多种长焦区聚焦超声采集频率的人体甲状腺光声成像

临床上常规的超声成像对甲状腺结节进行诊断时存在误诊和漏诊。研究了利用多种采集频率的长焦区聚焦换能器进行光声成像的方法。在模拟样品里埋入不同尺寸的血块模拟病变组织,采用不同中心频率的换能器对模拟样品进行光声成像,然后将血液注入正常人体甲状腺内部形成两处瘀血区,模拟病变甲状腺组织,经二维扫描重构出模拟病变甲状腺组织的三维光声图像。结果表明,不同频率的超声换能器对不同尺寸病灶体的探测灵敏度存在较大差异,5MHz的宽带换能器对几百微米直至毫米量级大小的病灶体均具有良好的灵敏度。获得了甲状腺及其内部两处瘀血区域的较高分辨率和对比度的三维图像。此项技术有望与超声成像技术结合,进一步提高甲状腺疾病诊断的准确率。     

Improvement of Lesion Detection in Scintigraphic Images by SVD Techniques for Resolution Recovery

The properties of singular value decomposition (SVD) are used to implement an SVD spatial domain pseudoinverse restoration filter. This type of filter is attractive for poor imaging conditions (low spatial resolution, high image noise) and is thus appealing for nuclear medicine images. The method might offer some advantages over more traditional frequency domain filter techniques since the restoration is performed on a local rather than global basis. High-contrast thyroid phantom images collected at different count densities and low-contrast liver phantom images were processed with the SVD filter. Restored images yielded improved spatial resolution, lesion contrast, and signal-to-noise ratio. The SVD pseudoinverse restoration filter implemented as an interactive process permits the operator to terminate filtering at a stage where the visually "best" image is obtained compared to the original data. Processed images suggest that the technique may have potential for improving lesion detection in nuclear medicine.     

3-D Rat Brain Phantom for High-Resolution Molecular Imaging

With the steadily improving resolution of novel small-animal single photon emission computed tomography (SPECT) and positron emission tomography devices, highly detailed phantoms are required for testing and optimizing these systems. We present a three-dimensional (3-D) digital and physical phantom pair to represent, e.g., cerebral blood flow, glucose metabolism, or neuroreceptor binding in small regions of the rat brain. The anatomical structures are based on digital photographs of the uncut part of a rat brain cryosection block. The photographs have been segmented into ventricles and gray and white matter and have been stacked afterwards. In the resulting voxelized digital phantom, tracer concentration in gray and white matter can be scaled independently. This is of relevance since, e.g., cerebral blood flow or metabolism are much higher in gray than in white matter. The physical phantom is based on the digital phantom and has been manufactured out of hardened polymer using rapid prototyping, a process in which complicated 3-D objects can be built up layer by layer. X-ray computed tomography and high-resolution SPECT images of the physical phantom are compared with the digital phantom. The detailed physical phantom can be filled bubble-free. Excellent correspondence is shown between details in the digital and physical phantom. Therefore, this newly developed brain phantom will enable the optimization of high-resolution imaging for recovery of complex shaped molecular distributions.      

Investigation of phantom circuit benefits for next generation xDSL systems

This paper is focused on measurements and analysis of phantom mode benefits in G.fast and next generation xDSL systems. The investigation is based on real measurements performed for a multi‐quad metallic cable together with theoretical evaluations of phantom circuit potentials. Because the presence of phantom circuits leads into increasing the summary crosstalk level in a metallic cable, the application of a phantom mode is questionable in practice. That is why the investigation was performed, and conclusions provided in this paper can be helpful to decide potential benefits of this method for future applications. The elimination of a crosstalk can be performed by using advanced modulation techniques such as vectored discrete multi‐tone modulation (VDMT); however, its application in practice is limited because of its complexity and computational demands. That is why several scenarios are currently being discussed with either no VDMT application or with only partial crosstalk compensation. Because of that, this paper is focused on comparing the results for a first scenario without using any far‐end crosstalk (FEXT) elimination technique, whereas a second scenario is based on partial FEXT suppression by VDMT application, to decide the effectiveness of using phantom modes in practice. Copyright © 2014 John Wiley & Sons, Ltd.     

