<p><strong>Background</strong> MRI performed at 3.0 T offers greater signal-to-noise ratio and better spatial resolution than does MRI performed at 1.5 T; however, for fetal MRI, there are concerns about the potential for greater radiofrequency energy administered to the fetus at 3.0-T MRI. <strong>Purpose</strong> To compare the specific absorption rate (SAR) and specific energy dose (SED) of fetal MRI at 1.5 and 3.0 T. <strong>Materials and Methods</strong> In this retrospective study, all fetal MRI examinations performed with 1.5- and 3.0-T scanners at one institution between July 2012 and October 2016 were evaluated. Two-dimensional (2D) and three-dimensional (3D) steady-state free precession (SSFP), single-shot fast spin-echo, 2D and 3D T1-weighted spoiled gradient-echo (SPGR), and echo-planar imaging sequences were performed. SAR, SED, accumulated SED, and acquisition time were retrieved from the Digital Imaging and Communications in Medicine header. Data are presented as mean ± standard deviation. Two one-sided tests with equivalence bounds of 0.5 (Cohen effect size) were performed, with statistical equivalence considered at &lt; .05. <strong>Results</strong> A total of 2952 pregnant women were evaluated. Mean maternal age was 30 years ± 6 (age range, 12-49 years), mean gestational age was 24 weeks ± 6 (range, 17-40 weeks). A total of 3247 fetal MRI scans were included, with 2784 (86%) obtained at 1.5 T and 463 (14%) obtained at 3.0 T. In total, 93 764 sequences were performed, with 81 535 (87%) performed at 1.5 T and 12 229 (13%) performed at 3.0 T. When comparing 1.5- with 3.0-T MRI sequences, mean SAR (1.09 W/kg ± 0.69 vs 1.14 W/kg ± 0.61), mean SED (33 J/kg ± 27 vs 38 J/kg ± 26), and mean accumulated SED (965 J/kg ± 408 vs 996 J/kg ± 366, &lt; .001) were equivalent. <strong>Conclusion</strong> Fetal 1.5- and 3.0-T MRI examinations were found to have equivalent energy metrics in most cases. The 3.0-T sequences, such as two-dimensional T1-weighted spoiled gradient-echo and three-dimensional steady-state free precession, may require modification to keep the energy delivered to the patient as low as possible. © RSNA, 2020</p>

<p><strong>BACKGROUND: </strong>Current methods to predict height and growth failure are imprecise. MRI measures of physeal cartilage are promising biomarkers for growth.</p>

<p><strong>PURPOSE: </strong>In the physis, to assess how 3D MRI volume measurements, and diffusion tensor imaging (DTI) measurements (tract volume and length) correlate with growth parameters and detect differences in growth. We compared patients exposed to cis-retinoic acid, which causes physeal damage and growth failure, with normal subjects.</p>

<p><strong>STUDY TYPE: </strong>Case-control.</p>

<p><strong>POPULATION: </strong>Twenty pediatric neuroblastoma survivors treated with cis-retinoic acid and 20 age- and sex-matched controls.</p>

<p><strong>FIELD STRENGTH/SEQUENCE: </strong>3T; DTI and 3D double-echo steady-state (DESS) sequences.</p>

<p><strong>ASSESSMENT: </strong>On distal femoral MR studies, physeal 3D volume and DTI tract measurements were calculated and compared to height.</p>

<p><strong>STATISTICAL TESTS: </strong>We used partial Spearman correlation, analysis of covariance, logistic regression, Wald test, and the intraclass correlation coefficient (ICC).</p>

<p><strong>RESULTS: </strong>The height percentile correlated most strongly with DTI tract volumes (r = 0.74), followed by mean tract length (r = 0.53) and 3D volume (r = 0.40) (all P &lt; 0.02). Only tract volumes and lengths correlated with annualized growth velocity. Relative to controls, patients showed smaller tract volumes (8.00 cc vs. 13.71 cc, P &lt; 0.01), shorter tract lengths (5.92 mm vs 6.99 mm, P = 0.03), and smaller ratios of 3D cartilage volume to tract length; but no difference (4.51 cc vs 4.85 cc) in 3D MRI volumes. The 10 patients with the lowest height percentiles had smaller tract volumes (5.07 cc vs. 10.93 cc, P &lt; 0.01), but not significantly different 3D MRI volumes. Tract volume is associated with abnormal growth, with an accuracy of 75%.</p>

<p><strong>DATA CONCLUSION: </strong>DTI tract volume of the physis/metaphysis predicts abnormal growth better than physeal cartilage volumetric measurement and correlates best with height percentile and growth velocity.</p>

<p><strong>EVIDENCE LEVEL: </strong>2 TECHNICAL EFFICACY: Stage 2.</p>