In studying the feasibility of developing tissue-targeted contrast media that can be administered as liquids and vaporized by an external stimulus such as ultrasound, we have investigated the properties of emulsions of nanometer-size particles containing perfluoropentane and 2H,3H-perfluoropentane. We found that the ultrasound intensity required to induce echographically significant vaporization can be controlled by changing the ratio of 2H,3H-perfluoropentane to perfluoropentane and that the intensity threshold increases as this ratio increases. Significant azeotropic phenomena were not observed when the perfluorocarbon mixtures were heated, which indicates that mechanisms other than azotropy are involved in the threshold change. The vaporization of 2H,3H-perfluoropentane may have been due not only to ultrasound energy but also to the energy deposited by ultrasonically induced bubbles of perfluoropentane. Our results might lead to a phase-shift contrast agent with controllable ultrasound energy for phase shifting.

It is known that the combination of laser light and its sensitizer is effective for noninvasive tumor treatment, referred to as photodynamic therapy. Using the combination of ultrasound and its sensitizer has also been suggested for a similar kind of tumor treatment, referred to as sonodynamic therapy. The purpose of this paper is to obtain such sensitizers accumulating selectively in tumors. Amphiphilic derivatives of rose bengal (RB) were synthesized to add a tumor-accumulating property to RB. One type of the synthesized RB derivatives (RBD3), having an alkyl chain with a branching carboxyl group, was found to be superior in amphiphilicity to the other types. Tumor tissue distribution of the synthesized derivatives in mice bearing colon 26 carcinoma was evaluated. It was found that RBD3s with carbon chain lengths of 12, 14, and 16 had higher concentrations in the tumor tissue than RB by more than 1 order of magnitude, several hours after administration. The concentrations correlated well with their water/1-octanol partition coefficients. Since RB is known to induce in vitro cell damage in combination with either laser light or ultrasound, the newly synthesized amphiphilic RB derivatives may be potentially useful as a tumor-selective sensitizer for both light and ultrasound.

Fine platelet particles of barium ferrite wereWe have studied the Ba-ferrite particles, which prepared by the hydrothermal precipitation technique. The were prepared by the hydrothermal precipitation magnetic properties such as magnetization, coercivity and method [9,lO]. There are some advantages in the temperature variation of the coercivity can be controlled by hydrothermal preparation : fine particles with narrow size the selection of the substitution elements. Non-stoichiometric distribution can be easily obtained. In the present paper, we Co2+-Ti4+ substitution yields the formation of the fine will report the preparation and the magnetic properties of particles, and further the replacement of Co2+ by Ni2' the Ba-ferrite particles, which are synthesized by the reduces the temperature variation degree of the coercivity. hydrothermal procedure.These fine particles are thought to be good candidates for highIn addition, fine acicular particles of metal a-Fe density recording. Furthermore, we briefly discussed on the have been considered as the other candidate for high density preparation procedure of fine a-Fe acicular particles.recording materials. We have studied the preparation of metal iron fine particles as well as Ba-ferrite particles. On some of the problems : narrowing particle size distribution, I INTRODUCTION increase in coercivity and resistance to environmental corrosion, we'll briefly present our experimental results. Magnetic iron oxide particles have been widely used in many applications such as pigments of paint, they have mechanical hardness and chemical stability. In magnetic recording media, it is well known that acicular iron oxide particles are coated on the substrate with longitudinal orientation. In t h~s configuration, the FeC136%0 and BaC1, were dissolved in distilled demagnetizing field causes instability of the remanent water, and the molar ratio of Fe3+/Ba2+ was adjusted to magnetization, as the recording density increases [l]. about 9. Some of the Fe3+ were replaced by other cations Therefore, there exists a limitation in the high density such as Co2+, Ni2+ and Ti4+ in order to inocllfy the recording of the longitudnal recording system. magnetic properties. The cationic solutions were mixedIn 1977, S. Iwasaki and Y. Nakamura reported with NaOH aqueous solution, and the alkaline suspensions the perpendicular magnetic recording system based on thin containing various amount of excess NaOH ( 3 to 9M ) were film media, in which the remanent magnetization cannot be prepared. Then the alkaline suspensions were inserted into reduced by the demagnetizing field[2]. Since then, many a stainless steel autoclave, and subjected to hydrothermal researchers have extensively studied and developed the treatment at temperature from 150 "C to 300 "C for four perpendicular recording system using thin film media of hours, followed by slow cooling to room temperature. The Co-Cr or others for high density recording [3,4]. In 1982, precipitates were separated with filtration, washed with Toshiba corporation...

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