Objective: To measure the reference values of main pulmonary artery [MPA] and ascending aorta [ASC] dimensions for Thai healthy population by using non-contrast axial cardiac magnetic resonance imaging [CMR].

Materials and Methods: Transaxial set of fast spin echo images through the chest were obtained from 91 healthy subjects. The present study design was epidemiological observational study and the measurement of MPA and ASC dimensions was performed at the level of the bifurcation of the right and left pulmonary arteries.

Results: The mean age of the study subjects was 38 years and 60% were women. The sex-specific MPA, ASC dimensions, and ratio PA (ratio of MPA to ASC diameter) shown as mean ± SD in men and women were 23.6±2.6 mm, 23.8±2.5 mm for MPA; 27±3.2 mm, 26.9±2.8 mm for ASC; and 0.88±0.1, 0.89±0.1 for ratio PA. The sex-specific ninetieth percentile cut-point in men and women for MPA and ratio PA were 27 mm, and 1.0. There were positive correlations between age and ASC dimension (r = 0.398, p<0.001), age and MPA/BSA ratio (r = 0.361, p<0.001), and MPA and BSA (r = 0.235, p = 0.025), but negative correlation between age and ratio PA (r = -0.276, p = 0.008).

Conclusion: The findings of this study suggest that the MPA and ASC dimensions for Thai population are similar in both genders but slightly smaller than in Western population. Additionally, the ratio PA are slightly increased. There were correlations between increasing age and larger ASC, higher MPA/BSA ratio, and smaller ratio PA.

Keywords: Main pulmonary artery [MPA], Ascending thoracic aorta [ASC], Ratio PA, Reference values