Multiparametric Mapping
Chia-Ying Liu, PhD
Scientist
The Johns Hopkins University, Maryland, United States
Chikara Noda, PhD
Research associate
The Johns Hopkins University, United States
Bharath Ambale-Venkatesh, PhD
Physicist
The John Hopkins Hospital
Baltimore, Maryland, United States
Emilia Hermann, MD
Assistant professor
Columbia University, United States
Graham Barr, MD, PhD
professor
Columbia University, New York, United States
David A. Bluemke, MD
MD
University of Wisconsin-Madison
Madison, Wisconsin, United States
Joao A. C Lima, MD
MD
The John Hopkins Hospital
Baltimore, Maryland, United States
Patients with chronic obstructive pulmonary disease (COPD) frequently develop hypoxia when cells or tissues in the body don’t get as much oxygen as they need. MR relaxometry has been exploited to measure the blood oxygen saturation. Various models have been developed to characterize the relationship between T2 and blood saturation. Oxygen saturation estimated by the MRI T2 mapping has shown a good agreement with invasive blood gas analysis in the porcine model. We hypothesize that cardiac T2 mapping might reflect cardiopulmonary oxygenation. The aim of this study was to investigate whether myocardial T2 and RV/LV blood T2 ratio correlate with cardiac structure and function, as well as pulmonary function in COPD patients.
Methods: 37 participants with COPD and 40 volunteers free from cardiopulmonary disease were included in this prospective study. All participants were imaged using a single 3T MRI system (Canon Medical Systems, Japan). COPD patients were imaged with cine, MOLLI for T1 mapping, and T2-prepared sequence for T2 mapping. Cardiac parameters were indexed to body surface area. Only T1 and T2 mapping were acquired in the volunteers. Regions of interest were drawn in the lumen of the RV and LV, with careful avoidance of papillary muscles and myocardium. The ratio of the T2 times of the RV divided by the LV blood pool was calculated. Mann-Whitney U test was used for comparison of T1 and T2 times between COPD and controlled volunteers. For the COPD cohort, linear regression analysis adjusted for demographics (age, sex, heart rate, and BMI for non-indexed cardiac MR parameters) was used to examine the association between T2 mapping and all parameters. A P value < 0.05 was considered statistically significant.
Results: RV/LV blood T2 ratios were lower in COPD than in volunteers (P< 0.001. Table 1). Myocardial T2 was not different between COPD and volunteers. Myocardial T1 was higher in COPD (P=0.04) but was not different between groups after accounting for age. In the COPD cohort, the RV/LV blood T2 ratio was directly associated with cardiac functional parameters but not to structure (Table 2). The RV/LV blood ratio was inversely related to smoking (pack years), and directly related to the post-bronchodilator ratio of the forced expiratory volume in 1 second (FEV1) to the forced vital capacity (FVC) (Figure 1).
Conclusion:
RV/LV blood T2 ratio was associated with cardiac functional parameters in patients with COPD. RV/LV blood T2 ratio was also positively related to the predicted FEV1/FVC ratio, a measurement of COPD status. An increased oxygen consumption increases the delivery of deoxygenated blood to the right heart as reflected by the lower RV T2 in COPD patients than in volunteers. The ratio potentially normalizes study technical and inter-subject dissimilarities by assessing the difference in blood oxygenation between the RV and LV. Therefore, RV/LV blood T2 ratio indexes cardio-pulmonary performance in patients with COPD.