The effects of common physiological parameters on the myocardial midwall T1 and blood T1 after correcting for age and gender differences. (A) Blood hematocrit is the principle driving force of blood T1s, but not myocardial T1, variation. (B) Increase in heart rate is associated with an increase in myocardial T1 and a decrease in blood T1s. (C) There is no relation between myocardial thickness and myocardial T1, but blood T1s change in opposite direction. (D) Increased body size does not influence myocardial T1, but decreases blood T1s. Note: statistical significance of marked correlations reaches Bonferroni-corrected significance of p < 0.002 (p < 0.05/18 comparisons including height and weight not shown here) for r2 > 0.15 (n = 62, A) and r2 > 0.026 (n = 374, B-D).