A clinical cardiac MRI protocol used in patients with suspected myocarditis or cardiomyopathy should always include a fat-saturated T2-weighted sequence (Carbone and Friedrich 2012). Because it suppresses signal from fat and flowing blood, this pulse sequence is highly sensitive for detecting fluids in tissues. It has approx. 80 % sensitivity in identifying myocardial edema and is also well suited for detecting concomitant pericardial effusion. Myocardial edema imaging using newer pulse sequences with much improved image quality provides useful additional diagnostic and prognostic information, allowing identification of acute or recent myocardial ischemic injury in patients with acute chest pain, distinguish acute from chronic myocardial infarction and contributing to the determination of myocardium at risk (Eitel and Friedrich 2011). Despite these advances, cardiac MRI is only a supplementary tool and not the first-line imaging modality in patients undergoing imaging for evaluation of myocarditis or cardiomyopathy.

Inflammation damages the cell membrane, resulting in a larger distribution volume of contrast medium in injured myocardium. This is one of the mechanisms underlying late enhancement in cardiac imaging.

However, the presence of late enhancement alone does not allow discrimination between inflammatory processes and scar tissue. Areas of late enhancement resulting from retention of contrast medium are seen in a variety of disorders associated with myocardial injury and edema, necrosis, or fibrosis (Manrique et al. 2009). Some additional features such as distribution and location of delayed enhancement may help the radiologist in narrowing the differential diagnosis among ischemic and nonischemic disorders. For instance, when contrast medium accumulates in the epicardium, a myocardial scar of ischemic origin is unlikely because such a scar is typically seen in a subendocardial location. Furthermore, delayed enhancement occurring in coronary artery territories can contribute to the differentiation between scar and edema. In unclear cases, acquisition of the delayed enhancement sequence can be repeated after 15–20 min. At this point in time, a scar still has high signal intensity due to delayed washout of contrast medium from injured myocardium, while edema has low signal intensity (Abdel-Aty and Schulz-Menger 2007; Aletras et al. 2008).

Imaging of ischemic myocardial injury is an important component of a cardiac MRI protocol and is done by assessing late enhancement, typically 12–15 min after administration of a Gd-DPTA-based contrast agent (e.g., gadobutrol as in the SHIP). Differential enhancement of infarcted myocardium is primarily due to diffusion and delayed clearance of contrast medium from the zone of infarction. In addition, myocardial injury shortens longitudinal relaxation (T1). Compared with other imaging methods, contrast-enhanced cardiac MRI is more sensitive in detecting even small subendocardial infarcts. Furthermore, the extent of delayed enhancement on MRI closely correlates with the size of myocardial injury determined by established methods (Kim et al. 1999; Saraste et al. 2008). In contrast, PET and SPECT usually detect large transmural infarcts or nearly transmural defects but may miss smaller, subendocardial infarcts (Wagner et al. 2003).

Cardiac MRI may also detect complications of acute myocardial infarction such as the development of left ventricular pseudoaneurysm (Jiji and Kramer 2011).

Single-shot sequences are widely used for delayed enhancement imaging, offering the advantage that all data can be acquired in a single cardiac cycle. This comes at the cost of a loss of image sharpness.

After administration of gadolinium-based contrast medium, infarcted myocardium exhibits delayed enhancement and can be identified using an inversion recovery (IR) sequence, which greatly improves contrast between viable myocardium and infarction. When magnitude reconstruction is used, IR delayed enhancement imaging is highly sensitive to the inversion time (TI) selected (Kellman et al. 2002). The optimal TI to null signal from viable myocardium (i.e., to render it dark) for an individual can be determined by obtaining a TI scout series with progressively larger TIs (TI surfing). Typical TIs are between 200 and 300 ms, depending on the amount of contrast medium administered (usually 0.1–0.2 mmol/kg body weight), time of image acquisition after contrast administration, and individual contrast medium clearance (Stork et al. 2007). An optimal TI enhances the contrast between dark viable myocardium and bright infarcted tissue. When delayed enhancement studies are performed with a phase-sensitive inversion recovery (PSIR) sequence, it is possible to use a nominal value of TI, which eliminates the need for TI surfing and achieves a consistent contrast over a wide range of TIs without artifacts due to incorrect polarity (Kellman et al. 2002).

