Siemens speeds PET/CT exams with extended field-of-view

June 12, 2006

In some cases more is, simply, more. Siemens’ decision to add crystal to build out the detector ring on its PET/CT scanner increases axial coverage by 33%, according to the company. The result is a jump in photon detection of 78%, which translates into faster scan times or higher quality images.

In some cases more is, simply, more. Siemens' decision to add crystal to build out the detector ring on its PET/CT scanner increases axial coverage by 33%, according to the company. The result is a jump in photon detection of 78%, which translates into faster scan times or higher quality images.

Improvements in speed and image quality result directly from the fewer bed positions needed to conduct a scan. The fewer bed positions, or stopping points along the body where data are acquired, the less time needed to complete a scan. This relates to increased patient comfort and decreased patient movement, which by themselves can produce better images, particularly with patients who have difficulty holding still for very long.

Alternatively, the scan time might remain the same, but the time at each bed position might be lengthened compared to traditional protocols, thereby increasing the number of counts and improving image quality.

A third element might be added to the equation: the dose of radiotracer. Optimizing photon count, bed position count, and radiotracer dose can translate into reduced patient radiation dose. Siemens executives believe dose might be reduced by as much as 50%.

"We can reduce the dose, we can increase throughput, and we can create and produce great images," said Michael Reiterman, president of Siemens Molecular Imaging.

To further optimize the process, Biograph TruePoint PET/CT automatically adjusts reconstruction and scatter correction algorithms to match the patient habitus.

The added performance possible with this latest scanner, which began shipping commercially last week, comes at a higher price to the customer. Exactly how much higher, Siemens is not willing to say. The clinical value, however, may be worth it.

Guests last week at a Siemens' educational forum in San Diego got a glimpse of what Siemens' Biograph TruePoint could mean in a clinical setting. PET/CT pioneer David Townsend, Ph.D., a professor of medicine and radiology at the University of Tennessee Medical Center in Knoxville, presented a technical explanation and case studies demonstrating how the extended field-of-view affects patient management.

The Biograph TruePoint has scanned more than 360 patients since it became operational at the UT in late February. The system, like others now rolling off Siemens' production line, features a new gantry and detector mounting design. The detector's four rings extend 21.6 cm, producing 32,448 individual pixels. The 33% increase in crystal material produces a 77% increase in sensitivity, according to Townsend.

The higher sensitivity leads to shorter scanning times per bed positions, because the detector records more photon counts. The larger axial field-of-view requires fewer bed positions to cover the same distance along the patient's length, reducing imaging time or dose.

"So now if we do the imaging (from neck to knee), we can cover the same axial field of view (as before) in four bed positions for a total time of eight minutes," Townsend said. "This reduces scan time by a factor of two, which can be traded for a factor-of-two reduction in dose."

Melanoma scans are possible now from head to toe in less than 25 minutes. Scans from neck to knee take much less time. Townsend described the case of a breast cancer patient who was initially scanned with an older generation system that required a scan time of 28 minutes for seven bed positions, each lasting four minutes. With Biograph TruePoint, the same quality scan was done in 15 minutes, with five bed positions lasting three minutes each.

Townsend reported on studies conducted at five and 10 minutes that produced diagnostically equivalent information. Comparisons of scans done at 2.5 minutes and 15 minutes showed no diagnostic difference, he said.

Biograph TruePoint performs well with the most challenging patients. Townsend reported a case involving a 267-pound patient who was imaged in 12 minutes using two-minute-per-bed-position scans over six positions. The short scan was particularly important in this case, as the patient suffered from claustrophobia.

"It produced a diagnostically satisfactory study that would not have been possible with older systems," Townsend said.

When scans extend as long as traditional studies, the detail is striking. Townsend showed images of a lung cancer patient examined for 20 minutes using four bed positions each lasting five minutes. The structure of the kidneys was clearly evident. Even shorter scans, such as a 10-minute study - two minutes each for five bed positions - generated extraordinary delineation of the spine.

"The scan quality we are getting is unparalleled," he said.