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A new method using a thin-film multilayer filter is described to couple light from high-power LEDs into a thin light guide such as an LCD backlight. Light emitted below the critical angle is reflected back to the LED and recycled. Large-angle emitted light passes the filter and is transported by total internal reflection in the light guide. The light guide can be as thin as 0.3mm for an LED of 1x1mm2, and the best coupling efficiency is estimated to be 82%. With this approach, a backlight system can be greatly simplified but also compactcollimators can be realized. In this paper the optical design and testing of the filter is described, and a 1mm thick, 6.5mm diameter collimator is presented. Measurements on prototypes show good agreement with the designed characteristics.

The contrast of iodine to soft tissue (water) decreases with higher tube voltage in reconstructed 3D X-ray images. Improved acquisition protocols with a tube voltage of about 80 kV for imaging iodine have been proposed earlier for diagnostic CT imaging. We investigate the contrast-to-noise ratio (CNR) and the CNR-to-dose ratio (CDR) for different concentrations of iodinated contrast agent inserts in water background. The tube voltage of the protocol is lowered from 123 kV to 83 kV in 10 kV steps. A series of measurements with 16 different settings of tube voltage, current and filter settings are investigated. The weighted computed tomography dose index CTDIW for the new protocol settings is measured. Four protocols with tube voltages between 83 kV and 103 kV and similar X-ray dose are compared to the original protocol. A low contrast phantom, containing a water filled cylinder with 5 tubes of different mixtures of iodine contrast inside a 32 cm PMMA ring, is imaged with each protocol. Increased contrast of the iodine filled tubes to the water background is clearly visible in the reconstructed volumes for lower tube voltage and less copper filtering. The best results are obtained with the (83 kV, 561 mA, 0.4 Cu) – protocol. This protocol may improve iodine contrast agent visibility in various 3D imaging applications. For large patients a higher tube voltage, e.g. the (103 kV, 325 mA, 0.4 Cu) – protocol, may be used to avoid tube power limitations at 83 kV. This protocol still has improved iodine imaging compared to the 123 kV protocol and a larger tube power reserve.

Differential phase-contrast imaging in the x-ray domain provides three physically complementary pieces of information: the attenuation,the differential phase-contrast, related to the refractive index, and the dark-field signal, related to the total amount of radiation scattered into very small angles. In medical applications, it is of the utmost importance to present to the radiologist all clinically relevant information in as compact a way as possible. Hence, the needarisis for a method to combine two or more of the above mentioned images into one image containing all information relevant for diagnosis. We present an image composition algorithm that fuses the attenuation image and the differential phase contrast image into a composite image. The composition is performed in a noise optimal way such that the composite image is characterized by minimal noise-power at each frequency component.

We developed a tri-modality imaging system for breast cancer imagingby integrating photoacoustic (PA) and thermoacoustic (TA) imaging techniques into a modified commercial ultrasound scanner. Laser and microwave excitation pulses were interleaved to enable PA and TA dataacquisition in parallel at the rate of 10 frames per second. The performance of the tri-modality imaging system was evaluated in-vitrousing phantom samples. A plastic tube (7 mm inner diameter, 25 mm length) filled with 30 mM methylene blue dye placed at a depth of 8.4cm in chicken breast tissue was successfully detected in PA images with an ultrasonic bandwidth of 1–5 MHz. The SNR at this depth was 15dB after averaging 200 signal acquisitions. Similarly, a plastic tube (7 mm inner diameter, 25 mm length) filled with high concentration salt water placed at a depth of 5.1 cm in porcine fat tissue was successfully detected in TA images. A PA noise-equivalent-sensitivityto methylene blue solution of 260 nM was achieved in chicken tissueat a depth of 3.4 cm and with a laser fluence of 17 mJ/cm2.

