Local SAR management strategies to use two-channel RF shimming for fetal MRI at 3 T

FIGURE S1. Local specific absorption rate (SAR) and temperature maps in slices through the maternal peak 10 g averaged local SAR (pSAR10g) and the maternal peak temperature for the circularly polarized (CP) birdcage mode (first and third rows) and the best shim settings optimizing |B₁⁺| average inside the fetus when using Strategy B2 (second and fourth rows). Locations of peak SAR or temperature are marked by black plus signs. Locations of the slices, the maternal pSAR10g, and maternal peak and average temperature are shown below each slice. Maximum pSAR10g or peak temperature across all models (in each row) is denoted by a bold blue font, and maximum average temperature across all models (in Rows 3 and 4) is denoted by a bold green font.

FIGURE S2. Local specific absorption rate (SAR) and temperature maps in slices through the fetal peak 10 g averaged local SAR (pSAR10g) and the fetal peak temperature for the circularly polarized (CP) birdcage mode (first and third rows) and the best shim settings optimizing |B₁⁺| average inside the fetus when using Strategy B2 (second and fourth rows). Locations of the slices, the fetal pSAR10g, average SAR (aveSAR), peak temperature, and average temperature are shown below each slice. Maximum pSAR10g or peak temperature across all models (in each row) is denoted by a bold blue font, and maximum aveSAR or average temperature across all models (in each row is denoted by a bold green font.

FIGURE S3. Local specific absorption rate (SAR) maps in the fetal peak 10 g averaged local SAR (pSAR10g) slices through the 3D fetus models for the circularly polarized (CP) birdcage mode (first row) and the best shim settings optimizing |B₁⁺| average inside the fetus when using Strategy B2 (second row). The fetal pSAR10g and average SAR (aveSAR) are shown below each slice. Maximum pSAR10g across all models (in each row) is denoted by a bold blue font, and the maximum aveSAR across all models (in each row) is denoted by a bold green font.

FIGURE S4. Temperature maps in the fetal peak temperature slices through the 3D fetus models for the circularly polarized (CP) birdcage mode (first row) and the best shim settings optimizing |B₁⁺| average inside the fetus when using Strategy B2 (second row). The fetal peak and average temperature are shown below each slice. Maximum peak temperature across all models (in each row) is denoted by a bold blue font, and maximum average temperature across all models (in each row) is denoted by a bold green font.

FIGURE S5. Different versions of model BCH4-2-1 with the fetus rotated around the head–foot axis by 20°, 160°, and 180°.

FIGURE S6. The change in maternal peak local specific absorption rate (SAR), fetal peak local SAR, fetal average SAR, average B₁⁺ magnitude inside the fetus, and coefficient of variation of B₁⁺ magnitude inside the fetus with fetal rotation of 20°, 160°, and 180° (first row) and with maternal translation of 5 cm in left, right, head, or foot directions (second row) for body model BCH4-2-1. Purple dots denote the circularly polarized birdcage mode (CP mode); green stars denote the RF shim settings, which improve transmit field inside the fetus compared with CP mode in the original model BCH4-2-1. F, foot; H, head; L, left; R, right.

TABLE S1. Mass density and thermal properties of fetal and peri-fetal tissues used in different simulations of the body model PW_II.

TABLE S2. Average and peak temperature and specific absorption rate (SAR) in mother, fetal tissues, and peri-fetal tissues for the fully detailed and simplified versions of body model PW_II with different thermal tissue properties as indicated in Supporting Information Table S1. SAR and temperature values in this study are also compared with those reported in Murbach et al.¹¹