A 1‐MHz linear phased array ultrasound system for imaging the major intracranial arteries

A linear phased array ultrasound system has been constructed to image the major intracranial arteries from the superior surface of the cranium. The transducer array consists of 20 elements, 1.54 mm wide and 15 mm long, with an interelement spacing of 0.19 mm. Ten elements are excited for each transmit pulse and excitation pulses are phased for nominal transmit focus of 7 cm. On the receive side, echo signals from each element are logarithmically compressed and dynamically focussed by variable delay lines to within ±25 ns of an ideal phase coherent system at the input to a summing amplifier. The transmit/receive response results in a −6 dB beamwidth of about 6 mm at a depth of 7 cm. A two‐dimensional image is formed by sequencing consecutive ten elements along the array. The major intracranial arteries imaged include the internal carotids in the intradural pertion of the siphon, the middle cerebrals as they travel laterally from the internal carotid arteries, the basilar artery, the posterior cerebral arte...