الفهرس 
ANATOMY OF THE LIVEROnly 14 pages are availabe for public view
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Abstract
FLL may be benign or malignant. Therapy requires an accurate diagnosis, which in turn relies primarily on appropriate imaging and image-guided biopsy. CT is the mainstay of hepatic imaging, but magnetic resonance imaging, ultrasound , and nuclear imaging all play a role in the workup.
Conventional MR imaging can be equivalent to—or better than—CT for detection of hepatic lesions, but the cost is greater and extension of the examination to the pelvis and chest with similar accuracy is not feasible. When intravenous contrast medium is contraindicated, or when the nature of a lesion remains equivocal after enhanced CT but clinical suspicion of hepatic tumor persists , MRI is indicated.
For FLL detection and characterization, Conventional MRI relies on T1-weighted, T2-weighted, and dynamic gadolinium-enhanced T1-weighted imaging .
DW MRI in the liver is a relative new and increasingly used imaging technique . It has the advantage that it can be obtained during a single breath-hold, there is no need to use contrast media and it provides unique information that reflects tissue cellularity and organization. The ADC maps can also provide quantitative measurements of tissue water diffusivity, which can be used not only for disease assessment, but also for the evaluation of disease response to treatment. However, it should be noted that DWI images are difficult to interpret since DWI is very sensitive to artifacts.
DW-MRI is superior to conventional T2-weighted MR imaging sequences for the detection of FLL.
In patients with chronic liver disease, the addition of DW-MRI to conventional dynamic gadolinium contrast-enhanced MR imaging can improve the detection of hepatocellular carcinomas.
DWI provided higher sensitivity and positive predictive value for the detection of HCC < 20 mm compared to conventional contrast enhanced MRI, These can be explained by the better contrasttonoise ratio and background suppression of normal liver parenchyma and vascular or bile structures in DWI.
DWI provides a high negative predictive value on the presence or absence of HCC and reduces the rate of unnecessary invasive diagnostic procedures and followup.
DWI provided higher sensitivity and specificity compared to conventional MRI with and without contrast for metastases detection especially small metastases < 10mm.
DWI could potentially used as an alternate non contrast sequence for detection of liver metastases in patients with poor renal function and in whom gadolinium is contraindicated.
DW-MRI combined with conventional unenhanced T1- and T2-weighted imaging was superior to tissue specific contrast SPIO enhanced T2-weighted MR imaging for the detection of liver metastases.
The combination of DW-MRI with liver specific contrast MnDPDP-enhanced T1-weighted imaging of the liver, resulted in the highest diagnostic accuracy for the detection of liver metastases compared with either technique on its own.
The diffusion-weighted MRI sequence with quantitative ADC measurements can be useful in the differentiation of benign and malignant liver lesions .
Both qualitative evaluation of high b-value DW-MR images and quantitative evaluation of ADC maps are employed for lesion characterization.
The ADC values of benign lesions are significantly higher than those of malignant lesions, with variable degrees of overlap between the pathological entities.
DW-MRI is useful in the differentiation of hepatic lesions with equivocal findings on gadolinium-enhanced MRI. The combination of gadolinium-enhanced MRI and diffusion-weighted MRI improves the characterization of hepatic lesions that produce contradictory results on PET/CT.
Pretreatment ADC values in tumors treated with chemotherapy seem to be useful in the prediction and evaluation of the treatment response of primary and secondary liver malignancies. High pretreatment ADC values associated with poor response to chemotherapy.
ADC measurements are promising for quantifying and predicting response of liver metastases to effective chemotherapy. The vast majority of studies showed that tumour ADC values tended to increase following successful intervention.
DWI may have an additional value in the evaluation and followup of local ablative therapies (like RFA and TACE ) in patients with liver tumors. Viable tumors after RFA appeared as hyperintense, and necrotic regions were recognized as hypointense areas on DWI. Suspected areas on DWI were more easily identified and analyzed in conjunction to conventional MR.
DWI added to conventional MRI could increase the sensitivity for determining the rate of ablation site recurrences especially in the case of atypical lesions following TACE.
In Conclusion:
DWI proved to be helpful in the characterization of focal liver lesions, but should always be used in conjunction with traditional MRI since there is great overlap between ADC values of benign and malignant lesions. DWI is useful in the detection of small HCC in the cirrhotic liver, with higher sensitivity, specificity and positive predictive value compared to conventional contrast enhanced imaging . This is also the case for the detection of metastases in the liver. It seems reasonable to use DWI in conjunction to conventional imaging.
ADC measurements are promising for quantifying and predicting response of liver metastases to effective chemotherapy both before initiation of treatment and early after treatment.
DWI is not yet commonly used in the followup after treatment of liver malignancies. DWI in the followup after RFA and TACE shows promising results in the detection of ablation site recurrences, especially in combination with conventional contrast enhanced imaging.