Cerebral blood flow volume measurements of the carotid artery and ipsilateral branches using two-dimensional phase-contrast magnetic resonance angiography

The optimal velocity encoding of phase-contrast magnetic resonance angiography （PC MRA） in measuring cerebral blood flow volume （BFV） ranges from 60 to 80 cm/s. To verify the accuracy of two-dimensional （2D） PC MRA, the present study localized the region of interest at blood vessels of the neck using PC MRA based on three-dimensional time-of-flight sequences, and the velocity encoding was set to 80 cm/s. Results of the measurements showed that the error rate was 7.0±6.0% in the estimation of BFV in the internal carotid artery, the external carotid artery and the ipsilateral common carotid artery. There was no significant difference, and a significant correlation in BFV between internal carotid artery ＋ external carotid artery and ipsilateral common carotid artery. In addition, the BFV of the common carotid artery was correlated with that of the ipsilateral internal carotid artery. The main error was attributed to the external carotid artery and its branches. Therefore, after selecting the appropriate scanning parameters and protocols, 2D PC MRA is more accurate in the determination of BFV in the carotid arteries.

Visibility in differential phase-contrast imaging with partial coherence source

This paper gives theoretical analysis of visibility of fringes, which is influenced by distances, temporal and spatial coherence of source, in hard x-ray differential phase-contrast imaging with microfocus x-ray source. According to the character of longitudinal periodicity of the interferogram, the setup is insensitive to mechanical drift and vibrations. The effect of temporal coherence of x-ray source is investigated and its related bandwidth is derived. Based on the theory of partially coherent light, it shows that the requirement for the spatial coherence of x-ray source is not strict and can be met by the general microfocus x-ray tube for x-ray differential phase-contrast imaging.

Anisotropic total variation minimization approach in in-line phase-contrast tomography and its application to correction of ring artifacts

In-line phase-contrast computed tomography（IL-PC-CT） imaging is a new physical and biochemical imaging method.IL-PC-CT has advantages compared to absorption CT when imaging soft tissues. In practical applications, ring artifacts which will reduce the image quality are commonly encountered in IL-PC-CT, and numerous correction methods exist to either pre-process the sinogram or post-process the reconstructed image. In this study, we develop an IL-PC-CT reconstruction method based on anisotropic total variation（TV） minimization. Using this method, the ring artifacts are corrected during the reconstruction process. This method is compared with two methods： a sinogram preprocessing correction technique based on wavelet-FFT filter and a reconstruction method based on isotropic TV. The correction results show that the proposed method can reduce visible ring artifacts while preserving the liver section details for real liver section synchrotron data.

Quantitative assessment of physiological cerebrospinal fluid flow in the cervical spinal canal with 3.0T phase-contrast cine MRI

A total of 50 healthy volunteers aged between 18 and 54 years underwent phase-contrast cine MR to assess cerebrospinal fluid flow characteristics in different regions of the vertebral canal. The results revealed that the cerebrospinal fluid peak flow velocity and peak flow rate in the systolic phase were significantly greater than those in the diastolic phase at the same level in the subarachnoid space of the cervical spinal canal. The ventral peak flow velocity and peak flow rate were significantly greater than the post-lateral peak flow velocity and flow rate, while there were no differences between left and right post-lateral subarachnoid peak velocity and flow rate. Moreover, there were no significant differences in peak flow velocity and peak flow rate between the systolic and diastolic phases, ventral, right post-lateral or left post-lateral peak flow velocity and peak flow rate at the same level in the subarachnoid space of the cervical spinal canal among different age groups （18 24, 25 34, 35-44, ≥45 years）.

Optimal velocity encoding during measurement of cerebral blood flow volume using phase-contrast magnetic resonance angiography

This study investigated the effect of velocity encoding on measurement of brain blood flow and blood volume of inflow and outflow using phase-contrast magnetic resonance angiography. A single two-dimensional phase-contrast magnetic resonance angiography slice was applied perpendicular to the internal carotid artery and the vertebral artery at C2 level. For each subject, the velocity encoding was set from 30 to 90 cm/s with an interval of 10 cm/s for a total of seven settings. Various velocity encodings greatly affected blood flow volume, maximal blood flow velocity and mean blood flow velocity in the internal carotid artery, but did not significantly affect vertebral arteries and jugular veins. When velocity encoding was 60-80 cm/s, the inflow blood volume was 655 _＋ 118 mL/min, and the outflow volume was 506 _＋ 186 mL/min. The ratio of outflow/inflow was steady at 0.78-0.83, and there was no aliasing in any of the images. These findings suggest that velocity encodings of 60 80 cm/s should be selected during measurement of cerebral blood flow volume using phase-contrast magnetic resonance angiography.

