Ovarian cancer has the highest mortality of all gynecologic cancers, with a five-year survival rate of only 30% or less. Current imaging techniques are limited in sensitivity and specificity in detecting early stage ovarian cancer prior to its widespread metastasis. New imaging techniques that can provide functional and molecular contrasts are needed to reduce the high mortality of this disease. One such promising technique is photoacoustic imaging. We develop a 1280-element coregistered 3-D ultrasound and photoacoustic imaging system based on a 1.75-D acoustic array. Volumetric images over a scan range of 80 deg in azimuth and 20 deg in elevation can be achieved in minutes. The system has been used to image normal porcine ovarian tissue. This is an important step toward better understanding of ovarian cancer optical properties obtained with photoacoustic techniques. To the best of our knowledge, such data are not available in the literature. We present characterization measurements of the system and compare coregistered ultrasound and photoacoustic images of ovarian tissue to histological images. The results show excellent coregistration of ultrasound and photoacoustic images. Strong optical absorption from vasculature, especially highly vascularized corpora lutea and low absorption from follicles, is demonstrated.
Ovarian cancer has the highest mortality of all gynecologic cancers with a five-year
survival rate of only 30%. Because current imaging techniques (ultrasound, CT, MRI, PET) are
not capable of detecting ovarian cancer early, most diagnoses occur in later stages (III/IV). Thus
many women are not correctly diagnosed until the cancer becomes widely metastatic. On the
other hand, while the majority of women with a detectable ultrasound abnormality do not harbor a
cancer, they all undergo unnecessary oophorectomy. Hence, new imaging techniques that can
provide functional and molecular contrasts are needed for improving the specificity of ovarian
cancer detection and characterization. One such technique is photoacoustic imaging, which has
great potential to reveal early tumor angiogenesis through intrinsic optical absorption contrast
from hemoglobin or extrinsic contrast from conjugated agents binding to appropriate molecular
To better understand the cancer disease process of ovarian tissue using photoacoustic
imaging, it is necessary to first characterize the properties of normal ovarian tissue. We have
imaged ex-vivo ovarian tissue using a 3D co-registered ultrasound and photoacoustic imaging
system. The system is capable of volumetric imaging by means of electronic focusing. Detecting
and visualizing small features from multiple viewing angles is possible without the need for any
mechanical movement. The results show strong optical absorption from vasculature, especially
highly vascularized corpora lutea, and low absorption from follicles. We will present correlation
of photoacoustic images from animals with histology. Potential application of this technology
would be the noninvasive imaging of the ovaries for screening or diagnostic purposes.
A 512-element photoacoustic tomography system for small animal imaging using a ring
ultrasound array has been developed. The system features a 5 MHz piezocomposite
transducer array formed into a complete circular aperture. Custom receiver electronics
consisting of dedicated preamplifiers, 8:1 multiplexed post-amplifiers, and a 64-channel
data acquisition module provide full tomographic imaging at up to 8 frames/second. We
present details of the system design along with characterization results of the resolution,
imaging volume, and sensitivity. Small animal imaging performance is demonstrated
through images of mice brain vasculature at different depths and real-time spectroscopic
scans. This system enables real-time tomographic imaging for functional photoacoustic
studies for the first time.
Three-dimensional imaging is very valuable in detecting and visualizing lesions from
multiple viewing angles. In addition, co-registered 3D imaging combining conventional
ultrasound and photoacoustic tomography allows visualization of tissue structures with
simultaneous structural and functional information.
We have developed a 1280 element 3D ultrasound imaging system based on a 1.75D
acoustic array. Complete volumetric images over the full scanning range can be achieved in a few
minutes. In conjunction with a Ti:Sapphire laser, the system has been used for photoacoustic
imaging. We present 3D co-registered images obtained with the system. Ultrasound and
photoacoustic co-registered images of phantoms with different optical and acoustical properties
are shown to demonstrate its advantage in cancer detection.
We have developed and tested a photoacoustic imaging system based on a 128 element curved-phased
ultrasonic array, which spans a quarter of a complete circle with a radius of curvature equal to 25mm. The center
frequency of the array is 5 MHz with 60% bandwidth. The physical dimensions of the elements are 10x0.3mm (elevation
x azimuth) with an elevation focus of 19mm. Earlier we reported acoustic measurements of the axial and lateral
resolutions of the system that were limited by the impulse response of the narrowband source used in the test. In this
paper we discuss photoacoustic characterization of the system including resolution and sensitivity. The array forms the
building block for a 512-element ring designed for complete tomographic imaging of small animals. Imaging results of
phantoms will be compared with simulations.
