الفهرس 
LIVER ANATOMYOnly 14 pages are availabe for public view
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Abstract
H
CC is the most common primary liver malignancy and usually occurs in the setting of cirrhosis.
Early detection of the HCC is an important aspect of the liver imaging that has implications for patient treatment and prognosis. The choice of imaging technique depends on the clinical question 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.
However, US-based screening for HCC has a sub-optimal sensitivity and specificity, especially when liver cirrhosis is present. Hence patients with an abnormal liver US showing cirrhosis or focal mass often undergo a contrast-enhanced CT or MRI examination.
MRI has advantages over CT in diagnosis of hepatic focal lesions because it is more accurate, no exposure to radiation and no use of nephrotoxic contrast agents, so MRI is sensitive and specific in detection and characterization of Hepatocellular carcinoma and follow up after treatment.
MRI with its many sequences, markedly helps in the detection of small lesions and in reaching the diagnosis easily. Although, even without CM, MRI offers significantly higher intrinsic soft-tissue contrast than CT, there are advantages in administering CM. Fast sequences are now available using breathhold techniques, so the use of dynamic scanning provides much information in terms of lesion characterization. Multiphasic dynamic gadolinium contrast enhanced T1 W images in hepatic arterial, portal venous and delayed phases improve the detection and characterization of HCC. However, the determination of contrast enhancement is not always easy to accomplish for hyperintense lesions on arterial phase dynamic image. Subtraction of unenhanced image from gadolinium-enhanced images has been pursued in an attempt to maximize the qualitative recognition of lesion enhancement.
Recent advances in MRI have led to a growing interest in optimizing and applying functional MRI methods for assessment of liver disease. These methods include diffusion-weighted imaging (DWI), perfusion-weighted MRI, MR elastography (MRE), and MR spectroscopy (MRS). These non-invasive methods can be repeatedly used in patients with liver diseases, limiting the need for biopsy.
The applications of diffusion-weighted imaging (DWI) in the liver include detection, characterization. and help monitor tumor response to therapy.
The ability to detect tumors with diffusion weighted imaging is based on the premise that tumors have increased cellularity compared with healthy background tissue.
Diffusion-weighted imaging (DWI) has proven to be of value in treatment monitoring of cancer patients because of its sensitivity for changes in tumor cellularity and cell membrane integrity.
The successful application of MR elastography (MRE) to detect hepatic lesions noninvasively, investigators have sought to evaluate its utility for characterizing and differentiation of focal hepatic lesions.
MR spectroscopy (MRS) is par¬ticular interesting as it can provide specific information on tumor pathophysiology and metabolism. This may include data on the type, grade and stage of the tumor, which thus can assist in further management of the disease.
Perfusion MRI could be used qualitative assessment applied for the differential diagnosis of focal liver lesions, by applying quantitative metrics to describe their vascular behavior.
It provides functional information about the microcirculation of liver parenchyma and focal liver lesions and appears to be a promising technique for evaluating liver metastases and HCC; for assessing the efficacy of local tumor ablation therapy; and for diagnosing cirrhosis and assessing its severity. However, standardization of imaging acquisition and analysis techniques need to be actively addressed for the technique to be widely adopted.