Noninvasive Raman tomographic imaging of canine bone tissue

Abstract

Abstract. Raman spectroscopic diffuse tomographic imaging has been demonstrated for the first time. It provides a noninvasive, label-free modality to image the chemical composition of human and animal tissue and other turbid media. This technique has been applied to image the composition of bone tissue within an intact section of a canine limb. Spatially distributed 785-nm laser excitation was employed to prevent thermal damage to the tissue. Diffuse emission tomography reconstruction was used, and the location that was recovered has been confirmed by micro-computed tomography ͑micro-CT͒ images. With recent advances, diffuse tomography shows promise for in vivo clinical imaging.1,2 In principle, algorithms developed for fluorescence imaging in tissue can be applied to Raman signals. Although the Raman effect is weaker than fluorescence, the scattered signal is detectable, and thus tomography is achievable. Here we demonstrate the first diffuse tomography reconstructions based on Raman scatter.Raman mapping and imaging are well-established techniques for examining material surfaces.3 Subsurface mapping of simple planar objects was reported recently 4,5 using fiber optic probes with spatially separated injection and collection fibers.6 Noninvasive measurements of bone Raman spectra were demonstrated at depths of 5 mm below the skin. 5Bone is promising for Raman tomography because the spectra are rich in compositional information, 7 which reflects bone maturity and health. Spectroscopically measured bone composition changes have been correlated with aging 8 and susceptibility to osteoporotic fracture. 9 The Raman spectrum of bone mineral is easily distinguished from the spectra of proteins and other organic tissue constituents, facilitating recovery of even weak signals by multivariate techniques.Assessments of bone quantity and quality are essential to detect and monitor fracture risk and fracture healing with disease or injury. Common sites for fracture with osteoporosis are the spine, proximal femur, and distal radius. Stress fractures are most frequently seen in the weight-bearing sites of the tibia and metatarsals. Fracture risk depends on bone geometry, architecture, and material properties, as well as the nature of applied load ͑magnitude, rate, and direction͒. As a result, noninvasive imaging and nondestructive analysis methods have been developed to assess many of these bone attributes that are increasingly important to clinical practice and basic research in orthopedics. 10 Current clinical in vivo methods include dual-energy x-ray absorptiometry ͑DXA͒, quantitative computed tomography ͑QCT͒, magnetic resonance imaging ͑MRI͒, ultrasound, and most recently, high-resolution peripheral QCT. Ex vivo analyses of bone specimens from patients or animals have also utilized these and other techniques.In this study, we couple micro-computed tomography ͑micro-CT͒ and diffuse optical tomography with Raman spectroscopy to recover spatial and composition information from bone tissue ex vivo. We demonstrate the first re...

Raman Assessment of Bone Quality

“…The first in vivo validation studies were performed on anesthetized mice and show good agreement between transcutaneous measurements and exposed bone measurements [65]. Ex vivo Raman tomography of the middiaphysis of a canine tibia of a width a thickness of over 30 mm has also been demonstrated [64]. Measurement times for the first-generation prototype systems range from 2 to 3 minutes for a single-point spectrum to as much as 1 hour for tomography.…”

Polarization control of Raman spectroscopy optimizes the assessment of bone tissue

“…Complementary to established x-ray-based diagnostics of bone, Raman spectroscopy (RS) is an emerging technology that offers nondestructive [3][4][5][6][7] measures of the biochemical nature of tissue. As an indication of its potential to assess fracture risk, RS detected differences in carbonate concentration relative to phosphate between bone samples from nonfracture patients and bones from osteoporotic fracture cases.…”

Raman spectroscopic analysis of combat-related heterotopic ossification development

“…For example, tomography techniques currently in development are able to model bone mineral density in three-dimensional space [48]. With such a model, the clinician may also be able to visualize areas of HO formation as well as monitor the maturation of each portion of the lesion(s), over time.…”