Diffusion-weighted MR imaging in the early diagnosis of periventricular leukomalacia

Diffusion-weighted imaging (DWI) has been shown to be highly sensitive in detecting acute cerebral infarction, but its use in detecting hypoxic–ischemic encephalopathy (HIE) in neonates is still controversial. Moreover, few reports concern pre-term infants with possible periventricular leukomalacia (PVL). We examined the ability of this technique to detect cerebral changes in the acute phase of PVL. Fifteen MR examinations were performed in 11 pre-term infants (mean age 3.4 days, range 2–6 days). Conventional DWI sequences, apparent diffusion coefficient (ADC) maps, and US obtained in the acute phase were compared. All the neonates underwent US follow-up up to 4 months after delivery; those with suspected PVL also underwent MRI follow-up for up to 2 months. Qualitative and quantitative evaluations were performed to assess the presence of DW changes compatible with PVL. Diffusion-weighted MRI showed signal hyperintensity associated with decreased ADC values in 3 subjects (27%). In these patients conventional MRI sequences were interpreted as normal and US (performed at the same time) as doubtful in 2 and compatible with PVL in 1 subject. The MRI and US follow-up confirmed severe damage in all these patients. In 1 neonate hemorrhages involving the germinative matrix were identified. In 8 neonates MRI was considered normal. In these subjects US follow-up (up to 4 months) confirmed no signs of PVL. Diffusion-weighted imaging may have a higher correlation with later evidence of PVL than does conventional MR imaging and US when performed in the acute phase of the disease.     

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.     

MR扩散加权成像对颅内囊性肿块的鉴别诊断价值

目的 :探讨MR扩散加权成像对颅内囊性肿块的鉴别诊断价值。方法 :搜集有手术病理结果的患者 3 1例 ,其中表皮样囊肿 9例 ,蛛网膜囊肿 15例 ,囊性颅咽管瘤 4例 ,颅底囊性变神经鞘瘤 3例。所有病例均行MR常规T1WI、T2 WI及DWI扫描 ,回顾性分析各组病例的MR常规及扩散加权成像表现。结果 :在MR扩散加权图像上 ,所有 7例表皮样囊肿均为显著高信号 ,而在指数扩散加权像及ADC图上为等信号 ;其余病变在扩散加权图像上为低信号或伴等信号。结论 :MR扩散加权成像有助于表皮样囊肿与其它颅内脑外囊性肿块的鉴别 ,表皮样囊肿的扩散加权高信号主要是由“T2余辉效应”而非水分子扩散受限所致。     

Diffusion-weighted MR imaging in a rat model of syringomyelia after excitotoxic spinal cord injury.

BACKGROUND AND PURPOSE: Recent experimental data have shown that an increase of excitatory amino acids and the initiation of inflammatory responses within the injured spinal cord may play a role in post-traumatic syringomyelia. The purpose of this study was to determine whether diffusion-weighted MR imaging with apparent diffusion coefficient (ADC) maps could provide earlier evidence of spinal cord cavitation in a rat model of syringomyelia than available with conventional MR imaging. METHODS: The spinal cord gray matter of four rats was injected with the alpha-amino-3 hydroxy-5 methyl-4 isoxazole propionic acid/metabotropic receptor agonist quisqualic acid. Animals were sacrificed at 1, 4, or 8 weeks after injection, and the spinal cords were fixed in formalin for 1 week and imaged with T1-, T2-, and diffusion-weighted sequences. One control specimen was also imaged. ADC maps were constructed from the diffusion-weighted data. Histopathologic analyses of sections stained with cresyl violet were compared with the MR images. RESULTS: By 1 week after injection, ADC maps at the level of injection showed areas within the gray matter of increased intensity and increased ADC values as compared with the control specimen. These bright areas corresponded to cysts or cavities within the cord parenchyma on the histopathologic sections. The ADC values within affected gray matter areas progressively increased at 4 and 8 weeks, also corresponding to cyst formation. Conventional T1- and T2-weighted images showed corresponding lesions with cystic characteristics at 4 and 8 weeks, but not at 1 week. CONCLUSION: In an animal model of syringomyelia, diffusion-weighted imaging with ADC maps detected cystic lesions within spinal cord gray matter before they were seen on conventional T1- and T2-weighted images.     

