P.A. Hultman

Bio: P.A. Hultman is an academic researcher. The author has contributed to research in topics: Imaging phantom & Intensive care. The author has an hindex of 3, co-authored 3 publications receiving 85 citations.

High-density flexible interconnect for two-dimensional ultrasound arrays

Abstract: We present a method for fabricating flexible multilayer circuits for interconnection to 2-D array ultrasound transducers. In addition, we describe four 2-D arrays in which such flexible interconnect is implemented, including transthoracic arrays with 438 channels operating at up to 7 MHz and intracardiac catheter arrays with 70 channels operating at up to 7 MHz. We employ thin and thick film microfabrication techniques to batch produce the interconnect circuits with minimum dimensions of 12-/spl mu/m lines, 40-/spl mu/m vias, and 150-/spl mu/m array pitch. The arrays show 50-/spl Omega/ insertion loss of -60 to -84 dB and a fractional bandwidth of 27 to 67%. The arrays are used to obtain real time, in vivo volumetric scans.

Update of two dimensional arrays for real time volumetric and real time intracardiac imaging

Abstract: The authors have previously described 2-D array transducers with up to several thousand elements operating at frequencies between 2.5 and 5.0 MHz for real time volumetric imaging. Lately, there has been interest in developing catheter based intracardiac imaging systems to aid in the precise tracking of anatomical features and intracardiac devices for improved diagnoses and therapies. The authors constructed several arrays for real time intracardiac volumetric imaging based upon 2 different designs; a 13/spl times/11=143 element 5.0 MHz 2-D array for side scanning applications, and a 10/spl times/10=100 element 7.0 MHz 2-D array for side scanning applications. The 5.0 MHz array fits into a 12 French (3.8 mm OD) catheter and the 7.0 MHz transducer is designed to fit into a 9 French (2.9 mm OD) catheter. The authors also constructed 2 transducers for transthoracic imaging; a 40/spl times/40 5.0 MHz 2-D array, and a 40/spl times/40 7.0 MHz 2-D array. The -6 dB fractional bandwidths for the transducers varied from 27% to 67%. All the transducers were constructed on a 6 layer polyimide interconnect. Both transthoracic and intracardiac volumetric images of ultrasound phantoms and animal models have been obtained using the Duke University real time volumetric imaging system which is capable of generating multiple planes at any desired angle and depth within a pyramidal volume.

Two dimensional arrays for real time volumetric and intracardiac imaging with simultaneous electrocardiogram

Abstract: The authors have previously described 2D arrays operating up to 7.0 MHz consisting of several thousand elements for transthoracic cardiac imaging and up to 200 elements for intracardiac imaging. Most recently, the authors have constructed a 10.0 MHz array that includes 120/spl times/120=14,400 elements for real time transthoracic volumetric imaging. The resulting bandwidth is 27% and the 50 Ohm insertion loss is -68 dB. Real time volumetric images in phantoms have been made. There is interest in developing catheter based intracardiac imaging systems to aid in the precise tracking of anatomical features and interventional devices for improved diagnoses and therapies. Potential clinical applications include guidance of cardiac electrophysiological mapping and ablation procedures, long term monitoring of ventricular volumes in intensive care units and guidance of cardiac revascularization procedures using laser and drug angiogenic agents. The authors have constructed catheter array transducers with ECG electrodes for collecting electrophysiological data simultaneously with their images. There are 5 ring electrodes and 1 tip electrode for each transducer. The transducers consist of a 13/spl times/11=143 element array operating at 5.0 MHz and fits into a 12 French catheter (OD=3.8 mm). The first transducer array design is for side scanning applications. The second transducer layout has been inclined to a 20/spl deg/ bevel to improve image acquisition. The -6 dB fractional bandwidths for the different arrays varied from 40% to 63%, and the 50 Ohm insertion loss for the transducers was approximately -64 dB. Both the transducers were constructed on a 6 layer flexible polyimide interconnect Real time phantom images and intracardiac volumetric images in animal models have been obtained using the Duke University real time volumetric imaging system, which is capable of generating multiple planes at any desired angle and depth within a pyramidal volume. The authors obtained in vivo images of the ventricles and atria as well as simultaneous acquisition of 3 bipolar intracardiac ECG signals. With the real time volumetric scanner, the authors also guided and monitored the RF ablation of an excised sheep left ventricle. Cross section and face on images show excellent contrast between ablated versus normal myocardium.

Integration of 2D CMUT arrays with front-end electronics for volumetric ultrasound imaging

Abstract: For three-dimensional (3D) ultrasound imaging, connecting elements of a two-dimensional (2D) transducer array to the imaging system's front-end electronics is a challenge because of the large number of array elements and the small element size. To compactly connect the transducer array with electronics, we flip-chip bond a 2D 16 times 16-element capacitive micromachined ultrasonic transducer (CMUT) array to a custom-designed integrated circuit (IC). Through-wafer interconnects are used to connect the CMUT elements on the top side of the array with flip-chip bond pads on the back side. The IC provides a 25-V pulser and a transimpedance preamplifier to each element of the array. For each of three characterized devices, the element yield is excellent (99 to 100% of the elements are functional). Center frequencies range from 2.6 MHz to 5.1 MHz. For pulse-echo operation, the average -6-dB fractional bandwidth is as high as 125%. Transmit pressures normalized to the face of the transducer are as high as 339 kPa and input-referred receiver noise is typically 1.2 to 2.1 rnPa/ radicHz. The flip-chip bonded devices were used to acquire 3D synthetic aperture images of a wire-target phantom. Combining the transducer array and IC, as shown in this paper, allows for better utilization of large arrays, improves receive sensitivity, and may lead to new imaging techniques that depend on transducer arrays that are closely coupled to IC electronics.

