|ECR 2019 / C-3178|
|Cardiac Magnetic Resonance imaging of infiltrative cardiomyopathies|
Infiltrative cardiomyopathies are a diverse group of cardiac diseases caused by the deposition of abnormal cells or substances within the myocardium. CMR combines good spatial resolution, lack of radiation, non-invasiveness, and three-dimensional imaging with highly reproducible measurements of the ventricular function.
The CMR protocol used in cases of infiltrative cardiomyopathies includes a general basic set of imaging sequences (Fig. 1) with additional sequences depending on the specific type of clinically suspected cardiomyopathy.
Scout images allow the correct positioning of the heart at the center of the surface coils, which improves signal to noise ratio. A stack of axial sections of the thorax (most commonly, half-Fourier rapid acquisition with relaxation enhancement or steady-state free precession - SSFP - sequences) is acquired to depict major non-cardiac pathologic processes and to provide planning information for the following sequences. SSFP cine sections are acquired in the vertical long axis (two-chambers – left atrium and ventricle; and three-chambers – left atrium, ventricle and left ventricular outflow tract) and horizontal long axis (four cardiac chambers).
A stack of short-axis sections from the mitral valve plane to the apex is used for quantitative asssessment of ventricular volumes and function. A qualitative visual analysis of the myocardial morphology and the contraction is performed by assessing the degree of myocardial thickness (normal <12 mm) and myocardial contraction (normal, mild hypokinesia, severe hypokinesia, akinesia, dyskinesia). The American Heart Association 17-segment model is used to indicate the each myocardial segment.
Black blood sequences, T1, T2 or STIR, are performed to look for evidence of oedema or myocardial fibrofatty infiltration.
The late gadolinium enhancement study (LGE) is then performed (following intravenous injection of a bolus of contrast agent of 0.15 - 0.2 mmol/Kg of body weight) to assess the presence, location, and extent of the infiltrative process (Fig. 2). Optimal contrast differentiation between normal and infiltrated myocardium is obtained on the TI scout (multiple acquisitions of a single midventricular section each with a different inversion time) by determining the exact time the signal of the normal myocardium is nulled which is obtained. Normal myocardial inversion times: 200-300msec at 6 minutes in a 1.5T scanner. Inversion time is adjusted as the examination progresses, to allow for contrast agent washout from the myocardium (since nulling time changes over time). A useful alternative is acquisition of phase-sensitive images by using an inversion-recovery SPGR or SSFP sequence . In the diagnosis of infiltrative processes is important to assess the extent of the enhancement (partial thickness or transmural) and its predominant distribution (subepicardial, midwall, or subendocardial).
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