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Postcards from
Washington, D.C. Editor’s note: These reports were prepared from press materials distributed at the Society of Nuclear Medicine (SNM) annual meeting last month in Washington, D.C. PET/CT Identifies ‘High-Risk’
Plaque “For the first time, we have shown that we can detect dangerous, high-risk plaque that causes heart attacks and strokes through the use of multidetector computed tomography (CT) imaging and a novel contrast agent,” said James H. Rudd, MD, a cardiologist and scientist with the Imaging Sciences Laboratory at Mount Sinai School of Medicine in New York City. Additionally, researchers combined CT imaging with PET imaging, “providing a new way to determine the amount of inflammation within atherosclerotic plaque and the chances of plaque causing a future heart attack or stroke,” he noted. “Using both imaging techniques together gave more information than using them separately,” Rudd said. “Each technique tells us something different about atherosclerosis,” he said. With CT imaging and N1177 (a nanoparticulate contrast agent used to improve the effectiveness of CT and provided by NanoScan Imaging, LLC), researchers “were able to determine the size of plaque, whether it was causing narrowing of the arteries and whether any inflammatory cells were involved,” said Rudd. “From the PET scan, we got extra information about whether the plaques were dangerous and whether they could lead to problems for patients,” he added. The combined imaging techniques focused “not only on the structure of plaque but also on the underlying molecular biology of the disease in the hope of guiding and monitoring future therapies,” said Rudd. Rudd explained that the Mount Sinai study was performed using an animal model of atherosclerosis that “behaves” like the disease in humans. Additional research needs to be done with heart disease and stroke patients “to see if our approach gives more information than the traditionally used technique of invasive x-ray coronary angiography,” he said. SPECT/CT Fusion Creates Synergy
for Heart Diagnosis “The idea is to combine two different images of the heart obtained by two different techniques: single photon emission computed tomography (SPECT) and cardiac computed tomography (CT) angiography,” said Piotr Slomka, PhD, a research scientist with the Artificial Intelligence in Medicine Program at Cedars Sinai. “By combining the physiological (or functional) images of the blood flow to the heart muscle at stress and at rest with the high-resolution anatomical depiction of coronary arteries and their blockages, we can determine the diagnosis of coronary artery disease more accurately,” Slomka added. Cardiac CT angiography produces details of coronary vessels of the heart. SPECT produces 3-D images of the blood flow to the heart muscle. “These scans are obtained at different times—and even at different locations—but our computer software puts the information together in 3-D,” Slomka explained. “This synergistic integration allows simultaneous analysis of the heart muscle blood flow with a highly accurate image of coronary arteries and their blockages. It eliminates the limitations of imaging with either SPECT or CT alone. “This combination could be accomplished also by specialized hybrid scanners; however, our software approach is more flexible since the combination is required only in a subset of cases. We can use the best possible CT angiography equipment and SPECT at much lower cost than the dedicated combined scanner. In any case, the hybrid scanners would still require software techniques similar to ours due to the heart motion,” he added. “The fusion can be used selectively for the diagnosis of patients who undergo one of the exams (either SPECT or CT angiography) with inconclusive results because there was some difficulty in interpretation. In these difficult cases, a complementary anatomical or physiological scan—and this kind of image integration—helps a physician make a better diagnosis,” said Slomka. He noted that additional research is needed to learn which patients would benefit most from the fusion imaging and automate the software to accurately align the images. Alcohol Injection Helps Manage
Bone Metastases “PEI may be a valuable adjunctive or secondary treatment to radioiodine therapy, and it may contribute to better management of thyroid cancer patients with bone metastasis,” said Kunihiro Nakada, MD, clinical assistant professor in the department of radiology at Hokkaido University Hospital. Reports indicate that this year, approximately 33,550 new cases of thyroid cancer will be diagnosed in the United States, and of those, more than 25,000 will occur in women. Thyroid cancer is a common cause of metastatic bone lesions. “Although thyroid cancer generally has a favorable prognosis, bone metastasis can be hard to be eradicate,” Nakada said. “Although radioiodine therapy and/or surgery are valuable therapeutic strategies, management of bone metastasis has been challenging since it is likely that bone metastasis will show resistance to radioiodine therapy or that a tumor cannot be surgically removed. “Our study is a therapeutic approach to treat metastatic bone tumor from thyroid cancer by injecting absolute ethanol directly into the tumor,” explained Nakada. “Absolute ethanol induces direct necrosis (cell death) of the tissue in the area where it is distributed. Therefore, if absolute ethanol is selectively injected into a malignant tumor, selective destruction of the tumor may be expected.” In the study, 12 patients with radioiodine-ineffective bone metastasis from thyroid cancer underwent PEI. More than 50% reduction in tumor volume was achieved in all study patients. “PEI appears effective in terms of [pain reduction] and tumor size reduction and does not induce significant systemic side effects,” noted Nakada. “In addition, PEI is a feasible treatment for radioiodine-ineffective tumors and has a potential for improving general performance or quality of life for selected patients.” Nakada noted that additional research should be done to optimize treatment, including determining doses of ethanol, number of times PEI sessions should be repeated, how to predict outcome earlier, and what other therapeutic options could be better combined with PEI to enhance efficacy. PET/CT Can Replace or Eliminate
