Thymus protocol (MRI)
Thymic MRI is a targeted mediastinal imaging protcol performed mainly to distinguish surgical from nonsurgical thymic lesions (eg. thymic hyperplasia, thymic cysts, and lymphoma).
Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's and referrer's preference, institutional protocols, patient factors, and time constraints.
Sequences
A good protocol for this purpose involves at least:
- T1 in-phase (IP) and out-of-phase (OOP)
- plane: axial
- sequence: in-phase (IP) and out-of-phase (OOP) T1-weighted fast incoherent gradient-echo imaging
- purpose: chemical shift artifact helps differentiate thymic hyperplasia and thymus gland tumors in patients 16 years of age or older
- T2 weighted
- plane: axial and sagittal
- sequence: double inversion recovery (IR) T2-weighted imaging, cardiac-gated preferable. A fat-saturated sequence should be considered in at least one plane
- purpose: thymic cysts will show marked T2 hyperintensity
- T1 weighted
- plane: axial
- sequence: fast spoiled gradient echo (eg. LAVA, VIBE)
- purpose: thymic cysts will show marked T2 hyperintensity
If the main purpose of the scan is the differentiation between thymic hyperplasia and malignancy or thymic cyst assessment, the sequences above should be sufficient in most of the cases. Additional sequences may be performed when other conditions are considered, and these may include:
- diffusion-weighted imaging (DWI)
- postcontrast sequences (Gd)
- plane: axial and coronal (at least two different planes or volumetric 3D)
- sequence: post-contrast fast spoiled gradient echo (eg. LAVA, VIBE) - dynamic post-contrast phases usually include acquisitions: immediately after contrast and at 1, 3, and 5 minutes
