Quantitative susceptibility mapping shows lower brain iron content in children with attention‐deficit hyperactivity disorder

Abstract To investigate the feasibility of quantitative susceptibility mapping in children with attention‐deficit hyperactivity disorder (ADHD), 53 children with ADHD aged 5–16 years were prospectively selected as the study group and 49 healthy children matched with age and gender were selected as the control group. All children underwent magnetic resonance imaging conventional sequence, 3D‐T1, and enhanced T2*‐weighted magnetic resonance angiography (ESWAN) sequence scanning. The iron content of brain regions was obtained through software postprocessing, and the iron content of brain regions of children with ADHD and healthy children was compared and analyzed to find out the characteristics of the iron content of brain regions of children with ADHD. The iron content in frontal lobe, globus pallidus, caudate nucleus, substantia nigra, putamen, and hippocampus of children with ADHD was lower than that of healthy children (p < .05). There was no significant difference in the content of iron in the left and right brain regions of children with ADHD (p > .05). The volume of frontal lobe and hippocampus of children with ADHD was lower than that of healthy children (p < .05). Iron content in brain areas such as globus pallidus, caudate nucleus, hippocampus, and putamen could distinguish children with ADHD (Area under curve [AUC] > 0.5, p < .05). Quantitative susceptibility mapping showed decreased iron content in some brain regions of children with ADHD.

various behavioral problems such as learning difficulties, emotional disorders, and tic disorders, which seriously affect the academic and emotional development of children and adolescents, and have a great impact on family relations, partnership, and social function establishment (Aricò, Arigliani, Giannotti, & Romani, 2020;Becker, 2020;Craig, Bondi, O'Donnell, Pepler, & Weiss, 2020;Drechsler et al., 2020); Hoogman, Stolte, Baas, & Kroesbergen, 2020;Montagna et al., 2020;Slobodin & Masalha, 2020;Turan, Tunctürk, Çıray, Halaç, & Ermiş, 2021. ADHD is a multifactorial disease, which is related to nerve development, accumulation or lack of trace elements, and some factors have not been identified. For example, in recent years, researchers have found that the content of trace element iron in children with ADHD is lower than that in healthy children, but we do not know whether the decrease of trace element iron content leads to the decrease of iron content in brain area of children with ADHD (Doom et al., 2018;Lopez et al., 2019;Robberecht, Verlaet, Breynaert, De Bruyne, & Hermans, 2020;Wang, Huang, Zhang, Qu, & Mu, 2017)?
Iron deficiency in the brain region can lead to hyperactivity symptoms such as mental laxity, irritability, and memory loss in the affected children (Arisaka, Ichikawa, Imataka, Koyama, & Sairenchi, 2020;Thirupathi & Chang, 2019;Vallée, 2017;Yu & Chang, 2019). How to accurately detect iron deficiency in the brain region of children with ADHD at an early stage by new technology so that they can be treated in time is one of the research hotspots for medical professionals.
Quantitative susceptibility mapping (QSM) is a new technology developed on the basis of susceptibility weighted Imaging in recent years to quantify the susceptibility distribution in biological tissues, and it uses magnetic resonance imaging phase information to detect magnetic sensitive substances and quantitatively calculate the magnetic susceptibility value of the substances. QSM technology can detect tiny changes in iron content in the brain, and has good specificity for spatial image comparison, with high sensitivity and reliability (Au et al., 2020;Tang et al., 2021;Uchida et al., 2019;Vinayagamani et al., 2020).
In this study, iron content values in each brain region of children were obtained by QSM technology, and iron content values in each brain region of children with ADHD and healthy children were compared and analyzed; the differences of iron content in each brain area of children with ADHD and healthy children were found, so as to accurately identify the characteristics of iron content in brain area of children with ADHD as soon as possible, so that it can be timely diagnosed and reasonably treated, improve the severity of children with ADHD's disease, and reduce the burden of family and society.

| MATERIALS AND METHODS
This study was approved by the Ethics Committee of Children's Hospital Affiliated to Chongqing Medical University (NO. 2019-221), and the family members of the study children signed an informed consent form before the examination.

