Here you don't want to be too early, because you want to load the liver with contrast and it takes time for contrast to get from the portal vein into the liver parenchyma. In aterial phase imaging the time window is narrow, since you have only limited time before the surrounding liver will start to enhance and obscure a hypervascular lesion.įor Late portal venous phase imaging it is different. So you start scanning at about 33 seconds, which is much later. However if you have a 64-slice scanner, you will be able to examine the whole liver in 4 seconds. If you have a single slice scanner, it will take about 20 seconds to scan the liver.įor late arterial phase imaging 35 sec is the optimal time, so you start at about 25 seconds and end at about 45 seconds. You have to adapt your protocol to the type of scanner, the speed of contrast injection and to the kind of patient that you are examining. This is comparable to late enhancement of infarcted scar tissue in cardiac MRI. There is wash out of contrast in all abdominal structures except for fibrotic tissue, because fibrotic tissue has a poor late wash out and will become relatively dense compared to normal tissue. Sometimes called "wash out phase" or "equilibrium phase". Only in this phase you will be able to detect small renal cell carcinomas. This is when all of the renal parenchyma including the medulla enhances. In this phase the liver parenchyma enhances through bloodsupply by the portal vein and you should see already some enhancement of the hepatic veins. Although hepatic phase is the most accurate term, most people use the term "late portal phase".
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