医学影像仿真人体模型及其临床应用

仿真人体模型是根据人体参数,用与人体组织具有相同或相近散射和吸收系数的“组织等效材料”制成的具有骨骼、肌肉、脏器的人体模型。它包括数字化虚拟人体模型、物理实体模型和二者结合的物理数学模型等3种类型。仿真体模在临床工作中应用广泛,可用于确定CT扫描方式及最佳扫描方案、优化患者的辐射剂量、设备评价及质量控制以及用于血管成像和对比剂注射方案研究。仿真体模模拟人体参数能避免不必要的辐射危害,未来在CT图像质控、设备评价、方案研究等方面前景十分可观。     

X-ray properties of an anthropomorphic breast phantom for MRI and x-ray imaging

The purpose of this study is to characterize the x-ray properties of a dual-modality, anthropomorphic breast phantom whose MRI properties have been previously evaluated. The goal of this phantom is to provide a platform for optimization and standardization of two- and three-dimensional x-ray and MRI breast imaging modalities for the purpose of lesion detection and discrimination. The phantom is constructed using a mixture of lard and egg whites, resulting in a variable, tissue-mimicking structure with separate adipose- and glandular-mimicking components. The phantom can be produced with either a compressed or uncompressed shape. Mass attenuation coefficients of the phantom materials were estimated using elemental compositions from the USDA National Nutrient Database for Standard Reference and the atomic interaction models from the Monte Carlo code PENELOPE and compared with human values from the literature. The image structure was examined quantitatively by calculating and comparing spatial covariance matrices of the phantom and patient mammography images. Finally, a computerized version of the phantom was created by segmenting a computed tomography scan and used to simulate x-ray scatter of the phantom in a mammography geometry. Mass attenuation coefficients of the phantom materials were within 20% and 15% of the values for adipose and glandular tissues, respectively, which is within the estimation error of these values. Matching was improved at higher energies (>20 keV). Tissue structures in the phantom have a size similar to those in the patient data, but are slightly larger on average. Correlations in the patient data appear to be longer than those in the phantom data in the anterior-posterior direction; however, they are within the error bars of the measurement. Simulated scatter-to-primary ratio values of the phantom images were as high as 85% in some areas and were strongly affected by the heterogeneous nature of the phantom. Key physical x-ray properties of the phantom have been quantitatively evaluated and shown to be comparable to those of breast tissue. Since the MRI properties of the phantom have been previously evaluated, we believe it is a useful tool for quantitative evaluation of two- and three-dimensional x-ray and MRI breast imaging modalities for the purpose of lesion detection and characterization.     

Optical and acoustic properties at 1064 nm of polyvinyl chloride-plastisol for use as a tissue phantom in biomedical optoacoustics

A novel optoacoustic phantom made of polyvinyl chloride-plastisol (PVCP) for optoacoustic studies is described. The optical and acoustic properties of PVCP were measured. Titanium dioxide (TiO2) powder and black plastic colour (BPC) were used to introduce scattering and absorption, respectively, in the phantoms. The optical absorption coefficient (mua) at 1064 nm was determined using an optoacoustic method, while diffuse reflectance measurements were used to obtain the optical reduced scattering coefficient (mu's). These optical properties were calculated to be mua = (12.818 +/- 0.001)ABPC cm(-1) and mu's = (2.6 +/- 0.2)S(TiO2) + (1.4 +/- 0.1) cm(-1), where ABPC is the BPC per cent volume concentration, and S(TiO2) is the TiO2 volume concentration (mg mL(-1)). The speed of sound in PVCP was measured to be (1.40 +/- 0.02) x 10(3) m s(-1) using the pulse echo transmit receive method, with an acoustic attenuation of (0.56 +/- 1.01) f(1.51+/-0.06)MHz (dB cm(-1)) in the frequency range of 0.61-1.25 MHz, and a density, calculated by measuring the displacement of water, of 1.00 +/- 0.04 g cm(-3). The speed of sound and density of PVCP are similar to tissue, and together with the user-adjustable optical properties, make this material well suited for developing tissue-equivalent phantoms for biomedical optoacoustics.     

