1. 简介 Introduction
2. 组织磁共振信号 Tissue MR signal: 要素 essentials
3. 脉冲序列 Pulse Sequences
4. 原发性颅内出血 Primary intracerebral hemorrhage
5. 血管畸形破裂 Ruptured vascular malformation
7. 硬膜下血肿 Subdural hematoma
6. 继发性出血 Secondary hemorrhage: 梗塞形成 Infarction, 肿瘤形成 Neoplasia。
对怀疑脑出血的患者进行影像学检查的主要目的是获得确切的具有病理学特征的证据。对急性出血的迅速诊断是采取正确治疗的关键一步。zh正确的判定一些潜在的病理学因素，如肿瘤，血管畸形或梗塞在治疗过程中也具有同等的重要性。 由于CT对于急性病变可以提供确切的影像学证据，因此它的应用对于诊断和治疗脑出血有着重要意义。由于它具有操作简单，适用性强，结果明了的优点，因此许多医院将它作为标准的诊断手段。 由于磁共振成像更加易于操作，脉冲序列对出血的高明感性成为标注化，磁共振相对于CT的优越性变的更加突出。磁共振的优点主要集中与：显示多层面病理解剖，多参数显示，包括对血管的化学成分的逐级的退化，同时它能够生成头颈部的血管系统影像。
The major imaging goal in suspected cerebral hemorrhage is complete sensitivity with high pathologic specificity. Accurate identification of acute hemorrhage is a critical step in planning appropriate therapy; the correct characterization of underlying pathology, such as neoplasia, vascular malformation, or infarction, is often of equal importance. The introduction of x-ray computed tomography (CT) significantly altered the clinical approach to cerebral hemorrhage by providing high sensitivity to acute lesions. This method remains the standard in many institutions because it is readily available, applicable to almost any patient, and produces results which are relatively easy to interpret. As proton magnetic resonance (MR) imaging becomes more readily available, and as pulse sequences optimally sensitive to hemorrhage become standardized, its advantages over CT will be more important. The major advantages of MR are: multiplanar display of pathoanatomy, the multiparametric nature of MR, including its sensitivity to the step-wise chemical degradation of blood, and its ability to produce images of the cerebral and cervical vasculature, magnetic resonance angiography (MRA).
磁共振中的信号根据所用脉冲的顺序以及所要成像组织的类型分为高信号或低信号（亮或者暗）。以下是一个各种组织分别在T1及T2加权像上如何显现的简要介绍。
Signal in MR images is high or low (bright or dark), depending on the pulse sequence
used, and the type of tissue in the image. The following tables are a general guide to how
tissue appears on T1- or T2- weighted images.
T1加权像中的暗影 Dark on T1-weighted image:
T1加权像中的亮影 Bright on T1-weighted image:
T2加权像中的亮影 Bright on T2-weighted image:
三脉冲序列策略被常规用于脑出血内部及周围病变改变的影像显示: 其中两个产生常规回波脉冲(SE), 第三个就是所谓的梯度脉冲(GE)。
Three pulse sequence strategies are routinely employed for the demonstration of signal alterations within and around a cerebral hemorrhage: two produce conventional spin echoes (SE), the third a so- called gradient echo (GE).
1) 短TR,短TE回波脉冲(或短TI,短TE 整合反转恢复回波脉冲) 影像主要用于显示高信号，这种信号常是病变爆发后产生，最早10小时，但典型是2-3天。并且高信号可持续几周甚至几个月。这种信号产生的化学基础是在某种pH条件下血色素自动氧化的产物高铁血红素。
Short TR, short TE spin echo (or short TI, short TE composite inversion recovery (IR) spin echo) images are used to demonstrate the high signal that develops at some time after the ictus, as early as 10 hours but typically 2-3 days, and persists for a variable length of time, from a few weeks to a few months. The chemical substrate of this signal has been postulated to be methemoglobin, the auto-oxidation product of hemoglobin under certain pH conditions.
