The Study Of Photoacoustic Technology In Bone Qualitative And Quantitative Assessment

The ultimate goal of this work is to develop a novel photoacoustic (QPA) platform for highly-sensitive and quantitative assessment of bone health. This paper for the first time, proposed four photoacoustic quantitative assessment method to evaluate the bone health.This paper for the first time, examined the feasibility of the photoacoustic imaging (PAI) technique in bone mass assessment. The optical and ultrasound penetration in bone have been studied. The feasibility of conducting 3D PA imaging of bone, and performing quantitative evaluation of bone mass by using PAI have been investigated.This paper for the first time, examined the feasibility of the newly developed photoacoustic spectrum analysis (PASA) technique in characterizing the microstructures bone. Both theoretical modeling and experimental measurements on well-established animal models were conducted. To extract the main features of the PA bone signal in the frequency domain, the power spectrum of the signal can be fit by linear regression, from which spectral parameters’slope’can be quantified. Slope is sensitive to the tissue heterogeneity, and can reflect the histological microstructures and the spatial distributions of the optical absorbing chemical components in porous trabecular bone. Moreover, slope is less susceptible to the variation in light fluence and, hence, is more reliable for objective assessment of bone microarchitecture (BMA).This paper for the first time, proposed the thermal photoacoustic (TPA) method in bone assessment. Unlike conventional photoacoustic PA methods which are mostly focused on the measurement of absolute signal intensity, TPA targets the change in PA signal intensity as a function of the sample temperature, i.e. the temperature dependent Grunineisen parameter which is closely relevant to the chemical and molecular properties in the sample. Based on the differentiation measurement, the results from TPA technique are less susceptible to the variations associated with sample and system, and could be quantified with improved accurately. Due to the fact that the PA signal intensity from organic components such as blood changes faster than that from non-organic mineral under the same modulation of temperature, TPA measurement is able to objectively evaluate bone mineral density (BMD) and its loss as a result of osteoporosis.The paper, for the first time, examined the feasibility of the newly developed physio-chemical spectrogram (PCS) technique in assessment the bone health. PCS, a two-dimensional (2D) spectrogram integrating microscopic to centimeter morphology and chemical components is generated by 1) performing PA scans of a tissue/material over a broad optical spectrum covering the absorption peaks of specific relevant chemical components,2) transforming the PA signals into the spatial frequency domain, and 3) arranging the spatial frequency power spectra side-by-side in the order of the wavelengths. Even without the spectral richness of optical and ultrasound contrast agents, these many tissue and material properties provide much orthogonal information that should be enough sensitivity for bone assessment.This integrated QPA platform can assess both bone mass and microstructure simultaneously without involving invasive biopsy or ionizing radiation. Since QPA is non-ionizing, non-invasive, and has sufficient penetration in both soft tissue and bone, not only focus on the changing of non-organic mineral but also the organic tissue, it has unique advantages for clinical translation.Besides, the paper for the first time, propose to apply the ultra-broad bandwidth optical ultrasonic detector in the PASA technology. The sensitivity of micro-ring detector has been examined in phantom and biological tissue in micro size. The results strongly suggests that applying the micro-ring in PASA method has the potential to sense the changes in the shape and size of biological tissue (like red blood cell (RBC), lipid cell).