الفهرس 
Introduction and aim of this workOnly 14 pages are availabe for public view
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Abstract
This study included 41 patients, 26 males and 15 females with focal hepatic lesions. All patients were examined by MRI and 20 of them were examined by triphasic contrast MRI. FLASH image provides good anatomic resolution while true FISP image provides high tumorliver contrast and can detect vascular invasion and peritumoral oedema. The tumor capsule is best depicted on FLASH image where it appears as a low intensity ring on the periphery of tumor. Central tumor scar appears hypointense on FLASH image and hypo or hyperintense on true FISP image. Peripheral nodular enhancement with centripetal filling is seen with hemangiomas, small hemangiomas may show immediate uniform enhancement. Large hemangiomas may have central areas of hemorrhage or fibrosis that do not fillin with contrast. Hepatic cysts reveal quite hypointensity on FLASH image, hyperintensity on true FISP image and on dynamic contrast study exhibit no enhancement. Hepatic abscesses appear as a hepatic cysts exhibiting hypointensity on FLASH image and hyperintensity on true FISP image but in dynamic MRI they show increased peripheral rim enhancement (the ?double target? sign) marginal enhancement after contrast administration. Recently breathhold imaging techniques facilitate dynamic contrast enhanced scanning of the liver, which has been proven to be especially useful for evaluating small HCCs within cirrhotic livers. Arterial phase dynamic gadolinium contrastenhanced MR imaging has been improve detection of HCC, often detecting early or small tumors that are isointense or not visible to surrounding liver on unenhanced sequences. HCC has a special characters that help to differentiate it from other liver masses. The most important characters are the presence of capsule, vascular invasion and mosaic pattern. These features can be detected either by T1WI (FLASH) and by T2WI (true FISP). Dynamic gadolinium enhanced MR imaging has been shown to improve detection of small HCC. On immediate gadoliniumenhanced images, the lesions exhibit diffuse enhancement and then washout on delayed images. On MR imaging the tumor capsules are often thin and usually have delayed contrast enhancement indicative of fibrosis. Most lesions measuring 2 cm or less in diameter exhibit diffuse homogeneous enhancement. Liver metastases are hypointense on FLASH and hyperintense on true FISP weighted images. However, the signal intensity of metastases on true FISP image is less than that of hemangiomas or cysts. After administration of intravenous gadolinium, hypervascular metastases show marked early enhancement as a continuous ring that fillin centrally on later images. Hypovascular metastases are seen as hypointense masses with peripheral rim enhancement that washes out rapidly. The peripheral washout sign is a specific sign for diagnosing liver metastases. In conclusion, MRI is an indispensable modality for evaluating the liver. MR imaging is used to detect and characterize focal hepatic lesions. Unparalleled soft tissue contrast, direct multiplanar capability, high temporal resolution in dynamic contrastenhanced imaging and lack of ionizing radiation are major advantages. MRI should be used whenever there is a question not answered by US and CT scan.