缺血性脑卒中的血氧水平依赖磁共振成像研究进展

缺血性脑卒中具有高发病率、高病死率、高致残率的特点[1],因而早期发现具有脑卒中风险的人群,并及时进行干预治疗,对脑卒中患者具有重要的意义。血氧水平依赖磁共振成像(blood-oxygenation-level-de-pendent MRI,BOLD MRI)可以反映局部脑组织氧代谢与氧供应间的差异,通过测量大脑氧代谢率和氧摄取分数,实现对脑缺血状态的监测,早期发现脑卒中并可以对治疗后的疗效进行评估。本文对缺血性脑卒中的 BOLD MRI 研究进展进行综述和讨论。     

Urinary tract imaging by nuclear magnetic resonance

Nuclear magnetic resonance scanning has already found application in the urinary tract in man. It is a method of producing diagnostic images from the radiofrequency signals which can be elicited from hydrogen nuclei when the abdomen is placed in a strong magnetic field and subjected to pulses of RF energy. Computer-generated images depict the distribution of signal-emitting nuclei, modified by their relaxation times and macroscopic motion. The images are tomographic and have great potential flexibility in plane orientation. Normal anatomy, space-occupying lesions and lesions characterized by local edema have been visualized to date, and as clinical experience is accumulated, a much greater range of pathology promises to be detectable by this technique.     

Urinary tract imaging by nuclear magnetic resonance

Nuclear magnetic resonance scanning has already found application in the urinary tract in man. It is a method of producing diagnostic images from the radiofrequency signals which can be elicited from hydrogen nuclei when the abdomen is placed in a strong magnetic field and subjected to pulses of RF energy. Computer-generated images depict the distribution of signal-emitting nuclei, modified by their relaxation times and macroscopic motion. The images are tomographic and have great potential flexibility in plane orientation. Normal anatomy, space-occupying lesions and lesions characterized by local edema have been visualized to date, and as clinical experience is accumulated, a much greater range of pathology promises to be detectable by this technique.     

Burn injury by nuclear magnetic resonance imaging

Nuclear magnetic resonance imaging has become a standard diagnostic procedure in clinical medicine and is well known to have hazards for patients with pacemaker or metallic foreign bodies. Compared to CT, the frequency of MRI examinations is increasing due to the missing exposure of the patients by X-rays. Furthermore, high-field magnetic resonance tomograph (MRT) with 3 T has entered clinical practice, and 7-T systems are installed in multiple scientific institutions. On the other hand, the possibility of burn injuries has been reported only in very few cases.Based on a clinical finding of a burn injury in a 31-year-old male patient during a routine MRI of the lumbar spine with standard protocol, the MR scanner was checked and the examination was simulated in an animal model.The patient received a third-degree burn injury of the skin of the right hand and pelvis in a small region of skin contact. The subsequent control of the MRI scanner indicated no abnormal values for radiofrequency (RF) and power. In the subsequent animal experiment, comparable injuries could only be obtained by high RF power in a microwave stove.It is concluded that ‘tissue loops’ resulting from a contact between hand and pelvis must be avoided. With regard to forensic aspects, the need to inform patients of such a minimal risk can be avoided if the patients are adequately positioned using an isolating material between the hands and pelvis. These facts must be emphasized more in the future, if high-field MRI with stronger RF gradients is available in routine imaging.     

