EJNMMI Physics最新文献

{"title":"Comparison of scatter and partial volume correction techniques for quantitative SPECT imaging of ²²⁵Ac.","authors":"Grigory Liubchenko, Guido Böning, Mikhail Rumiantcev, Adrian J Zounek, Mathias J Zacherl, Gabriel Sheikh, Sandra Resch, Rudolf A Werner, Sibylle I Ziegler, Astrid Delker","doi":"10.1186/s40658-025-00800-0","DOIUrl":"10.1186/s40658-025-00800-0","url":null,"abstract":"<p><strong>Background: </strong>The extreme low-count regime for clinical ²²⁵Ac-SPECT imaging poses a challenge to energy-window based scatter correction (EWSC) methods. Moreover, SPECT imaging suffers from partial volume effects (PVE), which can degrade quantification and lead to an underestimation of the absorbed dose estimations, especially in small structures such as lesions. The aim of this study was to investigate the impact of scatter correction and partial volume correction (PVC) techniques on post-therapeutic imaging of the three imageable photopeaks of ²²⁵Ac.</p><p><strong>Methods: </strong>A phantom with three 3D-printed spheres (191, 100, 48 ml) was imaged to compare transmission-dependent scatter correction (TDSC) to EWSC (440, 218 keV)/no scatter correction (no SC) (78 keV), as well as the impact of iterative Yang (IY)- and Richardson-Lucy (RL)-based PVC techniques, in terms of contrast-to-noise ratios (CNR) and recovery coefficients (RC). These scatter correction and PVC methods were also compared for a patient cohort, with two SPECT/CTs acquired 24 and 48 h after [²²⁵Ac]Ac-PSMA-I&T therapy, to evaluate their impact on kidney and lesion dosimetry.</p><p><strong>Results: </strong>In the phantom study, TDSC outperformed EWSC/no SC across all energy windows in terms of CNR, and in terms of RC for 218 and 78 keV energy windows under clinically relevant conditions. Application of PVC techniques resulted in a clear increase in RC and CNR across all energy windows. In the patient study, RBE-weighted kidney absorbed doses increased on average across all kidneys by 9 ± 4%, 30 ± 29% and 35 ± 29% for 440, 218 and 78 keV energy windows, respectively, when TDSC was applied. For lesion dosimetry, TDSC resulted in an average increase across all lesions by 16 ± 8% (218 keV) and 31 ± 30% (78 keV), and a decrease by 4 ± 8% (440 keV). In the patient study, IY-based PVC increased kidney absorbed doses by 172 ± 54%, 157 ± 45% and 146 ± 47%, for 440, 218 and 78 keV energy windows, respectively. RL-based PVC increased lesion absorbed doses by 34 ± 6%, 29 ± 8%, and 23 ± 10%, for 440, 218 and 78 keV energy windows, respectively.</p><p><strong>Conclusion: </strong>The phantom and patient studies demonstrated TDSC superiority over EWSC/no SC. PVC techniques substantially increased kidney (IY) and lesion (RL) absorbed doses, highlighting their value for post-reconstruction enhancement of ²²⁵Ac SPECT images.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"88"},"PeriodicalIF":3.2,"publicationDate":"2025-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12491142/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145211960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparison of SZ-HRX and LEHR collimators for reduced-duration 123I-ioflupane brain SPECT/CT: a phantom study.","authors":"Mathieu Pavoine, Kouider-Othmane Kelatma, Clémence Robert, Alexandre Rintaud, Samuel Guigo, Thomas Godefroy, Pierre-Yves Salaün, Solène Querellou, David Bourhis","doi":"10.1186/s40658-025-00795-8","DOIUrl":"10.1186/s40658-025-00795-8","url":null,"abstract":"<p><strong>Background: </strong>¹²³I-ioflupane Single Photon Emission Computed Tomography with Computed Tomography (SPECT-CT) imaging is widely used to assess dopaminergic denervation in parkinsonian syndromes, such as Parkinson's disease and atypical variants. Standard imaging generally uses low-energy high-resolution (LEHR) parallel-hole collimators, which require long acquisition times and minimal source-to-detector distance to optimize spatial resolution. Recently, the Smart-Zoom High-Resolution and eXtended magnification volume (SZ-HRX) solution was designed specifically for neurological applications. It incorporates multifocal collimators and a dedicated reconstruction algorithm, promising a reduction in acquisition duration, and an improvement in patient comfort by allowing detectors to be positioned further away from the head. The aim of this study is to investigate the performance of SZ-HRX system compared to LEHR collimators.