Benefit of Improved Performance with State-of-the Art Digital PET/CT for Lesion Detection in Oncology

Abstract

Latest digital whole-body PET scanners provide a combination of higher sensitivity and improved spatial and timing resolution. We performed a lesion detectability study on two generations of Siemens Biograph PET/CT scanners, the mCT and Vision, to study the impact of improved physical performance on clinical performance. Our hypothesis is that the improved performance of the Vision will result in improved lesion detectability, allowing shorter imaging times or equivalently, lower injected dose. Methods: Data were acquired with the Society of Nuclear Medicine and Molecular Imaging Clinical Trials Network torso phantom combined with a 20-cm diameter cylindrical phantom. Spherical lesions were emulated by acquiring spheres-in-air data, and combining it with the phantom data to generate combined datasets with embedded lesions of known contrast. Two sphere sizes and uptakes were used: 9.89 mm diameter spheres with 6:1 (lung) and 3:1 (cylinder) and 4.95 mm diameter spheres with 9.6:1 (lung) and 4.5:1 (cylinder) local activity concentration uptakes. Standard image reconstruction was performed: ordinary Poisson ordered subsets expectation maximization algorithm with point spread function and timeof-flight modeling and post-reconstruction smoothing with a 5 mm Gaussian filter. The Vision images were also generated without any post-reconstruction smoothing. Generalized scan statistics methodology was used to estimate the area under the localization receiver operating characteristic curve (ALROC). Results: Higher sensitivity and improved TOF performance of Vision leads to reduced contrast in the background noise nodule distribution. Measured lesion contrast is also higher on the Vision due to its improved spatial resolution. Hence, the ALROC values are noticeably higher for the Vision relative to the mCT. Conclusion: Improved overall performance of the Vision provides a factor of 4-6 reduction in imaging time (or injected dose) over the mCT when using the ALROC metric for lesions  9.89 mm in diameter. Smaller lesions are barely detected in the mCT, leading to even higher ALROC gains with the Vision. Improved spatial resolution of the Vision also leads to a higher measured contrast that is closer to the real uptake, implying improved quantification. Post-reconstruction smoothing, however, reduces this improvement in measured contrast, thereby reducing the ALROC values for small, high uptake lesions.

From a PMT-based to a SiPM-based PET system: a study to define matched acquisition/reconstruction parameters and NEMA performance of the Biograph Vision 450

“…A line source (inside diameter: 3 mm, outside diameter: 4.8 mm) was inserted axially into the cylinder at a radial position of 45 mm from the phantom center. The initial activity in the line source was 1156 MBq of 18 F. Thirty-ve frames of 240 s were acquired in 11.3 hours. The random coincidences were accounted for using the delayed coincidence technique.…”

“…A central cylindrical insert simulating lung tissue was added to the IEC phantom. The background was lled with a concentration of 5.4 kBq/mL of 18 F-FDG while the four smallest spheres were lled so that the contrast-to-background was 4:1 (the two largest spheres were lled with non-radioactive water). Acquisition was performed with the spheres' center aligned with the axial center of the FOV.…”

“…A small vial lled with 35 MBq of 18 F and a CT contrast agent (240 mg/mL) was used for this measurement. The vial was positioned at three transaxial coordinates: (0,1), (0,20), and (20,0) centimeters.…”

“…women evaluated for a breast cancer (injected activity: 173 MBq of 18 F-FDG, time delay between injection and imaging: 63 min, system used: Biograph mCT, reconstruction parameters: 3D OP-OSEM+PSF+TOF with three iterations, twenty-one subsets and no post-ltering). The second patient was a 78-year-old (56 kg, 1.57 m) women evaluated for a recurrence of follicular lymphoma (injected activity: 173 MBq of 18 F-FDG, time delay between injection and imaging: 60 min, system used: Vision 450, reconstruction parameters: 3D OP-OSEM+PSF+TOF with four iterations, ve subsets and no post-ltering). Vision 450 data were reconstructed by adapting the acquisition time to what was found by using the phantom experiment.…”

Evaluation of 18F-FDG PET/CT Images Acquired with a Reduced Scan Time Duration in Lymphoma Patients using the Digital Biograph Vision

“…With the advent of a new generation of silicon photomultiplier-based, so called digital PET/CT devices a reduction of the injected amount of 18 F-FDG appears feasible due to the higher detector sensitivity and improved coincidence timing resolution [8]: For example, phantom studies have shown that a reduction of acquisition time up to a factor of six is possible while maintaining a high diagnostic performance [9,10].…”