Cardiac relaxometry permits quantitative characterisation of myocardial tissue. Over the past fifteen years, it has grown from obscure research method to routine clinical tool, offering strong diagnostic and prognostic utility in some conditions. The goals of this session are to: (i) outline the key benefits of cardiac relaxometry methods with respect to clinical applications; (ii) describe the methodological details of cardiac relaxometry techniques, including T1, T2, T2*, and T1-rho mapping; and (iii) summarise current pitfalls of relaxometry methods in terms of acquisition, processing, and interpretation.
Target audience
Clinicians or scientists with an interest in quantitative myocardial tissue characterisation. A basic knowledge of cardiac MRI is assumed.Objectives
By the end of the session, attendees should be able to:
-Understand current and future applications of cardiac relaxometry;
-Describe how myocardial T1, T2, T2*, and T1-rho mapping methods work; and
-Recognise limitations in relaxometry methods in terms of acquisition and processing.
There are currently several parameters of interest for cardiac relaxometry. Specific applications, methodological details, and pitfalls are as follows.
T1 mapping – Mapping of T1 and extracellular volume (ECV) offers a means of identifying pathological changes in conditions such as Anderson-Fabry disease (1, 2) and amyloidosis (3), as well as diffuse changes that may be invisible to T1-weighted methods (4). Myocardial T1 is usually measured using a series of balanced steady-state free-precession (bSSFP) sets, each preceded by an inversion pulse (5), saturation pulse (6), or a combination of the two (7). These sequences are subject to several pitfalls—including Look-Locker correction, B0 inhomogeneity, and preparation pulse factors—that are summarised in several review papers (8-10).
T2 mapping – Cardiac T2 mapping methods (11) have shown utility in imaging myocardial oedema in the context of myocardial infarction (12) as well as myocarditis and takotsubo cardiomyopathy (13). They are typically applied using a T2 preparation module (14) in tandem with a bSSFP readout sequence. Multiple images are acquired, each with a different T2 preparation duration, to generate a T2 map. T2 mapping avoids many issues associated with T2-weighted sequences, including coil sensitivity artefacts (15), and poor timing of inversion preparation and readouts relative to the cardiac cycle (16); however, T2 mapping is subject to pitfalls of its own, with several in common with T1 mapping.
T2* mapping – These methods have been applied in myocardial iron overload in non-ischemic heart disease (17) and intramyocardial haemorrhage in ischemic heart disease (18) They are also thought to be sensitive to inflammation if applied in tandem with ultrasmall superparamagnetic particles of iron oxide (USPIO)(19). T2* mapping is applied using multiple gradient recalled echo readouts played at different echo times over several cardiac cycles. Off-resonance is particularly problematic for T2* mapping, though shimming routines have improved over the years.
T1-rho mapping – Spin-lock-based T1-rho mapping methods have recently shown promise for their contrast between healthy and pathological myocardium (20), but they are yet to find their own diagnostic niche. They are typically applied as a spin-lock preparation module with a bSSFP readout sequence; multiple spin-lock preparation times are used to give an estimate of the T1-rho dispersion.
Simulation-based methods can offer simultaneous T1, T2, and proton density mapping of the myocardium (21-23). Magnetic resonance fingerprinting is an extension of such methods, also offering T1, T2, and proton density maps (24), as well as other parameters modelled in the dictionary. It has recently been adapted to the heart (25); however, further work is required to improve precision and reduce computation times.
Discussion and Conclusion
Cardiac relaxometry offers several mechanisms for myocardial tissue characterisation, each of which is complementary to existing qualitative methods such as late gadolinium enhancement and T2-weighted imaging. Current methods show utility in groupwise comparisons through to individual clinical tests. For some conditions, mapping methods serve as weakly prognostic biomarkers that may prove beneficial when combined with other diagnostic information about an individual. In other, albeit quite rare, conditions cardiac relaxometry offers strong diagnostic data. If some of the pitfalls associated with cardiac relaxometry methods can be addressed, they may ultimately support more widespread clinical applications.1. Sado DM, White SK, Piechnik SK, Banypersad SM, Treibel T, Captur G, et al. Identification and assessment of Anderson-Fabry disease by cardiovascular magnetic resonance noncontrast myocardial T1 mapping. Circulation: Cardiovascular Imaging. 2013;6(3):392-8.