Preliminary study on the use of an inhomogeneous anthropomorphic Fricke gel phantom and 3D magnetic resonance dosimetry for verification of IMRT treatment plans

An inhomogeneous anthropomorphic phantom of the human thorax including lungs and spine was developed for verification of three-dimensional (3D) intensity-modulated radiotherapy (IMRT). The phantom and spinal cord were filled with undiluted Fricke gel, whereas the lungs were filled with a special low-density Fricke gel. Based on a computed tomography scan of the phantom, an intensity-modulated stereotactic radiotherapy plan for a bronchial carcinoma was calculated using an inverse planning system (KonRad, DKFZ Heidelberg, Germany). The plan consisted of seven beams delivered in a step and shoot technique out of 67 sub-fields. Immediately after irradiation 3D magnetic resonance (MR) imaging of the phantom was performed using a special pulse sequence for T1 relaxometry. From the MR image data maps of the longitudinal relaxation rate R1 = 1/T1 were calculated. The R1 maps were converted to dose-proportional image data and compared to planning data. Measurement and planning show good agreement in regions of standard Fricke gel with an average deviation below 5%. In regions of the low-density Fricke gel, deviations are higher due to a decreased signal-to-noise ratio in the MR measurement. In these areas also a different sensitivity of the dose response was observed as compared to standard Fricke gel. The inhomogeneous thorax phantom has proven to be a useful pre-clinical tool for 3D methodical verifications.     

An electrically-activated dynamic tissue-equivalent phantom for assessment of diffuse optical imaging systems

A novel design of solid dynamic phantom with tissue-like optical properties is presented, which contains variable regions of contrast which are activated electrically. Reversible changes in absorption are produced by localized heating of targets impregnated with thermochromic pigment. A portable, battery-operated prototype has been constructed, and its optical and temporal characteristics have been investigated. The phantom has been developed as a means of assessing the performance of diffuse optical imaging systems, such as those used to monitor haemodynamic changes in the brain and other tissues. Images of the phantom have been reconstructed using data acquired with a continuous wave optical topography system.     

Photocrosslinkable polyvinyl alcohol hydrogels that can be modified with cell adhesion peptides for use in tissue engineering

Photoactive polyvinyl alcohol hydrogels (PVA) have been investigated for use as tissue engineering scaffolds. These materials allow in situ polymerization for minimally invasive implantation methods. The mechanical properties of these materials can be tailored for a variety of soft tissue applications. The Young's modulus and ultimate tensile strength of PVA hydrogels are increased with increasing polymer concentration, and highly elastic hydrogels can be formed by altering the number of crosslinkable groups per chain. Fibroblasts homogeneously seeded within 3 mm thick PVA hydrogels remained viable throughout 2 weeks in culture, with no differences in viability across the thickness of the hydrogel. Cells seeded within the PVA hydrogels also produce extracellular matrix proteins, as indicated by the production of hydroxyproline during culture. Intrinsically cell non-adhesive, these PVA hydrogels were functionalized with the cell-adhesive peptide RGDS and found to support the attachment and spreading of fibroblasts in a dose-dependent manner. These results suggest that photopolymerizable PVA hydrogels are promising for tissue engineering applications.     

A dynamic optical imaging phantom based on an array of semiconductor diodes

An electrically-activated phantom for evaluating diffuse optical imaging systems has been designed based on an array of semiconductor diodes which are used to heat a thermochromic dye embedded in a solidified polyester resin with tissue-like optical properties. The array allows individual diodes to be addressed sequentially, thus simulating the movement of a small volume of contrasting optical absorption. Two designs of diode-array phantom are described and results of imaging experiments are presented.     

An innovative phantom for quantitative and qualitative investigation of advanced x-ray imaging technologies

