Delayed Enhancement MRI (DE-MRI)
The myocardial delayed enhancement study is performed about 10 minutes after injection of the contrast agent. Delayed enhancement translates a relative excess of gadolinium in the pathological tissues compared to the healthy tissues.
It is based on T1 weighted ultrafast gradient echo or steady state gradient echo sequences. The advantage of 3D acquisitions is their capacity to explore a large volume with a single breath-hold, whereas 2D acquisitions offer better spatial resolution (less blurring due to motion), and provide better visualization of transmural enhancement extension. The contrast of these sequences is optimized:
- Either by inversion - recuperation with a TI nulling the healthy myocardial signal. The TI is determined beforehand in a dedicated sequence (TI-scouting or Look locker) to test a range of TI so the user can choose the TI with the best suppression of the healthy myocardial signal (~ 300 msec).
- Or by PSIR technique (Phase Sensitive Inversion Recovery), which is more robust as it is independent of TI (Actually, TI can be difficult to adjust depending on the patient). This technique incorporates acquisition of reference slices in an ultrafast IR-GE sequence, without lengthening sequence time. These reference slices serve to correct the phase polarity of the slices at TI, restoring T1 contrast, as opposed to a simple magnitude analysis of the signal.
Delayed enhancement can signify:
- An ischemic edema (myocardial infarction in the acute phase)
- An inflammatory or infectious pathology (myocarditis) (figure 11.17)
- Fibrous reorganization (Sequelae of infarct, cardiomyopathies)
- A tumorous lesion