Campbell2

C H A P T E R 2 Magnetic Resonance Imaging in Orthopaedics 磁共振成像在骨科的应用 Dexter H. Witte Types of MRI ScansMRI扫描方式 Foot and Ankle足和踝 Knee膝关节 Hip髋关节 Spine脊柱 Shoulder肩关节 Wrist and Elbow腕关节和肘关节 Elbow肘关节 Tumor Imaging肿瘤扫描 Aside from routine roentgenography, no imaging method has as great an effect on the current practice of orthopaedics as magnetic resonance imaging (MRI). MRI provides unsurpassed soft tissue contrast and multiplanar capability with spatial resolution that approaches that of computed tomography (CT). Consequently, MRI has superseded older imaging methods such as myelography, arthrography, and even angiography. In some areas, such as the knee and shoulder, MRI has become a powerful diagnostic tool, helping the surgeon to evaluate structures that are otherwise invisible to noninvasive techniques. As an evolving technology, the ultimate role of MRI in orthopaedics is still to be determined. Continued improvements in both hardware and software will undoubtedly expand the role of MRI in orthopaedics and in other fields of medicine as well. 当前，除了常规 X线摄影外，尚无任何一种影像学检查 方法能像磁共振成像(MRI)那样对骨科临床产生如此巨大的 影响。由于 MRI 具有卓绝的软组织对比、多平面成像的能力 以及其空间分辨力近乎于 CT 等特点，因此，MRI 已取代一 些传统的影像检查方法，诸如脊髓造影、关节造影甚至血管 造影。在某些部位，如膝、肩，MRI 已成为一种举足轻重的 新的诊断工具。藉此，骨科医师能对一些以前采用非侵人性 检查方法未能显示的结构加以评估。尽管如此，MRI 与其他 新技术一样，其在骨科中的最终地位尚未确立，不过，无可 置疑的是，随着 MRI 扫描仪硬件、软件的不断改进，MRI 在 骨科及其他医学领域内的应用亦将拓宽、深化。 MRI is unrelated to any of the older imaging techniques. Magnetic resonance images are created by placing the patient in a strong magnetic field (approximately 30,000 times stronger than the earth's magnetic field). The magnetic force affects the nuclei within the field, specifically the nuclei of elements with odd numbers of protons or neutrons. The most abundant element satisfying this criterion is hydrogen, which is plentiful in water and fat. These nuclei, which are essentially protons, possess a quantum spin. When the patient's tissues are subjected to this strong magnetic field, protons align themselves with respect to the field. Since all imaging is performed within this constant magnetic force, this becomes the steady state, or equilibrium. In this steady state a radiofrequency (RF) pulse is applied, which excites the magnetized protons in the field and perturbs the steady state. After application of this pulse, a receiver coil or antenna listens for an emitted RF signal that is generated as these excited protons relax or return to equilibrium. This signal, with the help of localizing gradient fields and Fourier transformation, creates the MR image. MRI 是与以前所有的成像技术完全不一样的一种检查 方法。检查时，病人被置于强磁场内(外加磁场，约是地球 磁场强度的 30,00 倍)。磁力作用于磁场内的原子核，尤其 是那些含奇数(不成双)质子或中子的原子。由于氢原子核只 有一个质子，因此，符合上述法则的最丰富的元素是在人体 内水及脂肪中含量丰富广为分布的氢。氢原子核中的质子具 有自旋的固有本性，当病人的组织被置于强磁场内时，质子 群均按所在磁场的方向进行排列。由于全部成像均在此恒定 的磁力中完成，因此，此即形成一种稳定状态或称平衡状态。 在这种稳态下，再施加一种射频脉冲(RF)，可激励磁场中己 被磁化的质子群并扰乱原有稳态。施加上述脉冲之后、采用 一个接收线圈或天线，能监听所发出的射频信号，该信号是 在那些被激励的质子群弛豫或回复到平衡状态时产生的。借 助于梯度场定位以及傅立叶变换，以上信号形成了 MRI 图 像。 