The role of diffusion-weighted imaging in patients with brain tumors.

BACKGROUND AND PURPOSE: Diffusion-weighted images (DWIs) have been used to study various diseases, particularly since echo-planar techniques shorten examination time. Our hypothesis was that DWIs and tumor apparent diffusion coefficients (ADCs) could provide additional useful information in the diagnosis of patients with brain tumors. METHODS: Using a 1.5-T MR unit, we examined 56 patients with histologically verified or clinically diagnosed brain tumors (17 gliomas, 21 metastatic tumors, and 18 meningiomas). We determined ADC values and signal intensities on DWIs both in the solid portion of the tumor and in the peritumoral, hyperintense areas on T2-weighted images. We also evaluated the correlation between ADC values and tumor cellularity in both gliomas and meningiomas. RESULTS: The ADCs of low-grade (grade II) astrocytomas were significantly higher (P =.0004) than those of other tumors. Among astrocytic tumors, ADCs were higher in grade II astrocytomas (1.14 +/- 0.18) than in glioblastomas (0.82 +/- 0.13). ADCs and DWIs were not useful in determining the presence of peritumoral neoplastic cell infiltration. The ADC values correlated with tumor cellularity for both astrocytic tumors (r = -.77) and meningiomas (r = -.67). CONCLUSION: The ADC may predict the degree of malignancy of astrocytic tumors, although there is some overlap between ADCs of grade II astrocytomas and glioblastomas.     

Time course of cerebral infarction in the middle cerebral arterial territory: deep watershed versus territorial subtypes on diffusion-weighted MR images

PURPOSE: To examine possible differences between the evolution of cerebral watershed infarction (WI) and that of territorial thromboembolic infarction (TI) by using diffusion-weighted (DW) and T2-weighted magnetic resonance (MR) images and apparent diffusion coefficient (ADC) maps. MATERIALS AND METHODS: Fourteen patients with TI and nine with WI underwent MR imaging from the acute to chronic infarction stages. ADC maps were derived from DW images. Lesion-to-normal tissue signal intensity ratios on ADC maps (rADC), echo-planar T2-weighted images, and DW images were calculated. Lesion volumes at acute or early subacute infarction stages were measured on DW images, and final lesion volumes were estimated on fluid-attenuated inversion-recovery images. RESULTS: Analysis of variance revealed a significant difference in temporal evolution patterns of rADC between WI and TI (P <.001). rADC pseudonormalization following TI began about 10 days after symptom onset, but that following WI did not occur until about 1 month after symptom onset. The Pearson correlation coefficient between final and initial infarct volumes was 0.9899 for both infarction subtypes, indicating that the initial ischemic injury volume measured at the acute or early subacute stage predicted the final lesion volume fairly well. CONCLUSION: The evolution time of ADC is faster for TI than for WI. This difference, which likely originates from the different pathophysiologic and hemodynamic features of the two infarction types, might account for the relatively large range of ADC values reported for the time course of ischemic strokes.     

The study of cerebral hemodynamics in the hyperacute stage of fat embolism induced by triolein emulsion

PURPOSE: The purpose of this study was to evaluate the cerebral hemodynamic change in the hyperacute stage of cerebral fat embolism induced by triolein emulsion, by using MR perfusion imaging in cat brains. METHODS: By using the femoral arterial approach, the internal carotid arteries of 14 cats were infused with an emulsion of triolein 0.05 mL. T2-weighted (T2WI), diffusion-weighted (DWI), apparent diffusion coefficient (ADC) map, perfusion-weighted (PWI), and gadolinium-enhanced T1-weighted (Gd-T1WI) images were obtained serially at 30 minutes and 2, 4, and 6 hours after infusion. The MR images were evaluated qualitatively and quantitatively. Qualitative evaluation was performed by assessing the signal intensity of the serial MR images. Quantitative assessment was performed by comparing the signal-intensity ratio (SIR) of the lesions to the contralateral normal side calculated on T2WIs, Gd-T1WIs, DWIs, and ADC maps at each acquisition time and by comparing the relative cerebral blood volume (rCBV), cerebral blood flow (CBF), and mean transit times (MTT) of the lesions to the contralateral normal side calculated on PWI. RESULTS: In the qualitative evaluation of the MR images, the lesions showed hyperintensity on T2WIs, enhancement on the Gd-T1WIs, and isointensity on DWIs and the ADC maps. In the quantitative studies, SIRs on the Gd-T1WIs, DWIs, and ADC maps peaked at 2 hours after infusion. The SIRs on the T2WIs peaked at 4 hours after infusion and decreased thereafter. On PWIs, the rCBV, rCBF, and MTT of the lesion showed no significant difference from the contralateral normal side (P = .09, .30, and .13, respectively) and showed no significant change of time course (P = .17, .31, and .66, respectively). CONCLUSION: The embolized lesions induced by triolein emulsion showed no significant difference in cerebral hemodynamic parameters from those on the contralateral normal side. The result may suggest that consideration of the hemodynamic factor of embolized lesions is not necessary in further studies of the blood-brain barrier with triolein emulsion.     

