Time-resolved optical mammography using a liquid coupled interface

The reproducibility of optical mammography in healthy volunteers

This study was designed to determine the reproducibility of optical mammography. Eight healthy pre-menopausal volunteers were scanned at different time intervals (minutes, weeks and months apart) to investigate the effects of within-subject variation, between-subject variation and systematic variations on both the raw data and images. The study shows that the greatest source of variation in optical mammography raw data and images is between different subjects, and scans of the same subject are very reproducible. The averaged total haemoglobin concentration from the eight volunteers was (24 ± 10) µM, and the average tissue oxygen saturation was (70 ± 10)%, which is comparable with other data in the literature. The average absorption coefficient at 780 nm was (0.0048 ± 0.0017) mm(-1) and the average reduced scatter coefficient at 780 nm was (0.80 ± 0.12) mm(-1). Again, this is comparable with published values. When our data are combined with the published values, the weighted average total haemoglobin concentration and tissue oxygen saturation for pre-menopausal breasts are (29 ± 8) µM and (73 ± 3)%, respectively. The results of our study show that we can be reassured that any changes within the tumour region seen during neoadjuvant therapy are likely to be due to a real physiological response to treatment, as the physiological properties of the breast remain relatively constant. However, in this study, we cannot distinguish between a tumour response to treatment and systemic changes in the healthy breast.

Diffuse optical tomography in the presence of a chest wall

Diffuse optical tomography (DOT) has been employed to derive spatial maps of physiologically important chromophores in the human breast, but the fidelity of these images is often compromised by boundary effects such as those due to the chest wall. We explore the image quality in fast, data-intensive analytic and algebraic linear DOT reconstructions of phantoms with subcentimeter target features and large absorptive regions mimicking the chest wall. Experiments demonstrate that the chest wall phantom can introduce severe image artifacts. We then show how these artifacts can be mitigated by exclusion of data affected by the chest wall. We also introduce and demonstrate a linear algebraic reconstruction method well suited for very large data sets in the presence of a chest wall.

Optical parameters of embedded abnormalities in tissues as determined by Monte Carlo simulation

Photon propagation through tissue phantoms, made of heart, adipose, and spleen tissues was simulated by Monte Carlo procedure. To detect the presence of deep-seated abnormalities, phantoms of heart with adipose and spleen tissues embedded into it were created and simulations were performed to scan the tissue surface with a source and four detector model. Profiles drawn showed variation in parameters such as backscattered intensity in regions where adipose and spleen tissues were embedded. This study shows that depending on the type of embedded tissue the backscattered fraction as measured at 2 mm from the input fiber is altered. This is enhanced for adipose and decreased for spleen tissue. This is not only shown in scanned profiles on the surface but also in constructed images.

Monitoring the response to primary medical therapy for breast cancer using three- dimensional time-resolved optical mammography

Primary medical therapy is used to reduce tumour size prior to surgery in women with locally advanced breast cancer. Optical tomography is a functional imaging technique using near- infrared light to produce three-dimensional breast images of tissue oxygen saturation and haemoglobin concentration. Its advantages include the ability to display quantitative physiological information, and to allow repeated scans without the hazards associated with exposure to ionising radiation. There is a need for a non-invasive functional imaging tool to evaluate response to treatment, so that non-responders can be given the opportunity to change their treatment regimen. Here, we evaluate the use of optical tomography for this purpose. Four women with newly diagnosed breast cancer who were about to undergo primary medical therapy gave informed and voluntary consent to take part in the study. Changes in physiological and optical properties within the tumour were evaluated during the course of neoadjuvant chemotherapy. Optical imaging was performed prior to treatment, after the first cycle of chemotherapy, halfway through, and on completion of chemotherapy. Images of light absorption and scatter at two wavelengths were produced, from which images of total haemoglobin concentration and oxygen saturation were derived. All patients that showed a good or complete response to treatment on MRI showed a corresponding recovery in the haemoglobin concentration images. Changes in mean tumour total haemoglobin concentration could be seen four weeks into treatment. The tumour oxygen saturation was low compared to background in three out of four patients, and also showed a return to baseline over treatment. Optical imaging of the breast is feasible during primary medical therapy and can be used to assess response to treatment over six months.

