<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>Tendon insertion pathologies such as enthesitis and apophysitis in children can result from trauma, overuse syndrome and arthritis. Knowledge of the US appearance of normal joints by age might aid diagnosis of pathologies.</p>

<p><strong>OBJECTIVE: </strong>We describe the age-related sonographic features of the elbows, knees and feet in healthy children, providing a reference for the normal appearance of tendon insertions, apophyseal cartilage and bursae.</p>

<p><strong>MATERIALS AND METHODS: </strong>This is a prospective cross-sectional study of 30 healthy children. Children were grouped according to age: group 1 (4-9&nbsp;years, n = 11), group 2 (10-13&nbsp;years, n = 9) and group 3 (14-18&nbsp;years, n = 10). Children completed pain and function questionnaires and underwent a standardized joint examination by a pediatric rheumatologist. The common extensor, common flexor, quadriceps, patellar and Achilles tendons and plantar fascia insertions were evaluated with gray-scale and power Doppler ultrasound. The anterior elbow, suprapatellar and retrocalcaneal bursae were evaluated for fluid. We measured the apophyseal cartilage thickness at the enthesis. Correlation analyses examined associations between age and tendon thickness. We used ANOVA, with location as a repeated measure, to test for gender differences in cartilage thickness.</p>

<p><strong>RESULTS: </strong>Children had a median age of 12.4&nbsp;years and 55% were boys. All 360 entheses appeared normal on gray-scale imaging. There was a strong linear relationship between tendon thickness and age. Tendon vascularity was only present in young children (group 1), in 7/22 (32%) quadriceps tendons. Peri-tendinous power Doppler signal was seen at seven sites: two patellar, four quadriceps and one common flexor tendon, and all these children were in group 2. Suprapatellar bursal fluid &lt;3&nbsp;mm was detected in 9/60 (15%) knees. Of the children in group 1, boys had thicker apophyseal cartilage than girls at the medial epicondyle, patellar poles and os calcis (P &lt; 0.05).</p>

<p><strong>CONCLUSION: </strong>Tendon vascularity may be a normal finding in young children, and mild peri-tendinous vascularity is not uncommon in children 10-13&nbsp;years of age. Tendon thickness has a linear relationship with age; however cartilage thickness varies across sites and also differs as a function of gender.</p>