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Simplified decay scheme of I-124 with a transition probability .3%, *maximal energy (b+: positron emission, c: gamma emission, X: x-ray emission, e: electron capture). doi:10.1371/journal.pone.0071729.g001
Source publication
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.
For measuring the image qu...
Contexts in source publication
Context 1
... to the complex decay scheme of I-124 (see fig. 1, data taken from [6]) different challenges are to be met. Low energy photons cause strong geometry and vial dependency when measuring I-124 in dose calibrators. This fact requires additional efforts for correct activity quantification [7]. Furthermore, prompt gamma photons with an energy of 602.7 keV are emitted in cascade with about ...
Context 2
... decay scheme of I-124 is complex as it contains positron emission, electron capture and emission of x-rays and gamma-rays (see fig. 1). Due to the positron emission PET-imaging is possible; however, the branching ratio of positron emission with 22.5% is much lower than that for F-18 (96.7%). Longer measurements or higher activity concentrations are therefore necessary to get a similar image quality as compared to F-18. Furthermore, the emitted positrons have higher ...
Citations
... Other sources of background are mainly gamma rays, either from non-pure positron emitters, such as 86 Y and 124 I, or from prompt gamma rays from proton therapy. They can be corrected with background subtraction or prompt gamma rejection in proton therapy [8][9][10][11][12][13]. Another potential application is multiple nuclide imaging with Compton PET [14]. ...
The reduction of background events, such as random and scatter events, can improve positron emission tomography (PET) images quantitatively. The quantum entanglement property of annihilation photons has been theoretically studied and experimentally validated. Recently, simulation studies on PET image reconstruction using the quantum entanglement property of annihilation photons and studies on the measurement of entanglement and polarization properties with scintillation crystal arrays demonstrated that PET images with less background can be achieved. This study utilized the quantum entanglement property of annihilation photons in a typical PET system with block detectors. A data acquisition method for quantum entanglement PET (QEPET) and system response modelling for QEPET image reconstruction were proposed and implemented. An experimental study was conducted using a small animal PET system composed of Ce:GAGG scintillation crystals whose dimensions are 2.5 × 2.5 × 4mm3. The diameter of the system was 79.3 mm. Signals from all individual crystals were processed parallelly and independently; thus, Compton scatter and absorption crystals within a module were obtained directly. The 28 MBq experiment result revealed the random background ratio of QEPET was approximately 20% lower than that of PET and the count rate of QEPET was approximately 0.1% that of PET. Evaluation on reconstructed images from the 28 MBq experiment revealed that the signal-to-background ratio of QEPET was approximately two times better than that of PET while the signal-to-noise ratio of QEPET was about 77% of that of PET. The method proposed in this study is expected to improve PET images with high background, such as those with a high activity and high background gamma rays and improve range verification in proton therapy.
... Most PET scanners store triples in the list-mode data as a set of contiguous double coincidences. These double coincidences are not reconstructed, as they provide two incorrect origins of the radioisotope, reducing the perceived quality of the reconstructed image from these isotopes 17,20,26,27 with the solution often to reduce the detector energy window to omit the prompt gamma or to use another isotope entirely. It is important to note that mPET needs the combination of a prompt gamma and a pure emitting positron for the separation to occur and that the prompt gamma can be detected on the scanner and has a relatively high prompt emission rate to that of 29 and has yet to be used as part of PET reconstruction. ...
In conventional positron emission tomography (PET), only one radiotracer can be imaged at a time, because all PET isotopes produce the same two 511 keV annihilation photons. Here we describe an image reconstruction method for the simultaneous in vivo imaging of two PET tracers and thereby the independent quantification of two molecular signals. This method of multiplexed PET imaging leverages the 350–700 keV range to maximize the capture of 511 keV annihilation photons and prompt γ-ray emission in the same energy window, hence eliminating the need for energy discrimination during reconstruction or for signal separation beforehand. We used multiplexed PET to track, in mice with subcutaneous tumours, the biodistributions of intravenously injected [¹²⁴I]I-trametinib and 2-deoxy-2-[¹⁸F]fluoro-d-glucose, [¹²⁴I]I-trametinib and its nanoparticle carrier [⁸⁹Zr]Zr-ferumoxytol, and the prostate-specific membrane antigen (PSMA) and infused PSMA-targeted chimaeric antigen receptor T cells after the systemic administration of [⁶⁸Ga]Ga-PSMA-11 and [¹²⁴I]I. Multiplexed PET provides more information depth, gives new uses to prompt γ-ray-emitting isotopes, reduces radiation burden by omitting the need for an additional computed-tomography scan and can be implemented on preclinical and clinical systems without any modifications in hardware or image acquisition software.
