Imaging technique may detect earliest signs of PAH tissue changes
Novel approach may help in monitoring efficacy of PAH-targeted therapies
An imaging technique called 18F-FAPI PET may be able to detect the earliest signs of changes in blood vessel tissues that occur in pulmonary arterial hypertension (PAH), a new study reports.
According to researchers, this novel approach, which uses positron emission tomography or PET imaging, may help healthcare providers to better monitor PAH patients in the clinic.
“18F-FAPI PET could assist clinicians in monitoring the efficacy of PAH-targeted therapies, offering a new tool for personalized medicine,” Xinlu Wang, MD, PhD, study coauthor at the First Affiliated Hospital of Guangzhou Medical University in China, said in a press release.
The study stressed, however, that the data to date are limited, and more research will be needed to validate the utility of 18F-FAPI as a diagnostic test in PAH.
Titled “Targeting Fibroblast Activation Protein for Molecular Imaging of Fibrotic Remodeling in Pulmonary Arterial Hypertension,” the study was published in The Journal of Nuclear Medicine.
New 18F-FAPI PET technique uses PET imaging
PAH is marked by abnormally high pressure in the blood vessels that carry blood from the heart through the lungs. This abnormally high pressure is often associated with tissue remodeling, or tissue changes that cause the blood vessels to get too narrow. A type of cell called fibroblasts is centrally involved in this tissue remodeling.
As of now, the main methods used to diagnose and track PAH are hemodynamics, or measures of blood flow patterns, and echocardiography, which uses sound waves to visualize structures inside the body.
18F-FAPI PET is a new approach that uses PET imaging to track the uptake of a radioactive marker that binds to a protein involved in fibroblast activation — in other words, it aims to detect fibroblast activation. Because fibroblasts are known to be involved in PAH-related tissue remodeling, the team of researchers tested whether 18F-FAPI PET could be used to diagnose PAH.
“We know that during the remodeling process fibroblasts are activated,” said Cheng Hong, MD, PhD, coauthor of the study and a pulmonary vascular medicine specialist at the First Affiliated Hospital. “While PAH has traditionally been evaluated through hemodynamic measurements and echocardiography, my colleagues and I sought to determine if imaging the fibroblast activation protein could predict PAH disease progression.”
The ability to detect fibroblast activation in PAH patients is significant as it could provide an early marker of disease progression, potentially before irreversible structural changes occur.
The team first conducted experiments in rats. They found that 18F-FAPI PET signals were stronger in rats with PAH than in those without the condition, suggesting an accumulation of activated fibroblasts. The increase in 18F-FAPI PET signal was evident in PAH rats before there was an obvious change in hemodynamic measures, the researchers noted.
According to Wang, also a nuclear medicine specialist, “the ability to detect fibroblast activation in PAH patients is significant as it could provide an early marker of disease progression, potentially before irreversible structural changes occur.”
Approach tested first tested in rats, then in humans
The scientists then used the imaging technique to evaluate 38 people with PAH alongside 17 people without the disease. In line with the animal experiments, 18F-FAPI PET signals were stronger in the individuals with PAH. These signals correlated with pulmonary hemodynamic markers among PAH patients, the team also noted.
“These findings indicate that 18F-FAPI PET/CT can noninvasively and quantitatively visualize the fibroblast activation in PAH, offering a novel approach for disease evaluation,” the team wrote.
Five PAH patients had two 18F-FAPI PET scans done several months apart while undergoing treatment for the disease. Three of the patients showed a decrease in 18F-FAPI PET signal, which correlated with a clinical improvement. The other two patients did not show clinical improvement.
“Overall, the trend of 18F-FAPI uptake is consistent with the change of the patient’s condition,” the researchers wrote.
Wang noted that, “after PAH-targeted therapy, the uptake of 18F-FAPI in the right heart and pulmonary artery of patients decreased.” This suggests the “potential reversibility of fibroblast activation in PAH,” Wang added.
Importantly, according to the scientists, these data are limited to a small number of animals and people. As such, further studies are needed to confirm 18F-FAPI’s utility as a diagnostic test for use with PAH patients.
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