Diffusion-weighted MR imaging of intracerebral masses: comparison with conventional MR imaging and histologic findings

BACKGROUND AND PURPOSE: The purposes of this study were to find the role of diffusion-weighted MR imaging in characterizing intracerebral masses and to find a correlation, if any, between the different parameters of diffusion-weighted imaging and histologic analysis of tumors. The usefulness of diffusion-weighted imaging and apparent diffusion coefficient (ADC) maps in tumor delineation was evaluated. Contrast with white matter and ADC values for tumor components with available histology were also evaluated. METHODS: Twenty patients with clinical and routine MR imaging/CT evidence of intracerebral neoplasm were examined with routine MR imaging and echo-planar diffusion-weighted imaging. The routine MR imaging included at least the axial T2-weighted fast spin-echo and axial T1-weighted spin-echo sequences before and after contrast enhancement. The diffusion-weighted imaging included an echo-planar spin-echo sequence with three b values (0, 300, and 1200 s/mm(2)), sensitizing gradient in the z direction, and calculated ADC maps. The visual comparison of routine MR images with diffusion-weighted images for tumor delineation was performed as was the statistical analysis of quantitative diffusion-weighted imaging parameters with histologic evaluation. RESULTS: For tumors, the diffusion-weighted images and ADC maps of gliomas were less useful than the T2-weighted spin-echo and contrast-enhanced T1-weighted spin-echo images in definition of tumor boundaries. Additionally, in six cases of gliomas, neither T2-weighted spin-echo nor diffusion-weighted images were able to show a boundary between tumor and edema, which was present on contrast-enhanced T1-weighted and/or perfusion echo-planar images. The ADC values of solid gliomas, metastases, and meningioma were in the same range. In two cases of lymphomas, there was a good contrast with white matter, with strongly reduced ADC values. For infection, the highest contrast on diffusion-weighted images and lowest ADC values were observed in association with inflammatory granuloma and abscess. CONCLUSION: Contrary to the findings of previous studies, we found no clear advantage of diffusion-weighted echo-planar imaging in the evaluation of tumor extension. The contrast between gliomas, metastases, meningioma, and white matter was generally lower on diffusion-weighted images and ADC maps compared with conventional MR imaging. Unlike gliomas, the two cases of lymphomas showed hyperintense signal on diffusion-weighted images whereas the case of cerebral abscess showed the highest contrast on diffusion-weighted images with very low ADC values. Further study is required to find out whether this may be useful in the differentiation of gliomas and metastasis from lymphoma and abscess.     

Diffusion-weighted imaging of patients with subacute cerebral ischemia: comparison with conventional and contrast-enhanced MR imaging

BACKGROUND AND PURPOSE: The importance of diffusion-weighted imaging (DWI) for delineating acute ischemic lesions has been investigated extensively; however, few studies have investigated the role of DWI in the subacute stage of stroke. Because these lesions tend to appear bright throughout the first days of ischemia, owing to restricted diffusion, we speculated that DWI could also improve the detection of subacute infarcts as compared with conventional and contrast-enhanced MR imaging. METHODS: Interleaved echo-planar DWI with phase navigation was performed on a 1.5-T MR unit in a consecutive series of 53 patients (mean age, 66 +/- 14 years) with suspected recent cerebral ischemia. The interval between onset of clinical symptoms and MR imaging ranged from 1 to 14 days (mean, 6 +/- 4 days). Contrast material was given to 28 patients in a dose of 0.1 mmol/kg. RESULTS: DWI clearly delineated recent ischemic damage in 39 patients (74%) as compared with 33 (62%) in whom lesions were identified or suspected on conventional T2-weighted images. DWI provided information not accessible with T2-weighted imaging in 17 patients when evidence of lesion multiplicity or detection of clinically unrelated recent lesions was included for comparison. Subacute ischemic lesions were also seen more frequently on DWI sequences than on contrast-enhanced images (20 versus 13 patients). DWI was more likely to make a diagnostic contribution in the first week of stroke and in patients with small lesions or preexisting ischemic cerebral damage than was conventional MR imaging. CONCLUSION: Recent ischemic damage is better shown on DWI sequences than on conventional and contrast-enhanced MR images throughout the first days after stroke and may provide further information about the origin of clinical symptoms. Adding DWI to imaging protocols for patients with subacute cerebral ischemia is recommended.     

