SIMULTANEOUS IMAGING OF A lacZ-MARKED TUMOR AND MICROVASCULATURE MORPHOLOGY IN VIVO BY DUAL-WAVELENGTH PHOTOACOUSTIC MICROSCOPY

Photoacoustic molecular imaging,combined with the reporter-gene technique,can provide a valuable tool for cancer research.The expression of the lacZ reporter gene can be imaged using photoacoustic imaging following the injection of X-gal,a colorimetric assay for the lacZ-encoded enzymeβ-galactosidase.Dual-wavelength photoacoustic microscopy was used to non-invasively image the detailed morphology of a lacZ-marked 9L gliosarcoma and its surrounding microvasculature simultaneously in vivo,with a superior resolution on the order of 10μm.Tumor-feeding vessels were found,and the expression level of lacZ in tumor was estimated.With future development of new absorption-enhancing reporter-gene systems,we anticipate this strategy can lead to a better understanding of the role of tumor metabolism in cancer initiation,progression,and metastasis,and in its response to therapy.

Outperforming piezoelectric ultrasonics with highreliability single-membrane CMUT array elements

It has long been hypothesized that capacitive micromachined ultrasound transducers(CMUTs)could potentially outperform piezoelectric technologies.However,challenges with dielectric charging,operational hysteresis,and transmit sensitivity have stood as obstacles to these performance outcomes.In this paper,we introduce key architectural features to enable high-reliability CMUTs with enhanced performance.Typically,a CMUT element in an array is designed with an ensemble of smaller membranes oscillating together to transmit or detect ultrasound waves.However,this approach can lead to unreliable behavior and suboptimal transmit performance if these smaller membranes osilate out of phase or collapse at different voltages.In this work,we designed CMUT array elements composed of a single long rectangular membrane,with the aim of improving the output pressure and electromechanical efficiency.We compare the performance of three different modifications of this architecture:traditional contiguous dielectric,isolated isolation post(P),and insulated electrode-post(EP)CMUTs.EPs were designed to improve performance while also imparting robustness to charging and minimization of hysteresis.To fabricate these devices,a wafer-bonding process was developed with near-100%bonding yield.EP CMUT elements achieved electromechanical effciency values as high as 0.95,higher than values reported with either piezoelectric transducers or previous CMUT architectures.Moreover,all investigated CMUT architectures exhibited transmit effciency 2-3 times greater than published CMUT or piezoelectric transducer elements in the 1.5-2.0 MHz range.The EP and lip CMUTs demonstrated considerable charging robustness,demonstrating minimal charging over 500,000 collapse-snap-back actuation cycles while also mitigating hysteresis.Our proposed approach offers significant promise for future ultrasonic applications.