Usefulness of TI-scout images in the assessment of late gadolinium enhancement in children

LGE imaging is an established technique for detection of myocardial infarction and focal fibrosis [1]. However, there are limitations in detection of the lesions, particularly in areas of the myocardium adjacent to the blood pool and epicardial fat with standard LGE imaging. To overcome such limitations, the signal from the blood pool was completely or partially suppressed with or without T2 preparation between the inversion pulse and signal readout [4‐7]. Although both complete and partial suppression techniques are helpful, neither technique is completely satisfactory. With complete suppression of the signal from the blood pool, localization of an enhancing lesion across the myocardium becomes difficult as the interface between the blood pool and myocardium is lost. Partial suppression technique can also be limited in detection of myocardial lesions with signal intensity similar to that of the partially suppressed blood pool. In addition, the differentiation between the slow flow artifact along the endocardial surface and the true subendocardial or endocardial enhancement can be challenging.

In LGE imaging, T1-scout sequence is routinely acquired to identify the optimal myocardial nulling time. The acquired images show the changes in the signal intensity over time, that can be plotted visually or graphically. Usefulness of TI-scout imaging in the assessment of cardiomyopathies such as amyloid infiltration and hypertrophic cardiomyopathy has been reported [2, 3]. In our experience in pediatric patients, we also found that these TI-scout images are helpful in determining the presence or absence of LGE when it is questionable or when LGE involves the endocardium, or subendocardial or subepicardial myocardium (Figs. 2 and 3). Based on our initial experience, we started to acquire additional TI-scout images along the planes where the standard LGE images demonstrated inconclusive LGE. This retrospective analysis of our experience demonstrated: (1) TI-scout and standard LGE images are equally diagnostic in excluding LGE, (2) TI-scout images are more often better than standard LGE in detecting LGE, (3) TI-scout and standard LGE images are often complementary in both negative and positive diagnosis of LGE, and (4) TI-scout images are particularly advantageous over standard LGE images in detecting the LGE involving the endocardium, subendocardial myocardium or papillary muscles, and LGE with low level enhancement such as so-called gray zone LGE or heterogeneous enhancement. The advantages of TI-scout in detection of LGE demonstrated in this study might not be well appreciated in pathologic conditions showing consistently strong LGE such as transmural myocardial infarction and, therefore, in adult population. Furthermore, we emphasize that TI-scout imaging does not replace the standard LGE imaging but that TI-scout images augment LGE image interpretation.

Endocardial fibroelastosis is an important diagnosis in the newborns with left ventricular outflow tract obstruction and hypoplasia. Although it is associated with poor prognosis, it can be removed surgically to provide the left ventricle with an opportunity to grow for later biventricular repair [8]. In this regard, LGE imaging has been advocated as a valuable tool for accurate identification of endocardial fibroelastosis [9, 10]. However, the sensitivity of LGE imaging for detection of endocardial fibroelastosis has not been established and even questioned [11]. In our study, TI-scout images were more diagnostic than standard LGE images in all 4 patients with endocardial fibroelastosis (Figs. 1 and 3). In standard LGE images, endocardial fibroelastosis did not stand out strongly against the bright blood pool unless LGE was distinctly strong. TI-scout images enabled the detection of LGE as they show the difference in gadolinium kinetics between normal myocardium, fibrotic myocardium and blood pool (Figs. 1 and 3). Similarly, TI-scout images were useful in clearly defining the transmural or subendocardial involvement of myocardial infarction.

LGE of the papillary muscle that was seen exclusively in patients with previous surgery in this study may represent fibrosis related to ischemia or chronic mechanical burden associated with atrioventricular valve regurgitation [12‐15]. As the papillary muscles in the imaging plane may lack continuity with the remaining myocardium and are surrounded by the blood pool, LGE of the papillary muscles may escape detection with the standard LGE images alone because of the low contrast between the enhanced papillary muscles and blood pool. Therefore, complete or partial suppression of the blood pool signal was reported helpful in detection of LGE involving the papillary muscles [4, 6]. In our study, T1-scout images played the major role in the detection of LGE involving the papillary muscles (Fig. 3). In making the diagnosis of LGE of the papillary muscles, it is important to be sure that the enhancing structure is not the chordae tendinae that normally enhance in LGE imaging by cross-referencing the cine images.

In patients with HCM, identification of LGE is important for risk stratification and is associated with increased risk for sudden cardiac death or appropriate discharge of implantable cardioverter defibrillator as well as heart failure [16‐18]. The fibrotic myocardium in HCM typically is easily identifiable as areas with high signal intensities. However, it may also show low level LGE in the periphery of the strongly enhancing region [19, 20]. Furthermore, the hypertrophic myocardium may show diffusely heterogeneous LGE without clearly identifiable margins. As the areas of low level LGE called gray zones may also serve as arrhythmogenic foci, proper assessment of the extent of the gray zones has been advocated [19, 20]. In our study as well as in Amano et al. study, the areas of low level or heterogeneous signal intensities were much easier to perceive in TI-scout images than in standard LGE images. At least in one of the multiple TI-scout images, heterogeneity of the signal intensity is obvious and any uncertainty in standard LGE images can be eliminated with confidence (Fig. 5).