First pass myocardial perfusion MRI
Perfusion and delayed enhancement imagery are both performed after injecting the bolus of contrast agent (Gadolinium chelates). They explore two different aspects:
- First pass, early perfusion MRI examines myocardial tissue perfusion (wash in)
- Delayed enhancement MRI, looks for anomalies in the cinetics of contrast agent elimination (wash out).
The study of myocardial tissue perfusion in first pass MRI exploits the modifications in T1 relaxation time generated by the arrival of Gadolinium chelates in myocardial extracellular space.
To cover the entire left ventricle with good contrast and sufficient spatial and temporal resolution, the sequences can be of the types ultrafast GE, GE-EPI or steady state GE with balanced gradients. The T1 weighting of these sequences results from a saturation-recuperation preparation pulse: a 90° pulse destroys the longitudinal magnetization of the myocardial tissue to highlight the arrival of the contrast agent. In quantification, the relationship between contrast agent and signal intensity must be as linear as possible.
Acquisition calls for a multi-sliced interlaced mode: at each heartbeat, all the slices are acquired. The total sequence lasts about 1 minute, and breath-holding must be maintained as long as possible, particularly on arrival of the contrast bolus.
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