الفهرس 
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Abstract
Dynamic contrast-enhanced MRI enables an accurate assessment of the necrosis of HCC after TACE with the best accuracy observed at the arterial phase. So, the contrast-enhanced MRI helps in accurate measurement of tumor necrosis (Prajapati et al., 2012).
MRI is playing an increasingly important role in the evaluation of hepatic tumors after treatment, because of its high contrast resolution, lack of ionizing radiation and the possibility of performing functional imaging sequences. The superiority of MRI is achieved by the combination of multiplanar T1-weighted and T2-weighted images and serial dynamic imaging after gadolinium contrast administration in routine clinical practice (Lee et al., 2011).
For the assessment of tumor response or treatment effectiveness after chemoembolization, MRI is preferred to computed tomography (CT). Although contrast-enhanced CT is able to reveal residual or recurrent tumors as areas of hypervascularity, this appreciation is often muted compared with MRI, because of the lower sensitivity to contrast enhancement. Furthermore, it is often difficult to assess correctly contrast enhancement in such tumors adjacent to retained iodized oil on CT, because of beam hardening artifacts caused by iodized oil (Lee et al., 2011).
As retained iodized oil is best seen on CT images as an intense, hyperattenuating material located at the site of uptake, which usually appear in the region of the tumor, HCCs with complete uptake of iodized oil after TACE are considered to be completely necrotic. However, retained iodized oil in the tumor can mask enhancements within the tumor. Furthermore, in patients treated with TACE for HCC, it is sometimes difficult to monitor a marginal or remote tumor recurrence on multiphasic liver CT because of the presence of a variety of hyperattenuating lesions seen in the arterial phase images, i.e. lesions showing faint traces of iodized oil, masses previously injected with iodized oil (Lee at al., 2013).
Therefore, detection of subtle arterial enhancement around a retained iodized oil nodule can be difficult as the retained iodized oil nodule shows high attenuation on all phase images as well as the beam hardening artifact around retained iodized oil can make it difficult to evaluate the true arterial enhancement (Lee at al., 2013).
In contrast, MRI is not appreciably affected by the presence of iodized oil. Viable tumors are better depicted by the greater enhancement on hepatic arterial dominant phase images, relative to analogous CT images, supplemented with T2 information (Lee et al., 2011).