应用连续小波变换检测和增强DSA血管影像的研究

数字血管减影的影像中的血管像具有对比度低的特点。本文用一种全新的思想实现DSA影像中血管像的增强,即先应用小波变换技术检测血管边缘,使其从背景中分离出来,再应用对比度拉伸的方法进一步增强血管同背景的对比度,由于本文使用的连续小波变换可从不同方向上检测影像灰度变化情况,所以检测到的影像边缘更准确全面,而且由于噪声的小波变换的模较小,较好地抑制了减影像中的背景噪音,处理后的血管影像具有三维实体的视觉效果。     

多层螺旋CT三维血管造影在腹部血管性疾病中的临床应用

目的评价多层螺旋CT(MSCT)三维血管成像技术及其在腹部血管性疾病诊断中的应用价值。方法对45例可疑存在腹部血管性疾病的病人行MSCT造影增强检查,用GELight-speedUltra16层CT进行螺旋薄层CT扫描。扫描条件:扫描层厚1.25mm,螺距1.75∶1,转速0.5s/360°,120kV,350～400mA,扫描总时间10～15s。在独立工作站上进行三维腹部血管重组,使用不同的旋转轴观察腹部血管的空间解剖细节。结果全部病例三维腹部血管图像均能充分显示腹部血管的空间关系与解剖细节,为腹部血管性疾病病人提出明确诊断。结论MSCT三维腹部血管成像能够准确、直观地显示腹部血管的立体解剖特点,为腹部血管性疾病的诊断与治疗提供重要依据。     

肺血栓栓塞症MRI检查操作规程

三维增强MR血管造影（MR angiography，MRA）是一种无创性检查方法，用它进行MR肺动脉造影（MR pulmonary arteriography，MRPA）可准确地检出PTE主肺动脉、肺叶及肺段动脉内的栓子，对亚段肺动脉水平的栓子检出能力还有待于进一步研究。MRPA无放射性损害，很少引起过敏反应，使用对比剂[钆-二乙烯三胺五乙酸（Gd-DTPA）]无肾脏不良反应，检查简便、易行、经济，患者无须住院。     

再谈步进DSA下肢动脉造影的应用

目的:再次探讨并总结下肢动脉血管造影应用步进DSA技术在临床介入诊断及治疗中的应用。方法:我院使用美国GE公司INNOVA4100数字减影血管造影机,采用Seldinger技术,对36例下肢动脉血管病变患者行下肢动脉血管步进DSA检查。技术员进行图像采集曝光时,合理应用控制手柄来控制检查床的移动,使检查床移动与对比剂在血管内的流动速度同步,以获得一系列与血流速度一致的实时对比剂追踪下肢血管的影像。结果:36例患者下肢动脉血管步进DSA检查均顺利完成后,获得清晰完整的DSA的动态图像,对临床诊断与治疗提供明确造影依据。结论:常规下肢动脉造影路程长,范围广,需要分段多次进行造影。自从应用步进DSA技术在下肢动脉血管造影,可得到完整的动态血管造影图像,减少了额外地DSA造影次数及造影剂的大量注射,节省检查时间和治疗时间,提高诊治安全性,是值得广泛推广的一种好的检查方法。     

采用自适应跟踪算法对冠状动脉造影图中血管轮廊的自动识别

一、导言计算机辅助方法在以下两个方面提高了冠状动脉造影图的定量分析。第一:在确定冠状动脉狭窄度的方面自动化过程降低了观测者和观测器内的变化影响。第二:在需要大计算量的分析方法中(如从动脉造影图的序贯结构中测定冠状血流以及从双平面血管造影图来重建三维血管结构),高效率的计算机算法是核心本质。但是,目前的计算机成象系统的空间分辨率不足以支持冠状动脉造影图的全自动分析。在事先不知道狭窄的位置时,数字化为512     

