| The spinal cord is a clinically eloquent site within the central nervous system, containing important sensorimotor tracts confined within a small cross-sectional area. Spinal cord injury(SCI)is associated with physical and psychological disorder that causes disability and requires diagnose and intensive treatment in the early stage of the diesese.In fact,most patients with reversible clinical symptoms do not show any spinal cord abnormalities on conventional T2-weighted images.Therefore,an alternative imaging technique that permits assessment of relatively early changes is necessary. Characterization of the structural integrity of the spinal cord can be assessed using diffusion tensor imaging methods.DTI is rapidly becoming an established technique that non-invasively maps microscopic structural information of oriented tissue in vivo. Diffusion tensor MRI permits non-invasive determination of the course of nerve fiber tracts and is increasingly employed to guide neurosurgical interventions in order to minimize nerve injury as well as to observe the development of tracts and their changes in disease.The measurement of apparent diffusion coefficient and fractional anisotropy values provides unique quantitative information pertaining to structural and orientational features of spinal cord.Development and application of this technique may improve our understanding of the nature and evolution of structural damage in spinal cord disease.While DTI was being widely used to demonstrate subtle abnormalities in a variety of diseases in the brain,its use in spinal cord was limited.The requirements that need to be met in order to successfully produce these images fall into three main categories: a.high spatial resolution(the spinal cord is only 12 mm in diameter);b.insensitivity to motion(the spinal cord is surrounded by flowing CSF and is adjacent to structures that are moving due to respiration and swallowing);and c.insensitivity to spatially rapid changes in susceptibility(the spinal cord is adjacent to a large bony structure, the spinal column).These limitations largely ruled out the use.In this study,pulse sequence methodology and the applications of spinal cord diffusion tensor imaging will be described.The aim of the study was to study the feasibility and clinical values of DTI,both in in experimental rodent spinal cord acute injury models and the human being,the volunteers and cervical spondylosis cases were included.Additional goals were to demonstrate the three-dimensional fiber tracks of white matter of spinal cord and to assess for diffusion anisotropy.The possible future development of this field will be discussed,as well as areas of particular clinical interest. PURPOSE1.To establish an ideal animal model of spinal cord acute injury for the proper diffusion tensor magnetic resonance imaging.2.To observe the quantitative diffusion tensor magnetic resonance imaging feature of rabbit acute spinal cord injury model with different degree,evaluate the different compressed injury degree with spinal cord function.3.To observe the histopathologic changes of spinal cord tissue in rabbit spinal cord acute injury with different injury degree.4.To evaluate the correspondence analysis with diffusion tensor magnetic resonance imaging feature and histopathologic changes in the rabbit spinal cord acute injury,to investigate the feasibility and application of DTI.METHODSThe anatomy of rabbit thoracic vertebrae was studied in detail before establishing the acute injury model.The diameter with saggital and transverse direction of thoracic vertebral canal and diameter of thoracic spinal cord were measured.According to the measure data,different catheters with 1mm,2mm,3mm diameter balloon were chosen for different injury degree.21 rabbits with body weight between 2.5 and 4 kg used in the experiment were divided into three groups randomly according to different injury degree and received compression injuries at thoracic level T10,which caused different degree and reproducible lesions of the injured spinal cord parenchyma. Conventional and diffusion tensor MR imaging were performed with on 1.5 SINMENS Sonata MR scanner in vivo in anesthetized rabbits of each group pre and post injury.The ADC,FA were measured on a sagittal section in the lesion of each model.Animals were killed by overdose anesthesia,take out the injury spinal cord immediately.Take a 1cm3 spinal cord tissue to stained in 10%methanal,routine embedding,section,dyed by HE and observed under miscroscope and photography each sample.Take 1 mm3 spinal cord tissue stained in 2%glutaral,desiccation by 70-100%alcohol and acetone,Epon-812 routine embedding,stabilization by 1% osmium acid,and observed by 1200EX transmission electron miscroscope and photography.Histological pathology exam of the lesion in spinal cord were performed in each group.RESULTSExcept the additional overdose of anesthesia,and other two were picked out of the team because of additional spinal cord injury before fulfilling the balloon,the other 18 rabbit models were established and completed the MR and pathologic exam successfully(mild n=7;moderate n=5;severe n=6).ADC and FA were(1.15±0.39)×10-6mm2/s and(0.48±0.07)×10-3of spinal cord in mild injury group;ADC and FA values were(1.41±0.24)×10-6mm2/s and (0.39±0.15)×10-3in moderate group;ADC and FA values were(1.59±0.03)×10-6mm2/s and(0.30±0.10)×10-3on severe group.There was statistically significant difference(F=10.85,P=0.0012)between the ADC in spinal cord acute compression injury with different degree,and there was also statistically difference(F=4.64,P=0.027)between the FA in the lesion with different groups. Different spinal cord pathologic changes were confirmed in each group by histopathology results.The diffusion tensor magnetic resonance images and color diffusion tensor tracking maps of the spinal cord were obtained.CONCLUSIONS1.The rabbit acute injury model of