Phased Array Ultrasound System Research Articles

Design Strategies for Phased Array Ultrasound Systems in Nondestructive Testing

Design Strategies for Phased Array Ultrasound Systems in Nondestructive Testing

New Phased Array Ultrasound System Based on DSP/BOIS and PCI Bus

New Phased Array Ultrasound System Based on DSP/BOIS and PCI Bus

500-element ultrasound phased array system for noninvasive focal surgery of the brain: a preliminary rabbit study with ex vivo human skulls.

The aim of this study was to test a prototype MRI-compatible focused ultrasound phased array system for trans-skull brain tissue ablation. Rabbit thigh muscle and brain were sonicated with a prototype, hemispherical 500-element ultrasound phased array operating at frequencies of 700-800 kHz. An ex vivo human skull sample was placed between the array and the animal tissue. The temperature elevation during 20-30-sec sonications was monitored using MRI thermometry. The induced focal lesions were observed in T2 and contrast-enhanced T1-weighted fast spin echo images. Whole brain histology evaluation was performed after the sonications. The results showed that sharp temperature elevations can be produced both in the thigh muscle and in the brain. High-power sonications (600-1080 W) produced peak temperatures up to 55 degrees C and focal lesions that were consistent with thermal tissue damage. The lesion size was found to increase with increasing peak temperature. The device was then modified to operate in the orientation that will be used in the clinic and successfully tested in phantom experiments. As a conclusion, this study demonstrates that it is possible to create ultrasound-induced lesions in vivo through a human skull under MRI guidance with this large-scale phased array.

Pilot point temperature regulation for thermal lesion control during ultrasound thermal therapy

The fundamental goal of ultrasound thermal therapy is to provide proper thermal lesion formations for effective tumour treatment. The quality of the therapy depends mostly on its positional precision. To date, most ultrasound thermal therapy treatments have focused on the formation of power or temperature patterns. The non-linear and time-delay effects of thermal dose formation prohibit direct control of the thermal dose distribution. In the paper, the control of thermal lesions by regulation of the temperature of a pilot point is proposed. This scheme utilises the high correlation between temperature elevation and thermal dose at the forward boundary of thermal lesions. To verify the feasibility, a 2D ultrasound phased array system was used to generate thermal lesions of various sizes, and the temperature elevation required to generate a thermal dose threshold was investigated. Results showed that the required temperature elevation was found to be a reasonably constant value of 52.5 degrees C under differing conditions when the focal area was small. When the focal area under consideration was large, the required temperature elevation became a monotonic function of blood perfusion rate, ranging from 49.2 to 52.5 degrees C. When the reference temperature of the pilot point was set at a conservative value (52.5 degrees C), the thermal lesions were controlled precisely under a wide range of blood perfusion and power pattern changes, tested by using a more realistic model that takes into account thermal-induced attenuation and blood perfusion changes. This changed the complex thermal dose control problem into a simple temperature regulation problem, which makes implementation of thermal lesion control easier, giving the scheme a high potential for application to current ultrasound thermal therapy systems.

Treatment time reduction for large thermal lesions by using a multiple 1D ultrasound phased array system

To generate large thermal lesions in ultrasound thermal therapy, cooling intermissions are usually introduced during the treatment to prevent near-field heating, which leads to a long treatment time. A possible strategy to shorten the total treatment time is to eliminate the cooling intermissions. In this study, the two methods, power optimization and acoustic window enlargement, for reducing power accumulation in the near field are combined to investigate the feasibility of continuously heating a large target region (maximally 3.2 × 3.2 × 3.2 cm3). A multiple 1D ultrasound phased array system generates the foci to scan the target region. Simulations show that the target region can be successfully heated without cooling and no near-field heating occurs. Moreover, due to the fact that there is no cooling time during the heating sessions, the total treatment time is significantly reduced to only several minutes, compared to the existing several hours.

Quantitative estimation of attenuation in ultrasound video images: correlation with histology in diffuse liver disease.

