MRI of the thymus

W15 Limiting MRI to the area of interest to shorten image acquisition time is essential. A long image acquisition makes successful breath-holding difficult, with resultant motion artifact significantly compromising image evaluation. Hyperventilating the patient before each breath-hold can be helpful. Oxygen administration has been shown to be even more helpful in extending breath-hold capability [1]. Inand out-of-phase fast gradient-echo imaging is a rapid T1-weighted sequence that has been shown to be useful in distinguishing normal thymus and thymic hyperplasia from thymic neoplasms and lymphoma [2] and can serve as the T1-weighted unenhanced sequence for this examination. T2-weighted imaging of the mediastinum can be accomplished with double inversion recovery fast spin-echo imaging, a cardiac-gated black-blood fast spin-echo technique that requires approximately a 20to 25-second breath-hold per slice. Breath-hold duration will vary with the TR, which is dictated by the patient’s heart rate—bradycardia lengthens the TR and requisite breath-hold and tachycardia shorten the TR and breath-hold. Alternatively or in addition, rapid T2-weighted images can be obtained with nongated 2D axial balanced gradient-echo imaging, a sequence that requires an 8to 15-second breath-hold for the entire scan. Please note that these breathhold times and those that follow are estimates that can vary depending on scanning parameters, lesion size or required breadth of coverage, and whether or not cardiac gating is used. The T2-weighted coronal ultrafast spin-echo MRI of the Thymus