磁共振测定颈动脉粥样硬化特征与急性脑梗死的关系

目的:应用3.0T磁共振测定颈动脉斑块负荷、成分与急性脑梗死的发生及梗塞体积的相关性。方法:对62例急性颈内动脉供血区脑梗死患者行颈动脉血管壁磁共振检查,测量颈动脉管腔狭窄率和斑块负荷(最大管壁厚度及管壁体积标准化指数),评价斑块成分(坏死脂核,出血,钙化及纤维帽破裂),测得DWI急性脑梗死体积,计算OR值和Spearman秩相关系数。结果:症状侧颈动脉狭窄程度、最大管壁厚度、管壁体积标准化指数和斑块内出血、钙化和纤维帽破裂的发生率均高于非症状侧(P值均<0.05);症状侧颈动脉管壁体积标准化指数与同侧颈内动脉供血区急性脑梗死体积有较强的正相关(Spearman秩相关系数0.327,P<0.05)。斑块内出血和钙化是较强的急性脑梗死暴露因素(OR值分别为2.4和2.1,P值均<0.05)。结论:症状侧与非症状侧颈动脉斑块特征存在差异,且与急性脑梗死存在相关,提示这些特征可能为斑块不稳定重要因素。     

MRI评价缺血半暗带的研究进展

急性缺血性脑卒中（AIS）具有发病率高、病死率高、致残率高和复发率高的主要特点。缺血脑组织的影像研究对AIS病人的早期诊断和再灌注治疗有重要意义。介绍多种MR新技术对缺血组织进行评估的原理、方法和各自的优劣，并讨论评价缺血半暗带的MR参数及阈值。就国内外研究如何采用各种MR成像新序列对急性缺血性脑卒中进行诊断并鉴别缺血半暗带和梗死核心予以综述。      

Comparison of perfusion computed tomography with diffusion-weighted magnetic resonance imaging in hyperacute ischemic stroke

OBJECTIVE: In this study, perfusion CT and diffusion-weighted magnetic resonance imaging (DWI) were compared as means of assessing the ischemic brain in hyperacute stroke. METHODS: Twenty patients with ischemic stroke underwent perfusion computed tomography (CT) and magnetic resonance imaging (MRI) studies <3 hours after stroke onset. Cerebral blood flow thresholds were used to delineate the ischemic lesion, penumbra, and infarct. Correlations between the volume of the hypoperfused areas, the abnormality volume in admission DWI and follow-up CT/MRI studies, and the clinical National Institutes of Health Stroke Scale (NIHSS) scores were performed. RESULTS: The volume of the ischemic (core and penumbra) lesion on admission perfusion CT was correlated with the volume of admission DWI abnormalities (r=0.89, P=0.001). The infarcted core tissue volume (on admission CT) correlated more strongly (r=0.77, P=0.0001) than the admission DWI abnormality volume (r=0.69, P=0.002) with the follow-up infarct volume on fluid-attenuated inversion recovery images. A correlation was demonstrated between infarct volume in perfusion CT and follow-up DWI abnormality volume (r=0.89, r=0.77, P=0.002). Significant correlations were found between ischemic and infarct region volumes in perfusion CT and NIHSS admission and follow-up scores (P < or = 0.01). CONCLUSIONS: Both imaging modalities provide a sufficient assessment of the hyperacute brain infarct, with significant correlation between them and the clinical condition at admission. Perfusion CT allows differentiation of the penumbra and infarct core region with significant predictive value of follow-up infarct volume and clinical outcome.     

Obstetrical magnetic resonance imaging: maternal anatomy

Eleven patients whose pregnancies were at 34-36 weeks of gestational development underwent magnetic resonance (MR) imaging. Images of the maternal pelvis were assessed for anatomical changes of pregnancy in comparison with MR images of five non-pregnant volunteers. The relationship of the fetal presenting part to the internal os of the cervix was seen in all patients. Effacement of the cervix was identified when present. The maternal spine demonstrated disk abnormalities in nine patients. Changes in venous flow patterns were readily identified in all patients. The inferior vena cava was flattened or obliterated, a high signal was present in the iliac vessels (TE 56), and large collateral vessels were present.     