spinal cord in this study was an improved and useful model for diffusion tensor magnetic resonance examination,which maked the experiment simplification and standardization.2.The study showed that diffusion tensor in vivo MR imaging had the potential to be used in studying the progression of pathologic changes in spinal cord acute compression injury.Diffusion tensor MR imaging appears now as a major non-invasive tool in studying structure-function relationships between different injury degree and different pathologic characteristics of the injured spinal cord.Upcoming directions include the use of diffusion tensor MR imaging on in vivo animal models and their applications to clinics. PURPOSE1.To study the technical feasibility and parameter feature of diffusion tensor MR imaging in the normal cervical spinal cord.2.To acquire the normal values of DTI parameters in normal volunteers in order to offer the basis for the research of the cervical spinal cord disorders.3.To determine the methodology and application of diffusion tensor tracking in the normal cervical spinal cord.METHODSA total of 42 normal volunteers entered this study.Single shot echo planar diffusion tensor images were obtained in a 1.5T MR scanner using phased-array spinal coil.The values of apparent diffusion coefficient(ADC),fractional anisotropy(FA),λ1,λ2,andλ3,were measured in the interested regions at the level of each vertebral body in the cervical spinal cord in sagittal direction by using color maps generated from DTI data. The fibers of cervical spinal cord were visualized by using fiber tracking software (DTI TaskCard 1.69).RESULTS1.All subjects completed the single shot EPI examinations except two failed by obviously motion artifacts.The cervical spinal cords were clearly demonstrated on the post processing images,and there were no obvious artifacts on the diffusion tensor images.2.In the normal apinal cord,the average value of ADC was (942.49±73.49)×10-6mm2/s,and FA was(584.77±64.27)×10-3,λ1 was(1595.69±82.70)×10-6mm2/s,λ2 was(609.25±89.26)×10-6mm2/s,λ3 was(620.32±113.97)×10-6mm2/s,respectively.At the spinal canal level C1,the mean ADC was statistically higher than the ADC at the other levels(F=13.1491,P < 0.01),while the mean FA at this level was statistically lower than those at the other levels(F=28.2349,P < 0.01). The value ofλ1 was significantly higher than that ofλ2 andλ3(P<0.01),and there was no significant difference betweenλ2 andλ3(P>0.05).3.On the color-coded map of healthy volunteers,the normal spinal cord was depicted as blue inferior-superior fiber track,which indicates the water diffusion anisotropy in the direction parallel to the longitudinal axes of the spinal cord,while the cerebrospinal fluid was red.CONCLUSIONS1.The normal cervical spinal cord and its various parameters can be well demonstrated in vivo by using DTI with SE-EPI sequence,which will provide useful informations for the diagnosis and mechanism of disease in spinal cord.2.The various parameters of diffusion tensor imaging in spinal cord showed that water diffusion anisotropy in the direction parallel to the longitudinal axes of the spinal cord.3.As the only approach available to non-invasively study the three-dimensional architecture of white matter tracts,the state of the art of reconstruction of the axonal tracts in the spinal cord using diffusion tensor imaging was expected. PURPOSE1.To study the parameter feature of diffusion tensor MR imaging in the cervical spinal cord with spondylosis-related changes.2.To investigate the clinical application of diffusion tensor MR imaging in the spondylosis-related changes of the cervical spinal cord,compared with conventional MR imaging.METHODS31 patients with cervical spondylosis were examined with routine MRI and DTI on 1.5 SINMENS Sonata MR scanner using SE-EPI sequences and phased-array spinal coil.The patients were divided into two groups according to weather there were high signal lesions on T2-weighted images at the the lesion.Apparent diffusion coefficient (ADC),fractional anisotropy(FA)values were measured on a sagittal section on lesion of the spinal cord by using color maps generated from DTI data.The statistical significances were performed to the ADC and FA value.Calculate the sensitivities, specificities,positive predictive values and negative predictive values of T2-weighted images and DTI.RESULTS1.All 31 spondylosis cases completed the examinations with no obvious artifacts on the diffusion tensor images through post-processing.2.The mean ADC and FA of high signal lesions on T2-weighted images(9 patients) were(1183.44±121.96)×10-6mm2/s and(432.56±59.97)×10-3,there were statistically significant difference with the normal spinal cord(P < 0.01).Among the other 22 cases left with no abnormal high signal on T2-weighted images,there were 15 patients whose ADC and FA value at the lesion level had statistically significant difference with the normal spinal cord(P < 0.01).The mean ADC and FA of the fifteen patients were(1055.07±80.61)×10-6mm2/s and(501.87±41.09)×10-3.Among this group with no abnormal high signal on T2-weighted images,the other seven cases showed no significant difference(p>0.05)compared with normal cervical spinal cord.3.Sensitivities of T2-weighted images and DTI were 29.3%and 77.4%.Specificities of T2-weighted images and DTI were 71.0%and 22.6%.And positive predictive values of both T2-weighted fast SE images and DTI were 27.3%and 72.7%.Negative predictive values of both T2-weighted fast SE images and DTI were 75.9%and 24.1%.CONCLUSIONSDiffusion tensor imaging is a reliable tool in demonstrating the early spondylosis-related changes of the cervical spinal cord compared with conventional T2-weighted images.It can provide useful information for chronic injure and regeneration of the cervical spinal cord as for making differentiating clinical diagnosis.
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