急性缺血再灌注心肌磁共振成像实验研究

目的：通过MR灌注成保评价急性梗死心肌组织血流灌注特点。方法：采用结扎左前降支90min存灌注的方法建立为存灌注梗死心肌组，对6只犬行MRI灌注成保及延迟扫描，观察犬心肌缺血存灌注模型梗死心肌MRI特点。结果：犬心肌缺血存灌注梗死心肌MR灌注成保表现为灌注缺损区，延迟扫描表现为高信号。结论：MR灌注成保有助于评价心肌血流，诊断心肌缺血存灌注梗死心肌。     

Diffusion-weighted MR imaging in acute spinal cord ischemia

We report diffusion-weighted (DW) MR findings for acute spinal cord ischemia in a 56-year-old patient. MR imaging obtained approximately 3 h after symptom onset demonstrated an area of hyperintensity on DW images, but no conspicuous signal abnormality on T2-weighted images in the conus medullaris. DW imaging of the spinal cord can contribute to the early detection of spinal cord vascular compromise.     

猫急性脑静脉闭塞模型的MR扩散加权成像与病理学对照研究

目的用MR扩散加权成像(DWI)和病理学方法对急性脑静脉闭塞动物模型进行评价。方法家猫22只,用随机数字表法分为2组(手术组18只,假手术组4只)。采用开颅上矢状窦穿刺注射液体栓塞剂醋酸纤维素聚合物(CAP)联合双侧颈外静脉结扎制备急性脑静脉闭塞动物模型,在术后1、3、6、12、24、48h用DWI、T2WI、液体衰减反转恢复序列(fluid attenuated inversionrecovery,FLAIR)对模型行连续MR扫描,测量异常高信号最大层面相对面积(rs)比例、相对表观扩散系数(rADC)值,并和大体标本、光学显微镜及电子显微镜作对照研究。结果仅DWI能显示早期脑实质病变,3h后,DWI、T2WI及FLAIR均能显示病变,24h后,DWI呈高、等混杂信号改变。术后1h,与对照组比较,rADC下降至(50.2±6.9)%,3~12h间,rADC缓慢上升。平均上升速率每小时8.7%,12~24h间,rADC又下降,平均下降速率每小时4.75%,24~48h,rADC又缓慢上升至接近对照组的水平。1h和48h时间点,rADC差异有统计学意义(t=10.2335,P<0.01)。大体病理学14只猫上矢状窦及桥静脉及皮层静脉内见CAP凝固呈铸型改变,12h后窦旁皮层病变区被伊文思蓝不同程度蓝染。显微病理学见术后1~3h以细胞内毒性水肿为主,3~24h血管源性水肿逐渐出现并占优势,24~48h出现出血性脑梗死。假手术组4只猫均未见上述各种异常表现。结论DWI能区分脑静脉闭塞后的脑水肿类型,早期评价脑组织损伤的程度。     

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.     

Contrast-enhanced MR imaging of experimental acute tubular necrosis

Purpose: To demonstrate the involvement of the various renal structures in acute tubular necrosis (ATN).Material and Methods: In 15 rats, using a T1-/T2-weighted sequence, either gadodiamide alone, or gadodiamide in combination with sprodiamide (a susceptibility agent) were used to enhance the various anatomical substrates of the kidney. The results were compared to those of pathological verification.Results: Experimentally induced ATN of the rat kidney causes profound changes in the medulla, leaving the cortex largely intact. The difference between the normal cortex and the partially necrotic outer medulla, on the one hand, and the papillary region, was significantly enhanced with the combination, whereas a larger region composed of the inner and outer medulla was enhanced after the gadolinium chelate alone.Conclusion: The results varied considerably between the two procedures; the double contrast demonstrated a clear difference between the inner and outer medulla, and the gadolinium chelate alone demonstrated a clear difference between the medulla and the cortex. These results demonstrated a clear difference in the compartmentalization between the inner and outer medullary regions, providing complementary information about the pathological condition of the kidney.     

