An orthopaedic screw was designed with an optical tension-indicator to non-invasively quantify screw tension and monitor the load sharing between the bone and the implant. The screw both applies load to the bone, and measures this load by reporting the strain on the screw. The screw contains a colorimetric optical encoder that converts axial strain into colorimetric changes visible through the head of the screw, or luminescent spectral changes that are detected through tissue. Screws were tested under cyclic mechanical loading to mimic in-vivo conditions to verify the sensitivity, repeatability, and reproducibility of the sensor. In the absence to tissue, color was measured using a digital camera as a function of axial load on a stainless steel cannulated (hollow) orthopedic screw, modified by adding a passive colorimetric strain gauge through the central hole. The sensor was able to quantify clinically-relevant bone healing strains. The sensor exhibited good repeatability and reproducibility but also displayed hysteresis due to the internal mechanics of the screw. The strain indicator was also modified for measurement through tissue by replacing the reflective colorimetric sensor with a low-background X-ray excited optical luminescence signal. Luminescent spectra were acquired through 6 mm of chicken breast tissue. Overall, this research shows feasibility for a unique device which quantifies the strain on an orthopedic screw. Future research will involve reducing hysteresis by changing the mechanism of strain transduction in the screw, miniaturizing the luminescent strain gauge, monitoring bending as well as tension, using alternative luminescent spectral rulers based upon near infrared fluorescence or upconversion luminescence, and application to monitoring changes in pretension and load sharing during bone healing.
Vibro-acoustography is a speckle-free ultrasound based imaging modality that can visualize normal and abnormal soft
tissue through mapping stimulated acoustic emission. The acoustic emission is generated by focusing two ultrasound
beams of slightly different frequencies (Δ<i>f</i> = <i>f</i><sub>1</sub>-<i>f</i><sub>2</sub>) to the same spatial location and vibrating the tissue as a result of
ultrasound radiation force. Reverberation of the acoustic emission can create dark and bright areas in the image that
affect overall image contrast and detectability of abnormal tissue. Using finite length tonebursts yields acoustic emission
at Δf and at sidebands centered about Δf that originate from the temporal toneburst gating. Separate images are formed by
bandpass filtering the acoustic emission at Δf and the associated sidebands. The data at these multiple frequencies are
compounded through coherent or incoherent processes to reduce the artifacts associated with reverberation of the acoustic emission. Experimental results from a urethane breast phantom and <i>in vivo</i> human breast scans are shown. The reduction in reverberation artifacts are analyzed using a smoothness metric which uses the variances of the gray levels of the original images and those formed through coherent and incoherent compounding of image data. This smoothness metric is minimized when the overall image background is smooth while image features are still preserved. The smoothness metric indicates that the images improved by factors from 1.23-4.33 and 1.09-2.68 in phantom and <i>in vivo</i> studies, respectively. The coherent and incoherent compounding of multifrequency data demonstrate, both qualitatively and quantitatively, the efficacy of this method for reduction of reverberation artifacts.