Ichiro Sakuma
University of Tokyo
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Featured researches published by Ichiro Sakuma.
Atherosclerosis | 2011
Kwang Kon Koh; Ichiro Sakuma; Michael J. Quon
Reciprocal relationships between endothelial dysfunction and insulin resistance suggest that therapies improving endothelial dysfunction will simultaneously improve insulin sensitivity and other metabolic parameters. However, previous studies with some statins either did not alter insulin sensitivity or promoted insulin resistance despite significant improvements in endothelial dysfunction and decreases in circulating pro-inflammatory markers. This may be due to pleiotropic or off-target effects of some statins to cause insulin resistance by diverse mechanisms unrelated to endothelial dysfunction. Indeed, there is evidence of other differential metabolic actions of distinct statins including effects on hydroxymethylglutaryl-CoA reductase inhibition, isoprotenoid synthesis, calcium release, glucose transport, insulin secretion, and/or insulin resistance. Pravastatin increases expression of adiponectin mRNA, enhances adiponectin secretion, increases plasma levels of adiponectin, and enhances insulin sensitivity in mice and humans. Clinical studies including large scale randomized controlled trials demonstrate potential differences between individual statins, with pravastatin promoting risk reduction for new onset of diabetes. Conversely, other statins including atorvastatin, rosuvastatin, and simvastatin all promote significant increase in this risk. Given the frequent concordance of metabolic diseases including diabetes, obesity, and metabolic syndrome with cardiovascular diseases associated with hyperlipidemia, it is important to understand the potential metabolic risks and benefits of therapies with distinct statins. In this review, we discuss these differential effects of statins on metabolic homeostasis and insulin sensitivity.
IEEE Transactions on Biomedical Engineering | 2010
Hongen Liao; Takashi Inomata; Ichiro Sakuma; Takeyoshi Dohi
A 3-D augmented reality navigation system using autostereoscopic images was developed for MRI-guided surgery. The 3-D images are created by employing an animated autostereoscopic image, integral videography (IV), which provides geometrically accurate 3-D spatial images and reproduces motion parallax without using any supplementary eyeglasses or tracking devices. The spatially projected 3-D images are superimposed onto the surgical area and viewed via a half-slivered mirror. A fast and accurate spatial image registration method was developed for intraoperative IV image-guided therapy. Preliminary experiments showed that the total system error in patient-to-image registration was 0.90 ± 0.21 mm, and the procedure time for guiding a needle toward a target was shortened by 75%. An animal experiment was also conducted to evaluate the performance of the system. The feasibility studies showed that augmented reality of the image overlay system could increase the surgical instrument placement accuracy and reduce the procedure time as a result of intuitive 3-D viewing.
Medical & Biological Engineering & Computing | 2004
Chee-Kong Chui; Etsuko Kobayashi; Xian Chen; Toshiaki Hisada; Ichiro Sakuma
Uniaxial stress-strain data were obtained from in vitro experiments on 20 porcine livers for compressions, elongations and cycles of compression and then elongation. There were about 70 cylindrical samples, with diameter 7 mm and varying height (4–11 mm). The combined compression and elongation test provide a unified framework for both compression and elongation for applications such as computer-aided surgical simulation. It enable the zero stress state of the experimental liver sample to be precisely determined. A new equation that combined both logarithmic and polynomial strain energy forms was proposed in modelling these experimental data. The assumption of incompressibility was justified from a preliminary Poissons ratio for elongation and compression at 0.43±0.16 and 0.47±0.15, respectively. This equation provided a good fit for the observed mechanical properties of liver during compression-elongation cycles and for separate compressions or elongations. The root mean square errors were 91.92±17.43 Pa, 57.55±13.23 Pa and 29.78±17.67 Pa, respectively. In comparison with existing strain energy functions, this combined model was the better constitutive equation. Application of this theoretical model to small liver samples and other tissues demonstrated its suitability as the material model of choice for soft tissue.
Computer Aided Surgery | 1999
Etsuko Kobayashi; Ken Masamune; Ichiro Sakuma; Takeyoshi Dohi; Daijo Hashimoto
This paper describes a new type of laparoscopic manipulator system designed with regard to its safety and sterilization in medical settings. It consists of a laparoscope manipulator using a five-bar linkage mechanism, an optical zoom called the automatic microzoom laparoscope, and a man-machine interface called the Head-Mouse system. The movement of the laparoscope manipulator in the X-Y plane determines the angle of the laparoscope, and the optical zoom substitutes for back-and-forth movements. This system achieves intrinsic safety and ease of sterilization due to limitations in the range of movement. The system achieves high reliability because of the simplicity of both its mechanism and its software. The newly developed optical zoom avoids the possibility of contact with organs by eliminating the back-and-forth movements of the laparoscope required for close-up observation while preserving a high-quality laparoscopic image. The Head-Mouse system for man-machine interface was designed to avoid incorrect inputs by the surgeon. To evaluate the performance of this newly developed system, an experiment was conducted in which a surgeon used the system to perform an in vivo laparoscopic cholecystectomy on a pig.