Diffusion-weighted MR imaging of acute stroke: correlation with T2-weighted and magnetic susceptibility-enhanced MR imaging in cats

We evaluated the temporal and anatomic relationships between changes in diffusion-weighted MR image signal intensity, induced by unilateral occlusion of the middle cerebral artery in cats, and tissue perfusion deficits observed in the same animals on T2-weighted MR images after administration of a nonionic intravascular T2 shortening agent. Diffusion-weighted images obtained with strong diffusion-sensitizing gradient strengths (5.6 gauss/cm, corresponding to gradient attenuation factor, b, values of 1413 sec/mm2) displayed increased signal intensity in the ischemic middle cerebral artery territory less than 1 hr after occlusion, whereas T2-weighted images without contrast usually failed to detect injury for 2-3 hr after stroke. After contrast administration (0.5-1.0 mmol/kg by Dy-DTPA-BMA, IV), however, T2-weighted images revealed perfusion deficits (relative hyperintensity) within 1 hr after middle cerebral artery occlusion that corresponded closely to the anatomic regions of ischemic injury shown on diffusion-weighted MR images. Close correlations were also found between early increases in diffusion-weighted MR image signal intensity and disrupted phosphorus-31 and proton metabolite levels evaluated with surface coil MR spectroscopy, as well as with postmortem histopathology. These data indicate that diffusion-weighted MR images more accurately reflect early-onset pathophysiologic changes induced by acute cerebral ischemia than do T2-weighted spin-echo images.     

Gd-enhanced MR imaging of acute and chronic experimental demyelinating lesions

Experimental allergic encephalomyelitis, a demyelinating disease with marked similarity to multiple sclerosis, was produced in two of 12 dogs. All dogs were studied with serial MR imaging. T1- and T2-weighted MR images were obtained both before and after IV Gd-DTPA. Multiple, new periventricular white matter demyelinating lesions were observed after each clinical episode of the disease. Like multiple sclerosis, the acute lesions of experimental allergic encephalomyelitis on T2-weighted MR images were indistinguishable from the older, more chronic lesions. However, after Gd-DTPA, there was bright paramagnetic enhancement of the acute lesions and, in one animal, no enhancement of the chronic lesions on T1-weighted MR images. At necropsy, the differences in the MR paramagnetic enhancement correlated well with the relative histologic age of the demyelinating lesions. Our results suggest that MR with Gd-DTPA may be used to differentiate acute, active demyelinating lesions from the more chronic, inactive lesions in this animal model.     

MR imaging of acute cerebral infarction: experimental study with Gd-DTPA

To evaluate the sensitivity of MR imaging for acute cerebral infarction and the effectiveness of MR enhancement with Gd-DTPA, we created a canine model of cerebral infarction by transarterial embolization (TAE). The external and internal carotid arteries were embolized respectively through a transfemoral catheter. MR imaging was performed with the Yokogawa Medical System prototype superconducting MR machine "Resona" operating at 0.35 Tesla. MR enhancement was done with 0.4 mmol/kg of Gd-DTPA. Early detectability without Gd-DTPA was 60% (3/5) two hours after TAE and 67% (4/6) at three hours. MR imaging showed high-intensity lesions on the T2-weighted sequence (SE 2000/100). The T1-weighted sequence (SR 250-600/25-35) did not reveal any lesions four hours after TAE. Five animals which received Gd-DTPA showed abnormal enhancement in the brain parenchyma within 30 min after Gd injection on the T1 weighted sequence. Gd-DTPA enhancement not only improved early sensitivity for acute cerebral infarction when MR imaging without Gd-DTPA was negative, but also enhanced the size and number of lesions compared with SE 2000/100 images without enhancement. The breakdown of the blood-brain barrier was suggested to be an important factor in Gd-DTPA enhancement.     