大鼠膝关节周围微小动脉网分布及计数法的评价

背景:随着骨组织工程研究的不断深入和对骨代谢过程的不断认识,分析组织工程骨的血液供应和营养状况已成为目前的研究重点。目的:比较和评价常用的微小血管检测方法,明确各种方法的利弊,为研究组织工程骨内微血管的分布和计数提供借鉴意义。方法:分别用3种常用的血管评价法对SD大鼠膝关节周围微小动脉网进行分析对比,18只SD大鼠均分为免疫组化组、血管造影组、CT扫描重建组。结果与结论:免疫组化技术能观察到血管的分布范围,但是无法评价血管空间分布的整体情况。血管造影技术和CT检查则可以提供形象的血管空间分布图,但是CT检测时部分微小血管显示不清。免疫组化检出(26.50±3.02)条血管数明显多于血管造影(14.12±1.47)条和CT检测(9.00±1.79)条,其中CT检测组可检出的血管数最少。说明免疫组化和血管造影可以为微小血管提供微观和宏观的评价方法,从两个层面一起观察,更好的分析血管的情况,对微血管的评价有很好的借鉴意义。     

用两种体模作CT性能检测的对比研究

本文介绍使用两种不同的标准体模(AAPM体模和RMI461A体模),对3台新安装的CT设备作性能检测,把两组实验数据进行双边对比研究.结果:大多数性能项目,包括高对比度分辨率、影像均匀性和噪声、层厚偏差和CT值线性等的测量数据有较好的一致性.发现低对比度分辨率的测量值存在明显差异,可能是体模(插件)长期受X线照射,化学效应引起材料CT值漂移及本底对比度升高所致,需要用对比度-细节反比关系校正.本文还就当前CT性能检测的若干技术问题,包括检测方法与评价标准的改进等进行探讨.     

全数字超声多普勒血流测量系统研究

传统超声多普勒血流测量仪器使用模拟电路来完成信号采集与解调处理,此类系统容易受外界电磁环境、温度变化等因素的干扰,也难以运用现代信号处理技术来实现更高级的检测功能,例如多深度检测、功率M型多普勒血流成像以及编码激励成像等。本研究设计了一种全数字的超声多普勒血流信号采集处理系统,结合经典的自相关技术,实现了多深度检测和功率M型多普勒血流成像,并采用2周期基础码调制的13位Barker码编码激励方法,得到远高于传统方法的轴向空间分辨率。为验证该系统的有效性,首先利用该系统对多普勒体模进行检测实验研究,证明该系统能有效提高轴向空间分辨率;然后通过对大脑中动脉、前动脉血流检测,表明该系统可以显示出超声波发射方向上整个深度的血流信息,有利于血管的定位和识别。     

三维颅脑容积磁共振成像技术在颅脑磁共振增强检查的价值

目的 评价1.5 T HDx磁共振成像(MRI)系统新技术颅脑容积磁共振成像(BRAVO)在颅脑磁共振增强检查中的价值.方法 对31例颅脑肿瘤患者或町疑颅脑转移的患者行常规磁共振增强检查和BRAVO序列检查.分别计算自旋回波(SE)序列及BRAVO序列的病灶显示数量,采用χ2检验方法对结果进行比较;对比图像质量,分别测量两序列灰质、白质及背景噪声信号值,运用公式计算信噪比(SNR)、对比噪声比(CNR)以及灰白质对比度.结果 在31例颅脑MRI检查中,SE序列共显示病灶121个,BRAVO序列共显示病灶124个,两者比较其差异无统计学意义(P＞0.05);BRAVO与SE序列的白质信噪比(17.828 7±2.753 1和27.226 1±5.571 2),灰质信噪比(12.964 2±1.796 3和23.174 1±4.513 3)差异均有统计学意义(P＜0.05),sE序列的灰质、白质信噪比均高于BRAVO序列.BRAVO与SE序列的灰白质对比噪声比(CNRWM/GM)(4.865 2±1.1370和4.051 6±1.3900),灰白质对比度(635.211 3±136.385 0和93.494 2±25.1724),差异均有统计学意义(P＜0.05),BRAVO序列均高于SE序列.结论 BRAVO序列实现了磁共振颅脑增强容积快速扫描的可能,扫描一个序列能重建出多平面图像,同时以高空间分辨率、较少的血管搏动伪影以及较高的灰白纸对比度为颅脑磁共振扫描提供更广阔的前景,在颅脑磁共振增强检查中起到重要的补充作用.     

