The chest wall underneath the breast tissue affects near-infrared (NIR) diffusive waves measured with reflection geometry. With the assistance of a co-registered ultrasound, the depth and the tilting angle of the chest wall can be determined and are used to model the breast as a two-layer medium. Finite element method (FEM) is suitable for modeling complex boundary conditions and is adapted to model the breast tissue and chest wall. Four parameters of bulk absorption and reduced scattering coefficients of these two layers are estimated and used for imaging reconstruction. Using a two-layer model, we have systematically investigated the effect of the chest wall on breast lesion reconstruction. Results have shown that chest-wall depth, titling angle, and difference between optical properties of two layers of lesion and reference sites affect the lesion reconstruction differently. Our analysis will be valuable and informative to researchers who are using reflectance geometry for breast imaging. The analysis can also provide guidelines for imaging operators to minimize image artifacts and to produce the best reconstruction results.
The chest-wall underneath the breast tissue distorts the diffused near infra-red light measured at distant source-detector
pairs. Common image reconstruction method consider the media as homogeneous and applying the semi-infinite model.
In this paper, we have compared the performance of our two-layer model with semi-infinite model by simulation and a
clinical case. The results show that when the chest wall has significant effect on the measurement data, a benign lesion
with low absorption can be misled as a malignant case with high absorption by using semi-infinite model.
We have also shown the influence of mismatch geometry of breast tissue and chest-wall at lesion and reference sides on
the reconstructed image and a correction method has been introduced to reduce these effects. With the assistance of two
orthogonal co-registered ultrasounds, the geometry of the breast tissue and chest wall interface can be determined and
modeled as a two-layer medium with 3D finite element mesh. Since numerical algorithms based on finite element
methods (FEM) are suitable for complex geometry and boundary conditions, this method is adapted to model the chestwall.
Four parameters of bulk absorption and reduced scattering coefficients of the first and second layers are estimated
and used to characterize the optical properties of the medium. We used a finite element model based on modified born
approximation for image reconstruction. A mismatch correction algorithm has been applied to compensate the mismatch
geometry of the breast tissue and chest-wall interface at the reference and the lesion side.
In this report, clinical examples of using combined ultrasound and optical diffused wave technique to image tumor total hemoglobin concentration and tumor hypoxia are given. These examples demonstrate that the sensitivity and specificity of using tumor hemoglobin level as diagnostic index are much higher than that of tumor
hypoxia.
In this paper, we report simultaneous reconstruction of absorption and scattering heterogeneities using a dual mesh scheme based on finite element method (FEM). Column normalization has been applied to the weight matrix obtained from FEM forward model to correct the depth dependent problem and to alleviate the crosstalk between the absorption coefficient and scattering coefficient. With this approach, phantom targets with both absorption and scattering heterogeneities can be reconstructed with good contrast and resolution. With this approach, the contrast between malignant breast cancers and benign lesions can be further improved compared with that obtained from the modified Born approximation, where the bulk reduced scattering coefficient has been used for reconstructing absorption heterogeneities.
The chest-wall layer underneath the breast tissue consists of muscle layer and induces distortion to measured near infrared diffused wave when the patient is imaged in the supine position. In this paper, we present results of using a simple two-layer model to correct the chest wall induced distortion. Four parameters of absorption and reduced scattering coefficients of both layers are used to describe the optical properties of the model. With the initially estimated absorption and reduced scattering coefficients, an iterative search method is used to find the best fitted parameters to minimize the difference between the measurements obtained at normal breast region and the model data. Then, a correction method is applied to correct the chest wall mismatch between the lesion site and reference site. With this correction scheme, phantom targets located on top of the chest-wall phantom layer can be reconstructed with good contrast and resolution. With the a priori chest wall depth information obtained from ultrasound at both normal and lesion regions, the contrast between malignant breast cancers and benign lesions can be further improved compared with that obtained from the modified Born approximation, where semi-infinite boundary is used.
We present a frequency-domain near-infrared optical tomography system designed for breast cancer detection, in conjunction with conventional ultrasound. It features fast optical switching, three-wavelength excitations, and avalanche photodiode as detectors. Laser diodes at 660, 780, and 830 nm are used as light sources and their outputs are distributed sequentially to one of nine source fibers. An equivalent 130-dB isolation between electrical signals from different source channels is achieved with the optical switches of very low crosstalk. Ten detection channels, each of which includes a silicon avalanche photodiode, detect diffusive photon density waves simultaneously. The dynamic range of an avalanche photodiode is about 20 to 30 dB higher than that of a photomultiplier tube, thus eliminating the need for multistep system gain control. The entire system is compact in size (<0.051 m3) and fast in data acquisition (less than 2 sec for a complete scan). Calibration and the clinical experiment results are presented in the paper.
In this paper, a 3D dual-mesh imaging reconstruction method is demonstrated, which can reconstruct absorption and scattering coefficients simultaneously. In the dual-mesh scheme, the total number of voxels with unknown absorption and scattering perturbations are maintained on the same order of total measurements by using a fine grid for target region and a coarse grid for background region. Certain row/column normalization has been applied to alleviate the crosstalk between the absorption coefficient and scattering coefficient, and to minimize the depth dependent problem. Experimental results of targets with different absorption and scattering contrasts have shown that accurate reconstruction of both absorption and scattering coefficients can be achieved.
Noninvasive diagnosis of solid benign and malignant tumors presents a unique challenge to all imaging modalidies. Ultrasound is routinely used in conjunction with mammography to deffierenciate simple cysts from solid lesions. However, the overlapping appearances of benign and malignant lesions make ultrasound less useful in differenciating solid lesions, which results in a large number of normal biopsies. Optical tomography using near infrared diffused light has a great potentional for imaging functional parameters of tumor total hemoglogin concentration, oxygeon saturation, and metabolism, etc, and these parameters can differenciate benign from malignant lesions. However, optical tomography alone suffers from low spatial resolution and target localization uncertainty due to the intensive light scattering inside the tissue. Our aims were to combine diffused light imaging with conventional ultrasound for detection and diagnosis of solid lesions. Initial findings of palpable and non-palpable solid breast lesions have shown that early stage invasive cancers have much higher total hemoglobin concentration due to angiogenesis than benign lesions. Furthermore, the spatial distribution of the total hemoglobin concentration is well localized in small invasive cancer cases, and is quite diffused in benign lesions.
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