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Purpose: To develop and evaluate a free breathing non‐electrocardiograph (ECG) myocardial T1* mapping sequence using radial imaging to quantify the changes in myocardial T1* between rest and exercise (T1*reactivity) in exercise cardiac MRI (Ex‐CMR). Methods: A free‐running T1* sequence was developed using a saturation pulse followed by three Look‐Locker inversion‐recovery experiments. Each Look‐Locker continuously acquired data as radial trajectory using a low flip‐angle spoiled gradient‐echo readout. Self‐navigation was performed with a temporal resolution of ∼100 ms for retrospectively extracting respiratory motion. The mid‐diastole phase for every cardiac cycle was retrospectively detected on the recorded electrocardiogram signal using an empirical model. Multiple measurements were performed to obtain mean value to reduce effects from the free‐breathing acquisition. Finally, data acquired at both mid‐diastole and end‐expiration are picked and reconstructed by a low‐rank plus sparsity constraint algorithm. The performance of this sequence was evaluated by simulations, phantoms, and in vivo studies at rest and after physiological exercise. Results: Numerical simulation demonstrated that changes in T1* are related to the changes in T1; however, other factors such as breathing motion could influence T1* measurements. Phantom T1* values measured using free‐running T1* mapping sequence had good correlation with spin‐echo T1 values and was insensitive to heart rate. In the Ex‐CMR study, the measured T1* reactivity was 10% immediately after exercise and declined over time. Conclusion: The free‐running T1* mapping sequence allows free‐breathing non‐ECG quantification of changes in myocardial T1* with physiological exercise. Although, absolute myocardial T1* value is sensitive to various confounders such as B1 and B0 inhomogeneity, quantification of its change may be useful in revealing myocardial tissue properties with exercise. [ABSTRACT FROM AUTHOR]

Purpose: To develop a free‐breathing sequence, that is, Multislice Joint T1‐T2, for simultaneous measurement of myocardial T1 and T2 for multiple slices to achieve whole left‐ventricular coverage. Methods: Multislice Joint T1‐T2 adopts slice‐interleaved acquisition to collect 10 single‐shot electrocardiogram‐triggered images for each slice prepared by saturation and T2 preparation to simultaneously estimate myocardial T1 and T2 and achieve whole left‐ventricular coverage. Prospective slice‐tracking using a respiratory navigator and retrospective image registration are used to reduce through‐plane and in‐plane motion, respectively. Multislice Joint T1‐T2 was validated through numerical simulations and phantom and in vivo experiments, and compared with saturation‐recovery single‐shot acquisition and T2‐prepared balanced Steady‐State Free Precession (T2‐prep SSFP) sequences. Results: Phantom T1 and T2 from Multislice Joint T1‐T2 had good accuracy and precision, and were insensitive to heart rate. Multislice Joint T1‐T2 yielded T1 and T2 maps of nine left‐ventricular slices in 1.4 minutes. The mean left‐ventricular T1 difference between saturation‐recovery single‐shot acquisition and Multislice Joint T1‐T2 across healthy subjects and patients was 191 ms (1564 ± 60 ms versus 1373 ± 50 ms; P <.05) and 111 ms (1535 ± 49 ms vs 1423 ± 49 ms; P <.05), respectively. The mean difference in left‐ventricular T2 between T2‐prep SSFP and Multislice Joint T1‐T2 across healthy subjects and patients was −6.3 ms (42.4 ± 1.4 ms vs 48.7 ± 2.5; P <.05) and −5.7 ms (41.6 ± 2.5 ms vs 47.3 ± 2.7; P <.05), respectively. Conclusion: Multislice Joint T1‐T2 enables quantification of whole left‐ventricular T1 and T2 during free breathing within a clinically feasible scan time of less than 2 minutes. [ABSTRACT FROM AUTHOR]

Purpose: To develop and validate a saturation‐delay‐inversion recovery preparation, slice tracking and multi‐slice based sequence for measuring whole‐heart native T1. Method: The proposed free‐breathing sequence performs T1 mapping of multiple left‐ventricular slices by slice‐interleaved acquisition to collect 10 electrocardiogram‐triggered single‐shot slice‐selective images for each slice. A saturation‐delay‐inversion recovery pulse is used for T1 preparation. Prospective slice tracking by the diaphragm navigator and retrospective registration are used to reduce through‐plane and in‐plane motion, respectively. The proposed sequence was validated in both phantom and human subjects (12 healthy subjects and 15 patients who were referred for a clinical cardiac MR exam) and compared with saturation recovery single‐shot acquisition (SASHA) and modified Look‐Locker inversion recovery (MOLLI). Results: Phantom T1 measured by the proposed sequence had excellent agreement (R2 = 0.99) with the ground‐truth T1 and was insensitive to heart rate. In both healthy subjects and patients, the proposed sequence yielded nine left‐ventricular T1 maps per volume in less than 2 minutes (healthy volunteers: 1.8 ± 0.4 minutes; patients: 1.9 ± 0.2 minutes). The average T1 of whole left ventricle for all healthy subjects and patients were 1560 ± 61 and 1535 ± 49 ms by SASHA, 1208 ± 42 and 1233 ± 56 ms by MOLLI5(3)3, and 1397 ± 34 and 1433 ± 56 ms by the proposed sequence, respectively. The corresponding coefficient of variation of T1 were 6.2 ± 1.4% and 5.8 ± 1.6%, 5.3 ± 1.1% and 5.1 ± 0.8%, and 4.9 ± 0.8% and 4.5 ± 0.8%, respectively. Conclusion: The proposed sequence enables quantification of whole heart T1 with good accuracy and precision in less than 2 minutes during free breathing. [ABSTRACT FROM AUTHOR]

