Kawan Soetanto

Ultrasound speckle analysis based on the K distribution

The departure of speckle magnitude from Rayleigh statistics was applied to examine insonated phantoms with both low and high concentrations of scatterers. A mathematical model, the K distribution of Jakeman, was used to characterize non-Rayleigh statistics. This model contains a parameter, alpha, which characterizes the clustering of the scattering sites in a medium. It is shown from phantom experiments that alpha is linearly proportional to the log-scaled scatterer concentration in a range from about 1 to 30 scatterers per sample volume.

Fundamental studies on contrast images from different-sized microbubbles: analytical and experimental studies.

Microbubbles are very useful as ultrasound (US) contrast agents because of their excellent scattering properties. Because microbubbles of different sizes can be used for this purpose, the contrast images produced by different-sized microbubbles are studied in this paper. The contrast images from microbubbles of average sizes 35.5 microm and 2.1 microm were investigated experimentally. Although a low concentration of microbubbles produces contrast-enhanced images without artefacts, an excess of microbubbles results in distorted images. From experimental observation, the distortion of an image caused by microbubbles of average size 35.5 microm was mainly due to multiple scattering, and that by 2.1-microm microbubbles was due to the acoustic shadowing effect. With the use of the tissue-mimicking phantoms of known acoustical properties, the brightness of the contrast images from the microbubble suspension was calculated. The calculated and experimental results of the contrast images produced from microbubbles of average size 35.5 microm were closer to each other when there was no image distortion. When image distortion caused by multiple-scattering occurred, the experimental pixel brightness was higher. For smaller microbubbles of average size 2.1 microm, calculated results of free microbubbles showed a weaker contrast effect than the experimental results. By taking the effect of the coatings of microbubbles into consideration, the calculated brightness of contrast images became much closer to the experimental one.

Development of Magnetic Microbubbles for Drug Delivery System(DDS)

The purpose of this study is to develop a new ultrasonic contrast agent for the drug delivery system (DDS). Ferromagnetic materials or magnetic carbons were placed on the surfaces of the surfactant microbubbles developed in our laboratory for the above purpose. Multivalent ions such as calcium ions were used to place the ferromagnetic materials or magnetic carbons on the surfaces of the microbubbles. It was confirmed that the developed magnetic microbubbles could be lead by a permanent magnet. Furthermore, the performance of the magnetic microbubbles was evaluated by measuring the time dependence of the attenuation constant as one of their acoustic properties.

Study on the lifetime and attenuation properties of microbubbles coated with carboxylic acid salts.

Four kinds of surfactants, sodium laurate, sodium myristate, sodium palmitate and sodium oleate were used to study the effects of surfactant coatings on the lifetime and attenuation of microbubbles. The changes in the size distribution of microbubbles prepared with these surfactants in saline were measured with a Coulter Multisizer (Coulter Electronics Ltd., Luton, UK). Frequency characteristics of ultrasonic attenuation of the microbubble suspensions were measured between 400 kHz and 6 MHz. From the changes in attenuation in the microbubble suspensions over time, it was found that the lifetime of microbubbles in a suspension also depends on the frequency of the irradiating ultrasound. The effect of surfactants on the frequency characteristics of attenuation was also studied, and characteristics of the surfactant coating, including shell elasticity and shell friction parameters were calculated from the measurement results. Microbubbles produced with sodium palmitate had the longest lifetime and the smallest average size. The shell had very little effect on the ultrasonic properties of microbubbles produced with sodium palmitate, suggesting that the sodium palmitate microbubbles behaved ultrasonically as free microbubbles.

The surface characteristics of the sintered body of hydroxyapatite-zirconia composite particles

Abstract In this study, the surface characteristics of the sintered body were evaluated by means of confocal scanning laser microscopy and contact angle measurement. Laser microscopic observations showed that the addition of partially stabilized zircornia (PSZ) causes an increase in the fracture surface roughness. This increase was due to the particles in the sintered body bonding tightly together through the added PSZ. Consequently, the sintered body prepared in this manner had a high bulk strength, thus showing an advantage of PSZ. Furthermore, the contact angle value of the sintered body lapped surface was not significantly affected by the addition of PSZ. This suggests that the hydroxyapatite (HAP)-PSZ sintered body also has a potential for good biocompatibility with bone tissue.

