Fluorescence optical diffusion tomography using multiple-frequency data

A method is presented for fluorescence optical diffusion tomography in turbid media using multiple-frequency data. The method uses a frequency-domain diffusion equation model to reconstruct the fluorescent yield and lifetime by means of a Bayesian framework and an efficient, nonlinear optimizer. The method is demonstrated by using simulations and laboratory experiments to show that reconstruction quality can be improved in certain problems through the use of more than one frequency. A broadly applicable mutual information performance metric is also presented and used to investigate the advantages of using multiple modulation frequencies compared with using only one.     

X-ray imaging: a generalized approach using phase-space tomography

We discuss the role of coherence in x-ray imaging and consider how phase-space tomography can be used to extract information about partial coherence. We describe the application of phase-space tomography to x-ray imaging and recover the spatial coherence properties of a one-dimensional soft (1.5 keV) x-ray beam from a synchrotron undulator source. We present phase-space information from a Young's experiment and observe negative regions in the quasi-probability distribution. We show that, given knowledge of the coherence of the beam, we can use partially coherent diffraction data to recover fully coherent information, and we present some simple experimental demonstrations of this capability.     

Circular-array ultrasound holography imaging using the linear-array approach

A circular-array, pulse-echo, ultrasound holography imaging method is presented. The configuration of the measurement system is much simpler than that of traditional computed-tomography (CT) and compound beta-scan imaging. Wide-beam insonification is used. The geometrical differences of the circular array compared with a linear array system are corrected in the frequency domain of the hologram. The computation time of the reconstruction process for a circular image is practically the same as that of a linear array imaging process using the backward propagation (BP) principle. A fast Fourier transform (FFT) algorithm is directly used in the reconstruction process. Computer simulation shows that the resolution of this imaging method can surpass that of a linear-array system. In the preliminary experiments, 2-mm resolution was achieved in both the lateral and radial directions with an ultrasound frequency of 2 MHz.     

A new approach to radionuclide imaging using compressed sensing

Abstract

Single-photon emission computerised tomography (SPECT) and positron emission tomography (PET) are essential medical imaging tools, with inherent drawback of slow data acquisition process. We present a novel compressed sensing-based reconstruction of these images from significantly fewer measurements than traditionally required, thus demonstrating potential of reduction in scan time and radiopharmaceutical doze with benefits for patients and health care economics. Our work effectively shows that high fidelity two-dimensional (2D) SPECT/PET image is reconstructed using compressive sensing with considerably reduced numbers of samples in acquisition stage. The reconstruction of tomographic images is realised by compressed sensing the 2D Fourier projections of k-space data. These 2D projections being sparse in transform domain need fewer samples in k-space and are reconstructed without loss of fidelity. These undersampled Fourier projections can then be backprojected by employing the iterative reconstruction approach for a complete three-dimensional (3D) volume. Compressed sensing of a phantom image and PET bone scintigraphy with radial Fourier samples are performed. The reconstructions of these images are compared to conventionally sampled images using image quality measures like mean square error, peak signal-to-noise ratio and structure similarity (SSIM) index, showing high-quality image reconstruction.     

On a Bayesian approach to coherent radar imaging

In coherent imaging the object of interest is complex but only its amplitude is to be estimated. The object phase yields nuisance variables and in a proper Bayesian approach it is necessary to obtain a phaseless likelihood function. We investigate a two-dimensional case in which the target object is modelled as a collection of point scatterers having independent random phases. The phaseless likelihood function is determined exactly for a configuration of data samples in a uniformly spaced square array in spatial frequency when the target scatterers are confined to lattice positions of a “matched” spatial array. It is determined approximately when the target scatterers are arbitrarily positioned, at most one per conventional resolution cell. The relation between maximum likelihood and conventional Fourier transform imaging is explored and the feasibility of a CLEAN algorithmic technique in coherent imaging is considered.©1993 John Wiley & Sons Inc     

Multi-wavelength raman imaging using a small-diameter image guide with a dimension-reduction imaging array

A commercially available fiber-optic Raman probe was modified for high-resolution spectral Raman imaging using a 350 microm diameter optical fiber image guide coupled to a dimension-reduction imaging array (DRIA). The DRIA comprised 672 optical fibers, arranged as a square array (21 x 32 fibers) on one end and a linear array (672 x 1 fibers) on the other. An imaging spectrograph was used with the DRIA to acquire multi-wavelength Raman images from -250 to 1800 cm(-1) at a spectral resolution of approximately 5 cm(-1). The utility of this technique for in situ and remote Raman imaging is demonstrated by monitoring the polymerization of a model polymer, dibromostyrene (DBS), while simultaneously measuring the Raman Stokes/ anti-Stokes ratio as a function of sample heating time, over a sample area of approximately 4 x 1.6 mm.     

