A novel realistic three-layer phantom for intravascular ultrasound imaging

Intravascular ultrasound (IVUS) is an imaging modality that experienced a tremendous development over the last 20 years. Phantoms for IVUS are rare and poorly documented. The aim of this paper is to propose an original IVUS phantom that has geometries and specular textures closer to those of coronary arteries than conventional tube-like phantoms. The proposed phantom has a three-layer aspect, reproducing the intima, media and adventitia that compose the arterial wall. It is made of an agar-based compound, with water, glycerol and cellulose particles. Fourteen phantoms were quantified using IVUS. Six phantoms were evaluated by both photomacroscopy and IVUS. There was an excellent correlation between phantom dimensions evaluated by photomacroscopy and the nominal values (mold dimensions). The IVUS quantification of the phantom was closely correlated to the measurements obtained by photomacroscopy. These results demonstrate that a multilayer phantom, with known and reproducible dimensions and with realistic geometric and echographic properties has been developed.     

An MRI digital brain phantom for validation of segmentation methods

Knowledge of the exact spatial distribution of brain tissues in images acquired by magnetic resonance imaging (MRI) is necessary to measure and compare the performance of segmentation algorithms. Currently available physical phantoms do not satisfy this requirement. State-of-the-art digital brain phantoms also fall short because they do not handle separately anatomical structures (e.g. basal ganglia) and provide relatively rough simulations of tissue fine structure and inhomogeneity. We present a software procedure for the construction of a realistic MRI digital brain phantom. The phantom consists of hydrogen nuclear magnetic resonance spin-lattice relaxation rate (R1), spin-spin relaxation rate (R2), and proton density (PD) values for a 24 × 19 × 15.5 cm volume of a "normal" head. The phantom includes 17 normal tissues, each characterized by both mean value and variations in R1, R2, and PD. In addition, an optional tissue class for multiple sclerosis (MS) lesions is simulated. The phantom was used to create realistic magnetic resonance (MR) images of the brain using simulated conventional spin-echo (CSE) and fast field-echo (FFE) sequences. Results of mono-parametric segmentation of simulations of sequences with different noise and slice thickness are presented as an example of possible applications of the phantom. The phantom data and simulated images are available online at http://lab.ibb.cnr.it/.     

一种数字人脑部切片图像分割新方法

目的 提出一种人脑切片图像自动分割算法,以克服现有的方法对大量人工参与的依赖.方法 针对人脑切片图像的特征,提出一种基于区域生长的灰度直方图阈值化分割算法.首先通过区域生长过程对图像进行初始的粗分割,再用直方图阈值化方法进行二次细分割提取目标区域.结果 采用此方法准确有效地分割出了大脑白质和大脑皮质.结论 此算法结合切片图像的全局信息和局部信息应用于分割,是一种比较好的分割方法.     

Quantitative evaluation of 10 tractography algorithms on a realistic diffusion MR phantom

As it provides the only method for mapping white matter fibers in vivo, diffusion MRI tractography is gaining importance in clinical and neuroscience research. However, despite the increasing availability of different diffusion models and tractography algorithms, it remains unclear how to select the optimal fiber reconstruction method, given certain imaging parameters. Consequently, it is of utmost importance to have a quantitative comparison of these models and algorithms and a deeper understanding of the corresponding strengths and weaknesses. In this work, we use a common dataset with known ground truth and a reproducible methodology to quantitatively evaluate the performance of various diffusion models and tractography algorithms. To examine a wide range of methods, the dataset, but not the ground truth, was released to the public for evaluation in a contest, the "Fiber Cup". 10 fiber reconstruction methods were evaluated. The results provide evidence that: 1. For high SNR datasets, diffusion models such as (fiber) orientation distribution functions correctly model the underlying fiber distribution and can be used in conjunction with streamline tractography, and 2. For medium or low SNR datasets, a prior on the spatial smoothness of either the diffusion model or the fibers is recommended for correct modelling of the fiber distribution and proper tractography results. The phantom dataset, the ground truth fibers, the evaluation methodology and the results obtained so far will remain publicly available on: http://www.lnao.fr/spip.php?rubrique79 to serve as a comparison basis for existing or new tractography methods. New results can be submitted to fibercup09@gmail.com and updates will be published on the webpage.     

