Laminar optical tomography of the hemodynamic response in the lumbar spinal cord of rats

Abstract

Intrinsic optical imaging (IOI) has emerged as a very powerful tool to assess neuronal function in small animals. Although it has been used extensively in the brain, its application to the spinal cord is rare. The inability of intrinsic optical techniques to resolve different depths and embedded gray matter hampers their capacity to distinguish larger vasculature contributions of hemodynamic signals originating from motoneuron and interneuron activation. Laminar optical tomography (LOT) is a recently-developed method that fills the gap left between IOI and diffuse optical imaging. With distinct source-detector separations, light that propagates deeper into tissues can be distinguished from light originating from the surface, providing depth sensitivity. In this work, LOT is investigated for the first time to image spinal cord activation with simultaneous IOI of the cortex in rats. Such proof of concept provides a powerful imaging modality to study spinal cord activation and disruption after injury.

Mesoscopic Fluorescence Molecular Tomography for Evaluating Engineered Tissues

“…This regularization parameter is used to effectively control the influence of the model mismatch, noise, and systemic error during reconstruction [22]. Even in the case of over-determined systems such as LOT/MFMT systems in the de-scanned configuration [29, 38], regularization is still required. A typical formulation of the inverse problem in LOT/MFMT is: $$x^{\prime }={({\mathrm{A}}^{\mathrm{T}}\mathrm{normalA}+\lambda \mathrm{normalD})}^{-1}{\mathrm{normalA}}^{\mathrm{normalT}}\mathrm{b}$$ where b is the measurement vector, x ′ is the estimated fluorophore distribution, A is the Jacobian matrix, and λD is a regularization parameter.…”

“…The combination of dense spatial data sets with an accurate forward model enables 3D reconstructions of fluorophore distributions with a resolution of 100-200 μm at imaging depths of ~3 mm [27]. Initially, LOT/MFMT had been developed to image absorption contrast for hemodynamic imaging [28, 29] and cancer detection [30]. Then it was rapidly adapted to molecular imaging (fluorescent LOT or FLOT) using fluorescent contrast agents [31-34].…”

Review of mesoscopic optical tomography for depth-resolved imaging of hemodynamic changes and neural activities

“…86 In a recent study, Ouakli et al 86 investigated LOT for imaging spinal cord activation following electrode stimulation in the left hind paw, with simultaneous intrinsic optical imaging of the cortex in rats. This study indicates that LOT is a potentially powerful imaging method to study activation in the spinal cord and subsequent disruption after injury.…”

“…1(b) except only a 690-nm excitation light source was used, which means HbR was the principal chromophore providing absorption contrast. 86 Figures 4(a) and 4(b) show the simultaneously quantified activation in the cortex and spinal cord, in which Fig. 4(a) represents LOT signals from the first detector in the spinal cord at different time points after stimulation.…”

Dental imaging using laminar optical tomography and micro CT

“…Moreover, LOT is a fast imaging techniques that can be implemented for bed-side applications. LOT can be used to image the distribution of blood volume, oxygen saturation [6] and fluorescent markers [7][8]. As the mean volume of pulp in adult teeth is approximately 0.02cm 3 with a typical diameter of ~2~3mm, LOT may be a suitable imaging modality to perform functional and molecular imaging of the teeth pulp.…”