Effect of 18F-FDG uptake time on lesion detectability in PET imaging of early stage breast cancer.

Kristen A Wangerin,David A Mankoff,Hannah M Linden,Alena Novakova,Lanell M Peterson,Paul E Kinahan,Brenda F Kurland,Mark Muzi,Finbarr O'Sullivan

doi:10.18383/j.tom.2015.00151

Abstract

Prior reports have suggested that delayed 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) oncology imaging can improve the contrast-to-noise ratio (CNR) for known lesions. Our goal was to estimate realistic bounds for lesion detectability for static measurements within 1 to 4 hours between FDG injection and image acquisition. Tumor and normal tissue kinetic model parameters were estimated from dynamic PET studies of patients with early-stage breast cancer. These parameters were used to generate time-activity curves (TACs) for up to 4 hours, for which we assumed both nonreversible and reversible models with different rates of FDG dephosphorylation (k4). For each pair of tumor and normal tissue TACs, 600 PET sinogram realizations were generated, and images were reconstructed using the ordered subsets expectation maximization reconstruction algorithm. Test statistics for each tumor and normal tissue region of interest were output from the computer model observers and evaluated using a receiver operating characteristic analysis, with the calculated area under the curve (AUC) providing a measure of lesion detectability. For the nonreversible model (k4 = 0), the AUC increased in 11 of 23 (48%) patients for 1 to 2 hours after the current standard postradiotracer injection imaging window of 1 hour. This improvement was driven by increased tumor/normal tissue contrast before the impact of increased noise that resulted from radiotracer decay began to dominate the imaging signal. As k4 was increased from 0 to 0.01 min−1, the time of maximum detectability shifted earlier, due to decreasing FDG concentration in the tumor lowering the CNR. These results imply that delayed PET imaging may reveal inconspicuous lesions that otherwise would have gone undetected.

Highlights

Positron emission tomography (PET) is clinically used to determine the spread of breast cancer as well as response to therapy [1]
The tumor uptake increased for many hours before it began to plateau, which agrees with other reports that suggest that FDG uptake may increase for up to 6 hours before plateauing [4, 6, 7]
The standardized uptake values (SUVs) and channelized Hotelling observer (CHO) detectability results showed a trade-off between increasing tumor-to-background ratio and increasing image noise caused by radiotracer decay

Summary

Introduction

Positron emission tomography (PET) is clinically used to determine the spread of breast cancer as well as response to therapy [1]. Thie et al [10] discussed the potential for improved lesion detection with PET imaging at different times, stressing that contrast is a time-dependent quantity and concluding that choosing an optimum imaging time is a complicated task. Some studies have investigated dual time-point imaging to exploit this time dependence, comparing lesion standardized uptake values (SUVs) at earlier and later times [11, 12]. The goal of this work was to investigate whether and when there is an improved imaging time point for a single static PET scan. We hypothesized that imaging at a later time point than current clinical practice, such as 2 or 3 hours after injection, can improve the contrast-to-noise ratio (CNR).

Objectives

Methods

Results

Conclusion