Role Of Diffusion-weighted Imaging In Evaluating Brain Tumors And Tumor Lesions

Echo plannar diffusion-weighted(EP-DWI) provide unique information about the molecular translational of water.DWI has been primarily used to asscess acute ischemic stroke,because it has proven highly sensitive and specific in identifying acute ischemic infarction and in differentiating acute stroke from other disedse processes which present with acute neurologic deficits.DWI also provides unique information about other cerebral diseases,including neoplasms,intracranial infections and meningiomas and is becoming increasingly important in the assessment of these entites. DWI is becoming an essential sequence. In DWI,high-amplitude bipolar gradients senstize a T2-weighted MR image to the Brownian moton of water molecules.Nondiffusing stationary molecules show no such signal intensity on DWI is thus due to two intrinsic competing components:degree of T2 signal intensity and degree of diffusion.In this most common application DWI depicts hyperacute is chemic injury as high signal intensity in the lesion due to restricted diffusion.Occasionally,however,certain T2 hyperintense lesions can,in the absence of restricted diffusion,still appear hyperintense on DW images,a phenomenon called T2 shine-through. Investigators are able to distinguish the cause of high signal intensity on DWI by means of calculated ADC maps or ADC values. ADC is a value that measures the effect of diffusion independent of the influence of T2 shine-through. Brain tumours and tumours like leision are very common in the brain lesion,they imperil life and health of human being.Recent publications suggest that DWI and apparent diffusion coefficient (ADC) calculation can be helpful in establishing a differential diagnosis of brain lesions.The purpose of this study was to determine whether diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) can be used to distinguish brain tumor and tumor like lesions. From Novemeber 2003 to December 2004,we reviewed 54 leisions.All patients can be divided into three categories,including meningioma,gliomsa and intracranial lesions which display circular enhancement.Rank sum test were performed to calculate significance.All patients were studied using a 1.5T GE MR to achieve conventional MR and DWI. The DWI was acquired (b=0,1000) by using the echo planar imaging (EPI) sequence and fat was suppressed by placing frequency selenctive RF pulse before the pulse sequence. The ADC maps and values were calculated on a workstation.We recorded the ADC valves from the solid portion of the tumor and from perirumoral,hyperintense are as on T2 weighted images. The ADC values in our study represent averaged ADC of two to five regions of interest (ROI), each ROI was about 10 to 20 mm2. We also recorded signal intensities on DWI of the tumor and of the peritumoral hyerintense areas on T2 weighted images for possible contribution to tumor grading.Tumor specimens were graded according to criteria from the World Health Organ. Glimas are the most common brain tumors. On imaging studies,malignant gliomas usually are enhanced after intravenous contrast injection and show peritumoral edema, whereas, except for pilocytic astrocytoma and giant-cell astrocytoma,low-grade gliomas usually show littleto no abnormal enhancement or peritumoral edema.Differentiation of thest two types oftumors occasionally may be difficult,because low-grade astrocytomas also may show abnormal contrast enhancement and perritumoral edema.Although the ADC of gradeⅡastrocytoma and glioblastoma overlapped somewhat,the combination of rortine image interpretation and ADC had a higher predictive value.Our results indicate that lower ADC suggest malignant glioma whereas higher ADC suggest low-grade astrocytoma. Ⅰ-Ⅱgrade glioma ADC were(1.81±0.08)×10-3mm2/s,Ⅲ-Ⅳgrade glioma ADC were(1.40±0.07)×10-3mm2/s.These results agree with those of previous reports.The difference between of that was significance.We think reason of the difference of producing were cellaularity. Someone differential the malignant glioma and benign glioma by the perritumoral edema..Our findings do not support the hypothesis. We measured the ADC of peritumoral edema ,the ADCs where no significance. Meningiomas comprise approximately 14﹪to 20﹪of all intracranial tumors.Atypical meningiomas account a majority of all meningiomas,whereas malignant meningiomas are rare. Malignant and atypical meningiomas are more prone to recurrence and aggressive growth.It would be useful to distinguish among benign, malignant,and atypical meningiomas before resection,because this would aid in surgical and treatment planning.The distinction between beningn and malignant is not reliably on routine MR images. We hypothesized that the calculated ADC may be helpful in distinguishing benign from malignant. 15 patients with meningiomas were studied using MR imaging and diffusion weighted imaging. Rank sum test were performed to calculate significance.The meningiomas of all patients has markedly decreased ADCs,averaging( 0.89±0.07 ) ×10-3mm2/s.In normal opposite human tissue, the averageADC were (1.15±0.41)×10-3mm2/s. All of these meningiomas were hyperintense on the diffusion weighted images and hypointense on the corresponding ADC maps.The ADC of the other benign meningiomas were( 1.79±014 ) ×10-3mm2/s, In normal opposite human tissue, the averageADC were(1.24±0.25)×10-3mm2/s.All benign meningiomas the had ADC higher than that of normal brain.In this study, it seems that the calculation of the ADC can help us differenciate malignant meningiomas and bengin meningiomas. We hypothesize that all of these meningiomas showed hepointensity on the DWI because of the presence of increased amounts of fluid within these lesions.The presence of the increased fluid may allow for free movement of water molecules or less restriction to water diffusion. The differential diagnosis between intracerebral necrotic tumors and cerebral abscesses is occaionaly difficult with conventional MR imaging.Many abscesses,however,can be aspirated with CT or MR guidance and successfully treated with antibiotic therapy. We studied 19 patients with lesions riming enhancing to know whether significance of ADC.The ADC of abscess were (0.33±011)×10-3mm2/s,the ADC of cystic or necrotic tumors were (2.46±049)×10-3mm2/s. 1996 Ebsiu reported a case of brain abscess with a high signal intensity in the abscess cavity on diffusion weighted images associated with a low ADC value. He concluded that diffusion weighted imaging might enable on to distinguish brain ab scesses from cystic or necrotic tumors We are agree to them.Our results findings show low ADC values in abscesses,and these low ADC values are attributable to the presence of pus.Pus is a highly viscous,thick,mucoid fluid consisting of inflammatory cells,bacteria,proteoneous exudates and fibrinogen.Because of this high viscosity,diffusion water motion is severely curtailed.The high...