Apparent diffusion coefficient and fractional anisotropy in spinal cord: age and cervical spondylosis-related changes

PURPOSE: To present the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) change with age in the normal spinal cord and in cervical spondylosis. MATERIALS AND METHODS: A total of 11 normal volunteers and 79 cervical spondylosis patients entered this study. Line scan diffusion tensor images were obtained in a 1.5-Tesla whole-body scanner using a phased-array spine coil. The ADC and FA values were measured on a sagittal section. Spearman correlation of ADC/FA vs. age for normal spinal cord was calculated. RESULTS: The mean ADC of the normal spinal cord was 0.81 +/- 0.03 microm(2)/msec at the relatively wide C2-C3 level and 0.75 +/- 0.06 microm(2)/msec at the more narrow C4-C7 level. The FA at the corresponding level was 0.70 +/- 0.05 and 0.66 +/- 0.03, respectively. With age, ADC showed positive correlation (Spearman, r = 0.242) and FA exhibited negative correlation (Spearman, r = -0.244). A total of 54% of all spondylosis cases showed elevated ADC (P < 0.001) and decreased FA (P < 0.001) at the stenotic spinal canal level compared with the normal spinal cord. The average ADC and FA of high-signal lesions on T2-weighted images (seven patients) were 1.28 +/- 0.33 microm(2)/msec and 0.46 +/- 0.12, respectively. CONCLUSION: ADC increases and FA decreases with age in the normal spinal cord. Elevated ADC and reduced FA were measured in the spinal cord of spondylosis cases with clinical symptoms of myelopathy.     

Change of diffusion anisotropy in patients with acute cerebral infarction using statistical parametric analysis

Purpose We conducted statistical parametric comparison of fractional anisotropy (FA) images and quantified FA values to determine whether significant change occurs in the ischemic region. Materials and methods The subjects were 20 patients seen within 24 h after onset of ischemia. For statistical comparison of FA images, a sample FA image was coordinated by the Talairach template, and each FA map was normalized. Statistical comparison was conducted using SPM99. Regions of interest were set in the same region on apparent diffusion coefficient (ADC) and FA maps, the region being consistent with the hyperintense region on diffusion-weighted images (DWIs). The contralateral region was also measured to obtain asymmetry ratios of ADC and FA. Results Regions with areas of statistical significance on FA images were found only in the white matter of three patients, although the regions were smaller than hyperintense regions on DWIs. The mean ADC and FA ratios were 0.64 ± 0.16 and 0.93 ± 0.09, respectively, and the degree of FA change was less than that of the ADC change. Significant change in diffusion anisotropy was limited to the severely infarcted core of the white matter. Conclusion We believe statistical comparison of FA maps to be useful for detecting different regions of diffusion anisotropy. This article was presented at a Japan Radiological Society meeting in April 2005     

