Fat suppression imaging in neuroradiology with T2 weighted fast spin echo sequences

This paper describes the technical aspects, characteristics and clinical applications of fat suppression in T2 weighted fast spin echo (FSE) sequences in neuroradiology. Fat suppression is essential with FSE as this sequence is characterized by a high fat signal not only in T1 but also in T2 weighted images leading to image artifacts in FSE sequences compared with conventional spin echo imaging. Such artifacts may mask diseases producing a high signal in T2 weighted images in structures rich in fat such as the head (orbit, face) and spine (especially the bone marrow and epidural space). The most widely used far suppression techniques are 1) CHESS (chemical shift selective saturation) based on the chemical shift which only alters the fat signal and contrast; 2) STIR (short T1 inversion recovery) based on the relaxation times which alters the fat signal and contrast and all tissues with a T1 resembling fat. Fat suppression enhances the display of inflammatory or tumoral lesions (especially metastases) which would otherwise me masked by the high fat signal. Whichever technique is adopted, fat suppression is satisfactory and fast, there being no significant quantitative differences. There are slight differences in image quality which depend on a series of factors which will indicate one technique rather than the other (structures to be examined, homogeneity and power of the magnetic field size of the FOV, use of contrast medium, number of slices and type of sequences).