TABLE 1.
The effect of tissue detail and dielectric properties on maternal and fetal peak local SAR and fetal average SAR for circularly polarized birdcage mode, RF shim settings which improve imaging performance and the worst-case shim settings
| No. of maternal tissues | No. of fetal tissues | Amniotic fluid properties | Fetal tissue properties | Maternal pSAR10g (W/kg) | Fetal pSAR10g (W/kg) | Fetal aveSAR (W/kg) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CP | RFS | WC | CP | RFS | WC | CP | RFS | WC | |||||
| Murbach et al.11 | >70 | 17 | CSF | Adult | 29.6 (−8%) | NA | 39.9 (−10%) | 7.4 (3%) | NA | 21.3 (25%) | 1.1 (−35%) | NA | 2.8 (−39%) |
| This study | >70 | 17 | CSF | Adult | 32.5 (0%) | 16.5–32.2 (0%–l%) | 44.1 (0%) | 8.6 (18%) | 6.3–19.5 (−9% to 34%) | 23.1 (35%) | 1.2 (−29%) | 1.1–2.9 (−34% to −29%) | 3.2 (−31%) |
| >70 | 17 | CSF | Age adjusted | 32.5 (1%) | 16.3–32.3 (−1%to 1%) | 44.3 (0%) | 8.0 (11%) | 6.0–16.5 (3%–14%) | 18.9 (11%) | 1.5 (−10%) | 1.4–3.8 (−11% to −10%) | 4.2 (−10%) | |
| >70 | 17 | Peyman et al. 34 | Age adjusted | 32.3 | 16.5–32.2 | 44.2 | 7.2 | 5.4–15.3 | 17.1 | 1.7 | 1.5–4.2 | 4.6 | |
| >70 | 2 | Peyman et al.34 | Age adjusted | 32.6 (1%) | 16.1–32.5 (−3% to 2%) | 44.3 (0%) | 7.8 (7%) | 5.5–13.1 (−18% to 9%) | 15.0 (−12%) | 2.1 (24%) | 2.0–5.1 (19%−25%) | 5.5 (19%) | |
| 25 | 2 | Peyman et al.34 | Age adjusted | 33.3 (3%) | 16.8–33.3 (−4% to 8%) | 45.7 (4%) | 7.6 (6%) | 5.2–12.3 (−22% to 7%) | 14.2 (−17%) | 1.9 (13%) | 1.8–4.7 (11%−14%) | 5.2 (12%) | |
Note: The RFS values report SAR metrics within the improved imaging performance region and are listed as a range from lowest to highest SAR metric in this region. The first row lists the findings of Murbach et al.,11 who modeled a different body coil than this study. The second row reports SAR values found in this study with the same tissue property assignments as Murbach et al.11 Subsequent rows report modifications to the PW_II model. Percentage values in parenthesis show the change in SAR values with respect to those in row 4 (in bold type), which presents the most-detailed model with the most realistic tissue properties.
Abbreviations: aveSAR, average SAR; CP, circularly polarized birdcage mode; CSF, cerebrospinal fluid; NA, not applicable; pSAR10g, 10g averaged peak local SAR; PW_II, pregnant woman II; RFS, radiofrequency shimming; SAR, specific absorption rate; WC, worst-case shim settings.