8 research outputs found
Is the Image Quality of I-124-PET Impaired by an Automatic Correction of Prompt Gammas?
Objectives
The aim of this study is to evaluate the quality of I-124 PET images with and without prompt gamma compensation (PGC) by comparing the recovery coefficients (RC), the signal to noise ratios (SNR) and the contrast to F-18 and Ga-68. Furthermore, the influence of the PGC on the quantification and image quality is evaluated.
Methods
For measuring the image quality the NEMA NU2-2001 PET/SPECT-Phantom was used containing 6 spheres with a diameter between 10 mm and 37 mm placed in water with different levels of background activity. Each sphere was filled with the same activity concentration measured by an independently cross-calibrated dose calibrator. The âhotâ sources were acquired with a full 3D PET/CT (Biograph mCTÂź, Siemens Medical USA). Acquisition times were 2 min for F-18 and Ga-68, and 10 min for I-124. For reconstruction an OSEM algorithm was applied. For I-124 the images were reconstructed with and without PGC. For the calculation of the RCs the activity concentrations in each sphere were determined; in addition, the influence of the background correction was studied.
Results
The RCs of Ga-68 are the smallest (79%). I-124 reaches similar RCs (87% with PGC, 84% without PGC) as F-18 (84%). showing that the quantification of I-124 images is similar to F-18 and slightly better than Ga-68. With background activity the contrast of the I-124 PGC images is similar to Ga-68 and F-18 scans. There was lower background activity in the I-124 images without PGC, which probably originates from an overcorrection of the scatter contribution. Consequently, the contrast without PGC was much higher than with PGC. As a consequence PGC should be used for I-124.
Conclusions
For I-124 there is only a slight influence on the quantification depending on the use of the PGC. However, there are considerable differences with respect to I-124 image quality
RC of F-18, Ga-18 and I-124 with and without PGC as a function of sphere diameter.
<p>Reconstruction iterative with scatter correction and a Gauss-filter with a FWHM of 2 mm and a Sâ¶BGâ10â¶1.</p
Simplified decay scheme of I-124 with a transition probability >3%, *maximal energy (ÎČ+: positron emission, Îł: gamma emission, X: x-ray emission, Δ: electron capture).
<p>Simplified decay scheme of I-124 with a transition probability >3%, *maximal energy (ÎČ+: positron emission, Îł: gamma emission, X: x-ray emission, Δ: electron capture).</p
Relative contrast of F-18, Ga-68 and I-124 with and without PGC as a function of sphere diameter.
<p>Reconstruction iterative with scatter correction and a Gauss-filter with a FWHM of 2 mm and a Sâ¶BGâ10â¶1.</p
Specific activities and sphere-to-background-ratios used in PET-measurements.
<p>(SNR: Signal-to-noise ratio, RC: recovery coefficient).</p
Sinograms of I-124 phantom images with PGC (right) and without PGC (left), top: with background activity, bottom: without background activity.
<p>Sinograms of I-124 phantom images with PGC (right) and without PGC (left), top: with background activity, bottom: without background activity.</p
RC of I-124 with PGC depending on post-reconstruction filtering as a function of sphere diameter.
<p>Reconstruction iterative with scatter correction and a Sâ¶BGâ=â9.9â¶1.</p