</p><p><strong>Methods: </strong>A striatal phantom with 5 compartments (putamens, caudates, and background) was filled with different concentrations of ¹²³I-ioflupane to simulate various clinical situations. Tomographic acquisitions were performed on each LEHR and SZ-HRX system. The summation of dynamically acquired projections allowed testing different acquisition durations with the SZ-HRX collimator. Sensitivity and Spatial resolution were assessed and compared. The data were reconstructed according to EANM recommendations. Contrast-to-noise ratio (CNR), striatum-to-background ratio (SBR), coefficient of variation (CV), and normalized asymmetry index (NAI) were calculated for both systems and compared to the LEHR acquisition. To estimate the shortest SZ-HRX acquisition duration, a linear regression of all quantitative results were calculated between the two systems.</p><p><strong>Results: </strong>SZ-HRX collimation had superior performance characteristics than LEHR, with relative changes in CNR, CV, and SBR of + 99%, -28% and + 42% respectively, without any decrease in spatial resolution or change in asymmetry index. SZ-HRX system seems to be at least as good as LEHR system, up to 40% of scan time reduction.</p><p><strong>Conclusion: </strong>SZ-HRX collimation showed superior performance characteristics to LEHR collimation in the study of ¹²³I-ioflupane filled striatal phantom, enabling shorter acquisitions.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"86"},"PeriodicalIF":3.2,"publicationDate":"2025-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12484530/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145198827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improving data-driven gated (DDG) PET and CT registration in thoracic lesions: a comparison of AI registration and DDG CT.","authors":"Tinsu Pan, M Allan Thomas, Yang Lu, Dershan Luo","doi":"10.1186/s40658-025-00797-6","DOIUrl":"10.1186/s40658-025-00797-6","url":null,"abstract":"&lt;p&gt;&lt;strong&gt;Purpose: &lt;/strong&gt;Misregistration between CT and PET can result in mis-localization and inaccurate quantification of the tracer uptake in PET. Data-driven gated (DDG) CT can correct registration and quantification but requires a radiation dose of 1.3 mSv and 1 min of acquisition time. AI registration (AIR) does not require an additional CT and has been validated to improve registration and reduce the 'banana' misregistration artifacts around the diaphragm. We aimed to compare a validated AIR and DDG CT in registration and quantification of avid thoracic lesions misregistered in DDG PET scans.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;Thirty PET/CT patient data (23 with &lt;sup&gt;18&lt;/sup&gt;F-FDG, 4 with &lt;sup&gt;68&lt;/sup&gt;Ga-Dotatate, and 3 with &lt;sup&gt;18&lt;/sup&gt;F-PSMA piflufolastat) with at least one misregistered avid lesion in the thorax were recruited. Patient studies were conducted using DDG CT to correct misregistration with DDG PET data of the phases 30 to 80% on GE Discovery MI PET/CT scanners. Non-attenuation correction DDG PET and misregistered CT were input to AIR and the AIR-corrected CT data were output to register and quantify the DDG PET data. Registration and quantification of lesion SUV&lt;sub&gt;max&lt;/sub&gt; and signal-to-background ratio (SBR) of the lesion SUV&lt;sub&gt;max&lt;/sub&gt; to the 2-cm background mean SUV were compared for each of the 51 avid lesions.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;DDG CT outperformed AIR in misregistration correction and quantification of avid thoracic lesions (1.16 ± 0.45 cm). Most lesions (46/51, 90%) showed improved registration from DDG CT relative to AIR, with 10% (5/51) being similar between AIR and DDG CT. The lesions in the baseline CT were an average of 2.06 ± 1.0 cm from their corresponding lesions in the DDG CT, while those in the AIR CT were an average of 0.97 ± 0.54 cm away. AIR significantly improved lesion registration compared to the baseline CT (P &lt; 0.0001). SUV&lt;sub&gt;max&lt;/sub&gt; increased by 18.1 ± 15.3% with AIR, but a statistically significantly larger increase of 34.4 ± 25.4% was observed with DDG CT (P &lt; 0.0001). A statistically significant increase in SBR was also observed, rising from 10.5 ± 12.1% of AIR to 21.1 ± 20.5% of DDG CT (P &lt; 0.0001). Many registration improvements by AIR were still left with misregistration. AIR could mis-localize a lymph node to the lung parenchyma or the ribs, and could also mis-localize a lung nodule to the left atrium. AIR could also distort the rib cage and the circular shape of the aorta cross section.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusions: &lt;/strong&gt;DDG CT outperformed AIR in both localization and quantification of the thoracic avid lesions. AIR improved registration of the misregistered PET/CT. Registered lymph nodes could be falsely misregistered by AIR. AIR-induced distortion of the rib cage can also negatively impact image quality. Further research on AIR's accuracy in modeling true patient respiratory motion without introducing new misregistration or anatomical distortion is warranted.