Noise properties of multi-combination information in x-ray grating-based phase-contrast imaging

Grating-based x-ray phase contrast imaging has attracted increasing interest in recent decades as multimodal and laboratory source usable method.Specific efforts have been focused on establishing a new extraction method to perform practical applications.In this work,noise properties of multi-combination information of newly established information extraction method,so-called angular signal radiography method,are investigated to provide guidelines for targeted and specific applications.The results show that how multi-combination of images can be used in targeted practical applications to obtain a high-quality image in terms of signal-to-noise ratio.Our conclusions can also hold true for upcoming targeted practical applications such as biomedical imaging,non-destructive imaging,and materials science.

Effects of Tube Voltage on Phase-Contrast Imaging for Different Microfocus X-Ray Tubes

In the past decade, phase-contrast imaging (PCI) has become a hot research with an increased improvement of the image contrast with respect to conventional absorption radiography. In this paper, effects of tube voltage (kVp) on propagation-based phase-contrast imaging have been investigated with two types of microfocus x-ray tubes, a conventional sealed x-ray tube with the focal spot size of 13 - 20 μm and an open x-ray tube with minimum focal spot size less than 2 μm. A cooled x-ray CCD detector with the pixel size of 24 μm was used to acquire digital images. Two thin plastic sheets with different thickness were used as radiography phantoms. Two different phenomena were observed for the two x-ray tubes. For the open tube, phase-contrast effect has a slight drop with the increasing of tube voltage, however, it is opposite for the sealed tube. A further investigation indicates that the variation of focal spot size causes the abnormal result for the sealed tube. It also shows that phase-contrast effect is more sensitive to focal spot size than tube voltage.

Application of phase-contrast cine gnetic resonance imaging (MRI) in endoscopic aqueductoplasty

Objective To evaluate the application of phasecontrast cine magnetic resonance imaging (MRI) in endoscopic aqueductoplasty for patients with obstructive hydrocephalus. Methods The clinical diagnosis of hydrocephalus due to aqueduct obstruction in 23 patients was confirmed by phase contrast cine MRI examination.

In-line X-ray phase-contrast imaging of murine liver microvasculature ex vivo

Imaging blood vessels is of importance for determining the vascular distribution of organs and tumors.Phase-contrast X-ray imaging can reveal the vessels in much more detail than conventional X-ray absorption method.Visualizing murine liver microvasculature ex vivo with phase-contrast X-ray imaging was performed at Shanghai Synchrotron Radiation Facility.Barium sulfate and physiological saline were used as contrast agents for the blood vessels.Blood vessels of <Φ20μm could be detected by replacing resident blood with physiological saline or barium sulfate.An entire branch of the portal vein (from the main axial portal vein to the ninth generation of branching) could be captured in a single phase-contrast image.It is demonstrated that selective angiography based on phase contrast X-ray imaging,with a physiological material of low Z elements (such as saline) being the contrast agent,is a viable imaging strategy.Further efforts will be focused on using the technique to image tumor angiogenesis.

A new method of detecting interferogram in differential phase-contrast imaging system based on special structured x-ray scintillator screen

An x-ray scintillator screen with a special structure, functioning as detector and analyser grating, was proposed for collecting the interferogram of differential phase contrast imaging without absorption grating and difficulty of fabrication by a state of the art technique. On the basis of phase grating diffraction, a detecting model of the scintillator screen was built for analysing the phase and absorption information of objects. According to the analysis, a new method of phase retrievals based on two-images and the optimal structure of screen were presented.

Computational Fluid Dynamics and Its Impact on Flow Measurements Using Phase-Contrast MR-Angiography

Rationale and Objectives: Computational fluid dynamic (CFD) simulations are discussed with respect to their potential for quality assurance of flow quantification using commercial software for the evaluation of magnetic resonance phase contrast angiography (PCA) data. Materials and Methods: Magnetic resonance phase contrast angiography data was evaluated with the Nova software. CFD simulations were performed on that part of the vessel system where the flow behavior was unexpected or non-reliable. The CFD simulations were performed with in-house written software. Results: The numerical CFD calculations demonstrated that under reasonable boundary conditions, defined by the PCA velocity values, the flow behavior within the critical parts of the vessel system can be correctly reproduced. Conclusion: CFD simulations are an important extension to commercial flow quantification tools with regard to quality assurance.

