Y. Saijo

Low-intensity Ultrasound Induces a Transient Increase in Intracellular Calcium and Enhancement of Nitric Oxide Production in Bovine Aortic Endothelial Cells

Background: Nitric oxide (NO) plays a key role in regulating various biological processes including vasodilation, neurotransmission, inflammatory responses, the immune system and apoptosis. In endothelial cells, the production of NO is known to be enhanced in response to mechanical stimulation through intracellular calcium-mediated activation of endothelial nitric oxide synthase (eNOS). In this study, we investigated whether low-intensity ultrasound is capable of mechanically stimulating endothelial cells, which leads to an increase in intracellular calcium and enhancement of NO production. Methods and Results: Cultured bovine aortic endothelial cells (BAECs) were loaded with Calcium Green-1 AM, a calcium-sensitive fluorescent dye, and then exposed to low-intensity ultrasound for 1 min. During the exposure, an increase in fluorescence intensity was observed by laser scanning confocal microscopy. This result indicated that lowintensity ultrasound acted as a mechanical stimulus and induced a transient increase in intracellular calcium in BAECs. To measure the change in NO production, cultured BAECs were exposed to low-intensity ultrasound for 0 (control), 30 and 120 min while loaded with NO-sensitive fluorescent indicator dye DAF-2DA. The fluorescence intensities of the BAECs obtained by laser scanning confocal microscopy were increased in proportion to the exposure time, suggesting that lowintensity ultrasound enhanced NO production in the cells. Conclusions: Low-intensity ultrasound can mechanically stimulate BAECs, resulting in an enhancement of NO production through the activation of the intracellular calcium signaling pathway. Further studies are needed to elucidate the mechanism by which ultrasound increases NO production at a molecular level.

4C-4 B-Mode and C-Mode Imaging of Regenerated 3D Skin Model with 100 MHz Ultrasound

Regenerated skin with 3D structure is desired for the treatment of large burn and for the plastic surgery. High frequency ultrasound is suitable for non-destructive testing of the skin model because it provides information on morphology and mechanical properties. An acoustic microscope system capable of imaging B-mode and C-mode was developed for analysis of 3D skin model. C-mode imaging provided quantitative values of attenuation and sound speed. B-mode imaging showed fine structure of the model. Sound speed in C-mode and intensity in B-mode imaging showed higher values at the area of dense fibroblasts. The system can be used as the nondestructive evaluation tool in the process of producing 3D skin model and as the in vivo imaging system after transplantation.

P1D-3 A System for Tissue Characterization and Quantification of Calcium Regions in Intravascular Ultrasound

This paper presents a combination of signal processing and image processing techniques for automatic segmentation and characterization of intravascular ultrasound images. This system is comprised of two modules, the tissue characterization module and the calcium quantification module. The tissue characterization module is based on classification of RF signal performed by a self-organizing map (SOM) previously trained. The calcium quantification module, using the image generated by the envelop of the RF signal, performs an adaptive thresholding based on the Otsus method. The thresholding process is followed by the analysis of the acoustic shadow regime of the input image which permits to distinguish calcification regions from other small bright regions that, usually, still remain in the image after the thresholding processing

High Frequency Ultrasound Imaging of Cartilage-Bone Complex

High frequency ultrasound microscope with central frequency of 100 MHz was developed. The system was capable of (1) conventional C-mode acoustic microscope imaging of thinly sliced tissue, (2) ultrasound impedance imaging of the surface of in vitro thick tissue and (3) 3D ultrasound imaging of inside of the in vitro tissue. In the present study, cylindrical cartilage-bone unit specimens were removed from rat knee joints and evaluated with the equipment. The resolution was enough to visualize the articular cartilage surface morphology and the subchondral bone. Compared with histological sections observed by optical microscope, it can also differentiate the non-calcified zone and calcified zone of the articular cartilage. High frequency ultrasound microscope will provide important information of the structural changes of the articular cartilage.

