Leon Bakker

Diffuse Optical Tomography of the Breast: Initial Validation in Benign Cysts

PurposeThe purpose of this study was to validate a newly developed diffuse optical tomography (DOT) system on benign cysts in the breast.ProceduresEight patients with 20 benign cysts were included. Study procedures consisted of optical breast imaging and breast magnetic resonance imaging (MRI) for comparison. A reconstruction algorithm computed three-dimensional images for each of the four near-infrared wavelengths used by our DOT system (Philips Healthcare, Best, The Netherlands). These images were combined using a spectroscopic model to assess tissue composition and lesion size.ResultsTwenty cysts were analyzed in eight patients. By using the spectroscopic information, 13 of 20 cysts (65%) were visualized with DOT, confirming their high water and low total hemoglobin content. Lesion size and location showed good agreement with MRI; Pearson correlation coefficient was 0.7 (p < 0.01).ConclusionsDOT can visualize benign cysts in the breast and elucidate their high water and low total hemoglobin content by spectroscopic analysis.

Multilayer optics with spectral purity layers for the EUV wavelength range

Reported are the first calculations and experimental results of the deposition of EUV multilayer coatings that actively suppress the reflectance in the VUV wavelength range. In the undesired 100-200 nm band a factor of five reduction was achieved for one single optical element, while only a minor loss of 4.5% reflectance for λ = 13.5 nm, the operating wavelength of EUVL, was found.

Optical Fluorescence Imaging of Breast Cancer

We report on the first results obtained with the Philips diffuse optical tomography system and Schering AGs Omocianine fluorescent dye.

Automated 3D whole-breast ultrasound imaging: results of a clinical pilot study

We present the first clinical results of a novel fully automated 3D breast ultrasound system. This system was designed to match a Philips diffuse optical mammography system to enable straightforward coregistration of optical and ultrasound images. During a measurement, three 3D transducers scan the breast at 4 different views. The resulting 12 datasets are registered together into a single volume using spatial compounding. In a pilot study, benign and malignant masses could be identified in the 3D images, however lesion visibility is less compared to conventional breast ultrasound. Clear breast shape visualization suggests that ultrasound could support the reconstruction and interpretation of diffuse optical tomography images.

Image reconstruction and evaluation of system performance for optical fluorescence tomography

Diffuse optical tomography is a non-invasive method aiming at the detection of breast cancer. The sensitivity and specificity of the method can be increased if a fluorescent contrast agent is used that accumulates in malignant lesions. Recently, Philips developed an optical scanner, where the patient is lying on a bed, with one breast hanging freely in a cup containing an optical matching fluid. 507 optical fibers are mounted in the surface of the measurement cup. The breast is illuminated sequentially by half of these fibers while the other half is used to collect the light that is emanating from the breast. The system uses near-infrared light of continuous wave solid-state lasers to illuminate the breast at four different wavelengths. A complete measurement takes less than ten minutes and involves five breast scans: transmission data are collected for four wavelengths, and fluorescence data for excitation at one wavelength. Here, we present the image reconstruction scheme and a novel method to assess the system performance in terms of lesion detectability. This method uses a statistical significance test on simulated data with and without a lesion. It allows the quantification of the detectability of lesions for different size, position, or contrast of the lesion. It also allows to analyze the potential impact of system improvements or to judge the performance of an image reconstruction algorithm.

Debris mitigation for EUV sources using directional gas flows

Practical EUV sources not only generate the desired EUV radiation at a wavelength of 13.5 nm but also produce debris that severely limits the lifetime of the collecting optics in the lithographic system. In this paper, we address the possibility of reducing the exposure of the collecting optics to debris by using directional gas flows, focusing particularly on mitigation of ballistic microparticles. The purpose of the gas flow is to change the direction of the particles such that they can subsequently be captured by a foil trap. Two types of gas flows are considered: (i) longitudinal gas flows, i.e. with a flow direction essentially parallel to the velocity of the microparticles, and (ii) transversal gas flows, having a flow direction essentially perpendicular to that of the microparticles. We have conducted contamination experiments using both types of flows in Xe- and Sn-based experimental EUV sources with Ar gas. The experiments show that directional gas flows suppress microparticles in the same way a buffer gas does unless the flow velocity becomes of the same order as the thermal velocity of the gas (~ 102 m/s). A high-speed longitudinal gas flow is expected to be more efficient in thermalizing the microparticles than a stationary buffer gas; this could however not be confirmed due to experimental constraints. Our experiments with a high-speed transversal gas flow show that submicron debris particles can successfully be suppressed by one order of magnitude. A transversal gas flow combined with a suitable foil trap structure may thus present an effective method for mitigation of microparticles.

Optical mammography: improved sensitivity by combined absorption and fluorescence analysis

We present a method to enhance tumor detectability in breasts imaged with our optical fluorescence mammography system. During a measurement, transmission data at 4 wavelengths and fluorescence data for excitation at 1 wavelength are collected after injection of an optical contrast agent. The data are reconstructed into 3D images of the absorption and fluorescence distributions. Combining those images enables the identification of various breast tissue compounds. Here, we investigate the relevance of our method in phantom experiments.