Types of MRI Scans Although all studies involve magnetization and RF signals, the method and timing of excitation and acquisition of the signal can be varied to affect the contrast of the various tissues in the volume. Most musculoskeletal MRI examinations use the spin-echo technique, which produces T1-weighted, proton (spin) density, and T2-weighted images. T1 and T2 are tissue-specific characteristics. These values reflect measurements of the rate of relaxation to the steady state. By varying the timing of the application of RF pulses (TR, or repetition time) and the timing of acquisition of the returning signal (TE, or echo time), an imaging sequence can accentuate T1 or T2 characteristics. A fairly constant rule is that fat has a high signal (bright) on T1-weighted images, and fluid has a high signal on T2-weighted images. Structures with little water or fat, such as cortical bone, tendons, and ligaments, remain dark in all types of sequences. Faster imaging methods are becoming available. Fast spin-echo technique can reduce the length of T2-weighted sequences by two thirds or more. Unfortunately, some fast spin-echo sequences introduce blurring artifact, which can obscure tiny abnormalities such as meniscal tears. In addition, fat signal in fast spin-echo images remains fairly intense, a problem that can be eliminated by chemical shift fat-suppression techniques (Fig. 2-1). Fat suppression also can be achieved by using an inversion recovery (STIR) sequence. These fat-suppression techniques can be useful in the detection of edema in both bone marrow and soft tissue and therefore play an important role in the imaging of trauma and neoplasms. Another fast imaging method, gradient-echo technique, is used selectively for cartilage imaging (such as for the glenoid labrum). Most MR studies are composed of a number of imaging sequences or series, tailored to detect and define a certain pathological process. Because the imaging planes (axial, sagittal, coronal, oblique) and the sequence type (T1, T2, gradient-echo) are chosen at the outset, advanced understanding of the clinical problem is required to perform high-quality imaging. 尽管所有研究均涉及磁化和射频信号，但是，为了影响 被检部位各种组织的对比，可变通激励的方法、时间以及信 号采集模式。多数肌肉骨骼的 MRI 检查都采用自旋－回波 (spin-echo)技术，可产生 T1－加权(T1-weighted)质子(自旋 Spin)密度以及 T2－加权(T2-weighted)图像。各种组织的 T1 和 T2 时间均不同。T1 及 T2 值取决于给定组织的弛豫速 度或给定组织由磁化(状态)回复到稳定状态所需要的时间， 为了加重图像中 T1 或 T2 成分，则要改变成像序列中的射频 脉冲施加时间(TR 或重复时间 repetition)以及回波信号的 采集时间(TE 或回波时间 echo-time)。有一相当恒定的规 律，即脂肪在 T1-加权图像上具有高信号(明亮)而液体在 T2-加权图像上也表现高信号。当然，含有少量水分或脂肪 的组织结构如皮质骨、肌腱、韧带等则在所有类型序列中均 呈暗色。快速成像的方法逐渐被采用。快速自旋－回波检查 法可使 T2－加权序列的时间缩短 2/3 以上。令人遗憾的是， 有些快速自旋－回波序列会产生模糊伪影，会使微小的病变 如半月板撕裂显示不清楚，另外，脂肪信号在快速自旋－回 波图像上信号居高不下，仍呈清楚的高信号，这些问题可采 用化学位移脂肪抑制法(chemical shift fat-suppression)解决 （图 2－1），也可采用反转恢复序列(STIR)达到脂肪抑制。 这些脂肪抑制技术对发现骨髓和软组织的水肿很有用，因些 在损伤和肿瘤的成像中起着重要作用。另外一种快速成像法 为梯度－回波法，选择性地应用于软骨的成像(如关节盂 唇)。多数 MRI 检查是对许多成像系列所得到的信息进行综 合以发现及确定某种病理改变。由于成像平面(轴位、矢状 位、冠状位、斜位)及序列类型(T1，T2 梯度－回波)是在开 始检查时即进行了选择的，故而需要事先了解临床检查的目 的，以完成高质量的图像。 Fig. 2-1 Chemical shift fat-suppression technique. A, Axial fast spin-echo, T2-weighted image of large soft tissue mass in calf. Hyperintense fat blends with anterior and posterior margins of lesion. B, Addition of fat-suppression allows for better delineation of tumor margins. 图 2－1 化学位移脂肪抑制技术。 A 小腿轴向快速自旋－回波，T2 加权像下巨大软组织包块。病变前后边缘高密度脂肪 混杂信号。 B 附加脂肪抑制后使肿瘤边缘更加清晰。 