Reconstructed Absorption Coefficient Research Articles

Multi wavelength optical image feature fusion method for improving the reconstruction effect of cerebral hematoma

Diffuse optical tomography (DOT) under medical image guidance can be used to reconstruct images of subdural hematomas for monitoring purposes. However, when the shape of hematoma is irregular or the signal to noise ratio(SNR) of input signal is low, the accuracy and robustness of this method both decrease. In order to alleviate this situation and improve the reconstruction effect of cerebral hematoma images, a multi wavelength optical image feature fusion method was proposed in this paper. Experimental results show that the mean relative volume error (VRE) of the hematoma reconstruction model based on the multi-wavelength optical image feature fusion method is only 0.66 %, and the mean value of the average Manhattan distance (AMD) between the reconstructed absorption coefficient and the true absorption coefficient is 0.0052 mm−1. Compared with the model using single-wavelength optical image mapping feature extraction method, the multi-wavelength optical image feature fusion method reduces the average VRE of the model by 16.5 %, and the average AMD by 16.1 %. And compared with the model directly inputting single-wavelength optical information, its average VRE and average AMD decreased by 80.0 % and 27.8 %. This method has clinical application significance for the monitoring of subdural hematomas.

One-dimensional convolutional neural network for Jacobian in Diffuse Optical Tomography.

Non-linear least square minimization algorithms are often employed to solve Diffuse Optical Tomography (DOT) inverse problem. However, it is time-consuming to calculate the Jacobian matrix. This work has proposed a data-driven neural network method to improve computational efficiency. The singular value decomposition is employed to compute the updated Jacobian and a mapping from boundary measurements to the singular values based on a convolutional neural network (CNN) is learned to obtain the singular values. The method is validated with 3D numerical simulation data. We have demonstrated that the approach can save computation time compared to Adjoint method, and reconstructed absorption coefficient close to Adjoint method.Clinical Relevance- These results are not focused on clinical relevance currently, but in the future may be helpful to accelerant DOT reconstruction in clinic.

Compact ultrasound-guided diffuse optical tomography system for breast cancer imaging.

Near-infrared diffuse optical tomography (DOT) has demonstrated a great potential as an adjunct modality for differentiation of malignant and benign breast lesions and for monitoring treatment response in patients with locally advanced breast cancers. The path toward commercialization of DOT techniques depends upon the improvement of robustness and user-friendliness of this technique in hardware and software. In this study, we introduce our recently developed ultrasound-guided DOT system, which has been improved in system compactness, robustness, and user-friendliness by custom-designed electronics, automated data preprocessing, and implementation of a new two-step reconstruction algorithm. The system performance has been tested with several sets of solid and blood phantoms and the results show accuracy in reconstructed absorption coefficients as well as blood oxygen saturation. A clinical example of a breast cancer patient, who was undergoing neoadjuvant chemotherapy, is given to demonstrate the system performance.

Effects of the approximations of light propagation on quantitative photoacoustic tomography using two-dimensional photon diffusion equation and linearization

Quantitative photoacoustic tomography (QPAT) employing a light propagation model will play an important role in medical diagnoses by quantifying the concentration of hemoglobin or a contrast agent. However, QPAT by the light propagation model with the three-dimensional (3D) radiative transfer equation (RTE) requires a huge computational load in the iterative forward calculations involved in the updating process to reconstruct the absorption coefficient. The approximations of the light propagation improve the efficiency of the image reconstruction for the QPAT. In this study, we compared the 3D/two-dimensional (2D) photon diffusion equation (PDE) approximating 3D RTE with the Monte Carlo simulation based on 3D RTE. Then, the errors in a 2D PDE-based linearized image reconstruction caused by the approximations were quantitatively demonstrated and discussed in the numerical simulations. It was clearly observed that the approximations affected the reconstructed absorption coefficient. The 2D PDE-based linearized algorithm succeeded in the image reconstruction of the region with a large absorption coefficient in the 3D phantom. The value reconstructed in the phantom experiment agreed with that in the numerical simulation, so that it was validated that the numerical simulation of the image reconstruction predicted the relationship between the true absorption coefficient of the target in the 3D medium and the reconstructed value with the 2D PDE-based linearized algorithm. Moreover, the the true absorption coefficient in 3D medium was estimated from the 2D reconstructed image on the basis of the prediction by the numerical simulation. The estimation was successful in the phantom experiment, although some limitations were revealed.