2) 对怀疑有急性出血的患者，长TR，长TE信号影像对于显示整个病变的范围，包括由于梗塞，肿瘤，胶质细胞增生，或其它原发或继发的急性水肿引起的出血邻近的区域异常亮信号的显示起着很关键的作用。急性的血肿可能会有高，低或混合信号，这取决于患者的年龄，红细胞比容，局部的pH和氧分压以及成像系统的磁场强度。 对于磁场强度较高的磁共振系统(1.0 - 1.5 T), 这种影像在病变的部分有显著的信号丢失，(丢失程度与与场强平方成比例)，原因是出血组织的异常磁化。 磁化是磁场同象中止的反映。这种中止在在脑出血的病变部位的影像上是黑影。 有报道说还原型血红蛋白会增加磁化率，但在急性出血过程中化学变化非常复杂，这也是观察到的信号变化可变性的反映。所以，在在场强最高的时候，血块的中心可能会有低信号区，这是由于还原型血红蛋白的存在或是细胞内氧化型血红蛋白的存在造成得。
In the patient suspected of having acute hemorrhage, long TR, long TE images are critical for demonstration of the overall extent of the lesion, including those regions adjacent to the hemorrhage which are abnormally bright because of infarction, neoplasia, gliosis, other primary pathology or secondary acute edema. An acute hematoma may have high, low or mixed signal, depending on its age, its hematocrit, the local pH and oxygen tension, and the field strength of the imaging system. With higher field MR systems (1.0 - 1.5 Tesla), such images have significant signal loss (proportional to the square of the field strength) in portions of the lesion because of the abnormal magnetic susceptibility of hemorrhagic tissue. Magnetic susceptibility is a reflection of local interruptions of the homogeneity of the magnetic field, and such interruptions produced in parts of a hemorrhagic lesion make the image black. Deoxyhemoglobin has been reported to contribute to the increased magnetic susceptibility, but the chemistry of acute hemorrhage is extremely complex and this is reflected in the variability of observed signal changes. Thus, at highest field strengths, the core of the clot may have low signal, due to the presence of deoxyhemoglobin or of intracellular methemoglobin.
亚急性或慢性出血包含一定量的含铁血黄素，主要是溶酶体内以晶体形式存在的亚铁血黄素。这种物质被认为是制造了磁化并导致了长TR (SE)信号影像上信号的丢失。在血管畸形的影像中，由于流空效应产生的影像是诊断的一个线索。这种现象在长TR (SE)信号影像上可以清楚地观察到。
Subacute and chronic hemorrhage contains variable amounts of hemosiderin, the intralysosomal crystalline storage form of heme iron. This substance is thought to produce a magnetic susceptibility effect and consequent signal loss on long TR (SE) images. In cases of vascular malformation, the presence of a signal void caused by vascular structures containing flowing blood is a clue to the diagnosis. Such flow voids are best seen on long TR SE images.
3) 为了获得磁化时出血引发的改变，有必要使用GE技术进行快速成像。 这种方法的射频脉冲小于90度，不需要重聚焦。（180度度脉冲可以使用，成像过程中形成的回声是梯度“回声”－由扫描梯度过程中产生的。） GE 影像是T2像的必要组成部分，属于横向弛豫时间。 也就是说信号强度要受真实组织的横向弛豫(T2)和磁场中的多相性影响，这种多相性是由组织或成像系统产生的。 即使在低场强中GE影像对于急性出血具有较高的敏感性。 GE影像一个重要的特点是具有很低的采集时间(以秒计)。这在患者一旦由于急性脑出血而不能配合检查时就显得格外重要，如果对这些患者使用使用传统的成像技术，图像质量经常会由于人为的活动而降低。并且GE影像还具有非常，这种短的TE信号经常会用于对流动的物体产生高信号，即所谓的流动增强影像。 这种技术也常用于磁共振血管造影信号中。
In order to maximize sensitivity to hemorrhage-induced alterations in magnetic susceptibility, rapid images can be acquired using the GE technique. In this method, the excitation RF pulse is less than 90? no refocusing (180? pulse is applied, and the echo formed during imaging is a gradient "echo" --brought about by reversal of the read gradient. GE images are essentially maps of T2*, the observed transverse relaxation time. That is, signal intensity is affected by true tissue transverse relaxation (T2) and by inhomogeneities in the magnetic field -- produced by the tissue or the imaging system. GE images have very high sensitivity to acute hemorrhage even at lower field strengths. An important feature of GE images is the very low acquisition time (seconds). This is a significant advantage in cases of acute hemorrhage in which the patient is unable to cooperate; conventional spin-echo images of such patients are often degraded by motion artifact. Moreover, GE images with a very short TE (ca. 12 msec) may be used to produce high signal corresponding to flow, so-called flow-enhanced images. Such phenomena are also responsible for MRA signal.