A wide variety of MR imaging systems are commercially available. Scanners can be grouped roughly by field strength. High-field scanners are considered to have a field strength of 1 to 1.5 tesla (T). Low-field scanners operate at field strengths of 0.3 T or less. Currently there is much debate regarding the relative performance of high- and low-field systems. Each type of system has distinct advantages. For example, high-field scanners generate higher signal-to-noise images, allowing shorter scanning times, thinner scan slices, and smaller fields of view. Chemical shift fat suppression is not available in low-field scanners. Low-field scanners usually are of an "open" configuration that allows greater patient comfort and ease in imaging off-axis structures such as elbows and wrists. Low-field systems also are less expensive to purchase and operate. The quality and accuracy of low-field systems as compared with high-field scanners are debatable. Relatively few comparative studies have been published; however, some studies suggest that the difference in the diagnostic accuracy of high- and low-field scanners in the evaluation of menisci and ligaments of the knee is not significant. Whether this accuracy can be extrapolated to other musculoskeletal examinations is not yet known. High-field systems with an "open" configuration are on the horizon, and they combine many of the advantages of current high- and low-field scanners. 各种各样的 MRI 系统投入市场。扫描仪可按场强大小分 类。高磁场扫描仪具有 1～1.5 特斯拉（T）场强，低磁场扫 描仪在 0.3 或更低场强下工作。当前对于高磁场或低磁场的 相对性能方面有许多争论。每一种系统都有各自的优势。例 如，高磁场扫描仪产生高信噪比图像，缩短了扫描时间，扫 描层面更薄，可以看到更小的区域。化学位移脂肪抑制法在 低磁场扫描仪上无法获得。低磁场扫描仪通常是“开放”结 构，使高大病人在作诸如肘关节和腕关节等远轴组织的扫描 时较为舒适。同时低磁场扫描仪购买和运行均比较便宜。与 高磁场扫描仪相比，低磁场扫描仪的成像质量和精确性还有 争议。已有少数相关比较研究 报告 软件系统测试报告下载sgs报告如何下载关于路面塌陷情况报告535n,sgs报告怎么下载竣工报告下载 发表。然而一些研究表明， 高磁场和低磁场扫描仪对于评价膝关节半月板和韧带的诊 断精确度并没有显著差异。目前尚不知道这种精确性是否可 以外推到其它肌肉骨骼系统的检查。结合当前高磁场和低磁 场优点的具有“开放”结构的高磁场系统即将出现。 An image can be acquired in the main coil (the hollow tube in which the patient lies during the study). This may be satisfactory when studying the chest, abdomen, or pelvis, where a large area is to be evaluated. In the musculoskeletal system, the hips, thighs, or legs often are examined this way. However, for evaluation of smaller articular structures, such as the menisci of the knee or the rotator cuff, specialized surface coils are needed. Several types of surface coils are available, including coils tailored for specific body parts such as the spine, shoulder, wrist, and temporomandibular joints, as well as versatile flexible coils and a circumferential extremity coil. These coils serve as antennae placed close to the imaging volume, markedly improving signal and resolution. The drawback is that only limited areas can be studied. Recently, larger coils have been developed with phased-array technology, providing the improved signal that is seen in smaller coils with an expanded coverage area. These phased-array coils are commercially available for the knee, shoulder, and torso and are compatible with most new MR systems. Optimal coil selection is mandatory for high-quality imaging of joints or small parts. 通常，成像在主线圈(在检查时病人卧之检查床坐落的 空管为主线圈处)中获得。此足以检查胸部、腹或盆腔等部 大范围的结构。在肌肉骨骼系统，常用此法检查髋关节、(双 侧)股骨或小腿。然而当检查较小的关节结构，如膝关节半 月板或肩袖时，则需应用特殊的表面线圈。多种多样的表面 线圈已投入市场，包括对身体特殊部位设计的线圈，诸如： 脊柱、肩、腕、颞颌关节特制的专用线圈，还有多用的可变 形(flexible)线圈，以及可包绕四肢的线圈。这些线圈如同 天线放置于靠近需成像的受检部位，可明显增强信号及空间 分辨能力，不足之处是检查只能在有限的范围中进行。近来， 根据定相排列技术（phased-array technology）发展了较 大的线圈，使之在扩大覆盖范围后仍能获得在小线圈中所能 看到的改良信号。