Image: Medication-naïve ADHD patients (ADHD-nonmedicated) have reduced striatal (putamen (PUT), caudate nucleus (CN)) and thalamic (THL) magnetic field correlation (MFC) measures of brain iron compared to controls and psychostimulant medicated ADHD patients (ADHD-medicated); Brain iron measures in PUT, CN, THL or globus pallidus (GP) did not differ between controls and psychostimulant medicated ADHD patients. These statistical significant differences are visible in the MFC group maps (top row) but not in conventional relaxation rate maps: R2 (second row), R2*(third row), and R2\' (bottom row) (Photo courtesy of RSNA).
Image: Photograph of a Siemens Healthcare (Erlangen, Germany) Magnetom Trio MRI scanner (Photo courtesy of RSNA).
A new magnetic resonance imaging (MRI) technique offers a noninvasive way to measure iron levels in the brains of individuals with attention deficit hyperactivity disorder (ADHD).
The new findings were presented December 2013 at the annual meeting of the Radiological Society of North America (RSNA), held in Chicago (IL, USA). Researchers reported that the imaging technology could help physicians and parents make better informed decisions about medication.
ADHD is a common disorder in children and adolescents that can continue into adulthood. Symptoms include hyperactivity and difficulty staying focused, paying attention, and controlling behavior. The American Psychiatric Association reports that ADHD affects 3%–7% of school-age children.
Psychostimulant drugs such as Ritalin are among the drugs typical used to decrease ADHD symptoms. Psychostimulants affect levels of dopamine, a neurotransmitter in the brain associated with addiction. “Studies show that psychostimulant drugs increase dopamine levels and help the kids that we suspect have lower dopamine levels,” said Vitria Adisetiyo, PhD, postdoctoral research fellow at the Medical University of South Carolina (Charleston, SC, USA). “As brain iron is required for dopamine synthesis, assessment of iron levels with MRI may provide a noninvasive, indirect measure of dopamine.”
Dr. Adisetiyo and colleagues explored this possibility by measuring brain iron in 22 children and adolescents with ADHD and 27 healthy control children and adolescents employing an MRI technique called magnetic field correlation (MFC) imaging. The technique is comparatively new, having been introduced in 2006 by study coauthors and faculty members Joseph A. Helpern, PhD, and Jens H. Jensen, PhD. “MRI relaxation rates are the more conventional way to measure brain iron, but they are not very specific,” Dr. Adisetiyo said. “We added MFC because it offers more refined specificity.”
The findings demonstrated that the 12 ADHD patients who had never been on medication had substantially lower MFC than the 10 ADHD patients who had been on psychostimulant drugs or the 27 typically developing children and adolescents in the control group. In contrast, no significant group differences were detected using relaxation rates or serum measures. The lower brain iron levels in the nonmedicated group appeared to normalize with psychostimulant medication.
MFC imaging’s ability to identify noninvasively the low iron levels may help improve ADHD diagnosis and guide optimal treatment. Noninvasive techniques are especially important in a pediatric population, Dr. Adisetiyo noted. “This method enables us to exploit inherent biomarkers in the body and indirectly measure dopamine levels without needing any contrast agent,” she said.
If the findings can be repeated in larger studies, then MFC might have a future role in determining which patients would benefit from psychostimulants—an important consideration because the drugs can become addictive in some patients and lead to abuse of other psychostimulant drugs such as cocaine. “It would be beneficial when the psychiatrist is less confident of a diagnosis if you could put a patient in a scanner for 15 minutes and confirm that brain iron is low,” she concluded. “And we could possibly identify kids with normal iron levels who could potentially become addicts.”
Combined with replicating the findings in a larger population of patients, the researchers plan to expand their studies to look at the relationship between cocaine addiction and brain iron.
Medical University of South Carolina