PubMed Health⌕ Search

Biomedical subjects

Xavier Intes

Publications and source records attributed to Xavier Intes.

13 recordsLinked to original sources
PubMed2006

Extended kalman filtering for the modeling and analysis of ICG pharmacokinetics in cancerous tumors using NIR optical methods.

Compartmental modeling of indocyanine green (ICG) pharmacokinetics, as measured by near infrared (NIR) techniques, has the potential to provide diagnostic information for tumor differentiation. In this paper, we present three different compartmental models to model the pharmacokinetics of ICG in cancerous tumors. We introduce a systematic and robust approach to model and analyze ICG pharmacokinetics based on the extended Kalman filtering (EKF) framework. The proposed EKF framework effectively models multiple-compartment and multiple-measurement systems in the presence of measurement noise and uncertainties in model dynamics. It provides simultaneous estimation of pharmacokinetic parameters and ICG concentrations in each compartment. Moreover, the recursive nature of the Kalman filter estimator potentially allows real-time monitoring of time varying pharmacokinetic rates and concentration changes in different compartments. Additionally, we introduce an information theoretic criteria for the best compartmental model order selection, and residual analysis for the statistical validation of the estimates. We tested our approach using the ICG concentration data acquired from four Fischer rats carrying adenocarcinoma tumor cells. Our study indicates that, in addition to the pharmacokinetic rates, the EKF model may provide parameters that may be useful for tumor differentiation.

Adenocarcinoma↗
PubMed2005

Diffuse optical tomography with a priori anatomical information.

Diffuse optical tomography (DOT) poses a typical ill-posed inverse problem with a limited number of measurements and inherently low spatial resolution. In this paper, we propose a hierarchical Bayesian approach to improve spatial resolution and quantitative accuracy by using a priori information provided by a secondary high resolution anatomical imaging modality, such as magnetic resonance (MR) or x-ray. In such a dual imaging approach, while the correlation between optical and anatomical images may be high, it is not perfect. For example, a tumour may be present in the optical image, but may not be discernable in the anatomical image. The proposed hierarchical Bayesian approach allows incorporation of partial a priori knowledge about the noise and unknown optical image models, thereby capturing the function-anatomy correlation effectively. We present a computationally efficient iterative algorithm to simultaneously estimate the optical image and the unknown a priori model parameters. Extensive numerical simulations demonstrate that the proposed method avoids undesirable bias towards anatomical prior information and leads to significantly improved spatial resolution and quantitative accuracy.

Anatomy↗
PubMed2005

Time-domain optical mammography SoftScan: initial results.

RATIONALE AND OBJECTIVES: Near-infrared (NIR) technology appears promising as a noninvasive technique for breast cancer screening and diagnosis. The technology capitalizes on the relative transparency of human tissue in this spectral range and its sensitivity to the main components of the breast: water, lipid, and hemoglobin. In this study, the authors report quantitative measurements of these components and the functional contrast between healthy and diseased tissue. MATERIALS AND METHODS: A four-wavelength time domain optical imaging system was used to perform noninvasive NIR measurements in the breast of 49 women both pre- and postmenopausal, ages 24-80. Algorithms based on a diffusive model of light transport provided absolute bulk and local values of breast constituent concentrations. RESULTS: Important variations in the functional and structural NIR properties of the breast were observed. Demographics trend were noticed in accordance with breast physiology. In the 23 cases imaged with suspicious masses, the optical images were consistent with the mammographic findings. Substantial contrast between masses and adjacent tissue is observed. Moreover, consistent differences between malign and benign cases are found with optical imaging. CONCLUSION: The results of this pilot study illustrate the sensitivity of optical techniques to the composition of the breast. In addition, preliminary data suggest that benign and malignant tumors can potentially be noninvasively differentiated with optical imaging. Moreover, statistically significant discrimination based on deoxy-hemoglobin content between malign and benign cases was found with optical imaging (P = .0184, one-tailed t test).

Adult↗
PubMed2005

Non-PET functional imaging techniques: optical.

The strong and steady development of diffuse optical spectroscopy and tomography as new biomedical optics technologies promises to bring these optical techniques into clinical practice. This article provides a brief review of the light-tissue interaction, the instrumentation, and the theory relevant to this field. This is followed by a survey of the three main applications: brain imaging, muscle imaging, and breast imaging. Lastly, the future outlook of the technology is presented, highlighting the new promises based on recent breakthroughs.

Brain↗
PubMed2004

Diffuse optical tomography with physiological and spatial a priori constraints.

Diffuse optical tomography is a typical inverse problem plagued by ill-condition. To overcome this drawback, regularization or constraining techniques are incorporated in the inverse formulation. In this work, we investigate the enhancement in recovering functional parameters by using physiological and spatial a priori constraints. More accurate recovery of the two main functional parameters that are the blood volume and the relative saturation is demonstrated through simulations by using our method compared to actual techniques.

Algorithms↗
PubMed2003

Correlation between near-infrared spectroscopy and magnetic resonance imaging of rat brain oxygenation modulation.

We measure the tissue oxygen and haemoglobin concentrations in the rat brain during modulation of inhaled oxygen concentration (FiO2), using non-invasive frequency domain near-infrared oximetry. The rise in oxygenated haemoglobin concentration and the decline in deoxygenated haemoglobin concentration are demonstrated in correspondence with the modulation of FiO2, which is changed from 20% to 100% in increments of 20%. Furthermore, the tissue oxygenation saturation also shows the corresponding trend and changes ranging from approximately 70% to 90%. The relative changes in deoxygenated haemoglobin concentration are compared to the blood-oxygenation-level-dependent (BOLD) MRI signal recorded during a similar FiO2 protocol. A linear relationship with high correlation coefficient between the relative changes in the BOLD MRI signal and the NIRS signal is observed.

