Basic MRI sequences Part 1 by Radiology TV

Basic knowledge about the most commonly used MRI sequences. T1, T2, FLAIR, tirm dark fluid, T2*, SWI, DWI, STIR, TIRM, T1+contrast. This video shall give you a basic knowlege about the most commenly used MRI sequences. I don't want to talk so much about the technical details but instead focus on how to recognize a certain sequence and also what information this sequence can give you regarding image interpretation. Here you see a T1-weighted image. The most important feature that characterizes a T1 image compared to a T2 image is that water appears dark or hypointense as you say with MRI imaging. So here, on this image, the cerebrospinal fluid is dark because it consists mostly out of water. Also, an edema or most cerebral lesions appear dark on T1. Black on T1 would be air in the nasal sinuses, dense bone like the scull and calcium like in calcified lesions. Gray on T1 is the white as well as gray matter - the latter being faintly darker than the former. Bright or hyperintense objects on the other hand are fat containing structures as seen here with the subcutanous fat. Also a subacute hemmorhage appears bright. After contrast application all vascularized structues also appear bright. You can recognize a T1 image because basically it looks like a CT scan with the ventricles being dark whereas the scull is bright. In contrast to a CT scan are the orbits which contain fat also bright whearas the globes consisting mostly out of watery content are black. Vessels are normally not seen on a T1 image without contrast application so that in order to see normal vessels as well as vascular changes or a disruption of the blood-brain barrier it is useful to give i.v. contrast agent. The contrast agent used with MR imaging is gadolinium, a rare-earth metal. So the contrast enhanced T1 image looks like a non-contrast T1 weighted image but with bright arteries and veins. It is important to note that not every structure that is bright on a contrast enhanced T1 image is a vessel or hypervascular structure as fat containing lesions or a subacute hemmorhage already appears bright on a native T1 image. So it is always important to compare these two images or look at a subtruction image as seen here. As already mentioned the most important feature that differentiates a T2 image from T1 is that water appears bright as seen here with the cerebrospinal fluid. What else appears bright on T2 ? -- this would be a hyperacute or late subacute hemmorhage, an edema as well as most pathologic lesions. Also fat appears bright .... so that if you see a structure that is bright on both T2 as well as T1 image you can tell that it is eather a fat containing tissue or a late subacute hemmorhage. In order to differentiate fat or a subacute hemmorhage you have two options - you can either chose a fat saturated sequence so that if the lesion contains fat it becomes dark. Or you chose a blood sensitive sequence which is either a so called T2* image or a SWI which stand for suceptibility weighted imaging. On either of the last two mentioned sequences a subacute hemmorhage would show a black periphery and an heterogenous iso or hyperintense center. So again referring to the T2 weighted image you also see dark objects like the gray and white matter where the white matter appears a bit darker than the gray matter. Black on T2 is again air, dense bone and calcium - same as with T1 image. Another structure that is black on T2 are the vessels because the fast flowing blood doesn't give a signal. This is also called a flow void. So you can recognize a T2 weighted image by the bright cerebrospinal fluid as well as bright scalp and eyes. The vessels appear black. Once again speaking of the T2* or SWI imaging it is important to note that all structures that contain iron or calcium appear dark which would be blood as well as bone or calcified lesions as well as structues with iron deposition. Look for an all dark appearing image to recognize a T2* image.