| Patient information
Study group: prospectively selected 68 children with ADHD from January 2020 to May 2021, and 53 children with ADHD were included in the study. Control group: prospectively selected 61 healthy children aged 5-16 years from February 2020 to June 2021, and 49 children were included in the study. Children who were not included in the study had abnormal brain lesions or did not cooperate with the sedation of the children, which caused the images to have motion artifacts.
Inclusion criteria for children in the control group: Children's body mass index is between 15 and 18 kg/m 2 ; right-handed, no neurological disease, no other organ-related diseases, no other diseases that may affect brain function and structure, normal range of iron trace element detection in serum (6.5-9.85 μmol/L), there were no abnormal children in the routine head magnetic resonance examination. All the children who did not cooperate with the examination were sent to the sedation center of our hospital for examination after sedation. The sedation method was: taking dexamex 3 μg/kg nasal drop + chloral hydrate 40 mg/kg orally, and 20 min later, if the sedation depth was not enough, taking dexamex 1 μg/kg nasal drops again, and taking chloral hydrate 20 mg/kg orally if necessary. In order to calculate the volume of different brain regions, QSM values, we adopted the voxel-based morphometry (VBM) method. On the MATLAB 2018a platform, we use SPM12 software (http://www. fil.ion.ucl.ac.uk/spm/) to register the 3D-T1 sequence structure map with the QSM quantitative map, and use the CAT12 toolkit (http:// www.neuro.uni-jena.de/cat/) in the SPM12 software to segment the registered QSM structural quantitative map and, finally, extract each brain parameter values and iron content values ( Figure 1).

| Statistical analysis
Using SPSS 25.0 statistical software, measurement data are expressed as x AE s. The chi-square test was used to compare the gender of children in the study group and the control group. Two independent samples t test was used to compare the age, weight, Body Mass Index (BMI) value, trace element iron detection value of the study group and the control group. Two independent samples t test was used to compare the brain volume of children between the study group and the control group (p < .05 means the difference is statistically significant). An analysis of covariance was performed using age as a covariate to compare the iron content in the brains of children in the study and control groups. The receiver operating characteristic curve (ROC) analysis is used to evaluate the diagnostic value of brain iron content in the diagnosis of children with ADHD. When the AUC is greater than 0.5 and statistically significant, it is considered to be of diagnostic value. The closer the value is to 1, the higher the diagnostic value.

| Comparison results of patient information
There was no significant difference between the study group and the control group in age, gender, weight, BMI value, and trace iron detection value (p > .05) ( Table 1).

| Comparison results of brain iron content values
The iron content (total iron content in left and right brain regions)of the frontal lobe, globus pallidus, caudate nucleus, substantia nigra, putamen, hippocampus, and other brain regions of children with ADHD was lower than that of healthy children (p < .05); the difference in iron content between the left and right brain regions of children with ADHD was not statistically significant (p > .05); the brain total iron content of children with ADHD is lower than that of healthy children (p < .05) (Tables 2 and 3).

| Brain volume comparison results
The brain areas of the frontal lobe and hippocampus of children with ADHD are lower than healthy children (p < .05); the total brain  volume of children with ADHD is lower than that of healthy children (p < .05) (Table 4).

| ROC analysis results
The iron content of the brain regions such as globus pallidus, caudate nucleus, hippocampus, and putamen can distinguish children with ADHD (AUC > 0. 5, p < .05), and the hippocampus AUC (0.881) value is the highest (Figure 2; Table 5).

