Franck Amyot

Using noninvasive multispectral imaging to quantitatively assess tissue vasculature

This research describes a noninvasive, noncontact method used to quantitatively analyze the functional characteristics of tissue. Multispectral images collected at several near-infrared wavelengths are input into a mathematical optical skin model that considers the contributions from different analytes in the epidermis and dermis skin layers. Through a reconstruction algorithm, we can quantify the percent of blood in a given area of tissue and the fraction of that blood that is oxygenated. Imaging normal tissue confirms previously reported values for the percent of blood in tissue and the percent of blood that is oxygenated in tissue and surrounding vasculature, for the normal state and when ischemia is induced. This methodology has been applied to assess vascular Kaposis sarcoma lesions and the surrounding tissue before and during experimental therapies. The multispectral imaging technique has been combined with laser Doppler imaging to gain additional information. Results indicate that these techniques are able to provide quantitative and functional information about tissue changes during experimental drug therapy and investigate progression of disease before changes are visibly apparent, suggesting a potential for them to be used as complementary imaging techniques to clinical assessment.

Direct curvature correction for noncontact imaging modalities applied to multispectral imaging.

Noncontact optical imaging of curved objects can result in strong artifacts due to the objects shape, leading to curvature biased intensity distributions. This artifact can mask variations due to the objects optical properties, and makes reconstruction of optical/physiological properties difficult. In this work we demonstrate a curvature correction method that removes this artifact and recovers the underlying data, without the necessity of measuring the objects shape. This method is applicable to many optical imaging modalities that suffer from shape-based intensity biases. By separating the spatially varying data (e.g., physiological changes) from the background signal (dc component), we show that the curvature can be extracted by either averaging or fitting the rows and columns of the images. Numerical simulations show that our method is equivalent to directly removing the curvature, when the objects shape is known, and accurately recovers the underlying data. Experiments on phantoms validate the numerical results and show that for a given image with 16.5% error due to curvature, the method reduces that error to 1.2%. Finally, diffuse multispectral images are acquired on forearms in vivo. We demonstrate the enhancement in image quality on intensity images, and consequently on reconstruction results of blood volume and oxygenation distributions.

Normative database of judgment of complexity task with functional near infrared spectroscopy – Application for TBI

The ability to assess frontal lobe function in a rapid, objective, and standardized way, without the need for expertise in cognitive test administration might be particularly helpful in mild traumatic brain injury (TBI), where objective measures are needed. Functional near infrared spectroscopy (fNIRS) is a reliable technique to noninvasively measure local hemodynamic changes in brain areas near the head surface. In this paper, we are combining fNIRS and frameless stereotaxy which allowed us to co-register the functional images with previously acquired anatomical MRI volumes. In our experiment, the subjects were asked to perform a task, evaluating the complexity of daily life activities, previously shown with fMRI to activate areas of the anterior frontal cortex. We reconstructed averaged oxyhemoglobin and deoxyhemoglobin data from 20 healthy subjects in a spherical coordinate. The spherical coordinate is a natural representation of surface brain activation projection. Our results show surface activation projected from the medial frontopolar cortex which is consistent with previous fMRI results. With this original technique, we will construct a normative database for a simple cognitive test which can be useful in evaluating cognitive disability such as mild traumatic brain injury.

Principal component model of multispectral data for near real-time skin chromophore mapping

Multispectral images of skin contain information on the spatial distribution of biological chromophores, such as blood and melanin. From this, parameters such as blood volume and blood oxygenation can be retrieved using reconstruction algorithms. Most such approaches use some form of pixelwise or volumetric reconstruction code. We explore the use of principal component analysis (PCA) of multispectral images to access blood volume and blood oxygenation in near real time. We present data from healthy volunteers under arterial occlusion of the forearm, experiencing ischemia and reactive hyperemia. Using a two-layered analytical skin model, we show reconstruction results of blood volume and oxygenation and compare it to the results obtained from our new spectral analysis based on PCA. We demonstrate that PCA applied to multispectral images gives near equivalent results for skin chromophore mapping and quantification with the advantage of being three orders of magnitude faster than the reconstruction algorithm.

Quantitative principal component model for skin chromophore mapping using multi-spectral images and spatial priors

We describe a novel reconstruction algorithm based on Principal Component Analysis (PCA) applied to multi-spectral imaging data. Using numerical phantoms, based on a two layered skin model developed previously, we found analytical expressions, which convert qualitative PCA results into quantitative blood volume and oxygenation values, assuming the epidermal thickness to be known. We also evaluate the limits of accuracy of this method when the value of the epidermal thickness is not known. We show that blood volume can reliably be extracted (less than 6% error) even if the assumed thickness deviates 0.04mm from the actual value, whereas the error in blood oxygenation can be as large as 25% for the same deviation in thickness. This PCA based reconstruction was found to extract blood volume and blood oxygenation with less than 8% error, if the underlying structure is known. We then apply the method to in vivo multi-spectral images from a healthy volunteer’s lower forearm, complemented by images of the same area using Optical Coherence Tomography (OCT) for measuring the epidermal thickness. Reconstruction of the imaging results using a two layered analytical skin model was compared to PCA based reconstruction results. A point wise correlation was found, showing the proof of principle of using PCA based reconstruction for blood volume and oxygenation extraction.

