定量评估64层螺旋CT血管成像与DSA显示冠状动脉狭窄的能力和可靠性

目的定量评估64层螺旋CT（MSCT）与DSA2种成像方法显示冠状动脉狭窄及支架内再狭窄的能力和可靠性。方法应用心脏动态体模，设定心率为0、50、70、90次／min，对内径3mm的模拟冠状动脉（内设25％、50％、75％3段狭窄）及内径4mm的模拟带支架冠状动脉（支架段内设50％、75％2段狭窄）分别进行MSCT与DSA成像，将MSCT与DSA对应数据进行分析。结果（1）MSCT对25％、50％、75％3段狭窄的平均测量值为（30．0±1．4）％、（49．5±1．3）％、（72．9±3．9）％（P值分别为0．005、0．531、0．369）；DSA分别为（24．8±2．0）％、（48．2±2．1）％、（75．3±2．4）％（P值分别为0．883、0．180、0．796）。（2）MSCT图像伪影随心率增快而增加，心率≥70次／min影响变明显；DSA不受心率影响，所有心率下都可清晰地显示狭窄程度，无伪影。（3）MSCT与DSA测量血管狭窄程度有较好的相关性（r=0．995，P=0．000）。（4）MSCT可同时显示支架及支架内狭窄，但显示支架内狭窄能力有限，对50％狭窄分别显示为（46．4±4．5）％（心率为0）和（43．6±5．7）％（心率为50次／min），与标准值（50％）相比，差异有统计学意义（P〈0．05）。DSA可清晰显示支架内狭窄，但不能很好显示支架形态。结论（1）MSCT与DSA评价冠状动脉狭窄结果可靠，MSCT受心率的影响大，时间分辨率有待提高，作为排除性诊断有很高的临床应用价值；MSCT对于支架内再狭窄的判断尚有一定局限性，但在管径较粗和低心率条件下评价支架内再狭窄有一定价值。     

High-speed black blood imaging of vessel stenosis in the presence of pulsatile flow.

Stenosis phantoms were created to study the ability of "black blood" methods to image a vessel stenosis in the presence of pulsatile flow. Black blood images were acquired with a modified TurboFLASH (fast low-angle shot) method that eliminates flow signal by applying a set of prepulses before segmented data acquisition. With this high-speed approach, imaging can be completed within 16 seconds. This technique was compared with conventional spin-echo black blood, gradient-echo black blood, and gradient-echo bright blood methods. Loss of flow signal, which extended beyond the site of the stenosis, was seen on the gradient-echo bright blood images. The pattern of signal loss varied with the type of stenosis. Flow voids were achieved with spin-echo black blood imaging; however, substantial ghosting artifacts were seen. With gradient-echo black blood imaging, it was difficult to eliminate all flow signal, particularly for in-plane flow. The modified TurboFLASH method produced high-quality black blood images in a fraction of the time needed for spin-echo imaging. It showed no ghosting artifacts even in the presence of pulsatile flow.     

A dynamic two-dimensional phantom for ultrasound hyperthermia controller testing

A new thin layer phantom for testing hyperthermia controllers has been constructed and evaluated using an ultrasound hyperthermia system. The phantom's thermal behaviour agrees with the characteristics of the Pennes' bio-heat transfer equation (BHTE). In particular, the experimental and theoretical results agree in the following ways. First, with respect to the power deposition: for a given power magnitude and scan radius, the shape of the temperature distribution across the phantom corresponds to the shape predicted by the BHTE and the experimental and theoretical temperature values agree closely; when the power magnitude is varied at a fixed scan radius, the average temperature of the phantom varies linearly with the applied power, and as the scan radius is varied at a fixed power magnitude, the average temperature increases with decreasing scan radius size. Secondly, with respect to perfusion: increasing or decreasing the flow rate over the phantom simulates an increase or decrease in the BHTE perfusion term, and the estimated perfusion values are dependent on flow rate only, and are not functions of power or geometry. The combination of these experimental and theoretical results validate the phantom's potential for testing feedback control systems, particularly for future use in the development and verification of modelbased controllers. The use of this phantom should improve and accelerate the testing and evaluation of feedback control systems, and reduce the need for animal and human testing.     

四维小鼠全身体模及其在医学影像研究中的应用

医学成像模拟对描述、评估和优化医学成像设备而言是一个强有力的工具.模拟的关键是必须有研究对象解剖结构仿真体模或模型.四维小鼠全身体模为影像研究提供了小鼠解剖和生理的仿真模型.精确的模型与成像过程相结合,能提供研究对象在健康和疾病状态下不同的解剖和运动(心脏和呼吸)的大量逼真的成像数据.对研究解剖、生理、机体等因素对医学和小动物成像的影响来说,四维小鼠全身体模有巨大的潜力,其还可用于新仪器研究、图像采集策略、图像处理和重建方式、图像可视化和解释技术等.     

