弥漫性轴索损伤的MRI研究进展

脑弥漫性轴索损伤的重残率及死亡率都很高,因此早期准确诊断和治疗至关重要,影像学检查为其主要检查手段.就脑弥漫性轴索损伤MRI各个序列的研究进展予以介绍.     

磁共振在诊断弥漫性轴索损伤中的应用进展

弥漫性轴索损伤是脑外伤的严重类型,也是影像学诊断的难点。随着软硬件的更新和新序列的研发应用,MRI在弥漫性轴索损伤的诊断中起着越来越重要的作用。本文将磁共振成像各个序列对弥漫性轴索损伤的应用情况综述如下。     

Conspicuity of diffuse axonal injury lesions on diffusion-weighted MR imaging

OBJECTIVE: (1) To detect diffuse axonal injury (DAI) lesions by diffusion-weighted imaging (DWI), as compared with fluid-attenuated inversion recovery (FLAIR) imaging and (2) to evaluate hemorrhagic DAI lesions by b0 images obtained from DWI, as compared with gradient-echo (GRE) imaging. METHODS: We reviewed MR images of 36 patients with a diagnosis of DAI. MR imaging was performed 20 h to 14 days (mean, 3.7 days) after traumatic brain injury. We evaluated: (1) conspicuity of lesions on DWI and FLAIR and (2) conspicuity of hemorrhage in DAI lesions on b0 images and GRE imaging. RESULTS: DWI clearly depicted high-signal DAI lesions. The sensitivity of DWI to lesional conspicuity in DAI lesions was almost equal to that of FLAIR. The sensitivity of b0 images to identification of hemorrhagic DAI lesions was inferior to that of GRE. CONCLUSION: DWI is as useful as FLAIR in detecting DAI lesions. GRE imaging is still the superior tool for the evaluation of hemorrhagic DAI.     

联合SWI与DWI在急性脑弥漫性轴索损伤中的应用价值

目的：评价联合磁敏感成像（SWI）与扩散加权成像（DWI）在急性期脑弥漫性轴索损伤中的应用价值。方法：32例脑弥漫性轴索损伤急性期患者,所有患者行常规MRI序列、DWI及SWI序列全脑扫描。结果：共检出病灶313个,T1WI 78个,T2WI 207个,FLAIR 292个,DWI 286个,SWI 297个。SWI显示245个病灶内分布斑片状、点状出血灶,其它序列共显示43个内分布出血灶。SWI、DWI病灶检出率高于常规T2WI（χ2=82.465,χ2=59.584;P〈0.01）,SWI、FLAIR及DWI病灶检出率无明显差异（χ2=3.052;P〉0.05）。结论：联合SWI与DWI有利于提高急性脑弥漫性轴索损伤的检出率,有助于准确评价病变的严重程度,SWI与DWI应作为急性脑弥漫性轴索损伤的常规扫描序列组合。     

磁共振成像在弥漫性轴索损伤中的应用进展

弥漫性轴索损伤（diffuse axonal injury，DAI）是指在外力作用下头部旋转、成角运动造成的广泛的白质损害，是颅脑损伤患者致死、植物生存状态的重要原因。深入研究其影像学特征有助于提高其诊断水平和患者预后评估。磁共振成像（magnetic resonance imaging,MRI）技术于1988年由Gentry等。最早用于颅脑损伤的诊断，近年来在DAI诊断和研究中的应用日益广泛。     

Role of diffusion-weighted magnetic resonance imaging in prostate cancer evaluation

Purpose

The authors analysed the role of diffusion-weighted imaging (DWI) as an additional tool in magnetic resonance (MR) evaluation of prostate cancer.

Materials and methods

Forty-one patients with suspected prostate cancer underwent MR imaging (1.5 Tesla). A DWI sequence was added to the standard morphological protocol, with a maximum b value of 1,000 s/mm². Diffusion maps were obtained, and the apparent diffusion coefficient (ADC) was calculated by drawing a region of interest (ROI) over healthy tissue and areas suspicious for malignancy. Histology was considered the gold standard.

Results

The areas correctly classified by MR imaging (42/51) had a low signal intensity on T2-weighted imaging and low ADC value (0.99±0.15 mm²/s; p<0.01) compared with the healthy peripheral zone (PZ) (1.73±0.27 mm²/s; p<0.01). Nine areas classified as suspicious for malignancy on T2-weighted sequences showed high ADC (1.44±0.06 mm²/s; p<0.01) and were confirmed to be disease free by subsequent histological examination. The accuracy of morphofunctional MR imaging was 81.6% compared with 73.7% of the morphological analysis alone.

