Prospective right hemi-diaphragm navigator is commonly used in free-breathing coronary MRI. The navigator results in an increase in acquisition time to allow for re-sampling of the motion-corrupted k-space data. In this study, we are presenting a joint prospective-retrospective navigator motion compensation algorithm called compressed-sensing motion compensation (CosMo). The inner k-space region is acquired using a prospective navigator; for the outer k-space, a navigator is only used to reject the motion-corrupted data without reacquiring them. Subsequently, those unfilled k-space lines are retrospectively estimated using compressed sensing (CS) reconstruction. We imaged right coronary artery (RCA) in 9 healthy adult subjects. An under-sampling probability map and sidelobe-to-peak ratio (SPR) were calculated to study the pattern of under-sampling, generated by navigator. RCA images were then retrospectively reconstructed using CosMo for gating windows between 3–10 mm and compared with the ones fully acquired within the gating windows. Qualitative imaging score and quantitative vessel sharpness were calculated for each reconstruction. The probability map and SPR show the navigator generates a random under-sampling k-space pattern. There were no statistically significant differences between the vessel sharpness and subjective score of the two reconstructions. CosMo could be an alternative motion compensation technique for free-breathing coronary MRI that can be used to reduce scan time.

Medical knowledge of the skeleton including its structures has improved constantly over the past decades. Advanced imaging methods, mechanical testing and optical techniques have revealed insights into bone architecture and composition. Most of these advancements were possible due to the ex vivo investigation of biological tissues. Investigations of fresh tissue are generally preferred over preserved or fixed samples. However, chemical fixation is sometimes inevitable due to histological procedures or logistical reasons. The aim of this study was to investigate whether short-term chemical fixation with formaldehyde affects bone quality parameters obtained from Raman spectroscopy and if these effects last for intermediate sample storage of several hours. As formaldehyde induces cross-links to the organic components in bone tissue, we hypothesized that collagen-related parameters are particularly affected. Femurs of eight 17-week-old C57BL/6 mice were extracted and divided into two groups (N ¼ 8∕group). Samples of the first group were fixed by immersion in 4% formaldehyde (PFA-solution) for 12 h at 4°C (fixed group) while samples of the second group were left untreated (unfixed group). Raman spectroscopy was performed, and repeated after 4 h, to assess whether intermediate storage time influenced the obtained results. Based on resultant spectra, mineral-to-matrix ratio, carbonate-to-phosphate ratio, carbonate-to-amide I ratio, mineral crystallinity and collagen maturity were determined. Carbonate-to-phosphate ratio was the only parameter showing a significant difference between the first and the subsequent measurements. For both groups, ratios showed a decrease in carbonate substitution compared to the first measurement (percentage decrease: 3.1% in fixed, 4.7% in unfixed). Collagen maturity of samples, which were short-term fixed with formaldehyde, was significantly lower than of fresh, unfixed samples (percentage difference: 3.8%). Our study shows that Raman spectroscopy is able to detect changes in collagen structure initiated by formaldehyde and that changes in short-term fixed samples are minimally influencing bone material properties measured with Raman spectroscopy.

Fracture repair is a complex process that involves the interaction of numerous molecular factors, cell lineages and tissue types. These biological processes allow for an impressive feat of engineering: an elastic soft callus is progressively replaced by a more rigid and mineralized callus. During this reparative phase, the healing bone is exposed to a risk of re-fracture. Bone volume and bone quality are the two major factors determining the strength of the callus. Although both factors are important, often only bone volume is analyzed and reported in preclinical studies. Recent developments in techniques for examining bone quality in the callus will enable the rapid and detailed analysis of its material properties and its microstructure. This review aims to give an overview of the methods available for quantitatively phenotyping the bone callus in preclinical studies such as Raman spectroscopy, nanoindentation, scanning acoustic microscopy, in vivo micro-computed tomography (micro-CT) and high-resolution micro-CT. Consolidated and emerging experimental methods are described with a focus on their applicability, and with examples of their utilization.