Interstitial Diffuse Optical Tomography Research Articles

Feasibility of interstitial diffuse optical tomography using cylindrical diffusing fibers for prostate PDT

Interstitial diffuse optical tomography (DOT) has been used to characterize spatial distribution of optical properties for prostate photodynamic therapy (PDT) dosimetry. We have developed an interstitial DOT method using cylindrical diffuse fibers (CDFs) as light sources, so that the same light sources can be used for both DOT measurement and PDT treatment. In this novel interstitial CDF-DOT method, absolute light fluence per source strength (in unit of 1 cm−2) is used to separate absorption and scattering coefficients. A mathematical phantom and a solid prostate phantom including anomalies with known optical properties were used, respectively, to test the feasibility of reconstructing optical properties using interstitial CDF-DOT. Three dimension spatial distributions of the optical properties were reconstructed for both scenarios. Our studies show that absorption coefficient can be reliably extrapolated while there are some cross talks between absorption and scattering properties. Even with the suboptimal reduced scattering coefficients, the reconstructed light fluence rate agreed with the measured values to within ±10%, thus the proposed CDF-DOT allows greatly improved light dosimetry calculation for interstitial PDT.

Characterization of tissue optical properties for prostate PDT using interstitial diffuse optical tomography.

Photodynamic therapy (PDT) is an important treatment modality for localized diseases such as prostate cancer. In prostate PDT, light distribution is an important factor because it is directly related to treatment efficacy. During PDT, light distribution is determined by tissue optical property distributions (or heterogeneity). In this study, an interstitial diffuse optical tomography (iDOT) method was used to characterize optical properties in tissues. Optical properties (absorption and reduced scattering coefficients) of the prostate gland were reconstructed by solving the inverse problem using an adjoint model based on diffusion equation using a modified matlab public user code NIRFAST. In the modified NIRFAST method, linear sources were modeled for the reconstruction. Cross talking between absorption coefficients and reduced scattering coefficients were studied to have minimal effect, and a constrained optical property method (set either absorption coefficient or reduced scattering coefficient to be homogeneous) is also studied. A prostate phantom with optical anomalies was used to verify the iDOT method. The reconstructed results were compared with the known optical properties, and the spatial distribution of optical properties for this phantom was successfully reconstructed.

Optical property reconstruction for interstitial diffuse optical tomography

Optical property reconstruction for interstitial diffuse optical tomography

Reconstruction of in-vivo optical properties for human prostate using interstitial diffuse optical tomography

A CW interstitial diffuse optical tomography has been developed to characterize the in-vivo optical properties of prostate gland during photodynamic therapy. The spatial distributions of light fluence rate can be described by the diffusion equation. Optical properties of the prostate are reconstructed by solving the inverse problem with an adjoint method. The 3D reconstructed in-vivo optical properties for a human prostate is illustrated and compared with the results generated by a well-established point-by-point method. Moreover, the calculated fluence rate using the reconstructed optical properties matches the measured data.

SU‐FF‐I‐146: Reconstruction of Absorber Concentration Using a Linear Source Model for Interstitial Spectroscopic Diffuse Optical Tomography

Purpose: Light, photosensitizer and oxygen are the major components of Photodynamic therapy (PDT). With the implementation of interstitial diffuse optical tomography (iDOT), the optical properties of tumor tissue can be reconstructed spatially using an inverse algorithm. Further, the spatially‐resolved hemoglobin oxygen saturation and sensitizer distribution are expected to be established with the reconstructed optical properties. In this study, we incorporate a spectroscopy system with the existed iDOT to reconstruct the spatial distributions of absorber concentration. We especially focus on linear source system, because the acquisition time for a linear source system is much shorter than that for a point source system, making it more suitable for clinical use. Methods and Materials: A spectroscopic iDOT system has been developed to characterize the hemoglobin oxygen saturation and sensitizer concentration of the prostate gland during PDT. During data acquisition, isotropic detectors and the cylindrical fibers coupled to a white light source are inserted into the prostate gland, and absorption spectra are acquired along the detector insertion axis under the control of a motorized system. For our CW iDOT system, two dimensional optical properties of the prostate gland are reconstructed by solving the inverse problem with the use of an adjoint model based on diffusion theory. Results: To verify the accuracy of our methodology, we have performed measurements in an optically heterogeneous solid tissue‐simlulating phantom of known composition. We compare the spatial distribution images of optical properties and absorber concentration reconstructed for the phantom with the known results based on material composition. Results of clinical data reconstruction are also shown in this study. Conclusion: The results demonstrate that it is feasible to reconstruct the optical properties of the sample and the distributions of absorbers with known absorption spectra, indicating that reconstruction of hemodynamic and drug concentration in vivo is practical in clinical applications.

