Evaluations of Specific Absorption Rate and Temperature Increase Within Pregnant Female Models in Magnetic Resonance Imaging Birdcage Coils

Abstract

This paper presents a detailed numerical study of specific absorption rate (SAR) and temperature increase calculations within pregnant female models exposed to magnetic resonance imaging (MRI). Nine pregnant female models, representing different pregnant stages, were used for this study. SAR and temperature increase within and around fetuses at different pregnancy stages were calculated for two MRI operating modes (normal mode and first-level controlled mode) at 64 and 128 MHz. Local fetus energy deposition exceeds the International Electrotechnical Commission limit of 10 W/kg in the first-level controlled mode at 64 MHz. Fetus temperature exceeds or approaches 38 C for both frequencies in the first-level controlled mode at later stages of pregnancy. The core temperature limits for both modes and both frequencies are not exceeded. The results show higher maximum SAR and higher temperature at 64 MHz and during later pregnancy stages with a significant increase starting with the fifth month of pregnancy. Based on the results of this study, radiologists can minimize local fetus heating, especially late in pregnancy, by using normal mode sequences, which minimize the whole body SAR in the mother.Index Terms-Electromagnetic heating, finite-difference method, magnetic resonance imaging (MRI), pregnant woman, safety standards.

Numerical assessment of the reduction of specific absorption rate by adding high dielectric materials for fetus MRI at 3 T

“…Table 3. The result demonstrated that the obtained 10 g local SAR values of different tissues using our model without HDM were consistent with the data in [27], indicating the reliable simulation results in this work. Generally speaking, the results obtained here could obviously indicate the trend of the SAR values while undergoing a fetus MR scan with HDM.…”

“…Though the fetus MRI has mainly been clinically performed at 1.5 T, some research is currently underway to take advantage of the attractive benefits of fetus MRI at 3 T [18,19]. Despite obvious improvements in the image quality at 3 T, the specific absorption rate (SAR) usually increases significantly at the same time [12], which is the top priority concern of safety for the fetus [10,27,29]. Increased SAR results in increased tissue temperatures, which may be very harmful during pregnancy if they are above the safety level, with the higher probability of embryonic death, abortion, growth retardation and developmental defects [9].…”

Whole-body pregnant woman modeling by digital geometry processing with detailed uterofetal unit based on medical images

“…Four were built from 3-DUS images (6,7,8, and 11 WG) and 12 from MRI images (from 24 to 33 WG). The 3-DUS image datasets enabled us to create the first published pregnant woman models with embryo/fetus models built from medical images, acquired during the first trimester of pregnancy.…”

“…In [6], nine pregnant female models at each month of gestation were generated, embedding a UFU (which included the placenta), a bladder, and bones (based on segmented MRI data), into a computer graphics woman model. The abdomen of the woman was only scaled for models at stages beyond 4 months and the UFUs were scaled to simulate the different gestational ages.…”

Utero-Fetal Unit and Pregnant Woman Modeling Using a Computer Graphics Approach for Dosimetry Studies

“…Moreover, only a limited set of fetal tissues were distinguished (including soft tissues, skeleton, brain). The set of models proposed in [4] was the only one built using medical images, but UFU models at different gestational ages were obtained by scaling a single model extracted from MRI data obtained at 35 weeks of amenorrhea (WA). This transformation seems inappropriate as fetal limbs and organs do not develop at the same moment nor grow linearly.…”