OBJECTIVE: To allow quantified delivery of ultrasound to window chamber without optically obscuring the view through its glass windows.

Methods: Microscopic window chamber consists of a sheet-metal frame and a removable glass window. The frame is used to create a thin skin/tissue flap in the dorsal area of an animal. The flap provides convenient access for implantation of tumor into a defined location and allows in vivo growth to be continuously observed microscopically. The ultrasound stimulated/triggered drug delivery using microbubble carriers is one of current research topics, where imaging techniques of the delivery process at cellular level in-vivo is very beneficial. We designed a transducer that allows ultrasound energy delivery into a standard window chamber without optically obscuring access to the window. This permits use of fluorescent imaging techniques while ultrasound is delivered. The transducer consists of a 6.4 mm diameter, 3.5 MHz center frequency, PZT4 transducer bonded to an acoustical buffer rod. The buffer rod is made of fused quartz which is a low-ultrasound-attenuation and an optically-transparent material. The rod has a cylindrical shape of 6.4 mm diameter and is cut at 60 degree angle at the distal end from the PZT transducer (Fig. 1). Either ultrasound gel or a small drop of water is used to couple the distal end of the buffer rod placed directly onto the window chamber. The transducer is driven with RF generator at the resonant frequency of the transducer. Pressure field at 2 mm distance from the face of the acoustical rod was measured with scanning PVDF hydrophone. Efficiency of the transducer and spectral content of the acoustical output were calculated from pressure field.

Results: Spectral components generated in the buffer rod stayed 15dB below the fundamental signal and were considered insignificant. The rest of measured data will be presented at the meeting.

Conclusions: Acoustical rods represent an adequate and “dry” means of ultrasound energy transfer to microscopic window chamber permitting simultaneous use of optical imaging techniques.