When trying to read a chest x-ray we are taught that it is a good idea to have a system, an order of things to look at, to help you spot abnormalities. The same principle applies with MRI scans. There are many different approaches that can be taken and below is just one option. When you are trying to decipher MRI scans it is extremely useful to look at 'normal' MRIs. It is much easier to spot abnormalities if you are familiar with what things should look like. One of the best things you can do is spend some time going through normal scans. Proposed approach: 1- Identify the plane of the image- cross section (horizontal), sagittal (profile) or coronal (vertical from the front). 2-Identify the location of the image- may be written on the top of the MRI or you can figure it out by identifying anatomical structures. 3- Identify and contrast special dyes- special dyes are used to label certain structures, such as the heart or liver. These dyes make tissues appear as an especially strong image, and should be listed in the notes. 4- Compare and contrast the MRI to a normal image. In time, you will become so familiar with what things should look like that you will not need to complete this step. Having a good grasp on anatomy is essential to reading MRIs. Different types of MRI As we know, MRI creates images by picking up different signal intensities from different tissues depending on the hydrogen, or more specifically, proton content of that tissue. On normal MRIs (proton density or PD weighted), the greater the hydrogen content, the brighter the image. But radiologists and radiographers can programme the MRI machine to only pick up a certain direction of proton movement. T1 is when they programme the machine to only look at the longitudinal movement of protons. T1 images are usually used to look at normal anatomical details. T2 is the transverse movement of protons and is usually used to look at pathology because most tissues involved in disease tend to have a higher water content than normal. This image summarizes the signal intensity of various tissues at T1 and T2 weighted imaging. Key points: - Anatomical MRI is T1 weighted. T1 is best for looking at brain structure because fat appears very bright and bone marrow contains a great deal of fat. - Functional MRI is T2 weighted. Water and fluid are brighter on T2- ideal for tissue oedema. - White matter appears a light grey in T1 and a dark grey in T2. - Grey matter appears grey in both. - Cerebrospinal fluid (CSF) appears black in T1 and white in T2. STIR and FLAIR Short T1 Inversion Recovery or STIR is a fat suppression technique. That is all you really need to understand about it at this level. STIR is indicated in a number of different cases, but is particularly useful for suppressing the signal from normal adipose tissue to help reduce artefacts and improve visualisation. STIR sequencing is also very useful for looking at structures such as the adrenal glands, bone marrow and fatty tumours. Fluid Attenuation Inversion Recovery or FLAIR is a similar technique to suppress water. FLAIR is good for imaging cerebral oedema and periventricular or cortical lesions in conditions such as multiple sclerosis. Indications: Contraindications: Strengths and weaknesses: Examples: Source
