The ultrasound brain helmet: new transducers and volume registration for in vivo simultaneous multi-transducer 3-D transcranial imaging

Abstract

Because stroke remains an important and time-sensitive health concern in developed nations, we present a system capable of fusing 3-D transcranial ultrasound volumes acquired from two sides of the head. This system uses custom sparse array transducers built on flexible multilayer circuits that can be positioned for simultaneous imaging through both temporal acoustic windows, allowing for potential registration of multiple real-time 3-D scans of cerebral vasculature. We examine hardware considerations for new matrix arrays—transducer design and interconnects—in this application. Specifically, it is proposed that SNR may be increased by reducing the length of probe cables. This claim is evaluated as part of the presented system through simulation, experimental data, and in vivo imaging. Ultimately, gains in SNR of 7 dB are realized by replacing a standard probe cable with a much shorter flex interconnect; higher gains may be possible using ribbon-based probe cables. In vivo images are presented, showing cerebral arteries with and without the use of microbubble contrast agent; they have been registered and fused using a simple algorithm which maximizes normalized cross-correlation.

Design of a 2D sparse array transducer for integration into an ergonomic transcranial ultrasound system

“…For the purposes of comparison, the parameters common to all array configurations were set to have the same candidate values for all the array configurations. By iterating through all candidate parameter values for each configuration, all possible sparse array patterns have been simulated using (1), (2), (3) and (4). For each array configuration, the PSL and ISLR were calculated and stored.…”

“…Unfortunately, this is not practical to manufacture. For the transducer designed in this project, the aperture size is set to 3 cm in diameter to fit the size of the temporal window [4]. As the speed of sound in the brain is 1550 m/s [5], the operating wavelength will be 0.775mm if we operate at a 2MHz center frequency, which is common in such medical applications [2].…”

A super‐resolution ultrasound method for brain vascular mapping

“…The concentration of bubbles was estimated based on a maximum of 1.2 × 10 10 bubbles per ml of undiluted agent immediately following activation (http://www.definityimaging.com/pdf/DEFINITY %20Prescribing%20Information%20515987-0413.pdf), and assuming a loss of 50% of the bubble population due to handling. 26 A conservative estimate based on published work in humans 11 would suggest that the concentrations used in this study are approximately one one-thousandth of those in the blood stream for transcranial Doppler ultrasound.…”

“…However, since axial resolution for pulse-echo sonography depends on pulse length, which increases with decreasing frequency, this approach sacrifices resolution and has limited the use of ultrasound to imaging major vessels. 10,11 Here, we use a passive technique similar to those previously used in acoustics 12 and seismic imaging, 13 modifications of which have more recently been investigated to map cavitation activity during ultrasound therapy. 14,15 With passive beamforming techniques both the phase and amplitude information of the received signals are considered and axial resolution primarily depends on frequency and array aperture, and not on pulse length.…”

Noninvasive Diagnosis of Blood Flow for Transcranial Doppler Ultrasonography

“…The transcranial sonography in Ref. Lindsey et al (2011) has been proposed using 2.5 MHz 2D array probes. However, it is difficult to transmit ultrasound from the random position.…”