Background

Reference values for T1 mapping-derived extracellular volume fraction (ECV) in healthy individuals are not currently well established. Histological measurements in autopsy studies have shown decreasing ECV with healthy aging in men, however recent non-invasive measurements of ECV using different T1 mapping techniques are inconsistent with respect to the effect of aging and gender, with a relatively wide range of values depending on the method. The goal of the current study was to characterize native T1 and ECV as a function of age in healthy individuals (no cardiovascular risk factors or medication) with the SAturation-recovery single-SHot Acquisition (SASHA) method (Magn Reson Med. 2014 Jun;71(6):2082-95), providing comparison to existing literature.

Methods

Well characterized healthy individuals from the Alberta HEART study (BMC Cardiovasc Disord. 2014 Jul 25;14:91) underwent CMR on a Siemens 1.5T system (Sonata, Avanto) with T1 measurements using the SASHA pulse sequence. Imaging was performed on a mid-ventricular short-axis slice at baseline (pre-contrast) and ~15 minutes after intravenous administration of 0.15 mmol/kg gadobutrol. ECV was measured in the ventricular septum, calculated as (1-hct)*(Myocardium ΔR1)/(Blood ΔR1), where ΔR1 is 1/T1 post - 1/T1 pre, and hct was the most recent hematocrit.

Results

Native T1 and ECV measures were available from 44 individuals (60.7 ± 9.6 years, range 43-80, 15 male) free from cardiovascular disease, diabetes, hypertension, and not on any cardiovascular medication. Average native myocardial T1 value was 1189 ± 38 ms, which was increased in women compared to men (1201 ± 29 vs. 1167 ± 44 ms, p < 0.05), however did not vary significantly with age (Figure 1A; p = 0.59). Average ECV was 22 ± 2% (range 18-28%), and did not vary significantly with age (Figure 1B; p = 0.20) or gender (men: 21 ± 2% vs. women: 22 ± 2%; p = 0.14). SASHA ECV values were similar to a previous histology (p > 0.05) study. SASHA native T1 values were higher and SASHA ECV values were lower than inversion recovery based techniques in groups free of cardiovascular risk factors (native T1 comparisons only for 1.5T; p < 0.05 for all comparisons) (Table 1). Gender and age effects are noted to be different between methods (Table 1).

Figure 1
figure 1

A) SASHA native T 1 values vs. age. B) SASHA extracellular volume fraction (ECV) vs. age.

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Conclusions

SASHA ECV values showed no dependence on age or gender and were 14-27% smaller as compared to inversion-recovery techniques, but with good general agreement to histological studies. SASHA native T1 times are 19-20% longer than inversion-recovery techniques, and though they are longer in women, there is no age dependence. Significantly different ECVs by method reflect systematic differences in blood and myocardial T1 values (native and post-contrast), consistent with previous reports (Kellman, J Cardiovasc Magn Reson. 2014 Jan 4;16:2). Discrepancies in the relationship between native T1 and ECV by age and gender warrant more detailed comparison of methods as the field moves towards universal age/gender reference values.

Table 1 Comparison of native T1 and extracellular volume fraction between methods
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