应用Snake模型进行海马结构MR图像分割的研究

目的应用Snake模型对海马结构MR图像进行分割研究。方法在MR图像工作站上采集垂直于海马结构长轴的颅脑T1加权像,并进行图像预处理。研究设计Snake模型的快速Greedy算法程序,在计算机上用自编程序对含整个海马结构的多幅MR图像进行分割。Snake模型分割方法与人工分割方法进行比较。结果除由操作者给出初始轮廓外,Snake模型能从多幅MR图像中自动分割出海马结构。Snake模型分割与人工分割总的重叠率是84%,标准差s=8.03。结论Snake模型是一种快速、有效的海马结构MR图像分割方法,具有重要的临床应用价值。     

基于阈值分割的K-最近邻规则的磁共振脑图像分割算法的研究

目的:提取脑组织中的白质(WhiteMatter)、灰质(GreyMatter)和脑脊髓液(CSF)。方法:针对去除颅骨和肌肉等非脑部组织的磁共振脑图像,根据解剖学知识采用最大类别方差法(Otsu法)自动寻找阈值,以此为依据进行分类标记,再通过K-最近邻(K-NearestNeighbor,简称KNN)规则对大脑组织结构进行划分。结果:在脑部T1加权像中分割算法分别提取脑组织中的白质、灰质和脑脊髓液。结论:结果表明该算法具有较好的自动性和稳定性。     

原发性脑内淋巴瘤的影像诊断(附10例分析)

目的:对免疫功能正常患者的原发性脑内淋巴瘤影像进行分析。方法:对10例免疫功能正常、经病理证实的原发性脑内淋巴瘤的CT、MR所见进行回顾性分析。结果:肿瘤以单发为主,大多发生在幕上,CT扫描多表现为等或稍高密度肿块;MRT1加权像呈低信号,T2加权像呈高信号;CT和MR增强扫描病灶多呈明显均匀强化。结论:原发性脑内淋巴瘤少见,影像检查对诊断有重要帮助。     

人体标本踝关节韧带肌腱损伤1．5T和3．0T MR成像比较

目的：比较1．5T和3．0T踝关节MR图像在判定新鲜人体标本韧带肌腱病理表现中的价值。方法：13个新鲜的尸体踝关节标本在1．5T和3．0T机上行MR扫描，选择最优化的踝关节序列包括T1加权、脂肪抑制T2加权、脂肪抑制质子加权和短时反转恢复快速自旋回波序列。采用微创外科技术对5例标本人为地进行踝关节韧带损伤，然后对其行MR扫描。     

磁共振减影技术在脑膜显像中的应用

目的　评价一种简便的磁共振减影方法对正常脑膜成像的显示效果。方法　对 45例无颅脑疾患的志愿者行颅脑磁共振增强成像 ,对增强前后T1加权像行减影处理。选取不同的解剖层面 (后颅窝四脑室、大脑脚、侧脑室体和半卵圆中心 4个平面 ) ,通过主观判断和客观测量等方法评价、比较各解剖层面正常脑膜及软膜血管在减影图像与常规增强T1加权图像中的显示。结果　在 87%的受检者中 ,常规增强T1加权图像显示正常脑膜及软膜血管强化呈短片段 ,而减影图像则多呈连续强化。 2种成像方法显示强化脑膜范围与强化长度在所有解剖层面上均有显著性差异 (Ρ <0 .0 1)。减影图像中脑膜及软膜血管强化信号强度相对比值明显高于常规增强T1加权图像 (Ρ <0 .0 1)。主观评价脑膜强化均为轻到中度。结论　减影技术是一种能明确显示脑膜强化的简便方法。     

MR脑图像分割技术

磁共振成像技术的优秀的软组织对比度和无创伤性的特点决定了它在未来的医学和认知神经科学等研究领域中具有广阔的发展前景。无论是用于指导临床医学 ,还是用于认知神经科学的脑功能定位 ,首先就是要从图像中分割出医师和研究人员感兴趣的目标。本文主要介绍MR脑图像分割技术的原理及其应用。1　MR图像分割的复杂因素MR图像分割是理解和进一步处理MR图像的重要环节 ,很多研究人员都致力于探索和开发用于分割MR图像的算法[1,2 ] 。普通的计算机图像分割算法可基本分为基于像素的和基于区域的 ,但是在分析MR图像数据中需要考虑更多复杂…     

