T1 and T2 Mapping in Cardiology: “Mapping the Obscure Object of Desire”

Abstract

The increasing use of cardiovascular magnetic resonance (CMR) is based on its capability to perform biventricular function assessment and tissue characterization without radiation and with high reproducibility. The use of late gadolinium enhancement (LGE) gave the potential of non-invasive biopsy for fibrosis quantification. However, LGE is unable to detect diffuse myocardial disease. Native T1 mapping and extracellular volume fraction (ECV) provide knowledge about pathologies affecting both the myocardium and interstitium that is otherwise difficult to identify. Changes of myocardial native T1 reflect cardiac diseases (acute coronary syndromes, infarction, myocarditis, and diffuse fibrosis, all with high T1) and systemic diseases such as cardiac amyloid (high T1), Anderson-Fabry disease (low T1), and siderosis (low T1). The ECV, an index generated by native and post-contrast T1 mapping, measures the cellular and extracellular interstitial matrix (ECM) compartments. This myocyte-ECM dichotomy has important implications for identifying specific therapeutic targets of great value for heart failure treatment. On the other hand, T2 mapping is superior compared with myocardial T1 and ECM for assessing the activity of myocarditis in recent-onset heart failure. Although these indices can significantly affect the clinical decision making, multicentre studies and a community-wide approach (including MRI vendors, funding, software, contrast agent manufacturers, and clinicians) are still missing.

Molecular Imaging to Monitor Left Ventricular Remodeling in Heart Failure

“…ECV technique is a sensitive method to detect the distribution of the cellular and extracellular interstitial matrix compartments [6]. It has been shown to reflect the extent of myocardial fibrosis and has been validated against collagen volume fraction ( Table 1) [40].…”

“…Visualization of the myocardial tissue and detection of both acute and chronic MI can be done without CA. These techniques offer quantitative assessment of the alternations in the composition of myocardial tissue based on intrinsic water properties, longitudinal T 1 [7••, 42, 43] and transversal T 2 relaxations [42,44], to generate contrast within the myocardium [6]. T 1 -weighted images are typically used for anatomical imaging and T 2 -weighted images for edema and imaging of transient ischemia (Table 1) [45].…”

“…Both T 1 and T 2 mapping also allow visualization and quantification of global changes in the myocardium (Table 1) [11,44,46]. T 1 relaxation time is elevated during MI development [6,10,38,39,47] and it has been shown to distinguish between reversible and irreversible damages in post ST-elevation MI (STEMI) [22,48,49]. In chronic MI, native T 1 relaxation times are lower than in acute MI because edematous and necrotic tissues in the acute MI are replaced by smaller amounts of expanded extracellular collagen [7••, 50].…”

“…MI develops when reduced blood flow and lack of oxygen lead to death of cardiomyocytes via necrosis, inflammation, replacement of extracellular space by fibrosis, protein infiltration, and myocardial disarray [4,5]. Overall, fibrosis is thought to be the final common pathway in various myocardial diseases [6]. Intense fibrosis leads to scar formation [7••, 8-11], which further changes the shape and function of the left ventricle (LV) and can be manifested as dilation and thinning of the myocardium, hypertrophy of the remote areas surrounding MI, and overall decline of the heart function ( Fig.…”

T1 and T2 Mapping: The Next Giant Leap in Cardiac Imaging

“…In their review article, Mavrogeni et al [11] present the technical and clinical considerations associated with T1 imaging, including contrast-free (native) and postcontrast imaging together with extracellular volume (ECV) fraction calculations, and T2 imaging. Similarly to other articles discussing these techniques, their paper displays a fascination with these methods, as the authors describe mapping techniques as “the obscure object of desire” for every CMR center.…”