A new wire phantom for accurate measurement of acoustical resolution

This article describes a phantom which is easier to use and gives more accurate results than a phantom made from several pairs of solid wires. This phantom employs two concepts: spatially modulated wires and diverging wires. Spatially modulated wires, such as helically twisted wires, reflect the sound into a broad range of angles. This has two advantages. One, it is easier to align the transducer with the reflected beam. Two, the diffuse reflection is similar to the scattering from tissue, and the system gain need not be turned abnormally low. Diverging wires improve the accuracy and convenience of the measurement. Rather than many pairs of parallel wires, a single pair of wires which diverge from an apex is used. By scanning across this pair until the wires are just resolved, the resolution can be easily calculated.     

Development of a digital breast phantom for photoacoustic computed tomography

Photoacoustic (PA) imaging provides morphological and functional information about angiogenesis and thus is potentially suitable for breast cancer diagnosis. However, the development of PA breast imaging has been hindered by inadequate patients and a lack of ground truth images. Here, we report a digital breast phantom with realistic acoustic and optical properties, with which a digital PA-ultrasound imaging pipeline is developed to create a diverse pool of virtual patients with three types of masses: ductal carcinoma in situ, invasive breast cancer, and fibroadenoma. The experimental results demonstrate that our model is realistic, flexible, and can be potentially useful for accelerating the development of PA breast imaging technology.     

Disappearance of phantom pain after focal brain infarction

A patient with hemiplegia and hemihypoesthesia is presented in whom preexisting phantom limb pain disappeared with the appearance of a stroke localized by CT scan to the posterior internal capsule. Differentiation between the cutaneous sensation and the sensation of phantom limb pain that appeared later seems to support the assumed existence of a polysynaptic sensory pathway that conveys the sensations of deafferentation.     

A customizable 3-dimensional digital atlas of the canary brain in multiple modalities

Songbirds are well known for their ability to learn their vocalizations by imitating conspecific adults. This uncommon skill has led to many studies examining the behavioral and neurobiological processes involved in vocal learning. Canaries display a variable, seasonally dependent, vocal behavior throughout their lives. This trait makes this bird species particularly valuable to study the functional relationship between the continued plasticity in the singing behavior and alterations in the anatomy and physiology of the brain. In order to optimally interpret these types of studies, a detailed understanding of the brain anatomy is essential. Because traditional 2-dimensional brain atlases are limited in the information they can provide about the anatomy of the brain, here we present a 3-dimensional MRI-based atlas of the canary brain. Using multiple imaging protocols we were able to maximize the number of detectable brain regions, including most of the areas involved in song perception, learning, and production. The brain atlas can readily be used to determine the stereotactic location of delineated brain areas at any desirable head angle. Alternatively the brain data can be used to determine the ideal orientation of the brain for stereotactic injections, electrophysiological recordings, and brain sectioning. The 3-dimensional canary brain atlas presented here is freely available and is easily adaptable to support many types of neurobiological studies, including anatomical, electrophysiological, histological, explant, and tracer studies.     

Development of a 4-D digital mouse phantom for molecular imaging research.

PURPOSE: We develop a realistic and flexible 4-D digital mouse phantom and investigate its usefulness in molecular imaging research. METHODS: Organ shapes were modeled with non-uniform rational B-spline (NURBS) surfaces based on high-resolution 3-D magnetic resonance microscopy (MRM) data. Cardiac and respiratory motions were modeled based on gated magnetic resonance imaging (MRI) data obtained from normal mice. Pilot simulation studies in single-photon emission computed tomography (SPECT) and X-ray computed tomography (CT) were performed to demonstrate the utility of the phantom. RESULTS: NURBS are an efficient and flexible way to accurately model the anatomy and cardiac and respiratory motions for a realistic 4-D digital mouse phantom. The phantom is capable of producing realistic molecular imaging data from which imaging devices and techniques can be evaluated. CONCLUSION: The phantom provides a unique and useful tool in molecular imaging research. It can be used in the development of new imaging instrumentation, image acquisition strategies, and image processing and reconstruction methods.     

