الفهرس 
Anatomy of the LiverOnly 14 pages are availabe for public view
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Abstract
The characterization of focal hepatic lesions is an important aspect of liver imaging that has implications for patient treatment and prognosis. The choice of imaging test largely depends on the clinical question, availability, the clinician’s familiarity with the test, and the patient’s clinical condition. In general, US and CT remain the first imaging tests for screening and characterizing most patients with suspected liver tumors.
The detection and characterization of hepatic nodules in the multistage development of HCC in a cirrhotic liver represent a challenge. Although MRI, even without CM, offers significantly higher intrinsic soft-tissue contrast than CT, there are advantages in administering CM in MRI. Because fast sequences are available using breathhold techniques, the use of dynamic scanning provides much information in terms of lesion characterization. MR imaging has excellent soft-tissue contrast and, in combination with the selective use of extracellular contrast agents such as gadopentetate dimeglumine, has improved capability for liver lesion characterization. However, the development of tissue-specific contrast agents provides new possibilities for lesion characterization on the basis of its cellular composition and function rather than its vascularity and diffusion within its extracellular space. In terms of its ultimate target, the macrophage-monocytic phagocytes within the reticuloendothelial system, ferumoxides may be seen as analagous to 99mTc sulfur colloid used in nuclear medicine. The reticuloendothelial system component in the liver is the Kupffer’s cells, which are known to occur in a number of primary liver lesions, such as focal nodular hyperplasia, hepatocellular adenoma, and some early hepatocellular carcinomas. In addition to the presence of and uptake into Kupffer’s cells, the signal changes after ferumoxides administration depend on the dose, the rate of administration, and the timing of the scan after administration of contrast material. The contrast effects of ferumoxides are complex; both T1 and T2 shortening are described, with the T2 effect being more dominant.
Although the use of ferumoxides may have benefit in terms of characterization of lesions such as focal nodular hyperplasia, it may on occasion be detrimental in terms of lesion detection, depending on the baseline lesion-to-liver contrast. Although a signal intensity loss after ferumoxides administration suggests a benign cause, Kupffer’s cells may be found in early hepatocellular carcinoma, and ferumoxides uptake with resulting signal intensity reduction in these lesions. Kim et al reported that: Hypovascular lesion detection was better with SPIO-enhanced MR images than with gadolinium-enhanced MR images. Detection and characterization of hypervascular lesions were improved with gadolinium-enhanced MR images.
Different accuracy values of gadolinium and ferumoxides-enhanced MR imaging were determined in the detection of small and large HCCs in chronic liver diseases. For small lesions, gadolinium-enhanced imaging was significantly superior to ferumoxides-enhanced imaging, and for large lesions and in overall analysis for all lesions, no significant differences were identified between gadolinium and ferumoxides-enhanced MR imaging.
In conclusion: SPIO particles are indicated to varying degrees for the detection of HCC and the characterization of focal nodular hyperplasia, it is used most routinely to aid in the detection of HCC in high-risk patients, as detection of HCC in cirrhotic patients may be difficult with gadolinium alone, because of the parenchymal changes (fibrosis and regenerating nodules) and altered liver perfusion (collateral vessels, increased hepatic arterial flow relative to portal venous flow) caused by cirrhosis. The use of SPIO particles may help improve HCC detection in such patients, reported by Gandhi et al., 2006). Also SPIO enhancing imaging is useful as a problem solving technique for hypovascular lesions. However, because gadolinium is less expensive and gadolinium-enhanced MR imaging is less time consuming, dynamic gadolinium-enhanced MR imaging should be preferred for early detection of HCC.