Subarachnoid hemorrhage in the subacute stage: elevated apparent diffusion coefficient in normal-appearing brain tissue after treatment

PURPOSE: To prospectively evaluate whether subarachnoid hemorrhage (SAH) is associated with a change in the apparent diffusion coefficient (ADC) in normal-appearing brain parenchyma. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained for all patient and volunteer studies. One hundred patients (48 men, 52 women; mean age, 52 years +/- 12 [standard deviation]) with aneurysmal SAH underwent conventional and diffusion-weighted magnetic resonance (MR) imaging at a mean of 9 days +/- 3 after SAH to evaluate possible lesions caused by SAH, treatment of SAH, and vasospasm. Aneurysms were treated surgically (n = 70) or endovascularly (n = 30) before MR imaging. Diffusion-weighted MR imaging was performed at 1-year follow-up in 30 patients (10 men, 20 women; mean age, 51 years +/- 11). Thirty healthy age-matched volunteers (11 men, 19 women; mean age, 54 years +/- 16) underwent MR imaging with an identical protocol. ADC values were measured bilaterally in the gray and white matter (parietal, frontal, temporal, occipital lobes; cerebellum; caudate nucleus; lentiform nucleus; thalamus; and pons) that appeared normal on T2-weighted and diffusion-weighted MR images. Linear mixed model was used for comparison of ADC values of supratentorial gray matter and white matter; general linear regression analysis was used for comparison of ADC values of cerebellum and pons. RESULTS: In patients with SAH, the ADC values in normal-appearing white matter, with a single exception in the frontal lobe (P = .091), were significantly higher than they were in healthy volunteers (P /= .121). CONCLUSION: SAH and its treatment may cause global mild vasogenic edema in white matter and deep gray matter that is undetectable on T2-weighted and diffusion-weighted MR images but is detectable by measuring the ADC value in the subacute stage of SAH.     

MR line-scan diffusion-weighted imaging of term neonates with perinatal brain ischemia.

BACKGROUND AND PURPOSE: MR diffusion-weighted imaging provides early demonstration of neonatal brain infarction. The evolution and limitations of diffusion-weighted imaging findings in newborns, however, have not been evaluated. Using line-scan diffusion imaging (LSDI), we investigated perinatal ischemic brain injury. METHODS: Nineteen term newborns (age, 9 hours to 8 days; mean age, 2.6 days) with perinatal brain ischemia were evaluated using LSDI (1520/62.5/1 [TR/TE/excitations]) (b maximum = 750 s/mm2) and T1- and T2-weighted spin-echo (conventional) MR imaging. Follow-up examinations were performed in seven patients and autopsy in one. Apparent diffusion coefficients (ADCs) were measured in deep gray matter, white matter, the cortex, and focal lesions. RESULTS: Based on conventional MR imaging or pathologic findings, patients were divided into two groups. Group 1 (n = 12) had symmetric/diffuse injury consistent with global hypoperfusion. Group 2 (n = 7) had focal/multifocal injury suggesting cerebrovascular occlusion. ADCs were abnormal at initial examination in 10 newborns in group 1 and in all newborns in group 2. The results of LSDI were abnormal before conventional MR imaging was performed in three newborns in group 1. ADCs were maximally decreased between days 1 and 3 in deep gray matter, perirolandic white matter, and focal lesions. Delayed decreases in ADCs were observed in subcortical white matter from days 4 through 10 in three patients in group 1. CONCLUSION: After global hypoperfusion, LSDI showed deep gray matter and perirolandic white matter lesions before conventional MR imaging. LSDI may underestimate the extent of injury, however, possibly because of variations in the compartmentalization of edema, selective vulnerability, and delayed cell death. Differences in LSDI of symmetric/diffuse and focal/multifocal lesions may reflect differences in pathophysiology or timing of the injury. These findings may have implications for acute interventions.     