Spatial distribution of VEGF isoforms and chemotactic signals in the vicinity of a tumor

We propose a mathematical model that describes the formation of gradients of different isoforms of vascular endothelial growth factor (VEGF). VEGF is crucial in the process of tumor-induced angiogenesis, and recent experiments strongly suggest that the molecule is most potent when bound to the extracellular matrix (ECM). Using a system of reaction-diffusion equations, we study diffusion of VEGF, binding of VEGF to the ECM, and cleavage of VEGF from the ECM by matrix metalloproteases (MMPs). We find that spontaneous gradients of matrix-bound VEGF are possible for an isoform that binds weakly to the ECM (i.e. VEGF(165)), but cleavage by MMPs is required to form long-range gradients of isoforms that bind rapidly to the ECM (i.e. VEGF(189)). We also find that gradient strengths and ranges are regulated by MMPs. Finally, we find that VEGF molecules cleaved from the ECM may be distributed in patterns that are not conducive to chemotactic migration toward a tumor, depending on the spatial distribution of MMP molecules. Our model elegantly explains a number of in vivo observations concerning the significance of different VEGF isoforms, points to VEGF(165) as an especially significant therapeutic target and indicator of a tumors angiogenic potential, and enables predictions that are subject to testing with in vitro experiments.

Thin films of oriented collagen fibrils for cell motility studies.

Collagen films with oriented fibrils mimic tissues that have been remodeled by fibroblasts, which naturally tend to orient collagen fibrils in vivo. We have prepared thin films of ordered fibrils of collagen I, a major component of the extracellular matrix. The films were prepared by modifying a technique previously used to produce collagen I films for studies of cell morphology and intracellular signaling. By modifying the drying step, we were able to produce thin monolayers of collagen fibrils with consistent orientations over macroscopic (>100 microm) distances. We quantified the degree of orientation of the collagen fibrils using Fourier analysis of optical microscopy images. We also conducted experiments with vascular endothelial cells, and found that cell orientation and migration are well-correlated with fibril orientation. Using polarized cells, we showed oriented thin collagen film induces natural migration along the fibrils without using any sort of attractor. Taken together, these results demonstrate additional functionality and physiological relevance for a class of films being successfully applied in a variety of cell biology experiments.

TOPOLOGY OF THE HETEROGENEOUS NATURE OF THE EXTRACELLULAR MATRIX ON STOCHASTIC MODELING OF TUMOR-INDUCED ANGIOGENESIS

We have modeled tumor-induced angiogenesis; our model includes the phenomena of the migratory response of endothelial cells (ECs) to tumor angiogenic factors, and the interaction of ECs with the extracellular matrix (ECM). ECs switch between growth, differentiation, motility, or apoptotic behavior in response to the local topology and composition of the ECM. Assuming the ECM medium as a statistically inhomogeneous medium (some area support sprout growth, some not), we show that the ECM can be a natural barrier to angiogenesis. We study vascular network formation for several ECM distributions and topologies, and we find an analogy with percolation. A threshold exists, under which sprouts cannot reach the tumor. During the growth of the vascular network, a competition exists between the attraction exerted by tumor and the preferred path created by the ECM. We also examined the influence of branching on the tumor vascularization. Branching is a natural phenomenon which helps the tumor become vascularized. By increasing the number of sprouts, the vascular network increases the probability of reaching the tumor, as it can explore more pathways. Our simulations show after two branching events, the vascular network is very likely to reach the tumor.

Using Quantitative Imaging Techniques to Assess Vascularity in AIDS-Related Kaposi's Sarcoma

Three quantitative and non-invasive techniques were used to monitor angiogenesis in Kaposis sarcoma patients: thermography, laser Doppler imaging (LDI), and near-infrared spectroscopy. Before and after combination cytotoxic and anti-angiogenesis therapy, blood volume, oxygenated hemoglobin, temperature, and blood flow were analyzed. These three techniques are objective, easy to perform, and appear to be very sensitive in assessing changes in the lesions upon administration of therapy

A hematoma detector-a practical application of instrumental motion as signal in near infra-red imaging.

Abstract: In this paper we discuss results based on using instrumental motion as a signal rather than treating it as noise in Near Infra-Red (NIR) imaging. As a practical application to demonstrate this approach we show the design of a novel NIR hematoma detection device. The proposed device is based on a simplified single source configuration with a dual separation detector array and uses motion as a signal for detecting changes in blood volume in the dural regions of the head. The rapid triage of hematomas in the emergency room will lead to improved use of more sophisticated/expensive imaging facilities such as CT/MRI units. We present simulation results demonstrating the viability of such a device and initial phantom results from a proof of principle device. The results demonstrate excellent localization of inclusions as well as good quantitative comparisons.