Cardiac T1 calculations from MR spin-echo images

Area of Science:

• Medical Imaging
• Biophysics
• Cardiovascular MRI

Background:

• Cardiac triggering in MR spin-echo imaging typically restricts repetition times (TR) to integer multiples of the cardiac period (TC).
• Variations in cardiac period (TC) introduce TR irregularities, impacting the accuracy and precision of calculated spin-lattice relaxation (T1) values, particularly for myocardium.
• Existing methods face limitations due to these physiological variations.

Purpose of the Study:

• To quantify the impact of cardiac triggering restrictions on T1 accuracy and precision in MR spin-echo imaging.
• To investigate methods for improving T1 precision by modifying TR relative to the cardiac period (TC).
• To assess the effect of TR irregularities on T1 measurements.

Main Methods:

• Simulated cardiac-triggered spin-echo imaging sequences with varying TR values relative to the cardiac period (TC).
• Calculated spin-lattice relaxation (T1) values from pairs of images acquired with different TRs.
• Introduced controlled irregularities in TR to simulate physiological variations.

Main Results:

• Using TR values as fractions of TC (e.g., 1/2 TC and 2 TC) significantly improves T1 precision by up to 30% compared to integer multiples (TC and 2 TC) for a TC of 800 ms.
• TR irregularities, even of 15% around a mean TR of 800 ms, can cause a fourfold decrease in T1 measurement precision.
• Significant deviations in TC easily exceed 15%, highlighting the detrimental effect of physiological variability.

Conclusions:

• Employing fractional TR values in cardiac-triggered spin-echo imaging enhances T1 precision for myocardial tissue characterization.
• Minimizing TR irregularities to within +/- 15% of the mean cardiac period (TC) is critical for maintaining T1 accuracy and precision.
• Acquisition protocols should account for cardiac cycle variability to optimize MRI-based T1 quantification.