Time-resolved optical mammography and its preliminary clinical results

We have been developing an optical mammography prototype consisting of a multi-channel time-resolved spectroscopy system for breast cancer screening. The system utilizes the time-correlated single photon counting method, and the detector modules and the signal processing circuits were custom-made to obtain a high signal to noise ratio and high temperature stability with a high temporal resolution. Pulsed light generated by a Ti: Sapphire laser was irradiated to the breast, and the transmitted light was collected by optical fibers placed on the surface of a hemispherical gantry filled with an optical matching fluid. To reconstruct a 3D image of the breast, we employed a method using a time-resolved photon path distribution based on the assumption that scattering and absorption are independent of each other. We verified the possibility of human breast imaging by using a three-dimensional phantom model, which provides a simulation of human breast cancer, in the gantry. The clinical study was also started in January 2007. In a comparative study with conventional modalities, the breast cancers were detected as regions of optically higher absorption. Moreover, the results suggest that optical mammography is useful in monitoring the effects of chemotherapy.

Laser reflectance imaging of human chest for localization of internal organs

The normalized backscattered intensity (NBI) profiles at various locations of human thorax by multiprobe laser reflectometer are obtained. These data after digitization, interpolation, and filtering are color-coded and displayed as images on the outline of the human thorax. For optical characterization of tissues in terms of their parameters, scattering and absorption coefficients and the anisotropy parameter (g) are obtained by matching the measured NBI profile with that as obtained by Monte Carlo simulation procedure. Corresponding to the variation of the NBI over the various regions, the optical parameters show their respective changes. The maximum absorption and minimum scattering coefficients are observed at the areola, clavicle, sternum, scapula, and vertebral column. The minimum absorption and maximum scattering coefficients are observed at the pectoralis major of chest and rectus abdominis of abdomen regions, as compared to the other regions, attributed to their tissue compositional variations. To visualize the various tissues in lower regions of the thorax, the color-coded scheme of the NBI variation, as measured by the third fiber, is further expanded. By this procedure, the outlines of the heart and lungs, as detected through intercostals regions, are observed, which is in good agreement with that as determined by the chest radiograph of the same subject taken in PA position. Similarly the lower sections of the liver and stomach, due to their distinct optical parameters, are also observed.

Numerical modelling and image reconstruction in diffuse optical tomography

The development of diffuse optical tomography as a functional imaging modality has relied largely on the use of model-based image reconstruction. The recovery of optical parameters from boundary measurements of light propagation within tissue is inherently a difficult one, because the problem is nonlinear, ill-posed and ill-conditioned. Additionally, although the measured near-infrared signals of light transmission through tissue provide high imaging contrast, the reconstructed images suffer from poor spatial resolution due to the diffuse propagation of light in biological tissue. The application of model-based image reconstruction is reviewed in this paper, together with a numerical modelling approach to light propagation in tissue as well as generalized image reconstruction using boundary data. A comprehensive review and details of the basis for using spatial and structural prior information are also discussed, whereby the use of spectral and dual-modality systems can improve contrast and spatial resolution.

Investigation of detection limits for diffuse optical tomography systems: I. Theory and experiment

We present a statistical test using simulated photon migration data and a noise model derived from the hardware of a particular diffuse optical tomography system to predict its detection limits. Our method allows us to assess the spatial distribution of the detection sensitivity of arbitrary geometries and noise without requiring phantom measurements and reconstructions. We determine the minimal detectable lesion size at selected lesion positions and compare the predicted results with phantom measurements carried out in a cup geometry.

Three-dimensional time-resolved optical mammography of the uncompressed breast

Optical tomography is being developed as a means of detecting and specifying disease in the adult female breast. We present a series of clinical three-dimensional optical images obtained with a 32-channel time-resolved system and a liquid-coupled interface. Patients place their breasts in a hemispherical cup to which sources and detectors are coupled, and the remaining space is filled with a highly scattering fluid. A cohort of 38 patients has been scanned, with a variety of benign and malignant lesions. Images show that hypervascularization associated with tumors provides very high contrast due to increased absorption by hemoglobin. Only half of the fibroadenomas scanned could be observed, but of those that could be detected, all but one revealed an apparent increase in blood volume and a decrease in scatter and oxygen saturation.