For over 30 years, there have been parallel research environments associated with ultrasound propagation through cancellous bone; aimed at characterisation for osteoporotic fracture risk assessment and overcoming transcranial wave degradation for diagnostic imaging of the brain respectively. The Langton Concept offers a new approach applicable to both. It considers ultrasound propagation as an array of parallel sonic-rays, the transit time of each determined by the proportion of bone and marrow propagated. It also hypothesises that the primary ultrasound attenuation mechanism is phase-interference due to heterogeneity of transit time created by variations in thickness and composition [1].

The current ‘active’ solution to overcome transcranial wave degradation utilises a phased-array ultrasound transducer, necessitating complex electronic control of transmission delay for each individual element.

The author hypothesised that wave degradation could be minimised if both the propagation path-length (spatial) and transit-time (temporal) for all sonic-rays was made constant. A ‘passive’ spatial-temporal ultrasound phase-interference compensator (UPIC), consisting of two layered materials of variable thickness has been developed. An experimental study was performed in transmission-mode on six cylindrical acrylic step-wedge samples, ranging from 2 to 20 steps, each creating a corresponding number of sonic-rays of different transit time. A spatial-temporal matched UPIC model was designed for each step-wedge sample and replicated using 3D-printing. Time- and frequency-domain analysis demonstrated that incorporation of the UPIC successfully removed phase-interference induced wave degradation in all cases.

It is further hypothesised that the UPIC concept may a) be applicable to any ultrasound frequency, either single-element or multi-element array transducer, of any practicable dimension; and b) facilitate ultrasound imaging of other soft-tissues where propagation through bone has previously been considered an impediment.

1. Langton C M; 2011; 25th Anniversary of BUA for the assessment of osteoporosis – Time for a new paradigm?; Journal of Engineering in Medicine, 225, 113-125