The ability to perform routine monitoring of bone quality is crucial for patients with bone diseases such as osteoporosis. Current assessments of bone quality are expensive and cannot be used regularly without exposing patients to ionizing radiation. Alternatively, visible-near infrared (Vis-NIR) spectroscopy is a non-invasive, non-ionizing technique that can be used to assess the compositional properties of bone. Recently, studies have reported agreement between transcutaneous Vis-NIR spectroscopic measures of bone quality and conventional radiographic measures collected from the second metacarpal bone of the hand. Computational simulations using Monte-Carlo (MC) modeling offer a valuable tool to better understand the relative contributions from the underlying bone in comparison with the superficial skin, as well as to investigate the relative benefits of specific fiberoptic illumination/collection geometries for transcutaneous measurement of metacarpal bone. To inform the model, skin from above the 2nd metacarpal bone and the bone itself were dissected from human cadaver hands. Reflectance and transmittance measurements of the skin and bone tissues were taken using an integrating sphere setup in the range of 400 nm-1800 nm. Optical properties were estimated using the Inverse Adding Doubling (IAD) technique. MC models of skin-bone tissues were created using these estimated optical properties as well as physical measurements of tissue thickness, and simulations of fiber-optic Vis-NIR measurements were performed. Results indicate up to 30% of the absorbance signal arises from contributions from the bone in specific spectral ranges.
Musculoskeletal pathology of the knee commonly occurs with aging and as a result of injury. The incidence of anterior
cruciate ligament (ACL) injuries continues to increase annually, and may precede the eventual onset of osteoarthritis
(OA), a debilitating and prevalent disease characterized by cartilage degeneration. Early detection of OA remains
elusive, with current imaging methods lacking adequate sensitivity to detect early pathologic cartilage changes. We used
mid- and near- infrared (IR) spectroscopy through arthroscopic-based fiber-optic devices to assess cartilage damage and
differentiate tendon from ligament. Mid-IR spectroscopy is characterized by distinct bands and low penetration depth (<
10 μm) and near-IR spectroscopy is characterized by complex overlapping bands and greater penetration depths (< 1
cm). We have found that combined mid- and near-IR analysis greatly extends the information available through either in
the analysis of soft tissues, including cartilage, ligaments and tendons. We discuss here basic science studies and the
potential for translation to clinical research with novel arthroscopic probes.
Hyperspectral imaging is an emerging technology in the field of biomedical engineering which may be used as a noninvasive modality to characterize tumors. In this paper, a hyperspectral imaging system was used to characterize canine mammary tumors of unknown histopathology (pre-surgery) and correlate these results with the post-surgical histopathology results. The system consisted of a charge coupled device (CCD) camera, a liquid crystal tunable filter in the near infrared range (650-1100 nm) and a controller. Spectral signatures of malignant and benign canine mammary tumors were extracted and analyzed. The reflectance intensities of malignant tumor spectra were generally lower than benign tumor spectra over the entire wavelength range. Previous studies have shown that cancerous tissues have a higher hemoglobin and water content, and lower lipid concentration with respect to benign tissues. The decreased reflectance intensity observed for malignant tumors is likely due to the increased microvasculature and therefore higher blood content of malignant tissue relative to benign tissue. Peaks at 700, 840, 900 and 970 nm were observed in the second derivative absorption spectra, these peaks were attributed to deoxy-hemoglobin, oxy-hemoglobin, lipid and water respectively. A ‘Tissue Optical Index’ was developed that enhances contrast between malignant and benign canine tumors. This index is based on the ratio of the reflectance intensity values corresponding to the wavelengths associated with the four chromophores. Preliminary results from 22 canine mammary tumors showed that the sensitivity and specificity of the proposed method is 85.7% and 94.6% respectively. These results show promise in the non-invasive optical diagnosis of canine mammary cancer.