Conclusions

The addition of DWI to the standard protocol increases the overall diagnostic performance of MR imaging in detecting prostatic cancer. Thus, DWI can help the clinician determine the most appropriate management strategy for the patient.     

磁敏感加权成像对弥漫性轴索损伤的诊断价值

目的 探讨磁敏感加权成像(SWI)对弥漫性轴索损伤(DAI)的诊断价值及与临床、预后的关系.方法 对20例临床确诊为DAI的脑外伤患者行3.0 T MR常规序列扫描[包括T1WI、T2WI、液体衰减反转恢复(FLAIR)序列]及SWI序列扫描,格拉斯哥评分(GCS)为3.0～5.0分者8例,6.0～8.0分者4例,9.0～12.0分者8例.分别为伤后3 h至20 d内行MR扫描并加扫SWI序列,分别测量所有患者在MR常规序列扫描和SWI的病灶数量及体积.常规扫描序列和SWI检出病灶数量的比较采用Mann-Whitney U检验,病灶体积比较采用配对t检验,观察有无差异;SWI检查与临床、预后采用Pearson相关分析.结果 DAI病灶在SWI表现为:脑内皮髓质交界区、脑白质、基底节、胼胝体、脑干、小脑等区域散在大小不等的点状、串珠状、斑片状、条索状显著低信号灶(病灶直径＜2.0 cm),病灶分布呈多灶性,大小不均,边界清晰.MRI常规序列扫描共发现78个病灶;SWI序列共发现424个病灶,SWI序列发现病灶数量明显多于常规MR扫描(U=-15.447,P<0.01);分别测量MRI常规序列扫描和SWI序列发现的病灶体积为19 340 mm3和38 042 mm3,两者比较差异有统计学意义(t=5.870,P<0.01).其中SWI序列显示的病灶数量和病灶体积与GCS评分之间呈明显的负相关,相关系数分别为-0.802、-0.767,P值均<0.01.结论 SWI序列可以在DAI患者中发现更多的出血病灶及较常规扫描明显扩大的病灶体积,并且病灶的体积和数量与GCS评分密切相关,对DAI的诊断及判断患者的预后有很高的价值.

Abstract：

Objective To study the diagnostic value of susceptibility weighted imaging (SWI) in diffuse axonal injury (DAI) and investigate the relationship between SWI and clinical prognosis. MethodsTwenty patients (15 males and 5 females) with DAI were included in this study. Routine sequences (T1WI, T2WI and FLAIR) and SWI were performed on a 3.0 T MRI scanner. There were 8 cases whose Glasgow score scale (GCS) ranged from 3.0 to 5.0, 4 cases from 6.0 to 8.0 and 8 from 9.0 to 12.0. The interval time between injury and examination were from 3 hours to 20 days. The number and volume of lesions observed on SWI and routine sequence were compared using Mann-Whitney U-test and paired t-test. Pearson correlation was used to analyze the relationship between the number and volume of all lesions and GCS. Results The lesions showed punctate, beaded, patchy and cord-like hypointense signal with various size on SWI (lesion diameter <2.0 cm). Distribution of lesions was multifocal with clear boundary. Routine MRI scan found a total of 78 lesions, while SWI sequence detected 424 lesions. The number of the lesions found on SWI was more than that on conventional MRI (U=-15.447,P＜0.01). The total volume of the lesions measured on routine MRI and SWI were 19 340 mm3 and 38 042 mm3, respectively. The total volume measured on SWI was more than that on routine MR (t=5.870,P＜0.01). The number and volume of all lesions were negatively correlated with GCS (r=-0.802, -0.767, P＜0.01). Conclusion SWI sequence could find more bleeding lesions than the routine MRI sequences. The number and the volume of the lesions were closely related to GCS. SWI showed high value in the diagnosis and prediction of the prognosis of DAI.     

Whole-body diffusion-weighted magnetic resonance imaging

Diffusion-weighted magnetic resonance imaging (DWI) provides information on the diffusivity of water molecules in the human body. Technological advances and the development of the concept of diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) have opened the path for routine clinical whole-body DWI. Whole-body DWI allows detection and characterization of both oncological and non-oncological lesions throughout the entire body. This article reviews the basic principles of DWI and the development of whole-body DWI, illustrates its potential clinical applications, and discusses its limitations and challenges.     

