Ziel/Aim The potential for reducing the total acquisition time is particularly valuable for prostate cancer patients undergoing Ga-68-PSMA PET/CT examinations enhancing patient comfort, image quality, and throughput. The aim of this study is to optimise the acquisition time in Ga-68-PSMA examinations on a digital Biograph Vision PET/CT using an abdominal tumour phantom.
Previous publications introduced an array of collimated coincidence point sources for transmission imaging in PET. The design of the point source array matches transmission lines-of- response with emission ones in direct planes. The attenuation map is reconstructed front transmission projection data collected with single slice rebinning and nearest neighbor approximation imposed by the matching with emission acquisition geometry. Since transmission measurements are performed with an axially focused converging geometry, the goal of this work is to investigate potential improvements in attenuation map reconstruction by using an iterative cone beam reconstruction whose parameters depend on number of sources, source position and collimator design. By using Defrise's and anthropomorphic phantoms we demonstrated that iterative cone beam reconstruction improves axial resolution in the region between point sources when compared with present data processing.
The aim of this study was to investigate conditions for reliable quantification of sub-centimeter lesions with low18F,68Ga, and124I uptake using a silicon photomultiplier-based PET/CT system.A small tumor phantom was investigated under challenging but clinically realistic conditions resembling prostate and thyroid cancer lymph node metastases (6 spheres with 3.7-9.7 mm in diameter, 9 different activity concentrations ranging from about 0.25-25 kBq/mL, and a signal-to-background ratio of 20). Radionuclides with different positron branching ratios and prompt gamma coincidence contributions were investigated. Maximum-, contour-, and oversize-based partial volume effect (PVE) correction approaches were applied. Detection and quantification performance were estimated, considering a ±30 % deviation between imaged-derived and true activity concentrations as acceptable. A standard and a prolonged acquisition time and two image reconstruction algorithms (time-of-flight with/without point spread function modelling) were analyzed. Clinical data were evaluated to assess agreement of PVE-correction approaches indicating lesion quantification validity.The smallest 3.7-mm sphere was not visible. If the lesions were clearly observed, quantification was, except for a few cases, acceptable using contour- or oversized-based PVE-corrections. Quantification accuracy did not substantially differ between 18F, 68Ga, and 124I. No systematic differences between the analyzed reconstruction algorithms or shorter and larger acquisition times were observed. In the clinical evaluation of 20 lesions, an excellent statistical agreement between oversize- and contour-based PVE-corrections was observed.At the lower end of size (<10 mm) and activity concentration ranges of lymph-node metastases, quantification with reasonable accuracy is possible for 18F, 68Ga, and 124I, possibly allowing pre-therapeutic lesion dosimetry and individualized radionuclide therapy planning.
To develop and evaluate a new approach for spatially variant and tissue-dependent positron range (PR) correction (PRC) during the iterative PET image reconstruction.The PR distributions of three radionuclides (18F, 68Ga, and 124I) were simulated using the GATE (GEANT4) framework in different material compositions (lung, water, and bone). For every radionuclide, the uniform PR kernel was created by mapping the simulated 3D PR point cloud to a 3D matrix with its size defined by the maximum PR in lung (18F) or water (68Ga and 124I) and the PET voxel size. The spatially variant kernels were composed from the uniform PR kernels by analyzing the material composition of the surrounding medium for each voxel before implementation as tissue-dependent, point-spread functions into the iterative image reconstruction. The proposed PRC method was evaluated using the NEMA image quality phantom (18F, 68Ga, and 124I); two unique PR phantoms were scanned and evaluated following OSEM reconstruction with and without PRC using different metrics, such as contrast recovery, contrast-to-noise ratio, image noise and the resolution evaluated in terms of full width at half maximum (FWHM).The effect of PRC on 18F-imaging was negligible. In contrast, PRC improved image contrast for the 10-mm sphere of the NEMA image quality phantom filled with 68Ga and 124I by 33 and 24%, respectively. While the effect of PRC was less noticeable for the larger spheres, contrast recovery still improved by 5%. The spatial resolution was improved by 26% for 124I (FWHM of 4.9 vs. 3.7 mm).For high energy positron-emitting radionuclides, the proposed PRC method helped recover image contrast with reduced noise levels and with improved spatial resolution. As such, the PRC approach proposed here can help improve the quality of PET data in clinical practice and research.
Double-sided microstrip silicon crystals are tested as detectors for X-rays in the diagnostic energy range (10-100 keV) for digital radiography. An analog-to-digital converter (ADC) and CAMAC-based acquisition system is developed to study the imaging capabilities of a silicon mu strip detector with 100- and 200- mu m read-out pitch. The first images of submillimeter high contrast phantoms obtained with an X-ray mammography tube operating at high flux density are presented.< >
The key performance parameter of a Time-of-flight (TOF) positron emission tomography (PET) system is the time resolution, which has a direct effect on the TOF signal-to-noise ratio (SNR) gain. TOF gain has been modeled, simulated and measured in past literature, and advanced models have been proposed. In his work we are able to compare models and simulations with experimental data below 250ps time resolution, using a next generation Siemens SiPM PET/CT prototype scanner. TOF gain is assessed using uniform cylindrical phantoms of different diameters (20cm, 37cm). Filtered back projection (FBP) reconstruction was used for the reconstruction, in TOF and nonTOF version.A SNR TOF gain up to 3.9, equivalent to a TOF sensitivity gain of about 15.1, was measured in this preliminary experiment. In addition, results at variable random fraction are presented.