微机辅助CT脑灌注成像以及定量测量

目的：报告微机辅助CT脑灌注成像以及定量测量方法。方法：以PentiumⅡ300MHz微处理器，128MB内存，16MB显存，6G硬盘PC机和Windows98第2版为平台，用VissualC 为开发语言，根据中心容积定理，利用动态CT图像分析并计算脑血流动力学的有关参数，包括脑血流量（cerebral blood flow,CBF)，脑血容量（cerebral blood volume,CBV),平均通过时间（mean transit time,MTT)和峰值时间（time to peak,TTP)等。最后，将脑血流动力学数据根据色阶分别处理成脑血流量图（mapping of CBF)，脑血容量图（mapping of CBV)，平均通过时间图（mapping of MTT)和峰值时间图（mapping of TTP)。结果：动态增强CT图像经软件处理后可以在微机上显示脑组织的CBF，CBV，TTP和MTT灌注原始图像以及分割颅骨，皮下组织和脑室后的图像。急性脑缺血患者在MR T1加权像，T2加权像，平扫CT以及增强CT未显示的责任病灶，脑CT灌注图像可以清楚显示脑血流动力学的异常。结论：微机辅助CT脑灌注成像简单铁行，可显示常规CT和MR无法发现的早期脑缺血区的血流异常。与MR灌注成像相比更适用于急诊检查。     

新型MR兼容微波天线和标准MR兼容射频消融电极行肿瘤消融的体外伪影评估

正摘要目的评价和比较MR兼容原形微波敷料器和标准MR兼容射频敷料器在MR介导肿瘤切除时的伪影形态和直径。方法两者均于1.5 T MR设备上使用3种序列进行体模研究:T1加权三维容积插值屏气检查(VIBE)、T1加权快速小角度激发(FLASH)、T2加权快速自旋回波序列(TSE)。敷料器朝向主磁场(B0),层面方向可变。评估针尖位置差,并计     

MR脑脊液成像技术及其对颅内中线病变诊断的作用

目的:探讨MR脑脊液成像技术及其对颅中线病变的诊断作用.材料和方法:对160人次行颅内MR脑脊液成像技术,用3D MIP重建图像.结果:84例正常人M R脑脊液成像显示脑脊液呈均匀高信号,脑实质呈均匀低信号;脑脊液从侧脑室、第三脑室、导水管、第四脑室经正中孔至枕大池,形成一个连续完整的脑室系统造影图像.76例异常患者中,8例显示出常规T2WI图像不易显示的细节.1例阻塞性脑积水患者,MR脑脊液成像清楚显示梗阻原因为中脑导水管的局部粘连闭塞.2例脑室内肿瘤,1例延髓胶质母细胞瘤压迫四脑室,MR脑脊液成像可清楚显示病变的部位和范围.MR脑脊液成像还可帮助鞍区及颅后窝肿瘤进一步定位诊断.结论:MR脑脊液成像是一种新的无创伤,快捷的成像技术.对脑室系统疾病和脑脊液循环异常的疾病给予了直观明确的影像学资料,具有良好的临床应用前景.     

脑静脉窦闭塞的影像学表现

目的探讨脑静脉窦血栓形成的影像学表现,进一步提高对本病的认识。方法回顾性地分析36例脑静脉窦血栓形成的影像学(包括MR I,CT和DSA)资料,男15例,女21例,年龄23~59岁。结果MR上T1加权像及T2加权像脑实质内出现异常信号26例,其中散在脑实质内出血并长T1长T2异常信号者16例,长T1长T2信号者6例,4例可见脑室扩大,4例脑肿胀,显示脑沟、池变窄。25例脑静脉窦不强化,但可见皮层静脉异常强化。CT上见脑肿胀并出血者10例,伴脑缺血性低密度者5例,且可见随时间推移静脉窦密度减低;DSA证实,上矢状窦闭塞15例,单侧横窦闭塞8例,乙状窦闭塞7例,直窦闭塞4例,下矢状窦闭塞2例。结论脑静脉窦闭塞的影像表现与动脉性闭塞完全不同。CT和MR检查对诊断脑静脉窦闭塞具有重要意义,DSA仍为诊断该病的金标准。     

Rapid MR imaging of the pediatric brain using the fast spin-echo technique.