Diffusion tensor MR imaging in diffuse axonal injury

BACKGROUND AND PURPOSE: Disruption of the cytoskeletal network and axonal membranes characterizes diffuse axonal injury (DAI) in the first few hours after traumatic brain injury. Histologic abnormalities seen in DAI hypothetically decrease the diffusion along axons and increase the diffusion in directions perpendicular to them. DAI therefore is hypothetically associated in the short term with decreased diffusion anisotropy. We tested this hypothesis by measuring the diffusion characteristics of traumatized brain tissue with use of diffusion tensor MR imaging. METHODS: Five patients with mild traumatic brain injuries and 10 control subjects were studied with CT, conventional MR imaging, and diffusion tensor imaging. All patients were examined within 24 hours of injury. In each participant, diffusion tensor indices from homologous normal-appearing white matter regions of both hemispheres were compared. These indices were also compared between homologous regions of each patient and the control group. In two patients, diffusion tensor images from the immediate post-trauma period were compared with those at 1 month follow-up. RESULTS: Patients displayed significant reduction of diffusion anisotropy in several regions compared with the homologous ones in the contralateral hemisphere. Such differences were not observed in the control subjects. Significant reduction of diffusion anisotropy was also detected when diffusion tensor results from the patients were compared with those of the controls. This reduction was often less evident 1 month after injury. CONCLUSION: White matter regions with reduced anisotropy are detected in the first 24 hours after traumatic brain injury. Therefore, diffusion tensor imaging may be a powerful technique for in vivo detection of DAI.     

Extracranial applications of diffusion-weighted magnetic resonance imaging

Diffusion-weighted MRI has become more and more popular in the last couple of years. It is already an accepted diagnostic tool for patients with acute stroke, but is more difficult to use for extracranial applications due to technical challenges mostly related to motion sensitivity and susceptibility variations (e.g., respiration and air-tissue boundaries). However, thanks to the newer technical developments, applications of body DW-MRI are starting to emerge. In this review, we aim to provide an overview of the current status of the published data on DW-MRI in extracranial applications. A short introduction to the physical background of this promising technique is provided, followed by the current status, subdivided into three main topics, the functional evaluation, tissue characterization and therapy monitoring.     

Serial diffusion-weighted magnetic resonance imaging in methanol intoxication

We report the serial magnetic resonance imaging (MRI) findings in a case of methanol intoxication. A 50-year-old man who had accidentally ingested methanol was admitted to our institution. The patient was almost blind, and became comatose. The MRI showed bilateral putaminal lesions with restricted diffusion. The MRI, which was performed on the third day after admission, showed new lesions in the subcortical white matter. The patient's general condition improved. His visual acuity, however, did not improve.     

Role of magnetic resonance diffusion-weighted imaging in evaluating response after chemoembolization of hepatocellular carcinoma

Objective

To investigate the value of hepatocellular carcinoma pretreatment apparent diffusion coefficients (ADCs) and its ADCs changes after treatment in predicting and early monitoring the response after chemoembolization.

Materials and methods

Twenty-five responding and nine nonresponding hepatocellular carcinoma lesions were prospectively evaluated with magnetic resonance diffusion-weighted imaging in 24 h before and in 48 h after chemoembolization. Quantitative ADC maps were calculated with images with b values of 0 and 500 s/mm².

Results

Nonresponding lesions had a significantly higher pretreatment mean ADC than did responding lesions (1.726 ± 0.323 × 10⁻³ mm²/s vs.1.294 ± 0.185 10⁻³ mm²/s, P ≤ 0.001). The results of receiver operator characteristic (ROC) analysis for identification of nonresponding lesions showed that threshold ADC value of 1.618 × 10⁻³ mm²/s had 96.0% sensitivity and 77.8% specificity. After transarterial chemoembolization, responding lesions had a significant increase in %ADC values than did nonresponding lesions (32.63% vs. 5.24%, P = 0.025). The results of ROC analysis for identification of responding lesions showed that threshold %ADC value of 16.21% had 72% sensitivity and 100% specificity. No significant change was observed in normal liver parenchyma (P = 0.862) and spleen (P = 0.052).