A chemometric approach for brain tumor classification using magnetic resonance imaging and spectroscopy

A new classification approach was developed to improve the noninvasive diagnosis of brain tumors. Within this approach, information is extracted from magnetic resonance imaging and spectroscopy data, from which the relative location and distribution of selected tumor classes in feature space can be calculated. This relative location and distribution is used to select the best information extraction procedure, to identify overlapping tumor classes, and to calculate probabilities of class membership. These probabilities are very important, since they provide information about the reliability of classification and might provide information about the heterogeneity of the tissue. Classification boundaries were calculated by setting thresholds for each investigated tumor class, which enabled the classification of new objects. Results on histopathologically determined tumors are excellent, demonstrated by spatial maps showing a high probability for the correctly identified tumor class and, moreover, low probabilities for other tumor classes.     

X-ray imaging using a consumer-grade digital camera

The recent advancements in consumer-grade digital camera technology and the introduction of high-resolution, high sensitivity CsBr:Eu²⁺ storage phosphor imaging plates make possible a new cost-effective technique for X-ray imaging. The imaging plate is bathed with red stimulating light by high-intensity light-emitting diodes, and the photostimulated image is captured with a digital single-lens reflex (SLR) camera. A blue band-pass optical filter blocks the stimulating red light but transmits the blue photostimulated luminescence. Using a Canon D5 Mk II camera and an f1.4 wide-angle lens, the optical image of a 240×180 mm² Konica CsBr:Eu²⁺ imaging plate from a position 230 mm in front of the camera lens can be focussed so as to laterally fill the 35×23.3 mm² camera sensor, and recorded in 2808×1872 pixel elements, corresponding to an equivalent pixel size on the plate of 88 μm. The analogue-to-digital conversion from the camera electronics is 13 bits, but the dynamic range of the imaging system as a whole is limited in practice by noise to about 2.5 orders of magnitude. The modulation transfer function falls to 0.2 at a spatial frequency of 2.2 line pairs/mm. The limiting factor of the spatial resolution is light scattering in the plate rather than the camera optics. The limiting factors for signal-to-noise ratio are shot noise in the light, and dark noise in the CMOS sensor. Good quality images of high-contrast objects can be recorded with doses of approximately 1 mGy. The CsBr:Eu²⁺ plate has approximately three times the readout sensitivity of a similar BaFBr:Eu²⁺ plate.     

Hard-X-ray dark-field imaging using a grating interferometer

Imaging with visible light today uses numerous contrast mechanisms, including bright- and dark-field contrast, phase-contrast schemes and confocal and fluorescence-based methods. X-ray imaging, on the other hand, has only recently seen the development of an analogous variety of contrast modalities. Although X-ray phase-contrast imaging could successfully be implemented at a relatively early stage with several techniques, dark-field imaging, or more generally scattering-based imaging, with hard X-rays and good signal-to-noise ratio, in practice still remains a challenging task even at highly brilliant synchrotron sources. In this letter, we report a new approach on the basis of a grating interferometer that can efficiently yield dark-field scatter images of high quality, even with conventional X-ray tube sources. Because the image contrast is formed through the mechanism of small-angle scattering, it provides complementary and otherwise inaccessible structural information about the specimen at the micrometre and submicrometre length scale. Our approach is fully compatible with conventional transmission radiography and a recently developed hard-X-ray phase-contrast imaging scheme. Applications to X-ray medical imaging, industrial non-destructive testing and security screening are discussed.     

Density measurements of diamond-like coatings using a low energy accelerator

With the aid of nuclear physical methods based on the use of a low energy accelerator it is shown that the density of even a small, uneven and rough diamond-like coating prepared by mass-separated ion beam deposition can be determined reliably. The density of the coating corresponds to that of diamond. Outlines of the used methods, i.e. Rutherford backscattering and/or nuclear resonance shift combined with the use of a profilometer and Doppler shift attenuation, are presented.     