Administration, Inhalation↗
PubMed2003

In vivo continuous-wave optical breast imaging enhanced with Indocyanine Green.

We investigate the uptake of a nontargeted contrast agent by breast tumors using a continuous wave diffuse optical tomography apparatus. The instrument operates in the near-infrared spectral window and employs 16 sources and 16 detectors to collect light in parallel on the surface of the tumor-bearing breast (coronal geometry). In our protocol an extrinsic contrast agent, Indocyanine Green (ICG), was injected by bolus. Three clinical scenarios with three different pathologies were investigated. A two-compartment model was used to analyze the pharmacokinetics of ICG and preprocess the data, and diffuse optical tomography was used for imaging. Localization and delineation of the tumor was achieved in good agreement with a priori information. Moreover, different dynamical features were observed for differing pathologies. The malignant cases exhibited slower rate constants (uptake and outflow) compared to healthy tissue. These results provide further evidence that in vivo pharmacokinetics of ICG in breast tumors may be a useful diagnostic tool for differentiation of benign and malignant pathologies.

Adenocarcinoma↗
PubMed2002

Adaptive calibration for object localization in turbid media with interfering diffuse photon density waves.

The amplitude cancellation method that uses dual out-of-phase sources (a phased array system) can sensitively detect and locate small objects in turbid media. The balance of these two sources is crucial to the system's detection sensitivity and accuracy. We describe a convenient method with which to adaptively calibrate the amplitudes of the two sources at each scanning position by use of low-frequency modulation of the intensity of the in-phase and the antiphase sources. We achieve accurate localization ability of the phased array system by accounting for the influence of asymmetrical boundaries and the heterogeneous background absorption. Experimental data on human breast phantoms demonstrate that localization accuracy within several millimeters has been accomplished through this method.

Calibration↗
PubMed2002

Detection limit enhancement of fluorescent heterogeneities in turbid media by dual-interfering excitation.

We report on a quantitative comparison between the single-source and the dual-interfering-source configurations for the detection of fluorescent heterogeneities embedded in a piecewise highly scattering homogeneous fluorescent background. The study is based on simulations with analytical solutions of the frequency-domain fluorescent diffuse photon density waves and practical signal-to-noise ratio considerations. Results show that dual-interfering sources outperform single-source techniques for the detection of heterogeneities in terms of fluorophore concentration and lifetime contrast. To detect the same inhomogeneity, less concentration and lifetime contrast is required with dual-interfering sources.

Coloring Agents↗
PubMed2002

Projection access order in algebraic reconstruction technique for diffuse optical tomography.

Algebraic reconstruction technique (ART) is one of the popular image reconstruction techniques used in diffuse optical tomography (DOT). We investigate in this note the influence of the order in which data are accessed in ART. Simulations mimicking breast tissues in transmission geometry with contrast agent tumour enhancement were used to evaluate the image quality of the diverse projection access investigated. We show that by selecting proper projection access order, the convergence speed can be significantly improved when ART is used to perform DOT. Moreover, low-contrast detection is improved.

Image Processing, Computer-Assisted↗
PubMed2002

Analysis on performance and optimization of frequency-domain near-infrared instruments.

Frequency-domain near-infrared techniques have been widely used to detect the optical properties of biological tissues noninvasively. In this paper we propose an analytical model to evaluate the performance of frequency-domain instruments. Based on the diffusion equation and the transfer properties of optoelectronic components, we treat all parts, including the medium, as two-port networks and apply systematic methods to answer questions concerning frequency-domain instruments. Experiments show that this method can reasonably reflect the properties of the instrument within an accuracy of 7%. This kind of method can be used to design suitable instruments for various applications. We also analyze the selection of the instrument parameters to achieve optimal performance at an efficient cost using this analytical model.

Fiber Optic Technology↗
PubMedDate not supplied

Development of high-sensitivity near-infrared fluorescence imaging device for early cancer detection.

We have developed a high-sensitivity near-infrared (NIR) optical imaging system for noninvasive cancer detection based on the molecular-labeled fluorescent contrast agents. Recent developments in molecular beacons offer a way to selectively tag various precancer and cancer signatures and provide high tumor-to-background contrast. Near-infrared imaging can deeply probe tissue up to a couple of centimeters; thus, it possesses the potential for noninvasive detection of breast or lymph node cancer. A phase cancellation (in- and antiphase) device is used to increase the sensitivity in detecting fluorescent photons and the accuracy of tumor localization. The optoelectronic system consists of the laser diode sources, fiber optics, interference filter (to select the fluorescent photons), and the high-sensitivity photon detector (photomultiplier tube). The source-detector pair scans the tissue surface in multiple directions, and the localization image can be obtained by angular back-projection reconstruction. Simulations and experimental data demonstrated the feasibility of detection and localization offluorescent object embedded inside the highly scattering media. Tumor-bearing mouse model with injection of fluorescent contrast agents is used to simulate the human breast tumor labeled with molecular beacons. The system can detect fluorescent contrast agents as small as one nanomole at the depth of three centimeters, with a three-millimeter localization error. This instrument has the potential for tumor diagnosis and imaging, and the accuracy of the localization suggests that this system could help guide the clinical fine-needle biopsy. Also, this portable device would be complementary to x-ray mammography and provide add-on information on early diagnosis and localization of breast tumor.

Animals↗