Models based on the past can be helpful when trying to predict the future. So it has been with SPECT/CT. When vendors began pushing these hybrids five years ago, it was easy to see a bright future ahead.
Only a few years earlier, the combination of PET/CT had taken the marketplace by storm, igniting clinical interest in positron imaging after decades of neglect. Worldwide PET installations, numbered in tens during the late 1990s, leapt into the hundreds and then thousands. Who knew?
For years, we had thought the need for cyclotrons nearby to create fluorine-18 isotopes for the labeling of sugar molecules limited this modality to academic centers. But suddenly, almost miraculously, following the addition of CT, PET took off. Was it really so farfetched in 2004 to believe the same would happen to nuclear medicine, whose gamma cameras had been steadily declining in unit sales since the 1980s?
Expectations were high when Siemens and Philips took the plunge in 2005 and introduced the first clinical SPECT/CTs. GE had been on the market for years with a SPECT combined with a low-power, nondiagnostic CT, one with such poor performance that the CT component was used primarily for attenuation correction. Siemens and Philips execs believed the time was right for CT to supercharge SPECT, as it had done to PET. But there was a problem.
Looking back on this phenomenon, it’s apparent that there was more to the PET/CT boom than just the addition of anatomical imaging. The PET community had long been chipping away at the regulatory issues that had hamstrung the making of F-18, finally getting the FDA to ease its rules and allow broader production. The logistics of getting F-18 to PET scanners became simpler with the growth of distribution networks formed around cyclotrons strategically brought online to supply expanding clusters of PET/CTs. But it was a change in Medicare reimbursement that made all this possible and laid the groundwork for widespread payment for PET imaging.
Contrast this with what is going on now in nuclear medicine, and we see how the model of adding CT to SPECT falls short. Reimbursement is not growing, and the supply of technetium, the isotope most used in nuclear medicine, is shrinking rather than expanding, due to the instability of molybdenum suppliers.
And, whereas the majority of PET/CT applications are in oncology and only a few in cardiology, the picture is reversed in SPECT. The SPECT/CT hybrids are of limited use in nuclear cardiology unless the CT component can generate 64-plus slices, and such configurations are well beyond the budgets of most cardiology departments.
This is not to say that SPECT/CT is doomed. It has, in fact, begun to catch on. Siemens reports that its SPECT/CT sales were more than half of all its SPECT sales in the most recent quarter. But these are worldwide numbers that include sales in Europe, where cardiological applications are much fewer than in the U.S. The split in the U.S. between SPECT only and SPECT/CT sales, according to an industry source, is more in the range of 75:25, with SPECT a lopsided victor.
While SPECT/CT has a bright future, it will not be anywhere near as bright as PET/CT, as the growth of SPECT/CT will follow a much different path.