Tangible Modelling of Ventricular Aneurysm

Myocardial infarction (MI) may cause left ventricular aneurysms (LVAs) as the long-term and obsolete complications. Following MI, the scar will replace the necrotic lesion within a few weeks. As a result, a portion of the left ventricular free wall protrudes, which leads to appearance of LVAs. The three dimensional echocardiography, the computed tomography and the magnetic resonance imaging (MRI) are the most effective tools to diagnose the left ventricular volumetric function and its wall motion. And the primary choice to treat LVAs is surgical therapy, which is called the left ventricular reconstructive surgery (LVRS). The LVRS such as Dor procedure is performed to resume the left ventricular shape and its original myocardial fibre orientation as much as possible. Furthermore, we also have to consider the location of the couple of papillary muscle in order to maintain the mitral valvular functions. When the ventricle dilates due to the obsolete MI, the papillary muscles might be displaced away from the mitral valvular annulus, leading to decreased coaptaion of the mitral leaflets and mitral regurgitation. As the clinical status, the surgeons establish the surgical planning of LVRS according to their design, evidence and experience base on the diagnostic imaging, which is difficult to estimate the postoperative cardiac function and structure quantitatively. The purpose of this study was to support surgeons to examine more quantitative surgical strategies by dint of engineering approach as fabrication of diseased ventricular tangible elastic model and numerical analyses in each patient prior to the treatment. Then we developed a prototyping method of fabrication for elastic ventricular models by the normal sequence of MRI data, which could show the identical and quantitative representation of diagnostic imaging. It is anticipated that these methods could realise the quantitative images and expressions as well as the intercommunity to the strategy of surgical therapy to reduce the patients’ risk. As the results:

First Trial of the Chronic Animal Examination of the Artificial Myocardial Function

Thromboembolic and haemorrhagic complications are the primary causes of mortality and morbidity in patients with artificial hearts, which are known to be induced by the interactions between blood flow and artificial material surfaces. The authors have been developing a new mechanical artificial myocardial assist device by using a sophisticated shape memory alloy fibre in order to achieve the mechanical cardiac support from outside of the heart without a direct blood contacting surface. The original material employed as the actuator of artificial myocardial assist devices was 100um fibred-shaped, which was composed of covalent and metallic bonding structure and designed to generate 4–7 % shortening by Joule heating induced by the electric current input. Prior to the experiment, the myocardial streamlines were investigated by using a MDCT, and the design of artificial myocardial assist devices were refined based on the concept of Torrent-Guasp’s myocardial band theory. As the hydrodynamic or hemodynamic examination exhibited the remarkable increase of cardiac systolic work by the assistance of the artificial myocardial contraction in the originally designed mock circulatory system as well as in the acute animal experiments, the chronic animal test has been started in a goat. Total weight of the device including the actuator was around 150g, and the electric power was supplied percutaneously. The device could be successfully installed into thoracic cavity, which was able to be girdling the left ventricle. In the chronic animal trial, the complication in respect to the diastolic dysfunction by the artificial myocardial compression was not observed.

Hemodynamic response with an artificial myocardial assistance in chronic animal examination

Thromboembolic and haemorrhagic complications are the primary causes of mortality and morbidity in patients with artificial hearts, which are known to be induced by the interactions between blood flow and artificial material surfaces. The authors have been developing a new mechanical artificial myocardial assist device by using a sophisticated shape memory alloy fibre in order to achieve the mechanical cardiac support from outside of the heart without a direct blood contacting surface. The original material employed as the actuator of artificial myocardial assist devices was 100um fibred-shaped, which was composed of covalent and metallic bonding structure and designed to generate 4-7 % by Joule heating induced by the electric current input. Prior to the experiment, the myocardial streamlines were investigated by using a MDCT, and the design of artificial myocardial assist devices were refined based on the concept of Torrent-Guasp’s myocardial band theory. As the hydrodynamic or hemodynamic examination exhibited the remarkable increase of cardiac systolic work by the assistance of the artificial myocardial contraction in the originally designed mock circulatory system as well as in the acute animal experiments, the chronic animal test has been started in a goat. Total weight of the device including the actuator was around 150g, and the electric power was supplied percutaneously. The device could be successfully installed into thoracic cavity, which was able to be girdling the left ventricle. In the chronic animal trial, the complication in respect to the diastolic dysfunction by the artificial myocardial compression was not observed. Systolic pressure and aortic flow waveforms were elevated by the assistance using the device contraction synchronously by around 5%. And blood pressure response against the increase of aortic pressure was investigated under the myocardial assisted condition in order to examine the vascular tone which was controlled by vagal nervous activity.

