Katherine Louise Dextraze MS, Presenter: Nothing to Disclose

Christopher J. MacLellan BS, Abstract Co-Author: Nothing to Disclose

Trevor M. Mitcham BS, Abstract Co-Author: Nothing to Disclose

Marites Pasuelo Melancon PhD, Abstract Co-Author: Nothing to Disclose

Richard R. Bouchard PhD, Abstract Co-Author: Nothing to Disclose

Photoacoustic ultrasonic (PAUS) is capable of measuring temperature non-invasively while simultaneously providing anatomical images, making it a promising new technique for guiding and monitoring photothermal ablations.  In order to assess the potential clinical role of PAUS imaging, the technique was validated against the clinically accepted magnetic resonance thermal imaging approach (MRTI).

To facilitate co-registration between PAUS and MR images, a tissue-mimicking agar phantom was designed which had inclusions of gold nanoshells encapsulating super-paramagnetic iron oxide (SPIO) particles, where gold enhances the PA signal and SPIOs provide negative contrast on MRI. PA images were acquired on a Vevo LAZR (FUJIFILM VisualSonics Inc., Toronto, Ontario) PA-ultrasound small-animal imaging system (21MHz) operating at 710nm. MRTI experiments were performed using a 6-channel flex coil (GE Healthcare, Waukesha, WI) on a 3T MRI scanner (Discovery MR750, GE Healthcare, Waukesha, WI) using a fast multi gradient echo acquisition (16 echoes, 128x128 acquisition matrix, 25.6x25.6cm field of view, 3mm slice thickness, 60ms TR, 20⁰ flip angle, 2.9ms minimum TE and 1.6ms echo spacing). The accuracy and spatio-temporal resolution of PA thermography was cross-validated with both MRTI and a fluoroptic temperature sensor (LumaSense Technologies, Santa Clara, CA) in the custom-designed phantom. 

A thermally stable, dual-modality phantom was created for cross-validation of PA thermography and MRTI. PA thermography was characterized for thermal therapy guidance and compared to clinically-accepted MRI techniques and fluoroptic probe measurements. The PA signal was shown to change linearly across a temperature range of 35°C–55°C, within the limits of typical ablation temperature. Axial and lateral resolutions of PA images were sub-millimeter with a temporal resolution of 0.2s, which will accommodate precise real-time guidance and monitoring. 

The sub-millimeter resolution and centimeter-order penetration depths achievable with PAUS imaging have the potential to deliver active monitoring of both a targeted tumor microenvironment and nearby healthy tissue during thermal ablation.

The development of photoacoustic thermography as a precise, real-time technique for image-guidance and monitoring of thermal ablations will facilitate adaptive planning that may improve treatment efficacy.

Dextraze, K, MacLellan, C, Mitcham, T, Melancon, M, Bouchard, R, Characterization of Photoacoustic Thermography for Image-guidance and Monitoring of Photothermal Ablations.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011715.html