 So, for normal orbital anatomy, the things we want to look at are the optic nerve and its surrounding dural sheath. And we want to look at the extraocular muscles that come together posteriorly at a fibrous ring around the optic nerve called the annulus of Zin. And of course, the lacrimal gland in the superior lateral aspect of the orbit is another important reference point for us. So, this is a classic pair of imaging. One of these images is a T2-weighted coronal image with fat suppression and the other is a T1 post-contrast image with fat suppression. And between the two of them, these are really the workhorse of our orbital imaging. The fat suppression here is key, although every once in a while, it's nice to use the fat as an intrinsic contrast agent. Usually you just want to get it out of the way and use entirely fat suppressed techniques. On a T2-weighted image, the optic nerve has a classic target appearance. The nerve itself in the center is of low T2 signal, but there is a sleeve of CSF around the nerve and then around that is the dural sheath which is dark and blends into the surrounding dark fat and thus this target appearance of nerve, CSF, and dura and fat. What we are looking for in pathology is when there is a white-out of that nerve and it all looks white through there. The extra-ocular muscles are ringed around it, slightly brighter in signal but not as bright as the CSF. When we look to the post-contrast image, all of the extra-ocular muscles are extremely bright, very enhancing. These are the most vascular muscles in the body. They're fast twitch and they are extremely vascular and they are extremely enhancing. That's normal. But, look at the optic nerve and its nerve sheath. It has almost no enhancement. It practically blends into the background of the post-contrast image. So, if you can see the optic nerve well on a post-contrast image, that's a problem. It is the bright nerve that is the problem, it is the one that blends into the background. That is normal. Remember that there's only five extra-ocular muscles that we can see on a coronal image. We can see one, two, three, four rectus muscles and one oblique muscle, that's the superior oblique muscle. If you want to find the sixth extra-ocular muscle, that's the inferior oblique muscle. It does not go back to the annulus of Zin. It is only anterior and you can see it here on an axial high-resolution image as it runs from the bottom of the globe medially to insert upon the orbital rim. There is a classic differential diagnosis between Graves' disease, which is a thyroid orbitopathy, and Orbital Pseudotumor, which is an autoimmune inflammatory disease. Radiologists love to talk about the difference between these two and how you distinguish them. Clinicians laugh at us because one of these hurts and the other one does not. So Graves' disease is painless, Orbital Pseudotumor is painful. They almost never appear on the same differential diagnosis for the clinicians. So here's how we can tell them apart radiologically if you ever need to. Graves' disease affects both orbits symmetrically and it affects the extra-ocular muscles in a predictable pattern. First the inferior, then the medial, then the superior rectus muscle, and only in late stages the lateral rectus muscle and the oblique muscles are involved. Notice that the biggest muscle here is the inferior, then the medial, then maybe the superior rectus, and notice how symmetric it is. This is classic for Graves' disease. But Orbital Pseudotumor, the myositis form of Orbital Pseudotumor, affects usually a single muscle and a random single muscle, and it is not symmetric. So here the superior rectus complex is involved and it is just one muscle in large. This is more characteristic of Orbital Pseudotumor.