ECG-gated CMR plays a pivotal role in diagnosis, follow-up and risk stratification of DCM. ECG-gating is mandatory to investigate a moving organ like the heart. CMR allows a multiplanar investigation. A standard exam includes a stack of parallel short-axis (SA) slices of the LV and long axis views (2-, 3- and 4-chambers). Depending on the clinical hypothesis, other planes can also be acquired, such as left ventricle outflow tract (LVOT) and peculiar planes for the study of the right heart.

Cine-sequences are the gold standard for the assessment of wall motion abnormalities and the evaluation of bi-ventricular volumes and thus ventricular function. The most used cine-sequences are the so-called balanced steady-state free precession (b-SSFP), which provide an excellent myocardial blood pool contrast although they are sensitive to magnetic field inhomogeneity. These sequences can be used before and after contrast media administration, allowing the evaluation of myocardial enhancement.

By means of post-processing software, it is possible to evaluate end-systolic volume (ESV), end-diastolic volume (EDV) and LVEF. Furthermore, it is also possible to calculate LV mass by accurately defining both epicardial and endocardial border with a dedicated software.

Ventricle wall motion is evaluated on cine-images by measuring the myocardial thickening: 5 patterns of motion have been defined:

• normokinesia (normal myocardial contractility)
• hypokinesia (decreased contractility of the myocardium)
• dyskinesia (i.e. non-contemporaneous contraction of two or more ventricular segments)
• hyperkinesia (increased contractility of the myocardium)
• akinesia (absence of wall motion).

Even though myocardial contractility might be evaluated by eyeballing, quantitative methods allow a precise assessment of myocardial thickening during the cardiac cycle. There are, in fact, software that allow to reconstruct a 3D model of the beating heart, thus being able to quantify 2D-radial, circumferential and longitudinal myocardial strain.

T1 mapping is a technique that allows the creation of maps of T1 relaxation in which every pixel represents a single T1 value of the corresponding myocardial section. The most used sequence is a modified Look-Locker inversion recovery (MOLLI) which allows to acquire the images in a single breath-hold. T1 maps can be obtained before (T1 native) and after the intravenous administration of contrast medium (T1 post-contrast). An additional parameter that can be obtained by using T1 native, T1 post-contrast and hematocrit (Ht) is called extra-cellular volume fraction (ECV) and represents the proportion of myocardial interstitial space versus cellular space. Gadolinium distributes only into the interstitial space. Thus, areas of fibrosis (increased interstitial space) show a high value of T1 native, a low value of T1 post contrast (due to the presence of gadolinium) and a high value of ECV.

T1 mapping is particularly useful in the evaluation of myocardial fibrosis and also in myocardiopathies characterized by a diffuse infiltration of the myocardium by fibrosis or tissue deposits of other nature (i.e. amyloidosis, Anderson-Fabry Syndrome, etc.).

T2 mapping is another tissue characterization technique that allows the creation of maps of T2 relaxation values of the myocardial tissue. The most used sequences are b-SSFP bright-blood with a T2-preparation pulse-based sequence. This imaging technique is mainly useful to spot myocardial edema (e.g. in acute CAD, myocarditis, etc.).

After intra-venous administration of contrast medium, images are acquired with fast T1-weighted sequences during the first pass of Gadolinium in the ventricles, to evaluate myocardial perfusion defects. Thus, it is possible to qualitatively or even quantitatively assess differences in myocardium intensity which are due to ischemic or poorly perfused area. 10-20 minutes after contrast administration, images are acquired with a T1-weighted phase-sensitive inversion recovery (PSIR) sequence to evaluate areas of Gadolinium focal accumulation, with a time of inversion accurately chosen to nullify healthy myocardium signal. In such sequences, areas of increased extra-cellular space are brightly hyperintense: this phenomenon is known as Late Gadolinium Enhancement (LGE).

It is also possible to acquire images <240 seconds from the contrast injection with the same sequence used for LGE and with a high time of inversion (»440 ms), assessing Early Gadolinium Enhancement (EGE). Such datasets allow, for example, the assessment of intra-cardiac thrombi, which appear markedly hypointense compared to the healthy myocardium.