实性肺结节低剂量CT影像组学图像质量控制的体模研究

目的探讨影像组学在低剂量CT扫描条件下实性肺结节CT图像质量控制中的应用价值。方法使用CT750 HD CT分别在不同管电压及不同管电流下对胸部肺结节人体仿真模型进行扫描,记录不同扫描条件下的容积CT剂量指数(CTDIvol),测量并计算图像中结节的信噪比(SNR)和对比噪声比(CNR),分析辐射剂量、噪声与管电压管电流变化的规律,将所有扫描数据通过影像组学分析软件对实性结节的全部特征进行提取,使用R语言统计学软件对提取的特征参数进行主成分分析,选取主成分中对图像质量贡献较大的特征进行分析。对确定的重要特征参数进行单因素方差分析,揭示不同管电压下特征参数的差异,再进一步通过事后检验对不同管电压组之间进行两两比较,找出组间差异。结果辐射剂量在研究的范围内随管电压、管电流的增加而线性增加。肺结节的SNR和CNR总体变化趋势虽然与管电压及管电流的变化呈线性关系,但在低剂量下没有明确的变化趋势阈值存在,无法准确评价低辐射下图像质量。影像组学提取的所有特征参数中均质性、体素值总和及Haralick相关性是3个主要成分,其方差累计的贡献率为89.2%,且特征值均>1。特征参数均质性曲线显示出其变化趋势与管电压及管电流变化成相关性,且稳定性和一致性较好。均质性单因素方差分析结果显示在管电压140及120 kVp时,两组间的均质性值的变化差异无统计学意义(P=0.117),而在其他管电压间均质性值变化差异均有统计学意义(P<0.001)。当管电压在100 kVp、管电流≥60 mA时或管电压在80 kVp、管电流≥90 mA时,均质性无明显变化,可以得到满意的图像质量。结论影像组学分析方法可以有效定量化地评价和控制低辐射剂量下实性肺结节CT图像质量。     

A teaching phantom for sonographers.

An anthropomorphic torso section phantom is described that is intended for use during initial stages of ultrasonographer training. The phantom represents a section of the upper abdomen, with simulated ribs, liver, kidney with fat pad, gallbladder, aorta, and bowel gas. Positioned in the liver are ten simulated soft tissue masses, which produce a variety of typical echographic patterns. All simulated soft tissue components are formed of tissue-mimicking materials that match their corresponding tissue counterparts in terms of speed of sound, ultrasonic attenuation, and density. Construction details are presented and examples of images are shown.     

Tracking motion with tagged rapid gradient-echo magnetization-prepared MR imaging.

A technique for rapid assessment of tissue motion was developed by combining spatially selective radio-frequency tagging pulses with centric phase-encoding view ordering in a T1-weighted, magnetization-prepared gradient-echo acquisition sequence. This sequence allowed labeling and tracking of tissue motion with single-image acquisition times of less than 3 seconds. Multiple tagged bands 3mm thick were superimposed orthogonal to the imaging plane. Motion in the interval between tagging and the start of image acquisition could then be precisely determined. The technique was evaluated with phantom studies and then applied to human volunteers for assessment of skeletal muscle motion, phonation, and pelvic floor motion.     

Reblurred deconvolution method for chemical shift removal in F-19 (PFOB) MR imaging.

Perfluorocarbons such as perfluoroctylbromide (PFOB) can be used as contrast agents in the vascular system for fluorine-19 magnetic resonance imaging or as synthetic oxygen carriers. F-19 imaging has been proposed for studying the vascular system, capillary flow, tissue perfusion, and tumor oxygenation. A major difficulty is that F-19 compounds often have complex multipeak spectra. These peaks result in chemical shift artifacts, lower signal-to-noise ratios, and blurred images. Each peak also excites a different section when a section-select gradient is applied. Direct inverse filtering is the simplest deconvolution method for correcting such artifacts; however, two major difficulties present themselves: functional singularity and noise amplification at high frequencies. The use of a new reblurred deconvolution (RED) method appears to overcome these problems. Although this method is based on iterative deconvolution in the spatial domain, the computational overhead is negligible. Since the point spread function and object data are already available in the time domain as FID data, RED appears to be useful for eliminating chemical shift artifacts and suppressing noise amplification while restoring the original image without loss of resolution.     

基于可变翻转角技术快速测量组织T1值的可行性

目的 探讨可变翻转角结合三维（3D）容积内插快速扰相梯度回波（FSPGR）序列快速测量T1值的可行性。方法 采用不同浓度钆溶液作为模型,以单层反转恢复快速自旋回波（IR-FSE）序列为金标准,比较3D FSPGR可变翻转角组合（2、3个翻转角）和3D容积内插FSPGR可变翻转角组合（2、3、4个翻转角）测量模型T1值的准确性。结果 2、3个可变翻转角FSPGR与IR-FSE测量T1值高度相关（r=0.982和0.975,P均<0.001）;2、3、4个可变翻转角3D容积内插FSPGR与IR-FSE测量T1值亦高度相关（r=0.969、0.970和0.979,P均<0.001）,于不同时间所测得T1值的组内相关系数等于或接近1。结论 可变翻转角结合3D容积内插FSPGR可快速测量组织T1值,准确性及重复性较好。     

Accuracy and precision of MR velocity mapping in measurement of stenotic cross-sectional area,flow rate,and pressure gradient

Reliability of magnetic resonance (MR) velocity mapping to assess severity of stenosis was assessed in vitro. Steady flow at different flow rates through five stenoses with a central orifice area ranging from 17 to 176 mm² was measured with velocity mapping performed perpendicular to the stenotic jet. Besides determination of the stenotic cross-sectional area and flow rate, the pressure gradient was calculated with the modified Bernoulli equation and compared with manometer measurements. Cross-sectional areas were measured with an accuracy of ?76%, a precision of ?91%, and an error of ?19 mm². Flow rates had an accuracy of ?72%, a precision of ?94%, and an error of ?1.4 L/min. The modification of the Bernoulli equation limited its reliability to stenoses with areas of 35-113 mm². Pressure gradients were calculated with an accuracy of ?80%, a precision of ?88%, and an error of ?15 mm Hg. The method was applied in a single patient with aortic stenosis and gave estimates that agreed with those obtained by heart catheterization.