Purpose: To develop and evaluate a free breathing non-electrocardiograph (ECG) myocardial T 1 * mapping sequence using radial imaging to quantify the changes in myocardial T 1 * between rest and exercise (T 1 * reactivity ) in exercise cardiac MRI (Ex-CMR)., Methods: A free-running T 1 * sequence was developed using a saturation pulse followed by three Look-Locker inversion-recovery experiments. Each Look-Locker continuously acquired data as radial trajectory using a low flip-angle spoiled gradient-echo readout. Self-navigation was performed with a temporal resolution of ∼100 ms for retrospectively extracting respiratory motion. The mid-diastole phase for every cardiac cycle was retrospectively detected on the recorded electrocardiogram signal using an empirical model. Multiple measurements were performed to obtain mean value to reduce effects from the free-breathing acquisition. Finally, data acquired at both mid-diastole and end-expiration are picked and reconstructed by a low-rank plus sparsity constraint algorithm. The performance of this sequence was evaluated by simulations, phantoms, and in vivo studies at rest and after physiological exercise., Results: Numerical simulation demonstrated that changes in T 1 * are related to the changes in T 1 ; however, other factors such as breathing motion could influence T 1 * measurements. Phantom T 1 * values measured using free-running T 1 * mapping sequence had good correlation with spin-echo T 1 values and was insensitive to heart rate. In the Ex-CMR study, the measured T 1 * reactivity was 10% immediately after exercise and declined over time., Conclusion: The free-running T 1 * mapping sequence allows free-breathing non-ECG quantification of changes in myocardial T 1 * with physiological exercise. Although, absolute myocardial T 1 * value is sensitive to various confounders such as B 1 and B 0 inhomogeneity, quantification of its change may be useful in revealing myocardial tissue properties with exercise., (© 2022 International Society for Magnetic Resonance in Medicine.)

Purpose: To develop a free-breathing sequence, that is, Multislice Joint T 1 -T 2 , for simultaneous measurement of myocardial T 1 and T 2 for multiple slices to achieve whole left-ventricular coverage., Methods: Multislice Joint T 1 -T 2 adopts slice-interleaved acquisition to collect 10 single-shot electrocardiogram-triggered images for each slice prepared by saturation and T 2 preparation to simultaneously estimate myocardial T 1 and T 2 and achieve whole left-ventricular coverage. Prospective slice-tracking using a respiratory navigator and retrospective image registration are used to reduce through-plane and in-plane motion, respectively. Multislice Joint T 1 -T 2 was validated through numerical simulations and phantom and in vivo experiments, and compared with saturation-recovery single-shot acquisition and T 2 -prepared balanced Steady-State Free Precession (T 2 -prep SSFP) sequences., Results: Phantom T 1 and T 2 from Multislice Joint T 1 -T 2 had good accuracy and precision, and were insensitive to heart rate. Multislice Joint T 1 -T 2 yielded T 1 and T 2 maps of nine left-ventricular slices in 1.4 minutes. The mean left-ventricular T 1 difference between saturation-recovery single-shot acquisition and Multislice Joint T 1 -T 2 across healthy subjects and patients was 191 ms (1564 ± 60 ms versus 1373 ± 50 ms; P < .05) and 111 ms (1535 ± 49 ms vs 1423 ± 49 ms; P < .05), respectively. The mean difference in left-ventricular T 2 between T 2 -prep SSFP and Multislice Joint T 1 -T 2 across healthy subjects and patients was -6.3 ms (42.4 ± 1.4 ms vs 48.7 ± 2.5; P < .05) and -5.7 ms (41.6 ± 2.5 ms vs 47.3 ± 2.7; P < .05), respectively., Conclusion: Multislice Joint T 1 -T 2 enables quantification of whole left-ventricular T 1 and T 2 during free breathing within a clinically feasible scan time of less than 2 minutes., (© 2020 International Society for Magnetic Resonance in Medicine.)

Purpose: To develop and validate a saturation-delay-inversion recovery preparation, slice tracking and multi-slice based sequence for measuring whole-heart native T 1 ., Method: The proposed free-breathing sequence performs T 1 mapping of multiple left-ventricular slices by slice-interleaved acquisition to collect 10 electrocardiogram-triggered single-shot slice-selective images for each slice. A saturation-delay-inversion recovery pulse is used for T 1 preparation. Prospective slice tracking by the diaphragm navigator and retrospective registration are used to reduce through-plane and in-plane motion, respectively. The proposed sequence was validated in both phantom and human subjects (12 healthy subjects and 15 patients who were referred for a clinical cardiac MR exam) and compared with saturation recovery single-shot acquisition (SASHA) and modified Look-Locker inversion recovery (MOLLI)., Results: Phantom T 1 measured by the proposed sequence had excellent agreement (R 2  = 0.99) with the ground-truth T 1 and was insensitive to heart rate. In both healthy subjects and patients, the proposed sequence yielded nine left-ventricular T 1 maps per volume in less than 2 minutes (healthy volunteers: 1.8 ± 0.4 minutes; patients: 1.9 ± 0.2 minutes). The average T 1 of whole left ventricle for all healthy subjects and patients were 1560 ± 61 and 1535 ± 49 ms by SASHA, 1208 ± 42 and 1233 ± 56 ms by MOLLI5(3)3, and 1397 ± 34 and 1433 ± 56 ms by the proposed sequence, respectively. The corresponding coefficient of variation of T 1 were 6.2 ± 1.4% and 5.8 ± 1.6%, 5.3 ± 1.1% and 5.1 ± 0.8%, and 4.9 ± 0.8% and 4.5 ± 0.8%, respectively., Conclusion: The proposed sequence enables quantification of whole heart T 1 with good accuracy and precision in less than 2 minutes during free breathing., (© 2020 International Society for Magnetic Resonance in Medicine.)