Two-step reconstruction method using global optimization and conjugate gradient for ultrasound-guided diffuse optical tomography

Abstract

Abstract. Ultrasound-guided diffuse optical tomography (DOT) is a promising method for characterizing malignant and benign lesions in the female breast. We introduce a new two-step algorithm for DOT inversion in which the optical parameters are estimated with the global optimization method, genetic algorithm. The estimation result is applied as an initial guess to the conjugate gradient (CG) optimization method to obtain the absorption and scattering distributions simultaneously. Simulations and phantom experiments have shown that the maximum absorption and reduced scattering coefficients are reconstructed with less than 10% and 25% errors, respectively. This is in contrast with the CG method alone, which generates about 20% error for the absorption coefficient and does not accurately recover the scattering distribution. A new measure of scattering contrast has been introduced to characterize benign and malignant breast lesions. The results of 16 clinical cases reconstructed with the two-step method demonstrates that, on average, the absorption coefficient and scattering contrast of malignant lesions are about 1.8 and 3.32 times higher than the benign cases, respectively.

Improving DOT reconstruction with a Born iterative method and US-guided sparse regularization

“…In the past, we have attempted to simultaneously reconstruct both absorption and scattering distributions of breast lesions [36]. We had success in phantom data, but these algorithms are not robust for patient data when applied to a large patient database.…”

Development of a robust and fast calibration procedure for diffuse optical tomography

“…The genetic algorithm is used to estimate the initial absorption and reduced scattering coefficient for lesion area. [8] The output of genetic algorithm and the lesion location information are used for dual-mesh algorithm to reconstruct the lesion absorption at multiple wavelengths and the total hemoglobin. [9] The total computation time takes about 1 to 3 mins depending on the size of the lesion.…”

Estimation and imaging of breast lesions using a two-layer tissue structure by ultrasound-guided optical tomography

“…Recently, we have developed a two-step reconstruction method using GA followed by the CG method for simultaneous image reconstruction of absorption and scattering maps of targets inside a semi-infinite medium. 22 Briefly, GA was used to obtain an initial estimate of the optical properties of a lesion. Because coregistered US images were used to locate the target approximately in the middle of the probe, the target center and its radius in the z direction were estimated from US images, and its radius in spatial x and y dimensions (r x r y ) was iteratively estimated by GA. First, an initial population is generated, formed by certain individuals while each member is a possible solution of the optimization problem and can be represented by a vector of real numbers, for example, [μ am μ 0 sm r x r y ], where μ am and μ 0 sm are unknown maximum target absorption and reduced scattering coefficients.…”

“…Using this approach, the unknown variables have been reduced from four to two and the results are more accurate and robust. In addition, we have implemented a two-step reconstruction using a genetic algorithm (GA) and conjugate gradient (CG) method 22 to simultaneously reconstruct the absorption and reduced scattering maps of a target inside a twolayer tissue structure. Simulations and phantom experiments have been performed to validate the new reconstruction method, and a clinical example is given to demonstrate the feasibility of this approach.…”