Sensitivity analysis of imaging geometries for prostate diffuse optical tomography.

Endoscopic and interstitial diffuse optical tomography have been studied in clinical investigations for imaging prostate tissues, yet, there is no comprehensive comparison of how these two imaging geometries affect the quality of the reconstruction images. In this study, the effect of imaging geometry is investigated by comparing the cross-section of the Jacobian sensitivity matrix and reconstructed images for three-dimensional mathematical phantoms. Next, the effect of source-detector configurations and number of measurements in both geometries is evaluated using singular value analysis. The amount of information contained for each source-detector configuration and different number of measurements are compared. Further, the effect of different measurements strategies for 3D endoscopic and interstitial tomography is examined. The pros and cons of using the in-plane measurements and off-plane measurements are discussed. Results showed that the reconstruction in the interstitial geometry outperforms the endoscopic geometry when deeper anomalies are present. Eight sources 8 detectors and 6 sources 12 detectors are sufficient for 2D reconstruction with endoscopic and interstitial geometry respectively. For a 3D problem, the quantitative accuracy in the interstitial geometry is significantly improved using off-plane measurements but only slightly in the endoscopic geometry.

Interstitial diffuse optical tomography using an adjoint model with linear sources.

An improved interstitial diffuse optical tomography (iDOT) system has been developed to characterize the optical properties of prostate gland during the photodynamic therapy (PDT). Multiple cylindrical light diffusers with different lengths (instead of point sources used in an earlier version) and isotropic detectors are introduced interstitially in the prostate gland in-vivo. During the data acquisition, linear sources and detectors are stepping into prostate sequentially controlled by a motorized system. A computerized multi-channel attenuator system is developed to automatically control the power strength of each linear source and on times to speed up data acquisition. Three dimensional optical properties are obtained by solving the inverse problem of steady-state diffusion equation based on an adjoint model with Moore-Penrose scheme. The convergence, accuracy and the speed of the algorithms are tested in mathematical phantoms and in prostate simulating phantoms with known optical properties. For comparison, the optical properties of tissue simulating phantoms are also reconstructed using iDOT with multiple isotropic point sources. Data acquisition time in iDOT using linear sources is at least 10 times faster than using the point sources with the total data acquisition time to be less than 1 minutes. Reconstruction results showed both algorithms can successfully recover the optical properties. Reconstruction using linear sources/detectors acquisition mode is 20 times faster than the point sources/detectors method (30 minutes vs. 4 hours on a 3.4 GHz Pentium PC with 4 GB memory). We have demonstrated that linear-source/detector acquisition mode out-performs the point-source mode, and is more practical to be implemented in the clinical settings.

Two-dimensional/three dimensional Hybrid Interstitial Diffuse Optical Tomography of Human Prostate during Photodynamic Therapy: Phantom and Clinical Results.

We have developed an efficient Levenberg-Marquardt iterative algorithm utilizing a three-dimensional field measurements coupled to a two-dimensional optical property reconstruction scheme. This technique takes advantage of accurate estimation of light distribution in 3D forward calculation and reduced problem size and less computation time in 2D inversion. Important advances in terms of improving algorithm efficiency and accuracy include use of an iterative general minimum residual method (GMRES) for computing the field solutions, application of the dual mesh scheme and adjoint method for Jacobian construction, and implementation of normalization scheme to reduce the absorption-scattering cross talk. The synthetic measurement data were calculated for a cubic phantom containing a single absorption anomaly and a single scattering anomaly. The model had a background of μa=0.03mm-1 and μs'=1.4mm-1. The absorption and scattering anomalies have the μa = 0.06 mm-1 and μs' = 2.0 mm-1. Five sources and 72 detectors are used per slice. A typical human prostate is composed of 6 slices. The reconstruction images successfully recover the both anomalies with good localization. Experiment data from tissue simulated phantom are also presented. The clinical DOT imaging was performed before photodynamic therapy based on the protocol. The preliminary results showed the reconstructed prostate μa varied between 0.025 and 0.07 mm-1 and μs' ranged from 1.1 to 2 mm-1. These results show that this new 2D-3D hybrid algorithm consistently outperform the 2D-2D or 3D-3D counterparts.