Philips launches time-of-flight PET/CT at ECR

Philips Medical Systems released the world's first commercial time-of-flight PET/CT system March 3 at the European Congress of Radiology in Vienna. The system, scheduled to begin shipping to sites in Europe and the U.S. in June, will more than double image sensitivity, according to the company, allowing users to either markedly improve image quality or cut scan time by a third or more.

Whole-body PET scans with the Gemini TF (True Flight) will be done in less than 10 minutes, compared with 15 minutes or longer using conventional systems. This will hold true even for obese patients, who generally require additional scan time on conventional systems, said Jim Cavanaugh, director of global marketing for Philips Nuclear Medicine PET/CT.

"We are marketing this system as delivering less than 10-minute whole-body FDG imaging for everybody," he said. "There is no differentiation for large or small patients - that is one of the key features of this product. It helps the clinical workflow, because users don't have to worry about scheduling different time slots depending on patient size."

Alternatively, users of the Gemini TF will have the option to acquire data over the usual time period and generate images with increased sensitivity or specificity, said Piotr Maniawski, Philips senior marketing manager for PET/CT development.

"Those who don't care about time can choose to spend the usual length on a procedure and get a lot better image quality than they can today," he said.

The TF technology has been in beta testing at the University Hospitals of Pennsylvania. Studies there have produced enough data that the Philips team is confident the technology can meet its clinical potential, Cavanaugh said.

With a CE mark and FDA clearance in hand, Philips chose to unveil the product at the ECR, with follow-up showings at Academy of Molecular Imaging and Society of Nuclear Medicine conferences leading up to its routine shipping start in June. Regulatory clearances for Japan and China are expected in the fourth quarter of 2006.

Gemini TF will sit atop the company's PET/CT family in both performance and price, exacting a 20% premium over the Gemini GXL, which only began shipping in June 2005. Initially, the new system will be configured with a 16-slice CT. A 64-slice configuration will be available before the end of this year.

Cavanaugh described the company's latest model as being more than just a time-of-flight system.

"If Siemens and GE come out with time-of-flight systems of their own, ours will still be different in how we implement it," he said.

Gemini TF harnesses a new crystal material, electronics, and advanced reconstruction algorithms to deliver time-of-flight performance. In place of the GSO (gadolinium oxyorthosilicate) crystal built into the Gemini GXL detector, Philips has put a hybridized crystal constructed from lutetium and yttrium oxyorthosilicate, which the company refers to as LYSO.

Vendors for years have traded barbs over whose detector crystal provided the best response and, consequently, which supported the fastest data acquisition. Siemens' LSO and Philips' GSO each rapidly return to a resting state after emitting a flash of light in response to being struck by a high-energy photon, making them ready to emit another flash in about 60 nanoseconds.

Returning to the resting state in a time-of-flight PET/CT, however, is less important than the time needed to generate a flash of light in response to being hit by a gamma ray, the so-called rise time of the crystal. LYSO has a rise time on the order of 650 picoseconds or 650 trillionths of a second.

To fully realize the potential of this crystal, Philips developed improved electronics for recording the flashes and algorithms for processing signals. Time-of-flight PET/CT requires each positron event to be recorded. The detector must record each of the two gamma rays emitted at 180° angles following the annihilation of a positron by an electron. Each pair of gamma rays coming from a single event has a specific timing or position associated with them in the field-of-view. Therefore, they must be recorded as a distinct pair so the location of the annihilation event can be narrowed down.

The electronics involved must be extraordinarily fast. Those built into the Gemini TF sample the detector once every 25 picoseconds. This compares with the previous industry best of 500 picoseconds, according to Cavanaugh.

This sampling rate generates a lot of data, requiring a specially designed computing platform with advanced algorithms. Even so, reconstruction takes about 20 minutes. Fortunately, these calculations can begin when the first event is recorded.

"Because reconstruction can start as soon as the scan, you can effectively schedule patients every 20 minutes," Maniawski said.

The best pace possible on conventional systems is 30 to 45 minutes, Cavanaugh said.

For all its changes, Gemini TF looks on the outside like any other PET/CT in the Gemini portfolio. Like fellow family members, it features the characteristic OpenView gantry design, essentially an open space between the PET and CT. But what's under the covers promises to make a major difference in PE/CT studies.

Trade-offs in time and image quality, along with the algorithms built into Gemini TF, offer the possibility of fine-tuning a scan to meet differing clinical needs. Images can be acquired with the same diagnostic quality as current ones but in a third less time. Or time can be held constant but noise cut in half, while holding contrast resolution at a constant. Alternatively, contrast can be enhanced, while keeping noise at a constant.

If physicians want to use the system to detect absolutely everything, they can create an image with high contrast and a standard amount of noise. If they want to check whether a suspected lesion is, in fact, cancer, they can choose a less noisy image with lower contrast to visualize only the larger, more aggressive tumors.

"It is all a trade-off between specificity and sensitivity," Cavanaugh said. "It is really how the user wants the system to perform."