Use of Early T1 Mapping for MRI in Acute Myocarditis.

Abstract

HomeRadiologyVol. 295, No. 2 PreviousNext Reviews and CommentaryFree AccessEditorialUse of Early T1 Mapping for MRI in Acute MyocarditisCarlo N. De Cecco , Caterina B. MontiCarlo N. De Cecco , Caterina B. MontiAuthor AffiliationsFrom the Division of Cardiothoracic Imaging, Nuclear Medicine and Molecular Imaging, Department of Radiology and Imaging Sciences, Emory University Hospital, 1364 Clifton Rd NE, Suite EG45, Atlanta, GA 30322 (C.N.D.C., C.B.M.); and Department of Biomedical Sciences for Health, Università degli Studi di Milano, Milan, Italy (C.B.M.).Address correspondence to C.N.D.C. (e-mail: [email protected]).Carlo N. De Cecco Caterina B. MontiPublished Online:Mar 10 2020https://doi.org/10.1148/radiol.2020200171MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In See also the article by Palmisano et al in this issue.Carlo N. De Cecco, MD, PhD, is an associate professor of radiology and biomedical informatics in the division of cardiothoracic imaging at Emory University (Atlanta, Ga). He is board certified in radiology and nuclear medicine, and his main research focus is the development and application of advanced multimodality cardiac imaging techniques in clinical practice and the implementation of artificial intelligence in cardiothoracic imaging.Download as PowerPointOpen in Image Viewer Caterina B. Monti, MD, is a PhD student at the University of Milan, working in the department of radiology of IRCCS Policlinico San Donato. In 2019, she was a visiting scholar in Dr De Cecco's research group at the Emory University School of Medicine radiology department.Download as PowerPointOpen in Image Viewer Acute myocarditis (AM) is an inflammatory disease that may be the underlying basis for approximately 10% of dilated cardiomyopathies. It is the leading cause of sudden cardiac death in young people (age ≤ 35 years). For this reason, it is particularly important to correctly identify patients with AM (1).The reference standard for diagnosing AM is endomyocardial biopsy. However, noninvasive methods for detecting AM yield adequate sensitivity and specificity, both well above 80%. In particular, cardiac MRI with the aid of the Lake Louise criteria, proposed in 2009 (2) and updated in 2018 (3), is widely used to guide clinical decision making and may help to avoid invasive biopsy. The first version of Lake Louise criteria included T2-weighted MRI to depict myocardial edema, early gadolinium chelate enhancement T1 MRI (ie, within the first 1–3 minutes after contrast infusion) (4) to depict myocardial hyperemia, and late gadolinium–enhanced imaging to depict myocardial injury (ie, inflammation, necrosis, and fibrosis). The most recent update of Lake Louise criteria includes native T1 and T2 mapping (also for edema and hyperemia, respectively) instead of early T1- and T2-weighted images. Determination of myocardial T1 and T2 times allows for a more objective and reliable assessment of myocardial tissue properties.T1 and T2 mapping allow for calculation of tissue relaxation times by using different approaches (5). The most common sequence used for T1 mapping is modified Look-Locker inversion recovery. The modified Look-Locker inversion recovery sequence acquires T1-weighted images by using different inversion times during one breath hold in a specific phase of the cardiac cycle. T2 mapping is usually achieved with either multiecho dark-blood fast spin-echo sequences or bright-blood T2-preparation pulse-based sequences, with subsequent analysis of the T2-decay curve.Early postgadolinium chelate–enhanced T1 values are expected to reflect the status of inflammation and hyperemia that characterizes AM in view of the associated increase in extracellular space. Early postgadolinium chelate–enhanced T1 mapping values have not yet been integrated in the Lake Louise criteria because of their limited robustness compared with the other criteria (6).The work by Palmisano and colleagues (7) in this issue of Radiology suggests that early T1-based imaging may still be relevant in detecting AM. Palmisano et al analyzed both absolute T1 values and relative T1 shortening early and late, respectively, about 3 and 10–15 minutes after injection of contrast material. Forty-five participants with AM and 19 healthy control participants underwent cardiac MRI, which included sequences for the assessment of revised Lake Louise criteria and early T1 mapping. Early relative T1-shortening maps were generated as the ratio of the difference between early and native T1 values and native T1 values over the myocardium. Color-coded maps of early T1 shortening were generated with coregistration of native and early T1 maps. Palmisano et al observed