Using MRI to study the alterations in liver blood flow, perfusion, and oxygenation in response to physiological stress challenges: Meal, hyperoxia, and hypercapnia

Abstract

Background: Noninvasive assessment of dynamic changes in liver blood flow, perfusion, and oxygenation using MRI may allow detection of subtle hemodynamic alterations in cirrhosis.

Purpose: To assess the feasibility of measuring dynamic liver blood flow, perfusion, and T₂ * alterations in response to meal, hypercapnia, and hyperoxia challenges.

Study type: Prospective.

Subjects: Ten healthy volunteers (HV) and 10 patients with compensated cirrhosis (CC).

Field strength/sequence: 3T; phase contrast, arterial spin labeling, and $T_2^{*}$ mapping.

Assessment: Dynamic changes in portal vein and hepatic artery blood flow (using phase contrast MRI), liver perfusion (using arterial spin labeling), and blood oxygenation ( $T_2^{*}$ mapping) following a meal challenge (660 kcal), hyperoxia (target P_ET O₂ of 500 mmHg), and hypercapnia (target increase P_ET CO₂ of ∼6 mmHg).

Statistical tests: Tests between baseline and each challenge were performed using a paired two-tailed t-test (parametric) or Wilcoxon-signed-ranks test (nonparametric). Repeatability and reproducibility were determined by the coefficient of variation (CoV).

Results: Portal vein velocity increased following the meal (70 ± 9%, P < 0.001) and hypercapnic (7 (5-11)%, P = 0.029) challenge, while hepatic artery flow decreased (-30 ± 18%, P = 0.005) following the meal challenge in HV. In CC patients, portal vein velocity increased (37 ± 13%, P = 0.012) without the decrease in hepatic artery flow following the meal. In both groups, the meal increased liver perfusion (HV: 82 ± 50%, P < 0.0001; CC: 27 (16-42)%, P = 0.011) with faster arrival time of blood (HV: -54 (-56-30)%, P = 0.074; CC: -42 ± 32%, P = 0.005). In HVs, $T_2^{*}$ increased after the meal and in response to hyperoxia, with a decrease in hypercapnia (6 ± 8% P = 0.052; 3 ± 5%, P = 0.075; -5 ± 6%, P = 0.073, respectively), but no change in CC patients. Baseline between-session CoV <15% for blood flow and <10% for $T_2^{*}$ measures.

Data conclusion: Dynamic changes in liver perfusion, blood flow, and oxygenation following a meal, hyperoxic, and hypercapnic challenges can be measured using noninvasive MRI and potentially be used to stratify patients with cirrhosis.

Level of evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1577-1586.

Keywords: hypercapnia; hyperoxia; liver T2*; liver blood flow; liver perfusion; meal challenge.