PURPOSE: To evaluate diagnostic reliability and to establish optimal scanning techniques of a recently developed Fast Spin-echo MR pulse sequence that allows rapid proton density-weighted and T2-weighted imaging. METHODS: We compared lesion conspicuity and signal intensity measurements on Fast Spin-echo and conventional spin-echo sequences in 81 patients ranging from 1 week to 25 years in age on a 1.5-T MR unit. A total of 28 Fast Spin-echo dual-echo images (14 slice locations) were obtained in 2:08 minutes with a 256 x 128 matrix or in 3:12 minutes with a 256 x 192 matrix at a TR of 2000 msec and two excitations. RESULTS: Lesion conspicuity and characterization on Fast Spin-echo images compared favorably with conventional spin-echo images in our series when pseudo-TEs of 15 and 90 msec were employed for proton density-weighted and T2-weighted images, respectively. Fast Spin-echo images yielded diagnostic information in four nonsedated patients whose conventional spin-echo images were either degraded by motion or unobtainable. Fat signal remained bright on T2-weighted Fast Spin-echo images. Magnetic-susceptibility effects were slightly reduced with Fast Spin-echo but did not pose any diagnostic problem in our series. CONCLUSION: Diagnostically reliable rapid dual-echo brain images can be obtained with Fast Spin-echo sequences.     

Multispectral magnetic resonance image analysis using principal component and linear discriminant analysis

PURPOSE: To explore the possibilities of combining multispectral magnetic resonance (MR) images of different patients within one data matrix. MATERIALS AND METHODS: Principal component and linear discriminant analysis was applied to multispectral MR images of 12 patients with different brain tumors. Each multispectral image consisted of T1-weighted, T2-weighted, proton-density-weighted, and gadolinium-enhanced T1-weighted MR images, and a calculated relative regional cerebral blood volume map. RESULTS: Similar multispectral image regions were clustered, while dissimilar multispectral image regions were scattered in a single plot. Both principal component and linear discriminant analysis allowed discrimination between healthy and tumor regions on the image. In addition, linear discriminant analysis allowed discrimination between oligodendrogliomas and astrocytomas. However, the discriminant analysis method was partially capable of recognizing the tumor identity in unknown multispectral images. CONCLUSION: The proposed method may help the radiologist in comparing multispectral MR images of different patients in a more easy and objective way.     

Lateral geniculate nucleus: anatomic and functional identification by use of MR imaging.

BACKGROUND AND PURPOSE: MR imaging has the potential capacity for noninvasively depicting the anatomy and function of thalamic nuclei. The purpose of this study was to identify the lateral geniculate nucleus (LGN), which is the thalamic relay nucleus for vision, with anatomic and functional MR imaging at 1.5 T. METHODS: Three-millimeter-thick axial images were obtained from eight volunteers by using a double-echo turbo spin-echo sequence for proton density- and T2-weighted contrast and a spin-echo 3D gradient-echo sequence for T1-weighted contrast. Each participant underwent a visual activation experiment using gradient-echo echo-planar imaging at the same location as that of the anatomic study. RESULTS: In all cases, the LGN was recognized on proton density-weighted images as a small wedge-shaped area of high signal intensity relative to that of the surrounding white matter tracts. However, it was difficult to identify the LGN on T1- and T2-weighted images because of the smaller contrast-to-noise ratios between the LGN and the adjacent white matter tracts, compared with those of proton density-weighted images (P <.001). Bilateral thalamic activation and activation in the occipital cortex were shown in all participants. Each region of thalamic activation (23 +/- 3 mm2) was localized to the anatomically identified LGN. CONCLUSION: The excellent correspondence between the anatomically and functionally identified LGN confirms that MR imaging is an indispensable method for visualizing functional neuroanatomy in thalamic nuclei.     

Bone bruises: MR characteristics and histological correlation in the young pig

PURPOSE: To correlate magnetic resonance (MR) signal characteristics of bone bruises with histological findings. MATERIALS AND METHODS: In 14 tibiae of young pigs, bone bruises were created in the proximal tibial metaphysis. The signal intensity seen on the MR images were correlated with histological findings. The following findings were evaluated: (a) changes of signal intensity on the tibiae; (b) changes of histology on the tibiae; and (c) changes of (a) and (b) on follow-up examinations. RESULTS: We observed three types of injuries on T1-weighted images: focal or diffuse low signal, normal signal and linear low signal intensities. Severe hemorrhagic areas showed low signal intensities on all sequences of MR imaging. Fast spin-echo (FSE) T2-weighted images showed a more distinct low signal intensity than T1-weighted images. FSE short tau inversion recovery (STIR) and FSE fat saturated (FSE-FS) T2-weighted images showed similar signal intensities with FSE T2-weighted images. FS T1-weighted enhanced images showed low signal intensities with variable enhancements. Upon histological examination, hemorrhages and edemas were prominent at the subcortical areas of the contusion sites. The areas of dense, low signal intensities in all imaging sequences showed signs of severe hemorrhage. The areas of diffuse low signal and enhanced areas showed mixed areas of hemorrhages and edemas. Follow-up MR imaging showed evolution of the processes of hemorrhages and edemas with fatty marrow changes. CONCLUSIONS: MR imaging can depict changes in the bone marrow resulting from direct injury to the bone. MR imaging is a useful tool for evaluating the evolution of bone bruises.     

