Total-Body PET/CT Plus Innovative Image Reconstruction Yields Clear Cardiac Cycle Images

A total-body PET/CT scanner paired with an advanced sub-second molecular image technique can enable real-time blood-flow tracking and motion-frozen imaging of cardiovascular and respiratory functions, according to newly published research.

The findings, supported by funding from the National Institutes of Health and University of California Davis Innovative Development Award, were published in the Jan. 20 edition of the Proceedings of the National Academy of Sciences.

Investigators, led by UC-Davis project scientist Xuezhu Zhang, developed a 194-cm long total-body EXPLORER scanner, a three-dimensional medical imaging device that covers the entire body at once, allowing for simultaneous dynamic imaging of multiple organs with significantly higher sensitivity. They combined the machine with an innovative image reconstruction method called kernel expectation maximization.

“High temporal resolution PET is useful for studying blood flow, transit times, and fast radiotracer dynamics,” Zhang wrote. “It can also be used to freeze subject motion, either physiological, such as cardiac and respiratory motion, or involuntary body motion, thereby improving the effective spatial resolution of reconstructed images.”

The cardiac and respiratory motion captured in these PET images can also provide information for evaluating the biomechanical properties of various organs, he said. Study findings indicate combining the scanner and the reconstruction method allows for good-quality dynamic PET images at 100-ms temporal resolution.

For the study, researchers intravenously injected 256 MBq of ₁₈F-fluorodeoxyglucose into the right leg of a healthy 60-year-old woman before conducting a 60-minute total-body dynamic scan. They divided the first-minute data into 100-ms temporal frames and analyzed reconstructed images in order to demonstrate the high temporal resolution of this method for capturing fast tracer dynamics and real-time cardiac motion.

Reconstructed dynamic PET image analysis revealed good image quality even though there were fewer than 1 million true coincident events in each temporal frame. The 100-ms dynamic PET images identified cardiac blood pool changes effectively throughout the cardiac cycle with a clear delineation of the end-systolic and end-diastolic phases. The images also clearly showed the flow of the radiotracer with each contraction of the heart.

In addition, investigators compared images of four regions of interest – the left ventricle, ascending aorta, descending aorta, and myocardium – gathered by both a standard whole-body scanner and dynamic PET imaging. Results indicated dynamic PET imaging provided better results.

Existing imaging systems, including angiography, CT, MRI, and ultrasound, can offer fast imaging and specific anatomical information, but none offer real-time molecular imaging of physiology and biochemistry with total-body coverage, Zhang said.

Ultimately, this imaging technique could offer improved imaging in other areas, as well.

“This high-temporal resolution tracer imaging technique opens up the opportunity for new applications, such as studying fast pharmacodynamics, using shorter-lived radionuclides, and performing motion-frozen scans of the heart, lung, and gastrointestinal tract,” he wrote.

Additionally, he said, PET with high temporal resolution has potential applications in pinpointing normal and abnormal brain functions by directly measuring the absolute value of cerebral blood flow and cerebral metabolic rate of oxygen.