Trabecular bone scaffolding using a biomimetic approach

The current treatment of large bone defects has several disadvantages. An alternative for using grafts or bone cement for the filling of bone cavities is the use of a bone scaffold that provides a temporary load-bearing function. This paper describes a biomechanical design procedure for a personalized implant with a geometry that has a good fit inside the defect and an internal architecture that provides a scaffold with optimized mechanical properties. These properties are optimized for a load-bearing application, for avoiding stress shielding in the bone surrounding the implant and for activation of osteoblasts seeded inside the scaffold. The design is based on medical images both of the defect and of healthy bone tissue that is representative for the tissue being replaced by the scaffold. Evaluation of the scaffold's mechanical properties is done with high-resolution finite element analyzes of the scaffold and healthy bone. This allows matching of the scaffold and bone mechanical properties, thus giving the scaffold its biomimetic properties.     

Three-dimensional photoacoustic imaging using a two-dimensional CMUT array

In this paper, we describe using a 2-D array of capacitive micromachined ultrasonic transducers (CMUTs) to perform 3-D photoacoustic and acoustic imaging. A tunable optical parametric oscillator laser system that generates nanosecond laser pulses was used to induce the photoacoustic signals. To demonstrate the feasibility of the system, 2 different phantoms were imaged. The first phantom consisted of alternating black and transparent fishing lines of 180 μm and 150 μm diameter, respectively. The second phantom comprised polyethylene tubes, embedded in chicken breast tissue, filled with liquids such as the dye indocyanine green, pig blood, and a mixture of the 2. The tubes were embedded at a depth of 0.8 cm inside the tissue and were at an overall distance of 1.8 cm from the CMUT array. Two-dimensional cross-sectional slices and 3-D volume rendered images of pulse-echo data as well as photoacoustic data are presented. The profile and beamwidths of the fishing line are analyzed and compared with a numerical simulation carried out using the Field II ultrasound simulation software. We investigated using a large aperture (64 x 64 element array) to perform photoacoustic and acoustic imaging by mechanically scanning a smaller CMUT array (16 x 16 elements). Two-dimensional transducer arrays overcome many of the limitations of a mechanically scanned system and enable volumetric imaging. Advantages of CMUT technology for photoacoustic imaging include the ease of integration with electronics, ability to fabricate large, fully populated 2-D arrays with arbitrary geometries, wide-bandwidth arrays and high-frequency arrays. A CMUT based photoacoustic system is proposed as a viable alternative to a piezoelectric transducer based photoacoustic systems.     

Three-dimensional imaging using a new synthetic aperture focusingtechnique

The drawbacks of the multifrequency automatic focusing technique (MF-AFT) have been eased considerably when the scanned-frequency signals are transmitted simultaneously in a pulse. While the focusing capabilities of the MF-AFT are maintained, substantial reduction in data processing is obtained when the new procedure is used. In addition, the derived pulse can be tailored to further enhance the quality of the image produced by this new procedure. Simulation results are included to demonstrate the focusing capabilities of the procedure for both two- and three-dimensional objects     

Volumetric real-time imaging using a CMUT ring array

A ring array provides a very suitable geometry for forward-looking volumetric intracardiac and intravascular ultrasound imaging. We fabricated an annular 64-element capacitive micromachined ultrasonic transducer (CMUT) array featuring a 10-MHz operating frequency and a 1.27-mm outer radius. A custom software suite was developed to run on a PC-based imaging system for real-time imaging using this device. This paper presents simulated and experimental imaging results for the described CMUT ring array. Three different imaging methods--flash, classic phased array (CPA), and synthetic phased array (SPA)--were used in the study. For SPA imaging, two techniques to improve the image quality--Hadamard coding and aperture weighting--were also applied. The results show that SPA with Hadamard coding and aperture weighting is a good option for ring-array imaging. Compared with CPA, it achieves better image resolution and comparable signal-to-noise ratio at a much faster image acquisition rate. Using this method, a fast frame rate of up to 463 volumes per second is achievable if limited only by the ultrasound time of flight; with the described system we reconstructed three cross-sectional images in real-time at 10 frames per second, which was limited by the computation time in synthetic beamforming.     

