Quantitative blood oxygenation level-dependent (BOLD) response of the left ventricular myocardium to hyperoxic respiratory challenge at 1.5 and 3.0 T.

The aim of this study was to quantify the response of the myocardial transverse relaxation times (ΔT2*) to hyperoxic respiratory challenge (HRC) at different field strengths in an intra-individual comparison of healthy volunteers and in a patient with coronary artery disease. Blood oxygenation level-dependent (BOLD) cardiovascular MR (CMR) data were acquired in 10 healthy volunteers (five women, five men; mean age, 29 ± 3 years; range, 22-35 years) at 1.5 and 3.0 T. Medical air (21% O2 ), pure oxygen and carbogen (95% O2 , 5% CO2 ) were administered in a block-design temporal pattern to induce normoxia, hyperoxia and hyperoxic hypercapnia, respectively. Average T2* times were derived from measurements by two independent and blind readers in 16 standard myocardial segments on three short-axis slices per patient. Inter- and intra-reader correlations of T2* measurements were good [intra-class correlation coefficient (ICC) = 0.75 and ICC = 0.79, both p < 0.001]. During normoxia, the mean T2* times were 29.9 ± 6.1 ms at 1.5 T and 27.1 ± 6.6 ms at 3.0 T. Both hyperoxic gases induced significant (all p < 0.01) T2* increases (∆T2* hyperoxia: 1.5 T, 12.7%; 3.0 T, 11.2%; hyperoxic hypercapnia: 1.5 T, 13.1%; 3.0 T, 17.7%). Analysis of variance (ANOVA) results indicated a significant (both p < 0.001) effect of the inhaled gases on the T2* times at both 1.5 T (F = 17.74) and 3.0 T (F = 39.99). With regard to the patient imaged at 1.5 T, HRC induced significant T2* increases during hyperoxia and hyperoxic hypercapnia in normal myocardial segments, whereas the T2* response was not significant in ischemic segments (p > 0.23). The myocardial ∆T2* response to HRC can reliably be imaged and quantified with BOLD CMR at both 1.5 and 3.0 T. During HRC, hyperoxia and hyperoxic hypercapnia induce a significant increase in T2*, with ∆T2* being largest at 3.0 T and during hyperoxic hypercapnia in normal myocardial segments.