Phantom cell analysis of dynamic channel assignment in cellularmobile systems

In this paper, we propose phantom cell analysis for dynamic channel assignment. This is an approximate analysis that can handle realistic planar systems with the three-cell channel-reuse pattern. To find the blocking probability of a particular cell, two phantom cells are used to represent its six neighboring cells. Then, by conditioning on the relative positions of the two phantom cells, the blocking probability of that particular cell can be found. We found that the phantom cell analysis is not only very accurate in predicting the blocking performance, but also very computationally efficient. Besides, it is applicable to any traffic and channel-reuse patterns     

Vessel surface reconstruction with a tubular deformable model

Three-dimensional (3-D) angiographic methods are gaining acceptance for evaluation of atherosclerotic disease. However, measurement of vessel stenosis from 3-D angiographic methods can be problematic due to limited image resolution and contrast. We present a method for reconstructing vessel surfaces from 3-D angiographic methods that allows for objective measurement of vessel stenosis. The method is a deformable model that employs a tubular coordinate system. Vertex merging is incorporated into the coordinate system to maintain even vertex spacing and to avoid problems of self-intersection of the surface. The deformable model was evaluated on clinical magnetic resonance (MR) images of the carotid (n=6) and renal (n=2) arteries, on an MR image of a physical vascular phantom and on a digital vascular phantom. Only one gross error occurred for all clinical images. All reconstructed surfaces had a realistic, smooth appearance. For all segments of the physical vascular phantom, vessel radii from the surface reconstruction had an error of less than 0.2 of the average voxel dimension. Variability of manual initialization of the deformable model had negligible effect on the measurement of the degree of stenosis of the digital vascular phantom     

Phantom-based multimodal interactions for medical education and training: the Munich knee joint simulator

Simulation environments based on virtual reality technologies can support medical education and training. In this paper, the novel approach of an "interactive phantom" is presented that allows a realistic display of haptic contact information typically generated when touching and moving human organs or segments. The key idea of the haptic interface is to attach passive phantom objects to a mechanical actuator. The phantoms look and feel as real anatomical objects. Additional visualization of internal anatomical and physiological information and sound generated during the interaction with the phantom yield a multimodal approach that can increase performance, didactic value, and immersion into the virtual environment. Compared to classical approaches, this multimodal display is convenient to use, provides realistic tactile properties, and can be partly adjusted to different, e.g., pathological properties. The interactive phantom is exemplified by a virtual human knee joint that can support orthopedic education, especially for the training of clinical knee joint evaluation. It is suggested that the technical principle can be transferred to many other fields of medical education and training such as obstetrics and dentistry.     

Control of specific absorption rate distribution using capacitiveelectrodes and inductive aperture-type applicators: implications forradiofrequency hyperthermia

A method of controlling the specific absorption rate (SAR) distribution in radiofrequency hyperthermia is proposed. The superposition of the current density associated with capacitively coupled electrodes and that associated with H-field coupled inductive aperture-type applicators modifies the actual current distribution in the heating material. Using a two-dimensional finite element method, we have shown that "focusing" is possible such that the SAR at the center of a phantom can be adjusted to be approximately twice that in superficial regions, even though the wavelength is considerably greater than the dimensions of the phantom.     

Gaussian beam representation of aperture fields in layered, lossymedia: simulation and experiment

It is demonstrated that a three-dimensional electromagnetic field of a given linear polarization, emanating from an aperture source and propagating in a lossy medium, can be represented by an astigmatic Gaussian beam with complex source coefficients. The values of the coefficients can be determined experimentally by scans of the phase and amplitude of the field in the electric and magnetic principal planes near the aperture by means of a monopole probe and a liquid phantom (a phantom being a device that simulates the conditions encountered when radiation (e.g. microwaves) is deposited in biological tissues (e.g. human muscles) and permits a quantitative estimation of its effects). Once the source parameters are obtained, computations of the field everywhere else can be achieved rapidly. The theory is verified experimentally for bounded, homogeneous, and layered lossy media. Agreement is within 3% (relative to the maximum field at the aperture) over the entire scanned area     

应用先验插值校正CT金属伪影

针对CT系统在实际应用中出现的金属伪影问题,提出一种基于先验插值的金属伪影校正算法。文中通过预滤波、骨骼分割和软组织恢复步骤计算先验图像,并利用先验图像的正向投影对原始投影中的金属投影区进行插值校正。应用该算法对数值仿真图像和临床CT图像分别进行了校正重建实验。数值仿真实验表明,用提出算法校正的结果比线性插值金属伪影校正算法、归一化金属伪影校正算法校正的结果更接近理想体模。临床数据实验表明:该算法的重建结果有效抑制了金属伪影,清晰重建出金属边缘细节,极大地提高了重建图像的质量。     

Quantitative comparison of FBP,EM, and Bayesian reconstruction algorithms for the IndyPET scanner