MR imaging of experimental demyelination

Seventeen rabbit sciatic nerves undergoing experimental demyelination and 17 control nerves were imaged in vivo with a 0.3-T MR imaging system using a silicone chamber wrapped around the nerves to isolate them from surrounding tissues. Three pulse sequences were used for each nerve: (1) spin-echo 500/28 (TR/TE), (2) spin-echo 2000/56, and (3) inversion recovery 1000/300/30 (TR/TI/TE). Image intensity data were acquired for each nerve by placing a region of interest over the nerve and measuring pixel brightness within the region of interest by means of a computer algorithm. The mean signal intensity of the experimental nerve was then compared with the mean signal intensity of the contralateral control nerve on the same image. Histologic sections of the nerves were stained with Loyez's stain for myelin and thionin for glial cells. MR findings were then compared with histopathologic data. Experimental nerves showed distinct stages of demyelination. Two fundamental observations were surmised from the data: (1) Perceptible MR signal changes are associated with early nerve degeneration, in which there is demyelination in the absence of glial cell proliferation; these changes are appreciated as increased intensity on heavily T2-weighted sequence. In these nerves no signal changes are seen on T1-weighted sequences. (2) Perceptible MR signal changes are associated with more advanced nerve degeneration, in which there is an increase in the number of glial cells in the absence of further demyelination; these changes are appreciated as decreased intensity on T1-weighted sequences and markedly increased intensity on T2-weighted sequences, respectively. The results show that MR can distinguish stages of demyelination in degenerating nerves, thereby providing a powerful method for the diagnosis and characterization of demyelinating disease.     

Reversibility of experimental acute renal failure in rats: assessment with USPIO-enhanced MR imaging

The purpose of this study was to evaluate the potential reversibility of kidney lesions in an experimental model of acute renal failure using ultra-small particles of iron oxide (USPIO)-enhanced magnetic resonance (MR) imaging. This study was conducted in 21 uninephrectomized rats using a model of iodinated contrast media-induced renal failure. Thirteen rats received selective intraarterial renal administration of diatrizoate (370 mg/ml) and were compared with two control groups, including six animals injected with saline and two noninjected animals. MR imaging was performed 28 hours, 8 days, and 22 days after the procedure. Each MR session included axial and coronal T1- and coronal T2-weighted images before and after intravenous administration of 60 micromol Fe/kg of USPIO. The rats were sacrificed immediately after the last MR session for pathologic evaluation. MR images were qualitatively and quantitatively interpreted with respect to pathologic data, and differences were statistically studied. At day 22, histology showed 4 severely diseased kidneys with focal areas of necrosis, 5 mildly diseased kidneys with tubular vacuolization, and 12 normal kidneys. On quantitative data, a high correlation between the percentage of negative enhancement and histologic data was observed (P < 0.05). Qualitative interpretation showed a sensitivity and specificity of USPIO-enhanced T2-weighted MR images of 88% and 91%, respectively. Follow-up enhancement curves showed a constant increase of intrarenal USPIO negative enhancement in normal kidneys between day 1 and day 22, whereas all severely involved kidneys displayed higher USPIO negative enhancement at day 1 without significant changes over time until day 22. USPIO may be useful for in vivo follow-up of the reversibility of experimentally induced iodinated contrast media renal impairment in animals.     

急性脑缺血表观扩散系数成像的实验研究

用改良的线栓法大脑中动脉阻塞模型,探讨急性脑缺血及再灌注的表现扩散系数成像特点。方法：２０只ＳＤ大白鼠,分为４组：Ａ组（８只）,非再通组,Ｂ、Ｃ、Ｄ组（各４只）,分别于ＭＣＡＯ３０ｍｉｎ、１ｈ、２ｈ后再通,于不同时间点作ＡＤＣ成像和Ｔ２ＷＩ,并测量感兴趣区的ＡＤＣ、相对ＡＤＣ（ｒＡＤＣ）。结果：ＭＣＡＯ后１５ｍｉｎ好出现缺血区ＡＤＣ下降,而Ｔ２ＷＩ最早在栓塞后２ｈ出现异常。６ｈ内缺血区,ＡＤＣ及ｒ     