Effect of Calcium Chloride on Sodium Alginate Microbubbles as Ultrasound Contrast Agent

In order to stabilize microbubbles without coating layers to be used as ultrasound contrast agent, the viscosity of the liquid for storage has to be increased. Sodium alginate is a material which forms viscous liquid when its powder is dissolved in water. The viscosity may vary from 1 cP to about 100 cP when the amount of material used is increased from 0.1% to 1%. However, the viscosity is still not enough to make stable microbubbles which can be stored for over several weeks. In this paper, by adding calcium chloride to the sodium alginate solution, a gel-type solution is produced which has a high viscosity capable of holding microbubbles for a long time. By measuring the viscosity of the sodium alginate solution and the solution with calcium chloride solution added, it is known that the solution is changed from a Newtonian liquid to a non-Newtonian liquid when calcium chloride solution is added. Since the attenuation coefficient of microbubble dispersion is proportional to the number of microbubbles, the disappearance of microbubbles lowers the attenuation coefficient. Therefore, in this study, the attenuation coefficient is used as an estimating parameter for the lifetime of microbubbles.

Simulations of Contrast Effects from Free Microbubbles in Relation to Their Size, Concentration and Acoustic Properties.

To gain a deeper insight into the diagnostic images produced by microbubbles as ultrasound contrast agents, the basic acoustical properties such as the scattering cross section, extinction cross section and the expected backscattered power from different sized microbubbles are calculated. The results proved that the ratio of scattering to extinction cross section, size and concentration of microbubbles are the factors determining the maximum backscattered power received from microbubble dispersions. When microbubbles decrease in size, the energy loss by microbubbles upon ultrasound exposure gradually changes from loss by scattering to loss by absorption. As a result, the concentration of microbubbles required to produce a B mode image of the comparable brightness is increased. However, an increased concentration of microbubbles does not necessarily produce a clearer image. In this paper, it is further established that an optimum concentration exists at which the microbubbles give maximum backscattered power. The optimum microbubble concentration and the maximum backscattered power also depend on the depth of the microbubbles in the microbubble dispersion. In addition, the concentration of microbubbles necessary to produce the maximum backscattered power during resonance is less than that at other frequencies.

Change in size and number of sodium laurate microbubbles with time in saline at different air concentrations

The study of the annihilation mechanisms of microbubbles is a very important, topic in the development of ultrasound contrast agents. To gain better insight into the annihilation mechanisms, knowledge of the change in the number and size of microbubbles with time in saline is necessary. In this study, the use of a Coulter Multisizer is proposed, and the change in number and size of microbubbles is accurately measured. As a result, mechanisms for longevity and annihilation are suggested. Sodium laurate is used for tlle coating layer of tlle microbubbles. The measured longevity of sodium laurate microbubbles is compared with the results of a simulation of free air microbubbles. Although the coating layers lower the diffusion rate of air from microbubbles, diffusion still occurs. Tlle diffusion of air contributes to the size of the microbubbles and the dissolution of the surfactant coating layer causes a decrease in the number of microbubbles. The reasons for these assertions are discussed in this paper. When the concentration of dissolved air in saline is close to saturation, the annhilation mechanism of sodium laurate microbubbles changes to the dissolution of tlle coating layer into the solution. In addition, it is proposed from the experimental results that small particles less than 10 μm in size which dissolve slowly in saline are formed after the shrinking of microbubbles by diffusion.

Miniprobe transducer for tissue characterization

A design for PVDF transducers in which ultrasound transducers are fabricated at the tips of calipers (analog and digital) as miniprobes is proposed. A goal was to design a miniprobe transducer that is convenient to use during surgical operation. This probe will be able to estimate the speed and attenuation of sound, as well as backscattering from small regions. Measurement techniques for this purpose are suggested. Several prototype ultrasonic miniprobes are presented and discussed. The feasibility of this miniprobe was verified by using measurements of liquids and phantoms. The proposed technique will provide in vivo data, which is of major importance in the evaluation of tissue characterization. Measuring tissue properties in vivo is highly desirable to obviate concerns about changes of tissue properties following blood stains and coagulation, autolysis, temperature change, or fixation.<<ETX>>

Ferromagnetic ultrasound microbubbles contrast agent

Microbubbles have attracted attention as ultrasonic contrast agents because their ultrasonic scattering property is excellent in comparison with other ultrasonic contrast agents. In the development of ultrasound contrast agent, the main difficulties accounted are the making of small microbubbles less than 10 /spl mu/m and the elongation of the lifetime of microbubbles. A new ultrasonic contrast agent, which is microbubbles typed coating by surfactant, has been developed. The contrast images produced by different-sized microbubbles contrast agents are studied quantitatively. Furthermore, a ferromagnetic ultrasound contrast agent was also studied for its potential as a Drug Delivery System (DDS). In this paper, a new ultrasonic contrast agent for the Drug Delivery System will be discussed. Ferromagnetic materials are placed on the surfaces of the surfactant microbubbles developed in our laboratory for the above purpose. Multivalent ions such as calcium ions are used to put the ferromagnetic materials on the surfaces of the microbubbles. It is confirmed that the developed magnetic microbubbles could be lead by a permanent magnet. The performance of the magnetic microbubbles is evaluated by measuring the time dependence of the attenuation constant as one of their acoustic properties.