Parametric Reconstruction of Diffuse Optical Tomography Using Gaussian Mixture Model and Genetic Algorithm

The inverse problem of diffused optical tomography is highly ill-posed as well as often nonunique and unstable. The ill-posedness can be reduced by reducing the number of unknown values (e.g., adding soft or hard-prior constraints). In this paper, this has been achieved by parameterization of the tissue optical properties. The optical parameters of the tissue have been modeled by a Gaussian mixture model (GMM) of eight components, and the image is reconstructed by estimating the parameters of the mixture model. Therefore, the number of unknowns is drastically reduced while maintaining some amount of generality by using an 8 component GMM. Unlike conventional GMM, the parameters are estimated using the Genetic algorithm in a multi-step predictor-corrector model. A new cost function is proposed using mean square error and asymmetry measurement of detected intensity. Object centroid error, structural similarity index, maximum error and normalized root mean squared error of reconstructed absorption coefficients are evaluated for performance assessment and comparison. Extensive numerical and experimental results have been illustrated to show the potential of the proposed method. Use of CW (continuous wave) measurement and single imaging modality make the system cost effective and portable.

Investigation of noise properties in grating-based x-ray phase tomography with reverse projection method**Project supported by the National Basic Research Program of China (Grant No. 2012CB825800), the Science Fund for Creative Research Groups, the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant Nos. KJCX2-YW-N42 and Y4545320Y2), the National Natural Science Foundation of China (Grant Nos. 11475170, 11205157, 11305173, 11205189,

The relationship between noise variance and spatial resolution in grating-based x-ray phase computed tomography (PCT) imaging is investigated with reverse projection extraction method, and the noise variances of the reconstructed absorption coefficient and refractive index decrement are compared. For the differential phase contrast method, the noise variance in the differential projection images follows the same inverse-square law with spatial resolution as in conventional absorption-based x-ray imaging projections. However, both theoretical analysis and simulations demonstrate that in PCT the noise variance of the reconstructed refractive index decrement scales with spatial resolution follows an inverse linear relationship at fixed slice thickness, while the noise variance of the reconstructed absorption coefficient conforms with the inverse cubic law. The results indicate that, for the same noise variance level, PCT imaging may enable higher spatial resolution than conventional absorption computed tomography (ACT), while ACT benefits more from degraded spatial resolution. This could be a useful guidance in imaging the inner structure of the sample in higher spatial resolution.

TU‐A‐9A‐11: Gold Nanoparticles Enhanced Diffuse Optical Tomography: A Proof of Concept Study

Purpose:To investigate the feasibility and potential of gold nanoparticles (GNP) enhanced diffuse optical tomography (DOT) as a novel imaging strategy for tumor detection.Methods:Simulation was performed on a digital homogeneous cylindrical phantom of 30mm×30mm. Gold nanorods (GNR) with aspect ratio 3.9 and effective radius 21.86nm were used as contrast agent. The peak light absorption for these GNR occurs at 842nm within the near‐infrared region, with the absorption cross‐section of 1.97×10‐14m‐2 and scatter cross‐section of 1.07×10‐14m‐2. A 6mmdiameter sphere of GNR solution was positioned inside the tissue‐simulating phantom. Simulations were performed at the GNR concentration level of 1nM, 100pM and 10pM, respectively. The points representing laser sources and light detectors were around the phantom with 30o apart tangentially and 1mm apart axially for 9 rows. As one point being source, all the other points within the current row and nearby four rows become detectors. Hence there are 108 source points in total and 55 detector points corresponding to each source. Forward light transport at 842nm wavelength was run on a three‐dimensional mesh of 33186 nodes (∼0.5mm resolution) to acquire the light emission data. Reconstruction was performed on a coarse mesh of 19408 nodes (∼1mm resolution) with ∼20minutes on a 2.4GHz CPU and 8GB RAM computer.Results:The position of the GNR solution at 1nM, 100pM and 10pM concentration was reconstructed, respectively, with <1mm error. The GNR concentration was interpreted from the reconstructed absorption coefficient within the enhanced volume. The reconstructed maximum concentrations were 0.3nM, 120.0pM, and 5.3pM, respectively.Conclusion:To the best of our knowledge, this is the first time to apply GNP to enhance DOT. The simulation results showed the high sensitivity of GNP enhanced DOT, which is in pM concentration level, compared to the μM level for MRI agents and nM level for PET agents.

