Automatic Cardiac Self-Gating of Small-Animal PET Data

Abstract

Purpose: The cardiac gating signal (CGS) in positron emission tomography (PET) studies is usually obtained from an electrocardiography (ECG) monitor. In this work, we propose a method to obtain the CGS in small-animal PET using the acquired list-mode data without using any hardware or end-user input. Procedures: The CGS was obtained from the number of coincidences over time acquired in the lines-of-response connected with the cardiac region. This region is identified in the image as its value changes with frequencies in the range of 3 to 12 Hz. The procedure was tested in a study with 29 Wistar rats and 6 mice injected with 2-deoxy-2-[ 18 F]fluoro-D-glucose, which underwent a 45-min single-bed list-mode PET scan of the heart syncronized with an ECG. The estimated signals and the reconstructed images using eight-gated frames were compared with the ones obtained using the ECG signal from the monitor. Results: The differences of the PET-based CGS with respect to the ECG relative to the duration of the heartbeats were 5.6 % in rats and 11.0 % in mice. The reconstructed gated images obtained from the proposed method do not differ qualitatively with respect to the ones obtained with the ECG. The quantitative analysis of both set of images were performed measuring the volume of the left ventricle (LV) of the rats in the end-of-systole and end-of-diastole phase. The differences found in these parameters between both methods were below 12.1 % in the ESV and 9.3 % in the EDV with a 95 % confidence interval, which are comparable to the accuracy (7 %) of the method used for segmenting the LV. Conclusion: The proposed method is able to provide a valid and accurate CGS in small-animal PET list-mode data.

Towards quantitative small-animal imaging on hybrid PET/CT and PET/MRI systems

“…A novel respiratory gating method was proposed by Todica et al in which the alterations in the amplitude of the ECG signal and heart-beat variations during the breathing cycle of the rat heart scan have been detected and utilized as respiratory triggered signal to improve quantitative values [107]. Herraiz et al proposed a data-driven approach for automatic gating in small animal cardiac imaging which involves analyzing the count-rate variation of the heart in the frequency domain [94].…”

“…Moreover, it has been demonstrated that positron range effect depends significantly upon the physical properties of the medium and surrounding tissues. This has spurred the interest towards more accurate methods like CT-based tissue-dependent spatially-variant models which ultimately render artifact-free images, improved quality and better tumor delineation when using high-energy radioisotopes such as 68 Ga [87,94].…”

Image-Derived Input Functions for Quantification of A1 Adenosine Receptors Availability in Mice Brains Using PET and [18F]CPFPX

“…Previously, only the left ventricle was used as the region of interest to reduce the motion of heart and improve the precision. Recently, Herraiz et al (2016) and Verhaeghe et al (2018) showed that the left ventricle volume can be estimated by means of cardiac gating during PET acquisition. For this purpose, PET raw data were divided into time subsets according to the different phases of the heart activity.…”