... Recently, prompt gamma correction methods have been integrated into commercial PET reconstruction software and should be commissioned when available. With prompt gamma correction, quantification of 124 I PET images has been shown to be similar to that of 18 F PET in a phantom study when using a 10-min acquisition compared with a 2-min acquisition for 18 F (Preylowski et al., 2013). ...
... with RC being the recovery coefficient, C image the activity concentration in Bq/ml obtained from the reconstructed image, and C known the known activity concentration in Bq/ml in the phantom. The signal-tonoise ratios (SNR) of the images were calculated by dividing the difference of the activity concentrations in the sphere VOIs and the background VOI by the standard deviation in the background VOI, as given by equation (2) [31], ...
Background
To improve therapy outcome of Yttrium-90 selective internal radiation therapy (⁹⁰Y SIRT), patient-specific post-therapeutic dosimetry is required. For this purpose, various dosimetric approaches based on different available imaging data have been reported. The aim of this work was to compare post-therapeutic 3D absorbed dose images using Technetium-99m (99mTc) MAA SPECT/CT, Yttrium-90 (⁹⁰Y) bremsstrahlung (BRS) SPECT/CT, and ⁹⁰Y PET/CT.
Methods
Ten SIRTs of nine patients with unresectable hepatocellular carcinoma (HCC) were investigated. The 99mTc SPECT/CT data, obtained from 99mTc-MAA-based treatment simulation prior to ⁹⁰Y SIRT, were scaled with the administered ⁹⁰Y therapy activity. 3D absorbed dose images were generated by dose kernel convolution with scaled 99mTc/⁹⁰Y SPECT/CT, ⁹⁰Y BRS SPECT/CT, and ⁹⁰Y PET/CT data of each patient. Absorbed dose estimates in tumor and healthy liver tissue obtained using the two SPECT/CT methods were compared against ⁹⁰Y PET/CT.
Results
The percentage deviation of tumor absorbed dose estimates from ⁹⁰Y PET/CT values was on average −2 ± 18% for scaled 99mTc/⁹⁰Y SPECT/CT, whereas estimates from ⁹⁰Y BRS SPECT/CT differed on average by −50 ± 13%. For healthy liver absorbed dose estimates, all three imaging methods revealed comparable values.
Conclusion
The quantification capabilities of the imaging data influence ⁹⁰Y SIRT tumor dosimetry, while healthy liver absorbed dose values were comparable for all investigated imaging data. When no ⁹⁰Y PET/CT image data are available, the proposed scaled 99mTc/⁹⁰Y SPECT/CT dosimetry method was found to be more appropriate for HCC tumor dosimetry than ⁹⁰Y BRS SPECT/CT based dosimetry.
... This effect is enhanced by post-reconstruction filtering. Finally, previous single-centre studies show 68 Ga RC-curves similar [10] or somewhat better due to point spread function reconstruction [11] as observed in the current study. The EARL limits as applicable before 2019 (EARL1) are shown in Figs. 3 and 4, as all acquisitions were acquired before 2019 and therefore site-specific acquisition and reconstruction protocols are designed to meet the EARL1 limits. ...
Purpose
Performance standards for quantitative 18F-FDG PET/CT studies are provided by the EANM Research Ltd. (EARL) to enable comparability of quantitative PET in multicentre studies. Yet, such specifications are not available for 68Ga. Therefore, our aim was to evaluate 68Ga-PET/CT quantification variability in a multicentre setting.
Methods
A survey across Dutch hospitals was performed to evaluate differences in clinical 68Ga PET/CT study protocols. 68Ga and 18F phantom acquisitions were performed by 8 centres with 13 different PET/CT systems according to EARL protocol. The cylindrical phantom and NEMA image quality (IQ) phantom were used to assess image noise and to identify recovery coefficients (RCs) for quantitative analysis. Both phantoms were used to evaluate cross-calibration between the PET/CT system and local dose calibrator.