64排CT在体表血管疾病中检查方法的比较

目的：比较不同团注方法在64排CT在体表血管疾病中的应用价值。方法对60例疑似体表血管疾病的患者进行CT扫描,观察组30例从肘静脉团注射,对照组30例从足背静脉团注射,采用MPR、MIP及SVR显示血管。结果60例疑似体表血管疾病患者中,MSCTA检查与病理诊断符合率98.33%。观察组动脉供血图形显示率70.00%,静脉血管图像显示率30.00%,对照组静脉供血图形显示率73.33%,动脉血管图像显示率26.67%。结论MSCTA在体表血管疾病检查中选择不同的团注方法,对观察病变的动静脉构成各有独自的优越性,对选择治疗方法及观察疗效有重要的参考价值。     

High spatial resolution quantitative MR images: an experimental study of dedicated surface coils

Measuring spin-spin relaxation times (T2) by quantitative MR imaging represents a potentially efficient tool to evaluate the physicochemical properties of various media. However, noise in MR images is responsible for uncertainties in the determination of T2 relaxation times, which limits the accuracy of parametric tissue analysis. The required signal-to-noise ratio (SNR) depends on the T2 relaxation behaviour specific to each tissue. Thus, we have previously shown that keeping the uncertainty in T2 measurements within a limit of 10% implies that SNR values be greater than 100 and 300 for mono- and biexponential T2 relaxation behaviours, respectively. Noise reduction can be obtained either by increasing the voxel size (i.e., at the expense of spatial resolution) or by using high sensitivity dedicated surface coils (which allows us to increase SNR without deteriorating spatial resolution in an excessive manner). However, surface coil sensitivity is heterogeneous, i.e., it--and hence SNR--decreases with increasing depth, and the more so as the coil radius is smaller. The use of surface coils is therefore limited to the analysis of superficial structure such as the hypodermic tissue analysed here. The aim of this work was to determine the maximum limits of spatial resolution and depth compatible with reliable in vivo T2 quantitative MR images using dedicated surface coils available on various clinical MR scanners. The average thickness of adipose tissue is around 15 mm, and the results obtained have shown that obtaining reliable biexponential relaxation analysis requires a minimum achievable voxel size of 13 mm3 for a conventional volume birdcage coil and only of 1.7 mm3 for the smallest available surface coil (23 mm in diameter). Further improvement in spatial resolution allowing us to detect low details in MR images without deteriorating parametric T2 images can be obtained by image filtering. By using the non-linear selective blurring filter described in a previous work, the voxel size was reduced to 0.8 mm3, allowing us to detect microstructures such as fibrous septae while preserving precision in T2 measurements. This paper provides practical information allowing us to perform reliable T2 quantitative MR micro images. High resolution imaging with dedicated surface coils, which is only well-suited to near surface organs, might lead to highly valuable results in this context, especially to analyse the hypodermis involved in the lipodystrophy seen in patients with human immuno-deficiency virus (HIV).     