2. Thompson RB, Chow K, Khan A, Chan A, Shanks M, Paterson I, et al. T1 mapping with cardiovascular MRI is highly sensitive for Fabry disease independent of hypertrophy and sex. Circulation: Cardiovascular Imaging. 2013;6(5):637-45.
3. Karamitsos TD, Piechnik SK, Banypersad SM, Fontana M, Ntusi NB, Ferreira VM, et al. Noncontrast T1 mapping for the diagnosis of cardiac amyloidosis. JACC: Cardiovascular Imaging. 2013;6(4):488-97.
4. Neilan TG, Coelho-Filho OR, Shah RV, Feng JH, Pena-Herrera D, Mandry D, et al. Myocardial extracellular volume by cardiac magnetic resonance imaging in patients treated with anthracycline-based chemotherapy. The American journal of cardiology. 2013;111(5):717-22.
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6. Chow K, Flewitt JA, Green JD, Pagano JJ, Friedrich MG, Thompson RB. Saturation recovery single‐shot acquisition (SASHA) for myocardial T1 mapping. Magnetic resonance in medicine. 2014;71(6):2082-95.
7. Weingärtner S, Akçakaya M, Basha T, Kissinger KV, Goddu B, Berg S, et al. Combined saturation/inversion recovery sequences for improved evaluation of scar and diffuse fibrosis in patients with arrhythmia or heart rate variability. Magnetic resonance in medicine. 2014;71(3):1024-34.
8. Kellman P, Hansen MS. T1-mapping in the heart: accuracy and precision. Journal of cardiovascular magnetic resonance. 2014;16(1):2.
9. Higgins DM, Moon JC. Review of T1 Mapping Methods: Comparative Effectiveness Including Reproducibility Issues. Current Cardiovascular Imaging Reports. 2014;7(3):9252.
10. Cameron D, Vassiliou VS, Higgins DM, Gatehouse PD. Towards accurate and precise T1 and extracellular volume mapping in the myocardium: a guide to current pitfalls and their solutions. Magnetic Resonance Materials in Physics, Biology and Medicine. 2018;31(1):143-63.
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13. Thavendiranathan P, Walls M, Giri S, Verhaert D, Rajagopalan S, Moore S, et al. Improved Detection of Myocardial Involvement in Acute Inflammatory Cardiomyopathies Using T2 Mapping. Circulation: Cardiovascular Imaging. 2012;5(1):102-10.
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16. Wince WB, Kim RJ. T2-weighted CMR of the area at risk—a risky business? Nature Reviews Cardiology. 2010;7:547.
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18. Kali A, Tang RLQ, Kumar A, Min JK, Dharmakumar R. Detection of Acute Reperfusion Myocardial Hemorrhage with Cardiac MR Imaging: T2 versus T2*. Radiology. 2013;269(2):387-95.
19. Stirrat CG, Alam SR, MacGillivray TJ, Gray CD, Dweck MR, Raftis J, et al. Ferumoxytol-enhanced magnetic resonance imaging assessing inflammation after myocardial infarction. Heart. 2017;103(19):1528-35.
20. van Oorschot JW, El Aidi H, Jansen of Lorkeers SJ, Gho JM, Froeling M, Visser F, et al. Endogenous assessment of chronic myocardial infarction with T1ρ-mapping in patients. Journal of Cardiovascular Magnetic Resonance. 2014;16(1):104.
21. Blume U, Lockie T, Stehning C, Sinclair S, Uribe S, Razavi R, et al. Interleaved T1 and T2 relaxation time mapping for cardiac applications. Journal of Magnetic Resonance Imaging. 2009;29(2):480-7.
22. Kvernby S, Warntjes MJB, Haraldsson H, Carlhäll C-J, Engvall J, Ebbers T. Simultaneous three-dimensional myocardial T1 and T2 mapping in one breath hold with 3D-QALAS. Journal of Cardiovascular Magnetic Resonance. 2014;16(1):102.
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24. Ma D, Gulani V, Seiberlich N, Liu K, Sunshine JL, Duerk JL, et al. Magnetic resonance fingerprinting. Nature. 2013;495:187.
25. Hamilton JI, Jiang Y, Chen Y, Ma D, Lo W-C, Griswold M, et al. MR fingerprinting for rapid quantification of myocardial T1, T2, and proton spin density. Magnetic Resonance in Medicine. 2017;77(4):1446-58.