脑出血影像的时间依赖性的改变往往会出现在血色素有变化的区域，这种变化则是由于局部红细胞压积，pH值，和氧分压的变化所造成得。在这种条件下，由于分子环境的变化而改变了亚铁血红素原子核中不成对电子的数量，同时，由于化学变化而使不成对电子进入核内的能力降低或减弱。在体内，从血管中溢出的动脉血含有的大量氧和血红蛋白首先被去氧，接着自动氧化形成高铁血红蛋白。当网状内皮组织对出血，含铁血黄素以及以晶体形式储存的亚铁血红素产生反应时，就会刺激巨噬细胞和星形胶质细胞清除脑内的含铁血黄素，这一过程的速度取决于患者本身动员和激活吞噬功能的能力。在这一复杂过程中磁共振信号变化所代表的精确含义及化学变化还没有被证实，并且使用体外数据来解释生存患者的磁共振影像也不恰当。将来采用恰当的脉冲序列或许会提高对这一化学变化的认识。
Time-dependent changes in cerebral hemorrhage are to be expected in regions where changes in the hemoglobin molecule occur due to local alterations in hematocrit, pH, and oxygen tension. Under these conditions, the changing molecular environment produces alterations in the number of unpaired electrons in the heme nucleus as well as chemical changes that make the unpaired electrons more or less accessible to protons. In vivo, extravasated arterial blood, containing mostly oxyhemoglobin, is first deoxygenated, then undergoes auto-oxidation to methemoglobin. As the reticuloendothelial system begins to react to the hemorrhage, hemosiderin, the crystalline storage form of heme iron, begins to accumulate in macrophages and astrocytes. The pace of this process depends on the ability of a given patient's immune system to mobilize and activate cells which provide this scavenger function; over many years, hemosiderin is removed from the brain. The precise correspondence of MR signal changes and chemical changes in this complex process has not yet been verified, and the use of in vitro data to explain MR signals in live patients may not be entirely appropriate. In the future, proper choice of pulse sequences will perhaps reflect an improved understanding of these chemical substrates.
高血压性脑出血 Hypertensive hemorrhage
多年来，高血压性脑出血一直是原发性颅内出血的最常见病因。但随着控制血压技术的逐渐提高，许多医疗中心已发现因为这一因素引发脑出血的几率正在降低，而淀粉样血管病的引发的脑出血却日见常见。尽管高血压性脑出血和脑梗塞伴发继发性脑出血均与慢性动脉高压均有密切联系，但二者必须从病理解剖学和组织病理学上加以区别。慢性高血压伴有显微镜下血管病变即Charcot- Bouchard病变或动脉瘤时，是比较严重的。这些病变所处的位置就是原发性高血压性脑出血中血管破裂的部位，而且经常位于灰质深部。 出血的解剖位置根据发作的频率高低依次为壳，丘脑，小脑以及脑桥。
For many years hypertensive hemorrhage was unquestionably the most common cause of primary intracranial bleeding. With improved control of blood pressure, many centers have found this entity to be declining in incidence, with hemorrhage due to amyloid angiopathy (see below) now seen more commonly. Primary hypertensive hemorrhage must be distinguished from cerebral infarction with secondary bleeding on both pathoanatomic and histopathologic grounds --despite the strong association of both with chronic arterial hypertension. Severe, chronic hypertension is associated with microscopic vascular lesions called Charcot- Bouchard or miliary aneurysms. These lesions are the site of vascular rupture in primary hypertensive hemorrhage and are concentrated in the deep grey matter. The common anatomic sites of this type of hemorrhage are, in order of frequency: putamen, thalamus, cerebellum and pons.