Current constrained voltage scaled reconstruction (CCVSR) algorithm for MR-EIT and its performance with different probing current patterns

Conventional injected-current electrical impedance tomography (EIT) and magnetic resonance imaging (MRI) techniques can be combined to reconstruct high resolution true conductivity images. The magnetic flux density distribution generated by the internal current density distribution is extracted from MR phase images. This information is used to form a fine detailed conductivity image using an Ohm's law based update equation. The reconstructed conductivity image is assumed to differ from the true image by a scale factor. EIT surface potential measurements are then used to scale the reconstructed image in order to find the true conductivity values. This process is iterated until a stopping criterion is met. Several simulations are carried out for opposite and cosine current injection patterns to select the best current injection pattern for a 2D thorax model. The contrast resolution and accuracy of the proposed algorithm are also studied. In all simulation studies, realistic noise models for voltage and magnetic flux density measurements are used. It is shown that, in contrast to the conventional EIT techniques, the proposed method has the capability of reconstructing conductivity images with uniform and high spatial resolution. The spatial resolution is limited by the larger element size of the finite element mesh and twice the magnetic resonance image pixel size.     

Whole-brain high-resolution metabolite mapping with 3D compressed-sensing SENSE low-rank 1H FID-MRSI

There is a growing interest in the neuroscience community to map the distribution of brain metabolites in vivo. Magnetic resonance spectroscopic imaging (MRSI) is often limited by either a poor spatial resolution and/or a long acquisition time, which severely restricts its applications for clinical and research purposes. Building on a recently developed technique of acquisition-reconstruction for 2D MRSI, we combined a fast Cartesian ¹H-FID-MRSI acquisition sequence, compressed-sensing acceleration, and low-rank total-generalized-variation constrained reconstruction to produce 3D high-resolution whole-brain MRSI with a significant acquisition time reduction. We first evaluated the acceleration performance using retrospective undersampling of a fully sampled dataset. Second, a 20 min accelerated MRSI acquisition was performed on three healthy volunteers, resulting in metabolite maps with 5 mm isotropic resolution. The metabolite maps exhibited the detailed neurochemical composition of all brain regions and revealed parts of the underlying brain anatomy. The latter assessment used previous reported knowledge and a atlas-based analysis to show consistency of the concentration contrasts and ratio across all brain regions. These results acquired on a clinical 3 T MRI scanner successfully combined 3D ¹H-FID-MRSI with a constrained reconstruction to produce detailed mapping of metabolite concentrations at high resolution over the whole brain, with an acquisition time suitable for clinical or research settings.     

High-resolution polymer gel dosimetry by parameter selective MR-microimaging on a whole body scanner at 3T

High dose variations across small spatial distances, as present in brachytherapeutic applications or radiosurgery and especially gamma-knife therapy, are difficult to quantify by standard dosimetry. We demonstrate the possibility to obtain planar spatial resolutions for dose imaging at pixel sizes below 200 microm within multislice parameter selective MR imaging on polymer gels. The sensitivity of the transversal and longitudinal relaxation time as well as diffusivity on dose is shown. High spatial resolution is achieved by parameter selective microimaging of polymer gels on a high-field (3 T) whole-body MR system equipped with a dedicated strong gradient system and a small probe head matched to the sample size. In addition to the spin-spin relaxation rate R2 = 1/T2 we investigate the sensitivity of the longitudinal relaxation rate R1 = 1/T1 and the diffusivity Dapp in acrylic polymer gels on irradiation up to dose levels of about 20 Gy. Dose images are obtained after calibration of the corresponding MR parameters by known dose levels of gamma irradiation. Also the MR-parameter T1 may be used for dose imaging. The impact of all of the three parameters T1, T2, and diffusivity on obtained signal intensities in irradiated regions has to be taken into account in nonoptimized pulse sequences. Further, very high spatial resolution imposes several restrictions on the evaluation of R2, which have to be considered for quantitative dosimetry. These restrictions are discussed in detail. We also demonstrate the importance of such a high spatial resolution in case of a set of differently sized gamma-knife stereotactic irradiation schemes. Gel dosimetry based on MR parameter selective microimaging represents a potent alternative for the detection of dose distributions characterized by steep dose gradients, typical in brachytherapeutic and radiosurgical applications.     