Real-time volume imaging using a crossed electrode array

This paper describes a unique crossed electrode array for real-time volume ultrasound imaging. By placing orthogonal linear array electrode patterns on the opposite sides of a hemispherically shaped composite transducer substrate, a 2D array can be fabricated using a small fraction of the elements required for a traditional 2D array. The performance of the array is investigated using a computer simulation of the radiation pattern. We show that by using a 288-element crossed electrode pattern it is possible to collect large field of view volume images (60deg times 60degsector) at real-time frame rates (>20 volume images/s), with image contrast and resolution comparable to what can be obtained using a conventional 128-element linear phased array.     

Ultrasonic imaging using a computed point spread function

An explicit point spread function (PSF) evaluator in the frequency domain is described for an ultrasonic transducer operating in the pulse-echo mode. The PSF evaluator employs the patch element model for transducer field determination and scattered field assessment from a small but finite "point" reflector. The PSF for a planar transducer in a medium has been evaluated in the near and the far field. The computed PSFs were used to deconvolve and restore surface images, obtained experimentally, of a single hole and a five-hole cluster in an Al calibration block. A calibration plot is arrived at for estimating, without the need for deconvolution, the actual diameters of circular reflectors from apparent diameters obtained experimentally for a single-medium imaging configuration. The PSF, when the transducer and the point reflector are in two media separated by a planar interface, was evaluated in the near and far field. The computed PSFs were used to deconvolve and restore subsurface images, obtained experimentally, of flat bottom holes (FBHs) in an Al calibration block. We show that the PSF, in the presence of a planar interface, can be obtained from a single-medium PSF model using an effective single-medium path length concept. The PSFs and modulation transfer functions (MTFs) are evaluated for spherical focused and annular transducers and compared with those for the planar transducer. We identify imaging distances to get better-resolved images when using planar, spherical focused, and annular transducers.     

Stochastic inverse heat conduction using a spectral approach

An adjoint‐based functional optimization technique in conjunction with the spectral stochastic finite element method is proposed for the solution of an inverse heat conduction problem in the presence of uncertainties in material data, process conditions and measurement noise. The ill‐posed stochastic inverse problem is restated as a conditionally well‐posed L₂ optimization problem. The gradient of the objective function is obtained in a distributional sense by defining an appropriate stochastic adjoint field. The L₂ optimization problem is solved using a conjugate‐gradient approach. Accuracy and effectiveness of the proposed approach is appraised with the solution of several stochastic inverse heat conduction problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Network reliability assessment using a cellular automata approach

Two cellular automata (CA) models that evaluate the s–t connectedness and shortest path in a network are presented. CA based algorithms enhance the performance of classical algorithms, since they allow a more reliable and straightforward parallel implementation resulting in a dynamic network evaluation, where changes in the connectivity and/or link costs can readily be incorporated avoiding recalculation from scratch. The paper also demonstrates how these algorithms can be applied for network reliability evaluation (based on Monte-Carlo approach) and for finding s–t path with maximal reliability.     

Cellular manufacturing system design using a holonistic approach

We propose an integrated algorithm that will solve the part-family and machinecell formation problem by simultaneously considering the within-cell layout problem. To the best of our knowledge, this is the first study that considers the efficiency of both individual cells and the overall system in monetary terms. Each cell should make at least a certain amount of profit to attain self-sufficiency, while we maximize the total profit of the system using a holonistic approach. The proposed algorithm provides two alternative solutions; one with independent cells and the other one with inter-cell movement. Our computational experiments indicate that the results are very encouraging for a set of randomly generated problems.     

Robot selection using a fuzzy regression-based decision-making approach

Industrial robots, which enable manufacturing firms to produce high-quality products in a cost-effective manner, are important components of advanced manufacturing technologies. The performance of industrial robots is determined by multiple and conflicting criteria that have to be simultaneously considered in a robust selection study. In this study, a decision model based on fuzzy linear regression is presented for industrial robot selection. Fuzzy linear regression provides an alternative approach to statistical regression for modelling situations where the relationships are vague or the data set cannot satisfy the assumptions of statistical regression. The results obtained by employing fuzzy linear regression are compared with those of earlier studies applying different analytical methods to a previously reported robot selection problem.