Differential diagnosis of arachnoid cyst from subarachnoid space enlargement by phase-contrast cine MRI

Objectives To reveal the relationship of brain motion and cerebrospinal fluid (CSF) flow by phase-contrast cine MRI, and to evaluate this technique in differentiating between arachnoid cysts and subarachnoid space enlargement. Methods Using a phase-contrast cine MRI pulse sequence, we measured brain motion and CSF flow during the cardiac cycle in 10 healthy volunteers and 10 patients with MRI-suspected arachnoid cyst or subarachnoid space enlargement. CSF stroke volume curve was illustrated according to flow quantification, and time-signal intensity curve was traced. The two curves were compared. Results This study showed that brain motion was due to the volume difference between arterial and venous blood flow during a cardiac cycle, and thus drives CSF pulsation. Arachnoid cysts and subarachnoid space enlargement carried different curve patterns, demonstrating that phase-contrast MRI and flow quantification can be a useful and reliable technique for non-invasive evaluation of brain motion and CSF flow. Conclusion Arachnoid cysts can be successfully differentiated using phase-contrast cine MRI from subarachnoid space enlargement.

Enhanced quantitative X-ray phase-contrast images using Foucault differential filters

Several X-ray phase visualization methods are being real- ized for imaging of phase objects, such as biological and polymeric specimens. Grating-based phase-contrast imaging using a source-grating-attached X-ray tube that provides partially coherent X rays is one of the most successful methods in this field.

Phase-contrast Imaging Simulation Based on a Micro-CT System

Propagation-based phase-contrast imaging was simulated based on paraxial Fresnel-Kirchoff diffraction integral and spherical wave illumination. Under a developed micro-CT system parameters, the effects of focal-spot size and imaging geometry on phase-contrast imaging have been investigated using a 2-mm-thickness polystyrene edge phantom. An equivalent mono-energy was used to substitute the polychromatic spectrum of the micro-focus X-ray source. To consider effects of focal-spot size and detector resolution, the obtained phase-contrast image with an ideal point source was convolved with source intensity distribution and point spread function of detector. Simulations show reasonable influences of the two parameters which are in good agreement with experimental results.

Optimization of the in-line X-ray phase-contrast imaging setup considering edge-contrast enhancement and spatial resolution

Employing the approximation theory based on refraction and the definition of the total pointspread-function of the imaging system, the variation in the edge contrast of simple model samples is discussed with different source-to-sample and sample-to-detector distances, which actually means different spatial resolutions of the imaging system. The experiments were carried out with the Beamline 4W1A imaging setup at the Beijing Synchrotron Radiation Facility for simple model and insect samples. The results show that to obtain clear phase-contrast images of biologic tissues for the X-ray in-line imaging setup, with determined parameters such as the size of the X-ray source, the pixel size of the detector and the fixed source-to-sample distance, there is a range of optimized sample-to-detector distances. The analysis method discussed in this article can be helpful in optimizing the setup of X-ray in-line phase-contrast imaging.

An Improved Phase Retrieval Algorithm for X-ray In-line Phase-Contrast Imaging

Phase contrast imaging technique has been improved promptly in recent years. Among these techniques in-line phase-contrast imaging is widely used. Various algorithms for in-line phase retrieval have been proposed so far such as TIE(transport of intensity equation), CTF(contrast transfer function), first born-approximations, GSF(Gerchberg-Saxton-Fienup), etc. Bronnikov's algorithm(BA) is a type of linear algorithm that is simple and efficient. But it can only be used without absorption situations. In this paper, an improved algorithm based on BA was presented. The approach adds Δφ(x,y) to the phase map φ_b(x,y) retrieved by BA to make the reconstructed phase map more precise. Further, the approach was evaluated on simulated images and confirmed to be accurate at higher absorption rates.

