Our study reported T1 and ECV values of 87 healthy volunteers aged 20–60 years old and determined their dependence on age and sex. Our data showed that the T1 value of healthy adults was 1,261 ± 52, ECV value was 28.3% ± 2.9%. T1 and ECV value of females were higher than males, while ECV value of males increased with age. The T1 values of males and females and the ECV values of females were not related to age. Both the T1 and ECV values gradually increased from the basal to the apical of the heart. For the basal, T1 and ECV values between each segment showed significant differences. There were also significant differences for T1 value for different segments of the middle part. However, there was no differences for ECV value for different segments of the middle part. and for the apical, no differences for T1 and ECV value between different segments.
The T1 value of healthy adults calculated in our study was 1,261 ± 52, which was similar to the result reported by Kawel et al. (1,286 ± 59). Data from previous studies were highly inconsistent. For example, the T1 mapping reported by Jason J Lee et al. (1315 ± 39) was higher than found in our research. Most reports showed lower values than ours, such as the results from Yang Dong (1,202 ± 45) and Stefania Rosmini (1025 ± 38). These differences may come from different scanner fitting algorithms, pulse types, race, sample size, age group, and other unknown factors. Since the measured value of myocardial T1 value under 3T field strength is about 30–40% higher than that measured at 1.5T field strength[21, 22], T1 mapping under different field strengths should be discussed separately.
Contrary to changes in myocardial T1 values, ECV values measured by various studies are similar. Even with different magnetic field strengths in healthy adults, the reported ECV values did not change markedly. This finding was confirmed by a previous study, which showed that the ECV measured at 1.5T or 3.0T was very similar, ranging from 25–28%. Therefore, relative to T1 values, it is more meaningful to compare ECV values between different centers.
Our results showed that both T1 and ECV value in females are higher than in males. This result is consistent with the results obtained by most researchers[19, 20, 24, 25]. The possible reasons for this phenomenon may include blood pool pollution, which is a relatively large influencing factor because females’ hearts are thinner (on average), and some volume effects are more pronounced than males. Longer blood T1 value in the capillaries in the myocardium is also a reasonable explanation. The higher ECV value found in females than in males is also related to the lower hematocrit found in females. Our data showed that the ECV value was negatively correlated with hematocrit. Therefore, it is necessary to take sex into account when discussing T1 and ECV values of normal myocardium.
However, there is no consensus on the correlation between age and T1 and ECV value. We found that ECV value increased with age in males but not in females, which is consistent with the results shown by Liu et al. The T1 value of males and females had no correlation with age, which is similar to the data from Joseph J Pagano et al., and Piechnik et al. showed that there is no correlation between T1 and age in men, and there is a negative correlation between T1 and age in women. Ito et al. through histopathological studies, found that male interstitial myocardial fibrosis increased with age, but females did not show this change. Therefore, when interpreting the results of T1 and ECV values in the heart, age and sex must be considered.
Our research found that T1 mapping and ECV values gradually increased from basal to apical, consistent with the results reported by von Knobelsdorff-Brenkenhoff et al. This phenomenon can be explained by the partial volume effect of image acquisition at apical. The influence of MRI artifacts on the left ventricular apical is generally more significant.
Our research found that T1 and ECV values between each segment showed significant differences for the basal. There were also significant differences for T1 value for different segments of the middle part. However, there was no differences for ECV value for different segments of the middle part. and for the apical, no differences for T1 and ECV value between different segments. In their study, Messroghli et al. also did not find segmental changes in T1 values.However, studies by Kawel et al., von Knobelsdorff-Brenkenhoff et al., and Yang Dong showed that the T1 and ECV values of the septal wall were the highest. Their findings are consistent with the histological data of healthy myocardium. Studies have shown that the ventricular septal collagen content is higher compared with other regions. The mechanism of T1 or ECV values heterogeneity in different segments is still unclear. Rogers et al. believe that these differences are unlikely to represent actual regional differences in longitudinal relaxation. They may be related to many confounding factors, including susceptibility artifacts, issues related to receiver coil sensitivity, and the large distance between receiver coil components—the resulting signal gradient between the interval and the lateral myocardium.
This study has the following limitations. This study was single-center, single-supplier with a medium sample size. The relationship between the T1 and ECV values and the sex hormones was not analyzed.