OBJECTIVE: The purpose of this study is to ascertain whether magnetic resonance(MR) images taken after ethanol injection or microwave irradiation into feline brain can verify changes within the brain and offer valuable information about the spatial extent of the induced lesion. METHODS: In the ethanol injection experiment, nine male cats were divided into three groups including group I(n =3) treated with 0.1cc ethanol injection, group II(n=3) 0.2cc ethanol, and group III(n=3) 0.3cc ethanol into the feline brains. In the microwave irradiation experiment, twelve male cats were divided into four groups including group I(n=3) irradiated with 30 watt electrical power with 10 sec duration, group II(n=3) same power with 30 sec duration, group III(n=3) irradiated with 60 watt power with 10 sec duration, and group IV irradiated with 60 watt power with 30 sec duration. MR images were obtained in both ethanol injection and microwave irradiation experiments. Pathologic examinations were done after completion of MR imagings. RESULTS: Contrast-enhanced T1-weighted MR images showing nodular or rim enhancement were most reliable in delineating the extent of the necrosis induced by ethanol injection and microwave irradiation. The contrast enhancement corresponded with gliosis in normal brain surrounding the necrotic area and hypervascularity in ongoing necrotic area and adjacent normal brain. There were various enhancement patterns after ethanol injection with reflux of ethanol. In case of microwave irradiation, round or oval enhancements were shown with clear margin. The size of the enhancement was well correlated with the amount of injected ethanol and the amount of electrical power. Application time was not correlated with the size of enhancement in high electrical power group. The feature of the edema after ethanol injection was unpredictable and predictable in case of microwave irradiation. CONCLUSION: It is easy to predict the result in case of microwave irradiation, and the achieved results can be used as basic information in performing these procedures.