Data-constrained modelling of an anthracite coal physical structure with multi-spectrum synchrotron X-ray CT

A data-constrained modelling (DCM) approach with multi-spectrum synchrotron X-ray CT has been used to characterise the physical structure of Yangquan coal sample. Three sets of X-ray CT data have been acquired with monochromatic beam energies at 14, 18, and 30keV respectively. A DCM approach is used to derive compositional volume fractions on each voxel, by minimising the differences between the expected and CT reconstructed absorption coefficients with a nonlinear optimization algorithm. Voxel based 3D compositional maps are generated with colours and intensities representing compositions and volume fractions respectively. The results are relevant in quantitative modelling of coal-bed gas transportation and coal processing.

Global and local hard X-ray tomography of a centimeter-size tumor vessel tree

The visualization of the vascular network in tumors down to the smallest vessels requires high spatial resolution and reasonable contrast. Stained corrosion casts of the microvasculature network guarantee superior X-ray absorption contrast and highest reproduction fidelity. Tomography of a centimeter-size tumor, however, is unfeasible at the spatial resolution needed to reveal the smallest vessels. Therefore, local tomography has been performed to visualize the smallest capillaries within the region of interest. These three-dimensional data show the detailed morphology, but the reconstructed absorption coefficients obtained in local tomography differ substantially from the absorption coefficients retrieved from the less detailed global tomography data. This paper deals with the adaptation of local tomography data using the global data and considers two-parameter histogram matching of the radiographs, sinogram extension, and multi-parameter cupping correction. It is demonstrated that two-parameter histogram matching of the radiographs already provides reasonable agreement. The change of the lens in front of the detector's camera, however, significantly affects the obtained local X-ray absorption coefficients in the tomograms predominantly owing to the dissimilar point-spread functions of the two configurations used, and much less to the fact that one of the data sets was acquired in a local geometry.

TU‐G‐110‐06: Detection of Contrast Agents with a CdTe Semiconductor Detector Intended for Small Animal Imaging

Purpose: The objective of this study was to find out if a spectroscopic semiconductor detector from the Medipix2 family is capable to simultaneously resolve the K‐edges of iodine and gadolinium contrast agents present in a phantom at various concentrations. Employing a pixel pitch comparable to the range of X‐ray fluorescences generated in the CdTe sensor, the energy response function (ERF) of the detector system employed is heavily biased. Therefore, its detection limits prior to any corrections were determined in this work.Methods: The detector used delivers spectroscopic information by means of an adjustable energy window. The sensor of the detector is made of 1 mm thick cadmium telluride (CdTe) that has an active area of 4.2cm × 2.8cm and features a pixel pitch of 165um. The X‐ray source employed was operated at 70kVp that corresponds to a mean photon energy of roughly 40keV. A phantom containing six different concentrations (11.8umol/ml, 23.6umol/ml, 47.3ummol/ml, 118.2umol/ml, 236.4umol/ml and 472.8umol/ml) of iodine (Imeron300) and gadolinium (Multihance 0.5M) contrast agents was employed, containing capillary tubes with diameters of 1.6mm and 0.8mmin order to mimic blood vessels.Results: The K‐edges of iodine (33.2keV) and of gadolinium (50.2keV) could easily be detected for the 3 highest concentrations: 118.2umol/ml, 236.4umol/ml and 472.8umol/ml. With these concentrations the reconstructed absorption coefficients increased significantly between the energy windows 25–30keV and 35–40keV for iodine and between 42–47keV and 52–57keV for gadolinium. Conclusions: A pixel pitch of 165um is large enough to detect the absorption edges of iodine and gadolinium using a single tube voltage. However, quantitative measurements require the reconstruction of the acquired spectra by a precise knowledge of the ERFs of all photon energies involved.