&lt;/p","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"87"},"PeriodicalIF":3.2,"publicationDate":"2025-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12484437/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145198800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Large scale comparison of maximum likelihood scatter scaling and tail-fitted scatter scaling in LAFOV PET/CT.","authors":"Nanna Overbeck, Søren Holm, Mohammadreza Teimoorisichani, Maurizio Conti, Thomas Lund Andersen, Flemming Littrup Andersen","doi":"10.1186/s40658-025-00796-7","DOIUrl":"10.1186/s40658-025-00796-7","url":null,"abstract":"<p><strong>Background: </strong>Scatter scaling during the reconstruction of Positron Emission Tomography (PET) data is a crucial element for obtaining clinically applicable images with accurate quantification and high image quality. The current clinical standard for scatter scaling is fitting the tail regions of the single scatter simulation (SSS) estimate, which is termed Tail-Fitted Scatter Scaling (TFSS). This study aims to compare a Maximum Likelihood Scatter Scaling (MLSS) algorithm relative to TFSS using a NEMA IQ phantom investigation and a patient cohort including 500 patients using long axial Field-of-View (LAFOV) PET. The relative difference between the two scatter scaling algorithms was investigated using uptake values of 12 organs. Furthermore, the proximity of known regions showing high activity relative to the surrounding tissue was analysed.</p><p><strong>Results: </strong>The NEMA image quality phantom study showed agreement between the expected activity concentration and the MLSS reconstructions. MLSS showed uptake values of 137.3 ± 3.4 kBq/mL in the largest sphere and 34.6 ± 0.5 kBq/mL in the background, closely matching the true concentrations of 136.6 kBq/mL and 35.0 kBq/mL, respectively. TFSS provided uptake values of 133.7 ± 3.5 kBq/mL in the largest sphere and 33.0 ± 0.9 kBq/mL in the background. MLSS showed higher uptake in the cold areas relative to TFSS. Mean recovery coefficients (RC_mean) showed that MLSS generally had coefficients closer to 1 relative to TFSS across the spheres of the phantom. The findings of the patient study showed a numeric relative difference below 2% when investigating organ uptake through the 12 organs.</p><p><strong>Conclusion: </strong>MLSS provided results of high image quality comparable to the standard method of choice, TFSS, in the clinical routine. The phantom study showed that MLSS provided uptake values accurately relative to the known activity concentration, however less accurate within the cold sphere and insert. MLSS was found to provide robust results across a large patient cohort and is suggested as a suitable substitution for TFSS in the PET image reconstruction process.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"85"},"PeriodicalIF":3.2,"publicationDate":"2025-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12480279/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145184979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimization of ^99mTc-SPECT in the presence of ⁹⁰Y for radioembolization.","authors":"Camiel E M Kerckhaert, Martijn M A Dietze, Rob van Rooij, Marjolein B M Meddens, Niek Wijnen, Maarten L J Smits, Marnix G E H Lam, Hugo W A M de Jong","doi":"10.1186/s40658-025-00798-5","DOIUrl":"10.1186/s40658-025-00798-5","url":null,"abstract":"<p><strong>Background: </strong>^99mTc-macroaggregated albumin (MAA) imaging is part of the standard work-up procedure for radioembolization using ⁹⁰Y microspheres. In certain scenarios, it may be warranted to visualize the distribution of ^99mTc in co-presence of ⁹⁰Y, for example when validating intra-procedural ^99mTc-MAA imaging after ⁹⁰Y-therapy to enable single-session radioembolization. Another instance involves additional ^99mTc-MAA administration during the therapeutic procedure itself, e.g. when initial imaging reveals insufficient targeting of a specific liver segment. In these situations, crosstalk from ⁹⁰Y can result in reduced ^99mTc image quality and quantitative accuracy. This study investigates the feasibility and optimal method of ^99mTc SPECT imaging from combined ^99mTc+⁹⁰Y data using phantom experiments.