Myocardial infarction often leads to an increase in deposition of fibrillar collagen. Detection and characterization of this cardiac fibrosis is of great interest to investigators and clinicians. Motivated by the significant limitations of conventional staining techniques to visualize collagen deposition in cardiac tissue sections, we have developed a Fourier transform infrared imaging spectroscopy (FT-IRIS) methodology for collagen assessment. The infrared absorbance band centered at 1338 cm−1, which arises from collagen amino acid side chain vibrations, was used to map collagen deposition across heart tissue sections of a rat model of myocardial infarction, and was compared to conventional staining techniques. Comparison of the size of the collagen scar in heart tissue sections as measured with this methodology and that of trichrome staining showed a strong correlation (R = 0.93). A Pearson correlation model between local intensity values in FT-IRIS and immuno-histochemical staining of collagen type I also showed a strong correlation (R = 0.86). We demonstrate that FT-IRIS methodology can be utilized to visualize cardiac collagen deposition. In addition, given that vibrational spectroscopic data on proteins reflect molecular features, it also has the potential to provide additional information about the molecular structure of cardiac extracellular matrix proteins and their alterations.
Polarized Raman spectroscopy allows measurement of molecular orientation and composition and is widely used in the study of polymer systems. Here, we extend the technique to the extraction of quantitative orientation information from bone tissue, which is optically thick and highly turbid. We discuss multiple scattering effects in tissue and show that repeated measurements using a series of objectives of differing numerical apertures can be employed to assess the contributions of sample turbidity and depth of field on polarized Raman measurements. A high numerical aperture objective minimizes the systematic errors introduced by multiple scattering. We test and validate the use of polarized Raman spectroscopy using wild-type and genetically modified (oim/oim model of osteogenesis imperfecta) murine bones. Mineral orientation distribution functions show that mineral crystallites are not as well aligned (p<0.05) in oim/oim bones (28±3 deg) compared to wild-type bones (22±3 deg), in agreement with small-angle X-ray scattering results. In wild-type mice, backbone carbonyl orientation is 76±2 deg and in oim/oim mice, it is 72±4 deg (p>0.05). We provide evidence that simultaneous quantitative measurements of mineral and collagen orientations on intact bone specimens are possible using polarized Raman spectroscopy.
Polarized Raman spectroscopy is widely used in the study of molecular composition and orientation in synthetic and
natural polymer systems. Here, we describe the use of Raman spectroscopy to extract quantitative orientation
information from bone tissue. Bone tissue poses special challenges to the use of polarized Raman spectroscopy for
measurement of orientation distribution functions because the tissue is turbid and birefringent. Multiple scattering in
turbid media depolarizes light and is potentially a source of error.
Using a Raman microprobe, we show that repeating the measurements with a series of objectives of differing numerical
apertures can be used to assess the contributions of sample turbidity and depth of field to the calculated orientation
distribution functions. With this test, an optic can be chosen to minimize the systematic errors introduced by multiple
scattering events. With adequate knowledge of the optical properties of these bone tissues, we can determine if elastic
light scattering affects the polarized Raman measurements.
Arterial remodeling, i.e. changes in size and/or structure of arteries, plays an important role in vascular disease.
Conflicting findings have been reported as to whether an abundance of collagen causes inward or outward remodeling,
phenomena that result in either a smaller or larger lumen, respectively. We hypothesize that the amount, type and quality
of collagen influence the remodeling response. Here, we create mechanical injury to the rat carotid artery using a balloon
catheter, and this leads to inward remodeling. Treatment of the artery with Connective Tissue Growth Factor (CTGF)
causes outward remodeling. We investigated the arterial composition in injured CTGF-treated and non-CTGF-treated
and sham CTGF-treated and non-CTGF treated arteries 14 days post-injury (n = 7-8 per group) using infrared imaging.
A Perkin Elmer Spotlight Spectrum 300 FT-IR microscope was used for data collection. Cross-sections of paraffinembedded
arteries were scanned at 2 cm-1 spectral resolution with spatial resolution of 6.25 μm/pixel, and data analyzed
using Malvern Instruments ISys 5.0. Post-injury, we found a nearly 50% reduction in the average 1338/AM2 area ratio
(correlated to collagen helical integrity). The most dramatic change was a 600% increase in the 1660/1690 peak height
ratio, which has previously been related to collagen crosslink maturity. In all cases, CTGF treatment resulted in the
observed changes in peak parameters normalized back to control values. Overall, these preliminary studies demonstrate
that infrared imaging can provide insight into the underlying molecular changes that contribute to arterial disease.
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.