الفهرس 
? Radiological anatomy of the liverOnly 14 pages are availabe for public view
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Abstract
Hepatocellular carcinoma (HCC) is a highly prevalent disease and one of the most common causes of cancer- related death worldwide. Trans-catheter arterial chemoembolization of HCC lesions are promising treatment option for patients with liver tumors who are not eligible for surgery.
Thus, accurate diagnosis of a residual or recurrent tumor is crucial on the follow-up imaging studies after TACE. This allows successful management at an early stage of the disease, avoiding more complicated or advanced disease that has an unfavorable prognosis.
CT has long been the first imaging modality of liver and HCC imaging for both primary tumor characterization and post-treatment follow-up for response assessment.
Contrast- enhanced dynamic T1-weighted imaging with DWI can be advantageous in assessing treatment-related changes in HCC and was found to be superior to CECT in assessing patients who underwent Lipiodol-based TACE therapies. The beam-hardening effects of dense Lipiodol on CT can obscure small enhancing lesions. However, Lipiodol does not affect MR signal intensity characteristics, so that residual enhancing lesions can be easily detected, especially when image subtraction is used.
MRI permits the detection of anatomic, functional and molecular parameters in order to assess treatment response. Pre-contrast T1- and T2-weighted images gives information about the morphological changes as well as changes in the fluid content and fibrosis.
We found that T2 hyperintensity doesn’t only represents residual tumor but also could represent hemorrhage, liquefactive necrosis, or inflammatory infiltrate. Therefore, it was difficult to assess the viable HCC tumors after TACE by conventional spin echo imaging.
Contrast-enhanced MRI is sensitive to therapy-induced changes in blood volume and vascular permeability of the treated lesions which may be associated with tumor angiogenesis.
Diffusion weighted image gives an insight about water composition within the tumor, which helps in assessing the degree of tumor viability. The viable tumor cells have intact membranes causing diffusion restriction, whereas necrotic tumors have disrupted cell membrane allowing free water diffusion.
The apparent diffusion coefficient calculated in diffusion-weighted MRI has emerged as a good aiding biomarker of tumor response to therapy. The ADC is a measure of water mobility within tissues. The viable tumors are highly cellular with an intact cell membrane that prevents the mobility of water molecules resulting in a relatively low ADC. In contrast, the cellular necrosis increases membrane permeability, allowing free water molecules mobility with an increase in the ADC value.
In our current study, we evaluated the role played by MRI in the assessment of post chemoembolization of HCC. Eighty patients were evaluated by precontrast T1, T2, Fat Saturated as well as Dynamic contrast enhanced and respiratory triggered diffusion weighted MR sequences. The results were studied and intercorrelated.
The results of this study showed superior diagnostic performance of dynamic MRI compared to diffusion studies as dynamic MRI had a sensitivity of 90.9%, a specificity of 95.7%, PPV of 93.7 %, NPV of 93.7% and overall agreement of 94% compared to 100%, 65.2%, 68%, 100% and 80% respectively of diffusion weighted imaging.
The diffusion MRI was found to increase the sensitivity of local HCC detection, but on the expenses of examination specificity due to increased false positives. Those false positives may be attributed to the intra-lesional hemorrhage or liquefactive necrosis that causes diffusion restriction.
In our study, ADC variable was found to be a fair indicator to differentiate recurrent HCC from benign or pseudo- lesions.
In conclusion, in our study, we demonstrated that complementary dynamic and diffusion MRI achieve effective monitoring of tumour response to therapy. DW MR imaging is a rapid promising technique for the noninvasive evaluation of tumor response after TACE particularly when contrast medium administration is contraindicated or in patients who could not hold their breath adequately. Despite promising results, DWI cannot replace contrast-enhanced T1-weighted imaging for assessment of treated HCC response.