Continuous quantitative mapping of multi-organ T1 relaxation times with ShMOLLI to assess dose response in respiratory challenges at 3T
© Piechnik et al; licensee BioMed Central Ltd. 2013
Published: 30 January 2013
The performance of T1 mapping as a stable biomarker depends on its sensitivity to pathological changes and relative insensitivity to normal physiological variations or common clinical interventions, such as oxygen administration. We address the impact of breathing air supplemented with oxygen (O2) and/or carbon dioxide (CO2) on T1 values in healthy myocardium and selected extra-cardiac tissues.
6 normal control volunteers (age 35±4 years, 2 females) underwent serial T1-mapping using the Shortened Modified Look Locker Inversion Recovery (ShMOLLI, Piechnik et al. JCMR 2010, 12:69) at 3T (Siemens Trio). Subjects breathed through a mouthpiece to allow monitoring of O2 and CO2 content (Datex Normocap 200) during three 15-minute respiratory challenges as follows: 4 minutes of normal air, 5 minutes of supplemented target mixture with O2 (21-100%) and CO2 (0-5%), and 6 minutes of normal air (Fig. 1A). T1-mapping was performed back-to-back at end-expiration under automated breathing instructions. Regions of interest (ROIs) were drawn on T1 maps within the myocardium, left ventricular (LV) and right ventricular (RV) blood pools, liver parenchyma excluding major vessels, and the spleen. ROIs were followed semi-automatically for motion between breath-holds. The relationship between changes in T1 in each organ and the end-tidal (Et) gas content was assessed using general linear modelling.
ShMOLLI T1-maps can be acquired at a frequency of up to 3 per minute with excellent measurement consistency over extended periods of time, with potential use in the monitoring of physiological effects of respiratory challenges. T1 directly detects hyperoxygenation in arterial blood and its propagation downstream to some major organs such as the spleen. There was little evidence of major variation of T1 with O2 or CO2 in the other organs studied. Specifically, in comparison to normal T1 variability, myocardial T1 is relatively stable under feasible hyperoxia and hypercapnia.
National Institute for Health Research (NIHR) Oxford Biomedical Research Centre.
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