Reduction of Poisson noise in measured time-resolved data for time-domain diffuse optical tomography

A method to reduce noise for time-domain diffuse optical tomography (DOT) is proposed. Poisson noise which contaminates time-resolved photon counting data is reduced by use of maximum a posteriori estimation. The noise-free data are modeled as a Markov random process, and the measured time-resolved data are assumed as Poisson distributed random variables. The posterior probability of the occurrence of the noise-free data is formulated. By maximizing the probability, the noise-free data are estimated, and the Poisson noise is reduced as a result. The performances of the Poisson noise reduction are demonstrated in some experiments of the image reconstruction of time-domain DOT. In simulations, the proposed method reduces the relative error between the noise-free and noisy data to about one thirtieth, and the reconstructed DOT image was smoothed by the proposed noise reduction. The variance of the reconstructed absorption coefficients decreased by 22% in a phantom experiment. The quality of DOT, which can be applied to breast cancer screening etc., is improved by the proposed noise reduction.

Evaluation of Iterative Sparse Object Reconstruction From Few Projections for 3-D Rotational Coronary Angiography

A 3-D reconstruction of the coronary arteries offers great advantages in the diagnosis and treatment of cardiovascular disease, compared to 2-D X-ray angiograms. Besides improved roadmapping, quantitative vessel analysis is possible. Due to the heart's motion, rotational coronary angiography typically provides only 5-10 projections for the reconstruction of each cardiac phase, which leads to a strongly undersampled reconstruction problem. Such an ill-posed problem can be approached with regularized iterative methods. The coronary arteries cover only a small fraction of the reconstruction volume. Therefore, the minimization of the mbiL(1) norm of the reconstructed image, favoring spatially sparse images, is a suitable regularization. Additional problems are overlaid background structures and projection truncation, which can be alleviated by background reduction using a morphological top-hat filter. This paper quantitatively evaluates image reconstruction based on these ideas on software phantom data, in terms of reconstructed absorption coefficients and vessel radii. Results for different algorithms and different input data sets are compared. First results for electrocardiogram-gated reconstruction from clinical catheter-based rotational X-ray coronary angiography are presented. Excellent 3-D image quality can be achieved.

Reconstruction of optical properties of phantom and breast lesion in vivo from paraxial scanning data

We report on the reconstruction of absorption and reduced scattering coefficients of breast tissue in vivo of a patient with mastopathic disease. Distributions of times of flight of photons through the compressed breast were recorded by paraxial scanning. From data measured at four different source–detector offsets optical properties were reconstructed within the linear Rytov approximation by a fast inverse Fourier space method. Low-pass filtering in Fourier space was employed to remove excessive noise from high spatial frequency components and to reduce the computational efforts by a factor of 3, typically. The mammograms displaying reconstructed absorption and reduced scattering coefficients were compared with projection mammograms either obtained by time-window analysis of experimental data or based on average absorption and reduced scattering coefficients which were derived from measured temporal point spread functions within a simple homogeneous model. All inhomogeneities which were visible in the projection mammograms and which could be associated with specific breast tissue compartments could be correlated with inhomogeneities in the reconstructed absorption coefficient. In particular, the mastopathic disease was detected in the reconstructed absorption mammogram. In order to assess reliability of optical properties reconstructed from data obtained by paraxial scanning, corresponding phantom experiments and reconstructions of phantom optical properties were carried out. Because of the limited angular range sampled by the in vivo and phantom measurements, considerable blurring of the absorption coefficient occurs along the compression direction, compromising longitudinal resolution.

Near Infrared Diffusive Light Imaging with Ultrasound Localization

because there is no known robust stopping criterion to terminate iterative image reconstruction algorithms. No further iterations are needed with the a priori knowledge from co-registered ultrasound. Figure 1 shows an example of ultrasound assisted NIR image reconstruction.2 Figure 1(a) shows the contours of ultrasound image of two targets 1 cm in size. Figure 1(b) is the NIR image of the two targets. The target indicated by the white arrow in part (b) is displaced from its true location by about 1 cm and the reconstructed absorption coefficient is only 50% of the true value. With the ultrasound localization shown in part (a), the NIR image shown in Fig. 1(c) provides correction target locations and the reconstructed absorption coefficients are within 20% of the true values. By adding optical contrasts to ultrasonically detected lesions, the combined approach has great promise in improving breast cancer diagnosis.4 Optical contrasts will significantly improve diagnostic ultrasound in differentiating benign from malignant solid lesions.

