<p><strong>BACKGROUND: </strong>R2* relaxometry's capacity to calculate liver iron concentration (LIC) is limited in patients with severe overload. Hemosiderin increases in these patients, which exhibits a non-monoexponential decay that renders a failed R2* analysis.</p>

<p><strong>PURPOSE/HYPOTHESIS: </strong>To evaluate a biexponential R2* relaxometry model in children with different ranges of iron overload.</p>

<p><strong>STUDY TYPE: </strong>Retrospective.</p>

<p><strong>POPULATION: </strong>In all, 181 children with different conditions associated with iron overload.</p>

<p><strong>FIELD STRENGTH/SEQUENCE: </strong>1.5T, T *-weighted gradient echo sequence.</p>

<p><strong>ASSESSMENT: </strong>Bi- and monoexponential R2* relaxometry were measured in the liver using two regions of interest (ROIs) using a nonproprietary software: one encompassing the whole liver parenchyma (ROI-1) and the other only the periphery (ROI-2). These were drawn by a single trained observer. The residuals for each fitting model were estimated. A ratio between the residuals of the mono- and biexponential models was calculated to identify the best fitting model. Patients with 1) residual ratio ≥1.5 and 2) R2* ≥R2* were considered as having a predominant biexponential behavior.</p>

<p><strong>STATISTICAL TESTS: </strong>Nonparametric tests, Bland-Altman plots, linear correlation, intraclass correlation coefficient. Patients were divided according to their LIC into stable (n = 23), mild (n = 58), moderate (n = 61), and severe (n = 39).</p>

<p><strong>RESULTS: </strong>The biexponential model was more suitable for patients with severe iron overload when compared with the other three LIC categories (P &lt; 0.001) for both ROIs. For ROI-1, 37 subjects met criteria for a predominant biexponential behavior. The slow component (5.7%) had a lower fraction than the fast component (94.2%). For ROI-2, 22 subjects met criteria for a predominant biexponential behavior. The slow component (4.7%) had a lower fraction than the fast component (95.2%). The intraobserver variability between both ROIs was excellent.</p>

<p><strong>DATA CONCLUSION: </strong>The biexponential R2* relaxometry model is more suitable in children with severe iron overload.</p>

<p><strong>LEVEL OF EVIDENCE: </strong>3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019.</p>

<p><strong>OBJECTIVE: </strong>To determine the optimal MRI protocol and sequences for liver and cardiac iron estimation in children.</p>

<p><strong>METHODS: </strong>We evaluated patients ≤18 years with cardiac and liver MRIs for iron content estimation. Liver T2 was determined by a third-party company. Cardiac and Liver T2* values were measured by an observer. Liver T2* values were calculated using the available liver parenchyma in the cardiac MRI. Linear correlations and Bland-Altman plots were run between liver T2 and T2*, cardiac T2* values; and liver T2* on dedicated cardiac and liver MRIs.</p>

<p><strong>RESULTS: </strong>139 patients were included. Mean liver T2 and T2* values were 8.6 ± 5.4 ms and 4.5 ± 4.1 ms, respectively. A strong correlation between liver T2 and T2* values was observed (r = 0.96, p &lt; 0.001) with a bias (+4.1 ms). Mean cardiac bright- and dark-blood T2* values were 26.5 ± 12.9 ms and 27.2 ± 11.9 ms, respectively. Cardiac T2* values showed a strong correlation (r = 0.81, p &lt; 0.001) with a low bias (-1.0 ms). The mean liver T2* on liver and cardiac MRIs were 4.9 ± 4.7 ms and 4.6 ± 3.9 ms, respectively. A strong correlation between T2* values was observed (r = 0.96, p &lt; 0.001) with a small bias (-0.2 ms).</p>

<p><strong>CONCLUSION: </strong>MRI protocols for iron concentration in the liver and the heart can be simplified to avoid redundant information and reduce scan time. In most patients, a single breath-hold GRE sequence can be used to evaluate the iron concentration in both the liver and heart.</p>

<p>A 5-year-old male with sickle cell disease presented with pain, dark urine, and fatigue 10 days after a red blood cell (RBC) transfusion. Laboratory evaluation demonstrated severe anemia, blood type O+, and anti-D in the serum. Anti-D in a D+ patient led to RH genotyping, which revealed homozygosity for RHD*DAU4 that encodes partial D antigen. Anti-D in this patient whose RBCs exclusively express partial D caused a delayed hemolytic transfusion reaction after exposure to D+ RBCs. The finding of anti-D in a D+patient should be investigated by molecular methods to help distinguish an alloantibody from an autoantibody.</p>