Development, characterization, and quality assurance of advanced x-ray imaging technologies require phantoms that are quantitative and well suited to such modalities. This note reports on the design, construction, and use of an innovative phantom developed for advanced imaging technologies (e.g., multi-detector CT and the numerous applications of flat-panel detectors in dual-energy imaging, tomosynthesis, and cone-beam CT) in diagnostic and image-guided procedures. The design addresses shortcomings of existing phantoms by incorporating criteria satisfied by no other single phantom: (1) inserts are fully 3D--spherically symmetric rather than cylindrical; (2) modules are quantitative, presenting objects of known size and contrast for quality assurance and image quality investigation; (3) features are incorporated in ideal and semi-realistic (anthropomorphic) contexts; and (4) the phantom allows devices to be inserted and manipulated in an accessible module (right lung). The phantom consists of five primary modules: (1) head, featuring contrast-detail spheres approximate to brain lesions; (2) left lung, featuring contrast-detail spheres approximate to lung modules; (3) right lung, an accessible hull in which devices may be placed and manipulated; (4) liver, featuring contrast-detail spheres approximate to metastases; and (5) abdomen/pelvis, featuring simulated kidneys, colon, rectum, bladder, and prostate. The phantom represents a two-fold evolution in design philosophy--from 2D (cylindrically symmetric) to fully 3D, and from exclusively qualitative or quantitative to a design accommodating quantitative study within an anatomical context. It has proven a valuable tool in investigations throughout our institution, including low-dose CT, dual-energy radiography, and cone-beam CT for image-guided radiation therapy and surgery.     

An activatable multimodal/multifunctional nanoprobe for direct imaging of intracellular drug delivery

Multifunctional nanoparticles integrated with imaging modalities (such as magnetic resonance and optical) and therapeutic drugs are promising candidates for future cancer diagnostics and therapy. While targeted drug delivery and imaging of tumor cells have been the major focus in engineering nanoparticle probes, no extensive efforts have been made towards developing sensing probes that can confirm and monitor intracellular drug release events. Here, we present quantum dot (Qdot)-iron oxide (IO) based multimodal/multifunctional nanocomposite probe that is optically and magnetically imageable, targetable and capable of reporting on intracellular drug release events. Specifically, the probe consists of a superparamagnetic iron oxide nanoparticle core (IONP) decorated with satellite CdS:Mn/ZnS Qdots where the Qdots themselves are further functionalized with STAT3 inhibitor (an anti-cancer agent), vitamin folate (as targeting motif) and m-polyethylene glycol (mPEG, a hydrophilic dispersing agent). The Qdot luminescence is quenched in this nanocomposite probe (“OFF” state) due to combined electron/energy transfer mediated quenching processes involving IONP, folate and STAT3 agents. Upon intracellular uptake, the probe is exposed to the cytosolic glutathione (GSH) containing environment resulting in restoration of the Qdot luminescence (“ON” state), which reports on uptake and drug release. Probe functionality was validated using fluorescence and MR measurements as well as in vitro studies using cancer cells that overexpress folate receptors.     

基于量子点的多功能纳米粒材料在多模态成像和癌症治疗中的应用

纳米粒技术在生物医学领域的应用,为今后肿瘤的检测和诊断方法提供了广阔的前景。半导体量子点在生物医学领域逐渐受到了广泛的关注。文章就基于量子点的多功能纳米材料在多模态成像和癌症治疗中的应用做了简单的概述。首先介绍基于量子点的多功能纳米粒子的多模态成像;其次介绍基于量子点的多功能纳米粒在癌症治疗中的研究应用,其中包含了同时成像和化学治疗、同时成像和光动力学治疗,以及同时成像和基因传递的研究。最后,对基于量子点的多功能纳米粒的生物医学应用前景进行了展望。     

Accuracy of two heterogeneity dose calculation algorithms for IMRT in treatment plans designed using an anthropomorphic thorax phantom