以下是高血压性脑出血发生时的基本过程：动脉血压瞬时升高后血管突然破裂而产生一短暂出血期。血液渗入组织并积聚直至颅内压升高后会抑制进一步的出血，并限制病变的范围。在没有进行磁共振检查之前，发生的许多组织学改变很大程度的影响到了最终得到的影像。脑实质和血管内皮的损害引发了水肿并进一步导致了脑结构之间的相互移位。X线衰减较多而磁共振高信号的区域代表水肿脑组织中所含有的水分。这在旋转－反射成像的图像中是最清楚的，但在T2加权GE像中也能观察到。在出血的部位经常可以看到一小部分病变包含着大部分浓缩的血细胞。 这一中心周围是损伤的组织和血液，这一区域的磁共振既有来自损伤脑组织水肿后产生的高信号，又有因局部血液聚集诱发的磁场多相性引起的质子散射而产生的低信号。在T2加权的SE和GE图像时所看到的低信号光晕是由于局部磁场梯度而导致T2缩短造成得。这种磁场梯度由于脑内组织类型的不同而产生的。GE影像对这种磁场有较高的敏感性，并且可以弥补光晕中的信号衰减。
The following sequence of events is postulated to occur in hypertensive hemorrhage: A transient elevation of arterial pressure leads to vessel rupture and a very brief period of actual bleeding. Blood dissects through the tissue and accumulates only until rising intracranial pressure results in tamponade of further bleeding, limiting the lesion size. During the period before MR image acquisition, numerous tissue changes occur that have an important impact on the appearance of images ultimately obtained. Brain parenchymal damage and vessel endothelial damage incite edema (cytotoxic and vasogenic) and consequent progressive displacement of adjacent brain structures, as seen in this case. Regions of lowest x-ray attenuation and high MR signal represent high water content in edematous non-hemorrhagic brain. This is best seen with spin-echo images, but is demonstrable with highly T2-weighted GE images as well. A small portion of the lesion, containing the most concentrated blood, is often seen within the hemorrhage. Surrounding this core is usually a mixture of damaged tissue and blood, and MR signal in this region is a combination of high signal from damaged edematous brain and low signal due to diffusion of protons through the local blood-induced field inhomogeneities. The low signal halo seen on T2-weighted SE and GE images represents T2* shortening that is due to local magnetic field gradients (susceptibility differences) produced by abrupt transition from one tissue type (edematous brain) to another (hemorrhagic brain). GE images are quite sensitive to such field inhomogeneities and demonstrate increasing signal loss in the halo with increasing TE.
