title: Saturation pulse design for quantitative myocardial T1 mapping.
abstract: BACKGROUND
  Quantitative saturation-recovery based T1 mapping sequences are less sensitive to systematic errors than the Modified Look-Locker Inversion recovery (MOLLI) technique but require high performance saturation pulses. We propose to optimize adiabatic and pulse train saturation pulses for quantitative T1 mapping to have <1 % absolute residual longitudinal magnetization (|MZ/M0|) over ranges of B0 and [Formula: see text] (B1 scale factor) inhomogeneity found at 1.5 T and 3 T.
  
  
  METHODS
  Design parameters for an adiabatic BIR4-90 pulse were optimized for improved performance within 1.5 T B0 (±120 Hz) and [Formula: see text] (0.7-1.0) ranges. Flip angles in hard pulse trains of 3-6 pulses were optimized for 1.5 T and 3 T, with consideration of T1 values, field inhomogeneities (B0 = ±240 Hz and [Formula: see text]=0.4-1.2 at 3 T), and maximum achievable B1 field strength. Residual MZ/M0 was simulated and measured experimentally for current standard and optimized saturation pulses in phantoms and in-vivo human studies. T1 maps were acquired at 3 T in human subjects and a swine using a SAturation recovery single-SHot Acquisition (SASHA) technique with a standard 90°-90°-90° and an optimized 6-pulse train.
  
  
  RESULTS
  Measured residual MZ/M0 in phantoms had excellent agreement with simulations over a wide range of B0 and [Formula: see text]. The optimized BIR4-90 reduced the maximum residual |MZ/M0| to <1 %, a 5.8× reduction compared to a reference BIR4-90. An optimized 3-pulse train achieved a maximum residual |MZ/M0| <1 % for the 1.5 T optimization range compared to 11.3 % for a standard 90°-90°-90° pulse train, while a 6-pulse train met this target for the wider 3 T ranges of B0 and [Formula: see text]. The 6-pulse train demonstrated more uniform saturation across both the myocardium and entire field of view than other saturation pulses in human studies. T1 maps were more spatially homogeneous with 6-pulse train SASHA than the reference 90°-90°-90° SASHA in both human and animal studies.
  
  
  CONCLUSIONS
  Adiabatic and pulse train saturation pulses optimized for different constraints found at 1.5 T and 3 T achieved <1 % residual |MZ/M0| in phantom experiments, enabling greater accuracy in quantitative saturation recovery T1 imaging.
authors.affiliation: Department of Biomedical Engineering, Faculty of Medicine and Dentistry, 1082 Research Transition Facility, University of Alberta, Edmonton, AB, T6G 2V2, Canada. kelvin.chow@ualberta.ca.
authors.forename: Kelvin
authors.initials: K
authors.lastname: Chow
authors.affiliation: National Institutes of Health, Department of Health and Human Services, National Heart, Lung and Blood Institute, Bethesda, MD, USA. kellman@nih.gov.
authors.forename: Peter
authors.initials: P
authors.lastname: Kellman
authors.affiliation: Cardiovascular MR R&D, Siemens Medical Solutions USA, Inc., Chicago, IL, USA. bruce.spottiswoode@siemens.com.
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Spottiswoode
authors.affiliation: National Institutes of Health, Department of Health and Human Services, National Heart, Lung and Blood Institute, Bethesda, MD, USA. sonia.nielles-vallespin@nih.gov.
authors.forename: Sonia
authors.initials: S
authors.lastname: Nielles-Vallespin
authors.affiliation: National Institutes of Health, Department of Health and Human Services, National Heart, Lung and Blood Institute, Bethesda, MD, USA. araia@nhlbi.nih.gov.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Arai
authors.affiliation: Cardiovascular Division, Departments of Medicine, Radiology and Medical Imaging, University of Virginia Health System, Charlottesville, VA, USA. msalerno@virginia.edu.|Biomedical Engineering, University of Virginia Health System, Charlottesville, VA, USA. msalerno@virginia.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Salerno
authors.affiliation: Department of Biomedical Engineering, Faculty of Medicine and Dentistry, 1082 Research Transition Facility, University of Alberta, Edmonton, AB, T6G 2V2, Canada. richard.thompson@ualberta.ca.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Thompson
mesh_terms: D000818:Animals; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D023421:Models, Animal; D009206:Myocardium; D019047:Phantoms, Imaging; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D013552:Swine