Siemens Raises Resolution Bar in PET-, SPECT-CT
Today, Siemens Healthcare announced the development of two new hybrid scanners—one FDA approved, one pending 510K approval—that could potentially put to rest forever the “abominable-snowman” aspect of nuclear imaging. xPECTThe FDA-approved Biograph mCT Flow and FlowMotion employs a continuous table motion rather than the standard step-and-shoot technique, enabling the continuous acquisition of data. This advance offers several advantages, according to Kirk A. Frey, MD, PhD, chief of division of nuclear medicine at the University of Michigan Hospitals, where the scanner is deployed. During a press conference earlier today, Frey offered the example of the protocol for a head/neck PET-CT examination: He begins the scan with relatively slow table motion, which allows additional counts and enables the reconstruction of images with greater spatial resolution over the primary area of interest, speeding up the movement over the abdomen/pelvis, and further picking up speed over the proximal areas. In addition to offering organ-specific signal acquisition flexibility, the scanner continuously gathers signal from the isotope rather than stopping and imaging from designated stations, improving resolution at the edges where lesions previously may have been “lost in the noise,” Frey says. “The edges were under-sampled,” Frey says. “Flow motion puts the center of scan view from top to bottom, so there are no longer these areas fraught with noise.” James Williams, MD, CEO, Siemens Molecular Imaging, attributed the continuous-acquisition innovation to several factors, explaining that the mechanical stability of the table has to be good enough to support continuous movement without sacrificing spatial resolution. "This is no mean feat,” he says. “It also required a lot more processing bandwidth, [as well as] rethinking how we think about PET-CT reconstruction.” Rather than compress scan time, Frey has used the technology in practice to tailor the exam to the needs of each patient. “Our approach has been to keep image acquisition time relatively consistent, but to reallocate time on areas where the yield will be more important. The main impact is better matching of time over organs, rather than an acceleration of overall time.” One SPECT-CT Data Set Jerry Froelich, MD, FACR, director of nuclear medicine and molecular imaging, University of Minnesota, was also on hand during the press conference to share his experience with the second scanner, the xSpect Symbia Intevo, pending 501K approval. “If we look at the background of bone imaging, our focus to date has been bone,” Froelich said of the SPECT-CT standard of care. CT provided location, but mechanical registration frequently resulted in misregistration, with little ability to use the structural data inherent in the CT data set, he said. With xSpect, Siemens merges the two datasets into one. “We take the CT data and SPECT data, and in the process of reconstruction, we actually merge the data,” Froelich explains. “This allows us to move the SPECT data to the resolution of CT and create one dataset. We can actually produce quantification.” Froelich says the potential for SPECT using the new technology is “phenomenal,” and although the focus has been on bone to date, other applications will be developed, perhaps even resulting in the retrieval of some abandoned isotopes from mothballs. “I think the opportunities are endless,” he stated. Williams said he expects both scanners to be available in 2013.