Cine PC-MRI技术在Arnold-Chiari畸形手术疗效评估中的应用

目的探讨相位对比电影-磁共振成像(Cine PC-MRI)技术在小脑扁桃体下疝(Arnold-Chiari)畸形手术疗效评估中的应用。方法选取2018年8月—2022年9月期间多中心收集的65例行Arnold-Chiari畸形手术治疗的患者作为研究对象。术后均随访6个月。比较患者术前、术后6个月的预后、生活质量、寰齿间距(ADI)值、脊髓空洞直径、后颅窝斜坡长度、枕骨大孔横径、后颅窝高径长度及脑脊液流速,随访期间的并发症情况。结果术后6个月,患者芝加哥Chiari结果量表(CCOS)评分及健康相关生活质量评分(HRQoL)高于术前(P<0.05);随访期间,有3例进行枕大池重建术的患者伤口发生脑脊液漏,给予腰大池引流,7d后伤口愈合良好。术后6个月,患者寰齿间距(ADI)值及脊髓空洞直径低于术前;后颅窝斜坡长度及后颅窝高径长度长于术前;桥脑延髓池层面、中脑导水管层面及颈椎间盘层面的每搏输出量(SV)、平均流量(MF)均高于术前;头向峰值流速(Vumax)、足向峰值流速(Vdmax)均低于术前(P<0.05)。结论Arnold-Chiari畸形患者经外科手术治疗可有效改善预后并提高生活质量,但行枕大池重建术时要注意防范脑脊液漏的发生,而Cine PC-MRI技术可为Arnold-Chiari畸形患者手术治疗疗效评估提供有效依据。

对比增强SWI对不同病理类型肺癌脑转移瘤的诊断价值

目的:探讨对比增强磁敏感加权成像(CE-SWI)与常规对比增强T 1WI成像(CE-T 1WI)对不同病理类型肺癌脑转移瘤的检出率差异,分析脑转移瘤内出现对比剂诱导相移(CIPS)与原发性肺癌病理类型间的关联性。方法:搜集经病理证实的79例原发性肺癌患者,其中腺癌组40例,鳞癌组18例,小细胞癌组21例,均行颅脑MR常规平扫、SWI、CE-T 1WI及CE-SWI检查,比较CE-SWI与CE-T 1WI检出的脑转移瘤数目及转移瘤内是否存在CIPS,转移灶经3个月后随访证实。结果:CE-T 1WI与CE-SWI对腺癌脑转移瘤的检出率差异有统计学意义(χ^(2)=5.05,P=0.025),对鳞癌(χ^(2)=0.00,P=1.000)与小细胞癌(χ^(2)=0.27,P=0.603)脑转移瘤的检出率差异无统计学意义。腺癌组、鳞癌组、小细胞癌组三组间CIPS阳性率差异有统计学意义(χ^(2)=11.13,P=0.004),其中鳞癌组与腺癌组(χ^(2)=11.08,P=0.001)、鳞癌组与小细胞癌组(χ^(2)=8.26,P=0.004)间差异有统计学意义,腺癌组与小细胞癌组间差异无统计学意义(χ^(2)=0.131,P=0.717)。结论:CE-SWI对肺腺癌脑转移瘤的检出较CE-T 1WI更有优势。肺腺癌、小细胞癌脑转移瘤的CIPS阳性率较鳞癌显著增高,CE-SWI可为肺癌脑转移瘤MRI检查常规序列的有利补充,为临床诊疗提供更多重要参考信息。

7T磁共振成像在脑小血管病中的应用进展

脑小血管病在老年人群具有很高的发病率,可显著增加脑卒中和痴呆的发生风险。迄今为止,该疾病尚无有效的临床和体液生物标志物,诊断鉴别高度依赖于MRI。然而,由于临床影像的空间分辨率所限,脑小血管损害难以直接评价,因此研究者们主要使用一些反映脑实质损害的影像标志物来评估小血管损伤。近年来,随着超高场(7T)MRI技术的不断成熟,其在脑小血管病领域的研究亦日趋广泛。7T-MRI能够直接评估脑小血管结构、功能,并显著提高微小脑实质病灶的检测敏感性,为脑小血管病机制研究和精准诊断提供了重要工具。本文将回顾近年来基于7T-MRI的脑小血管病研究,并讨论潜在的问题和未来研究方向,为相关研究工作者提供借鉴。

基于最大对比度的联合相位误差校正方法

针对高分辨率逆合成孔径雷达(ISAR)成像过程中,因目标转动所引入的转动相位误差无法被忽略,以及由于转动相位误差使得传统平动相位误差校正方法性能严重下降的问题,提出了一种基于最大对比度的联合相位误差校正的方法,可同时校正残余的平动相位误差和转动相位误差,进一步提高成像的质量。首先利用传统的运动补偿方法对回波信号进行处理,其次根据最大对比度准则,将相位误差校正问题转化为最大对比度优化问题,最后利用改进的拟牛顿算法进行求解。该方法能使高分辨率ISAR进行精准成像,且所得图像聚焦效果良好。通过对仿真数据和实测数据的处理,验证了文中方法的有效性。