The sequences described before are extremely useful in diagnosis and follow-up of DCM.

Main MRI features of DCM may be summarized as follows:

-Cine b-SSFP

• LV or bi-ventricular dilatation
• LVEF decrease and EDV increase
• Thinning of the ventricle wall (<5.5 mm)

Fig. 1: Male Patient (60 yo) affected by DCM associated to alcohol abuse. LV dilatation showed in 4-chambers (A), 2-chambers (B), short-axis (C) views with b-SSFP cine sequences.

Fig. 2: Male Patient (65 yo) affected by an idiopathic form of DCM. The LV is dilated and severely hypokinetic. The first picture (A) is a 3-chambers view of LV in end-diastolic phase. The second picture (B) is a 3-chambers view of LV in end-systolic phase. Both the images were acquired with a b-SSFP cine- sequence. As it possible to foresee LVEF is severely decreased.

-LGE, EGE, T1 mapping

• Early forms of DCM could also not show any sign of LGE.
• Fibrosis in DCM typically involves basal and medio-ventricular septal segment with an intramyocardial pattern but with disease progression fibrosis could also involve other segments . Rarely, LGE is transmural or subepicardial-intramyocardial. A subendocardial pattern of LGE is very rare in DCM and it is often a sign of fibrosis secondary to ischemic events.
• Possible presence of intra-cardiac thrombi that could be well characterized with EGE sequences.
• T1-mapping is important for differential diagnosis with infiltrative myocardiopathies and other diseases characterized by increased extra-cellular volume. Furthermore, it represents an important parameter regarding risk stratification and prognosis.

Fig. 3: Male Patient (55 yo) affected by a genetic form of DCM. Intra-myocardial LGE localized in infero-septal basal segment showed in 4-chambers (A) and short-axis (B) views.

Fig. 4: Male Patient (47 yo) affected by an idiopathic form of DCM. The LV is dilated and it is possible to see an apical thrombus in 2-chambers (A) and short-axis (B) views with cine b-SSFP. The thrombus is also intensely hypointense in PSIR sequences, as it is possible to see in 2-chambers view (C).

Fig. 5: Male Patient (51 yo) affected by DCM secondary to myocarditis. In the first mid-ventricular short-axis view it is possible to see areas of increased ECV values (A) mostly in the interventricular septum. In the other mid-ventricular short-axis view it is also possible to see a non-ischemic intra-myocardial LGE in the interventricular septum (B).
References: Centro Cardiologico Monzino - Milan, Italy

-T2 mapping

• It is crucial in the diagnosis of pathologies that can prelude to DCM, such as myocarditis. It can also be useful in differential diagnosis with acute CAD, in which myocardial edema is associated with the vascular territory of the obstructed vessel.

Fig. 6: Male Patient (61 yo) affected by an DCM secondary to acute lymphocitic myocarditis. In these short-axis views (A,B,C) it is possible to see areas of increased T2 values concerning the antero-lateral wall.
References: Centro Cardiologico Monzino - Milan, Italy

Risk stratification and prognosis

Several studies have demonstrated the association between high values of T1 native and ECV and adverse cardiovascular events. ECV, in particular, has been assessed as an independent risk factor for major adverse cardiovascular events (MACE)

The presence of LGE is a strong independent predictor of sudden cardiac death, hospitalization and overall mortality. Furthermore, also the extension of fibrosis and the intramyocardial pattern of LGE are positively correlated with MACE.

A reduced LVEF has been negatively associated with long term survival. Current guidelines suggest to implant an ICD in patients with a LVEF <30-35% (assessed with echocardiography) to prevent SCD. CMR has shown to be the most accurate imaging technique concerning the evaluation of cardiac volumes, thus being useful regarding the clinical indications for the implant of an ICD. Although it did not show any significative impact regarding long-term survival, some authors demonstrated that the implant of an ICD halved the risk of SCD.