Transcranial passive acoustic mapping with hemispherical sparse arrays using CT-based skull-specific aberration corrections: a simulation study

• Published in: Physics in medicine & biology 2013-07, Vol.58 (14), p.4981-5005
• Main Authors: Jones, Ryan M, O'Reilly, Meaghan A, Hynynen, Kullervo
• Format: Article
• Language: English
• Subjects: Acoustics; Algorithms; beamforming; biomedical acoustics; Feasibility Studies; focused ultrasound; Humans; Image Processing, Computer-Assisted - methods; Models, Biological; Organ Specificity; passive acoustic mapping; Skull - anatomy & histology; Skull - diagnostic imaging; sparse phased arrays; Tomography, X-Ray Computed; transcranial brain therapy; Ultrasonography
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/58/14/4981

The feasibility of transcranial passive acoustic mapping with hemispherical sparse arrays (30 cm diameter, 16 to 1372 elements, 2.48 mm receiver diameter) using CT-based aberration corrections was investigated via numerical simulations. A multi-layered ray acoustic transcranial ultrasound propagation model based on CT-derived skull morphology was developed. By incorporating skull-specific aberration corrections into a conventional passive beamforming algorithm (Norton and Won 2000 IEEE Trans. Geosci. Remote Sens. 38 1337-43), simulated acoustic source fields representing the emissions from acoustically-stimulated microbubbles were spatially mapped through three digitized human skulls, with the transskull reconstructions closely matching the water-path control images. Image quality was quantified based on main lobe beamwidths, peak sidelobe ratio, and image signal-to-noise ratio. The effects on the resulting image quality of the source's emission frequency and location within the skull cavity, the array sparsity and element configuration, the receiver element sensitivity, and the specific skull morphology were all investigated. The system's resolution capabilities were also estimated for various degrees of array sparsity. Passive imaging of acoustic sources through an intact skull was shown possible with sparse hemispherical imaging arrays. This technique may be useful for the monitoring and control of transcranial focused ultrasound (FUS) treatments, particularly non-thermal, cavitation-mediated applications such as FUS-induced blood-brain barrier disruption or sonothrombolysis, for which no real-time monitoring techniques currently exist.