الفهرس 
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Abstract
SUMMARY AND CONCLUSION
L
iver cancer is the sixth most common cancer worldwide and the second leading cause of cancer mortality. In recent years, five-year survival rates of HCC have considerably improved due to earlier detection and curative therapies.
Surgical resection or transplantation is the standard treatment of HCC. However, most patients are not eligible for resection and the waiting list for liver transplantation is long. Locoregional therapies can be performed as curative treatment, mainly in small HCC, or before transplantation.
Trans-catheter arterial chemoembolization of HCC lesions is a technique now widely applied to the treatment of hepatic malignancies, aims to deliver treatment to a target tumor volume by means of a percutaneously placed intra-arterial catheter within an artery that supplies the tumor.
The main idea for TACE is the fact that more than 80% of the blood supply of HCC is derived from the hepatic artery, in contrast to 20–30% of the blood supply of hepatic parenchyma.
TACE is suitable for patients with multiple liver masses or a large tumor that is not amenable to for percutaneous ablation therapy. It is useful in local tumor control, preventing tumor progression, prolonging survival, and controlling symptoms. It can also be used solely or in combination with other minimally invasive procedures as a neoadjuvant therapy, or prior to liver transplantation or resection.
Monitoring tumor response to loco-regional therapy is an increasingly important task in oncologic imaging. Early favourable response generally indicates effectiveness of therapy, and may result in significant survival benefit. Early identification of treatment failure is also critical in patient management, since a repeat treatment cycle can be performed before disease progression occurs.
The treated lesions after TACE are replaced by necrosis & usually exhibits hypointense signal in T1WIs. T1 hyperintensity could be observed if proteinaceous fluid or haemorrhage is present. The decreased T2 signal is distinctive feature for treated lesions as a result from arterial occlusion and subsequent substantially diminished tissue fluid. T2 hyperintensity can represent haemorrhage, liquefactive necrosis, or inflammatory infiltrate. On dynamic contrast enhanced sequences, complete tumor necrosis shows the absence of contrast enhancement within an ablated lesion.
For unsuccessful TACE treatment, the prominent sign in pre-contrast images is seen in T2WIs as residual hyperintense areas of the tumour. In post contrast sequences, a focal enhanced region after contrast administration seen admixed within necrotic regions usually represents viable neoplastic tissue regardless of overall tumor size changes. Another characteristic feature of viable tumor tissue or partial response is an irregular peripheral nodular enhancement that measures ≥ 5 mm with rapid washout in the portal venous phase.
Diffusion weighted imaging (DWI) is promising for the non-invasive evaluation of tumor response particularly when contrast medium administration is contraindicated or in patients who could not hold their breath adequately. DWI 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 (ADC) calculated in diffusion-weighted MRI has emerged as a good aiding biomarker of tumor response to therapy. Early tumor response is identified as increase in ADC value as compared to pre-treatment. ADC ratio, comparing values from baseline to 1 month after TACE, is an independent predictor of progression-free survival.
In conclusion, diffusion weighted MR imaging and dynamic MR imaging achieve the effective monitoring of tumor response to therapy