With the advent of intensity-modulated radiation therapy (IMRT), the inclusion of heterogeneity corrections is further complicated by the conformal delivery of many small beams forming steep dose gradients. Radiation treatment planning has evolved to take into account even small changes in tissue density so that the dose to tumor can be further optimized. However, different treatment planning systems incorporate different heterogeneity correction algorithms, and it is unclear whether any of these algorithms are superior to others in terms of accurately predicting delivered radiation doses relative to measurement in a clinical setting. The purpose of this study was to determine the accuracy of heterogeneity dose calculations from two widely used IMRT treatment planning systems (Pinnacle and Corvus) against measurement. These two systems handle heterogeneity dose corrections by means of a collapsed-cone convolution superposition algorithm and a finite-size pencil-beam algorithm with one-dimensional depth scaling correction, respectively. Treatment plans were generated by each system using an anthropomorphic thorax phantom, routine clinical lung tumor constraints, and a common prescribed dose. Dose measurements made by thermoluminescent detectors (TLDs) and radiochromic film positioned within the phantom's lung and offset tumor insert were then compared with the calculated values. The collapsed cone convolution superposition dose calculation algorithm provided clinically acceptable results (+/-5% of the normalization dose or 3 mm distance to agreement) in the designed treatment plan and delivery. The pencil-beam algorithm with an effective pathlength correction showed reasonable agreement within the gross tumor volume, overestimated dose within a majority of the planning target volume, and underestimated the extent of the penumbral broadening, yielding only about 60% accuracy when judged by the above criterion. Even judged by a more generous criterion (+/-7% /7 mm), the results were clinically unfavorable (at only about 80% accuracy). To ascertain the dose in heterogeneous regions such as the tumor-lung interface and the peripheral lung dose near the tumor, the superposition convolution algorithm that accounts for lateral scatter and electron transport should be used. The use of the pencil-beam algorithm with only an effective pathlength correction may result in the dose to the target being overestimated. As a result, a full understanding of any treatment planning system's heterogeneity algorithm is required prior to clinical implementation.     

基于EEG的酒精依赖对脑功能的影响

目的研究酒精依赖对个体脑电信号的影响,以期了解酒精依赖对个体健康的影响。方法基于亨利(纽约州立大学)实验所得的102例脑电数据,对数据进行预处理,去除伪迹,提取脑电特征波并计算包含功率谱、R值和重心频率在内的脑电参数,进行统计学分析,以讨论分析酒精依赖患者与健康人的脑电差异。结果相对于健康人,酒精依赖患者的脑电中α波相对功率减小,其中以顶区和枕区最为显著。θ波功率减小,在颞叶的变化较为明显。β波相对功率在各个脑区均大幅提高。全脑区R值均减小,重心频率均增大。结论相对于健康人群,酒精依赖患者的脑电信号普遍向高频迁移,表明酒精依赖可以使大脑皮质的兴奋度增强,脑活动更为复杂。     

Poly(vinyl alcohol) cryogel phantoms for use in ultrasound and MR imaging

Poly(vinyl alcohol) cryogel, PVA-C, is presented as a tissue-mimicking material, suitable for application in magnetic resonance (MR) imaging and ultrasound imaging. A 10% by weight poly(vinyl alcohol) in water solution was used to form PVA-C, which is solidified through a freeze-thaw process. The number of freeze-thaw cycles affects the properties of the material. The ultrasound and MR imaging characteristics were investigated using cylindrical samples of PVA-C. The speed of sound was found to range from 1520 to 1540 m s(-1), and the attenuation coefficients were in the range of 0.075-0.28 dB (cm MHz)(-1). T1 and T2 relaxation values were found to be 718-1034 ms and 108-175 ms, respectively. We also present applications of this material in an anthropomorphic brain phantom, a multi-volume stenosed vessel phantom and breast biopsy phantoms. Some suggestions are made for how best to handle this material in the phantom design and development process.     

痛觉的脑成像研究进展

痛觉是日常生活中最重要的感觉之一,痛觉的机理非常复杂.随着20世纪90年代各种脑成像技术的成熟,现在人们对于大脑的痛觉处理过程有了更好的理解.综述了痛觉脑成像的研究方法,包括电生理技术和脑功能成像技术,重点关注了这些技术在痛觉研究方面的相关成果.指出了解剖学上的痛觉处理机制.并分析了目前痛觉脑功能成像研究存在的缺陷和不足.     

Engineered multifunctional nanomaterials for multimodal imaging of retinoblastoma cells in vitro

Multifunctional nanoparticles are next generation materials that can be simultaneously used for imaging, diagnosis, and delivery of drugs. However, materials intended for cancer diagnosis need to be investigated for its cell uptake, toxicity, and effectiveness. In the current work, we have synthesized fluorescent iron oxide nanoparticles and evaluated its efficacy against retinoblastoma cell imaging. The iron oxide nanoparticles were synthesized and stabilized using oleic acid. Sulforhodamine B was adsorbed onto albumin over the oleic acid-capped iron oxide nanoparticles. Our results demonstrated good cell uptake in a time-dependent manner and nanoparticles were found to localize in the cytosol. Further, the nanoparticles exhibited excellent negative contrast in magnetic resonance imaging (MRI) experiments and with no cytoxicity (5–100?μg/mL iron oxide nanoparticles) to both normal as well as cancer cells demonstrating its biocompatibility. Thus, this novel material integrates the ability to image tissues with high sensitivity by MRI and specifically visualize Y79 retinoblastoma cells by fluorescence imaging with no toxicity.     