Endoscopy for Crohn’s Patients “Our study is the first one demonstrating the value of PET/CT in Crohn’s disease,” said Roland Hustinx, MD, PhD, head of the nuclear medicine division at the University Hospital of Liège and professor of nuclear medicine at the University of Liège. “PET/CT imaging—with the radiotracer fluorodeoxyglucose or FDG—could be used as a first-step test in patients with clinical or biological signs suggesting active disease,” Hustinx said. “PET/CT can answer the major question: What is the activity of the disease?” Crohn’s disease, an inflammatory bowel disease that can affect the digestive system, has no medical cure, and its causes are unknown. Once the disease begins, it can fluctuate between periods of remission and relapse. During relapses, symptoms—varying in nature, frequency, and intensity—include abdominal pain, diarrhea, and worsening general physical condition. Crohn’s and related diseases most commonly begin during adolescence and early adulthood. “The clinical course of the disease is characterized by a succession of periods of clinical relapses and remissions,” Hustinx said. “Its diagnosis relies on clinical and biological signs (markers of inflammation in the blood) as well as direct examination of the bowel using ileocolonoscopy, an endoscopic examination of the large bowel, where the last part of the small bowel (ileum) is also examined,” added Hustinx. “Endoscopic evaluation—a diagnostic medical procedure in which a small, flexible tube with a light and lens is inserted into the body to assess the interior surfaces of an organ—is the gold standard to answer, ‘What is the activity of this disease?’” Hustinix said. The answer to this question will decide whether the clinician prescribes a treatment likely to be effective but also costly and associated with side effects. “Ileocolonoscopy is invasive, unpleasant for the patient, sometimes incomplete due to unreachable segments, and can only assess mucosal lesions, while the disease may sometimes affect deeper parts of the bowel wall,” he indicated. “The big advantage of PET/CT is that it is noninvasive, simple, fast, and without any side effects. There was no preparation for the patients, except that they fasted for six hours. Each study took less than 20 minutes,” said Hustinx. “If the PET/CT is positive, the doctor should confirm the results using endoscopy. If the PET/CT is negative, there would be no need for the endoscopy, given the high negative predictive value of the technique,” he added. Hustinx noted that in the study, all bowel areas that showed severe endoscopic lesions were also correctly identified with PET/CT, and there were no cases where PET/CT showed normal activity and ileocolonoscopy [showed] active Crohn’s. “PET/CT has, therefore, the potential to deeply modify the exploration algorithm of patients with Crohn’s, reducing the number of endoscopic examinations and allowing a better, noninvasive monitoring of the disease’s activity,” Hustinx said. Hustinix noted that the results need to be confirmed on a larger scale, and his team is currently conducting a study evaluating the capacity of PET/CT to assess patients’ response to biological treatments, which have shown potential for obtaining mucosal healing in Crohn’s disease. “This mucosal healing has been associated with higher sustained quality of life, lower rate of hospitalization, and lower need for surgery,” he said. “A sustained clinical remission—and a control of intestinal lesion—has become the target of new treatment strategies. PET/CT Effectively Diagnoses
Graft Infections “Our pioneering results show that PET/CT imaging has the potential to become a single-step, noninvasive technique for diagnosis of infection with a complex group of patients,” explained Ora Israel, MD, director of nuclear medicine and research operations at Rambam Health Care Campus in Haifa, Israel. “Infected blood vessel grafts, while uncommon, are removed in a complex surgical procedure. Sparing unnecessary high-risk operations in patients, who are often severely debilitated, is of major significance. PET/CT imaging—fluorodeoxyglucose or FDG—can effectively diagnose graft involvement and differentiate it from infection that affects only soft tissue infection in its vicinity.” An infected graft requires surgery to remove the involved implant, while infection of the soft tissues near the graft requires intravenous administration of high doses of antibiotics, Israel noted. She added that diagnosing a prosthetic vascular graft infection can be a clinical challenge, and making the situation even more difficult, early treatment is important due to the relatively high rates of limb damage that can lead to amputation and death. “Blood vessels can be occluded due to disease processes—often as a complication of diabetes—decreasing blood flow to various regions of the body and occurring more commonly in the lower limbs,” Israel said. She said prosthetic grafts are inserted to artificially restore and ensure blood circulation through the obstructed blood vessels to areas that would otherwise suffer from the lack of sufficient blood supply. “Graft infection is an uncommon but potentially severe complication following prosthetic vascular reconstruction,” noted Israel. The overall frequency of this complication ranges between 0.5% to 5% and occurs a few months after surgery. Delay in treatment of an infected vascular graft can lead to life-threatening complications such as sepsis or hemorrhage, with limb amputation and death occurring in more than 50% of patients, she indicated. The clinical presentation is often subtle and nonspecific. “Combined PET/CT, therefore, enables both diagnosis of infection and determination of its precise localization, facilitating the diagnosis and guiding the appropriate treatment strategy,” Israel said. “These initial findings encourage additional investigations on the role of PET/CT in larger patient populations with suspected vascular graft infection. It also opens new options for additional, previously unsought clinical applications for the use of FDG-PET/CT in other infection and inflammation processes.”
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