A preliminary report of brain edema in patients with uremia at first hemodialysis: evaluation by diffusion-weighted MR imaging

BACKGROUND AND PURPOSE: The dynamics of brain-water content associated with hemodialysis in patients with severe azotemia remains obscure. To investigate whether either interstitial or cytotoxic edema is responsible for dialysis disequilibrium syndrome (DDS), we used diffusion-weighted MR imaging (DWI) to measure the apparent diffusion coefficient (ADC), which is sensitive for detecting tissue water dynamics. METHODS: Eight consecutive patients with end stage renal disease (ESRD) and blood urea nitrogen level of more than 100 mg/dL (160.9 +/- 53.1 mg/dL) were recruited. Conventional MR images, DWI, and clinical manifestations were obtained before and after the 1st hemodialysis. The ADC values were determined for regions of normal-appearing gray and white matter and for regions of hyperintensity of white matter on T2-weighted MR imaging. RESULTS: Foci of bright areas of white matter were found in all patients on T2-weighted images. The ADC values of the patients with ESRD, in white matter and gray matter before and after hemodialysis, were greater than those of the healthy controls (P < .005). Regarding the impact of hemodialysis, the ADC of frontal lobe white matter increased significantly after hemodialysis (1.09 +/- 0.11 versus 1.03 +/- 0.11, P = .036). We did not find the specific area of brain edema reported in posterior leukoencephalopathy and the osmotic demyelination syndrome. CONCLUSIONS: These results suggest that severe azotemia in end stage renal disease leads to interstitial brain edema reflected as increased ADC, and the further increased ADC reflects that edema associated with 1st hemodialysis is interstitial rather than cytotoxic in nature.     

Evidence for cytotoxic edema in the pathogenesis of cerebral venous infarction

BACKGROUND AND PURPOSE: The pathogenesis of cerebral venous infarction (CVI) remains controversial, with uncertainty over whether cytotoxic edema plays a role. Recent animal studies have shown that cytotoxic edema reliably occurs in acute CVI and precedes the onset of vasogenic edema. Our hypothesis was that cytotoxic edema would also occur in acute human CVI and would be detectable as an area of restricted diffusion on diffusion-weighted images. METHODS: Twelve subjects with acute cerebral venous thrombosis confirmed by MR venography underwent both conventional MR and echo-planar diffusion-weighted imaging (maximum diffusion sensitivity [b=1000 s/mm(2)]). Images were examined for areas of CVI that were identified as T2 hyperintensity, diffusion hyperintensity, or hemorrhage. The percent change in apparent diffusion coefficient (ADC) and T2 signal as well as the T2/diffusion volume were calculated within areas of edematous CVI. Regression techniques were used to examine the relationship of these variables to symptom duration. RESULTS: Ten regions of CVI were detected in seven subjects, all showing T2 hyperintensity. Two of these regions were predominantly hemorrhagic and did not display diffusion hyperintensity. The remaining eight regions displayed diffusion hyperintensity that was associated with a decreased ADC. ADC values increased with symptom duration (r(2) = 0.96; P <.006). Both T2 hyperintensity and T2/diffusion volume peaked approximately 2 days after symptom onset. CONCLUSION: Restricted water diffusion suggesting cytotoxic edema is commonly found in subjects with acute CVI and decreases over time. This supports an important etiologic role for cytotoxic edema in the pathogenesis of CVI.     

Diffusion-weighted MR imaging of encephalitis.

OBJECTIVE: Our purpose was to evaluate how well diffusion-weighted MR imaging shows viral or bacterial encephalitis in comparison with conventional MR imaging that includes T1- and T2-weighted spin-echo and fluid-attenuated inversion-recovery sequences. CONCLUSION: In nine of the 13 patients examined, diffusion-weighted imaging was superior to other diagnostic imaging sequences (fluid-attenuated inversion-recovery sequences in eight patients and a T2-weighted spin-echo sequence in one patient). Diffusion-weighted imaging can serve as a method of detecting early encephalitic changes.     