An EEG-based functional connectivity measure for automatic detection of alcohol use disorder

BackgroundThe abnormal alcohol consumption could cause toxicity and could alter the human brain’s structure and function, termed as alcohol used disorder (AUD). Unfortunately, the conventional screening methods for AUD patients are subjective and manual. Hence, to perform automatic screening of AUD patients, objective methods are needed. The electroencephalographic (EEG) data have been utilized to study the differences of brain signals between alcoholics and healthy controls that could further developed as an automatic screening tool for alcoholics.MethodIn this work, resting-state EEG-derived features were utilized as input data to the proposed feature selection and classification method. The aim was to perform automatic classification of AUD patients and healthy controls. The validation of the proposed method involved real-EEG data acquired from 30 AUD patients and 30 age-matched healthy controls. The resting-state EEG-derived features such as synchronization likelihood (SL) were computed involving 19 scalp locations resulted into 513 features. Furthermore, the features were rank-ordered to select the most discriminant features involving a rank-based feature selection method according to a criterion, i.e., receiver operating characteristics (ROC). Consequently, a reduced set of most discriminant features was identified and utilized further during classification of AUD patients and healthy controls. In this study, three different classification models such as Support Vector Machine (SVM), Naïve Bayesian (NB), and Logistic Regression (LR) were used.ResultsThe study resulted into SVM classification accuracy = 98%, sensitivity = 99.9%, specificity = 95%, and f-measure = 0.97; LR classification accuracy = 91.7%, sensitivity = 86.66%, specificity = 96.6%, and f-measure = 0.90; NB classification accuracy = 93.6%, sensitivity = 100%, specificity = 87.9%, and f-measure = 0.95.ConclusionThe SL features could be utilized as objective markers to screen the AUD patients and healthy controls.     

Evaluation of intestinal protozoan morphology in polyvinyl alcohol preservative: comparison of zinc sulfate- and mercuric chloride-based compounds for use in Schaudinn's fixative.

As a result of disposal problems related to the use of mercury compounds, many laboratories have considered switching from mercuric chloride-based Schaudinn's and polyvinyl alcohol (PVA) stool preservatives to other non-mercury-based preservatives. The primary use for PVA-preserved specimens is the permanent stained smear, the most important technique in the routine ova and parasite examination for the identification and confirmation of intestinal protozoa. A comparison of organism recovery and morphology of the intestinal protozoa was undertaken with PVA containing either a zinc sulfate base or the "gold standard" mercuric chloride base. Paired positive fecal specimens (106 from 64 patients) were collected and examined microscopically by the trichrome stain technique. There were 161 instances in which organism trophozoite and/or cyst stages were identified and 3 in which human cells were identified. Morphology, clarity of nuclear and cytoplasmic detail, overall color differences, and the ease or difficulty in detecting intestinal protozoa in fecal debris, as well as the number of patients with a missed diagnosis, were assessed from the permanent stained smear. Overall organism morphology of the intestinal protozoa preserved in zinc sulfate-PVA was not always equal in nuclear and cytoplasmic detail or range of color after permanent staining to that seen with mercuric chloride-PVA. However, the same organisms were usually identified in both specimens, with the exception of situations in which organism numbers were characterized as rare (no organisms per 10 oil immersion fields at x1,000 magnification but at least one organism in the smear) [9 of 161 (5.6%)] or the organism was missed because of poor morphologic detail [12 of 161 (7.5%)]. In only six of these cases [6 of 161 (3.7%)] did the results involve pathogens. The patient diagnosis was missed in four cases of amebiasis and two cases of giardiasis; in both situations the organism numbers were rare. There were no discrepant results with Dientamoeba fragilis. Overall agreement between the two PVA-based results was 87.0% (140 of 161); when the instances of rare organisms were disregarded, the overall agreement was 92.5% (149 of 161). On the basis of these findings, zinc-PVA is viable substitute for mercuric chloride-PVA used for trichrome permanent stained smears.