W. Burchert

Assessment of myocardial viability by use of 11C-acetate and positron emission tomography : Threshold criteria of reversible dysfunction

BACKGROUND Dual positron emission tomography (PET) imaging with a perfusion tracer and 18F-fluorodeoxyglucose (FDG) can detect myocardial viability. This approach may be replaced by a single 11C-acetate study, which enables quantification of both regional blood flow and oxidative metabolism. The significance of acetate-derived indexes for myocardial viability is examined. METHODS AND RESULTS Thirty postinfarct patients with akinetic ventricular segments, a mean ejection fraction of 42 +/- 11%, and high-grade coronary obstructions were studied with serial 11C-acetate PET scanning before and 7 +/- 5 months after coronary revascularization. Acetate PET was tested against FDG and serial assessments of segmental wall motion. Sixty of 155 severely dysfunctional LV segments improved postoperatively, and regional blood flow increased. Flow estimates after revascularization suggested little fibrosis in reversible segments. At baseline, blood flows differed between normal myocardium, reversible dysfunction, and irreversible dysfunction (1.04 +/- 0.27, 0.73 +/- 0.18, and 0.43 +/- 0.18 mL.min-1.g-1, respectively; P < .001). Oxidative metabolic rates were reduced only in irreversibly injured LV segments. Multivariate analysis identified the acetate perfusion index as the only independent predictor of postoperative recovery. Its predictive accuracy was similar to that of FDG imaging but superior to indexes of flow-metabolic mismatch or oxidative metabolism. CONCLUSIONS After myocardial infarction, quantitative indexes of perfusion and oxidative metabolism from acetate PET indicate a critical threshold beyond which tissue is irreversibly injured. Findings support the use of blood flow as a marker of myocardial viability in chronic postinfarct patients with modestly reduced ejection fractions.

Alterations in glucose metabolism associated with liver cirrhosis persist in the clinically stable long-term course after liver transplantation

With increasing long‐term survival rates after orthotopic liver transplantation (OLT), metabolic alterations complicating the clinical course, such as diabetes mellitus (DM), become increasingly important. Liver cirrhosis is associated with severe alterations in glucose metabolism. However, it is currently unclear whether these changes are reversed by successful OLT. We therefore characterized glucose metabolism in patients with liver cirrhosis and normal fasting glucose levels before OLT (cir), in the clinically stable long‐term course after OLT (OLT), and control subjects (con) using oral glucose tolerance tests (cir = 100, OLT = 62, con = 32), euglycemic‐hyperinsulinemic clamps (cir = 10, OLT = 27, con = 14), and positron emission tomography (PET) scan analysis with 18F‐fluorodeoxyglucose (FDG) as a tracer (cir = 7, OLT = 7, con = 5). Fasting insulin and C‐peptide levels were significantly elevated in patients with liver cirrhosis compared with both control subjects (P < .001) and patients after OLT (P < .001). After OLT, insulin was normalized, whereas C‐peptide remained elevated (P < 0.01). In the patients with liver cirrhosis, 27% had a normal glucose tolerance, 38% had an impaired glucose tolerance (IGT), and 35% were diabetic. After OLT, 34% had a normal glucose tolerance, 29% an IGT, and 37% were diabetic. Comparison of the same patients before and after OLT demonstrated that IGT or diabetes before OLT was the major risk factor for these conditions after OLT, which was independent of either immunosuppression (cyclosporine vs FK506) or low‐dose prednisolone. Total glucose uptake was reduced in patients with liver cirrhosis to less than half the values in control subjects (21.2 ± 2.8 vs 43.7 ± 2.4 μmol/kg/minute, respectively, P < .001), whereas patients after OLT showed intermediate values (35.7 ± 1.4 μmol/kg/minute, P < 0.05 vs con, P < 0.01 vs cir). This difference was caused by a reduction in nonoxidative glucose metabolism in patients with liver cirrhosis compared with control subjects (7.4 ± 1.9 vs 28.7 ± 1.8 μmol/kg/minute, respectively, P < .01) and patients after OLT (20.1 ± 1.4 μmol/kg/minute, P < 0.05 vs con and OLT). In the PET study, skeletal muscle glucose uptake was significantly reduced in patients with liver cirrhosis compared with control subjects (3.5 ± 0.4 vs 11.8 ± 2.5 μmol/100g/minute, respectively, P < .05). After OLT, muscle glucose uptake improved compared with patients with liver cirrhosis (5.9 ± 1.0 μmol/100g/minute, P < .05) but remained significantly lower than in control subjects (P < .05). In conclusion, these results demonstrate that preexisting IGT or diabetes are the major risk factors for IGT and diabetes after OLT. This finding was independent of the immunosuppressive medication. The peripheral insulin resistance in cirrhosis is characterized by a decrease in nonoxidative glucose disposal that is improved, but not normalized, after OLT. (Liver Transpl 2004;10:1030–1040.)

Positronenemissionstomographie 2013 in Deutschland: Ergebnisse der erhebung und standortbestimmung

AIM The working group on positron emission tomography (PET) of the DGN (German Society of Nuclear Medicine) initiated this first survey to collect and analyse information on the practise of PET in Germany in the year 2008. METHODS A questionnaire was sent to PET performing facilities (medical practices, hospitals, university hospitals and others) for retrospective data acquisition. Details regarding the equipment and examination procedures were examined as well as indications and number of studies. In addition, the role of PET within the diagnostic process was evaluated. RESULTS Responses from 65 sites were analysed. Their technical equipment consisted of 77 PET scanners (40 of them were combined PET/CT devices). About 63500 PET studies had been performed with 86% in the field of oncology, 8% in neurology and 3% in cardiology. The radiotracers were labelled with 18F in 91% of the studies, whereas 68Ga was used in 4% and 11C in 3%. The analyses revealed lung tumours as the most investigated tumour entity, followed by malignant lymphoma, tumours of the gastro-intestinal tract and prostate cancer (about 14000, 6000, 5000 and 2000). Corresponding to the new scanners and software procedures, the number of studies with attenuation correction by CT was high (68%) and nearly all studies were reconstructed iteratively (99%). The PET images were analysed quantitatively in the majority of cases (91%). The clinical reports, which included image documentation for the greater part, were posted regularly within 3 days. However, in 70% of the sites electronic transfer possibilities were used additionally to speed up the diagnostic process. The high standard of quality was demonstrated by the fact, that 40 facilities were engaged in a tumour board. Further on, one third of the physicians had gained a PET certification awarded by the DGN. CONCLUSION Relative to the high general standard of diagnostic instrumentation in Germany, PET is less established, in particular when compared with other industrialised countries such as USA and Switzerland.

Approaches to Quantitative Analysis of Amino Acid Transport and Metabolism

Unlike in the case of glucose utilization, there is an ongoing debate on which kinetic model might be best suitable for the description of amino acid metabolism, in order to facilitate a quantitative interpretation of the PET data obtained from the applications of amino acids. Although these PET data have been obtained mostly from investigations of tumors, basic questions on the uptake processes in normal brain can be addressed, using these data sets, by analyzing reference regions and non-tumorous brain areas. Some protocols have been especially designed to establish a quantitative model for protein synthesis in normal brain and to increase the knowledge about the transport mechanisms.