EJNMMI Physics最新文献

Purpose: Lung tumors, which receive dual-blood-supply from the pulmonary and bronchial arteries, may exhibit distinct kinetic parameters compared to other malignancies. This study aimed to investigate the impact of various factors on the kinetic parameter quantification of [¹⁸F]F-FAPI-42 dynamic PET/CT and to establish an acceptable shortened acquisition time for lung cancer.

Methods: A total of 19 patients with lung tumors underwent 60-minute total-body dynamic [¹⁸F]F-FAPI-42 PET/CT imaging. Tumor kinetic metrics (K₁ to K₃ and K_i) were calculated using a two-tissue irreversible comparative (2TiC) model. The effects of different image-derived input function (IDIF) models (derived from the right ventricle [RV], left ventricle [LV], and descending aorta [DA]), as well as tumor location, pathohistological subtype and size on kinetic parameters were evaluated. Additionally, the mean standardized uptake value (SUV_mean), tumor-to-background ratio (TBR), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were assessed to determine an acceptable shortened acquisition time.

Results: The time-activity curve (TAC) of the RV exhibited the earliest and highest peak, followed by those of the LV and DA. Impact of IDIF model and tumor size on kinetic parameters of primary tumors was observed. Specifically, in the RVIF model, size of tumor > 3 cm exhibited higher K₂ and K₃ than those with size ≤ 3 cm (P < 0.05). Similar findings were also noted for K₃ in the LVIF model (P < 0.05), but not in the DAIF model. Tumor location and pathohistological subtype had no significant impact on kinetic parameters quantification. Regarding acquisition time, the RVIF model achieved kinetic parameters equivalent to those at 60 min in 26 min, while the LVIF and DAIF models required 36 min. At 26 min, the tumors were clearly visualized, with SUV_mean, SNR, CNR and TBR being equivalent or nearly approaching the values observed at 60 min.

Conclusion: The RVIF model appears to be more suitable than the DAIF model for quantifying kinetic parameters in [¹⁸F]F-FAPI-42 PET dynamic imaging of lung cancer, with an acceptable shortened acquisition time of 26 min.

Purpose: This study aimed to evaluate the accuracy of time-integrated activity (TIA) estimation using single-time-point (STP) data combined with nonlinear mixed-effects modelling (NLMEM) and population-based model selection (PBMS) in 73 patients with benign thyroid disease.

Methods: Biokinetic data of ¹³¹I were collected from 73 patients with benign thyroid conditions, including Graves' disease, toxic nodular goitre, and non-toxic goitre. Uptake measurements were taken at 2, 6, 24, 48 (73 patients), 96 h (53 patients) or 120 h (20 patients) after administration. The best sum-of-exponentials function (SOEF) with four adjustable parameters, identified in our recent study (Hardiansyah et al. EJNMMI Phys, 2025) by PBMS NLMEM, and the SOEF EANM standard operating procedure (SOP) with three adjustable parameters were then employed to conduct a NLMEM-based STP dosimetry at different time points, i.e. s1TIA and s2TIAs, respectively. In addition, STP dosimetry was performed using the EANM SOP approach (Hänscheid et al. EJNMMI, 2013) to calculate TIAs (hTIAs). The accuracy of the computed s1TIAs, s2TIAs and hTIAs was evaluated by calculating the relative deviations (RDs), mean absolute percentage errors (MAPEs), root-mean-square errors (RMSEs), and percentage of absolute RDs of sTIAs and hTIAs exceeding 5% (%RD5) and 10% (%RD10) with the reference TIAs obtained from the four parameters NLMEM fit to all time points data.

Results: Of the time points included, 120 h after administration was found as the optimal time point for STP dosimetry based on the mean ± SD of RD (RMSE, MAPE, %RD5, %RD10) of s1TIA, s2TIAs, and hTIA of 2% ± 4% (4%,3%,25%,0%), 13% ± 6% (14%,13%,90%,60%) and -3% ± 5% (6%,5%,55%,0%), respectively.

Conclusions: While s1TIA typically produced better ¹³¹I TIA estimates for benign thyroid disease than the hTIA recommended in the EANM SOP, the STP calculation from NLMEM using SOEF EANM SOP s2TIAs was inferior to hTIA. With the best SOEF model, NLMEM provides satisfactory and reasonable STP estimates.

Background: 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.

Methods: 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.

Results: 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.

Conclusion: 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.

Background: 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.

Methods: 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.

Results: 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.

Conclusion: SZ-HRX collimation showed superior performance characteristics to LEHR collimation in the study of ¹²³I-ioflupane filled striatal phantom, enabling shorter acquisitions.

Background: 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.

Results: 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.

Conclusion: 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.

Background: ^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.

Results: 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.

Conclusion: ^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.

Introduction/aim: 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.

Methods: 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.

Results: 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%.

Conclusions: 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.