Engineering Support in Surgical Strategy for Ventriculoplasty

Endoventricular patch plasty, called the Dor procedure, is performed as a heart reconstruction for the surgical treatment of the patients with severe heart failure associated with anteroapical large myocardial infarction. The authors have been establishing a new engineering method for the individual simulation of operational procedure in order to determine the optimal left ventricular size and shape and to estimate the volumetric reduction after the surgical ventricular restoration in each patient. In this study, three individual ventricular shapes were fabricated by numerically resampled data which were obtained from the diagnostic magnetic resonance imaging in each subject. Prior to the fabrication of the models, epi- or endocardial envelope curve was outlined without papillary muscles or tendinous cords in each end-diastolic and end-systolic phase for the compatible reference in echocardiogram, computed tomography or magnetic resonance imaging investigations. And the mechanical silicone rubber models were made by the use of female moulding for the discussion of each subject among surgeons. In this paper, we examined a methodology for the simulation of ventriculoplasty by using a silicone rubber model and evaluated the capability of quantitative expression of ejection fraction.

Radio Frequency Signal Analysis for Tissue Characterization of Coronary Artery: In Vivo Intravascular Ultrasound Study

Intravascular ultrasound (IVUS) is an important clinical tool that provides high resolution cross-sectional image of coronary artery. However, it is difficult to accurately classify plaque composition by conventional IVUS images. In the present study, we apply self-organizing map (SOM) of radiofrequency (RF) signal spectra for automatic plaque classification in IVUS diagnosis. IVUS data were acquired with a commercially available IVUS system with the central frequency of 40 MHz. We used double SOM classifier. The 1st classifier is supervised-SOM, learned four structures (blood, catheter, shadow, and outer lumen) based on spectral parameters. The 2nd classifier is unsupervised-SOM, used for classifying remained data, which were not classified the 1st classifier. We defined categories on the 2nd SOM by using K-means clustering method. Finally, color codes were assigned to the plaque component values, and the tissue color coded maps were reconstructed. Results suggest that the proposed technique is useful for automatic characterization of plaque components in IVUS image.

Support Mechanism of a Newly-Designed Mechanical Artificial Myocardium using Shape Memory Alloy Fi bres

As the heart failure is caused by the decrease in the myocardial contraction, the direct mechanical myocardial assistance in response to physiological demand, that is, the synchronous support of the contractile function from outside of the heart, might be effective. The purpose of this study was to develop an artificial myocardium which was capable of supporting the cardiac contraction directly by using the shape memory alloy fibres based on nanotechnology. Some methodologies using novel devices other than the artificial hearts are proposed so far with severe heart disease. However, it was also anticipated that the decrease in cardiac functions owing to the diastolic disability might be caused by using those ‘static’ devices. Then, this study was focused on an artificial myocardium using shape memory alloy fibres with a diameter of 100 – 150 um, and the authors examined its mechanism in a mock circulatory system as well as in animal experiments using goats. Basic characteristics of the material were evaluated prior to the hydrodynamic or hemodynamic examination using a mock ventricular model. The results were as follows: a) The length of the structure was able to be adjusted so that the system could wrap the whole heart effectively. b) In the hydrodynamic study using the mock circulatory system, the myocardial system was able to pump a flow against the afterload of arterial pressure level. c) In the animal experiments, aortic pressure and flow rate were elevated by 7 and 15% respectively by the mechanical assistance of the artificial myocardium, which was driven synchronising with the electrocardiogram, and also, d) The anatomically-identical shape of the artificial myocardium might be more effective for the assistance. In conclusion, it was indicated that this controllable artificial myocardial support system was effective for the mechanical cardiac support for the chronic heart failure.