Abstract
We have designed an environmentally-controlled chamber for near infrared spectroscopic imaging (NIRSI) to monitor changes in cortical bone water content, an emerging biomarker related to bone quality assessment. The chamber is required to ensure repeatable spectroscopic measurements of tissues without the influence of atmospheric moisture. A calibration curve to predict gravimetric water content from human cadaveric cortical bone was created using NIRSI data obtained at six different lyophilization time points. Partial least squares (PLS) models successfully predicted bone water content that ranged from 0–10% (R = 0.96, p < 0.05, root mean square error of prediction (RMSEP) = 7.39%), as well as in the physiologic range of 4–10% of wet tissue weight (R = 0.87, p < 0.05, RMSEP = 14.5%). Similar results were obtained with univariate and bivariate regression models for prediction of water in the 0–10% range. Further, we identified two new NIR bone absorbances, at 6560 cm−1 and 6688 cm−1, associated with water and collagen respectively. Such data will be useful in pre-clinical studies that investigate changes in bone quality with disease, aging and with therapeutic use.
Highlights
Cortical bone water content has been evaluated through several destructive and nondestructive techniques[1,2,8,9,10,11]
A small chamber was designed to evaluate near infrared region (NIR) data collection from wet and dry bone samples in low and high relative humidity (RH), with the goal of determining which environment was most stable for data collection
The current study demonstrates optimal conditions for collection of near infrared spectroscopic imaging (NIRSI) data for evaluation of water from bone samples
Summary
Cortical bone water content has been evaluated through several destructive and nondestructive techniques[1,2,8,9,10,11]. Gravimetric analysis is considered a gold standard method for evaluation of water content in biological tissues[12] Since this method is destructive and time consuming, it has motivated development of nondestructive techniques that can be applied for assessment of water related to bone quality. Rajapakse et al.[20] non-destructively evaluated compositional changes in aging cadaveric cortical bone tissues by NIRSI for skeletal quality assessment, and correlated matrix (4608 cm−1) and water absorbances to MRI-derived water content in www.nature.com/scientificreports/. MRI imaging of water has the advantage of being applicable to clinical studies, and several studies have investigated changes in water content in tissues for bone quality assessment[23,26,27]. The repeatability of studies may be challenging, in particular during water calibration studies[29]
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