Automated model‐based quantitative analysis of phantoms with spherical inserts in FDG PET scans

Jeong

Arthritis & Rheumatology

et al. 2019

Objective Clinical joint count assessment is important for detecting synovitis but its reliability is a subject of controversy. This study was undertaken to assess the correlation of positron emission tomography (PET)–derived parameters in 68 joints with disease activity and to compare the reliability of joint counts between PET with computed tomography (CT) and clinical assessment in patients with rheumatoid arthritis (RA). Methods We enrolled 91 patients with active RA (69 in a development group and 22 in a validation group) who underwent concurrent 18F‐fluorodeoxyglucose (18F‐FDG)–PET‐CT and clinical disease activity evaluation. PET‐derived parameters were compared with disease activity assessed using clinical joint count parameters. A Disease Activity Score (DAS) using counts of PET‐positive joints was developed, and then validation studies were performed in an independent group. Results The number of PET‐positive joints (of 28 and 68 joints) was significantly correlated with the swollen joint count (SJC) and tender joint count (TJC) and the DAS in 28 joints using the erythrocyte sedimentation rate (DAS28‐ESR). Intraobserver and interobserver reliability of PET for the affected joint counts were excellent. Interobserver reliability between nuclear medicine physicians and rheumatologists was good for the SJC and TJC in both 28 joints and 68 joints. After multivariate analyses, including ESR and patient's global assessment of disease activity (PtGA) in addition to PET‐derived parameters, the PET/DAS was derived as (0.063 × number of PET‐positive joints in 28 joints) + (0.011 × ESR) + (0.030 × PtGA). A significant correlation between the PET/DAS and the DAS28‐ESR was confirmed in the validation group (P < 0.001). Conclusion PET‐CT could serve as a sensitive and reliable method in the evaluation of disease activity in RA patients, and may be applicable as a research tool, particularly in clinical trials.

Section: Discussionmentioning

confidence: 99%

Development and Validation of an ¹⁸F‐Fluorodeoxyglucose–Positron Emission Tomography With Computed Tomography–Based Tool for the Evaluation of Joint Counts and Disease Activity in Patients With Rheumatoid Arthritis

Jeong

Arthritis & Rheumatology

et al. 2019

“…The Society of Nuclear Medicine and Molecular Imaging (SNMMI) Clinical Trials Network (CTN) torso phantom was used ( Figure 1). This 30-cm-long phantom consists of a uniform background region and two lung regions filled with Styrofoam beads that emulate the attenuation and activity of human lung (12). An additional 20-cm diameter x 30-cm long cylindrical phantom was placed axially below the CTN phantom to act as a uniform liver region.…”

Section: Phantommentioning

confidence: 99%

“…The CTN phantom was filled according to the recommended instructions (12). The activity concentration in the CTN phantom and uniform cylinder was 5.2 and 5.3 kBq/cc on the Vision and mCT scanners, respectively.…”

Section: Data Acquisitionmentioning

confidence: 99%

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

et al. 2020

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.

“…A SNMMI Clinical Trials Network (CTN) oncology phantom was scanned on the PennPET Explorer scanner ( Ulrich et al 2018 ). The CTN phantom has an axial length of 30 cm, which falls short compared with the axial FOV.…”

Section: Simulations and Experimentsmentioning

confidence: 99%

Practical joint reconstruction of activity and attenuation with autonomous scaling for time-of-flight PET

Matej

Karp

2020

Phys. Med. Biol.

Recent research has showed that attenuation images can be determined from emission data, jointly with activity images, up to a scaling constant when utilizing the time-of-flight (TOF) information. We aim to develop practical CT-less joint reconstruction for clinical TOF PET scanners to obtain quantitatively accurate activity and attenuation images. In this work, we present a joint reconstruction of activity and attenuation based on MLAA (maximum likelihood reconstruction of attenuation and activity) with autonomous scaling determination and joint TOF scatter estimation from TOF PET data. Our idea for scaling is to use a selected volume of interest (VOI) in a reconstructed attenuation image with known attenuation, e.g. a liver in patient imaging. First, we construct a unit attenuation medium which has a similar, though not necessarily the same, support to the imaged emission object. All detectable LORs intersecting the unit medium have an attenuation factor of e −1 ≈ 0.3679, i.e. the line integral of linear attenuation coefficients is one. The scaling factor can then be determined from the difference between the reconstructed attenuation image and the known attenuation within the selected VOI normalized by the unit attenuation medium. A four-step iterative joint reconstruction algorithm is developed. In each iteration, (1) first the activity is updated using TOF OSEM from TOF list-mode data; (2) then the attenuation image is updated using XMLTR—a extended MLTR from non-TOF LOR sinograms; (3) a scaling factor is determined based on the selected VOI and both activity and attenuation images are updated using the estimated scaling; and (4) scatter is estimated using TOF single scatter simulation with the jointly reconstructed activity and attenuation images. The performance of joint reconstruction is studied using simulated data from a generic whole-body clinical TOF PET scanner and a long axial FOV research PET scanner as well as 3D experimental data from the PennPET Explorer scanner. We show that the proposed joint reconstruction with proper autonomous scaling provides low bias results comparable to the reference reconstruction with known attenuation.