DECADE: A Temporally-Consistent Unsupervised Diffusion Model for Enhanced Rb-82 Dynamic Cardiac PET Image Denoising

TL;DR

The proposed DECADE (A Temporally-Consistent Unsupervised Diffusion model for Enhanced Rb-82 CArdiac PET DEnoising), an unsupervised diffusion framework that generalizes across early- to late-phase dynamic frames that enables effective unsupervised denoising of Rb-82 dynamic cardiac PET without paired training data.

Abstract

Rb-82 dynamic cardiac PET imaging is widely used for the clinical diagnosis of coronary artery disease (CAD), but its short half-life results in high noise levels that degrade dynamic frame quality and parametric imaging. The lack of paired clean-noisy training data, rapid tracer kinetics, and frame-dependent noise variations further limit the effectiveness of existing deep learning denoising methods. We propose DECADE (A Temporally-Consistent Unsupervised Diffusion model for Enhanced Rb-82 CArdiac PET DEnoising), an unsupervised diffusion framework that generalizes across early- to late-phase dynamic frames. DECADE incorporates temporal consistency during both training and iterative sampling, using noisy frames as guidance to preserve quantitative accuracy. The method was trained and evaluated on datasets acquired from Siemens Vision 450 and Siemens Biograph Vision Quadra scanners. On the Vision 450 dataset, DECADE consistently produced high-quality dynamic and parametric images with reduced noise while preserving myocardial blood flow (MBF) and myocardial flow reserve (MFR). On the Quadra dataset, using 15%-count images as input and full-count images as reference, DECADE outperformed UNet-based and other diffusion models in image quality and K1/MBF quantification. The proposed framework enables effective unsupervised denoising of Rb-82 dynamic cardiac PET without paired training data, supporting clearer visualization while maintaining quantitative integrity.

Figures (6)

• Figure 1: DECADE consists of a diffusion model training stage and a sampling stage. During Training Stage A, the model is pre-trained on 2-7 minute mean static PET images. Three Gaussian-smoothed consecutive noisy frames are then used as conditional input into ControlNet to refine the pre-trained model. In the sampling stage, the unconditional diffusion model is applied for time steps from 1000 to 950, followed by the use of ControlNet from time steps 950 to 0. Noisy frames are incorporated at each time step to guide the denoising process.
• Figure 2: Example dynamic frames and $K_1$ images of a rest scan from the Vision 450 dataset. The radiology report indicates the patient has no myocardial defect. DECADE achieved superior denoising performance across all dynamic frames. The denoised frames and $K_1$ map produced by DECADE exhibit the lowest noise levels and the most similar tracer distribution to the original dynamic frames.
• Figure 3: An example subject from the Vision 450 dataset with a confirmed myocardial defect. The clinical report indicates a partially reversible perfusion defect in the basal to apical inferior, basal inferolateral, and basal inferoseptal walls. The catheteriztion study confirms the appearance of dominant LCx with severe calcified stenosis. Dynamic frames, $K_1$ images, $k_2$ images, and polar maps before and after denoising are shown. $K_1$ images are displayed in axial view, horizontal long-axis view (HLA), vertical long-axis view (VLA), and short-axis view (SA). DECADE achieves superior denoising performance across all dynamic frames over time, producing $K_1$ maps with reduced noise. Notably, the stress polar map's noise artifact near the apex region disappears after denoising, and the boundary of the myocardium becomes more apparent. Importantly, the myocardial defect, pointed out by a blue arrow in the VLA and SA views of parametric images and polar map, remains visible and even easier to detect after denoising due to improved parametric image quality. The defect in the $k_2$ image is also indicated by higher uptake in the defect region of the VLA and SA view.
• Figure 4: A normal subject from the Vision 450 dataset. The radiology report indicates this patient has no myocardial defects. DECADE also produces visually appealing denoised results for this patient on dynamic frames. The denoised images exhibit a more uniform distribution and significantly lower noise levels. The contour of the myocardium is better depicted in all views of the $K_1$ and $k_2$ images.
• Figure 5: Comparison results on an example rest scan from the Quadra Bern dataset. 15% dynamic frames are used as noisy inputs, and 100% scans are used as ground truth to compare with denoised results. DECADE successfully generalizes to the downsampled Quadra Bern dataset without fine-tuning or re-training. The denoised images from DECADE preserve structural details of anatomical regions and ensure quantitative accuracy. In contrast, underestimation occurs with N2V, and overestimation occurs with the self-supervised UNet and DDIM for dynamic frames.