3．0T弥散张量成像FA值和ADC值在颅脑恶性星形细胞瘤中的运用

目的：探讨磁共振弥散张量成像FA值和ADC值在颅脑恶性星形细胞瘤中的应用价值。方法：收集经手术及组织病理学证实的恶性星形细胞瘤患者14例,术前行常规MRI平扫、DTI检查、增强扫描及1H-MRS检查,工作站自动生成各向异性指数图（FA图）及表观弥散系数图（ADC图）,定义肿瘤实质区为最高Cho／Cr和Cho／NAA比值、异常强化、T2WI信号异常区;定义瘤体边缘为Cho／Cr和Cho／NAA比值异常、无强化、T2WI信号异常区;定义瘤周水肿区为正常MRS表现、无强化、T2WI信号异常区;定义正常白质区为正常MRS表现、无强化、T2WI信号正常区（肿瘤同侧或对侧）;分别测量上述区域的FA1—4值、ADC1—4值,分析比较上述4个区FA值、ADC值有无统计学差异。结果：肿瘤实质区、瘤体边缘、瘤周水肿区及正常白质区平均FA值为FA1：0．1822±0．0583,FA2：0．2947±0．0786,FA3：0．1769±0．0942,FA4：0．6668±0．0817。肿瘤实质区、瘤体边缘、瘤周水肿区与正常自质区比较差异有高度显著性（P=0．000）,瘤体边缘与肿瘤实质区、瘤周水肿区之间差异有高度显著性（P〈0．005）,肿瘤实质区与瘤周水肿区差异无显著性（P〉0．05）;平均ADC值为ADC1：11．132±4．101,ADC2：11．175±2．983,ADCB：14．939±2．857,ADCA：7．265±0．914（单位10^-3mm^2／s）。瘤体实质部、肿瘤边缘及瘤周水肿区与正常脑白质区ADC值差异有高度显著性（P〈0．005）;瘤体实质部、肿瘤边缘与瘤周水肿区差异有高度显著性（P〈0．005）;而瘤体实质部与肿瘤边缘差异无显著性（P〉0．05）。结论：FA值和ADC值对高级别星形细胞瘤浸润范围的划定有重要价值。     

Diffusion-weighted MR imaging of subdural empyemas in children

BACKGROUND AND PURPOSE: Subdural empyema (SDE), an infection of the subdural space, occurs most often in pediatric patients as a complication of meningitis, sinusitis, or otitis media. Diffusion-weighted imaging (DWI) has been used in the past to investigate intracerebral infections. The purpose of this study was to determine the signal intensity characteristics of SDE on DWIs as well as the corresponding apparent diffusion coefficient (ADC) maps. METHODS: MR studies of 10 patients with SDEs were retrospectively reviewed. Included were routine sequences and DWI, which consisted of an axial single-shot echo-planar spin-echo sequence (TR/TE, 4000/110) with b values of 0, 500, and 1000 s/mm(2). Signal-intensity characteristics on routine MR images and DWIs were evaluated. In seven patients, ADC values of the lesions were calculated by using two b values. Follow-up imaging study was performed in seven patients. RESULTS: In nine patients, the empyema was hyperintense on DWIs. In the remaining patient, the empyema showed mixed hyperintensity and hypointensity. ADC values were lower than those of normal cortical gray matter and much lower than those of reactive subdural effusions. In all seven patients with persistent clinical signs of infection, the empyemas were hyperintense on follow-up DWIs. CONCLUSION: SDE had high signal intensity on DWIs and low signal intensity on ADC maps, with an ADC value lower than that of the normal cortical gray matter. Diffusion MR imaging can be valuable in distinguishing SDE from effusion and in the follow-up of subdural collections.     

Hypoxic-ischemic brain injury in the neonatal rat model: relationship between lesion size at early MR imaging and irreversible infarction

BACKGROUND AND PURPOSE: By using a neonatal rat hypoxia-ischemia (HI) model, we studied the relationship between lesion volume-measured by diffusion-weighted imaging (DWI) and T2-weighted imaging (T2WI) at an early time point-and irreversible infarct volume. We also evaluated the optimal apparent diffusion coefficient (ADC) threshold that provides the best correlation with irreversible infarct size. MATERIALS AND METHODS: Twenty-three neonatal rats underwent right common carotid artery ligation and hypoxia. MR imaging was performed 1-2 hours post-HI by using DWI and T2WI and at day 4 post-HI by using T2WI. Lesion volumes relative to whole brain (%LV) were measured on ADC maps by using different relative ADC thresholds 60%-80% of mean contralateral ADC and T2WI. Pearson correlation and multiple linear regression analysis were used to study the relationships between ln(%LV) at MR imaging and %LV at histopathology. RESULTS: At 1-2 hours post-HI, all lesion volume measurements on DWI were significantly correlated with the infarct volume on histopathology, with the best correlation attained at the 80% ADC threshold (r = 0.738; P < .001). The estimated regression formula was %LV on histopathology = 20.60 + 3.33 ln(%LV on 80% ADC threshold) (adjusted R(2) = 0.523; P < .001). Lesion volume at 1-2 hours post-HI tended to underestimate the final infarct volume. CONCLUSION: Early post-HI MR imaging by using DWI correlates moderately well with the size of irreversible infarct, especially when measured by using a relative ADC threshold of 80% mean contralateral ADC.     

