4D PET/CT Could Produce Inaccurate Tumor Imaging Unless Patient's Respiratory Pattern Highly Stable

Nongated PET imaging with 4D computed tomography (CT) may be useful for imaging patients who do not benefit from the use of respiratory gating, most notably patients with erratic breathing.

"Breathing irregularities can lead to significantly underestimated lesion activity in respiratory-gated PET imaging," said Boon-Keng Teo, PhD, assistant professor of radiation oncology at the University of Pennsylvania (Philadelphia, PA, USA), who presented the findings at SNM's 58th annual meeting, held June 4-8, 2011, in San Antonio, TX, USA. "Nongated PET imaging corrected with 4D CT may be more effective for imaging patients with irregular breathing. This could potentially lead to a more robust and quantitatively accurate reading of active tumors."

Respiratory gating technologies have greatly improved the diagnostic quality of PET imaging, which provides functional images of physiologic processes occurring in the body. Sensors in respiratory gating systems positioned on or around the patient monitor the phase of the breathing cycle. They then transmit data about the patient's breathing to the scanning technology for image processing. Instead of creating one fluid image that shows motion artifacts, respiratory-gated PET imaging is similar to a series of photos taken during different phases of the respiratory cycle that are grouped together to create a series of images corresponding to each phase. The difficulty is that patients with respiratory disease, heart conditions, or other serious disease are likely to be breathing unevenly. Respiratory gating systems are designed to work with normal breathing patterns, but not with irregular respiratory cycles.

Researchers conducted phantom studies to compare respiratory-gated PET imaging with nongated PET imaging corrected with 4D CT. The imaging modality utilizes X-ray technology and complex data processing to produce very high-resolution images of structural anatomy. Phantom studies were performed with inanimate objects and specialized motion devices that move in a controlled manner in order to simulate tumors in respiratory motion. The 4D PET and CT studies were conducted in succession with a hybrid PET/CT system. Various degrees of motion irregularities were simulated to study their impact on the accuracy of 4D PET for suppressing motion artifacts.

The study's findings revealed that nongated PET with 4D CT imaging could be an alternative to respiratory-gated PET imaging for determining tumor activity in patients with highly irregular breathing. These findings could change imaging protocols for patients with uneven breathing and possibly improve overall accuracy of tumor detection, thereby informing clinicians about appropriate treatments and perhaps even surgical planning for better cancer management.

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