Introduction
Current cardiac MRI protocols strive for efficiency, and more sites are moving to 30-minute scan slots and automated scanning to reduce idle time and reduce patient discomfort1. However, while rapid scanning with little time between the application of one pulse sequence and the next may not impact qualitative image sequences (i.e. cine), such a set-up has the potential to impact measured T1 and/or T2 values if insufficient time is allowed for complete relaxation of the magnetization between scans, impacting diagnostic accuracy. Thus, this study aims to assess the differences in T1 and T2 values measured in the myocardium using both clinically standard pulse sequences (MOLLI2, bSSFP3) and cardiac Magnetic Resonance Fingerprinting (MRF)4 when scans are performed with and without rest periods (breathhold commands) after cine or mapping sequences.
Methods
Two healthy subjects were scanned in this IRB-approved study on a 1.5T MRI scanner at a mid-ventricular short-axis slice. Three pulse sequences for quantitative tissue property mapping were assessed: T1 mapping with MOLLI2, T2 mapping with bSSFP3, and simultaneous T1-T2 mapping with MRF4. T1 and T2 maps were produced5,6,7 in 2 distinct datasets for each subject: with and without rest periods (breathhold commands) after cine or mapping sequences. The mean T1 and T2 values for each myocardial segment ROI were collected and compared within the same set of data utilizing 1-sample t-tests to assess statistical significance.
Results
When breathhold instructions were present in the protocol, there were no statistically significant differences in either T1 or T2 values in quantitative tissue property mapping sequences compared to baseline measurements. However, when breathhold instructions were removed from the protocol and sequences were applied directly back-to-back, there were statistically significant decreases in T1 values measured using both MOLLI and MRF.
Figure 1. (A) Control MOLLI T1 map of short-axis mid-ventricle with full rest interval. (B) MOLLI T1 map of short-axis mid-ventricle immediately post-cine without a pause for breathhold commands, showing decreased T1 values in the myocardium. (C) Control bSSFP T2 map of short-axis mid-ventricle with full rest interval. (D) bSSFP T2 map of short-axis mid-ventricle immediately post-cine without a pause for breathhold commands, showing consistent T2 values in the myocardium.
Conclusions
The results of this study suggest that while it is possible to induce significant decreases in T1 values measured using MOLLI and MRF if sufficient time for relaxation between sequential scans is not provided, the time required to give a breathhold command (approximately 8 seconds) is sufficient to ensure relaxation of the magnetization given and collect reliable measurements.
References
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