To determine the relationship between the attenuation of backscatter intensity in B-scan images of the liver and diffuse liver disease in order to assess the usefulness of this method in providing quantitative objective characterization of diffuse liver diseases in general and in fatty liver in particular. Twenty-four healthy volunteers and 28 patients with elevated liver enzyme levels who underwent liver biopsy were included in this study. An automatic far-field slope (FFS) algorithm that estimates the decrease in amplitude of the backscattered echo as a function of beam depth was implemented on the noncompensated image that was acquired on a commercial phased-array ultrasound system fitted to a custom-built interface card. The images were processed at a work-station. All scans were acquired repeatedly, read, and graded blindly by experienced ultrasound radiologists. Histology obtained via needle biopsy was reviewed without knowledge of the ultrasound findings. Analysis of the FFS data for fatty infiltration in all patient groups yielded a sensitivity of 67%, a specificity of 77%, a positive predictive value (PPV) of 77%, negative predictive value (NPV) of 67%, and an accuracy of 71%. The mean score of the ultrasound reviewers showed a sensitivity of 82%, a specificity of 66%, a PPV% of 68%, an NPV of 81%, and an accuracy of 72%. Normal FFS values (false-negative) were found in five patients with proved fatty infiltration. All of these patients had coexistent moderate to severe hepatic inflammation. However, FFS data in patients with uncomplicated (pure) fatty infiltration revealed a sensitivity of 100%, a specificity of 80%, a PPV of 89%, an NPV of 100%, and an accuracy of 92%. The best ultrasound score yielded a sensitivity of 100%, a specificity of 60%, a PPV of 80%, an NPV of 100%, and an accuracy of 85% in the same patients. The data demonstrate an excellent sensitivity (100%) of the FFS values in patients with uncomplicated fatty infiltration. This was also the only group of patients in whom the FFS score was superior to the radiologists' best score. The FFS method can be used as a tool to follow up the response to a clinical or research treatment and to obtain standardization of pattern interpretation independently of the individual reader.

An image-guided ultrasound phased array system for noninvasive surgery

An integrated image-guided therapeutic phased array system for noninvasive surgical applications is being developed. The therapeutic array utilizes piezocomposite transducer technology and operates (therapeutically) at 1 and 2 MHz. It has 64 elements on a spherical shell with a geometric center at 100 mm from its apex. The array was shown to be capable of producing well-defined thermal lesions in tissue media at depths from 40 to 60 mm and to scan therapeutic foci up to ±15 mm from its geometric center. Image guidance is provided by a modified diagnostic ultrasound scanner which, in addition to providing standard B-scan images of the target region, provides real-time images of the temperature rise due to the therapeutic beam. The temperature information is obtained using a correlation based algorithm for echo displacement estimation, which can be directly related to local variation in tissue temperature due to the therapeutic beam. A complete description of the system will be given along with illustrative examples of image-guided tissue ablation and temperature estimation and control. In addition, experimental data demonstrating the use of the therapeutic array in an imaging mode will be presented. [Work funded by NIH Grant CA66602.]

Phased array ultrasound system and method for cardiac ablation

An ultrasound system and method for performing relatively non-invasive cardiac ablation on a patient. The system of the present invention includes a plurality of ultrasound transducers forming a phased array that is to be located externally of the patient. The array a focused beam of sufficient energy to ablate a predetermined cardiac tissue volume. The system is capable of refocusing the beam so that acoustical aberrations encountered by the beam, as it is transmitted through inhomogeneous body tissues between the array and the treatment volume, are taken into account and will not impede operation of the system. To refocus the beam, the system includes a senor which senses the phase distribution caused by the aberrations allowing a controller to calculate a compensating driving phase distribution and accordingly drive the array. The system also allows for real time correction of the beam's position enabling the beam to follow a moving myocardial target volume.

Design and experimental evaluation of an intracavitary ultrasound phased array system for hyperthermia.

For evaluating the feasibility of treating prostate cancer, a 64-element linear ultrasound phased array applicator for intracavitary hyperthermia was designed and constructed. A 64-channel ultrasound driving system including amplifiers, phase shifters, and RF power meters was also developed to drive the array. The design of the array and driving equipment are presented, as are the results of acoustical field measurements and in vitro perfused phantom studies performed with the array. Several techniques for heating realistically sized tumor volumes were also investigated, including single focus scanning and two techniques for producing multiple stationary foci. The results show that the operation of the array correlated closely with the theoretical model. When producing a single stationary focus, the array was able to increase tissue temperature by 12 degrees C in vitro in perfused phantom. With some minor improvements in array design, intracavitary phased arrays could be evaluated in a clinical environment.