that early T1 shortening was significantly different between participants with AM and healthy control participants (P < .001). In fact, early T1 shortening displayed a high diagnostic performance, with an area under the receiver operating characteristic curve value of 0.97 (95% confidence interval: 0.94, 1.00), a sensitivity of 93% (42 of 45), and a specificity of 100% (19 of 19). Early T1 shortening also showed excellent interobserver reproducibility, with an intraclass correlation coefficient of 0.98 (95% confidence interval: 0.96, 1.00). In this regard, the performance of early T1 shortening was better than that of late T1 shortening and comparable to that of native T1 and T2 mapping. This finding would ideally smooth the path for inclusion of early T1 mapping in diagnostic cardiac MRI protocols for AM.Should T1-based imaging again be part of routine cardiac MRI protocols in detecting AM? The results of the study by Palmisano et al (7) show that, despite being regarded as the least robust among the original Lake Louise criteria (2), early T1-based imaging may still provide important information. In fact, Palmisano et al elaborate in detail the rationale by which the increase in early T1 shortening was expected in participants with AM. Gadolinium chelate is an extracellular contrast agent, which shortens the T1 signal in tissues in proportion to its presence in the extracellular matrix. In AM, the interstitial myocardial component is increased because of inflammation, which leads to vasodilation, hyperemia, and increased vessel permeability. Thus, more gadolinium chelate will accumulate in the extracellular space of the myocardium in participants with AM, leading to more prominent T1 shortening. The evaluation of early T1 shortening compared with early T1 provides the benefit of the use of a relative parameter and is therefore less prone to confounders related to previous myocardial conditions such as fat infiltration or fibrosis. The diagnostic performance of early T1 shortening was observed to trend to a borderline increase compared with that of early T1 (area under the receiver operating characteristic curve for early T1, 0.93; 95% confidence interval: 0.87, 0.99; P = .05 with early T1 shortening), and the confidence interval for early T1 shortening was entirely above 0.90. Moreover, the diagnostic accuracy of early T1 shortening appears promising compared with that observed in a recent meta-analysis (8), which highlighted a sensitivity of 80% and specificity of 87% for AM via cardiac MRI myocardial mapping approaches.However, a study by Lundin et al (9) compared early and late T1 mapping for the detection of AM and concluded that the use of early T1 mapping did not significantly improve the diagnostic accuracy of cardiac MRI in AM. However, their study did not include the analysis of relative T1 shortening and relied on skeletal muscle as a reference, despite concluding that skeletal muscle was not an appropriate reference tissue because of its changing characteristics in patients with AM. The use of relative T1 shortening may help overcome this limitation, which is reflected by the high diagnostic performance with this parameter.One potential limitation of the study by Palmisano et al may have been that early T1-based imaging sometimes displayed inconsistent image quality, varying greatly among different systems and technical parameters (10). Currently, early T1 mapping is mostly used in specialized centers with extensive experience in cardiac MRI and early T1-based imaging analysis. However, the use of a parameter derived from quantitative mapping, with defined and objective thresholds, would likely be advantageous for aiding the diagnosis of AM in settings with varied experience and diverse characteristics. Early T1 shortening, because it is a relative measurement, should be less prone to interference from technical and imager-specific parameters because variations originating from such causes are expected to be systematic and proportional. Nevertheless, findings from the study by Palmisano et al (7) may need to be validated with larger multivendor multicenter studies by using different sequences and techniques for T1 mapping.In conclusion, whereas early T1 imaging is not included in the revised Lake Louise criteria because of its limitations, results from the study by Palmisano et al (7) suggest that its use as an imaging biomarker in detecting myocardial hyperemia might help improve the diagnostic accuracy for AM.Disclosures of Conflicts of Interest: C.N.D.C. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: disclosed institutional research support from Siemens. Other relationships: disclosed no relevant relationships. C.B.M. disclosed no relevant relationships.