VIBE MRI for evaluating the normal and abnormal gastrointestinal tract in fetuses

OBJECTIVE: The great potential of MRI for assessing gastrointestinal abnormalities in fetuses has been described. T1-weighted images may add additional information to T2-weighted images in diagnosing fetal gastrointestinal abnormalities. The objective of this study was to assess the performance of a 3D volumetric interpolated breath-hold sequence (VIBE) in evaluating the normal and abnormal fetal gastrointestinal tract. CONCLUSION: VIBE provides high-quality T1-weighted and 3D MR colonography images for the evaluation of the normal and abnormal gastrointestinal tract in fetuses, and 3D MR colonography provides excellent delineation of the meconium.     

The pelvis: T2-weighted fast spin-echo MR imaging.

Fast spin-echo (SE) T2-weighted magnetic resonance (MR) imaging provides images with highly T2-weighted contrast in substantially reduced imaging times. In a prospective evaluation, fast SE T2-weighted imaging of the pelvis was compared with conventional SE T2-weighted imaging in 30 consecutive patients in whom pelvic pathologic conditions were suspected. Three reviewers independently analyzed the images for (a) overall image quality, (b) pelvic organ definition, (c) conspicuity of pelvic fluid, and (d) conspicuity of pelvic pathologic conditions. Fast SE images were rated superior to conventional SE T2-weighted images in 60% (54 of 90) of the case reviews for overall image quality, in 69% (62 of 90) for pelvic organ definition, in 63% (57 of 90) for conspicuity of pelvic fluid, and in 68% (43 of 63) for conspicuity of pelvic pathologic conditions. The fast SE examinations were typically three to four times faster than conventional SE T2-weighted examinations. No pathologic findings seen on conventional SE T2-weighted images were undetected on fast SE images. Fast SE images may replace conventional SE T2-weighted images in MR imaging of the pelvis.     

Brain: gadolinium-enhanced fast fluid-attenuated inversion-recovery MR imaging

PURPOSE: To determine the clinical utility of gadolinium-enhanced fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging of the brain by comparing results with those at gadolinium-enhanced T1-weighted MR imaging with magnetization transfer (MT) saturation. MATERIALS AND METHODS: In 105 consecutive patients referred for gadolinium-enhanced brain imaging, FLAIR and T1-weighted MR imaging with MT saturation were performed before and after administration of gadopentetate dimeglumine (0.1 mmol per kilogram of body weight). Pre- and postcontrast images were evaluated to determine the presence of abnormal contrast enhancement and whether enhancement was more conspicuous with the FLAIR or T1-weighted sequences. RESULTS: Thirty-nine studies showed intracranial contrast enhancement. Postcontrast T1-weighted images with MT saturation showed superior enhancement in 14 studies, whereas postcontrast fast FLAIR images showed superior enhancement in 15 studies. Four cases demonstrated approximately equal contrast enhancement with both sequences. Six cases showed some areas of enhancement better with T1-weighted imaging with MT saturation and other areas better with postcontrast fast FLAIR imaging. Superficial enhancement was typically better seen with postcontrast fast FLAIR imaging. CONCLUSION: Fast FLAIR images have noticeable T1 contrast making gadolinium-induced enhancement visible. Gadolinium enhancement in lesions that are hyperintense on precontrast FLAIR images, such as intraparenchymal tumors, may be better seen on T1-weighted images than on postcontrast fast FLAIR images. However, postcontrast fast FLAIR images may be useful for detecting superficial abnormalities, such as meningeal disease, because they do not demonstrate contrast enhancement of vessels with slow flow as do T1-weighted images.     