| DISCUSSION
Brain basal ganglia is an important neurological function area, which is closely related to sensory, motor, visual, and behavioral functions, and the basal ganglia is located in the deep part of the brain, where nerve cells are concentrated, mainly composing the caudate nucleus and putamen, globus pallidus, substantia nigra, etc.
These neural structure and brain cortex and cerebellum common  Note: An analysis of covariance was performed using age as a covariate to compare the iron content in the brains of children in the study and control groups (a corrected αlevel was taken to control for a total FDR less than 0.05, the number of comparisons was 9, and α' was set at .05/9 = .0056, that is, a p value less than .0056 was considered a statistically significant difference).
The results show that the iron content in hippocampus of children with ADHD is lower than that of healthy children, the decrease of iron content may lead to abnormal hippocampal development, and ultimately lead to the abnormal mental activity of children with ADHD.
The results of the study found that children with ADHD only have abnormal brain areas such as the frontal lobe and hippocampus (lower than healthy children), but the areas with abnormal iron content include the frontal lobe, globus pallidus, caudate nucleus, substantia nigra, putamen, hippocampus, and other brain areas. The number of brain areas with abnormal iron content is more than the number of brain areas with abnormal volume, which means that abnormal brain areas in children with ADHD may not cause abnormal brain areas. The frontal lobe, hippocampus, and other brain regions of children with ADHD are lower than healthy children, which may be caused by the backward development of the frontal lobe, hippocampus, and other brain regions of children with ADHD than healthy children.
The results of the study found reduced iron content in frontal, temporal, and basal ganglia brain regions in children with ADHD, along with abnormalities in the volume of frontal and hippocampal brain regions (lower than healthy children), which is consistent with the findings of Chen et al. (lower brain volume in children with HDAD than healthy children) (Chen, Su, et al., 2021;Chen, Soldan, et al., 2021;Shi et al., 2021), suggesting that the reduced volume of frontal and hippocampal brain regions may be due to decreased iron content in brain regions (reduced iron content in brain regions leads to abnormal development of nerve cells in brain regions, and abnormal development of nerve cells leads to delayed development of brain regions, which eventually leads to decreased volume of brain regions).
The normal volume of the basal ganglia brain regions and the decrease in the volume of the frontal and temporal lobes and other brain regions may be due to the fact that the frontal and temporal lobes and other brain regions are larger and developing faster in children, and the decrease in iron content leads to a delay in the development of the brain regions, which eventually leads to a significant decrease in the volume of the brain regions. The basal ganglia brain regions are normal in volume, probably because of their small size and early development (the child's brain develops from the bottom up, from the inside out, and from the back to the front). These brain regions (e.g., the nucleus accumbens, pallidum, etc.) do not change much in volume as children get older. Although decreased iron levels in these brain regions can lead to delayed development of brain regions, the T A B L E 3 Iron content of brain regions in children [x ± s, ppb (Â10 À9 )] differences are not significant compared to healthy children because of their small size. This ultimately resulted in a statistically insignificant difference in the volume of basal ganglia brain regions between children with ADHD and healthy children.
The results of the study found that the brain volume and iron content of the left and right sides of the children with ADHD were not statistically significant, suggesting that the abnormalities of the brain areas of the children with ADHD are symmetrical changes. The results of the study showed that the iron content of certain brain regions of children with ADHD was reduced, but the trace element iron test results were within the normal range, suggesting that changes in the iron content of the brain regions of ADHD may be more sensitive.
The results of the study in Figure 2 and Table 5 show that the iron content of brain regions such as globus pallidus, caudate nucleus, hippocampus and putamen can distinguish children with ADHD (AUC > 0.5, p < .05). Therefore, these brain regions can be used as the brains of children with ADHD key brain areas for imaging diagnosis.

| Limitations of this study
This study is a single-center study, and the results may be regional to some extent; fewer children with ADHD were included in the study, which may have some limitations, most of the children with ADHD included in this study were first-time visitors to our psychology F I G U R E 2 ROC curve analysis results of iron content in brain regions. department and had not taken medication for psychiatric disorders, and only five children had been taking psychotropic medication for 1-3 months. The above deficiencies need to be further improved in the future research.
In conclusion, QSM technology can show reduced iron content in some brain regions of children with ADHD, which can distinguish children with ADHD and contribute to the diagnosis of children with ADHD.

ACKNOWLEDGMENTS
The authors would like to thank "Lisha Nie (GE Healthcare, MR Research China, Beijing)" for providing software support.

TRIAL REGISTRATION
This study protocol was registered at the Chinese clinical trial registry (ChiCTR2100046616).