Properties of phantom tissuelike polymethylpentene in the frequency range 20-70 MHZ.

Quantitative ultrasound (QUS) has been used to characterize soft tissues at ordinary abdominal ultrasound frequencies (2 to 15 MHz) and is beginning application at high frequencies (20 to 70 MHz). For example, backscatter and attenuation coefficients can be estimated in vivo using a reference phantom. At high frequencies, it is crucial that reverberations do not compromise the measurements. Such reverberations can occur between the phantom's scanning window and transducer components as well as within the scanning window between its surfaces. Transducers are designed to minimize reverberations between the transducer and soft tissue. Thus, the acoustic impedance of a phantom scanning window should be tissuelike; polymethylpentene (TPX) is commonly used because of its tissuelike acoustic impedance. For QUS, it is also crucial to correct for the transmission coefficient of the scanning window. Computation of the latter requires knowledge of the ultrasonic properties, viz, density, speed and attenuation coefficients. This work reports values for the ultrasonic properties of two versions of TPX over the high-frequency range. One form (TPX film) is used as a scanning window on high-frequency phantoms, and at 40 MHz and 22°C was found to have an attenuation coefficient of 120 dB/cm and a propagation speed of 2093 m/s.

A new 15-50 MHz array-based micro-ultrasound scanner for preclinical imaging.

Most institutions now have a suite of imaging tools to follow mouse models of human disease. Micro-ultrasound is one of these tools and is second after whole-mouse fluorescence or bioluminescent imaging, in terms of installed systems. We report in this paper the first commercially available array transducer-based ultrasound imaging system that enables micro-ultrasound imaging at center frequencies between 15 and 50 MHz. At the heart of the new scanner is a laser-machined high-frequency 256 element, linear transducer array capable of forming dynamic diffraction limited beams. The power of the linear array approach is embodied in the uniform high resolution maintained over the full field of view. This leads to greatly expanded scope for real-time functional imaging that is demonstrated in this paper. The unprecedented images made with the new imaging system will enable many new applications not previously possible. These include real-time visualization of flow in the mouse placenta, visualization of flow development in the embryo, studies of embryonic to adult cardiac development/disease, and studies of real-time blood flow in mouse models of tumour angiogenesis.