Abstract
Acquisition time and injected activity of 18F-fluorodeoxyglucose (18F-FDG) PET should ideally be reduced. However, this decreases the signal-to-noise ratio (SNR), which impairs the diagnostic value of these PET scans. In addition, 89Zr-antibody PET is known to have a low SNR. To improve the diagnostic value of these scans, a Convolutional Neural Network (CNN) denoising method is proposed. The aim of this study was therefore to develop CNNs to increase SNR for low-count 18F-FDG and 89Zr-antibody PET. Super-low-count, low-count and full-count 18F-FDG PET scans from 60 primary lung cancer patients and full-count 89Zr-rituximab PET scans from five patients with non-Hodgkin lymphoma were acquired. CNNs were built to capture the features and to denoise the PET scans. Additionally, Gaussian smoothing (GS) and Bilateral filtering (BF) were evaluated. The performance of the denoising approaches was assessed based on the tumour recovery coefficient (TRC), coefficient of variance (COV; level of noise), and a qualitative assessment by two nuclear medicine physicians. The CNNs had a higher TRC and comparable or lower COV to GS and BF and was also the preferred method of the two observers for both 18F-FDG and 89Zr-rituximab PET. The CNNs improved the SNR of low-count 18F-FDG and 89Zr-rituximab PET, with almost similar or better clinical performance than the full-count PET, respectively. Additionally, the CNNs showed better performance than GS and BF.
Highlights
18 F-fluorodeoxyglucose (18 F-FDG)positron emission tomography (PET) is essential in staging of a broad spectrum of malignancies [1–3]
We trained noise-specific Convolutional Neural Network (CNN) models, to address the difference in noise levels seen for different scan acquisition times and injected activity in 18 F-FDG PET
Due to the dose limits of 89 Zr, the overall image quality was impaired, and no high quality 89 Zr-antibody PET images were available for training a CNN
Summary
18 F-fluorodeoxyglucose (18 F-FDG)positron emission tomography (PET) is essential in staging of a broad spectrum of malignancies [1–3]. PET scan is acquired using a scan duration of 2 min per bed position and an injected activity of 3.7 MBq/kg. A shorter scan duration per bed position could ideally decrease the total scan duration, and minimize movement artefacts and increase patient comfort and throughput. A reduction of injected activity would decrease the radiation burden for the patient, and makes it possible to perform more frequent 18 F-FDG. A shorter scan duration and lower injected activity would result in a lower signal-to-noise ratio (SNR). Poor scan quality due to low-count (LC) is observed for 89 Zr-antibody PET scans, which are obtained after relatively low injected activity imposed by the radiation burden of 89 Zr [4]. Denoising LC whole-body 18 F-FDG and 89 Zr-antibody PET scans is of interest for improving image quality
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