Results
The survey across Dutch hospitals showed a large variation in clinical 68Ga PET/CT acquisition and reconstruction protocols. 68Ga PET/CT image noise was below 10%. Cross-calibration was within 10% deviation, except for one system to overestimate 18F and two systems to underestimate the 68Ga activity concentration. RC-curves for 18F and 68Ga were within and on the lower limit of current EARL standards, respectively. After correction for local 68Ga/18F cross-calibration, mean 68Ga performance was 5% below mean EARL performance specifications.
Conclusions
68Ga PET/CT quantification performs on the lower limits of the current EARL RC standards for 18F. Correction for local 68Ga/18F cross-calibration mismatch is advised, while maintaining the EARL reconstruction protocol thereby avoiding multiple EARL protocols.
... Quantification using this radionuclide is, however, hampered by the presence of a prompt g-emission that could potentially lead to false coincidences. Some manufacturers have a built-in prompt g-correction, which, for 124 I, leads to acceptable image quantification (18). Other nuclides that could potentially be used for pretherapeutic PET-based dose planning are 44 Sc, 68 Ga, and 86 Y (19). ...
The aim of this review is to provide an overview of the most recent technological developments in state-of-the-art equipment and tools used for dosimetry in radionuclide therapies. This includes, but is not restricted to calibration methods of imaging systems. In addition, a summary of new developments that consider the influence of small-scale dosimetry and of biological effects on radionuclide therapies is given. Finally, the present-day limitations of patient-specific dosimetry such as bone-marrow dosimetry or dosimetry of alpha emitters are discussed.
... However, for both the calibration factor and soft-tissue sphere RC measurements, we still observe an underestimation of 10-12% in measured radioactivity concentration compared to 18 F. Although Preylowski et al (2013) showed that implementation of the prompt-gamma correction method did not result in a notable increase in 124 I RC values for the Biograph mCT system, they reported similar RC values for 124 I and 18 F, in contrast to our results. This discrepancy cannot be completely resolved, but is most likely related to an imprecise 124 I calibration factor of the dose calibrator (Jentzen et al 2008, Jentzen 2010, Beattie et al 2014. ...
... Therefore, the effective PET spatial image resolution was assessed using line sources in water for both 18 F and 124 I. The spatial resolution of 124 I (5.0 mm) was 0.7 mm degraded compared to 18 F (4.3 mm), as a result of the high-energy positrons emitted by 124 I, in good agreement with reported 124 I PET/CT spatial resolution measurements (Jentzen et al 2008, Gregory et al 2009, Preylowski et al 2013. In contrast, using point sources in air, Soderlund et al (2015) reported equal 124 I and 18 F PET spatial resolution values for the Biograph mMR. ...
The aim was to investigate the quantitative performance of 124I PET/MRI for pre-therapy lesion dosimetry in differentiated thyroid cancer. Phantom measurements were performed on a PET/MRI system (Biograph mMR, Siemens Healthcare) using 124I and 18F. The PET calibration factor and the influence of radiofrequency coil attenuation were determined using a cylindrical phantom homogeneously filled with radioactivity. The calibration factor was 1.00 ± 0.02 for 18F and 0.88 ± 0.02 for 124I. Near the radiofrequency surface coil an underestimation of less than 5% in radioactivity concentration was observed. Soft-tissue sphere recovery coefficients were determined using the NEMA IEC body phantom. Recovery coefficients were systematically higher for 18F compared to 124I. In addition, the six spheres of the phantom were segmented using a PET-based iterative segmentation algorithm. For all 124I measurements, the deviations in segmented lesion volume and mean radioactivity concentration relative to the actual values were smaller than 15% and 25%, respectively. The effect of MR-based attenuation correction (3- and 4-segment μ-maps) on bone lesion quantification was assessed by using radioactive spheres filled with a K2HPO4 solution mimicking bone lesions. The 4-segment µ-map resulted in an underestimation of the imaged radioactivity concentration up to 15%, whereas the 3-segment μ-map resulted in an overestimation up to 10%. For twenty lesions identified in six patients, a comparison of 124I PET/MRI to PET/CT was performed with respect to segmented lesion volume and radioactivity concentration. The interclass correlation coefficients showed excellent agreement in segmented lesion volume and radioactivity concentration (0.999 and 0.95, respectively). In conclusion, accurate quantitative 124I PET/MRI with the aim of performing radioiodine pre-therapy lesion dosimetry in differentiated thyroid cancer is feasible.