淀粉样血管病 Amyloid angiopathy
七十年代中期，神经病理学家开始报道老年人的脑叶出血与脑内和脑膜中等血管上的淀粉沉积有密切关系。目前，脑内淀粉样血管病已被公认为是引起原发性颅内出血的主要病因，尤其在老年和血压正常的人群中中多发。淀粉是一种分子量为4200Da的蛋白质，它可以渗透到血管壁内，替代平滑肌细胞，而使血管壁变脆。它具有特殊的折光性并与许多中枢神经系统疾病有关，包括阿尔兹罕默氏病，淀粉可能是致病因素之一。在正常老年人脑内也能发现淀粉沉积。淀粉样血管病引发的出血几乎都发生在皮层和皮层下白质，并且病变部位经常含有蛛网膜下腔血管的成分。最好发的部位是额叶和顶叶，最不易发生的部位是颞叶和枕叶。这些特点对于鉴别淀粉样血管病和高血压脑出血引发的脑出血有重要意义，后者常发生在脑内深部的灰质结构。
In the mid-1970's, neuropathologists began to report the strong association of lobar cerebral hemorrhage in elderly patients with the deposition of amyloid in medium-sized cortical and leptomeningeal vessels. Cerebral amyloid angiopathy is now accepted as a major cause of primary intracranial hemorrhage, particularly in those who are normotensive and elderly. Amyloid is a 4200 dalton protein that infiltrates vessel walls, replaces smooth muscle cells in the media, and may make the vessel structurally brittle. It has characteristic staining properties (apple green birefringence with Congo red staining viewed under polarized light) and has been associated with a large number of central nervous system diseases, including Alzheimer's disease, in which it may have a pathogenetic role. Amyloid is also found in brains of normal old people. Hemorrhage due to amyloid angiopathy almost always occurs in the cerebral cortex and subcortical white matter, and lesions often contain a component of subarachnoid blood. The most common anatomic sites are frontal and parietal lobes; the least common are temporal and occipital lobes. These features serve to distinguish amyloid from hypertensive hemorrhage, which usually affects deep grey structures.
CT上经常显示一个高信号衰减区外周围绕一圈低信号衰减光晕，这种影像与相应的出血和继发性水肿是相一致的。随应用磁共振技术的不同，MR影像上显示一大范围的密度影。例如：病变的中心在短TR、短TE影像上经常显示是一个不均匀的高信号区，这是脑实质出血后几天所表现出的特有磁共振影像特征，硬膜下出血的影像上也经常会有这种表现。
CT usually demonstrates a high attenuation region surrounded by a halo of abnormally low attenuation, consistent with acute hemorrhage and secondary edema, respectively. MR images demonstrate a large range of signal intensities, depending on the MR technique employed. For example, the core of the lesion is often a heterogeneous region of very high signal on the short TR, short TE image, an MR characteristic of parenchymal hemorrhage older than a few days; subdural blood can also have this MR appearance in these lesions.
长TR影像作为一种增加功能的TE，对病变中心显影更多的不均匀高信号区，这可能是源于出血产生的顺磁效应，即主要磁场的局部由于顺磁材料产生的磁性差异产生的一种结果。通过将短TE和长TE影像的比较(如: TE=40 相对 TE=80)可以看到这种现象的效果。在病变中心经过局部不均磁场80 ms发生的质子散射要比40 ms发生的多，所以许多含有质子旋转的影像会产生信号丢失。出血中心的周围是一圈高信号区，与水肿组织中的水在长T2中的影像是一致的。
Long TR images show greater signal heterogeneity within the lesion core as a function of increasing TE, probably because of the paramagnetic properties of hemorrhage: the main magnetic field is locally augmented by paramagnetic material and therefore a susceptibility difference is produced. The effect of this phenomenon can be appreciated by comparing the shorter with the longer TE images (e.g.: TE=40 versus TE=80). More proton diffusion through local field inhomogeneity has occurred in the lesion core after 80 ms than after 40 ms, and therefore more of the image contains proton spins that have lost phase coherence, resulting in signal loss. Surrounding the core of the hemorrhage is very high signal consistent with the long T2 of water in edematous tissue.
通过增加TE(如:TE = 12, 30 and 50 msec)产生的系列GE影像能够显示病变核心区域的信号衰减过程，还能显示硬膜下信号从高到低的变化。
Serial GE images acquired with increasing TE (e.g.:TE = 12, 30 and 50 msec), will demonstrate progressive signal loss within the lesion core and a change in the subdural signal from high to low. As in the SE images, but to a differing extent, signal intensity reflects the combined contributions of relaxation time and susceptibility difference.