</p><p><strong>Results: </strong>An anthropomorphic torso phantom with two liver tumor inserts was filled with ^99mTc without (single-isotope) and with ⁹⁰Y (dual-isotope) in various activities and isotope concentrations. Three collimators (low energy high resolution: LEHR, medium energy: ME, and high energy: HE) and three methods to compensate for ⁹⁰Y crosstalk in the ^99mTc photo peak window (Monte Carlo-based, dual-energy-window and triple-energy-window correction) were evaluated. No substantial dead-time effects were observed in the clinically relevant activity range, up to approximately 12 GBq ^99mTc+⁹⁰Y (ratio 1:20) with LEHR, 29 GBq with ME and > 30 GBq with HE. Compared to the clinical standard (single-isotope ^99mTc imaging with LEHR collimator), contrast recovery typically decreased from 70.0 ± 1.3% to 49.0 ± 0.9% (LEHR), 61.2 ± 1.5% (ME) or 62.1 ± 1.4% (HE) due to ⁹⁰Y crosstalk. Compensation methods increased contrast recovery, with Monte Carlo-based correction combined with a ME or HE collimator yielding the best recovery at 68.5 ± 1.6% and 68.3 ± 1.5%, respectively. Visual image quality in terms of resolution and scatter contamination was superior when using a ME collimator. Lung shunt fractions were also severely affected by ⁹⁰Y crosstalk when using LEHR, but could be effectively mitigated using a ME or HE collimator.</p><p><strong>Conclusion: </strong>^99mTc imaging in the presence of ⁹⁰Y leads to substantial image degradation due to crosstalk effects. Monte Carlo-based crosstalk compensation in combination with a ME or HE collimator was identified as the most accurate, robust and visually optimal reconstruction method for ^99mTc SPECT from dual-isotope data.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"84"},"PeriodicalIF":3.2,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12463788/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145136999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Correction: Phantom imaging demonstration of positronium lifetime with a long axial field‑of‑view PET/CT and ¹²⁴I.","authors":"Lorenzo Mercolli, William M Steinberger, Narendra Rathod, Maurizio Conti, Paweł Moskal, Axel Rominger, Robert Seifert, Kuangyu Shi, Ewa Ł Stępień, Hasan Sari","doi":"10.1186/s40658-025-00801-z","DOIUrl":"10.1186/s40658-025-00801-z","url":null,"abstract":"","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"83"},"PeriodicalIF":3.2,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12443642/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145074528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimizing dosimetry in Y-90 microsphere radioembolization: GPU-accelerated Monte Carlo simulation versus conventional methods for high-volume setting.","authors":"Liu Hongming, Liang Ziwei, Hu Ziyi, Qu Shuiyin, Hu Ankang, Yan ShuChang, Wu Zhen, Zhang Hui, Li Junli, Qiu Rui","doi":"10.1186/s40658-025-00794-9","DOIUrl":"10.1186/s40658-025-00794-9","url":null,"abstract":"&lt;p&gt;&lt;strong&gt;Background: &lt;/strong&gt;Yttrium-90 (&lt;sup&gt;90&lt;/sup&gt;Y) microsphere radioembolization has shown unique advantages in treating both primary and metastatic liver cancer and was introduced into China in 2022. Despite the development of various dosimetric models-ranging from empirical to voxel-based approaches-practical implementation remains challenging. With over 370,000 new liver cancer cases annually and limited access to certified &lt;sup&gt;90&lt;/sup&gt;Y treatment centers, Chinese interventional oncology departments face increasing pressure to balance dosimetric accuracy with clinical efficiency. This study aims to develop a GPU-based fast Monte Carlo project for accurate voxel-level dose calculation and to evaluate its performance alongside existing dosimetric strategies, with the goal of supporting optimized clinical workflows in high-volume settings.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;A fast Monte Carlo simulation algorithm was developed using Graphics Processing Unit (GPU) acceleration and applied retrospectively to eight patients diagnosed with hepatocellular carcinoma or metastatic colorectal cancer. The dosimetric performance of the GPU-based approach was compared against direct Monte Carlo (MC) simulations, the Medical Internal Radiation Dose (MIRD) formalism, the Voxel S-value (VSV) method, and the Local Energy Deposition (LED) model. Voxel- and organ-level dose accuracy were quantified using metrics such as Mean Absolute Relative Error (MARE), Relative Standard Deviation (RSD), and D95 in dose volume histogram. Statistical comparisons were conducted using Shapiro-Wilk normality tests and repeated measures ANOVA to assess inter-method differences.