Cardiac MRI consists of using MRI to study heart anatomy, physiology, and pathology.
In comparison to other techniques, cardiac MRI offers:
- improved soft tissue definition
- protocol can be tailored to likely differential diagnoses
- a large number of sequences are available
- dynamic imaging provides functional assessment
- no ionizing radiation
- MRI safety still requires consideration
Cardiac MRI can be technically challenging. In particular, a comprehensive understanding of cardiac imaging planes is required for scan planning.
Dark blood Imaging
Dark blood imaging may be based on spin echo or steady-state free precession sequences. The fast acquisition time of the sequences minimizes respiratory and cardiac movement artifacts. However, a low signal/noise ratio results in inferior spatial resolution.
These can be T1, T2, or proton density weighted sequences:
- T1 weighted sequences achieve better anatomic definition
- T2 and PD weighted sequences reach better tissue characterization
White blood Imaging
The main advantage of white blood imaging is its fast acquisition. It can obtain movement sequences and allows studying cardiac function and movement.
Flux quantification sequences
Inversion Recovery sequences
These imaging techniques use additional 180º pulses to null signal from blood and other tissues, and, therefore, improve contrast.
The most used sequence is STIR.
Perfusion imaging (also known as first-pass images)
These are T1 weighted, gradient-echo sequences. Image acquisition is performed 3 minutes after gadolinium contrast administration. If there is a hypoenhanced area, this implies a zone of myocardial infarction that is non-viable.
Viability study delayed (also known as myocardial enhancement study)
These are T1 weighted, gradient-echo sequences. Image acquisition is performed 10 minutes after gadolinium contrast administration.
Focal myocardial fibrosis has a delayed gadolinium contrast wash out. So hyperenhancement indicates a myocardial scar, thus an evolved myocardial infarction.
Usually, an extra inversion pulse is used to improve contrast between fibrosis and the surrounding myocardium.