually produced by Monte Carlo simulations with the interaction point forced to the center of a large water phantom. This paper proposes another type of basic kernel, with which perfectly accurate primary and scatter absorbed dose calculations can be performed within a semi-infinite water phantom under certain irradiation conditions.

Journal Article↗