We report an optical mammography study on eight patients with breast cancer who underwent neoadjuvant chemotherapy. Of these eight patients, six were responders (tumor size decreased by more than 50%) and two were nonresponders (tumor size decreased by less than 50%). The goals of this study are (1) to characterize the temporal evolution of the hemoglobin concentration ([HbT]) and saturation (SO2) in breast tissue during the course of treatment in responders and non-responders, and (2) to define a quantitative index that is capable of identifying responders and nonresponders during treatment. We found that both [HbT] and SO2 decreased by a greater amount in responders than in non-responders during therapy. This result applied to both cancerous and healthy breast, but the discrimination of responders and non-responders was more significant with SO2 measurements in the cancerous breast. A cumulative response index defined in terms of SO2 measurements in the cancerous breast achieved a 100% sensitivity and 100% specificity for the identification of responders and non-responders at therapy midpoint. These results confirm the potential of optical mammography in assessing response to neoadjuvant chemotherapy during treatment, thus offering the opportunity to consider alternative options to ineffective treatment regimens.
We present a study of the bilateral symmetry of human breast hemoglobin saturation maps measured with a broadband optical mammography instrument. We have imaged 21 patients with unilateral breast cancer, 32 patients with unilateral benign lesions, and 27 healthy patients. An image registration process was applied to the bilateral hemoglobin saturation (SO2) images by assigning each pixel to the low, middle, or high range of SO2 values, where the thresholds for the categories were the 15th and 85th percentiles of the individual saturation range. The Dice coefficient, which is a measure of similarity, was calculated for each patient’s pair of right and left breast SO2 images. The invasive cancer patients were found to have an average Dice coefficient value of 0.55±0.07, which was significantly lower than the benign and healthy groups (0.61±0.11 and 0.62±0.12, respectively). Although differences were seen in a group analysis, the healthy patient Dice coefficients spanned a wide range, limiting the diagnostic capabilities of this SO2 symmetry analysis on an individual basis. Our results suggest that for assessing the SO2 contrast of breast lesions, it may be better to select a reference tissue in the ipsilateral rather than the contralateral breast.
We are developing a new instrument for diffuse optical mammography in parallel plate geometry that operates over a
broad spectral range of 600-1000 nm, features a scan time of 1-2 min, and allows for dynamic measurements at a
selected region of interest. Furthermore, this new instrument is capable of depth discrimination of optical
inhomogeneities embedded in the examined tissue by using multiple off-axis detection fibers. Using a solid silicone
phantoms, mimicking breast tissue with 39 mm thickness, we demonstrate the capability of this instrument to recover the
depth of blood-vessel-like structures to within ~2 mm. Additionally, we demonstrate the capability of this instrument to
perform dynamic optical measurements with a temporal sampling rate as high as 20 Hz. We describe our plans to
integrate this rich spectral, spatial, and temporal information into a single instrument for translation into clinical
measurements on breast cancer patients.
The imaging of shape perturbation and chromophore concentration using Diffuse Optical Tomography (DOT) data can be mathematically described as an ill-posed and non-linear inverse problem. The reconstruction algorithm for hyperspectral data using a linearized Born model is prohibitively expensive, both in terms of computation and memory. We model the shape of the perturbation using parametric level-set approach (PaLS). We discuss novel computational strategies for reducing the computational cost based on a Krylov subspace approach for parameteric linear systems and a compression strategy for the parameter-to-observation map. We will demonstrate the validity of our approach by comparison with experiments.
We present a method to compensate for breast tissue thickness variability in broadband, continuous-wave, parallel plate optical mammography. Tissue thickness information is relevant for the recovery of chromophore concentrations within the breast using continuous-wave, diffusion-based models that assume the breast to be in slab geometry. This method compensates for the discrepancy between the actual phantom or breast shape and the models assumed slab geometry by approximating the thickness of the probed tissue volume. In this work, we applied our tissue thickness compensation algorithm on a breast shaped, homogeneous, tissue-mimicking phantom. Using the thickness found from our algorithm (referred to as our “estimated thickness”) as an input into a continuous-wave, diffusion based model, we recovered the absorption coefficient throughout all scanned pixels in the phantom and found an overall deviation of 12% from the true absorption coefficient. By using the known phantom thickness, we found a strong shape bias within the absorption coefficient recovery and a larger overall deviation of 29%. To test the algorithm on in vivo measurements, we applied this tissue thickness compensation method to a human breast cancer optical mammogram scan. Since the exact thickness of the breast at each pixel is unknown, we compared these results to when a uniform breast thickness is assumed and found a drastic improvement of cancer visualization. This method allows for parallel plate, continuous-wave optical imaging to compensate for the tissue thickness variability at each scanned pixel when modeling the breast data in slab geometry. This compensated thickness is needed as an input to the model in order to accurately map the breast chromophore concentrations and enhance the image contrast of cancer.
We present diffuse optical mammography images that capitalize on the large optical absorption contrast (two orders of magnitude) between blood vessels and breast tissue, thus displaying breast vasculature. We have found a good correspondence between blood vessels displayed in the optical mammogram and those visible in the x-ray mammogram from the same subject in the same view (craniocaudal). By using broadband spectral information (wavelength range: 650-900 nm), we measured the hemoglobin saturation for the blood vessels displayed in the optical mammogram, for which we obtained an average value of 70%. In order to assess the z-axis depth of optical inhomogneities detected in this planar scanning approach, we have introduced pairs of detector optical fibers that are off-axis with respect to the illumination optical fiber. The spatial shift between the locations of the optical inhomogeneities in the two off-axis images can be translated into a depth measurement through a quasi-universal depth-shift reference curve. We report Monte Carlo simulations that show how this depth-shift reference curve is affected by the distance between the source and detector scanning planes (sample thickness) and to the specific arrangement of the two off-axis detectors. Liquid tissue-like phantoms were used to test this depth assessment approach for an absorbing rod placed at a depth of 33.6 mm. The depth measured with our method over the rod length ranged within 33-35 mm, in excellent agreement with the actual rod depth. The ability to identify blood vessels, measure their hemoglobin saturation, and assess their depth within breast tissue is a valuable feature that can advance optical mammography by providing additional structural and functional information about breast tissue.
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