Medical & Biological Engineering & Computing | 2007
Chee-Kong Chui; Etsuko Kobayashi; Xian Chen; Toshiaki Hisada; Ichiro Sakuma
Knowledge of the biomechanical properties of soft tissue, such as liver, is important in modelling computer aided surgical procedures. Liver tissue does not bear mechanical loads, and, in numerical simulation research, is typically assumed to be isotropic. Nevertheless, a typical biological soft tissue is anisotropic. In vitro uniaxial tension and compression experiments were conducted on porcine cylindrical and cubical liver tissue samples respectively assuming a simplistic architecture of liver tissue with its constituent lobule and connective tissues components. With the primary axis perpendicular to the cross sectional surface of samples, the tissue is stiffer with tensile or compressive force in the axial direction compared to that of the transverse direction. At 20% strain, about twice as much force is required to elongate a longitudinal tissue sample than that of a transverse sample. Results of the study suggest that liver tissue is transversely isotropic. A combined strain energy based constitutive equation for transversely isotropic material is proposed. The improved capability of this equation to model the experimental data compared to its previously disclosed isotropic version suggests that the assumption on the fourth invariant in the constitutive equation is probably correct and that anisotropy properties of liver tissue should be considered in surgical simulation.
international conference of the ieee engineering in medicine and biology society | 2004
Hongen Liao; Nobuhiko Hata; Susumu Nakajima; Makoto Iwahara; Ichiro Sakuma; Takeyoshi Dohi
This paper describes an autostereoscopic image overlay technique that is integrated into a surgical navigation system to superimpose a real three-dimensional (3-D) image onto the patient via a half-silvered mirror. The images are created by employing a modified version of integral videography (IV), which is an animated extension of integral photography. IV records and reproduces 3-D images using a microconvex lens array and flat display; it can display geometrically accurate 3-D autostereoscopic images and reproduce motion parallax without the need for special devices. The use of semitransparent display devices makes it appear that the 3-D image is inside the patients body. This is the first report of applying an autostereoscopic display with an image overlay system in surgical navigation. Experiments demonstrated that the fast IV rendering technique and patient-image registration method produce an average registration accuracy of 1.13 mm. Experiments using a target in phantom agar showed that the system can guide a needle toward a target with an average error of 2.6 mm. Improvement in the quality of the IV display will make this system practical and its use will increase surgical accuracy and reduce invasiveness.
IEEE Transactions on Biomedical Engineering | 2014
Junchen Wang; Hideyuki Suenaga; Kazuto Hoshi; Liangjing Yang; Etsuko Kobayashi; Ichiro Sakuma; Hongen Liao
Computer-assisted oral and maxillofacial surgery (OMS) has been rapidly evolving since the last decade. State-of-the-art surgical navigation in OMS still suffers from bulky tracking sensors, troublesome image registration procedures, patient movement, loss of depth perception in visual guidance, and low navigation accuracy. We present an augmented reality navigation system with automatic marker-free image registration using 3-D image overlay and stereo tracking for dental surgery. A customized stereo camera is designed to track both the patient and instrument. Image registration is performed by patient tracking and real-time 3-D contour matching, without requiring any fiducial and reference markers. Real-time autostereoscopic 3-D imaging is implemented with the help of a consumer-level graphics processing unit. The resulting 3-D image of the patients anatomy is overlaid on the surgical site by a half-silvered mirror using image registration and IP-camera registration to guide the surgeon by exposing hidden critical structures. The 3-D image of the surgical instrument is also overlaid over the real one for an augmented display. The 3-D images present both stereo and motion parallax from which depth perception can be obtained. Experiments were performed to evaluate various aspects of the system; the overall image overlay error of the proposed system was 0.71 mm.
Information Systems | 2003
Ichiro Sakuma; Yosuke Nishimura; Chee-Kong Chui; Etsuko Kobayashi; Hiroshi Inada; Xian Chen; Toshiaki Hisada
There is a need to determine biomechanical properties of liver tissue to develop realistic elastic deformable liver model for computer aided surgery. In this report, we introduced a method to measure mechanical properties using surgical instant adhesive (surgical glue). The method made easier to define the mechanical boundary conditions for test pieces. It also makes it possible to conduct both compression and elongation test on the same test piece. In actual deformation of liver during surgical intervention, the tissue is subject both to compression and elongation. Identification of mechanical properties in the range where mechanical force changes from compression to elongation is important. We can identify the stress-strain relationship of liver samples in the transition range from compression to elongation. We also investigated viscoelastic properties by compressing the sample at different velocities. The obtained results can be applied to non linear FEM analysis of liver tissue.