Phase-sensitive reconstruction is used to remove the background phase while preserving the sign of the desired magnetization during IR. The phase-sensitive reconstruction method reduces the variation in apparent infarct size observed in magnitude images as TI is changed. Phase-sensitive detection also has the advantage of decreasing the sensitivity to changes in tissue T1 with increasing delay from contrast medium injection (Kellman et al. 2002) (Fig. 7.4).

There are certain pitfalls one must be aware of when interpreting delayed enhancement images. Mural thrombi do not take up contrast medium and will appear dark, just like normal myocardium. Regions of microvascular obstruction after acute myocardial infarction also have low signal intensity (Jiji and Kramer 2011). Hence, it is not possible to reliably differentiate thrombus, microvascular obstruction, and viable myocardium, precluding accurate estimation of infarct size (Karamitsos et al. 2009).

The use of specialized pulse sequences allows myocardial perfusion imaging by assessing contrast medium inflow and clearance from the myocardium. Myocardial perfusion can be assessed at rest and stress. Pharmacologic stress is induced by administration of adenosine or dobutamine. Areas of reduced myocardial perfusion show delayed contrast medium uptake, i.e., after administration of contrast medium, they remain dark longer than well-perfused myocardium (Karamitsos et al. 2011).

Myocardial perfusion MRI allows noninvasive assessment of myocardial viability and differentiation of infarcted areas from dysfunctional but viable myocardium (Saraste et al. 2008; Wellnhofer et al. 2004). In conjunction with cine MRI and delayed enhancement imaging, cardiac perfusion MRI enables reliable detection of coronary stenosis >70 % (De Mello et al. 2012).

Cardiac MRI also has an important role in diagnosing less common diseases of the heart such as arrhythmogenic right ventricular cardiomyopathy, cardiac sarcoidosis, myocardial involvement in amyloidosis, and tumors of the heart. Moreover, it can contribute to the detection of pericardial or endocardial disease (ACCF/ACR/AHA/NASCI/SCMR 2010).

Due to time constraints, a cardiac MRI examination performed as part of a whole-body MRI protocol cannot include all components of a comprehensive cardiac MRI study. The cardiac MRI protocol used in the SHIP included cine sequences for functional assessment in four-chamber, three-chamber, and two-chamber views as well as short-axis views for left ventricular function assessment. Strict axial cine sequences were acquired for evaluation of right ventricular function. A fat-saturated T2-weighted pulse sequence was deliberately not included although edema may persist for some time after a myocardial event. Delayed enhancement imaging was performed using an inversion recovery single shot sequence with magnitude reconstruction, highly sensitive to the inversion time (TI) selected and a phase-sensitive inversion recovery (PSIR) single shot sequence acquired 15 min after administration of 0.15 mmol/kg body weight of gadobutrol. The PSIR sequence used in the SHIP MRI protocol creates two image data records. First dataset contains images with magnitude reconstruction, in the second dataset phase-sensitive reconstruction images are generated.

The following sections give an overview of the most common incidental findings detected by cardiac MRI performed as part of a whole-body screening examination.

Areas of delayed myocardial enhancement are the most common incidental findings in the heart at screening MRI. Note, however, that delayed enhancement is a mere descriptive term and provides no clues to possible underlying causes, which are multifarious (Kim et al. 2006). Classic causes include acute and chronic myocardial infarction, cardiomyopathy, and acute or chronic myocarditis (Stork et al. 2007). In a cardiac MRI protocol, late enhancement sequences enable accurate and noninvasive quantification of the extent of myocardial infarction (gold standard). The transmural extent of delayed enhancement may be used to predict functional outcome in ischemic heart disease (Saraste et al. 2008).