Stabilization of Gas Bubbles Released from Water-Soluble Carbohydrates Using Amphiphilic Compounds: Preparation of Formulations and Acoustic Monitoring of Bubble Lifetime
The ultrasound contrast agents Echovist® and Levovist® (Bayer AG, Schering AG, Germany) are based on the release of gas bubbles from milled α-d-galactose. In diagnostic ultrasound, for this class of contrast agents, there is a need for prolonged contrast duration. To investigate if new carbohydrate compositions could prolong the lifetime of the gas bubbles, α-d-galactose was mixed with other carbohydrates or amphiphiles with varying log P. Acoustic attenuation vs. time (390 s) area under the curve (A390) and bubble half-time (t½) were used as measures of prolonged lifetime of gas bubbles. The products, to which 0.1% of a lipophilic carboxylic acid (5β-cholanic acid, behenic acid, and melissic acid) has been added, showed more than 5, 7 and 11 times enhancement of A390, respectively, compared with the reference compound 2 (RC2) corresponding to the commercial product Levovist®. The half-time t ½ of the same compounds was prolonged more than 6 times compared with RC2. A partial least square (PLS) statistical analysis confirmed that, for additives, high log P carboxylic acids lead to the highest A390. The present results bear a promise of products with a more persistent in vivo ultrasound contrast effect than the commercially available agents.
Perfluorocarbon-loaded micro and nanosystems for medical imaging: A state of the art
Abstract Perfluorocarbons (PFCs) are fluorinated compounds widely used in the past as oxygen carriers. They have been the focus of research as contrast agents for ultrasonography and fluorine magnetic resonance imaging (MRI). For ultrasonography, most contrast agents use gaseous PFCs and some are approved for clinical use. Liquid PFCs, however, are being studied for the past decade due to their improved stability under ultrasound waves. For fluorine MRI, liquid PFCs are preferred due to their higher fluorine concentration, but for the moment no product is on the market yet. For both these imaging modalities, a large body of formulation is needed to allow safe PFC injection in the bloodstream. In this review, we will focus on PFC encapsulation into micro and nanosystems for medical imaging purposes, from research to the clinics.
Local Gas Holdup and Mass Transfer in a Bubble Column Using an Ultrasonic Technique and a Neural Network
The gas holdup and the volumetric mass transfer coefficient are very important parameters for mass transfer operation in bubble columns. These parameters have been major subjects for many researches for a long time. In this study, a novel technique of ultrasonics and neural network has been proposed to determine the local gas holdup and the volumetric mass transfer coefficient in a two-dimensional bubble column simultaneously. The measurement parameters of the energy attenuation and the time shift difference of ultrasound are used to obtain the local gas holdup and the volumetric mass transfer coefficient in dispersed systems of air-water and air-glycerol solution using the neural network reconstruction. In the range studied, the representative results of the proposed technique show a good agreement with the experimental data.