PHILADELPHIA — The race to find clinical cardiology applications for combined PET/CT technology is officially on, now that the results from the first round of studies have been presented at the annual meeting of the Society of Nuclear Medicine.
Combined PET/CT scanners have stimulated interest in imaging circles by offering clinicians the ability to combine noninvasive assessments of anatomy and function in one imaging session.
Based on the studies presented at the meeting—which showed the technology to be more sensitive at detecting stenotic/ischemic coronary artery disease (CAD) than coronary angiography and proved it useful in usually hard-to-image obese patients—combined PET/CT seems to be living up to all of the excitement the prospect of its use had generated.
In a study of 25 patients with known CAD, researchers at University Hospital Zurich (Switzerland), evaluated the feasibility and image quality of integrated PET/CT to assess coronary anatomy and perfusion.
Patients underwent contrast-enhanced CT angiography with retrospective ECG gating and rest, and adenosine stress myocardial perfusion PET scans using N-13 ammonia. The patients were also assessed by coronary angiography. Six patients already had undergone coronary artery bypass graft procedures. Of note, 22 of the 25 were male.
For each patient, the researchers evaluated a total of 100 segments from four vessels—left main coronary artery, left anterior descending coronary artery, left circumflex artery, and right coronary artery. They also analyzed the 12 bypass grafts. The CT scans take only a few minutes, and the PET scans take about an hour.
With conventional angiography, the researchers found 65 normal vessel segments, compared with 51 normal vessels identified by CT. “A few of the lesions considered as not significant by angiography, revealed ischemia on the PET scan,” said P.T. Siegrist, M.D., of the hospital. Overall PET/CT imaging had a sensitivity of 90% and a specificity of 98%.
The researchers also compared the decision whether to revascularize based on the PET/CT findings to the clinical decision for revascularization obtained by using PET alone to assess myocardial perfusion and coronary angiography to assess anatomy. Only the combination of a stenotic lesion and ischemia prompted a decision to revascularize.
With conventional angiography, 11 vessel segments qualified for revascularization. Likewise, PET/CT identified 11 vessel segments that qualified for revascularization. “We found excellent agreement [between] two techniques for determining whether revascularization was needed or not,” Dr. Siegrist said.
The study was funded in part by GE Medical Systems and Amersham Health.
In a similar study, researchers at Brigham and Women's Hospital in Boston combined rubidium-82 PET scans to assess myocardial perfusion and CT to assess anatomy in patients known or suspected of having CAD.
Marcelo F. Di Carli, M.D., and his colleagues from Brigham and Women's Hospital, Boston, performed gated rest/stress 82Rb PET/CT myocardial perfusion imaging on 94 consecutive patients (41 women) with known (21 patients) or suspected (73 patients) CAD. Stress imaging was performed with dipyridamole, adenosine, or dobutamine infusions. The studies were completed in about 45 minutes.
Most patients were overweight or obese, with an average body mass index of 30. In spite of this, the image quality was very good or excellent for all of the patients. In all, 38 patients were found to have abnormal myocardial perfusion, and 2 patients had probable myocardial perfusion abnormalities. Myocardial perfusion was normal in 53 patients and probably normal in 1 patient, Dr. Di Carli said.
PET/CT assessment of myocardial perfusion using