| Background: Circular enhanced brain lesions is a common imaging finding, among which are metastasis ,astrocytoma and abscess . When being enhanced, these three kinds of lesions will show following imaging features: the center is the low-intensity, ring enhancement in the middle, peripheral edema without enhancement. These three different lesions can cause almost same clinical symptoms and signs. Therefore, accurate diagnosis is critical for prompt and proper treatment. No remarkable improvement of the rate of exactness of the diagnosis was shown before operation, though there were many studies and reports about the circular enhanced brain lesions on MRI. Uncertain and misdiagnosed cases were reported repeatedly. Hence it is necessary for us to find an impersonal, scientific, practical way to differentiate one from another. The maximum likelihood method, namely the probability discrimination, measures and analyzes the various kinds of imaging findings of these three kinds of lesions and convert the probability of different lesions into identification index. Sum up the various identification index in order to avoid misdiagnosis. Based upon which, we determine the type of the lesions, namely differentiate diagnosis. Purpose:1. Review the MRI images of circular enhanced brain lesions retrospectively, sum up the characteristic signs of brain metastasis, astrocytoma and brain abscess .2. Analyze the diagnosis and differentiate diagnosis value of the various sign in brain metastasis, astrocytoma and brain abscess.3. Establish a comparatively impersonal, scientific, practical approaches for higher diagnosis rate.4. Compare the diagnosis result of conventional method and the maximum likelihood method and analyze their diagnosis efficiency.Materials and methods:1 .Common datum: MRI studies of 180 cases were analyzed retrospectively. There were 60 cases with brain metastasis, 35 males and 25 females ,aged 31-80 years(average age of 54);60 cases of astrocytoma, 32 males, 28 females, aged 2-76 years( average of 39.86);60 cases of brain abscess, 20 males, 40 females, aged 7-70 years( average of 26). 136 cases were proved surgically and pathologically .30 cases were proved by fine needle aspiration biopsy, while 14 cases were proved clinicaly.2.Scaning equipment and examining method: 180 cases were examined by using 0.3T MR scanner(AIRIS I). Head coil were used . Both pre and post-enhancement study were performed.3 .The observation index of circular enhanced brain lesions : the part, location, number , size, figure (shape), structure, thickness of the circular enhancement wall, interior andexterior margin of the circular enhancement > the signal characteristics of the circular enhancement wall and inner after and before being enhanced ^ the degree of peripheral edema.4. Statistics: the accounting data X2 test, R*C form test and the maximum likelihood methodwere applied. The testing level a =0. 05 0 Results:1. The positions which are most likely to be developed of brain metastasis > brain abscess can be summed up in turns as parietal lobe > frontal lobe > temporal lobe n occipital lobe and cerebellum. While for astrocytoma, frontal lobe ^ parietal lobe n temporal lobe > occipital lobe and cerebellum. But the difference among the three has no statistic significance.2. 86.7% of metastatic with multiple lesions foci locating in the juncture of grey matter and white matter, 65.0% of which is of small lesions, 81.7% of which is roughly round shape, 8.3% of which has the multi loculi, 6.7% of which has multi mural nodules, 48.3% of which have thick circular enhancement with 41.7% uneven thickness, 75.0% of which with irregular wall, while 81.7% of which with smooth outer walls of the lesions, 3.3% of which with hypo-intensity rim on T2WI, 6.7% which with fluid-fluid level, 15.0% of which with hyper-intensity on Tl WI in the lesions, 63.3% of which with III0 peripheral edema, without displaying of daughter ring sign % circular wall notch sign?90% of astrocytoma was solitary. 78.3% locating at grey matter. 46.7% of them with roughly round shape. 53.3% of them were irregular in shape. 38.3% with multi loculation. 38.3% with multi mural nodules. 51.7% with irregular wall. 40.0% with thickened walls. 6.7% with fluid-fluid level. 3.3% with central hyper-intensity on Tl WI. 61.7% with II ° peripheral edema .Daughter ring sig^ circular wall notch sign-, hypo-intensity rim on T2WI haven't been shown.81.7% of the brain abscess was solitary. 75.0% locating at the juncture of grey matter and white matter. 55.0% of them were midsized. 80% of them were roughly round in shape. 35.0% with daughter ring sign. 3.3% with multi mural nodule. 15.0% with circular wall notch sign, 73.3% with thin walls. 71.7% with smooth regular walls. 53.3% with hype-intensity rim on T2WI, 66.7% with fluid-fluid level. 3.3% with hyper-intensity on Tl WI. 60.0% with II ° peripheral edema. No multi locular lesions were seen.3. The correct rate of diagnosis of brain metastasis ^ astrocytoma and brain abscess by applying the maximum likelihood method was 92% % 90% n 85% respectively. Though the partnership X2 test shows no statistically significance between the two approaches .(X2=0.0014, P=0.9993>0.05) ,but the correct rate of diagnosing the three kind of lesions was raised, compared with the conventional way. Conclusion1. the sign that most likely indicating brain metastasis are by turns as: multi lesions % III0 peripheral edema > hyper-intensity on Tl WI inside the lesions. Small lesions, lesions located at the juncture of grey matter and white matter.2. the sign that most likely indicating astrocytoma are by turns are: multi locular lesion^ multi mural nodule > lesions locating at white matter, the lesions are irregular in shape.3. The sign that most likely indicating brain abscess are by turns are: daughter ring sigm circular wall notch sig^ hypo-intensity rim on T2WK fluid-fluid leveh thin walls.4. The maximum likelihood method is a valuable probability discrimination approach to be applied in the diagnosis and differentiation of circular enhancement lesions on MRI. Compared with the conventional method, the maximum likelihood method raised the exactness of the diagnosis of the three common circular enhancement brain lesions asbrain metastasis % astrocytom^ brain abscess. Though it has no statistically significance, it still could be applied to the daily routine study, Particularly for the young physicians. It is a relatively impersonal, scientific, practical way of diagnosis with higher exactness rate. 5. It might be for the first time in this study that the maximum likelihood method was helpfulfor the diagnosis and discrimination of circular enhancement brain lesions.
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