Volumetric ultrasound imaging using 2-D CMUT arrays

Abstract: Recently, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as a candidate to overcome the difficulties in the realization of 2-D arrays for real-time 3-D imaging. In this paper, we present the first volumetric images obtained using a 2-D CMUT array. We have fabricated a 128/spl times/128-element 2-D CMUT array with through-wafer via interconnects and a 420-/spl mu/m element pitch. As an experimental prototype, a 32/spl times/64-element portion of the 128/spl times/128-element array was diced and flip-chip bonded onto a glass fanout chip. This chip provides individual leads from a central 16/spl times/16-element portion of the array to surrounding bondpads. An 8/spl times/16-element portion of the array was used in the experiments along with a 128-channel data acquisition system. For imaging phantoms, we used a 2.37-mm diameter steel sphere located 10 mm from the array center and two 12-mm-thick Plexiglas plates located 20 mm and 60 mm from the array. A 4/spl times/4 group of elements in the middle of the 8/spl times/16-element array was used in transmit, and the remaining elements were used to receive the echo signals. The echo signal obtained from the spherical target presented a frequency spectrum centered at 4.37 MHz with a 100% fractional bandwidth, whereas the frequency spectrum for the echo signal from the parallel plate phantom was centered at 3.44 MHz with a 91% fractional bandwidth. The images were reconstructed by using RF beamforming and synthetic phased array approaches and visualized by surface rendering and multiplanar slicing techniques. The image of the spherical target has been used to approximate the point spread function of the system and is compared with theoretical expectations. This study experimentally demonstrates that 2-D CMUT arrays can be fabricated with high yield using silicon IC-fabrication processes, individual electrical connections can be provided using through-wafer vias, and flip-chip bonding can be used to integrate these dense 2-D arrays with electronic circuits for practical 3-D imaging applications.

An integrated circuit with transmit beamforming flip-chip bonded to a 2-D CMUT array for 3-D ultrasound imaging

Abstract: State-of-the-art 3-D medical ultrasound imaging requires transmitting and receiving ultrasound using a 2-D array of ultrasound transducers with hundreds or thousands of elements. A tight combination of the transducer array with integrated circuitry eliminates bulky cables connecting the elements of the transducer array to a separate system of electronics. Furthermore, preamplifiers located close to the array can lead to improved receive sensitivity. A combined IC and transducer array can lead to a portable, high-performance, and inexpensive 3-D ultrasound imaging system. This paper presents an IC flip-chip bonded to a 16times16-element capacitive micromachined ultrasonic transducer (CMUT) array for 3-D ultrasound imaging. The IC includes a transmit beamformer that generates 25-V unipolar pulses with programmable focusing delays to 224 of the 256 transducer elements. One-shot circuits allow adjustment of the pulse widths for different ultrasound transducer center frequencies. For receiving reflected ultrasound signals, the IC uses the 32-elements along the array diagonals. The IC provides each receiving element with a low-noise 25-MHz-bandwidth transimpedance amplifier. Using a field-programmable gate array (FPGA) clocked at 100 MHz to operate the IC, the IC generated properly timed transmit pulses with 5-ns accuracy. With the IC flip-chip bonded to a CMUT array, we show that the IC can produce steered and focused ultrasound beams. We present 2-D and 3-D images of a wire phantom and 2-D orthogonal cross-sectional images (Bscans) of a latex heart phantom.

Microsystem technologies for implantable applications

Abstract: Microsystem technologies (MST) have become the basis of a large industry. The advantages of MST compared to other technologies provide opportunities for application in implantable biomedical devices. This paper presents a general and broad literature review of MST for implantable applications focused on the technical domain. A classification scheme is introduced to order the examples, basic technological building blocks relevant for implantable applications are described and finally a case study on the role of microsystems for one clinical condition is presented. We observe that the microfabricated parts span a wide range for implantable applications in various clinical areas. There are 94 active and 67 commercial 'end items' out of a total of 142. End item refers to the total concept, of which the microsystem may only be a part. From the 105 active end items 18 (13% of total number of end items) are classified as products. From these 18 products, there are only two for chronic use. The number of active end items in clinical, animal and proto phase for chronic use is 17, 13 and 20, respectively. The average year of first publication of chronic end items that are still in the animal or clinical phase is 1994 (n = 7) and 1993 (n = 11), respectively. The major technology–market combinations are sensors for cardiovascular, drug delivery for drug delivery and electrodes for neurology and ophthalmology. Together these form 51% of all end items. Pressure sensors form the majority of sensors and there is just one product (considered to be an implantable microsystem) in the neurological area. Micro-machined ceramic packages, glass sealed packages and polymer encapsulations are used. Glass to metal seals are used for feedthroughs. Interconnection techniques such as flip chip, wirebonding or conductive epoxy as used in the semiconductor packaging and assembly industry are also used for manufacturing of implantable devices. Coatings are polymers or metal. As an alternative to implantable primary batteries, rechargeable batteries were introduced or concepts in which energy is provided from the outside based on inductive coupling. Long-term developments aiming at autonomous power are, for example, based on electrostatic conversion of mechanical vibrations. Communication with the implantable device is usually done using an inductive link. A large range of materials commonly used in microfabrication are also used for implantable microsystems.