Near Infrared Diffusive Light Imaging with Ultrasound Localization

because there is no known robust stopping criterion to terminate iterative image reconstruction algorithms. No further iterations are needed with the a priori knowledge from co-registered ultrasound. Figure 1 shows an example of ultrasound assisted NIR image reconstruction.2 Figure 1(a) shows the contours of ultrasound image of two targets 1 cm in size. Figure 1(b) is the NIR image of the two targets. The target indicated by the white arrow in part (b) is displaced from its true location by about 1 cm and the reconstructed absorption coefficient is only 50% of the true value. With the ultrasound localization shown in part (a), the NIR image shown in Fig. 1(c) provides correction target locations and the reconstructed absorption coefficients are within 20% of the true values. By adding optical contrasts to ultrasonically detected lesions, the combined approach has great promise in improving breast cancer diagnosis.4 Optical contrasts will significantly improve diagnostic ultrasound in differentiating benign from malignant solid lesions.

Simultaneous near-infrared diffusive light and ultrasound imaging

We have constructed a near-real-time combined imager suitable for simultaneous ultrasound and near-infrared diffusive light imaging and coregistration. The imager consists of a combined hand-held probe and the associated electronics for data acquisition. A two-dimensional ultrasound array is deployed at the center of the combined probe, and 12 dual-wavelength laser source fibers (780 and 830 nm) and 8 optical detector fibers are deployed at the periphery. We have experimentally evaluated the effects of missing optical sources in the middle of the combined probe on the accuracy of the reconstructed optical absorption coefficient and assessed the improvements of a reconstructed absorption coefficient with the guidance of the coregistered ultrasound. The results have shown that, when the central ultrasound array area is in the neighborhood of 2 cm x 2 cm, which corresponds to the size of most commercial ultrasound transducers, the optical imaging is not affected. The results have also shown that the iterative inversion algorithm converges quickly with the guidance of a priori three-dimensional target distribution, and only one iteration is needed to reconstruct an accurate optical absorption coefficient.

Design of near-infrared imaging probe with the assistance of ultrasound localization.

A total of 364 optical source-detector pairs were deployed uniformly over a 9 cm x 9 cm probe area initially, and then the total pairs were reduced gradually to 60 in experimental and simulation studies. For each source-detector configuration, three-dimensional (3-D) images of a 1-cm-diameter absorber of different contrasts were reconstructed from the measurements made with a frequency-domain system. The results have shown that more than 160 source-detector pairs are needed to reconstruct the absorption coefficient to within 60% of the true value and appropriate spatial and contrast resolution. However, the error in target depth estimated from 3-D images was more than 1 cm in all source-detector configurations. With the a priori target depth information provided by ultrasound, the accuracy of the reconstructed absorption coefficient was improved by 15% and 30% on average, and the beam width was improved by 24% and 41% on average for high- and low-contrast cases, respectively. The speed of reconstruction was improved by ten times on average.

Systematic diffuse optical image errors resulting from uncertainty in the background optical properties

We investigated the diffuse optical image errors resulting from systematic errors in the background scattering and absorption coefficients, Gaussian noise in the measurements, and the depth at which the image is reconstructed when using a 2D linear reconstruction algorithm for a 3D object. The fourth Born perturbation approach was used to generate reflectance measurements and k-space tomography was used for the reconstruction. Our simulations using both single and dual wavelengths show large systematic errors in the absolute reconstructed absorption coefficients and corresponding hemoglobin concentrations, while the errors in the relative oxy- and deoxy- hemoglobin concentrations are acceptable. The greatest difference arises from a systematic error in the depth at which an image is reconstructed. While an absolute reconstruction of the hemoglobin concentrations can deviate by 100% for a depth error of ñ1 mm, the error in the relative concentrations is less than 5%. These results demonstrate that while quantitative diffuse optical tomography is difficult, images of the relative concentrations of oxy- and deoxy-hemoglobin are accurate and robust. Other results, not presented, confirm that these findings hold for other linear reconstruction techniques (i.e. SVD and SIRT) as well as for transmission through slab geometries.