MR imaging of acute spinal cord injury: results of an experimental study in dogs

A weight-drop model was used to induce 16 acute lesions of varying severity in the spinal cords of eight mongrel dogs. The subsequent 3- to 7-hr postinjury MR images (0.5 T) were assessed. T1-weighted images contributed little information. Injection of gadolinium tetra-azacyclododecane tetraacetic acid did not result in significant enhancement. T2-weighted sequences offered precise detection and delineation of the lesions, displaying fusiform hyperintense signal abnormalities that corresponded to both edema and hemorrhage. In low-impact injuries, abnormalities were small and centrally located, sparing the periphery of the spinal cord. In these cases hemorrhage was minimal and limited to the center of the lesion. In severe-impact injuries, MR showed widespread longitudinal extension with involvement of the periphery of the spinal cord. In the most severe injuries, a central heterogeneous signal component was frequently observed opposite the site of impact because of important hemorrhage within the cord. Overall, hyperintense areas correlated closely with lesion severity, as demonstrated by pathologic findings. T2-weighted MR images obtained at 0.5 T were found to be reliable in the evaluation of acute spinal cord trauma.     

MR of acute experimental allergic encephalomyelitis

Acute experimental allergic encephalomyelitis, an animal model of CNS inflammatory and demyelinating disease, was produced in guinea pigs and imaged with MR. Correlation of histopathology with MR revealed acute mononuclear perivascular inflammatory changes and edema corresponding to the high-intensity abnormalities observed on long repetition time (TR) images. Our results suggest that in acute multiple sclerosis the high intensity noted on long TR images may be secondary to associated inflammatory changes rather than to demyelination.     

MR imaging of acute coccidioidal meningitis

BACKGROUND AND PURPOSE: Our purpose was to describe the MR imaging findings in patients with acute coccidioidal meningitis. METHODS: Fourteen patients (11 men, three women; 22-78 years old; mean age, 47 years) with coccidioidal meningitis underwent neuroimaging within 2 months of diagnosis. Thirteen patients had MR imaging and one had an initial CT study with a follow-up MR examination 5 months later. Initial and follow-up MR images were evaluated for the presence of ventricular dilatation, signal abnormalities, enhancement characteristics, sites of involvement, and evidence of white matter or cortical infarction. The patterns of enhancement were characterized as focal or diffuse. Pathologic specimens were reviewed in two patients. RESULTS: Ten of the 14 images obtained at the time of initial diagnosis showed evidence of meningitis. All of the initially abnormal studies showed enhancement in the basal cisterns, sylvian fissures, or pericallosal region. Subsequent studies, which were available for three of the four patients with normal findings initially, all eventually became abnormal, with focal enhancement seen on the initial abnormal examination. Other abnormalities seen at presentation included ventricular dilatation (six patients) and deep infarcts (four patients). Pathologic specimens in two patients showed focal collections of the organism corresponding to the areas of intense enhancement on MR images. CONCLUSION: Early in its disease course, coccidioidal meningitis may show areas of focal enhancement in the basal cisterns, which may progress to diffuse disease. Pathologically, the areas of enhancement represent focal collections of the organism. Deep infarcts and communicating hydrocephalus are associated findings.     

急性胰腺炎的MRI评价

轻型急性胰腺炎在MRI上主要表现为胰腺小叶间隔增厚和胰周信号异常;重症急性胰腺炎常伴有出血、坏死和胰周不同程度的积液.MRI在显示出血、胰管的完整性以及揭示急性胰腺炎的病因方面有独特的价值,MRI严重度指数是评价急性胰腺炎严重程度的可靠方式.     

急性胰腺炎的MRI评价

轻型急性胰腺炎在MRI上主要表现为胰腺小叶间隔增厚和胰周信号异常;重症急性胰腺炎常伴有出血、坏死和胰周不同程度的积液。MRI在显示出血、胰管的完整性以及揭示急性胰腺炎的病因方面有独特的价值,MRI严重度指数是评价急性胰腺炎严重程度的可靠方式。