الفهرس 
Gross and MRI AnatomyOnly 14 pages are availabe for public view
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Abstract
Liver lesions can be classified on the basis of both
unenhanced and contrast-enhanced images. On
unenhanced imaging, classification can be based upon the
signal intensity and delineation of lesions on conventional
T2-weighted and T1- weighted images as well as on opposed
phase T1- weighted images or T1-weighted images acquired
with fat suppression. Thus, on unenhanced imaging, lesions
with a high fluid content, lesions containing fat and lesions
with internal hemorrhage can be detected and readily
diagnosed. Unfortunately, unenhanced imaging alone cannot
always differentiate reliably between benign and malignant
lesions and in many cases, additional information from
contrast-enhanced imaging is necessary for accurate
differential diagnosis (Grazioli et al., 2009).
The availability of contrast agents with markedly
different properties means that lesions can be classified on
the basis of different enhancement patterns on contrastenhanced imaging. Thus, lesions can be classified according
to their behavior on dynamic imaging following the
administration of extra cellular contrast agents (in a similar
manner to that which occurs on dual phase spiral CT
imaging), and to their behavior on delayed imaging following
the administration of contrast agents targeted either to the hepatocytes or the Kupffer cells. In the dynamic phase of
contrast enhancement after the administration of gadoliniumbased contrast agents, lesions can be classified according to
whether they demonstrate hyper vascular or hypo vascular
enhancement patterns or delayed persistent enhancement on
T1-weighted acquisitions during the arterial, portal-venous
and equilibrium phases, respectively. Within these three
major groups of lesions, lesions can be classified further
according to the presence or absence of certain characteristic
features. For example, a central scar within a hyper vascular
lesion in a non cirrhotic liver that shows low signal intensity
on Tl-weighted images and high signal intensity on T2-
weighted images may be indicative of FNH. Similarly, a
hypo vascular lesion with a hyper vascular rim that shows
contrast agent washout at 10-15 min post-injection and halo
sign on T2-weighted images may be indicative of a
metastasis of adenocarcinoma. Finally, a lesion that shows
nodular enhancement in the arterial phase followed by
centripetal filling-in in the subsequent phases and high signal
intensity on T2-Weighted images may be indicative of a
haemangioma (Schneider et al., 2010).
Whereas the enhancement seen on dynamic T1-
weighted imaging gives information on the morphologic
characteristics of lesions, that seen on delayed phase images
after the injection of agents targeted either to the hepatocytes (e.g. Gd-BOPTA, Gd-EOB-DTPA, Mn-DPDP) or Kupffer
cells (SPIO agents, USPIO agents) gives information on the
cellular content and cellular functionality of lesions. In the
case of Gd-BOPTA, the information gained in the delayed
phase is additional to that seen in the dynamic phase and may
serve to distinguish lesions of hepatocellular origin such as
FNH that may be able to take up the agent, from lesions of
hepatocellular origin such as HCC that have lost this ability
and lesions of non-hepatocellular origin that are also unable
to take up the agent. Similarly, lesions can be classified into
different groups on the basis of their ability to take up GdEOB-DTPA, Mn-DPDP and iron oxide particles. However,
the lack of a dynamic imaging capability combined with the
sometimes overlapping levels of enhancement of different
primary benign and malignant liver lesions often makes
accurate differential diagnosis difficult with these agents
(Schneider et al., 2010).