BackgroundCardiac sarcoidosis (CS) is a potentially fatal condition lacking a single test with acceptable diagnostic accuracy. 18F-FDG PET/CT has emerged as a promising imaging modality, but is challenged by physiological myocardial glucose uptake. An alternative tracer, 68Ga-DOTANOC, binds to somatostatin receptors on inflammatory cells in sarcoid granulomas. We therefore aimed to conduct a proof-of-concept study using 68Ga-DOTANOC to diagnose CS. In addition, we compared diagnostic accuracy and inter-observer variability of 68Ga-DOTANOC vs. 18F-FDG PET/CT.MethodsNineteen patients (seven female) with suspected CS were prospectively recruited and dual tracer scanned within 7 days. PET images were reviewed by four expert readers for signs of CS and compared to the reference standard (Japanese ministry of Health and Welfare CS criteria).ResultsCS was diagnosed in 3/19 patients. By consensus, 11/19 18F-FDG scans and 0/19 68Ga-DOTANOC scans were rated as inconclusive. The sensitivity of 18F-FDG PET for diagnosing CS was 33 %, specificity was 88 %, PPV was 33 %, NPV was 88 %, and diagnostic accuracy was 79 %. For 68Ga-DOTANOC, accuracy was 100 %. Inter-observer agreement was poor for 18F-FDG PET (Fleiss’ combined kappa 0.27, NS) and significantly better for 68Ga-DOTANOC (Fleiss’ combined kappa 0.46, p = 0.001).ConclusionsDespite prolonged pre-scan fasting, a large proportion of 18F-FDG PET/CT images were rated as inconclusive, resulting in low agreement among reviewers and correspondingly poor diagnostic accuracy. By contrast, 68Ga-DOTANOC PET/CT had excellent diagnostic accuracy with the caveat that inter-observer variability was still significant. Nevertheless, 68Ga-DOTANOC PET/CT looks very promising as an alternative CS PET tracer.Trial registrationCurrent Controlled Trials NCT01729169.Electronic supplementary materialThe online version of this article (doi:10.1186/s13550-016-0207-6) contains supplementary material, which is available to authorized users.
Background
Dynamic whole-body (D-WB) FDG PET/CT is a recently developed technique that allows direct reconstruction of multiparametric images of metabolic rate of FDG uptake (MRFDG) and “free” FDG (DVFDG). Multiparametric images have a markedly different appearance than the conventional SUV images obtained by static PET imaging, and normal values of MRFDG and DVFDG in frequently used reference tissues and organs are lacking. The aim of this study was therefore to: (1) provide an overview of normal MRFDG and DVFDG values and range of variation in organs and tissues; (2) analyse organ time-activity curves (TACs); (3) validate the accuracy of directly reconstructed MRFDG tissue values versus manually calculated Ki (and MRFDG) values; and (4) explore correlations between demographics, blood glucose levels and MRFDG values. D-WB data from 126 prospectively recruited patients (100 without diabetes and 26 with diabetes) were retrospectively analysed. Participants were scanned using a 70-min multiparametric PET acquisition protocol on a Siemens Biograph Vision 600 PET/CT scanner. 13 regions (bone, brain grey and white matter, colon, heart, kidney, liver, lung, skeletal muscle of the back and thigh, pancreas, spleen, and stomach) as well as representative pathological findings were manually delineated, and values of static PET (SUV), D-WB PET (Ki, MRFDG and DVFDG) and individual TACs were extracted. Multiparametric values were compared with manual TAC-based calculations of Ki and MRFDG, and correlations with blood glucose, age, weight, BMI, and injected tracer dose were explored.
Results
Tissue and organ MRFDG values showed little variation, comparable to corresponding SUV variation. All regional TACs were in line with previously published FDG kinetics, and the multiparametric metrics correlated well with manual TAC-based calculations (r2 = 0.97, p < 0.0001). No correlations were observed between glucose levels and MRFDG in tissues known not to be substrate driven, while tissues with substrate driven glucose uptake had significantly correlated glucose levels and MRFDG values.
Conclusion
The multiparametric D-WB PET scan protocol provides normal MRFDG values with little inter-subject variation and in agreement with manual TAC-based calculations and literature values. The technique therefore facilitates both accurate clinical reports and simpler acquisition of quantitative estimates of whole-body tissue glucose metabolism.
Using purely creatinine-based GFR estimates can lead to complications in clinical practice, especially when correct GFR values are mandatory, like when calculating adequate chemotherapy dosage, and should be used with caution. When the more accurate nuclear medicine methods are unavailable due to cost or accessibility issues, our study showed that the new CKD-EPI appears to reflect GFR results more accurately than MDRD, and thus should be the method of choice for estimating GFR.
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