儿童型肾上腺脑白质营养不良的2D-1H MRSI和DTI初步应用

目的探讨2D-MRSI和DTI在儿童型肾上腺脑白质营养不良的综合应用价值.方法对3例儿童型肾上腺脑白质营养不良患儿行2D-MRSI、DTI和常规MRI检查,比较病变区域代谢物NAA/Cho、NAA/Cr和Cho/Cr比值与ADC和FA的关系,以及它们与T2WI信号强度的相关性;测量常规MRI阴性的ALD额顶叶白质的ADC和FA值有无异常.结果病变T2WI信号强度与NAA/Cho比值和FA负相关,与ADC正相关,即T2WI信号越高,NAA/Cho越低、ADC越高及FA越低,且具有从外到内的层次性.各种代谢物比值以NAA/Cho 比值与ADC和FA相关最密切.DTI不能发现常规MRI阴性的ALD白质病变.结论 MRSI和DTI与常规MRI表现具有一定的相关性,2D-MRSI和DTI可为儿童型肾上腺脑白质营养不良诊断提供更多的信息.     

Spontaneous intracerebral hematoma on diffusion-weighted images: influence of T2-shine-through and T2-blackout effects

BACKGROUND AND PURPOSE: On diffusion-weighted (DW) images, primary hematomas are initially mainly hyperintense, and then hypointense during the first few days after stroke onset. As in other brain disorders, variations in the T2 relaxation time of the hematoma influence the DW imaging signal intensity. Our aim was to evaluate the contribution of the T2 signal intensity and apparent diffusion coefficient (ADC) changes to signal intensity displayed by DW imaging through the course of hematoma. METHODS: The MR images of 33 patients with primary intracranial hemorrhage were retrospectively reviewed. Variations in T2-weighted echo planar images, DW imaging signal intensity, and apparent diffusion coefficient (ADC) ratios (core of hematoma/contralateral hemisphere) were analyzed according to the putative stages of hematoma, as seen on T1- and T2-weighted images. RESULTS: On both T2-weighted echo planar and DW images, the core of the hematomas was hyperintense at the hyperacute (oxyhemoglobin, n = 11) and late subacute stages (extracellular methemoglobin, n = 4), while being hypointense at the acute (deoxyhemoglobin, n = 11) and early subacute stages (extracellular methemoglobin, n = 7). There was a positive correlation between the signal intensity ratio on T2-weighted echo planar and DW images (r = 0.93, P < .05). ADC ratios were significantly decreased in the whole population and in each of the first three stages of hematoma, without any correlation between DW imaging findings and ADC changes (r = 0.09, P = .6). CONCLUSION: Our results confirm that the core of hematomas is hyperintense on DW images with decreased ADC values at the earliest time point, and may thus mimic arterial stroke on DW images. T2 shine-through and T2 blackout effects contribute to the DW imaging findings of hyperintense and hypointense hematomas, respectively, while ADC values are moderately but consistently decreased during the first three stages of hematoma.     