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;The GPU-based Monte Carlo code demonstrated high accuracy and computational efficiency. Using direct MC simulation as the reference, the GPU-based approach yielded the lowest voxel-level variability, with median RSDs in high-activity transverse regions reaching - 1.13%, indicating superior consistency. Corresponding MARE were 4.53% for the GPU method, compared to 6.71% for VSV and 49.36% for LED, confirming its dosimetric reliability. At the organ level, the GPU-based method achieved RSDs of 0.35% ± 0.80% (tumor), -0.45% ± 0.76% (liver), 1.41% ± 4.45% (lung), and - 1.43% ± 1.23% (spleen), significantly outperforming alternative models. Notably, VSV and LED substantially underestimated lung dose (-52.19% ± 23.87%, -53.71 ± 22.17%), highlighting their limited applicability in heterogeneous regions. In contrast, the dose of spleen (F = 3.26, p = 0.069) and kidneys (F = 3.22, p = 0.071) did not show statistically significant differences between methods. In terms of computational performance, the GPU-based code delivered a remarkable 1,296-fold speed-up over traditional MC simulations, enabling efficient voxel-level dosimetry suitable for clinical workflows.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusion: &lt;/strong&gt;The GPU-based fast Monte Carlo simulation provides a highly accurate and computatio","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"82"},"PeriodicalIF":3.2,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12401777/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144947103","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Bridging physics and practice: evaluating sensitivity, septal penetration, and detector dead time in terbium-161 gamma-camera imaging.","authors":"Frida Westerbergh, Lisa McDougall, Philipp Ritt, Julia G Fricke, Nicholas P van der Meulen, Cristina Müller, Roger Schibli, Damian Wild, Peter Bernhardt","doi":"10.1186/s40658-025-00792-x","DOIUrl":"10.1186/s40658-025-00792-x","url":null,"abstract":"<p><strong>Introduction/aim: </strong>Terbium-161 (¹⁶¹Tb) has emerged as a promising therapeutic radionuclide, yet standardized imaging guidelines are lacking. This study aimed to characterize a SPECT/CT system, currently used in an ongoing clinical trial (BETA PLUS; NCT05359146), focusing on sensitivity, septal penetration, and dead-time effects.</p><p><strong>Methods: </strong>Measurements were conducted on a Siemens Symbia Intevo system using two collimators: low-energy high-resolution (LEHR) and medium-energy low-penetration (MELP). Two energy windows were evaluated: 75 keV ± 10% and 48 keV ± 20%. Planar sensitivity and penetration were assessed using a ¹⁶¹Tb-filled Petri dish. Penetration fractions were determined as a function of distance for each collimator-window combination. Dead time was measured intrinsically for each detector using a set of ¹⁶¹Tb point sources. SPECT measurements of a homogenous cylinder phantom were performed to assess count rate performance and predict activity levels at which dead-time effects could occur. To evaluate the potential impact of dead time in patient imaging, SPECT projection data from patients treated with 1 GBq of [¹⁶¹Tb]Tb-DOTA-LM3 (n = 8) was analyzed.</p><p><strong>Results: </strong>Sensitivity was comparable for both collimators at 75 keV (LEHR: 15.7 cps/MBq, MELP: 18.5 cps/MBq) and increased at 48 keV (LEHR: 44.4 cps/MBq, MELP: 67.9 cps/MBq). Maximum penetration occurred at 75 keV with the LEHR collimator (7.5% at 10 cm). In acquired spectra, more than half of the detected counts (51.6%) appeared above the 75 keV window with LEHR, compared to only 12.2% with MELP. Dead-time analyses revealed non-linear detector responses at wide-spectrum count rates exceeding 93 kcps, corresponding to in-field activities of 1.4-2.0 GBq for LEHR and 1.7-2.2 GBq for MELP. The dead-time constant was determined to 0.42 µs for both detector heads, however, the maximum recorded count rate differed significantly (384 kcps vs. 546 kcps). The median and maximum wide-spectrum count rate for patients treated with [¹⁶¹Tb]Tb-DOTA-LM3 was estimated to ~ 20 and ~ 40 kcps per GBq 3 h p.i., respectively, when imaged with LEHR, corresponding to a maximum estimated dead-time loss of 1.7%.</p><p><strong>Conclusions: </strong>While high-quality ¹⁶¹Tb SPECT imaging is feasible, careful consideration is essential; the wide range of photons emitted will produce a higher wide-spectrum count rate as compared to ¹⁷⁷Lu. The use of low-energy collimators increases penetration and scatter, impairing quantitative accuracy and elevating the wide-spectrum count rate, which may intensify dead-time effects. At therapeutic activity levels (e.g., 7.4 GBq), dead time should be closely monitored to ensure reliable quantification.