We quantitatively compare filtered backprojection (FBP), expectation-maximization (EM), and Bayesian reconstruction algorithms as applied to the IndyPET scanner--a dedicated research scanner which has been developed for small and intermediate field of view imaging applications. In contrast to previous approaches that rely on Monte Carlo simulations, a key feature of our investigation is the use of an empirical system kernel determined from scans of line source phantoms. This kernel is incorporated into the forward model of the EM and Bayesian algorithms to achieve resolution recovery. Three data sets are used, data collected on the IndyPET scanner using a bar phantom and a Hoffman three-dimensional brain phantom, and simulated data containing a hot lesion added to a uniform background. Reconstruction quality is analyzed quantitatively in terms of bias-variance measures (bar phantom) and mean square error (lesion phantom). We observe that without use of the empirical system kernel, the FBP, EM, and Bayesian algorithms give similar performance. However, with the inclusion of the empirical kernel, the iterative algorithms provide superior reconstructions compared with FBP, both in terms of visual quality and quantitative measures. Furthermore, Bayesian methods outperform EM. We conclude that significant improvements in reconstruction quality can be realized by combining accurate models of the system response with Bayesian reconstruction algorithms.     

Experimental characterization of helical coils as hyperthermiaapplicators

A series of helical-coil hyperthermia applicators have been designed for treating human limbs. Several experiments to determine their operating characteristics were conducted using muscle-equivalent, cylindrical, and lower-body-shaped phantoms. It was found that this kind of applicator has to be operated at resonances which are both sharp and load-dependent. This can have significant clinical implications, since changes in the position of the patient and/or the tissue dielectric properties with temperature can produce a severe mismatch. Moreover, even though the patterns of energy deposition were found to be relative transversely uniform and axially belt-shaped within the cylindrical phantoms, they were strongly dependent on the shape of the phantom and of the coil for the more realistic human-shaped phantom. Intense local heating was observed whenever the winding of the helical coil was within a few millimeters of the surface of the human-shaped phantom. The tests with the human-shaped phantom showed that there can be significant energy deposition outside of the region intended for treatment     

Novel Specific Absorption Rate (SAR) Measurement Method Using a Flat Solid Phantom

A novel specific absorption rate (SAR) measurement method is presented that employs a flat solid phantom with multiple embedded E-field probes. A radio device under test traverses over them during the scanning process. The solid phantom provides stable dielectric properties and easy handling, while the multiple E-field probes contribute to shortening the time for measuring the SAR distribution. This method can also be used as an alternative to that employing flat phantoms filled with liquid. Based on the numerical approach, the measurement system configuration is designed to obtain the SAR distributions with an error of within 10% at 900 and 1950 MHz, focusing on the following points: dimensions of the flat solid phantom, size of the E-field probe, and distance between the E-field probes. The experimental setup for the frequency of 1950 MHz confirms that the proposed measurement method obtains the average SARs over 10 and 1 g with an error of within 10% compared to the computed values.     

An RF concentrating method using inductive aperture-typeapplicators

A method for concentrating electromagnetic (EM) energy of a low frequency in hyperthermia is proposed. The phantom together with boli are placed between a pair of inductive aperture-type applicators. The calculated results show that the method can heat the deep portion of the phantom without overheating the fat layers excessively     

Dry phantom composed of ceramics and its application to SARestimation

A dry phantom material having the same electric properties in the UHF band as biological tissues is developed. The new composite material is composed of microwave ceramic powder, graphite powder, and bonding resin. This material overcomes the various problems inherent in the conventional jelly phantom material, such as dehydration and deterioration due to invasion of bacteria or mold. This phantom material makes it possible to accomplish highly reliable and precise estimation of specific absorption rate (SAR) in biological systems. Dry phantom models of spheres and human heads are fabricated. Experiments are performed to estimate the SAR of human heads exposed to microwave sources by using the thermography method. Since this material removes the necessity of the phantom shell, the surface SAR distribution can be readily obtained     

A software data generator for radiographic imaging investigations

A software data generation tool, intended to be used in radiographic applications, has been developed. The application integrates a phantom design module and an imaging simulator. Phantoms can be described either as a set of geometrical objects or voxels, or as contours drawn on multiple tomographic slices. Radiographic projections of the phantoms are formed on the basis of a simulated irradiation process with selectable imaging parameters. A comparison between actual projection images from a physical and a simulated phantom shows good correspondence. The application was used for digital tomosynthesis (DTS) investigations and has proven to be a useful tool in the study of tomographic noise. Further development is expected to expand the use of the application to more areas of radiological imaging research     