Applications of sliding window reconstruction with cartesian sampling for dynamic contrast enhanced MRI

Applications of dynamic contrast enhanced MR imaging are increasing and require both high spatial resolution and high temporal resolution. Perfusion studies using susceptibility contrast in particular require very high temporal resolution. The sliding window reconstruction is a technique for increasing temporal resolution. It has previously been applied to radial and spiral sampling, but these schemes require extensive correction and interpolation during image reconstruction. Fourier raw data can be reconstructed simply and quickly using the fast fourier transform (FFT). This paper presents a new Fourier-based sampling scheme and sliding window reconstruction that facilitates fast scanning without needing correction or interpolation. This technique can be used on virtually any MR scanner since it requires no specialized hardware. It is implemented here as a dual gradient echo sequence providing simultaneous T(1)- and T(2)*-weighted images with a time resolution of 1.1 s.     

High resolution imaging of the mouse inner ear by microtomography: a new tool in inner ear research

A newly developed desktop microtomograph was used to evaluate whether it is suitable for visualizing the three-dimensional (3D) morphology of the mouse inner ear (at a micrometer level) and whether it is applicable as a fast screening tool to detect hereditary abnormalities in this organ. To this end, the epistatic circler, a mutant mouse showing abnormal circling behaviour, was used as a model. The inner ears were dissected out, formaldehyde-fixed, and scanned at maximal resolution along the longitudinal axis. After segmentation, stacks of tomographic images were used for 3D reconstruction of the bony labyrinth. Finally, the obtained data were correlated with subsequent conventional histological examination. The spatial resolution (8 microm) achieved by this instrument, was found to be far superior to that obtained by conventional computer tomography (CT) and magnetic resonance (MR)-imaging equipment. The technique provides detailed tomographic images of the bony labyrinths and enables an adequate 3D reconstruction of the inner ear structures in this small mammal. In addition, it allows a screening for pathologic specimens prior to the more time- and labour-consuming histological techniques, which are still essential to gather information at a (sub)cellular level. This imaging technique can be regarded as a valuable tool in future research on hereditary inner ear abnormalities.     

High-resolution 3D isotropic MR imaging of mouse flank tumours obtained in vivo with solenoid RF micro-coil

The investigation of mouse flank tumours by magnetic resonance imaging (MRI) is limited by the achievable spatial resolution, which is generally limited by the critical problem of signal-to-noise ratio. Sensitivity was improved by using an optimized solenoid RF micro-coil, built into the animal cradle. This simple design did not require extensive RF engineering expertise to construct, yet allowed high-resolution 3D isotropic imaging at 60 x 60 x 60 microm(3) for a flank tumour in vivo, revealing the heterogeneous internal structure of the tumour. It also allowed dynamic contrast enhanced (DCE) experiments and angiography (MRA) to be performed at 100 x 100 x 100 microm(3) resolution. The DCE experiments provided an excellent example of the diffusive spreading of contrast agent into less vascularized tumour tissue. This work is the first step in using high-resolution 3D isotropic MR to study transport in mouse flank tumours.     

Iterative three-dimensional expectation maximization restoration of single photon emission computed tomography images: application in striatal imaging

Single photon emission computed tomography imaging suffers from poor spatial resolution and high statistical noise. Consequently, the contrast of small structures is reduced, the visual detection of defects is limited and precise quantification is difficult. To improve the contrast, it is possible to include the spatially variant point spread function of the detection system into the iterative reconstruction algorithm. This kind of method is well known to be effective, but time consuming. We have developed a faster method to account for the spatial resolution loss in three dimensions, based on a postreconstruction restoration method. The method uses two steps. First, a noncorrected iterative ordered subsets expectation maximization (OSEM) reconstruction is performed and, in the second step, a three-dimensional (3D) iterative maximum likelihood expectation maximization (ML-EM) a posteriori spatial restoration of the reconstructed volume is done. In this paper, we compare to the standard OSEM-3D method, in three studies (two in simulation and one from experimental data). In the two first studies, contrast, noise, and visual detection of defects are studied. In the third study, a quantitative analysis is performed from data obtained with an anthropomorphic striatal phantom filled with 123-I. From the simulations, we demonstrate that contrast as a function of noise and lesion detectability are very similar for both OSEM-3D and OSEM-R methods. In the experimental study, we obtained very similar values of activity-quantification ratios for different regions in the brain. The advantage of OSEM-R compared to OSEM-3D is a substantial gain of processing time. This gain depends on several factors. In a typical situation, for a 128 x 128 acquisition of 120 projections, OSEM-R is 13 or 25 times faster than OSEM-3D, depending on the calculation method used in the iterative restoration. In this paper, the OSEM-R method is tested with the approximation of depth independent resolution. For the striatum this approximation is appropriate, but for other clinical situations we will need to include a spatially varying response. Such a response is already included in OSEM-3D.     

