Stress fracture is a common condition in athletes and military personnel yet objective methods for detection and tracking of stress fractures (e.g., MR and scintigraphy) remain complex and expensive. Methods involving ultrasound are in common use; however, they are thus far subjective (relying on patient report of pain). The goal of this work is to develop quantitative and sensitive ultrasonic evaluation methods that could be deployed broadly in smaller clinical setting for use by a wide range of medical professionals. Such methods would complement beam-formed images of the bone surface by adding information about even sub-wavelength features. We have demonstrated that small imperfections on the bone surface significantly alter the characteristics of the reflectivity as made evident in the relative magnitude of the specular vs. diffuse scatter. In this paper we will present our work toward developing methods for acquiring, enhancing, visualizing, and evaluating such effects. We will present results from measurements with ex vivo bone samples and phantoms, and discuss the ultimate applicability of our methods to in vivo diagnosis.
Short optical pulses emitted from a tunable Q-switched laser (800 to 2000 nm) generate laser ultrasound (LUS) signals at the surface of biological tissue. The LUS signal’s acoustic frequency content, dependence on sample type, and optical wavelength are observed in the far field. The experiments yield a reference dataset for the design of noncontact LUS imaging systems. Measurements show that the majority of LUS signal energy in biological tissues is within the 0.5 and 3 MHz frequency bands and the total acoustic energy generated increases with the optical absorption coefficient of water, which governs tissue optical absorption in the infrared range. The experimental results also link tissue surface roughness and acoustic attenuation with limited LUS signal bandwidth in biological tissue. Images constructed using 810-, 1064-, 1550-, and 2000-nm generation laser wavelengths and a contact piezoelectric receiver demonstrates the impact of the generation laser wavelength on image quality. A noncontact LUS-based medical imaging system has the potential to be an effective medical imaging device. Such a system may mitigate interoperator variability associated with current medical ultrasound imaging techniques and expand the scope of imaging applications for ultrasound.
In this paper, a distant acoustic-laser NDE technique is proposed, utilizing a high powered standoff parametric
acoustic array (PAA) and laser Doppler vibrometry (LDV), for the detection of debonding and delamination
in multi-layer composite systems. Fiber-reinforced polymer wrapped concrete cylinder specimens with artificial
defect were manufactured and used in the validation of the technique. Low-frequency (50 Hz 2 kHz) and highfrequency
(2 kHz 7 kHz) focused sound waves were generated by PAA, and surface dynamic signatures of the specimens were remotely measured by LDV. From the results it is found that the proposed technique successfully
captures the presence of near-surface debonding/delamination.
This paper addresses a potential method to advance acoustic landmine detection by increasing operator and equipment standoff range from the minefield and developing a lightweight system that is potentially more practical than many currently researched systems. In this study, a parametric array acoustic source is evaluated to understand its potential for landmine detection. The array can transmit audible signals over 100 meters in air and has a weight of just four pounds. A proof-of-concept system was built at M.I.T. Lincoln Laboratory that uses a commercial parametric source to insonify the ground and excite buried mines. A commercial laser vibrometer was then used to measure the displacement velocity at the ground surface on and off the mine. This system has been demonstrated at an outdoor landmine facility and has measured signatures from buried anti-personnel mines. The overall concept shows promise; however, the parametric source used in this preliminary test was developed for home entertainment and will require substantial modification to be practical for landmine detection.