适用于膝关节、肩关节和躯干并与许多新 式 MR 系统相兼容的定相排列线圈已投入市场。选择理想的 表面线圈是获取高质量关节或小的结构成像所必须的。 CONTRAINDICATIONS Some patients are not candidates for MRI. Absolute contraindications to MRI include intracerebral aneurysm clips, cardiac pacemakers, automatic defibrillators, biostimulators, implanted infusion devices, internal hearing aids, and metallic orbital foreign bodies. Cardiac valve prostheses can be safely scanned. Relative contraindications include first-trimester pregnancy, middle ear prostheses, and penile prostheses. Generally, internal orthopaedic hardware and orthopaedic prostheses are safe to scan, although ferrous metals can create local artifact that can obscure adjacent tissues. Metal prostheses may also become warm during the examination, although this is rarely noticed by the patient and almost never requires termination of the study. Patients with metal external fixation devices should not be scanned. 有些病人不适合做 MRI 检查。MRI 绝对禁忌证包括：脑 内动脉瘤夹、心脏起搏器(cardiac pacemakers)、自动除颤 器 (automatic defibrillators) 、 生 物 刺 激 器 (biostimulaters)、植入的灌输装置(implanted infusion devices)、内助听器以及眼眶内金属异物。除 pre-6000 系 列 start-Edwards 瓣膜外，心脏瓣膜假体均可安全扫描。 相对禁忌证包括：妊娠的前三个月及中耳假体、阴茎假 体等。骨科植入金属物及骨科人工假体均可安全扫描，尽管 含铁金属物会产生局部的伪影，使邻近组织的影像模糊。金 属假体也有可能在检查中受损，虽然病人很少注意到也几乎 从没要求中止检查。有金属性外固定装置的病人不应进行检 查。 Fig. 2-2 Partial tear of calcaneal tendon. A, Sagittal T1-weighted image demonstrates markedly thickened calcaneal tendon containing areas of intermediate signal (arrow). B, Sagittal fat-suppressed, T2-weighted image exhibits fluid within tendon substance, indicating partial tear (arrow). 图 2－2 跟腱部分断裂。 A 矢状面 T1－加权图像，显示跟腱明显增厚并含有中等信号区（↑）； B 矢状面脂肪抑制， T2－加权图像显示肌腱内有液体，提示部分撕裂（↑）。 Foot and Ankle足与踝 One of the more complex anatomical regions in the human body is the foot and ankle. The complexity of midfoot and hindfoot articulations and the variety of pathological conditions in the tendon and ligament make evaluation difficult from a clinical and imaging perspective. The role of MRI in the foot and ankle is less well defined than in the shoulder and knee. Most examinations of the foot and ankle are performed to evaluate tendinopathy, articular disorders, and osseous pathological conditions, often after trauma. MRI can be quite useful when the examination is directed at solving a certain clinical problem, but it should not be used as a screening study for nonspecific pain because the yield is low. Given the small size of structures to be examined, optimal imaging is achieved on a high field strength (greater than 1.0 T) magnet, and the use of a surface coil, typically an extremity coil, is mandatory. Most studies are directed at the midfoot, hindfoot, or ankle. A small field of view (8 to 12 cm) should be used to obtain appropriate resolution. Images can be prescribed in orthogonal or oblique planes, with combinations of T1-weighted, T2-weighted, and fat-suppressed sequences. The examination should be tailored to best define the clinically suspected problem. 足与踝是人体中解剖较复杂的部位之一。中足及后足的 关节结构的复杂性及肌腱、韧带病理表现的多样化，增加了 临床及影像观察的复杂性。 MRI 对足、踝部检查的作用不如对肩及膝部检查作用 那样确切。多数足及踝的检查常作为对创伤后肌腱病变关节 紊乱及骨病理的评估。若为解决临床上某个难题而做 MRI 检查是非常有用的，但对非特异性的疼痛不应用做筛选性检 查，因为阳性率是低的。高磁场强度(大于 1.0Tesla)扫描机 采用表面线圈特别是四肢线圈可望使特定的小区域结构得 到令人满意的图像。临床中大多数是对中足、后足或踝关节 进行检查。为取得良好的分辨率，应采用小的观察野(8～ 10cm)。扫描拟用垂直的平面或斜位平面，T1－加权、T2－ 加权及脂肪抑制序列相结合。