Myocardial viability protocol (MRI)

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The MRI myocardial viability protocol encompasses a set of different MRI sequences for the assessment of myocardial viability.

Note: This article aims to frame a general concept of a cardiac MRI protocol in the setting of acute or chronic myocardial infarction.

Protocol specifics will vary depending on additional clinical questions, differential diagnosis, MRI scanner type, specific hardware and software, radiologist and perhaps referrer preference, patient factors e.g. arrhythmia or breathing problems or implants, specific indications and time constraints.

Indications

1.5 vs 3 tesla

Cardiac MRI examinations can be performed on both 1.5 and 3 tesla. The majority of examinations is nevertheless still conducted on 1.5 tesla magnets since the acquisition at 3 tesla requires a lot of adjustments and careful shimming to avoid flow and dark banding artefacts especially concerning steady-state free precession cine imaging.

Applications that may benefit from increased field strength .

Patient preparation

Checking indications, contraindications, explanation of the examination and obtaining informed consent is obvious as in other examinations. In case of a stress test, there are certain issues which require consideration are explained specifically in that protocol.

Beyond that patient preparation for cardiac MRI includes the following:

  • instruction how to breathe
  • an electrocardiogram signal need to be acquired

Patient positioning

A cardiac MRI is conducted in the supine position.

Technical parameters

Coil

Multi-phased-array coils are recommended.

  • anterior surface coil, posterior coil
  • cardiac coil
Scan geometry
  • in-plane spatial resolution: will vary with the sequence
  • field of view (FOV):  will vary, for most planes a FOV ≤320 mm is recommended
  • slice thickness: varies with the sequence and is usually 6-10 mm 
Planning

The cardiac imaging planes differ from the normal axial, coronal and sagittal body planes :

  • overview
    • angulation: strictly axial
    • volume: from the thoracic inlet to diaphragm
  • horizontal long axis view or 4-chamber view (4ch)
    • angulation: along the left ventricular long axis through the apex and the centers of the mitral and tricuspid valves
    • volume: including the anterior and inferior wall or a single slice
  • left ventricular vertical long axis view or 2-chamber view (2ch)
    • angulation: along the left ventricular long axis through the left ventricular apex and the center of the mitral valve
    • volume: including septum and left ventricular free wall or single slice
  • sagittal left ventricular outflow tract (LVOT) or 3-chamber view (3ch)
    • angulation: through the left ventricular apex,  the center of the mitral valve and the left ventricular outflow tract and aortic valve
    • volume: including the anterolateral and inferoseptal left ventricular wall
  • short-axis view (sax)
    • angulation: perpendicular to the left ventricular long axis
    • volume: stack usually including the atrioventricular valves and the cardiac apex or 3 single slices through basal, midventricular and apical zones

Sequences

Standard sequences
  • T2 black-blood or SSFP
    • purpose: overview, depiction of the cardiac surroundings and greats vessels
    • technique: T1 black-blood, T2 black-blood, SSFP ideally over 1-2 breath-holds
    • planes: axial
  • cine imaging
    • purpose: left ventricular wall motion, left ventricular volumetry
    • technique: cine SSFP or spoiled GRE
    • planes: 2ch, 4ch, 3ch and short-axis views
  • resting perfusion (C+)
    • purpose: for the assessment of myocardial ischemia
    • technique: saturation recovery with GRE, GRE-EPI hybrid or SSFP readout
    • planes: short axis,  long axis* optional
  • late gadolinium enhancement (C+)
    • purpose: for the evaluation of myocardial viability (myocardial necrosis and myocardial scar tissue)
    • technique: 2D and 3D IR GRE, PSIR
    • planes: 2ch, 4ch, 3ch and short-axis views
    • inversion time (TI) as determined by TI scout (Look-Locker) or fixed (PSIR)
Optional sequences
  • T2 weighted imaging
  • T1 mapping
  • T2 mapping
    • purpose: cardiac tissue characterization (myocardial edema)
    • technique: T2-TSE, T2p-SFFP, GraSE
    • planes: short-axis views
  • stress perfusion (C+)
    • purpose: for the assessment of myocardial ischemia ​(should not be performed in acute myocardial infarction or acute coronary syndromes)
    • technique: saturation recovery with GRE, GRE-EPI hybrid or SSFP readout
    • planes: short axis,  long axis* optional
  • early gadolinium enhancement (C+)

(*) indicates optional planes

Practical points

The following considerations can be made in certain conditions:

  • single-shot modules or free breathing with real-time image acquisition in patients with difficulties to hold their breath
  • abdominal bands in profound respiratory motion
  • peripheral pulse gating in patients with a weak ECG signal
  • postponing the exam in patients with severe pleural effusion and related ghosting artifacts and breathing problems until after pleural drainage
  • cine imaging
    • in atrial fibrillation or cardiac arrhythmia, it might be worthwhile to switch to prospective gating
  • perfusion imaging
    • a test run should be performed before the actual perfusion scan to check image quality
    • the breath-hold should start before contrast reaches the left ventricle
    • a sufficient number of images should be acquired 50-60 heartbeats to ensure contrast has passed through the left ventricle
  • late gadolinium enhancement
    • 2D IRGRE or sequences with SFFP readout in patients with poor breath-holding capabilities
    • inversion time should be increased by 10ms every 1-2 minutes
    • acquisition in mid or late diastole to minimize motion artifacts
    • saturation bands across the spinal column and anterior chest wall can help to reduce ghosting artifacts