Hepatic vascular anatomy on magnetic resonance imaging

This study evaluated the ability of magnetic resonance imaging (MRI) to depict the hepatic vasculature and surgical anatomy of the liver using the transaxial, coronal, and sagittal planes. Retrospective analysis of the abdominal MRI examinations of 94 patients was performed. The spin-echo imaging technique was used to obtain transaxial images in all patients and coronal and sagittal sections in 35 of these patients. Overall, the hepatic vasculature was better delineated on the longer repetition rates (2000 msec TR) and the first echo images (28 msec TE). The inferior vena cava, right and middle hepatic veins, and main and right portal veins were seen in 100% of the cases in the transaxial plane. The left hepatic vein was seen in 98%, the left portal vein in 93%, and the hepatic artery in 44% in the transaxial plane. In the sagittal and coronal planes, the inferior vena cava and main and right portal veins were seen in 100% of cases. The other hepatic vasculature was less frequently demonstrated. In the sagittal plane, the right hepatic vein was seen in 85% of the cases, the left hepatic vein in 62%, the middle hepatic vein in 90%, the left portal vein in 90%, and the hepatic artery in 14%. In the coronal plane, the right hepatic vein was seen in 85% of cases, the left hepatic vein in 14%, the middle hepatic vein in 79%, the left portal vein in 71%, and the hepatic artery in 7%. These results are from preliminary work. Further developments with MRI technology may render better visualization of hepatic vasculature.     

Diffusion weighted magnetic resonance imaging in stroke

Diffusion weighted magnetic resonance imaging has evolved from an esoteric laboratory experiment to a critical aspect of routine clinical care of the patient presenting with symptoms suspicious of acute ischemic stroke. The purpose of this article is to review the basis of diffusion weighted imaging (DWI), to consider its application in acute stroke and to recognize potential pitfalls and stroke mimics that might be encountered. Included in the discussion are comments on the elimination of 'T2 shine through' phenomena as well as construction of pixel-by-pixel maps of the apparent diffusion coefficient (ADC). Furthermore, discussion of techniques such as parallel imaging (using SENSE) and PROPELLER sequences will be introduced as methods potentially allowing DWI to be utilized in areas usually associated with prohibitive susceptibility artifact (e.g. the base of the brain). Finally, the concept of interventional therapeutic approaches to salvaging ischemic tissue is introduced, both in terms of the ischemic penumbra (defined by a diffusion/perfusion mismatch) and also in terms of the potential reversibility of the diffusion-weighted hyperintensity, associated with the lesion core.     

Obstetrical magnetic resonance imaging: fetal anatomy

Nine patients who were 34-36 weeks pregnant underwent magnetic resonance (MR) imaging. Sagittal images using spin echo technique (TR 2.0 sec, TE 28 msec) were optimal for delineating fetal anatomy. The fetal cardiovascular, pulmonary, and central nervous systems were depicted in all cases. The heart and major vessels were readily seen due to the natural contrast of flowing blood. The intensity of the fluid-filled lungs greatly increased with a longer TR or TE, delimiting thorax from liver. The brain was relatively featureless due to the lack of gray-white matter differentiation. The umbilical cord within the amniotic fluid and its insertion into the placenta and fetus was identified in all cases. MR is a new modality for fetal imaging that offers tissue-characterization information that complements the superior anatomic detail of ultrasound scanning.     

Improvements in snap-shot nuclear magnetic resonance imaging

New variants of the ultra-high-speed echo-planar imaging technique have been used to obtain snap-shot images of adult patients and volunteers at 0.1 T. Modified pulsed-gradient sequences together with non-linear signal sampling and activity screened gradients have greatly improved the image quality obtainable by single-shot methods. A particular variant, modulus blipped echo-planar single-pulse technique (MBEST), although slightly slower than the blipped echo-planar single-pulse technique (BEST), is experimentally more robust and incorporates intrinsic T2 weighting. An account of these improvements together with some experimental results is presented.     

Tomographic imaging with nuclear magnetic resonance

A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR). Resonant frequency is proportional to magnetic field strength, so that spatial resolution is achieved by frequency selection and magnetic field shaping. The results of scanning a phantom and two rats are presented.