Magnetic resonance imaging and histologic findings of experimental cerebral fat embolism

RATIONALE AND OBJECTIVES: The purpose of this study was to determine whether cerebral fat embolism demonstrated reversible or irreversible findings in magnetic resonance (MR) imaging over time and to compare the features in MR images with histologic findings in a cat model. MATERIALS AND METHODS: MR images were obtained serially at 2 hours, 1 and 4 days, and 1, 2, and 3 weeks after embolization with 0.05 mL of triolein into the internal carotid artery in 19 cats. Any abnormal signal intensity and change in the signal intensity were evaluated on T2-weighted images, T1-weighted images, diffusion-weighted images (DWIs; including apparent diffusion coefficient [ADC] maps), and gadolinium-enhanced T1-weighted images (Gd-T1WI) over time. After MR imaging at 3 weeks, brain tissue was obtained and evaluated for light microscopic (LM) examination using hematoxylin-eosin and Luxol fast blue staining. For electron microscopic examination, the specimens were obtained at the cortex. The histologic and MR findings were compared. RESULTS: The embolization lesions showed hyperintensity on T2-weighted images, hyperintensity, or isointensity on DWIs, hypointensity, or isointensity on ADC maps and contrast enhancement on Gd-T1WIs at 2 hours. The T2-weighted hyperintensity extended to the white matter at day 1 and decreased thereafter. Contrast enhancement decreased continuously from day 1, and hyperintensity on DWI decreased after day 4. Hypointensity on ADC maps became less prominent after day 4. By week 3, most lesions had reverted to a normal appearance on MR images and were correlated with LM findings. However, small focal lesions remained in the gray matter of 8 cats and in the white matter of 3 cats on MR images, and this correlated with the cystic changes on LM findings. Electron microscopic examination of the cortical lesions that reverted to normal at week 3 in MR images showed that most of these lesions appeared normal but showed sporadic intracapillary fat vacuoles and disruption of the endothelial walls. CONCLUSIONS: The embolized lesions of the hyperacute stage were of 2 types: type 1 lesions, showing hyperintensity on DWIs and hypointensity on ADC maps, have irreversible sequelae, such as cystic changes; whereas type 2 lesions, showing isointensity or mild hyperintensity on DWIs and ADC maps, reverted to a normal appearance in the subacute stage.     

Water diffusion compartmentation at high b values in ischemic human brain

BACKGROUND AND PURPOSE: We studied the evolution of brain water compartments during the early stage of ischemic stroke. METHODS: Diffusion-weighted imaging was performed at 1.5 T in 10 volunteers and 14 patients with stroke. We used a single-shot echo-planar technique with 11 b values of 0-5000 s/mm(2). Regions of interest were selected in the white matter (WM) and striatum of the volunteers and in the ischemic core of the patients. Measurements were fitted on the basis of a biexponential decay with the b factor as follows: S(b) = S(0)[(f(slow) x exp(-b x ADC(slow)) + (f(fast) x exp(-b x ADC(fast))] where S(b) is the signal intensity in the presence of a diffusion gradient, S(0) is the signal intensity without diffusion sensitization, ADC(slow) and ADC(fast) are the respective apparent diffusion coefficients (ADCs) of slow diffusing compartments (SDCs) and fast diffusing compartments (FDCs), and f(slow) and f(fast) the respective contributions to the signal intensity of SDC and FDC. RESULTS: In healthy subjects, FDC represents 74.3 +/- 3.1% of brain water, with ADC(fast) = (124.6 +/- 12.0) x 10(-5) mm(2)/s and ADC(slow) = (15.5 +/- 3.9) x 10(-5) mm(2)/s. In stroke, decreased FDC (49.1% +/- 10.9%; P = 1.05 x10(-5)) and increased ADC(slow) ([22.4 +/- 8.1] x 10(-5) mm(2)/s; P = 8.07 x 10(-3)) were observed, but ADC(fast) was not significantly changed ([135.6 +/- 25.7] x 10 (-5) mm(2)/s; P =.151). CONCLUSION: The restricted diffusion observed in the early stroke is mainly related to a redistribution of water from the FDC to the SDC.     

Acute cerebral infarction: quantification of spin-density and T2 shine-through phenomena on diffusion-weighted MR images.

