The ability to acquire functional and anatomic information in a single scheduled exam offers many clinical and workflow benefits. But making the most of a hybrid imaging system involves far more than simply pressing the "on" switch. With the advent of multislice SPECT/CT, radiologists and nuclear medicine physicians are taking a long, hard look at how these systems will fit into clinical practice.
High-resolution CT scanners are becoming commonplace in many nuclear medicine departments. At Miami Baptist Hospital in Florida, for example, nuclear physicians expect to have four diagnostic CT scanners installed by summer, with the addition of two SPECT/CT systems to the two PET/CTs already in place. The experience the department has gained in running a PET/CT service should be useful in slotting SPECT/CT into the workflow, said Dr. Jack Ziffer, the hospital's chief of radiology.
In common with the majority of U.S. institutions, nuclear medicine at Miami Baptist operates within the radiology department. Many members of Ziffer's team hold dual board certification in nuclear medicine and radiology. Because of this dual competence, disputes over reporting competence between nuclear physicians and CT radiologists are less likely to occur. Having one person read the fused scans makes more sense than shuttling images between different doctors, Ziffer said.
Cases in which the CT and nuclear data appear to disagree will benefit most from a reading by one doctor, Ziffer said. Comparison of both image sets by the same physician is also useful when the anatomic and functional images on their own suggest borderline normal findings. Morphing the two can add weight to an all-clear diagnosis.
Departments upgrading from gamma cameras with nondiagnostic CT to systems with diagnostic CT capability should rethink their reporting process, said Dr. Richard Wahl, director of John Hopkins University Medical Center nuclear medicine/PET.
Images acquired on the current breed of single-slice CT scanners, which have slow scan speeds, can be read by most nuclear medicine physicians, he said. Interpretation of 16-slice MSCT data, however, requires a much greater familiarity with cross-sectional anatomy.
"If they are comfortable with anatomic information in the area they are examining and they have sufficient training, then people with nuclear medicine backgrounds are fully capable of interpreting these studies," said Wahl, who holds dual board certification in nuclear medicine and radiology. "But I think it will remain to be seen what the diagnostic requirements of these new hybrid SPECT/CT scanners are."
Turf issues may be more likely to arise in Europe, where nuclear medicine and radiology are generally regarded as separate specialties, and fewer doctors hold dual board certification. The tussle over ownership of SPECT/CT could draw in cardiologists as well, given the likely application of MSCT in myocardial perfusion imaging (see page 38).
The solution lies in collaboration rather than competition among specialists, said Prof. Dr. Torsten Kuwert, chair of nuclear medicine at the University of Erlangen in Germany. The nuclear medicine department at Erlangen began using a multislice SPECT/CT system in April. Although the department includes a number of qualified radiologists, responsibility for the CT portion falls to the institute for Diagnostic Radiology, headed by Prof. Dr. Werner Bautz. The institute's radiologists have real-time access to all CT images acquired on the SPECT/CT system. A written agreement specifies the circumstances under which they should report the CT data.
"If we are performing only a low-dose CT for attenuation correction, and the patient already has a diagnostic CT, then I doubt the radiologists will submit a report of their own," Kuwert said. "But if we perform a contrast-enhanced diagnostic CT, they will do a separate report, and both departments will then produce a joint report. That's the agreement."
Experts agree that combining a gamma camera and a diagnostic CT scanner will not automatically yield improved imaging results. Achieving the best of both worlds may require compromising and altering protocols.
Physiological motion must be taken into account in fusing the SPECT and CT data, even if the patient has remained in the same position for both scans, said Kirk Frey, Ph.D., chief of nuclear medicine and director of PET at the University of Michigan Medical Center.
"If you are doing a maximum inspiration spiral CT of the chest, and then the patient is imaged with SPECT during tidal respiration, the two sets of data will be anatomically discordant," he said. "We need some algorithmic development to decide how best to reconcile the two, particularly in the thorax and upper abdomen, where respiratory motion is likely to produce artifact."
The use of contrast with CT may also have to be reconsidered. Data on the compatibility of oral and intravenous contrast with PET/CT will not necessarily transfer directly to SPECT/CT.
"In single-photon imaging, the artifact from contrast material is likely to be a more severe and serious problem. There will need to be more thought given to when contrast is administered relative to the collection of data and what impact that might have on the quality of the SPECT. For example, we won't be giving dilute oral barium to a bone scan patient prior to SPECT," Frey said.
Certain SPECT exams require the use of iodine radioisotopes. Prior administration of iodinated CT contrast agents should probably be avoided in such cases, and contrast-enhanced CT should be performed later or not at all.
Multislice SPECT/CT could also expand opportunities for entirely new exam protocols through the use of either novel tracers or older probes that were previously deemed too unspecific, said Prof. Ora Israel, director of nuclear medicine at the Rambam Medical Center and Faculty of Medicine in Haifa, Israel.