in this sequence fat tissue signal is maximized. This issue enables detection of subtle signal changes in the medullary part of bone, as well as to accurately detect the effacement of fat tissue pads, particularly in critical areas such as the orbit and the pterygopalatine fossa. Plain SE T1 sequence has two major indications:
• Patients examined for lesions of unclear etiology. In this case, additional information is provided regarding signal pattern of the lesion, therefore supporting the differential diagnosis task.
• Patients followed up after treatment. In this scenario a plain SE T1 sequence helps to retrospectively assess the enhancement pattern of a suspect lesion, therefore it offers clues to discriminate a recurrent lesion from scar tissue.
After the administration of paramagnetic contrast agent (Gd-DTPA, 0.2 ml/kg body weight), a SE T1 sequence is acquired in all three planes. Fat-sat prepulses may be applied to both TSE T2 and enhanced SE T1 sequences to increase lesion conspicuity (particularly in malignant tumors) and to delineate the relationships between a lesion and intraorbital/pterygopalatine fat tissue. The main disadvantage on fat-sat TSE T2 sequences is represented by the loss of a natural contrast agent. Fat tissue (suppressed), bone, and muscular structures all display a hypointense signal, resulting in a difficult delineation of the interface between normal and pathologic tissues. On the other hand, post-contrast fat-sat SE T1 requires a considerable increase of repetition time (TR) that influences both T1 weighting of images and acquisition time. These pitfalls may be solved only by decreasing the number of acquired slices and, therefore, the anatomic coverage. As a result, in our experience, fat-sat technique is preferably applied to SE T1 sequences in collaborative patients, focusing on restricted anatomic areas.
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