... Iodine-124 is a positron emitter with a long half-life (4.17 days) and a complex decay scheme, with many high energy -emissions and high energy positron emission ( max = 2.14 MeV, 23% abundance) [87]. It can be produced using different nuclear reactions, with the 124 Te(p,n) 124 I reaction being currently the most commonly used [86]. ...
The combination of the size-dependent properties of nanomaterials with radioisotopes is emerging as a novel tool for molecular imaging. There are numerous examples already showing how the controlled synthesis of nanoparticles and the incorporation of a radioisotope in the nanostructure offer new features beyond the simple addition of different components. Among the different nanomaterials, iron oxide-based nanoparticles are the most used in imaging because of their versatility. In this review, we will study the different radioisotopes for biomedical imaging, how to incorporate them within the nanoparticles, and what applications they can be used for. Our focus is directed towards what is new in this field, what the nanoparticles can offer to the field of nuclear imaging, and the radioisotopes hybridized with nanomaterials for use in molecular imaging.
... Furthermore, even higher energy gammas are present, which can downscatter into the energy window, or increase the dead time. For such a radionuclide, TOF results in a better SNR for the same number of counts [5,87]. It is expected that recent developments in PET/CT technology, combined with a careful application of correction methods for the prompt gammas [88], further facilitate the use of 124 I-PET/ CT [89] (or tracers labeled with other radionuclides such as 89 Zr [90]) with an improved image quality and a more accurate quantification [91]. ...
In recent years, there have been multiple advances in positron emission tomography/computed tomography (PET/CT) that improve cancer imaging. The present generation of PET/CT scanners introduces new hardware, software, and acquisition methods. This review describes these new developments, which include time-of-flight (TOF), point-spread-function (PSF), maximum-a-posteriori (MAP) based reconstruction, smaller voxels, respiratory gating, metal artefact reduction, and administration of quadratic weight-dependent (18)F-fluorodeoxyglucose (FDG) activity. Also, hardware developments such as continuous bed motion (CBM), (digital) solid-state photodetectors and combined PET and magnetic resonance (MR) systems are explained. These novel techniques have a significant impact on cancer imaging, as they result in better image quality, improved small lesion detectability, and more accurate quantification of radiopharmaceutical uptake. This influences cancer diagnosis and staging, as well as therapy response monitoring and radiotherapy planning. Finally, the possible impact of these developments on the European Association of Nuclear Medicine (EANM) guidelines and EANM Research Ltd. (EARL) accreditation for FDG-PET/CT tumor imaging is discussed.
... This is supported by a phantom study with I-124, which also requires the same PGC algorithm. 26 The study demonstrated contrast recovery with I-124 images incorporating PGC was comparable to when the phantom was filled with F-18, which does not require PGC. However, as with other works that study the impact of technical factors on MBF, there is no ground truth and no convenient way to compare with a gold standard of MBF and, as such, we can only report relative changes of MBF as a consequence of PGC. ...
Background
Rubidium-82 myocardial perfusion imaging is a well-established technique for assessing myocardial ischemia. With continuing interest on myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements, there is a requirement to fully appreciate the impact of technical aspects of the process. One such factor for rubidium-82 is prompt gamma compensation (PGC). This study aims to assess the impact of PGC on MBF and MFR calculated from dynamic Rb-82 data. Methods
Dynamic rest and stress images were acquired on a Siemens Biograph mCT and reconstructed with and without PGC in 50 patients (29 male). MBF and MFR were measured in the three main coronary territories as well as globally. ResultsWith PGC, statistically significant reductions in MBF were observed in LAD (−6.9%), LCx (−4.8%), and globally (−6.5%) but only in obese patients. Significant increases in MBF were observed in RCA (+6.4%) in only nonobese patients. In very obese patients, differences of up to 40% in MBF were observed between PGC and non-PGC images. In nearly all cases, similar PGC differences were observed at stress and rest so there were no significant differences in MFR; however, in a small number of very obese patients, differences in excess of 20% were observed. ConclusionPGC results in statistically significant changes in MBF, with the greatest reductions observed in the LAD and LCx territories of obese patients. In most cases, the impact on stress and rest data is of similar relative magnitudes and changes to MFR are small.