Conclusion

High pretreatment mean ADC value of hepatocellular carcinoma was predictive of poor response to chemoembolization. A significant increase in %ADC value was observed in lesions that responded to chemoembolization.     

磁敏感加权成像在弥漫性轴索损伤中的应用

目的：探讨磁敏感加权成像（SWI）技术在弥漫性轴索损伤（DAI）中的临床应用价值。方法收集临床诊断为DAI的患者25例,均行常规T1WI、T2WI、液体衰减反转恢复（FLAIR）、弥散加权磁共振成像（DWI）及SWI。结果25例患者中SWI较常规序列能清楚地显示脑内微小出血灶。结论在DAI患者中,SWI可提供更多的影像信息,在诊断DAI和治疗方案的制定中具有重要的临床应用价值。     

Traumatic axonal injury revealed by postmortem magnetic resonance imaging: A case report

In forensic investigations, it is important to detect traumatic axonal injuries (TAIs) to reveal head trauma that might otherwise remain occult. These lesions are subtle and frequently ambiguous on macroscopic evaluations. We present a case of TAI revealed by pre-autopsy postmortem magnetic resonance imaging (PMMR).A man in his sixties was rendered unconscious in a motor vehicle accident. CT scans revealed traumatic mild subarachnoid hemorrhage. Two weeks after the accident he regained consciousness, but displayed an altered mental state. Seven weeks after the accident, he suddenly died in hospital. Postmortem computed tomography (PMCT) and PMMR were followed by a forensic autopsy.PMMR showed low-intensity lesions in parasagittal white matter, deep white matter, and corpus callosum on three-dimensional gradient-echo T1-weighted imaging (3D-GRE T1WI). In some of these lesions, T21-weighted imaging also showed low-intensity foci suggesting hemorrhagic axonal injury. The lesions were difficult to find on PMCT and macroscopic evaluation, but were visible on antemortem MRI and confirmed as TAIs on histopathology.From this case, it can be said that PMMR can detect subtle TAIs missed by PMCT and macroscopic evaluation. Hence, pre-autopsy PMMR scanning could be useful for identifying TAIs during forensic investigations.     

Multishot diffusion-weighted PROPELLER magnetic resonance imaging of the abdomen

OBJECTIVE: The objective of this study was to evaluate the feasibility of using multishot PROPELLER for diffusion-weighted imaging (DWI) of the abdomen. MATERIALS AND METHODS: Diffusion-weighted abdominal imaging was performed in 9 healthy volunteers and 3 patients using both single-shot DW-SE-EPI and multishot DW-PROPELLER (BLADE sequence). We compared ADC measurements in phantoms, liver and pancreatic tissues and performed qualitative comparisons of the diffusion-weighted images and ADC maps provided by these 2 techniques. RESULTS: DW-PROPELLER significantly improved image quality (P < 0.05) with reduced geometric distortion and artifact. The ADC values of phantoms and abdominal organs measured by DW-PROPELLER were generally greater than those measured by single-shot DW-SE-EPI. The ADC values measured by both DWI techniques were significantly different for liver tissues but not for pancreatic tissues (P < 0.05). Preliminary patient studies demonstrated clearly distinguished lesion areas from surrounding normal liver tissues in the DW-PROPELLER images. DW-PROPELLER offers the potential for high-resolution DWI of the abdomen. CONCLUSIONS: The multishot DW-PROPELLER sequence is a promising technique for DWI of abdominal organs. Future clinical studies will evaluate the use of DW-PROPELLER technique for abdominal oncologic imaging applications.     

Diagnostic performance of diffusion-weighted magnetic resonance imaging in esophageal cancer

The purpose of this study was to assess the value of diffusion-weighted magnetic resonance imaging (DWI) in detecting esophageal cancer and assessing lymph-node status, compared with histopathological results. DWI was prospectively performed in 24 consecutive patients with esophageal cancer, using the diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) sequence. DWIBS images were fused with T2-weighted images, and independently and blindly evaluated by three board-certified radiologists, regarding primary tumor detectability and lymph-node status. Apparent diffusion coefficients (ADCs) of the primary tumor and lymph nodes were also measured. Average primary tumor detection rate was 49.4%, average patient-based sensitivity and specificity for the detection of lymph-node metastasis were 77.8 and 55.6%, and average lymph-node group-based sensitivity and specificity were 39.4 and 92.6%. There were no interobserver differences among the three readers (P < 0.0001). Mean ADC of detected primary tumors was 1.26 ± 0.29×10⁻³ mm²/s. Mean ADC of metastatic lymph nodes (1.46 ± 0.35×10⁻³ mm²/s) was significantly higher (P < 0.0001) than that of nonmetastatic lymph nodes (1.15 ± 0.24 mm²/s), but ADCs of both groups overlapped. In conclusion, this study suggests that DWI only has a limited role in detecting esophageal cancer and nodal staging.     