Transcranial color-coded real-time sonography in adults.

We investigated the diagnostic potential of transcranial color-coded real-time sonography in 52 individuals using a phased-array ultrasound system with color-coded blood flow representation. Ultrasound scans in the axial and coronal planes were feasible through temporal acoustic bone windows in 49 subjects, enabling depiction of the main parenchymal and vascular structures as well as the ventricular system. Color-coded representation of blood flow in the cerebral vessels allowed unequivocal identification of the circle of Willis within the anatomic black-and-white B-mode image of the parenchymal structures. In Doppler mode, vascular blood flow phenomena may be analyzed semiquantitatively using the Doppler frequency spectrum. This noninvasive, serially applicable, mobile beside method may complement conventional neuroradiologic imaging methods, allowing on-line studies of functional processes within the adult brain.

Segmentation of echocardiographic images using mathematical morphology.

A semiautomatic technique for isolating the ventricular endocardial border in echocardiograms from a commercially available two-dimensional phased array ultrasound system is presented. This method processes echo images using mathematical morphology to reduce the effects of range and azimuth variation inherent in echo. After morphological filtering, the endocardial border is extracted with traditional segmentation methods. Further processing of the resulting border using binary morphology produces a region of interest suitable for derivation of motion parameters of the endocardium. The area and the shape of semiautomatically-derived regions correlate well (r>0.93) with those defined by expert observers in a study of induced ischemia in seven canines.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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 arteries as they follow the lateral aspect of the midbrain, and the perical-losal artery as it travels posteriorly along the superior surface of the corpus callosum. It is our interest to interface this linear phased array system with an on-line digital moving target indicator system to produce a two-dimensional image of only the intracranial arteries. [Work supported by NINCDS grant NS-06655.]

Dynamic cardiac imaging using a focused, phased-array ultrasound system

A two-dimensional ultrasound imaging system capable of producing high resolution, cross-sectional images of the heart in real-time has been developed. This system relies upon phased-array principles to rapidly steer and focus the ultrasound beam through the cardiac structures under investigation. A hand-held, linear array of 24 transducers is manipulated on the anterior chest wall to image various cardiac structures. Images of high line density are presented in selectable sector arcs to a maximum of 90 degrees. This imaging system has proved particularly useful for the detection of a variety of left ventricular and cardiac valvular disease.

Dynamic cardiac imaging using a focused, phased-array ultrasound system : Kisslo JA, vonRamm OT, Thurstone FL: Am J Med 63: 61–68, 1977

Dynamic cardiac imaging using a focused, phased-array ultrasound system : Kisslo JA, vonRamm OT, Thurstone FL: Am J Med 63: 61–68, 1977

Cardiac imaging using a phased array ultrasound system. II. Clinical technique and application.

A new two-dimensional ultrasound imaging system capable of producing high resolution tomographic images of the heart in real time has been developed. This system relies on phased array principles to rapidly steer the ultrasound beam through the structures under investigation. A hand-held linear array of 16 ultrasound transducers with overall dimensions of 14 mm at the site of contanct may be readily manipulated to image various cardiac structures. The resulting images are displayed in a circular sector format, 60 degrees in azimuth and typically 15 cm in range. At his maximum range, image frames consisting of 256 lines are generated at the rate of 20 frames/second. High azimuthal resolution throughout the field of view is assured by a focused transmit beam and by sweeping the focus of the receiver is synchrony with the range of returning echoes. Azimuthal resolution varies from 2 to 5 mm throughout the field of view while range resolution is 1.5 mm. This imaging system has proven particularly useful for the delineation of left ventricular spatial geometry by the identification of endocardium, myocardium, papillary muscles and interventricular septum. High quality images of anterior and posterior mitral leaflets, aortic root and aortic leaflets as well as left atrium and other cardiac structures have been obtained.