Cerebral aneurysms treated by Guglielmi detachable coils: evaluation with diffusion-weighted MR imaging

BACKGROUND AND PURPOSE: The most frequent and serious complications of endovascular treatment of intracranial aneurysms with Guglielmi detachable coils (GDCs) are ischemic lesions caused by thromboembolic events. Diffusion-weighted MR imaging appears to be the most sensitive technique for detecting early ischemic phenomena. We evaluated this technique for the detection of brain changes in patients who underwent GDC treatment of aneurysms. METHODS: Twenty patients with a cerebral aneurysm were studied with diffusion-weighted imaging before and after endovascular treatment with GDCs. Aneurysms were located in the anterior (n = 16) or posterior (n = 4) circulation. Bleeding had occurred in 11 patients. MR studies, including fast fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted sequences, were scheduled before, 2 to 4 hours after, and 48 hours after treatment. MR images, including apparent diffusion coefficient (ADC) maps, were assessed for the presence of acute ischemic stroke lesions. RESULTS: In all patients, the aneurysm was excluded without neurologic worsening. In 18 patients, diffusion-weighted and FLAIR images showed no evidence of recent ischemic lesions after treatment. In one patient, an asymptomatic frontobasal hyperintense signal on diffusion-weighted images with a drop of ADC values corresponding to an acute ischemic lesion was observed. In another patient, multiple silent lesions were seen on diffusion-weighted images after embolization. These silent lesions were not all located in the vascular territory of the aneurysm's parent artery. CONCLUSION: This preliminary study suggests that diffusion-weighted MR imaging is a potentially useful tool for monitoring patients after endovascular treatment of a cerebral aneurysm. While small asymptomatic lesions can be observed on these images after embolization, their exact prevalence should be evaluated in a larger series.     

Diffusion-weighted MR imaging in patients with phenylketonuria: relationship between serum phenylalanine levels and ADC values in cerebral white matter

PURPOSE: To prospectively determine the relationship between serum phenylalanine levels and apparent diffusion coefficient (ADC) values in the cerebral white matter of patients with phenylketonuria (PKU). MATERIALS AND METHODS: Institutional review board approval was obtained, and participants provided informed consent. Magnetic resonance (MR) imaging, which included T1- and T2-weighted, fluid-attenuated inversion-recovery (FLAIR), and diffusion-weighted examinations, was performed in 21 patients with PKU (nine male and 12 female patients; age range, 3-44 years; mean age, 19.4 years). ADC values in deep cerebral white matter were calculated for each patient. Serum phenylalanine levels were obtained in all patients within 12 days after MR imaging. Serum phenylalanine levels were measured in 16 patients 1 year before MR imaging. ADC values in cerebral white matter and serum phenylalanine levels were compared. A total of 21 control subjects (12 male and nine female patients; age range, 3-33 years; mean age, 20.6 years) underwent MR imaging. ADC values in cerebral white matter were compared with serum phenylalanine levels by using the Pearson correlation. RESULTS: Abnormal high signal intensity in white matter on T2-weighted and FLAIR MR images was noted in patients with PKU who had serum phenylalanine levels of more than 8.5 mg/dL (514.2 micromol/L). Diffusion in posterior deep cerebral white matter tended to be restricted in patients when increased serum phenylalanine levels were measured after MR imaging (r = -0.62). There was a correlation between ADC values in posterior cerebral white matter and serum phenylalanine levels measured 1 year before MR imaging (r = -0.77). ADCs of control subjects were significantly higher than ADCs of patients with PKU (P < .005). CONCLUSION: Posterior deep white matter in patients with PKU and a serum phenylalanine level of more than 8.5 mg/dL showed high signal intensity in white matter on T2-weighted and FLAIR MR images and revealed decreased ADC. We suggest that to avoid brain-restricted diffusion due to hyperphenylalanemia, patients with PKU should maintain serum phenylalanine levels of less than 8.5 mg/dL (514.2 micromol/L).     

Arterial hyperintensity on fast fluid-attenuated inversion recovery images: a subtle finding for hyperacute stroke undetected by diffusion-weighted MR imaging