Pulse oximeters measure a patient’s heart rate and blood oxygenationby illuminating the skin and measuring the intensity of the light that has propagated through it. The measured intensities, called photoplethysmograms (PPGs), are highly susceptible to motion, which candistort the PPG derived data. Part of the motion artifacts are considered to result from sensor deformation, leading to a change in emitter-detector distance. It is hypothesized that these motion artifacts correlate to movement of the emitter with respect to the skin. This has been investigated in a laboratory setup in which motion artifacts can be reproducibly generated by translating the emitter with respect to a flowcell that models skin perfusion. The top of the flowcell is a diffuse scattering Delrin skin phantom under which a cardiac induced blood pulse is modeled by a changing milk volume. By illuminating the flowcell, a PPG can be measured. The emitter’s translation has been accurately measured using self-mixing interferometry (SMI). The motion artifacts in the PPG as a result of emitter motion are shown to correlate with the emitter’s displacement. Moreover, it is shown that these artifacts are significantly reduced by a least-mean-square algorithm that uses the emitter’s displacement measured via SMI as artifact reference.

We present an integrated photoacoustic and ultrasonic three-dimensional (3D) volumetric imaging system based on a two-dimensional (2D) matrix array ultrasound probe. A wavelength-tunable dye laser pumpedby a Q-switched Nd:YAG laser serves as the light source and a modified commercial ultrasound imaging system (iU22, Philips Healthcare) with a 2D array transducer (X7-2, Philips Healthcare) detects both the pulse-echo ultrasound and photoacoustic signals. A multichannel data acquisition system acquires the RF channel data. The imaging system enables rendering of co-registered 3D ultrasound and photoacoustic images without mechanical scanning. The resolution along the azimuth, elevation, and axial direction are measured to be 0.66 mm, 0.91and 0.84 mm for photoacoustic imaging. In vivo 3D photoacoustic mapping of the sentinel lymph node was demonstrated in a rat model usingmethylene blue dye. These results highlight the clinical potentialof 3D PA imaging for identification of sentinel lymph nodes for cancer staging in humans.

We report on the use of diffuse optical spectroscopy analysis of breast spectra acquired in the wavelength range from 500 to 1600 nm with a fiber optic probe. A total of 102 ex vivo samples of five different breast tissue types, namely adipose, glandular, fibroadenoma, invasive carcinoma and ductal carcinoma in situ from 52 patients weremeasured. A model deriving from the diffusion theory was applied tothe measured spectra in order to extract clinically relevant parameters such as blood, water, lipid, and collagen volume fractions, b-carotene concentration, average vessels radius, reduced scattering amplitude, Mie slope and Mie-to-total scattering fraction. Based on a classification and regression tree algorithm applied to the derived parameters, a sensitivity-specificity of 98%-99%, 84%-95%, 81%-98%, 91%-95%, and 83%-99% were obtained for discrimination of adipose, glandular, fibroadenoma, invasive carcinoma, and ductal carcinomain situ, respectively; and a multiple classes overall diagnostic performance of 94%. Sensitivity-specificity values obtained for discriminating malignant from non-malignant tissue were compared to existing reported studies by applying the different classification methodsthat were used in each of these studies. Furthermore, in these reported studies, either lipid or b-carotene was considered as adipose tissue precursors. We estimate both chromophore concentrations and demonstrate that lipid is a better discriminator for adipose tissue than b-carotene.

Photoacoustic tomography (PAT) is a molecular imaging technology. Unlike conventional reporter gene imaging, which is based on fluorescent proteins, photoacoustic reporter gene imaging is based on opticalabsorption. Using lacZ, one of the most widely used reporter genesin biology, this work demonstrated several key merits of PAT. We proved that the expression of lacZ can be imaged by PAT as deep as 5.0cm in biological tissue with resolutions of ~1.0 mm and ~0.4 mm in the lateral and axial directions, respectively. We further demonstrated non-invasive simultaneous imaging of a lacZ-marked tumor and itssurrounding microvasculature in vivo by dual-wavelength acoustic-resolution photoacoustic microscopy, with a lateral resolution of 45 µmand an axial resolution of 15 µm. Finally, using optical-resolutionphotoacoustic microscopy, we showed sub-cellular localization of lacZ expression, with a lateral resolution of a fraction of a micron.These results suggest that PAT is potentially a complementary tool to conventional optical fluorescence imaging of reporter genes for linking biological studies from the microscopic to the macroscopic scales.