Acoustic angiography is a contrast-enhanced, superharmonic microvascular imaging method. It has shown the capability of high-resolution and high-contrast-to-tissue-ratio (CTR) imaging for vascular structure near tumor. Dual-frequency ultrasound transducers and arrays are usually used for this new imaging technique. Stacked-type dual-frequency transducers have been developed for this vascular imaging method by exciting injected microbubble contrast agent (MCA) in the vessels with low-frequency (1-5 MHz), moderate power ultrasound burst waves and receiving the superharmonic responses from MCA by a high-frequency receiver (>10 MHz). The main challenge of the conventional dual-frequency transducers is a limited penetration depth (<25 mm) due to the insufficient receiving sensitivity for highfrequency harmonic signal detection. A receiver with a high receiving sensitivity spanning a wide superharmonic frequency range (3rd to 6th) enables selectable bubble harmonic detection considering the required penetration depth. Here, we develop a new dual-frequency transducer composed of a 2 MHz 1-3 composite transmitter and a polyvinylidene fluoride (PVDF) receiver with a receiving frequency range of 4-12 MHz for adjustable harmonic imaging. The developed transducer was tested for harmonic responses from a microbubble-injected vessel-mimicking tube positioned 45 mm away. Despite the long imaging distance (45 mm), the prototype transducer detected clear harmonic response with the contrast-to-noise ratio of 6-20 dB and the -6 dB axial resolution of 200-350 μm for imaging a 200 um-diameter cellulose tube filled with microbubbles.
Acoustic Angiography is a new approach to high-resolution contrast enhanced ultrasound imaging enabled by ultra-broadband transducer designs. The high frequency imaging technique provides signal separation from tissue which does not produce significant harmonics in the same frequency range, as well as high resolution. This approach enables imaging of microvasculature in-vivo with high resolution and signal to noise, producing images that resemble x-ray angiography. Data shows that acoustic angiography can provide important information about the presence of disease based on vascular patterns, and may enable a new paradigm in medical imaging.
We describe early stage experiments to test the feasibility of an ultrasound brain helmet to produce multiple
simultaneous real-time 3D scans of the cerebral vasculature from temporal and suboccipital acoustic windows of the
skull. The transducer hardware and software of the Volumetrics Medical Imaging real-time 3D scanner were modified to
support dual 2.5 MHz matrix arrays of 256 transmit elements and 128 receive elements which produce two simultaneous
64° pyramidal scans. The real-time display format consists of two coronal B-mode images merged into a 128° sector,
two simultaneous parasagittal images merged into a 128° × 64° C-mode plane, and a simultaneous 64° axial image.
Real-time 3D color Doppler images acquired in initial clinical studies after contrast injection demonstrate flow in several
representative blood vessels. An offline Doppler rendering of data from two transducers simultaneously scanning via the
temporal windows provides an early visualization of the flow in vessels on both sides of the brain. The long-term goal is
to produce real-time 3D ultrasound images of the cerebral vasculature from a portable unit capable of internet
transmission, thus enabling interactive 3D imaging, remote diagnosis and earlier therapeutic intervention. We are
motivated by the urgency for rapid diagnosis of stroke due to the short time window of effective therapeutic intervention.