American Journal of Physiology-heart and Circulatory Physiology | 1998
Atsushi Tamada; Yuichi Hattori; Hideki Houzen; Yoichi Yamada; Ichiro Sakuma; Akira Kitabatake; Morio Kanno
The mechanism of the diminished inotropic response to β-adrenoceptor stimulation in diabetic hearts was studied in enzymatically isolated diabetic rat ventricular myocytes in comparison with age-matched controls. The increases in contractions and intracellular Ca2+ concentration ([Ca2+]i) transients produced by isoproterenol were markedly diminished in diabetic myocytes. The inotropic and [Ca2+]iresponses to forskolin and dibutyryl cAMP (DBcAMP) were also reduced. No significant difference was found in the stimulating effects of isoproterenol, forskolin, and DBcAMP on the L-type Ca2+ current ( I Ca) between control and diabetic myocytes. The rise of [Ca2+]iin response to rapid caffeine application, an index of sarcoplasmic reticulum (SR) Ca2+ content, was significantly decreased in diabetic myocytes. Isoproterenol, forskolin, and DBcAMP enhanced this [Ca2+]iresponse to caffeine in control myocytes more markedly than in diabetic myocytes. The changes in the isoproterenol responses observed in diabetic myocytes were prevented by insulin therapy. We conclude that 1) diabetes causes an impairment of the contractile and [Ca2+]iresponses of cardiac myocytes when stimulated at both β-adrenoceptors and the postreceptor level without affecting the I Ca response and 2) altered SR functions of uptake and/or release of Ca2+ may primarily contribute to the diminished β-adrenergic response.The mechanism of the diminished inotropic response to beta-adrenoceptor stimulation in diabetic hearts was studied in enzymatically isolated diabetic rat ventricular myocytes in comparison with age-matched controls. The increases in contractions and intracellular Ca2+ concentration ([Ca2+]i) transients produced by isoproterenol were markedly diminished in diabetic myocytes. The inotropic and [Ca2+]i responses to forskolin and dibutyryl cAMP (DBcAMP) were also reduced. No significant difference was found in the stimulating effects of isoproterenol, forskolin, and DBcAMP on the L-type Ca2+ current (ICa) between control and diabetic myocytes. The rise of [Ca2+]i in response to rapid caffeine application, an index of sarcoplasmic reticulum (SR) Ca2+ content, was significantly decreased in diabetic myocytes. Isoproterenol, forskolin, and DBcAMP enhanced this [Ca2+]i response to caffeine in control myocytes more markedly than in diabetic myocytes. The changes in the isoproterenol responses observed in diabetic myocytes were prevented by insulin therapy. We conclude that 1) diabetes causes an impairment of the contractile and [Ca2+]i responses of cardiac myocytes when stimulated at both beta-adrenoceptors and the postreceptor level without affecting the ICa response and 2) altered SR functions of uptake and/or release of Ca2+ may primarily contribute to the diminished beta-adrenergic response.
International Journal of Cardiology | 2013
Soo Lim; Yae Min Park; Ichiro Sakuma; Kwang Kon Koh
Lowering low-density lipoprotein-cholesterol (LDL-C) is the primary target in the management of dyslipidemia in patients at high risk of cardiovascular disease. However, patients who have achieved LDL-C levels below the currently recommended targets may still experience cardiovascular events. This may result, in part, from elevated triglyceride (TG) levels and low levels of high-density lipoprotein-cholesterol (HDL-C). Low HDL-C and high TG levels are common and are recognized as independent risk factors for cardiovascular morbidity and mortality. Furthermore, atherogenic dyslipidemia, characterized by low levels of HDL-C, high TG, and small, dense LDL particles, is a typical phenotype of dyslipidemia in subjects with insulin resistance and metabolic syndrome. Therefore, to reduce further the risk of coronary heart disease (CHD), raising HDL-C and lowering TG may be the secondary therapeutic target for patients who achieve LDL-C levels below the currently recommended targets but are still at risk of CHD. However, whether increasing HDL-C levels alone reduces CHD has not yet been confirmed in large randomized clinical trials, and whether functional HDL is more important than HDL-C in reducing CHD remains controversial. Large CHD endpoint trials that include many patients with diabetes are underway to compare combination treatments with statin and niacin, fibrates, or cholesteryl ester transfer protein inhibitors with statin alone treatments. In this review, we discuss the rationale and importance of increasing HDL-C levels with and without lowering TG levels in the treatment and prevention of cardiovascular events.