Photoacoustic imaging is a promising non-invasive imaging technology due to its ability to combine the enhanced contrast of optical absorption with the spatial resolution of acoustic imaging. Co-registered three-dimensional (3-D) ultrasound and photoacoustic imaging takes advantage of both modalities to allow visualization of tissue structures within a volume using simultaneous structural and functional information. 1.75D acoustic arrays are well-suited for this application due to their ability to scan in 3-D volumes rapidly and accurately while maintaining a reasonable system complexity and cost. We have designed, fabricated, and tested a 1.75D 1280-ch ultrasound system for co-registered 3-D ultrasound and photoacoustic imaging. The system features a 1.75D 1280-channel ultrasound array with a center frequency of 5MHz and 80% bandwidth. The electronics includes 1280 high-voltage pulsers, 40 32-to-1 multiplexers, amplification circuitry, and a 40-channel data acquisition circuit. The system is able to drive the entire array simultaneously, and each array element independently, to scan a 3-D volume within +/- 40 degrees in azimuth direction and +/- 10 degrees in elevation respectively. System performance including axial and lateral resolution has been characterized and compared with simulations. Co-registered 3-D ultrasound and photoacoustic imaging has been successfully performed on phantoms with different geometries and contrast.
Real-time photoacoustic imaging requires ultrasonic array receivers and parallel data acquisition systems for the simultaneous detection of weak photoacoustic signals. In this paper, we introduce a newly completed ultrasonic receiving array system and report preliminary results of our measured point spread function. The system employs a curved ultrasonic phased array consisting of 128-elements, which span a quarter of a complete circle. The center frequency of the array is 5 MHz and the bandwidth is greater than 60%. In order to maximize the signal-to-noise ratio for photoacoustic signal detection, we utilized special designs for the analog front-end electronics. First, the 128 transducer-element signals were routed out using a 50-Ohm impedance matching PCB board to sustain signal integrity. We also utilize 128 low-noise pre-amplifiers, connected directly to the ultrasonic transducer, to amplify the weak photoacoustic signals before they were multiplexed to a variable-gain multi-stage amplifier chain. All front-end circuits were placed close to the transducer array to minimize signal lose due to cables and therefore improve the signal-to-noise ratio. Sixteen analog-to-digital converters were used to sample signals at a rate of 40 mega-samples per second with a resolution of 10-bits per sample. This allows us to perform a complete electronic scan of all 128 elements using just eight laser pulses.
We have introduced a three-dimensional (3-D) ultrasound imaging system for use in a combined ultrasound and near-infrared (NIR) imager for breast imaging. Compared with commercial ultrasound scanners which can only provide a single 2-D cross-section image at one scan, this 3-D system can provide 3-D co-registered ultrasound images for constraining regions of interest for 3-D NIR imaging reconstruction at one scan. The 3-D high-resolution ultrasound system consists of a state-of-the-art 1.75D ultrasound array of 1280 elements manufactured by Tetrad Inc. We have developed corresponding circuitry to drive the 1.75D array. The circuitry consists of 1280 parallel transmission channels, a 1280-to-40 multiplexer and 40 parallel receiving/data acquisition channels. A Texas Instrument DSP board has been embedded to speed up on-board data processing. We have tested the 3-D ultrasound imaging system with a 3-D ultrasound calibration phantom.
We have constructed a nearly real-time combined imager suitable for simultaneous ultrasound and near infrared (NIR) diffusive light imaging and co-registration. The imager consists of a combined probe and associated electronics for data acquisition. A 2D ultrasound array occupies the center of the combined probe, while 12 dual wavelength laser source fibers (780 nm and 830 nm) and 8 optical detector fibers are deployed in the periphery. We have experimentally evaluated the effects of missing optical sensors in the middle of the combined probe upon the accuracy of the reconstructed optical absorption coefficient, and assessed the improvements of reconstructed absorption coefficient with the guidance of the co-registered ultrasound. The results have shown that when the central ultrasound array area is in the neighborhood of 2 X 2 cm2, which corresponds to the size of most commercial ultrasound transducers, the quality of optical images will not be degenerated. In addition to the acoustic information for cancer discrimination, NIR image reconstruction becomes much easier and more reliable. According to our results, the iterative inversion algorithm converges very fast with the guidance of a priori target temporal and spatial distributions. Only one iteration is needed to reconstruct accurate optical absorption coefficient.
A total of 364 optical source-detector pairs were uniformly deployed over a 9 x 9 cm2 probe area initially, and then the total pairs were gradually reduced to 60 in experimental studies. For each source-detector configuration, 3D images of a 1 cm diameter absorber of different contrasts were reconstructed form the measurements made with a frequency domain system. The results have shown that more than 160 source-detector pairs are needed to reconstruct absorption coefficient within 60% of the true value and appropriate spatial and contrast resolution. However, the error in target depth estimated from 3D images was more than 1 cm in all source-detector configurations. With the a priori target depth information provided by ultrasound, the accuracy of the reconstructed absorption coefficient has been improved by 15% and 3% on average for high and low contrast cases, respectively. The speed of reconstruction has been improved by 10 times on average.