改良版燕尾单在整形手术铺单中的应用

整形科手术因为专科的特点,涉及全身各个部位,很多时候都是同时进行多个部位的手术,皮肤表面暴露的范围较大,经常需要铺置多个无菌区域。传统的铺巾方法一直采用180cm×80cm中单、90cm×80cm小单层层叠加,操作步骤繁琐,易滑脱[1]等。为了严格达到无菌操作要求,简化铺巾程序,曾经使用传统的剖腹单,虽然可以满足以上要求,但因为头面部手术时,术中多数需要转动头部,气管插管管道被覆盖于大单下面不利     

A new, improved flotation device for deep-water exercise

The purpose of this study was to determine the position and size of flotation devices that permit deep-water exercise with the exerciser's thoracolumbar spine in a vertical position and without restriction of movement of the arms and legs. The buoyant force of the flotation device had to be at least 94.0 N to allow the exerciser to be suspended in water with the head above water. The position of the flotation devices had considerable influence on the thoracolumbar angle. When the large pad with a buoyant force of 55.0 N covered the lower abdominal wall and the small pad with a buoyant force at 39.0 N was located over the lower back, the exerciser's thoracolumbar spine assumed an almost vertical position. Anterior placement of the flotation devices resulted in marked extension of the thoracolumbar spine. Conversely, posterior placement of the buoyant devices resulted in flexion of the thoracolumbar spine. On the basis of these results, an ideal flotation device for deep-water exercise can now be developed.     

A realistic three dimensional FEM of the human head

A realistic three-dimensional finite element model (FEM) of the human head has been developed. Separate layers for the scalp, skull, cerebrospinal fluid (CSF) and brain were modelled. Hexahedral elements, a special master matrix assembly technique and an iterative successive over-relaxation (SOR) solution scheme were employed. This approach enabled rapid modelling with minimal memory requirements, which makes this method practical if used for electrical impedance tomography (EIT) or source localization inverse problems. Compared to scalp electrodes, subdural voltage sensing electrodes were three to four times more sensitive close to an oedema or source region, if it was peripheral, but this decreased to 30%-40% for central oedema or source regions. Scalp current injecting electrodes are preferable, since the maximum allowable current is 10 times larger than that of the subdural ones. The distance of voltage sensing electrodes from a region to be imaged highly affects sensitivity, so depth electrodes will be more sensitive, provided that they are close to the region of interest. Finally, the electrode size has significant effects on the input or transfer impedance.     

A deformable digital brain atlas system according to Talairach and Tournoux

Brain atlases are valuable tools which assist neurosurgeons during the planning of an intervention. Since a printed atlas book has several disadvantages-among them the difficulty to map the information onto a patient's individual anatomy-we have developed a digital version of the well-established stereotaxic brain atlas of Talairach and Tournoux. Our atlas system is mainly dedicated to assist neurosurgical planning, and its benefits are: (i) a three-dimensional (3D) representation of most brain structures contained in the Talairach atlas; (ii) a nonrigid matching capability which warps the standard atlas anatomy to an individual brain magnetic resonance imaging (MRI) dataset in a few minutes and which is able to take deformations due to tumors into account; (iii) the integration of several sources of neuroanatomical knowledge; (iv) an interface to a navigation system which allows utilization of atlas information intraoperatively. In this paper we outline the algorithm we have developed to achieve 3D surface models of the brain structures. Moreover, we describe the nonrigid matching method which consists of two tasks: firstly, point correspondences between the atlas and the patient are established in an automatic fashion, and secondly these displacement vectors are interpolated using a radial basis function approach to form a continuous transformation function. To generate appropriate target structures for the first of these tasks, we implemented a quick segmentation tool which is capable to segment the cortex and ventricles in less than 5 min. An evaluation shows that our nonrigid approach is more precise than the conventional piecewise linear matching, though it should be further improved for the region around the deep grey nuclei. Summarizing, we developed a Win32 program which permits the convenient and fast application of standardized anatomy to individual brains which potentially contain tumors.