Aging and gender effects in native T1 and extracellular volume fraction assessment using SASHA

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

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

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