Myocardial T1 mapping as a diagnostic tool in pediatric patients with a concern for cardiac disease

Background

Myocardial tissue characterization with both native T1 mapping and T1 mapping following gadolinium based contrast agents (T1 enhanced) has emerged as an important asset of CMR imaging [1]. However, there is only minimal experience in pediatrics [2]. Native T1 has shown to be a marker of myocardial edema, and may play a role in pathologic states such as myocarditis [3]. T1 enhanced mapping has shown to be a useful biomarker for disease sates with diffuse fibrosis, such as hypertrophic cardiomyopathy (HCM), and is comparable to myocardial biopsy [4].

Purpose: To examine the effectiveness of CMR myocardial characterization by native T1 and T1 enhanced mapping in a heterogenous group of pediatric patients with signs concerning for cardiomyopathy or myocarditis.

Methods

We reviewed our initial experience of an ongoing study with T1 mapping in 10 subjects (aged 15.4 ± 2.5 years). All patients underwent CMR due to signs suggestive of cardiac disease. Cohort included 4 patients with concern for myocarditis, 4 with concerns for HCM, and 2 with concern for myocardial ischemia. 3 of the acquisitions were made in 3T Acheiva^TM, remainder used 1.5T Ingenia^TM scanner (Philips Healthcare, Best Netherlands).

Acquisition Protocol: All clinically indicated MRI sequences were performed, including delayed enhanced phase sensitive inversion recovery sequence, after injection of contrast (Magnevist^TM). T1 mapping (modified Look Locker - MOLLI) sequence was performed prior to contrast injection and post contrast (15 minutes after contrast) injection. The MOLLI sequence had a bSSFP readout TR/TE/α = 3/1.5 ms/20°; A 5,5,3 inversion acquisition scheme was used, and acquisition time was 13 heart beats.

Data Analysis

The T1 was measured by manually drawing a region of interest at both the interventricular septum and the free wall after exporting the data to a custom made Matlab^TM program. Pixels with a zero value - representing a noisy T1 fit were ignored from the calculations.

Results

The native and enhanced T1 were calculated for all patients except 1 who had significant artifact in the free wall on the native T1 sequence. The 2 patients with concern for myocardial ischemia, and 1 patient with possible HCM were assessed on the 3T. As assessed on the 1.5T, the native T1 of the free wall in patients who were clinically treated for myocarditis (n = 3) was significantly higher than the native T1 in all other patients (n = 4), 1094 ± 38 ms vs. 986 ± 23 ms (p < 0.05). Likewise, the septal T1 enhanced of patients who were diagnosed with HCM (n = 3) was lower than the remaining patients (n = 4), 460 ± 16 ms vs. 533 ± 16 ms (p <0.05).

Conclusions

Myocardial characterization may be an effective tool in pediatric patients with a potential diagnosis of cardiomyopathy or myocarditis. Within a heterogenous group of patients, the native T1 was able to distinguish myocarditis from other potential cardiac disorders, while the enhanced T1 was able to distinguish HCM.