Hypertrophic cardiomyopathy protocol (MRI)

The MRI hypertrophic cardiomyopathy protocol encompasses a set of different MRI sequences for the cardiac assessment in case of suspected hypertrophic cardiomyopathy.

Note: This article aims to frame a general concept of a cardiac MRI protocol in the assessment of hypertrophic cardiomyopathy or left ventricular hypertrophy. 

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

• hypertrophic cardiomyopathy
• left ventricular hypertrophy
• (aortic valve disease)

1.5 vs 3 tesla

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

The MRI hypertrophic cardiomyopathy protocol should be rather conducted on a system from which normal values for T1 mapping are available.

The acquisition at 3 tesla requires a lot of adjustments and careful shimming to avoid flow and dark banding artifacts, 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.

In the case of a stress test, certain issues require consideration that is 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
• 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 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
• coronal left ventricular outflow tract view (LVOT)
  • angulation: perpendicular to the 3-chamber view through the left ventricular outflow tract and aortic valve in a coronal oblique fashion
  • volume: a single slice
• aortic valve stack*
  • angulation: parallel to the aortic valve and perpendicular to the sagittal and coronal left ventricular outflow tract 3-chamber view
  • volume:  including 1-2 slices of the outflow tract, the aortic valve and the aortic root

Sequences

Standard sequences

• T2 black-blood or SSFP
  • purpose: overview, depiction of the cardiac surroundings and greats vessels, assessment of mediastinal lymphadenopathy in suspected sarcoidosis
  • 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, coronal LVOT, aortic valve stack* (in aortic valve disease)
• late gadolinium enhancement (C+)
  • purpose: for the evaluation of myocardial viability (myocardial fibrosis 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 TI (PSIR)

Optional sequences

• phase-velocity imaging
  • purpose: flow measurements (flow measurements LVOT, aortic root*)
  • technique: velocity-encoded cine gradient-echo sequences
  • planes: in-plane 3ch and/or coronal LVOT, through-plane LVOT parallel to the aortic valve, sinotubular junction* (aortic valve disease)
• T1 mapping
  • purpose: cardiac tissue characterization (myocardial fibrosis)
  • technique: MOLLI, ShMOLLI, SASHA, STONE, SAPPHIRE etc.
  • planes: short-axis views, 4ch or 2ch

(*) 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 in patients with a weak ECG signal
• if an aortic valve stack is included and flow measurements are also obtained in the aorta this protocol can be also used in the assessment of aortic valve disease
• cine imaging
  • in atrial fibrillation or cardiac arrhythmia, it might be worthwhile to switch to prospective gating
  • consider MRI tagging or feature tracking to detect slow contracting wall segments
• flow imaging
  • expect an increased velocity in the left ventricular outflow tract, Venc should be adjusted
• T1 mapping
  • for extracellular volume calculation dedicated postprocessing software is recommended
  • for extracellular volume 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
  • increase TI 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 artefacts