Speaking in a plenary presentation, Kalender, director of the Institute of Medical Physics at the University of Erlangen Nuremberg, Germany, examined the state-of-the-art in X-Ray CT, with a particular focus on future developments. He noted that top-of-the-range systems are now able to perform whole-body CT scans in 10-12 s, and that scanners are continuing to progress from four to 16 to 64 slice.
"The question being asked is 'will this progression continue?'," he told World Congress delegates. "But I would advise everyone to be patient, 64 is fine, we have perfect performance there. Maybe we'll see 128 slice, but it won't keep going." So if further advances won't come from simply continuing to increase the slice number, what will be the next technology innovations to impact this field?
One area to keep a close eye on, said Kalender, is dual-source CT. First introduced in 2005, dual-source CT employs two complete measurement systems that rotate together and enable fast data acquisition. He mentioned Siemens' dual-source Somatom Definition Flash, launched last year. This system can perform thoracic CT in 0.7s, removing the need for breath hold. A cardiac CT scan takes just 0.26s - less than half a heartbeat. "It's important that the scan is taken during one heart beat, and at the minimum radiation dose," Kalender added.
Another advantage of having two X-ray sources is that they can be used at two different tube voltages. This dual-energy CT scanning can differentiate various tissue types and thus provide information as to the composition of the tissue being scanned. Kalender notes that there were 10 dual-energy applications approved by the US Food and Drug Administration in 2007, including, for example, dual-energy cardiac perfusion and direct bone removal. "I think we'll hear quite a bit more about dual-energy in the future," he said.
Elsewhere, Kalender highlighted breast CT as an area showing great potential. While MR imaging is used to help overcome the limitations of standard mammography, CT is also being investigated for this application. He cited the emergence of a dedicated breast CT scanner at the University of California, Davis. Developed in the laboratory of John Boone, initial clinical tests have proved promising.
But with new applications being implemented and approved for clinical use, could the ever-present issue of dose become a consideration? Kalender noted that there are now many, successful ways to reduce the dose to the patient. The real task, however, lies in communicating dose values to the public, who tend to be wary of CT. "These values are no secret, we have good tools to calculate dose," he said.
He quoted that a multislice CT scan delivers an average effective dose per of 10 mSv (calculated in Germany, in 2003). While this compares favourably with the natural background levels of 1-10 mSv/year, the aim is to reduce it further. "These values have to come down, and they will come down," he added.
As for what lies ahead, Kalender is confident that - with its high temporal resolution and short examination times - the technology has a critical role to play. The delivered dose is in the range of natural background radiation, though this still needs to come down further. Diversification, in terms of combination scanners such as PET/CT and SPECT/CT systems, could also be significant. "People think that MR will take over - but I claim that there is a future for CT," he concluded.