PURPOSE: To quantify the relative contributions of spin density and T2 effects ("shine through") on diffusion-weighted (DW) magnetic resonance (MR) images of acute and subacute cerebral infarction. MATERIALS AND METHODS: In 30 patients, 1.5-T imaging was performed within the first 7 days after onset of cerebral infarction. Estimates of T2, spin density, and apparent diffusion coefficient (ADC) in the region of stroke and contralateral normal brain were computed by means of standard regression techniques after quadruple-echo conventional MR imaging and single-shot echo-planar DW imaging with a maximum b value of 1,000 sec/mm2. Expected signal intensity (S) enhancement ratios resulting from independent changes in T2, spin density, and ADC were then calculated for the DW sequence. RESULTS: The overall SI of cerebral infarction on DW images was significantly higher than that of normal brain throughout the 1st week after stroke (mean relative SI enhancement ratio, 2.29; P < .001). During the first 2 days after stroke, decreased ADC within the stroke region made the dominant contribution to increased SI on DW images. By day 3, increased T2 values in the stroke region became equally important, and, from days 3-7, the contribution to SI from T2 effects became dominant. A slight increase of spin density in the stroke region made a relatively small and constant contribution to DW SI over the 1st week. CONCLUSION: The increased SI of subacute cerebral infarction on DW images reflects not only a shortening of ADC but a prolongation of T2 and spin-density values.     

3.0 T MR扩散加权成像评价兔肝VX2瘤射频消融治疗的实验研究

目的 探讨3.0 T MR DWI评价兔肝VX2瘤射频消融治疗疗效的价值.方法 新西兰大白兔22只.20只用于建立VX2瘤模型,2只健康正常兔用于行正常肝射频消融术对照.于VX2瘤种植后14～21 d(平均17 d),对符合实验条件瘤兔(病灶位于肝实质内,最大直径≤3 cm,坏死病灶直径≤整个病灶直径的1/2)行3.0 T常规MRI和功能DWI.对瘤兔及对照组正常兔行射频消融治疗,射频消融术后7～10 d(平均8 d)行3.0 T常规MRI及DWI.所有射频消融治疗兔行MR检查后均行病理检查.测量兔肝VX2瘤、正常兔肝射频消融治疗前后ADC值,分析兔肝VX2瘤射频消融治疗前后3.0 T MR常规成像、ADC值特征,并与病理对照.同一b值射频消融治疗后不同组织间ADC值比较采用重复测量资料方差分析.结果 20只实验组兔肝VX2瘤模型均建立成功,1例肿瘤突出于肝表面、1例肿瘤病灶出现明显坏死未纳入实验.所有18个瘤灶及2例正常兔肝射频消融均成功.兔VX2瘤T1WI序列表现为低或等信号,T2WI为高信号.肝VX2瘤兔射频消融治疗后7～10 d,射频消融病灶T1WI序列表现为低或稍高信号,T2WI为混杂信号.T2WI序列周边环形稍高信号为肉芽组织,增强扫描明显强化,T2WI序列低、中等信号为凝固性坏死.坏死组织在DWI图上为低信号,活性肿瘤组织位于病灶周边,呈结节状,在T2WI、DWI图上为等或稍高信号.肿瘤标本为灰白色,部分肿瘤组织间夹杂增生血管、少许肉芽组织.b值为600 s/mm2时,射频消融治疗后活性肿瘤组织(9只)、坏死组织(18只)、肉芽组织(18只)、正常组织(18只)ADC值分别为:(1.227±0.140)×10-3、(0.702±0.050)×10-3、(1.918±0.124)×10-3、(1.739±0.044)×10-3mm2/s,各组间ADC值差异具有统计学意义(P＜0.01).b值分别为200、400、600、800、1000 s/mm2时治疗后坏死组织、活性残留或复发肿瘤组织、肉芽组织、正常肝组织间ADC值差异具有统计学意义(P＜0.01).结论 兔VX2瘤模型适合3.0 T MR评价射频消融治疗疗效的动物实验研究,对射频消融治疗基础及临床应用研究具有重要价值.     

