| A needle-based imaging system has been developed for high frequency ultrasound applications. A 775 mum by 540 mum PZT imaging transducer is mounted in the bevel of a needle to create a probe, and the needle rotated about its axis to generate radial sweep images. Characterization of these probes, operating at a frequency of 41 MHz, has shown the ability of the system to routinely obtain axial and lateral resolution levels of 44 mum and 95 mum respectively. Other measured specifications include an 80% bandwidth, and 4--8 mm ultrasound penetration depth in ex vivo kidney and liver tissues. In vitro phantom work has demonstrated the system's ability to clearly quantify sub-millimeter cast vessels, with image quality and resolution far surpassing clinical intravascular ultrasound systems, which utilize similar transducers. Images of ex vivo human liver and kidney tissue samples show good structural correlation with corresponding histology sections. Differentiation based on tissue type was performed using spectral slope and intercept parameters. Preliminary in vitro pulsed wave Doppler studies have demonstrated the feasibility of detecting blood flows on the order of 1--2 mm/s using the needle probe. |