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging is generally acknowledged to be more sensitive in detecting acute stroke than is conventional MR imaging. Our purpose in the present study was to evaluate the utility of fast fluid-attenuated inversion recovery (FLAIR) MR imaging compared with that of diffusion-weighted MR imaging for the diagnosis of hyperacute stroke. METHODS: We reviewed patient records and cerebral MR images from all patients in a 13-month period from whom diffusion-weighted and fast-FLAIR imaging were obtained within 6 hours after symptom onset (n = 11). Special attention was paid to the presence or absence of arterial hyperintensity on FLAIR images and abnormally high-signal regions on diffusion-weighted images in the affected vascular territories. RESULTS: Arterial hyperintensity was found in eight of 11 patients, all of whom had embolic or thrombotic infarctions with middle cerebral arterial (MCA) distribution. Arterial hyperintensity was negative in the remaining three patients; the vascular territories were the posterior circulation region in two of these patients and the MCA region in one, and the types of infarction in these same patients were lacunar in two and embolic in one. Regions with high-signal diffusion abnormalities relevant to the patients' symptoms were found in 10 of 11 patients. One patient showed no diffusion abnormalities but the presence of arterial hyperintensity in the affected MCA territory on the initial MR examination, and manifested embolic infarction along with arterial hyperintensity on the initial FLAIR image. CONCLUSION: Although diffusion-weighted MR imaging is highly sensitive to stroke, diffusion-weighted MR imaging alone may not rule out a possible infarction. Arterial hyperintensity on FLAIR images can precede diffusion abnormalities and may provide a clue to the early detection of impending infarction.     

Intracranial epidermoid cysts: diffusion-weighted, FLAIR and conventional MR findings

PURPOSE: To compare diffusion-weighted echo-planar imaging (DW) with spin-echo (SE), and fluid-attenuated inversion recovery (FLAIR) sequences in the evaluation of epidermoid cysts (ECs), and to evaluate T2 shine-through effect. MATERIALS AND METHODS: Fifteen patients were imaged prospectively in two different 1.5 T magnetic resonance (MR) units with standard head coils with SE, FLAIR and DW echo planar imaging sequences. The qualitative and quantitative assessments were performed by two radiologists in consensus. Apparent diffusion coefficient (ADC) values were obtained from all ECs. Exponential DW images are obtained in 11 cases to eliminate T2 shine-through effects. The results are analyzed with variance analysis (ANOVA) and Bonferroni t method. RESULTS: FLAIR sequence was superior to T1- and T2-weighted sequences in showing ECs. In 13 cases, the borders of the lesions could be delineated from the surrounding structures with only DW imaging where ECs were markedly hyperintense. The ADC values of ECs are significantly lower than CSF (P < 0.001), and significantly higher than deep white matter (P < 0.01). On exponential DW images, ECs had similar intensity with brain parenchyma showing that the real cause of the hyperintensity of the lesions on trace images is the enhanced T2 effect of the tissue. CONCLUSION: FLAIR sequence is superior to the conventional MR sequences in demonstrating the ECs and DW imaging is superior to other MR sequences in delineating the borders of the ECs. Exponential DW images had shown that the hyperintensity in the trace images are caused by increased T2 effect of the lesion rather than the decrease in ADC values.     

新生儿缺氧缺血性脑病的MR诊断及临床相关因素分析

目的：探讨磁共振成像对新生儿缺氧缺血性脑病（hypoxic ischemic encephalopathy,HIE)的诊断价值及临床的相关性。方法：搜集62例临床诊断为HIE的患儿，对其进行常规MRI的T1WI、T2WI及FLAIR序列检查。结果：HIE患儿MRI的T1WI及FLAIR序列病灶检出率明显高于T2WI（P＜0.05)；早产儿病变区域多位于脑室旁、室管膜下及基底区；足月儿病变区域多位于大脑皮质及颞顶部；新生儿HIE早期Apgar评分与MRI脑白质损伤影像分级及远期后遗症有一定相关性，非绝对相关，而另与胎龄有关。结论：MRI对HIE的诊断有高度的敏感性；不同胎龄HIE患儿脑损伤区域不同，后遗症状亦不相同。     

Assessment of diffusion and perfusion deficits in patients with small subcortical ischemia

