Myocardial T1 and T2 Mapping: Techniques and Clinical Applications

Abstract

Cardiac magnetic resonance (CMR) imaging is widely used in various medical fields related to cardiovascular diseases. Rapid technological innovations in magnetic resonance imaging in recent times have resulted in the development of new techniques for CMR imaging. T1 and T2 image mapping sequences enable the direct quantification of T1, T2, and extracellular volume fraction (ECV) values of the myocardium, leading to the progressive integration of these sequences into routine CMR settings. Currently, T1, T2, and ECV values are being recognized as not only robust biomarkers for diagnosis of cardiomyopathies, but also predictive factors for treatment monitoring and prognosis. In this study, we have reviewed various T1 and T2 mapping sequence techniques and their clinical applications.

Keywords: Cardiomyopathy; Extracellular matrix; Heart; MRI, T1 mapping; Myocardium; Native T1; T2 mapping.

Fig. 1. Representative short-axis images of native T1, post-contrast T1 and T2, and extracellular volume fraction (ECV) maps of control subject.

Pixels in generated map represent corresponding T1, T2, and ECV values of regions of interest in myocardium or other cardiac structures. Myocardium and other cardiovascular structures each have tissue-specific T1, T2, and ECV values.

Fig. 2. Apparent T1^* and true T1 recovery.

Comparison of longitudinal magnetization using standard inversion recovery and Look–Locker (LL) T1 mapping methods. With LL method, T1 recovery to steady state is achieved more rapidly and often denoted as apparent T1 (T1^*). IR = inversion recovery, RF = radiofrequency

Fig. 3. Modified Look–Locker inversion recovery (MOLLI) with 5(3)3 protocol.

MOLLI method features several modifications intended to improve accuracy and precision. This protocol employs two inversions and acquires three or five images after first and second inversions, with three RR intervals for T1 recovery. Images are sorted according to inversion time to perform pixel-wise three-parameter fitting. ECG = electrocardiogram, RR = the time interval between two consecutive R waves in the electrocardiogram, SSFP = steady-state free precession

Fig. 4. Shortened modified Look–Locker inversion recovery (ShMOLLI).

ShMOLLI method employs conditional analysis algorithm that can distinguish between short and long T1 values using curve-fitting errors and, therefore, features shorter scan time than original MOLLI. Long T1 samples use set of samples from first inversion to estimate T1, whereas short T1 samples use set of samples from all inversions. ECG = electrocardiogram, SSFP = steady-state free precession, TI = Inversion time

Fig. 5. Saturation recovery single shot (SASHA).

SASHA method acquires data at successive heartbeats by saturation recovery over RR-interval at different saturation times, using initial unperturbed image. Accuracy and precision depend on choice of two- or three-parameter fitting model. ECG = electrocardiogram, RR = the time inverval between two consecutive R waves in the electrocardiogram

Fig. 6. T2 mapping scheme with T2 preparation modules.

T2-weighted images are acquired with different T2 preparation times, with same trigger delay time (TD), to ensure same cardiac cycle phase during breath-hold. T1 recovery time is needed to allow complete T1 recovery. This preparation module employs 90° and 180° pulses to create T2 decay via spin-spin relaxation during T2 preparation time. Module concludes with spoiler gradient for removal of residual transverse magnetization. ECG = electrocardiogram, GRE = gradient echo, SSFP = steady-state free precession

Fig. 7. T1 mapping in dilated cardiomyopathy (DCM).

DCM is characterized by ventricular dilation and systolic dysfunction without other loading conditions. Approximately 30% of patients with DCM exhibit mid-wall late gadolinium enhancement (LGE) in regions that do not correspond to coronary artery territories. This imaging characteristic is known to be prognostic factor for DCM. However, many patients do not exhibit LGE—they usually present with increased native T1 and extracellular volume fraction values in areas without LGE. T1 mapping can detect diffuse myocardial abnormalities in areas that appear normal on LGE sequences.

Fig. 8. T1 mapping in hypertrophic cardiomyopathy (HCMP).

HCMP is cardiac muscle disease characterized by abnormal left ventricle hypertrophy (LVH) in absence of another cause of LVH. Multifocal late gadolinium enhancement (LGE) is usually observed in hypertrophied muscles. T1 mapping can detect myocardial abnormalities in areas that do not exhibit LGE.

Fig. 9. T1 mapping in Fabry disease (FD).

Left ventricle hypertrophy and late gadolinium enhancement (LGE) of inferolateral left ventricle wall are characteristic features of FD. However, only 50% of patients with FD exhibit LGE. In T1 mapping, decrease in septal native T1 value is characteristic feature that distinguishes FD from other cardiomyopathies.

Fig. 10. T1 and T2 mapping in amyloidosis.

Global, circumferential, subendocardial late gadolinium enhancement (LGE) with distribution in non-coronary arterial territory is hallmark of amyloidosis. However, characteristic LGE patterns do not always occur. In patients with amyloidosis, marked elevations in native T1 and extracellular volume fraction values are characteristic imaging features, which do not overlap with those of other diseases. However, T2 values are not increased in patients with amyloidosis.

Fig. 11. T1 and T2 mapping in myocarditis.

Late gadolinium enhancement (LGE) pattern in myocarditis is usually observed on lateral inferior wall of left ventricle, with subepicardial and mid-wall distribution. Non-contrast mapping parameters and T1 and T2 values are useful for diagnosis of myocarditis.