When should we recommend use of dual time-point and delayed time-point imaging techniques in FDG PET?

Abstract

FDG PET and PET/CT are now widely used in oncological imaging for tumor characterization, staging, restaging, and response evaluation. However, numerous benign etiologies may cause increased FDG uptake indistinguishable from that of malignancy. Multiple studies have shown that dual time-point imaging (DTPI) of FDG PET may be helpful in differentiating malignancy from benign processes. However, exceptions exist, and some studies have demonstrated significant overlap of FDG uptake patterns between benign and malignant lesions on delayed time-point images. In this review, we summarize our experience and opinions on the value of DTPI and delayed time-point imaging in oncology, with a review of the relevant literature. We believe that the major value of DTPI and delayed time-point imaging is the increased sensitivity due to continued clearance of background activity and continued FDG accumulation in malignant lesions, if the same diagnostic criteria (as in the initial standard single time-point imaging) are used. The specificity of DTPI and delayed time-point imaging depends on multiple factors, including the prevalence of malignancies, the patient population, and the cut-off values (either SUV or retention index) used to define a malignancy. Thus, DTPI and delayed time-point imaging would be more useful if performed for evaluation of lesions in regions with significant background activity clearance over time (such as the liver, the spleen, the mediastinum), and if used in the evaluation of the extent of tumor involvement rather than in the characterization of the nature of any specific lesion. Acute infectious and non-infectious inflammatory lesions remain as the major culprit for diminished diagnostic performance of these approaches (especially in tuberculosis-endemic regions). Tumor heterogeneity may also contribute to inconsistent performance of DTPI. The authors believe that selective use of DTPI and delayed time-point imaging will improve diagnostic accuracy and interpretation confidence in FDG PET imaging.

SUVmax of 2.5 should not be embraced as a magic threshold for separating benign from malignant lesions

“…Thus, while focal hepatic activity with an SUV max of 3.5-4.0 is common on 1-hour PET imaging (and regarded benign), it may be suspicious for malignancy if PET image acquisition was done 2-3 hours after FDG injection. Along with several background tissues (including blood pool, liver, spleen, lungs, pancreas, lymph nodes and skeletal muscle) [13], inflammatory lesions also tend to exhibit decreased FDG activity, while cancers (particularly aggressive, rapidly proliferating cancers) often show increasing FDG activity with increasing radiotracer distribution time [6,14]. These phenomena form the basis for performing dual time-point or delayed PET imaging, which may improve lesion detection and characterization.…”

Dual-time point 18FDG-PET/CT imaging may be useful in assessing local recurrent disease in high grade bone and soft tissue sarcoma

“…The granulomas may arise many years after the initial trauma or procedure in the form of tumor-like soft-tissue masses [26][27][28]. Multiple studies have indicated that lesions of active inflammation and infection may have higher 18 FDG activity on DTPI, similar to that in malignant lesions, thus resulting in suboptimal diagnostic performance of DTPI [29][30][31].…”

Ocena przydatności badań opóźnionych 18F-FDG PET/CT w różnicowaniu zmian łagodnych i złośliwych

“…Ze względu na powszechną dostępność oraz relatywnie wysoką czułość i swoistość, 18F-FDG PET/CT znalazła szerokie zastosowanie w onkologii jako narzędzie wykrywania nowotworów pierwotnych oraz zmian przerzutowych do tkanek miękkich i kości, oceny przedoperacyjnej guzów oraz monitorowania leczenia [1][2][3][4]. Ponadto, pozytonowa tomografia emisyjna w połączeniu z badaniem tomografii komputerowej umożliwia ocenę charakterystyki biologicznej guza nowotworowego w odniesieniu do budowy anatomicznej analizowanego obszaru [1,5].…”

“…Pomimo, że fluorodeoksyglukoza nie jest znacznikiem swoistym (ang. non tumor-specific) [4,[11][12][13], należy do najczęściej stosowanych radiofarmaceutyków w radioizotopowej diagnostyce onkologicznej.…”

“…Wcześniejsze publikacje podają, że badania opóźnione podnoszą czułość i swoistość metody 18 F-FDG PET/CT i mogą służyć codziennej praktyce klinicznej [4,11,[20][21][22][23].…”