Through-transmission medical imaging using phase-insensitive pyroelectric ultrasonic detectors

Abstract

Ultrasonic Computed Tomography (UCT) has been unable to rival its x-ray counterpart in terms of reliably distinguishing different tissue pathologies. Conventional piezoelectric detectors deployed in UCT are phase-sensitive and it is well established that their use can give rise to phase-cancellation artefacts that mask true tissue structure. In contrast, phase-insensitive detectors are more immune to this effect, although sufficiently sensitive devices for clinical use are not yet available. This paper establishes proof-of-concept for a novel phase-insensitive transducer for UCT. The detector employs an acoustic absorber to convert received acoustic intensity into heat that is subsequently detected using the pyroelectric response of a thin piezoelectric membrane bonded intimately to the absorber. The paper explores UCT application of the phase-insensitive detectors, comparing with traditional detection methods. Results are presented for a range of detector apertures; tomographic reconstruction images being compared using stable two-phase phantoms containing inserts as small as 3 mm. The project has demonstrated that the new detectors are significantly less susceptible to refraction and phase-cancellation artefacts, generating realistic images in situations where conventional techniques were unable to do so. The novel detector holds promise as the basis of a new type of clinical UCT system.