Noise characteristics of 3-D and 2-D PET images

The authors analyzed the noise characteristics of two-dimensional (2-D) and three-dimensional (3-D) images obtained from the GE Advance positron emission tomography (PET) scanner. Three phantoms were used: a uniform 20-cm phantom, a 3-D Hoffman brain phantom, and a chest phantom with heart and lung inserts. Using gated acquisition, the authors acquired 20 statistically equivalent scans of each phantom in 2-D and 3-D modes at several activity levels. From these data, they calculated pixel normalized standard deviations (NSD's), scaled to phantom mean, across the replicate scans, which allowed them to characterize the radial and axial distributions of pixel noise. The authors also performed sequential measurements of the phantoms in 2-D and 3-D modes to measure noise (from interpixel standard deviations) as a function of activity. To compensate for the difference in axial slice width between 2-D and 3-D images (due to the septa and reconstruction effects), they developed a smoothing kernel to apply to the 2-D data. After matching the resolution, the ratio of image-derived NSD values (NSD_2D/NSD_3D)² averaged throughout the uniform phantom was in good agreement with the noise equivalent count (NEC) ratio (NEC_3D/NEC_2D). By comparing different phantoms, the authors showed that the attenuation and emission distributions influence the spatial noise distribution. The estimates of pixel noise for 2-D and 3-D images produced here can be applied in the weighting of PET kinetic data and may be useful in the design of optimal dose and scanning requirements for PET studies. The accuracy of these phantom-based noise formulas should be validated for any given imaging situation, particularly in 3-D, if there is significant activity outside the scanner field of view     

A comparison of similarity measures for use in 2-D-3-D medicalimage registration

A comparison of six similarity measures for use in intensity-based two-dimensional-three-dimensional (2-D-3-D) image registration is presented. The accuracy of the similarity measures are compared to a “gold-standard” registration which has been accurately calculated using fiducial markers. The similarity measures are used to register a computed tomography (CT) scan of a spine phantom to a fluoroscopy image of the phantom. The registration is carried out within a region-of-interest in the fluoroscopy image which is user defined to contain a single vertebra. Many of the problems involved in this type of registration are caused by features which were not modeled by a phantom image alone. More realistic “gold-standard” data sets were simulated using the phantom image with clinical image features overlaid. Results show that the introduction of soft-tissue structures and interventional instruments into the phantom image can have a large effect on the performance of some similarity measures previously applied to 2-D-3-D image registration. Two measures were able to register accurately and robustly even when soft-tissue structures and interventional instruments were present as differences between the images. These measures were pattern intensity and gradient difference. Their registration accuracy, for all the rigid-body parameters except for the source to film translation, was within a root-mean-square (rms) error of 0.53 mm or degrees to the “gold-standard” values. No failures occurred while registering using these measures     

A digital filtration technique for scatter-glare correction based on thickness estimation

In order to quantitate anatomical and physiological parameters such as vessel dimensions and volumetric blood flow, it is necessary to make corrections for scatter and veiling glare, which are the major sources of nonlinearities in videodensitometric digital subtraction angiography (DSA). A convolution filtering technique has been investigated to estimate scatter-glare distribution in DSA images without the need to sample the scatter-glare intensity for each patient. This technique utilizes exposure parameters and image gray levels to assign equivalent Lucite thickness for every pixel in the image. The thickness information is then used to estimate scatter-glare intensity on a pixel-by-pixel basis. To test its ability to estimate scatter-glare intensity, the correction technique was applied to images of a Lucite step phantom, anthropomorphic chest phantom, head phantom, and animal models at different thicknesses, projections, and beam energies. The root-mean-square (rms) percentage error of these estimates was obtained by comparison with direct scatter-glare measurements made behind a lead strip. The average rms percentage errors in the scatter-glare estimate for the 25 phantom studies and the 17 animal studies were 6.44% and 7.96%, respectively. These results indicate that the scatter-glare intensity can be estimated with adequate accuracy for a wide range of thicknesses, projections, and beam energies using exposure parameters and gray level information     

A dry phantom material composed of ceramic and graphite powder

Details of an artificially synthesized dry phantom material developed for experimental studies of microwave exposure to the human body are shown. The material is solid and can simulate electrical characteristics of high water content biological tissues such as muscles and the brain. The material is composed of high-ϵ_r ceramic powder, graphite powder, and bonding resin. Any shape of phantom models can be constructed to simulate different parts of the body, as well as the head. The paper reports the synthesis technique to obtain the desired complex permittivity and the fabrication technique of the phantom models for usage of specific absorption rate (SAR) estimation at 900 MHz