MRI Detects Brain Volume Changes in Opioid Users

Researchers at the Yale School of Medicine used MRI and fMRI to detect structural and functional alterations in specific brain regions of individuals with opioid use disorder, according to the study's results published in Radiology.

Opioids are a class of drugs that include synthetic opioids such as fentanyl, prescription pain relievers like oxycodone, and illegal narcotics, including heroin. Opioids have a high potential for misuse, and opioid use is a major contributor to drug overdoses in the US.

According to the National Institute on Drug Abuse, in 2021, approximately 2.5 million adults in the US had opioid use disorder. Provisional data from Centers for Disease Control and Prevention's National Center for Health Statistics indicate there were an estimated 81,083 overdose deaths involving opioids in the US during 2023.

"We are in the midst of an opioid epidemic, with millions affected worldwide and more than 80,000 deaths related to opioid overdoses in the US last year alone," said Saloni Mehta, MBBS, postdoctoral associate in the Department of Radiology and Biomedical Imaging at the Yale School of Medicine. "We need to get a better understanding of the system-level neural alterations associated with opioid use disorder."

In the study, Dr. Mehta and colleagues conducted a secondary analysis of data from the National Institutes of Health-funded Collaboration Linking Opioid Use Disorder and Sleep Study (CLOUDS), comparing participants with opioid use disorder on methadone treatment and healthy controls. The data included structural MRI and functional MRI (fMRI) exams performed between February 2021 and May 2023.

Resting state fMRI allows researchers to measure brain activity by detecting changes in blood flow. With resting state fMRI, the connectivity between neural regions—known as resting state networks—can be observed while the brain is at rest.

Researchers analyzed CLOUDS structural MRI data for 103 individuals with opioid use disorder and 105 individuals from the control group. They also analyzed the resting state fMRI data on 74 participants with opioid use disorder and 100 controls. The individuals with opioid use disorder were all recently stabilized with medication for the disorder (less than 24 weeks). The median age in the group with opioid use disorder was 37 years, and 40% were women. In the control group, the median age was 27 years, and 55% were women.

"Previous studies have been performed on small sample sizes, many of which included no women," Dr. Mehta said. "Ours is a moderate sample size, approximately half of which is female."

Whole-brain analysis revealed structural and functional alterations in opioid receptor-dense regions in the opioid use disorder group compared to healthy controls. In individuals with opioid use disorder, the thalamus and right medial temporal lobe of the brain were smaller in volume, while the cerebellum and brainstem were larger in volume than in controls. In the individuals with opioid use disorder, all these brain regions also had increased functional connectivity compared to controls.

"We observed widespread increases in global connectivity in individuals with opioid use disorder," Dr. Mehta said. "Our goal is to understand better what could have caused these alterations to inform new treatment targets."

The results also revealed that women in the group with opioid use disorder had smaller medial prefrontal cortex volume, compared to males in the same group.

"We found that alteration patterns in the medial prefrontal cortex—a core region involved in many mental health conditions—were different between men and women in the group with opioid use disorder," Dr. Mehta said. "This highlights the importance of assessing sex differences in opioid use disorder neuroimaging studies."

Dr. Mehta said the study builds a foundation for future research to investigate potential behavioral implications of these brain differences and whether they are permanent.

"Our eventual goal is to examine how brain alterations in individuals with opioid use disorder may be linked to outcome measures," she said.