CT starts to shape up as nuclear medicine's best friend

June 1, 2005

The marriage between PET and CT worked so well it made CT almost a standard component of any PET purchase. As installations of SPECT/CT begin, observers are waiting to see how this latest hybrid compares.

The marriage between PET and CT worked so well it made CT almost a standard component of any PET purchase. As installations of SPECT/CT begin, observers are waiting to see how this latest hybrid compares.

The concept of combined SPECT/CT units is certainly not new. A hybrid featuring a single-slice CT component has been available since 2000, and more than 450 such systems have been installed to date. The addition of low-resolution nondiagnostic CT to SPECT studies has improved attenuation correction and general localization of pathology.

But the appetite of nuclear physicians and radiologists for greater clarity from SPECT/CT has been whetted by the performance of multislice PET/CT. The latest hybrid SPECT/CT systems come complete with an integrated diagnostic-quality CT scanner. Manufacturers are offering two-, six-, 10-, and 16-slice CT. These new hybrids hold the potential to further improve attenuation correction and precisely correlate SPECT signals with anatomic positions. Combining CT and SPECT studies into a single exam could improve workflow.

Despite the attention lavished on PET and PET/CT over the past few years, SPECT remains the bread and butter of nuclear radiologists' workload. The potential market for SPECT/CT is therefore far larger than that for PET/CT.

"We perform five to 10 times more SPECT than PET in our department," said Prof. Dr. Torsten Kuwert, chair of nuclear medicine at the University of Erlangen in Germany. "If we have a machine that really gives us this predicted jump in diagnostic accuracy, then it will add considerably to the value of SPECT."

The economic arguments are more complex, however. SPECT is a relatively low-cost imaging modality compared with PET. Adding a state-of-the-art CT to SPECT thus multiplies the final purchase price by a far larger factor than adding CT to PET.

A department with a budget to buy a new MSCT scanner, however, may be willing to dig a little deeper and gain functional imaging capabilities. In this case, high-end SPECT/CT could have the edge over PET/CT.

"For the radiologist who is going to buy CT anyway, adding SPECT is an incremental cost on top," said Dr. Stanley Goldsmith, director of nuclear medicine at New York-Presbyterian Hospital/Weill Cornell Medical Center. "It will enable them to do good-quality nuclear medicine whenever they have the need for it, and the rest of the time they can use it as a full diagnostic CT."

The first systems to roll off the production line are being put through their paces at hospitals in Europe and the U.S. More orders are in the pipeline. Only time will tell whether combined SPECT/CT imaging is cost-effective and adds clinical value. But the likelihood is that CT-free SPECT will eventually become part of radiology's history, according to Goldsmith.

"SPECT without hybrid imaging is like reading with one eye closed. Hybrid imaging opens both eyes," he said. "The people who make these scanners may be a little ahead of the curve, but it shows that they are impressed enough with this technique to take the gamble. In the long run, I think they are going to be proved right."

This special section was compiled by Paula Gould, contributing editor of Diagnostic Imaging Europe.