MRI对前列腺中央腺体T2WI低信号结节的良恶性分析

目的:探讨前列腺中央腺体T2WI低信号良、恶性结节的MRI表现,以提高鉴剐诊断的能力.方法:符合纳入标准的19例前列腺癌结节和61例前列腺增生患者经多序列MRI检查并经组织病理学证实.对两者在T2WI上的信号和边缘.DWI信号强度和ADC值、及多期DCE的最大信号强度和时间信号强度曲线的类型进行比较分析.结果:19例前列腺癌结节T2WI上边界不清、部分不清16例,边缘清楚3例,呈均质低信号;61例前列腺增生结节边缘不清及部分边界不清共34例,边缘清楚27例,信号均匀30例,信号不均匀31例.两者具有显著性的差异(P=0.007).于DWI,前列腺癌结节信号强度(b值为800 s/mm2)为60.6±10.7明显高于增生结节(49.7±8.5)(t值为 5.793,P=0.00).前列腺癌结节ADC值为(0.83±0.18)×10-3mm2/s,明显高于增生结节(1.17±0.24mm2/s)(t值为0.4 60,P=0.00).多期DCE,前列腺癌的最大信号强度为385.60±108.27,增生结节的最大信号强度为393.21±111.28(t值为-0.270,P=0.788),两者比较没有显著性差异.前列腺癌时间信号强度曲线以速升速降为主,而增生结节以渐进型和速升平台型为主,两者具有显著性差异(P=0.00);其中速升速降型和渐进型曲线于组间具有显著性差异).结论:前列腺中央叶T2WI低信号结节中,前列腺癌与前列腺增生于T2 WI边缘和信号均匀性、DWI的信号强度和ADC值、曲线类型均有差异.故MRI多序列成像分析助于对中央腺体T2WI低信号结节良恶性的鉴别诊断.     

急性脑梗塞磁共振弥散加权成像的演变特征

目的：研究临床急性脑梗塞病变在弥散加权（DW）MRI上的表现规律。材料和方法：用单次激发平面回波弥散加权MRI和MRI其他技术对47例脑梗塞患者和14例非脑梗塞患者进行了对比研究。分别测量梗塞灶ACD图、DWI和T2WI的信号强度，绘出时间-信号强度图。分别在DWI和T2WI上测量梗塞面积．比较两者的关系。结果：急性脑梗塞发病后局部ACD逐渐降低．至12h达到峰值．以后逐渐升高。弥散加权MRI对急性脑梗塞病变非常敏感和特异，发病3h内T2WI为阴性，DW－MRI全部显示了梗塞灶；发病24h内T2WI所显示的梗塞灶面积明显小于DWI。发病7天内梗塞灶在DWI上与正常脑信号比均＞2．0．非脑梗塞病变均＜2．0。结论：急性脑梗塞病变在DW．MRI上有特征性演变规律，DW．MRI能快速、敏感、准确地诊断急性脑梗塞     

Correlation study of 3T-MR-DTI measurements and clinical symptoms of cervical spondylotic myelopathy

Objective

To discuss the correlation between diffusion tensor imaging (DTI) measurements, diffusion tensor tractography and the clinical symptoms of cervical spondylotic myelopathy.

Methods

Based on the Japanese Orthopedics Association (JOA) score, 104 cervical spondylotic myelopathy cases were first divided into four groups: mild, moderate, severe and serious groups. According to lesion signal characteristics, all cases were again divided into three groups: A(N/N): normal signal in both T1WI and T2WI; B (N/H): normal signal in T1WI but high signal in T2WI; and C (L/H): low signal in T1WI and high signal in T2WI. The apparent diffusion coefficient (ADC), fractional anisotropy (FA), λ1, λ2, and λ3 were measured and diffusion tensor tractography was performed in the seriously compressed section of the spinal cord.

Results

The FA values were positively correlated with JOA scores (r = 0.883, P < 0.05), and significantly different among four JOA groups (P < 0.05). The ADC, λ2, and λ3 were significantly different among the moderate, severe and serious groups as well as among the A, B, and C groups (P < 0.05). Declining FA values were found associated with increasing fiber bundle damage.

Conclusions

The FA values and the change patterns of fiber bundle were more sensitive than T2WI for spinal cord lesion, and were positively correlated with clinical symptoms.     

