characterization and staging of liver lesions seen on other imaging tests. MRI also has a role as a noninvasive means of imaging the biliary tree. (See "Magnetic resonance cholangiopancreatography".)

 

 

●Some of the uses of hepatobiliary MRI include the evaluation of:

 

•Hepatic steatosis (see 'Clinical role' above)

 

•Hemangiomas (see 'Hemangiomas' above)

 

•Focal nodular hyperplasia and hepatic adenomas (see 'Focal nodular hyperplasia and hepatic adenomas' above)

 

•Hepatocellular carcinoma (see 'Hepatocellular carcinoma' above)

 

•Metastatic disease (see 'Metastases' above)

 

•Liver masses in patients with cirrhosis (see 'Imaging the cirrhotic liver' above)

 

•Iron overload (see 'Iron overload' above)

 

•Pancreatic cancer (see 'Pancreatic cancer' above)

 

●MRI uses a strong magnetic field to align rotating hydrogen protons within the tissue being imaged. During realignment of the protons, energy is released and sampled at different time intervals. The measured signal intensity from this energy depends upon the degree and rate of realignment within a very specific time period, which in turn depends upon the water and fat content of the different tissues. These signals are then converted into gray scale cross-sectional images that can be depicted in multiple planes or in three dimensions.

 

●The T1 relaxation time (and the resulting T1-weighted image) refers to the time required for protons to fully realign within an external magnetic field following exposure to a radio wave pulse of specific strength and duration. T1-weighted sequences are used to detect fatty liver, to determine segmental and vascular anatomy, and to detect and characterize liver lesions. (See 'T1 sequences' above.)

 

●The T2 relaxation time (and the resulting T2-weighted image) describes the rate at which protons are put out of phase with respect to adjacent protons. T2-weighted sequences are used to differentiate between cysts, hemangiomas, hepatocellular carcinoma (HCC), and metastases. Heavily T2-weighted images can also be used in the diagnosis of hemochromatosis and, in patients with cirrhosis, to differentiate siderotic nodules from hepatocellular carcinoma. (See 'T2 sequences' above.)

 

●Techniques have been developed whereby the signal arising from blood (arterial or venous) flowing into a region of interest is detected and depicted as an angiographic image in multiple planes. Unlike conventional angiography, no intravenous or arterial contrast material is required, and the direction of flow is easily determined. (See 'MR angiography' above.)

 

●Dynamic contrast-enhanced MR uses paramagnetic contrast agents (such as gadopentetate dimeglumine) that act in a similar manner to the CT iodinated contrast agents. The use of contrast agents improves the characterization of liver tumors. However, there have been cases of nephrogenic systemic fibrosis related to the use of gadolinium in patients with renal disease. (See 'MR contrast agents' above and "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced renal failure", section on 'Gadolinium'.)

 

Content 2

Notes:

a Giant cavernous hemangioma may be more irregular and not homogeneous. After gadolinium injection, a hemangioma demonstrates enhancement with early peripheral enhancement and late complete filling. Persistent hyperintensity on T1-weighted delayed images is very specific for hemangioma, and helps differentiate it from other vascular hepatic lesions. Hemangiomas cannot easily be differentiated from well circumscribed angiosarcomas. Hepatic cysts may have similar characteristics to hemangiomas but do not enhance following gadolinium administration.

The tagged red blood cell study is less expensive and equally specific for vascular lesions. Thus, MRI should be reserved for the evaluation of lesions that are smaller than 2 cm, or are located adjacent to the heart or to major intrahepatic vessels [1].

 

 

 

 

 

 

 

 

  • Abnormal MRI Findings

Discloses mass lesions in the liver or dilation of the biliary system. Hepatic blood flow can be investigated by arteriography and isotope scans. Gallium scanning is useful in detecting neoplasms and abscesses in the liver.

Liver biopsy is a relatively safe method of obtaining tissue for histologic examination (Table 42-1). Blind biopsy using a cutting needle is indicated for diffuse lesions of the liver. Radiologically directed fine-needle aspiration biopsy is indicated when it is necessary to examine a localized lesion.