SPECT/CT Tracks Stem Cell Migration

Scientists are utilizing a noninvasive fusion imaging method, single photon emission computed tomography (SPECT)/CT, to accurately track stem cells' destinations after being injected into the body to treat hearts damaged by myocardial infarction in animal models.

In the study, investigators from the department of radiology and the Institute of Cell Engineering at Johns Hopkins University (Baltimore, MD, USA; www.jhu.edu), surgically induced heart attacks in seven dogs, six of which later received mesenchymal stem cells (MSCs) labeled with a radioactive tracer and magnetic resonance imaging (MRI) contrast agent to enhance image quality. Both the contrast agent and tracer are extensively used in both research and routine clinical practice.

The internal distribution of the injected stem cells was monitored with SPECT/CT and MRI scanners immediately after injection as well as at multiple time points over seven days to assess whether the MSCs preferentially migrated or targeted in on injured cardiac tissue. Earlier studies in animals were only able to demonstrate targeting by examining the tissue microscopically after death.

The team's findings, published in the September 6, 2005, issue of the journal Circulation, revealed redistribution of the radiolabeled MSCs from the initial localization in the lungs to the target organ, the heart, at 24 hours post-injection. Furthermore, the cells remained visible in SPECT/CT images until seven days after the injection. Combining the two techniques, SPECT and CT, greatly enhanced anatomic mapping and localization, allowing scientists to know more precisely what cells or organs were taking up the radiolabeled tracer.

SPECT/CT also showed redistribution of the MSCs to nontargeted organs, such as the spleen, liver, and kidney. Measuring the radiation levels in tissues obtained from the animals after their death confirmed these findings. MRI, because of its lower sensitivity, was unable to demonstrate targeted cardiac localization of MSCs.

"Our study demonstrates that SPECT/CT imaging is well-suited to dynamically track the biodistribution and movement of stem cells to both target and nontarget organs,” said lead investigator Dr. Dara L. Kraitchman, associate professor of radiology in the Russell H. Morgan Department of Radiology and Radiological Science at John Hospkins. "Such a noninvasive means of studying stem cell movement could be very helpful in monitoring therapeutic safety and efficacy in clinical trials.” Dr. Kraitchman reported that she and coworkers predict that this method will be useful in developing tailored therapies for future patient trials.