Feasibility and reproducibility of BOLD and TOLD measurements in the liver with oxygen and carbogen gas challenge in healthy volunteers and patients with hepatocellular carcinoma

Purpose To quantify baseline relaxation rates R2∗ and R₁ in the abdomen, their changes after respiratory challenges, and their reproducibility in healthy volunteers and patients with hepatocellular carcinoma (HCC) at 1.5T and 3.0T. Materials and Methods R2∗ measurements were acquired in the liver in 8 volunteers and 27 patients with 34 HCCs using multiecho T2∗ at baseline and after respiratory challenges with 100% oxygen (O₂) and carbogen (CB = 95%O₂/5%CO₂). R₁ was measured at 1.5T in one volunteer and 21 patients with 23 HCCs. Test-retest coefficient of variation (CV) was assessed in 10 subjects. Intra- and interobserver variability of R2∗ and R₁ measurements was assessed in 12 and 10 patients, respectively. Parameters for HCC, liver, and muscle were compared between baseline and after gas challenges. Results We observed that R2∗ and R₁ imaging of HCCs with O₂ and CB is feasible and reproducible (test-retest CV R2∗<15%/R₁<5%; intra- and interobserver intraclass correlation coefficient R2∗>0.88/R₁>0.7 and CV R2∗<7%/R₁<3% at 1.5T). R2∗ measurements were observed to be less reproducible at 3.0T (CV<35%). There was a statistically significant decrease in R2∗ values in HCC before and after O₂ (P = 0.02) and increase in R₁ after O₂ (P = 0.004). CB had no significant effect (P R2∗ = 0.47/R₁ = 0.278). Conclusion R2∗ measurements in HCC and liver parenchyma are more reproducible at 1.5T than at 3.0T, and with O₂ than with CB challenge. We observed a decrease in R2∗ and an increase in R₁ of HCCs from baseline in response to O₂ challenge, as expected with increased tissue and blood oxygenation.