Native T1 introduces a new modality to examine the myocardium’s foundational disease mechanisms, which are reflected in changes in tissue composition and structure [10].
Increases in native myocardial T1 values are nonspecific and can be seen in a variety of myocardial disorders other than acute myocardial infarction, such as cardiac amyloidosis, hypertrophic and dilated cardiomyopathy, diffuse fibrosis, and chronic infarct scars [10].
The main aim of this study is to compare the potential utility of segmental quantification of myocardial fibrosis using native T1 mapping to late contrast enhancement imaging in different forms of cardiomyopathy.
Our findings indicate that quantitative fibrosis assessment can be performed in a less expensive and safer manner by avoiding the use of gadolinium contrast agents, also more “patient-friendly” because it does not require cannulation of the antecubital vein, which may be beneficial, particularly for repeated examinations to detect progressive fibrotic changes.
Eighty-two patients were included in our study (10 as control), used to derive specific reference range for native T1 values. Seventy-two as diseased, the majority of the cases were DCM (69.4%,), 16% were HCM, 4.1% were amyloidosis, 6.9% were non compaction, and 2.7% were sarcoidosis of total 72 cases.
The current study found that the native T1 values of patients with LGE were significantly higher than those of patients without LGE, as well as standard controls. These findings in agreement with a study performed by Puntmann et al. [11] on HCM showed that increase of native T1 values in patients with HCM in comparison to controls was observed both in segments with and without LGE.
Whereas Pfluger et al. [12] showed no significant difference in myocardial T1 native values in patients with heart failure. The disparity with the latter findings may lie in the differences in patient selection, as well as imaging techniques and field strength used, which could explain the difference in the measurements of longitudinal relaxation in native myocardium
There was no significant elongation of T1 values at the basal and mid inferior segments noticed in the current study, which could be explained by T1-mapping using lock locker inversion recovery technique which sometimes demonstrate typical susceptibilities artifacts and partial volumes effects, beside the diaphragmatic motion contributed to inferior wall artifacts. Since artifacts may trigger falsely high or low T1 values, future methods for assessing the quality and strength of T1-maps are essential.
In the present study, we evaluated all segments to determine the minimum average T1 value of each patient and detect diffuse fibrosis, while most of the previous research focus on the inter-ventricular septum because of the high prevalence of fibrosis in the inter-ventricular septum and the lack of susceptibility artifacts.
Based on results from the current study, the native T1 relaxation time of 1070 ms appears to be the most suitable threshold for fibrosis evaluation, as it demonstrated the best combination of agreement and association with fibrosis. The threshold of 1070 ms can be used to assess fibrosis, inflammation, and edema associated with patients with different forms of cardiomyopathy on non-contrast-enhanced T1 mapping which is found similar to some extent to a previous study that reported T1 mapping is able to detect changes caused by both edema and myocyte necrosis, and thus conserve to function as a “LGE T2W” combination [13].
T1 values were higher in LGE segments than in non-LGE segments (HCM group with LGE 1080.4 ± 42.60 versus no LGE 1046.4 ± 82.41, P<0.01; while in DCM group with LGE 1117.3 ± 76.26 ms versus no LGE 1071.8 ± 60.12 ms, P<0.01). However, in both HCM and DCM, T1 values were significantly higher than normal even in segments not affected by LGE (P<0.01). These results are not far from Hoey et al. [14] who stated that non-contrast T1 values are significantly elevated in DCM and HCM compared with normal controls. As expected, myocardial segments with focal fibrosis identified by LGE showed higher T1 values. Furthermore, T1 values were increased in segments without LGE in both HCM and DCM. This suggests that T1 mapping and LGE test overlapping but distinct myocardial pathologies. This could be due to microscopic fibrosis which is difficult to be detected by LGE
We observed also that 80 segments assessed in the patients with cardiac amyloidosis (CA) showed elevation in T1 values (1143.0 ± 101.95 ms), compared to healthy controls (1055.9 ± 29.0 ms, p = 0.001). These findings are consistent with Moon et al. [15] who reported that patients with CA showed increased TI in the LV cavity (1097 ± 43 ms), compared to patients with HCMP (1026 ± 64 ms), or healthy controls (967.7 ± 34 ms, both p value= 0.001).
As regards patients with LV non-compaction, in this study, two cases only show late gadolinium enhancement which was located mostly in the mid anterior and anteroseptal segments of the myocardium in LVNC patients. We found the native T1 values in LVNC patients with and without LGE were significantly higher than in the normal controls (1053.4 ± 79.42 ms vs 1015.5 ± 56.29 ms, p value< 0.001 ). This findings are consistent with Zhou et al. [16] who stated that the mean native T1 value of normal controls, LGE(−) LVNC patients, and LGE(+) patients was 1098.8 ± 40.8 ms, 1140.6 ± 32.8 ms, and 1181.4 ± 53.7 ms, respectively.
The results for correlating the native T1 values to the LGE were in agreement with Suttie et al. [17], who stated that T1 mapping is more efficient in detecting myocardial changes in patients with cardiomyopathies compared to the traditional ways of measuring the myocardial wall thickness and LGE. Also, Sibley et al. [18] stated that T1 time correlates with interstitial fibrosis in patients with cardiomyopathy including those without focal LGE.
Direct comparison of absolute native T1 values between this study and the previous studies for example by Edwards et al. is not possible due to the different imaging platforms used (3T vs 1.5T); also they measured native T1 values of the inter-ventricular septum at basal and mid-myocardial levels only [13].
In this study, we conclude that native T1 mapping is a simple test to perform in patients with suspected diffuse fibrosis, which can be overlooked by traditional LGE imaging. In addition, in subjects with a low pre-test likelihood of cardiomyopathy or in whom contrast administration is contraindicated.
Limitations and future directions
There are some limitations to this study. First, the sample size was relatively small. However, 1312 ROIs were assessed including those of patients and healthy volunteers. Second, since myocardial T1 values are scanner and sequence based to some degree, the thresholds shown in the present study cannot be extrapolated to other institutions. Third, in the current study, the observers’ experience in placing ROIs on the T1 mapping may have resulted in slightly higher intra- and inter-observer variability of native T1 values (i.e., about 4.0 %) than in previous studies (i.e., 2.0–4.8%). Fourth, we did not compare the cardiac function parameters with T1 value in our patients. Fifth, this research relied on clinical validation and other diagnostic studies for reported cases of infiltrative cardiomyopathy (amyloidosis and sarcoidosis) and myocarditis rather than endo-myocardial biopsy (EMB) as a reference standard, so it lacks direct histopathological confirmation. As a result, histopathological studies are needed to determine if quantitative assessments of global and segmental native T1 values correspond with actual myocardial fibrosis, and whether T1 is related to the prognosis. Sixth, our research focused on the utility of non-contrast T1 mapping for diagnosing cardiomyopathies. Additional post-contrast T1 measurements provide information on the extracellular volume fraction, and these measurements may be used to determine the relative contributions of extracellular and intracellular water changes to the non-contrast T1 values. As a result, post-contrast T1 mapping should be investigated in the future studies.