检查应该限定用于解决临床上 悬而未决的问题。 Fig. 2-3 Tibialis posterior tendon tear. A, Axial T1-weighted image reveals swollen, ill-defined region of intermediate signal intensity, representing fluid and abnormal tendon (arrow). B, Axial fat-suppressed, T2-weighted image shows thickened tendon (arrow) surrounded by hyperintense fluid. 图 1－3 胫骨后肌腱撕裂。A 轴位 T1－加权图像显示肿胀、中等强度信号、边缘模糊提示积液和异常的肌腱（↑）。 B 轴位脂肪抑制 T2－加权图像显示肌腱增粗（↑），周围有高强度的液体。 TENDON INJURIES MRI excels in the evaluation of pathological conditions in the numerous tendons about the ankle joint. Most commonly affected are the calcaneal and tibialis posterior tendons. In chronic tendinitis, the calcaneal tendon thickens and becomes oval or circular in cross section. The enlarged tendon maintains low signal on all sequences. When partially torn, the tendon demonstrates focal or fusiform thickening with interspersed areas of edema or hemorrhage that brighten on T2-weighted series (Fig. 2-2). With complete rupture, there is discontinuity of the tendon fibers. Similarly, abnormalities of tibialis posterior tendon can be confidently diagnosed with MRI. Increased fluid in the sheath of the tendon indicates tenosynovitis. Insufficient or ruptured tendons can appear thickened, attenuated, or even discontinuous (Fig. 2-3). Occasionally, similar abnormalities are seen in the other flexor tendons or peroneus tendons (Fig. 2-4). 肌腱损伤 MRI 对踝关节周围诸多肌田病变的检查优于其他的检查 方法。最常受累者为跟腱及胫骨后肌腱。在慢性肌腱炎中， 跟腱变厚，横断面上变成卵圆形或圆形。增厚的肌腱在所有 的扫描序列上均保持低信号。当跟腱部分撕裂时，肌腱显示 局灶或纺锤形的增厚，其中杂以散在水肿或出血区，后者在 T2－加权图像上呈高信号(图 2—2)。当完全断裂时，肌腱 纤维不连续。同样，胫后肌腱炎症或断裂时，用 MRI 可做出 明确诊断。腱鞘内液体增多提示腱鞘炎，部分或完全断裂的 肌腱可表现增厚、变细，甚至不连续(图 2－3)。其他屈肌 腱或腓骨肌腱也偶尔可见到类似的异常表现(图 2－4)。 Fig. 2-4 Peroneus longus tendon rupture. A, Coronal T1-weighted image through midfoot shows increased diameter of peroneus longus tendon (arrows). B, Coronal fat-suppressed, T2-weighted image reveals fluid signal within ruptured tendon (arrow). 图 2－4 腓骨长肌腱断裂。 A 经中足冠状面 T1－加权图像，显示腓骨长肌腱增粗（↑）； B 冠状面脂肪抑制 T2－加权图像， 显示在破裂的肌腱中有液体信号（↑）。 LIGAMENT INJURIES韧带损伤 Although ligamentous injuries about the ankle are common, at this time MRI has a limited role in their evaluation. The medial and lateral stabilizing ligaments of the tibiotalar and talocalcaneal joints, as well as the distal tibiofibular ligaments, usually can be seen with proper positioning of the foot. The imaging status of ligaments about the ankle, however, does not change the treatment in most patients. MRI has been useful in evaluating the lateral recess of the ankle joint in patients with chronic ankle sprains and impingement. Regions of fibrosis frequently are seen in the lateral gutter, especially when fluid is present in the ankle joint. 虽然踝关节周围韧带的损伤很常见，但目前 MRI 对其 诊断作用尚有限。足部在恰当的体位时，通常可见到胫距、 距跟关节的内外侧固定韧带及远例胫腓韧带。但在多数病人 中，这些韧带影像所见不会改变其治疗 措施 《全国民用建筑工程设计技术措施》规划•建筑•景观全国民用建筑工程设计技术措施》规划•建筑•景观软件质量保证措施下载工地伤害及预防措施下载关于贯彻落实的具体措施 。对于慢性踝关 节扭伤和撞击症病人，MRI 可用来评价踝关节外侧踝穴。 通常可见到外侧踝穴局灶性纤维化，特别是踝关节积液。 OTHER DISORDERS OF FOOT AND ANKLE 足与踝的其他疾患 As elsewhere in the body, bone marrow disorders, avascular necrosis (AVN) or fracture (Fig. 2-5), and osteochondral injuries (Fig. 2-6) are well delineated. The excellent anatomical information provided by MRI allows detection and definition of masses in the foot. One mass unique to the foot is a Morton neuroma. Usually found in the third metatarsal interspace distally, it is most often a clinical diagnosis based on the presence of pain on the plantar surface of the foot at this location. Unlike most other tumors, this lesion lacks increased signal on T2-weighted sequences. 