Radiofrequency thermal ablation: correlation of hyperacute MR lesion images with tissue response

PURPOSE: To investigate the hypothesis that the outer boundary of the hyperintense region observed in hyperacute (several minutes post-ablation) T2 and gadolinium contrast-enhanced (CE) T1-weighted magnetic resonance (MR) lesion images is an accurate predictor of eventual cell death from radiofrequency (RF) thermal ablation. MATERIALS AND METHODS: A low-field, open MR imaging system was used to guide an ablation electrode into a thigh muscle of five rabbits and acquire in vivo T2 and CE T1-weighted MR volumes. Ablation occurred by applying RF current for two minutes with the electrode's temperature maintained at 90 degrees +/- 2 degrees C. After fixation, we sliced and photographed the tissue at 3 mm intervals, using a specially designed apparatus, to obtain a volume of tissue images. Digital images of hematoxylin and eosin (H&E) and Masson trichrome-stained histologic samples were obtained, and distinct regions of tissue damage were labeled using a video microscopy system. After the MR and histology images were aligned using a three-dimensional registration method, we compared tissue damage boundaries identified in histology with boundaries marked in MR images. RESULTS: The lesions have distinct zones of tissue damage histologically: a central zone of necrotic cells surrounded by an outer zone with cells that appeared non-viable and associated with marked interstitial edema. In 14 histology images from five lesions, the inner and outer boundaries of the outer zone were compared with the boundaries of a hyperintense rim that surrounds a central hypointense region in the T2 and CE T1-weighted MR images. For T2 and CE T1-weighted MR images, respectively, the mean absolute distance was 1.04 +/- 0.30 mm (mean +/- SD) and 1.00 +/- 0.34 mm for the inner boundaries, and 0.96 +/- 0.34 mm and 0.94 +/- 0.44 mm for the outer boundaries. The mean absolute distances for T2 and CE T1-weighted MR images were not sufficiently different to achieve statistical significance (P = 0.745, 0.818, for the inner and outer boundary, respectively). CONCLUSION: In hyperacute T2 and CE T1-weighted MR lesion images, observations strongly suggest that the outer boundary of the hyperintense rim corresponds to the region of eventual cell necrosis within a distance comparable to our ability to measure. This is good evidence that during RF ablation procedures, MR lesion images can be used to accurately localize the zone of irreversible tissue damage at the lesion margin.     

MR imaging of the anterior intermeniscal ligament: classification according to insertion sites

Our objective was to study the frequency of anterior intermeniscal ligament on MR imaging and to make a classification according to its insertion sites on MR images. Sagittal T1-weighted and thin-section transverse T2*-weighted MR images of the knee were prospectively evaluated in 229 subjects without significant synovial effusion or total rupture of the anterior cruciate ligament. By using thin-section transverse images, the ligament was classified into three types according to its insertion sites (type A: between anterior horns of medial and lateral menisci; type B: between anterior horn of medial meniscus and anterior margin of lateral meniscus; type C: between anterior margins of medial and lateral menisci). On sagittal images location of the ligament was determined with respect to a line drawn between anterior of the tibial epiphysis and posterior of the intercondylar notch to look for a relation between its type on transverse images and location on sagittal images. Separately, arthroscopy was made in 36 patients to verify the MR assessment of the presence of the ligament. Anterior intermeniscal ligament was found in 53% of the subjects. Type B was the most common group (58%). Magnetic resonance imaging has a sensitivity and a specificity of 67 and 100%, respectively, in the detection of the ligament. Types A and C had a statistically significant location posterior and anterior, respectively, to the master line on sagittal images. In arthroscopy, the ligament was either cord-like (67%) or flat (33%) in appearance. Routine sagittal MR images can help identify anterior intermeniscal ligament.     

MR signal intensity of the optic radiation.

PURPOSETo determine whether a hyperintense layer adjacent to the lateral ventricle on T2-weighted MR images represents the optic radiation.METHODSWe reviewed 11 brain specimens from patients with nonneurologic diseases and MR images from 43 healthy volunteers. The MR images in a patient with cerebral infarction involving the lateral geniculate body were also reviewed to evaluate wallerian degeneration of the optic radiation.RESULTSThe external sagittal stratum, composed of the optic radiation, showed a pale layer in specimens stained by Bodian''s method. On high-power microscopic views of the specimens, the axons of the external sagittal stratum were large and separated by wide translucent spaces. In the volunteers, the external sagittal stratum appeared hyperintense on T2-weighted MR images and hypointense on T1-weighted images. The MR images in a patient with cerebral infarction showed hyperintensity within the layer corresponding to the external sagittal stratum.CONCLUSIONSThe hyperintense layer on T2-weighted images represents the external sagittal stratum, or optic radiation. The signal intensity of the external sagittal stratum reflects histologic characteristics of low axonal density.