We have designed, fabricated and tested a new 128-channel laser optoacoustic imaging system (LOIS-128) for cancer
diagnostics consisting of an acoustic probe with 128 PVDF transducers, a digital signal processor with 128 independent
channels, and software for reconstruction of optoacoustic images. The system was capable of continuous planar imaging
(at rates up to 1 Hz) of small (less than 1 cm) tumors at depths over 6 cm. The directivity of the optoacoustic transducers
used in LOIS-128 assured that signal detection at all angles within a narrow imaging slice was at least 40% of the
maximal signal. The signal detection was better than 70% of the maximum for about 75% of the image in the image
slice and close to zero for signals coming from out of the image slice. LOIS-128 could image high-aspect-ratio objects
with about 0.5 mm resolution. Finally, with the designed image reconstruction algorithm we were able to estimate
absorption coefficients for test objects with accuracy of at least 5%.
The developing realization that acute coronary events, such as myocardial infarctions, can be caused by the sudden disruption of relatively small, rupture-prone plaques has led to increased exploration of clinical techniques that identify "vulnerable plaque" and differentiate it from "stable" plaque. Intravascular optoacoustic imaging promises to be such a technique. It has the capability of measuring the thickness of the plaque cap, the size of the underlying lipid reservoir, and other structural features known to be related to the vulnerability of the plaque. Inside an artery, optoacoustic imaging must necessarily be done in the backward mode, with irradiation and detection close to the same site on the tissue surface. With test phantoms simulating the optical and acoustic properties of the arterial wall, we have been able to show that backward-mode imaging is feasible. Modification of the ultrasonic detector used to allow irradiation and detection at the same point on the same surface affects the signal in a predictable way. The effect of the probe on the signal can reliably be removed by deconvolution of the measured signal to take into account the detector response.
Optoacoustic imaging is a promising new tool for the detection and diagnosis of breast cancer. It is progressing from research study to clinical evaluation. We have now built a complete laser optoacoustic imaging system (LOISTM) consisting of a laser illumination system, a 32-element ultrasonic detector probe, signal amplifiers, and a computer with software for image generation. This report describes initial tests to explore the clinical viability of the system. Our results show that the system has sufficient sensitivity to reveal cancerous tumors already identified with X-ray and/or ultrasound imaging, that it has the resolution to show faithfully the size and shape of those tumors, that comparison of images taken at 755 and 1064 nm is indicative of whether or not a suspicious lesion is cancerous, and that the depth of sensitivity of the system is sufficient to detect tumors throughout an average-sized breast.
Laser Optoacoustic Imaging System (LOIS) combines high tissue contrast based on the optical properties of tissue and high spatial resolution based on ultrawide-band ultrasonic detection. Patients undergoing thermal or photodynamic therapy of prostate cancer may benefit from capability of LOIS to detect and monitor treatment-induced changes in tissue optical properties and blood flow. The performance of a prototype LOIS was evaluated via 2D optoacoustic images of dye-colored objects of various shapes, small tubes with blood simulating veins and arteries, and thermally coagulated portions of chicken breasts imbedded tissue-mimicking gelatin phantoms. The optoacoustic image contrast was proportional to the ratio of the absorption coefficient between the embedded objects and the surrounding gel. The contrast of the venous blood relative to the background exceeded 250%, and the contrast of the thermally coagulated portions of flesh relative to the untreated tissue ranged between -100% to +200%, dependent on the optical wavelength. We used a 32-element optoacoustic transducer array and a novel design of low-noise preamplifiers and wide-band amplifiers to perform these studies. The system was optimized for imaging at a depth of ~50 mm. The system spatial resolution was better than 1-mm. The advantages and limitations of various signal-processing methods were investigated. LOIS demonstrates clinical potential for non- or minimally-invasive monitoring of treatment-induced tissue changes.
Both digital and physical phantoms are essential to the development of any new imaging modality. Digital phantoms are simply data sets that approximate the signals that would be measured by the imaging equipment. Physical phantoms are objects with similar physical properties to the human body. We compare several mathematical procedures for calculation of digital phantoms for optoacoustic imaging in general and describe convenient ways to construct physical phantoms for optoacoustic breast imaging. LOIS accurately reconstructs the expected images from both.
Aggressive malignant tumors may be diagnosed based on relative concentration of oxyhemoglobin and deoxyhemoglobin in the tumor microvasculature. Optoacoustic images of breast cancer and prostate cancer may be acquired at two laser wavelengths matching maximum of oxyhemoglobin (1064-nm, Nd:YAG laser) and deoxyhemoglobin (760-nm, Alexandrite laser). Two optoacoustic systems operating in forward and backward mode respectively for breast cancer and prostate cancer detection, employing arrays of ultravide-band piezoelectric transducers and multichannel electronics was described. After systems testing and calibration in phantoms, initial experiments were performed on patients with suspicious tumors. Quantitative analysis of two-color optoacoustic images was correlated with biopsy and histology. Possibility for tumor differentiation was demonstrated.
Optoacoustic tomography combines advantages of pronounced optical contrast between different tissues and high resolution of ultrawide-band ultrasound imaging. Laser pulses may be effectively used to produce acoustic sources in tissue with enhanced optical absorption. Ultrasonic waves can propagate in biological tissue with minimal distortion and deliver diagnostic information to the surface of tissue, where they may be detected with temporal resolution by piezoelectric transducers. Current status of the optoacoustic tomography applied in early detection of cancerous lesions in the breast (utilizing forward mode) and in oral cavity (utilizing backward mode) is reviewed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.