Diagnostic utility of diffusion-weighted magnetic resonance imaging in diabetic mastopathy

We report the clinical findings in a 36-year-old woman with diabetic mastopathy. The lesion showed heterogeneous segmental enhancement on magnetic resonance imaging (MRI), resembling a malignant lesion, but diffusion-weighted imaging (DWI) showed no abnormalities and the apparent diffusion coefficient value did not decrease. This case emphasizes the utility of DWI for differentiating diabetic mastopathy from malignant breast lesions. The value of DWI lies in its ability to exclude the possibility of malignant breast lesions and thus to avoid unnecessary biopsy.     

Prediction of recovery from a post-traumatic coma state by diffusion-weighted imaging (DWI) in patients with diffuse axonal injury

Introduction To determine whether diffusion-weighted magnetic resonance (MR) imaging findings combined with initial clinical factors indicate the depth of shearing lesions in the brain structure and therefore relate to coma duration in diffuse axonal injury (DAI). Methods A total of 74 adult patients (48 male and 26 female) with DAI were examined with conventional MR imaging and diffusion-weighted MR imaging between 2 hours and 20 days after injury. Apparent diffusion coefficient (ADC) maps were obtained and the mean ADC values of each region of interest (ROI) were measured using MRI console software. The involvement of the brainstem, deep gray matter, and corpus callosum was determined for each sequence separately as well as for the combination of all sequences. The correlations between MR imaging findings indicating the presence of apparent brain injury combined with initial clinical factors were determined. Results Clinical characteristics, such as initial score on the Glasgow coma scale (GCS), age and number of all lesions, and ADC scores were predictive of the duration of coma. Conclusion It was possible to predict post-traumatic coma duration in DAI from cerebral MR imaging findings combined with clinical prognostic factors in the acute to subacute stage after head injury. Age, ADC scores, GCS score and number of lesions were highly significant in predicting coma duration. The technique presented here might provide a tool for in vivo detection of DAI to allow the prediction of the coma duration during the early stages in patients with traumatic brain injury. This paper is funded by Guangdong Provincial Department of Science and Technology, China (Grant No. 2005B33801010).     

Thin-section diffusion-weighted magnetic resonance imaging of the brain with parallel imaging

BACKGROUND: Thin-section diffusion-weighted imaging (DWI) is known to improve lesion detectability, with long imaging time as a drawback. Parallel imaging (PI) is a technique that takes advantage of spatial sensitivity information inherent in an array of multiple-receiver surface coils to partially replace time-consuming spatial encoding and reduce imaging time. PURPOSE: To prospectively evaluate a 3-mm-thin-section DWI technique combined with PI by means of qualitative and quantitative measurements. MATERIAL AND METHODS: 30 patients underwent conventional echo-planar (EPI) DWI (5-mm section thickness, 1-mm intersection gap) without parallel imaging, and thin-section EPI-DWI with PI (3-mm section thickness, 0-mm intersection gap) for a b value of 1000 s/mm(2), with an imaging time of 40 and 80 s, respectively. Signal-to-noise ratio (SNR), relative signal intensity (rSI), and apparent diffusion coefficient (ADC) values were measured over a lesion-free cerebral region on both series by two radiologists. A quality score was assigned for each set of images to assess the image quality. When a brain lesion was present, contrast-to-noise ratio (CNR) and corresponding ADC were also measured. Student t-tests were used for statistical analysis. RESULTS: Mean SNR values of the normal brain were 33.61+/-4.35 and 32.98+/-7.19 for conventional and thin-slice DWI (P>0.05), respectively. Relative signal intensities were significantly higher on thin-section DWI (P<0.05). Mean ADCs of the brain obtained by both techniques were comparable (P>0.05). Quality scores and overall lesion CNR were found to be higher in thin-section DWI with parallel imaging. CONCLUSION: A thin-section technique combined with PI improves rSI, CNR, and image quality without compromising SNR and ADC measurements in an acceptable imaging time.