Improving B1+-inhomogeneity tolerance by resolving non-bijection in MP2RAGE R ₁ mapping: A 2D look-up table approach demonstrated at 3 T.

TY - JOUR

T1 - Improving B1+-inhomogeneity tolerance by resolving non-bijection in MP2RAGE R 1 mapping

T2 - A 2D look-up table approach demonstrated at 3 T.

AU - Ruijters, Lenno

AU - Lund, Torben Ellegaard

AU - Vinding, Mads Sloth

N1 - © 2024 The Author(s). Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.

PY - 2025/4

Y1 - 2025/4

N2 - Purpose: Regarding in vivo, robust longitudinal relaxation rate (R1) mapping, the goal of the present paper is two-fold. First, to verify that non-bijective mapping in magnetization-prepared 2 rapid gradient echo (MP2RAGE) imaging can be resolved through a two-dimensional look-up table approach. Second, that the expanded parameter space from this can be used to improve (Formula presented.) -inhomogeneity tolerance without other prerequisites. Theory: By deriving a second contrast from the magnitude images of the MP2RAGE acquisition, ambiguities in the original MP2RAGE image resulting from non-bijective transfer curves can be resolved. Such ambiguities may occur when protocols are optimized, such as for higher (Formula presented.) -inhomogeneity tolerance. A 2D look-up table approach combines the available information to resolve these ambiguities during mapping. Methods: At 3 T, we acquired MP2RAGE images with standard acquisition parameters and (non-bijective) parameters optimized for (Formula presented.) -inhomogeneity tolerance. From 3 subjects across multiple sessions, we assessed the (Formula presented.) -inhomogeneity tolerance through excitation-pulse amplitude scalings. Results: The R1 maps resulting from the (Formula presented.) -optimized protocols showed greatly reduced (Formula presented.) effects across images but without additional scanner time. Meanwhile, these maps could only successfully be derived by a 2D look-up table approach. Conclusion: We show that it is possible to optimize for (Formula presented.) -inhomogeneity tolerance in MP2RAGE through sequence-parameter settings, while still successfully estimating the R1 map with a two-dimensional look-up table approach. This without the need for an additional (Formula presented.) map. The increased parameter space enabled by the two-dimensional look-up table approach may further be used to adjust MP2RAGE acquisitions for improved scan times, signal-to-noise ratio, and/or contrast-to-noise ratio.

AB - Purpose: Regarding in vivo, robust longitudinal relaxation rate (R1) mapping, the goal of the present paper is two-fold. First, to verify that non-bijective mapping in magnetization-prepared 2 rapid gradient echo (MP2RAGE) imaging can be resolved through a two-dimensional look-up table approach. Second, that the expanded parameter space from this can be used to improve (Formula presented.) -inhomogeneity tolerance without other prerequisites. Theory: By deriving a second contrast from the magnitude images of the MP2RAGE acquisition, ambiguities in the original MP2RAGE image resulting from non-bijective transfer curves can be resolved. Such ambiguities may occur when protocols are optimized, such as for higher (Formula presented.) -inhomogeneity tolerance. A 2D look-up table approach combines the available information to resolve these ambiguities during mapping. Methods: At 3 T, we acquired MP2RAGE images with standard acquisition parameters and (non-bijective) parameters optimized for (Formula presented.) -inhomogeneity tolerance. From 3 subjects across multiple sessions, we assessed the (Formula presented.) -inhomogeneity tolerance through excitation-pulse amplitude scalings. Results: The R1 maps resulting from the (Formula presented.) -optimized protocols showed greatly reduced (Formula presented.) effects across images but without additional scanner time. Meanwhile, these maps could only successfully be derived by a 2D look-up table approach. Conclusion: We show that it is possible to optimize for (Formula presented.) -inhomogeneity tolerance in MP2RAGE through sequence-parameter settings, while still successfully estimating the R1 map with a two-dimensional look-up table approach. This without the need for an additional (Formula presented.) map. The increased parameter space enabled by the two-dimensional look-up table approach may further be used to adjust MP2RAGE acquisitions for improved scan times, signal-to-noise ratio, and/or contrast-to-noise ratio.

KW - 2D look-up table

KW - B1+ inhomogeneity

KW - MP2RAGE

KW - R-mapping

KW - non-bijective data

UR - http://www.scopus.com/inward/record.url?scp=85208781194&partnerID=8YFLogxK

U2 - 10.1002/mrm.30363

DO - 10.1002/mrm.30363

M3 - Journal article

C2 - 39529499

SN - 0740-3194

VL - 93

SP - 1712

EP - 1722

JO - Magnetic Resonance in Medicine

JF - Magnetic Resonance in Medicine

IS - 4

ER -