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"81"},"PeriodicalIF":3.2,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12390893/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144947143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phantom imaging demonstration of positronium lifetime with a long axial field-of-view PET/CT and ¹²⁴I.","authors":"Lorenzo Mercolli, William M Steinberger, Narendra Rathod, Maurizio Conti, Paweł Moskal, Axel Rominger, Robert Seifert, Kuangyu Shi, Ewa Ł Stępień, Hasan Sari","doi":"10.1186/s40658-025-00790-z","DOIUrl":"10.1186/s40658-025-00790-z","url":null,"abstract":"<p><strong>Purpose: </strong>Measuring the ortho-positronium (oPs) lifetime in human tissue bears the potential of adding clinically relevant information about the tissue microenvironment to conventional positron emission tomography (PET). Through phantom measurements, we investigate the voxel-wise measurement of oPs lifetime using a commercial long-axial field-of-view (LAFOV) PET scanner.</p><p><strong>Methods: </strong>We prepared four samples with mixtures of Amberlite XAD4, a porous polymeric adsorbent, and water and added between 1.12 and 1.44 MBq of ¹²⁴I. The samples were scanned in two different setups: once with a couple of centimeters between each sample (15 min scan time) and once with all samples taped together (40 min scan time). For each scan, we determine the oPs lifetime for the full samples and at the voxel level. The voxel sizes under consideration are 10.0³ mm³, 7.1³ mm³ and 4.0³ mm³.</p><p><strong>Results: </strong>Amberlite XAD4 allows the preparation of samples with distinct oPs lifetime. Using a Bayesian fitting procedure, the oPs lifetimes in the whole samples are 2.52 ± 0.03 ns, 2.37 ± 0.03 ns, 2.27 ± 0.04 ns and 1.82 ± 0.02 ns, respectively. The voxel-wise oPs lifetime fits showed that even with 4.0³ mm³ voxels the samples are clearly distinguishable and a central voxels have good count statistics. However, the situation with the samples close together remains challenging with respect to the spatial distinction of regions with different oPs lifetimes.</p><p><strong>Conclusions: </strong>Our study shows that positronium lifetime imaging on a commercial LAFOV PET/CT is feasible using ¹²⁴I.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"80"},"PeriodicalIF":3.2,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12379202/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144947172","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A critical phantom study of the energy window used for ^99mTc quantitative explorations with a ring CZT SPECT system.","authors":"Alain Seret, Claire Bernard","doi":"10.1186/s40658-025-00793-w","DOIUrl":"10.1186/s40658-025-00793-w","url":null,"abstract":"<p><strong>Background: </strong>This study investigated, mainly for quantitative ^99mTc explorations with a ring CZT SPECT system (GE HealthCare Starguide), the use of a narrow symmetric or a fully asymmetric energy window to reject scattered photons. The results were compared with the manufacturer's post-acquisition dual energy window approach.</p><p><strong>Methods: </strong>Two uniform and two cold and hot rod contrast cylindrical phantoms of various sizes were scanned with the Starguide system to acquire a very high number of counts. After rebinning the list-mode files for different energy windows, data were reconstructed with manufacturer's iterative algorithm including attenuation correction, resolution recovery and eventually scatter correction, but without any regularization technique. Cold rod residual scatter fraction, hot and cold rod contrast recovery coefficient, coefficient of variation in phantom uniform areas and quantification accuracy using calibration with one of the homogeneous phantoms were, among others, computed.</p><p><strong>Results: </strong>Narrow symmetric photopeak-centred windows or fully asymmetric (≥ 140 keV) window led, on one hand, to decreased scatter residual fraction and sensitivity and, on the other hand, to increased noise, cold and hot recovery coefficients when compared to a standard 15-20% wide symmetric window. With a 6-7% wide symmetric window we obtained very comparable results to the dual energy window scatter correction used by the manufacturer for all measured parameters, but larger recovery coefficients especially for small hot objects in a cold background. Similar results were obtained with the fully asymmetric window at the cost of a higher noise level resulting from a drastic reduction of the sensitivity.</p><p><strong>Conclusions: </strong>Narrow symmetric or asymmetric energy windows were found an interesting alternative to the standard dual energy window method to reject ^99mTc scattered photons. As a key feature, they allowed to avoid the erasing of small hot objects in a null background that was observed with the standard dual energy window scatter correction.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":"12 1","pages":"79"},"PeriodicalIF":3.2,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12368274/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144947138","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}