与身体其他部位一样，骨髓疾患、缺血性坏死(AVN)或骨 折(图 2—5)以及骨软骨损伤(图 2－6)在 MRI 图像上可良好 显示。用 MRI 显示清晰的解剖结构可以发现并确诊足部肿 物。一种足部特有的单发性肿瘤称为 Morton 神经瘤，通常 见于第三跖趾关节。临床常根据足底面相应部位出现疼痛即 做出诊断。不同于大多数其他肿瘤，此病变在 T2－加权图 像上不表现信号增强。 Fig. 2-5 Avascular necrosis of talus. Fat-suppressed proton density– weighted image reveals focus of abnormal signal in talar dome (arrow) after fracture of talar neck. 图 2－5 距骨缺血性坏死。脂肪抑制质子密度加权图像显 示距骨颈骨折后有异常信号的距骨顶部病灶（↑）。 Another condition for which MRI would seem especially well suited is infection in the foot of a diabetic patient. Because of the excellent depiction of bone marrow, osteomyelitis can be detected quite early, perhaps 7 to 10 days before roentgenographic abnormalities are visible (Fig. 2-7). The anatomical information provided by MRI can assist in surgical planning by defining the extent of disease. Certain fat-suppressed sequences are so sensitive that reactive marrow edema can be seen even before frank osteomyelitis. Although the sensitivity of MRI for osteomyelitis approaches 100%, the reported specificity is less. As with scintigraphy, in patients with neuropathic disease the specificity is reduced further; therefore the current workup of the diabetic foot often involves a combination of scintigraphy, MRI, laboratory data, and physical examination. Nevertheless, a normal MRI marrow signal essentially excludes osteomyelitis. 特别适合采用 MRI 检查的另外一种情况为糖尿病人的足部 感染，因为对骨髓显示极佳，故对骨髓炎可做出非常早期的 诊断，可能在传统 X线检查能发现异常之前 7—10 天即可发 现(图 2－7)。MRI 所提供的解剖信息可帮助外科医生根据病 变的范围拟定治疗 计划 项目进度计划表范例计划下载计划下载计划下载课程教学计划下载 。采用特定的脂肪抑制序列进行检 查，可以敏感到在骨髓炎症状明显出现之前见到反应性骨髓 水肿。虽然 MRI 对骨髓炎检查的敏感性可达 100％，但据报 道其特异性较低。与核素检查相似，对患神经性疾患的病人， MRI 的特异性进一步降低。然而，当正常的 MRI 骨髓信号表 现时则基本上可以除外骨髓炎。 Fig. 2-6 Osteochondritis dissecans of talus in college football player. A, Coronal T1-weighted image shows osteochondral fragment in medial talar dome. Loss of fat signal suggests sclerosis or fibrosis (arrow). B, Coronal fat-suppressed,T2-weighted image demonstrates fluid signal between lesion and host bone (arrowheads), indicating unstable fragment. C, Coronal fat-suppressed, spoiled gradient-echo technique reveals abnormal decreased signal (arrow) in overlying articular cartilage, indicating defect confirmed by arthroscopy. 图 2－6 大学足球运动员的距骨剥脱性骨软骨炎的断面图像。 A 冠状面 T1－加权图像示距骨内侧顶部有骨软骨碎片 （↑），缺乏脂肪信号提示硬化或纤维化； B 冠状面脂肪抑制，T2－加权图像见病变与宿骨之间存在液体信号（△）， 提示不稳定的碎片； C 冠状面脂肪抑制扰相位梯度－回波技术，见在表面的关节软骨处有异常的低信号（↑），提示缺 损损并已由关节镜所证实。 Fig. 2-7 Osteomyelitis in foot of diabetic patient. A, Lateral roentgenogram of hindfoot reveals no abnormalities. B, Sagittal fat-suppressed, T2-weighted image shows increased signal in calcaneal marrow (arrow), indicating osteomyelitis. 图 2－7 糖尿病患者足部骨髓炎。 A 后足侧位 X线片未 发现异常。B 矢状面脂肪抑制 T2－加权图像示跟骨髓内有 增高信号（↑），提示骨髓炎。 Knee The knee is the most frequently studied region of the appendicular skeleton. Standard extremity coils allow high-resolution images of the commonly injured internal structures of the joint. MRI has essentially replaced arthrography for the evaluation of internal derangement of the knee. The routine MRI examin