磁共振由于对血管结构中的流动性物质有较高的敏感性，所以对怀疑有血管畸形患者进行无创性诊断时它具有很大的优越性。无论是否有临床出血病史，磁共振都可将有明显血管改变或无明显血管改变的病变显示出来。根据使用的磁共振技术和发病后的时间，可以从磁共振图像上观察到这种疾病的所表现出的多样性。
Partly because of high sensitivity to flow in vascular structures, MR represents a significant advance in the non-invasive assessment of patients suspected of vascular malformation. Lesions angiographically both evident and cryptic can be demonstrated by MR in cases with or without clinically documented hemorrhage. A variety of signal profiles may be seen in this disease, depending on the MR technique employed, and the time after ictus.
急性期(发病数小时内), T1加权像显示异常低信号；T2加权像显示异常高信号。GE图像中，经常可以看到不均匀密度信号影周围有一圈黑色包绕。
Acutely (within hours of the ictus), the T1-weighted images usually demonstrate abnormally low signal; the T2-weighted images abnormally high signal. On the GE images, one can often see a black rim that surrounds regions with heterogeneous signal intensity.
以下是新鲜血肿的影像学特点：1)明显病变内T1 和 T2弛豫时间延长，如TR SE 图像中的高信号。2)由于出血部位或出血部位与脑组织间的区域的磁性系数差异而产生的边缘效应，这些效应缩短了T2弛豫时间，但在GE影像中可以很清晰看到。高场强时，血块的中心在T2加权像上是低信号影，这是由于细胞内的高铁血红蛋白或还原型血红蛋白存在产生的。如果有脑室内出血并且发病后患者始终保持仰卧位，凝结的血块会形成一个侧脑室的模型。
To summarize, these are the image features of fresh hematoma: 1) prolongation of bulk T1 and T2 relaxation times within the clot evident usually as high signal on long TR SE images, and 2) edge effects due to differences in magnetic susceptibility within the hemorrhage or between hemorrhage and brain; these effects shorten T2* and are best demonstrated by the GE image. At highest field strengths, the core of the clot may have low signal on T2-weighted images, due to the presence of intracellular methemoglobin or of deoxyhemoglobin. If there is intraventricular bleeding, and if the patient has been maintained in the supine position since the ictus, the clot can form a cast of the lateral ventricles.
血肿实质周围部分的影像是病因学诊断的重要线索：一个的大的信号透空区周围散在若干小的信号透空区，这是AVM部分血流的影像。这些血管有可能在以后的血管造影上显示出来。应用短TE的GE图像对负载血流的结构(正常及异常的血管和中脑导水管)显示高信号，即所谓的血流增强影像。由于钙化也能形成长TR影像上的信号透空区，所以短TE的GE图像可以提供确认血流的来源确切证据。短TE的GE图像上的高信号焦点代表AVM中的血流，这也可作为支持诊断的依据。
Adjacent to the parenchymal hematoma is often the clue to the etiologic diagnosis: a large signal void, and/or several smaller ones nearby, reflect flow in portions of an AVM. These vessels may or may not ultimately be documented at angiography. GE images acquired with very short TE's often have high signal in flow-bearing structures (normal and abnormal blood vessels and the aqueduct of Sylvius), so-called flow enhanced images. Such images are an important source of confirmatory evidence of flow, since signal void seen on long TR images can arise for other reasons, principally calcification. The short TE GE can show a small focus of high signal representing flow within the AVM, a finding that supports the diagnosis.