层面选择方向扩散加权成像在中脑大脑脚间产生高信号的机制

目的 研究层面选择方向扩散加权成像(DWIs)在中脑大脑脚问产生高信号的机制.方法 健康志愿者10名,以邻近中脑大脑脚问为中心进行MR扫描:(1)采用心电门控(ECG),测量收缩期与舒张期扩散敏感因子(b值)为0和1000 mm2/s的单独DWIs,比较两期测量中脑亮点区MR信号强度及表观扩散系数(ADC)值.(2)变换选层方向,分别采集平行于颅底、平行于系统Y轴,Y-Z坐标30°夹角的单独DWIs,观察中脑亮点形状的变化.(3)采集全脑6个方向DWI,利用扩散张量成像(DTI)白质纤维束追踪成像技术显示以亮点区为种子的神经纤维束走行起止,测量亮点区及其相连邻近纤维走行区的ADC值与各向异性分数(FA)值.将测量得到的亮点区ADC及FA值与相连邻近纤维走行区的ADC及FA值分别进行配对t检验,比较两者之间的差异.结果 心脏收缩期采集的DWIs信号强度分别为296.28±38.19、153.81±37.91,舒张期分别为295.36.±38.84、154.03±37.52,两者间差异无统计学意义(t值分别为1.34、0.62,P值均＞0.05);心脏收缩与舒张期测量的ADC值分别为(6.07±2.20)×10-4、(6.69±1.44)×10-4 mm2/s,两者间差异无统计学意义(t=0.94,P＞0.05).纤维束追踪显示中脑高信号亮点位于小脑上脚神经纤维束的中脑交叉区.常规扫描层面上,DWIs高信号亮点表现为狭长心形和狭长条形,其形状随扩散敏感梯度施加方向的变化而改变.多方向DWI测量亮点区与结合臂区的ADC值分别为(10.61±3.42)×10-4与(9.24±2.21)×10-4 mm2/s,两者间差异无统计学意义(t=0.61,P＞0.05).亮点区FA值为O.43±0.13,结合臂FA值为0.61±0.08,两者间差异有统计学意义(t=8.32,P＜0.05).结论 中脑水平DWIs亮点征象由小脑上脚在中脑层面神经纤维及交叉区的各向异性造成,因此,其亮点信号的形状与DWIs的选层层面方向有关,与心动周期相关的脑搏动对亮点征象无影响.     

Evaluation of white matter anisotropy in Krabbe disease with diffusion tensor MR imaging: initial experience

PURPOSE: To compare diffusion tensor magnetic resonance imaging with conventional T2-weighted imaging for evaluation of white matter changes in patients with Krabbe disease. MATERIALS AND METHODS: In eight patients with Krabbe disease and eight age-matched control subjects, anisotropy maps were generated with diffusion tensor data by using echo-planar imaging with diffusion gradient encoding in six directions. Anisotropy maps and T2-weighted images were visually inspected. Relative anisotropy (RA) and normalized T2-weighted signal intensity in white matter tracts and gray matter nuclei were quantitatively compared between patients and controls (paired Student t test). RESULTS: Loss of diffusion anisotropy appeared on anisotropy maps as areas of decreased hyperintensity in patients with Krabbe disease. Differences in RA between Krabbe disease patients and control subjects were significant in eight of nine white matter structures studied (P =.001-.01) and in basal ganglia (P =.04). T2-weighted signal intensity was also significantly different in the same white matter structures (P =.006-.049) but not in basal ganglia. In the three patients imaged after stem cell transplantation, mean RA was between the RAs of untreated patients and control subjects. CONCLUSION: Diffusion tensor-derived anisotropy maps (a) provide a quantitative measure of abnormal white matter in patients with Krabbe disease, (b) are more sensitive than T2-weighted images for detecting white matter abnormality, and (c) may be a marker of treatment response.     

Diffusion/perfusion MR imaging of acute cerebral ischemia

In vivo echo-planar MR imaging was used to measure apparent diffusion coefficients (ADC) of cerebral tissues in a comprehensive noninvasive evaluation of early ischemic brain damage induced by occlusion of the middle cerebral artery (MCA) in a cat model of acute regional stroke. Within 10 min after arterial occlusion, ADC was significantly lower in tissues within the vascular territory of the occluded MCA than in normally perfused tissues in the contralateral hemisphere. Sequential echo-planar imaging was then used in conjunction with bolus injections of the magnetic susceptibility contrast agent, dysprosium DTPA-BMA, to characterize the underlying cerebrovascular perfusion deficits. Normally perfused regions of brain were identified by a dose-dependent 35-70% loss of signal intensity within 6-8 s of contrast administration, whereas ischemic regions appeared relatively hyperintense. These data indicate that sequential diffusion/perfusion imaging may be useful in differentiating permanently damaged from reversibly ischemic brain tissue.