Original ArticleEnhanced definition PET for cardiac imaging
Introduction
Reconstruction techniques have an impact on image quality and quantitative analysis in cardiac PET. Recently, new high-resolution reconstruction techniques which take advantage of resolution recovery principles have been presented.1, 2, 3, 4 In particular, high definition reconstruction for PET (HD·PET) has been introduced by Siemens Healthcare Molecular Imaging (Knoxville, TN).5 Unlike the classic reconstruction techniques, this new iterative reconstruction algorithm compensates for the distortions introduced in the final images by the circular geometry of the scanner. The result is an image with improved spatial resolution and a better control of the noise.5
In this work, we hypothesized that HD·PET provides cardiac images with a higher technical quality and we aimed to verify this in a cardiac phantom and in patient images. We tested the impact of HD·PET on image contrast, noise and myocardium wall thickness. We compared HD·PET reconstruction to regular 2D and 3D reconstruction techniques used at our institution. Phantom experiments were performed with Fluorine-18 and patient images were obtained with Fluorine-18 fluorodeoxyglucose (18F-FDG)6 and perfusion studies were obtained using Rubidium-82.7 We show significant improvements in technical cardiac image quality with the use of the high-resolution reconstruction.
Section snippets
PET Acquisition and Reconstruction
All images were acquired on a Siemens Biograph-64 TruePoint PET/CT with the TrueV option. This 3D system consists of a 64-slice CT and a PET scanner with 4 rings of lutetium oxyorthosilicate (LSO) detectors with a detector element dimensions of 4 × 4 × 20 mm3.8 The image plane spacing is 2 mm. The PET axial and transaxial FOV are 216 and 605 mm, respectively. The coincidence time window and the energy window are respectively 4.5 ns and 425-650 keV. The data was acquired in list mode format. A
Reconstruction Time
For all the reconstructions, we used Windows XP PC with two 2.33 GHz Intel Xeon processors. After the list mode sorting phase, the reconstruction time of the static images (matrix size 168 × 168 × 109) was 1 minute 57 seconds for 2D-AWOSEM (3 iterations 8 subsets, 24 ML equivalent iterations), 1 minute 58 seconds for 3D-AWOSEM (3 iterations 14 subsets, 42 ML equivalent iterations) and 2 minutes 35 seconds for HD·PET (4 iterations and 14 subsets, 56 ML equivalent iterations). The gated
Discussion
HD·PET modeling of the 3D detector spatial response during the reconstruction step is designed to better control the noise in the reconstructed images in general.5 In this work, we have shown that HD·PET improves significantly the technical image quality of cardiac studies. The noise, contrast and wall thickness were improved in phantom, viability studies and perfusion studies (static and gated).
The change in contrast and wall thickness can in most part be explained by the improved spatial
Conclusions
Our work on both phantom and patient cardiac studies showed that HD·PET significantly improved defect definition, image resolution, contrast and contrast-to-noise and provided equivalent functional quantitative information compared to standard reconstruction techniques. This improved technical quality could lead to improved performance of cardiac PET/CT. Further evaluation of the clinical impact of HD·PET on cardiac imaging would appear to be warranted.
Acknowledgments
The authors thank Jimmy Fermin and Brandi N. Huber from Cedars-Sinai Medical Center for their help with the PET acquisition, Heidi Gransar for her help with the statistical analysis and Michael Casey from Siemens Healthcare for his help with the setting up of the High Definition.
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