磁共振常常可以显示血管造影所不能发现的AVM。AVM是一个由多种异常血管，胶质组织和沉积的血红素组成的混合体。 T1加权的IR影像显示一个明显低信号分界，结合T2加权像可以看到病变的中心呈现亮影，表明是由于胶质组织，血红素或水肿组织使T2弛豫时间延长所至。同时还能看到的一圈黑影代表慢性血肿或血红素的沉积。 磁共振无法显示这种病变周围的水肿。AVM中的血流在T2加权像上是一个信号透空区。短 TE GE 技术以及新近发展的MRA技术可以显示动脉血流，乙状窦，窦汇和四脑室流动的脑脊液。 并不是总能在影像上看到AVM中的血流，如果图片上看不出血流效应，就要考虑其它有可能的诊断，如低分化胶质瘤。
The angiographically cryptic AVM is often demonstrated by MR. These lesions are known to contain a mixture of abnormal vessels of various sizes, gliotic tissue, and hemosiderin. T1-weighted IR images show a sharply demarcated focus of low signal, while with T2-weighted images, the lesion center is bright, reflecting prolongation of T2 expected in gliotic, hemorrhagic, or edematous tissue; again a black halo can be seen which represents T2* shortening associated with chronic hemorrhage and is postulated to reflect hemosiderin deposition. There is usually no MR evidence for acute edema surrounding theses lesions. Flow in the AVM itself can be seen as a signal void on T2-weighted images. The short TE GE technique, or more recently developed MRA methods, demonstrates flow in arteries, sigmoid sinuses and torcula, and flowing CSF in the upper fourth ventricle. Flow in the AVM itself is not always observed, and when flow effects are not demonstrated, other diagnostic possibilities must be entertained, particularly low-grade glioma.
单纯硬膜下血肿(SDH),由皮层静脉破裂引起，但并不直接接触脑表面，应与擦伤引起的硬膜下血肿从病理学角度加以鉴别。急性期，T1加权像上血肿与正常皮层信号相差不大，但有一条异常的黑影带提示有急性的擦伤，并且水肿还延长了T2加权像的整体弛豫时间。在长TR/TE上可以看到两个区域的弛豫时间延长的T2加权像。高信号区的区域往往被一条低信号带隔开。这条低信号带可能是两个区域不同磁性系数的分界。GE像上的低信号带看齐来要比SE像上的宽，进一步提示可能是磁场系数不同产生的。
Pure subdural hematoma (SDH), in which there is rupture of bridging cortical veins and a hematoma not in direct contact with the brain surface, is distinguished pathologically from SDH with adjacent contusion. Acutely, the T1-weighted image demonstrates the hematoma to have signal nearly the same as normal cortex, and an underlying darker irregular band reflecting the acute contusion and edema which has prolonged bulk T1 relaxation. Prolonged T2 relaxation in both regions is reflected in the long TR/TE. These images demonstrate high signal regions usually separated by a narrow strip of very low signal. The narrow strip presumably reflects a boundary between two regions with different magnetic susceptibilities, producing proton dephasing and signal loss as described above. The narrow strip appears wider on the GE than on SE images, a further indication that susceptibility differences are responsible.
脑梗塞是继发性颅内出血最常见的诱因。作为脑梗塞(无论使用或不使用抗凝治疗)的的并发症之一，对对它的发病几率也不是很清楚。对于小的出血，磁共振比CT敏感，并且加大强度后还能看到更小的病变。这种影像被认为是由于梗塞的栓子移向远处后坏死脑组织的重新灌注形成的。
Infarction is the most common cause of secondary intracerebral hemorrhage. Its frequency of occurrence as a complication of cerebral infarction (with or without anticoagulant therapy) is not precisely known; MR is more sensitive CT to small hemorrhages, and very small lesions are being seen with increasing frequency. They are thought to result from the reperfusion of necrotic brain after embolic material has migrated distally from the site of occlusion.
当脑膜瘤，肺癌，垂体腺瘤，恶性胶质瘤，髓母细胞瘤等肿瘤发生出血时，从影像上可能会将肿瘤误认为出血。
Hemorrhage into neoplasm occurs in choreocarcinoma, melanoma, renal cell, bronchogenic carcinoma, pituitary adenoma, glioblastoma multiforme and medulloblastoma. These tumors may present as hemorrhage.
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