BACKGROUND AND PURPOSE: Using perfusion- and diffusion-weighted MR imaging in acute ischemic stroke of the middle cerebral artery (MCA), previous studies have shown a typical pathophysiologic pattern that is characterized by a perfusion deficit larger than the diffusion lesion (mismatch), with the final lesion usually comprising the initial diffusion lesion (core) plus parts of the initial mismatch area. Little is known about underlying pathophysiology in small ischemic stroke. In this study, we used perfusion- and diffusion-weighted MR imaging to investigate the underlying pathophysiology of small subcortical ischemia. METHODS: Six consecutive patients (age range, 42-76 years) with small subcortical ischemia were examined by using a 1.5-T MR system 2-5, 22-55, and 144-392 hours after the onset of symptoms. T2-weighted, diffusion-weighted imaging at b=0 s/mm2 and b=1000 s/mm2, and bolus-track perfusion-weighted imaging were performed. Lesion sizes were determined on the basis of T2-weighted findings as well as those of apparent diffusion coefficient (ADC) maps and CBF. RESULTS: In every patient, the initial CBF lesion was smaller than the initial ADC lesion. Both the CBF lesion and the ADC lesion increased in size from first to second examination. In all instances, however, the CBF lesion remained smaller than the ADC lesion. The CBF lesion observed during the acute phase and the one seen on the following days were both smaller than the final T2 lesion. CONCLUSION: Our data suggest that in contrast to previous findings in MCA ischemia in small subcortical infarcts tissue damage may spread beyond the area of the initial perfusion disturbance. In light of the small number of patients, further studies will have to address the relevance of this observation.     

Traumatic brain injury: diffusion-weighted MR imaging findings.

BACKGROUND AND PURPOSE: Diffuse axonal injury (DAI) accounts for a significant portion of primary intra-axial lesions in cases of traumatic brain injury. The goal of this study was to use diffusion-weighted MR imaging to characterize DAI in the setting of acute and subacute traumatic brain injury. METHODS: Nine patients ranging in age from 26 to 78 years were examined with conventional MR imaging (including fast spin-echo T2-weighted, fluid-attenuated inversion-recovery, and gradient-echo sequences) as well as echo-planar diffusion-weighted MR imaging 1 to 18 days after traumatic injury. Lesions were characterized as DAI on the basis of their location and their appearance on conventional MR images. Trace apparent diffusion coefficient (ADC) maps were computed off-line with the diffusion-weighted and base-line images. Areas of increased signal were identified on the diffusion-weighted images, and regions of interests were used to obtain trace ADC values. RESULTS: In the nine patients studied, isotropic diffusion-weighted images showed areas of increased signal with correspondingly decreased ADC. In one case, decreased ADC was seen 18 days after the initial event. CONCLUSION: Decreased ADC can be demonstrated in patients with DAI in the acute setting and may persist into the subacute period, beyond that described for cytotoxic edema in ischemia.     

大鼠超急性期脑缺血的磁共振扩散加权成像研究

目的：利用磁共振扩散加权成像（DWI）评价大鼠超急性期脑缺血的诊断价值。方法：12只Wistar雄性大鼠,采用线栓法制作右侧大脑中动脉闭塞（MCAO）脑缺血模型,分别于栓塞后1h和6h行大鼠冠状位磁共振DWI、T2WI和T1WI检查,并测量缺血区DWI异常高信号的体积、表观扩散系数（ADC）值,将所测值进行比较。磁共振检查结束后处死大鼠,断头取脑行TTC染色,并与DWI结果进行比较。结果：大鼠MCAO后1h进行MRI扫描右侧大脑中动脉供血区DWI可见异常稍高信号,ADC为低信号,T2WI和T1WI均未见异常信号;MCAO后6hDWI可见明显高信号,较1hADC值显著减低（P〈0.01）,DWI上梗死灶体积显著扩大（P〈0.01）,T2WI显示缺血区异常高信号,T1WI可见稍低信号。TTC染色者均显示脑梗死灶,与MCAO后6h的DWI显示脑缺血范围一致。结论：DWI对超急性期脑梗死较常规MRI敏感,是超急性期脑缺血重要的检查方法。     

Case report: diffusion-weighted MRI in anterior spinal artery stroke of the cervical spinal cord

The authors present a case of anterior spinal artery stroke demonstrated by diffusion-weighted MRI (DWI) using single-shot echo-planar imaging. DWI clearly demonstrated hyperintensity with a decreased apparent diffusion coefficient (ADC) at 26 hours after onset. At 28 days, there was persistent hyperintensity with an increased ADC, corresponding to T2-weighted hyperintensity in the whole spinal gray matter at the C2-C7 vertebral level. DWI provided satisfactory images and was helpful for diagnosing and evaluating anterior spinal artery stroke.