Feasibility of a novel design of high resolution parallax-free Compton enhanced PET scanner dedicated to brain research

A novel concept for a positron emission tomography (PET) camera module is proposed, which provides full 3D reconstruction with high resolution over the total detector volume, free of parallax errors. The key components are a matrix of long scintillator crystals and hybrid photon detectors (HPDs) with matched segmentation and integrated readout electronics. The HPDs read out the two ends of the scintillator package. Both excellent spatial (x, y, z) and energy resolution are obtained. The concept allows enhancing the detection efficiency by reconstructing a significant fraction of events which underwent Compton scattering in the crystals. The proof of concept will first be demonstrated with yttrium orthoaluminate perovskite (YAP):Ce crystals, but the final design will rely on other scintillators more adequate for PET applications (e.g. LSO:Ce or LaBr3:Ce). A promising application of the proposed camera module, which is currently under development, is a high resolution 3D brain PET camera with an axial field-of-view of approximately 15 cm dedicated to brain research. The design philosophy and performance predictions based on analytical calculations and Monte Carlo simulations are presented. Image correction and reconstruction tools required to operate this transmissionless device in a research environment are also discussed. Better or similar performance parameters were obtained compared to other known designs at lower fabrication cost. The axial geometrical concept also seems to be promising for applications such as positron emission mammography.     

High resolution MR based polymer dosimetry versus film densitometry: a systematic study based on the modulation transfer function approach

Precise methods of modem radiation therapy such as intensity modulated radiotherapy (IMRT), brachytherapy (BT) and high LET irradiation allow for high dose localization in volumes of a few mm3. However, most dosimetry methods-ionization chambers, TLD arrangements or silicon detectors, for example-are not capable of detecting sub-mm dose variations or do not allow for simple dose imaging. Magnetic resonance based polymer dosimetry (MRPD) appears to be well suited to three-dimensional high resolution relative dosimetry but the spatial resolution based on a systematic modulation transfer function (MTF) approach has not yet been investigated. We offer a theoretical construct for addressing the spatial resolution in different dose imaging systems, i.e. the dose modulation transfer function (DMTF) approach, an experimental realization of this concept with a phantom and quantitative comparisons between two dosimetric systems: polymer gel and film dosimetry. Polymer gel samples were irradiated by Co-60 photons through an absorber grid which is characterized by periodic structures of different spatial period (a), the smallest one at width of a/2 = 280 microm. The modulation in dose under the grid is visualized via calibrated, high resolution, parameter-selective (T2) and dose images based on multi-echo MR imaging. The DMTF is obtained from the modulation depth of the spin-spin relaxation time (T2) after calibration. Voxel sizes below 0.04 mm3 could be achieved, which are significantly smaller than those reported in MR based dose imaging on polymer gels elsewhere, using a powerful gradient system and a highly sensitive small birdcage resonator on a whole-body 3T MR scanner. Dose modulations at 22% of maximum dose amplitude could be observed at about 2 line pairs per mm. The polymer DMTF results are compared to those of a typical clinical film-scanner system. This study demonstrates that MR based gel dosimetry at 200 microm pixel resolution might even be superior, with reference to relative spatial resolution, to the results of a standard film-scanner system offering a nominal scan resolution of 200 microm.