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.
Two studies have been conducted using real time 3D ultrasound and an automated robot system for carrying out surgical
tasks. The first task is to perform a breast lesion biopsy automatically after detection by ultrasound. Combining 3D
ultrasound with traditional mammography allows real time guidance of the biopsy needle. Image processing techniques
analyze volumes to calculate the location of a target lesion. This position was converted into the coordinate system of a
three axis robot which moved a needle probe to touch the lesion. The second task is to remove shrapnel from a tissue
phantom autonomously. In some emergency situations, shrapnel detection in the body is necessary for quick treatment.
Furthermore, small or uneven shrapnel geometry may hinder location by typical ultrasound imaging methods. Vibrations
and small displacements can be induced in ferromagnetic shrapnel by a variable electromagnet. We used real time 3D
color Doppler to locate this motion for 2 mm long needle fragments and determined the 3D position of the fragment in
the scanner coordinates. The rms error of the image guided robot for 5 trials was 1.06 mm for this task which was
accomplished in 76 seconds.
We describe catheter ring arrays for real-time 3D ultrasound guidance of devices such as vascular grafts, heart valves
and vena cava filters. We have constructed several prototypes operating at 5 MHz and consisting of 54 elements using
the W.L. Gore & Associates, Inc. micro-miniature ribbon cables. We have recently constructed a new transducer using a
braided wiring technology from Precision Interconnect. This transducer consists of 54 elements at 4.8 MHz with pitch
of 0.20 mm and typical -6 dB bandwidth of 22%. In all cases, the transducer and wiring assembly were integrated with
an 11 French catheter of a Cook Medical deployment device for vena cava filters. Preliminary in vivo and in vitro testing
is ongoing including simultaneous 3D ultrasound and x-ray fluoroscopy.
We have integrated real time volumetric ultrasound imaging and ultrasound ablation in the same intracardiac catheter. This single device could be used to visualize ablation sites in three dimensions immediately prior to inducing necrosis to eliminate cardiac arrythmias. After the course of therapy, the ablated tissue could be examined ultrasonically. The 12 Fr catheter includes a 2D transducer array for imaging and a single element piston for ablation. The imaging transducer consists of 38 active elements built on a multilayer flex circuit operating at 5.2 Mhz. The ablation piston is a 4 mm by 2 mm piece of air backed PZT-4. Our real time 3D scanner (Volumetrics Medical Imaging) and the 2D array were used to image phantom targets. The spatial peak, temporal average intensity (I<sub>SPTA</sub>) and acoustic power of the ablation beam were measured using a hydrophone. A 7 mm thick slab of beef was imaged and then ablated for 1 minute. The ultrasound ablation piston produced an I<sub>SPTA</sub> of nearly 30 W/cm<sup>2</sup> and a corresponding acoustic power of 2.6 W. The electrical to acoustic power efficiency of the transducer was 39%. The minute long ablation produced a transmural lesion in the beef 2mm by 4 mm by 7 mm deep.
We have previously described 2D arrays of several thousand elements operating up to 5.0 MHz for transthoracic cardiac imaging. Lately, there has been interest in developing catheter based intracardiac imaging systems to aid in the precise tracking of anatomical features for improved diagnoses and therapies. We have constructed several arrays for real time intracardiac volumetric imaging based upon two different designs; a 10 X 10 equals 100 element 5.0 MHz forward looking 2D array, and a 13 X 11 equals 143 element 5.0 MHz 2D array for side scanning applications.