Myocarditis protocol (MRI)

The MRI myocarditis protocol encompasses a set of different MRI sequences for the cardiac assessment in case of suspected myocardial inflammation.

Note: This article aims to frame a general concept of a cardiac MRI protocol in the above setting. 

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

• myocarditis
• cardiac sarcoidosis
• Tako tsubo cardiomyopathy
• myocardial infarction with non-obstructed coronary arteries (MINOCA)
• can be used for the assessment of many cardiomyopathies

1.5 vs 3 tesla

Cardiac MRI examinations can be generally performed on both 1.5 and 3 tesla.

The cardiac MRI myocarditis protocol should be rather conducted on a system from which normal values for T1 mapping or T2 mapping are available.

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.

An application that may benefit from increased field strength is late gadolinium enhancement ^1,2.

Patient preparation

Checking indications, contraindications, explanation of the examination and obtaining informed consent is obvious as in other examinations.

Beyond that patient preparation for cardiac MRI includes the following:

• instruction how to breathe
• an electrocardiogram signal need to be acquired
• hematocrit required for extracellular volume calculation

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 ^1-4:

• overview
  • angulation: strictly axial
  • volume: from the thoracic inlet to the 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 or view 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, a depiction of the cardiac surroundings, evaluation for mediastinal lymphadenopathy in suspected cardiac sarcoidosis
  • technique: T2 black-blood, SSFP ideally over 1-2 breath-holds
  • planes: axial
• cine imaging
  • purpose: left ventricular wall motion, left ventricular volumes
  • technique: cine SSFP or spoiled GRE
  • planes: 2ch, 4ch, 3ch and short-axis views
• T2 weighted imaging
  • purpose: for the evaluation of myocardial edema, myocardial hemorrhage, area at risk
  • technique: T2 STIR black-blood
  • planes: short-axis view, 2ch* or 4ch*
• 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

• T1 mapping
  • purpose: cardiac tissue characterization (myocardial edema, myocardial fibrosis, myocardial scar tissue)
  • technique: MOLLI, ShMOLLI, SASHA, STONE, SAPPHIRE etc.
  • planes: short-axis views, 4ch or 2ch
• T2 mapping
  • purpose: cardiac tissue characterization (myocardial edema)
  • technique: T2-TSE, T2p-SFFP, GraSE
  • planes: short-axis views

(*) 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 holding their breath
• abdominal bands in profound respiratory motion
• peripheral pulse gating inpatient with a weak ECG signal
• postponing the exam in patients with severe pleural effusion and related ghosting artefacts and breathing problems until after pleural drainage
• cine imaging
  • in atrial fibrillation or cardiac arrhythmia, it might be worthwhile to switch to prospective gating
• T2 weighted imaging
  • short-axis acquisition with MRI integrated body coil (Q-body) only for assessment of myocardial edema with T2 myocardium / skeletal muscle ratio, especially if no mapping is available ⁵
• T1 mapping*
  • for extracellular volume calculation dedicated postprocessing software is recommended
  • for extracellular volume calculation, hematocrit should be obtained on the same day
• late gadolinium enhancement
  • 2D IRGRE or sequences with SFFP readout in patients with poor breath-holding capabilities
  • inversion time (TI) should be increased by 10ms every 1-2 minutes
  • acquisition in mid or late diastole to minimize motion artefacts
  • saturation bands across the spinal column and anterior chest wall can help to reduce ghosting artifacts