The impact of different reconstruction parameters on quantitative 99mTc-DPD SPECT/CT values in the assessment of cardiac transthyretin amyloidosis.

AIM: To assess in a phantom and in a clinical study the influence of different reconstruction parameters on quantitative SPECT/CT values in the assessment of cardiac transthyretin amyloidosis (ATTR-CA). METHOD: A hybrid SPECT/CT camera with a proprietary software for SPECT/CT-based quantification of myocardial uptake of 99mTc-DPD was used. Images were reconstructed with 6 different protocols, differing in iterations, subset and Gaussian filter. Quantitative values were tested in phantom and clinical studies across different reconstruction protocols. Values were automatically calculated both as kBq/ml and as maximum, mean and peak standardized uptake value (SUV). RESULTS: The standard parameters provided by the manufacturer (reconstruction 1) yielded higher accuracy in quantifying, with measuring 97.1% of the expected activity in the phantom. Reconstructions with higher Gaussian filter caused a systematic underestimation of quantified values of 27.2% (p < 0.01). Results were replicated in the clinical study consisting of 155 patients with suspected ATTR-CA, wherein changing the number of iterations and subsets was not associated with a statistically significant difference in quantitative values compared to reconstruction 1, while a higher Gaussian filter caused inaccurate quantification with up to 24% of difference measured. CONCLUSION: Different reconstruction parameters can impact quantitative values on 99mTc-DPD SPECT/CT. Therefore, parameters should be maintained consistently across different acquisitions and different centres.

Internal dosimetry study of [82Rb]Cl using a long axial field-of-view PET/CT.

PURPOSE: Long axial field-of-view (LAFOV) positron emission tomography (PET) systems allow to image all major organs with one bed position, which is particularly useful for acquiring whole-body dynamic data using short-lived radioisotopes like 82Rb. METHODS: We determined the absorbed dose in target organs of three subjects (29, 40, and 57 years old) using two different methods, i.e., MIRD and voxel dosimetry. The subjects were injected with 407.0 to 419.61 MBq of [82Rb]Cl and were scanned dynamically for 7 min with a LAFOV PET/CT scanner. RESULTS: Using the MIRD formalism and voxel dosimetry, the absorbed dose ranged from 1.84 to 2.78 µGy/MBq (1.57 to 3.92 µGy/MBq for voxel dosimetry) for the heart wall, 2.76 to 5.73 µGy/MBq (3.22 to 5.37 µGy/MBq for voxel dosimetry) for the kidneys, and 0.94 to 1.88 µGy/MBq (0.98 to 1.92 µGy/MBq for voxel dosimetry) for the lungs. The total body effective dose lied between 0.50 and 0.76 µSv/MBq. CONCLUSION: Our study suggests that the radiation dose associated with [82Rb]Cl PET/CT can be assessed by means of dynamic LAFOV PET and that it is lower compared to literature values.

Long-axial field-of-view PET/CT for the assessment of inflammation in calcified coronary artery plaques with [68 Ga]Ga-DOTA-TOC.

PURPOSE: Inflamed, prone-to-rupture coronary plaques are an important cause of myocardial infarction and their early identification is crucial. Atherosclerotic plaques are characterized by overexpression of the type-2 somatostatin receptor (SST2) in activated macrophages. SST2 ligand imaging (e.g. with [68 Ga]Ga-DOTA-TOC) has shown promise in detecting and quantifying the inflammatory activity within atherosclerotic plaques. However, the sensitivity of standard axial field of view (SAFOV) PET scanners may be suboptimal for imaging coronary arteries. Long-axial field of view (LAFOV) PET/CT scanners may help overcome this limitation. We aim to assess the ability of [68 Ga]Ga-DOTA-TOC LAFOV-PET/CT in detecting calcified, SST2 overexpressing coronary artery plaques. METHODS: In this retrospective study, 108 oncological patients underwent [68 Ga]Ga-DOTA-TOC PET/CT on a LAFOV system. [68 Ga]Ga-DOTA-TOC uptake and calcifications in the coronary arteries were evaluated visually and semi-quantitatively. Data on patients' cardiac risk factors and coronary artery calcium score were also collected. Patients were followed up for 21.5 ± 3.4 months. RESULTS: A total of 66 patients (61.1%) presented with calcified coronary artery plaques. Of these, 32 patients had increased [68 Ga]Ga-DOTA-TOC uptake in at least one coronary vessel (TBR: 1.65 ± 0.53). Patients with single-vessel calcifications showed statistically significantly lower uptake (SUVmax 1.10 ± 0.28) compared to patients with two- (SUVmax 1.31 ± 0.29, p < 0.01) or three-vessel calcifications (SUVmax 1.24 ± 0.33, p < 0.01). There was a correlation between coronary artery calcium score (CACS) and [68 Ga]Ga-DOTA-TOC uptake, especially in the LAD (p = 0.02). Stroke and all-cause death occurred more frequently in patients with increased [68 Ga]Ga-DOTA-TOC uptake (15.63% vs. 0%; p:0.001 and 21.88% vs. 6.58%; p: 0.04, respectively) during the follow-up period. CONCLUSION: [68 Ga]Ga-DOTA-TOC as a marker for the macrophage activity can reveal unknown cases of inflamed calcified coronary artery plaques using a LAFOV PET system. [68 Ga]Ga-DOTA-TOC uptake increased with the degree of calcification and correlated with higher risk of stroke and all-cause death. [68 Ga]Ga-DOTA-TOC LAFOV PET/CT may be useful to assess patients' cardiovascular risk.

New thresholds in semi-quantitative [18F]FDG PET/CT are needed to assess large vessel vasculitis with long-axial field-of-view scanners.

AIM: [18F]FDG PET/CT proved accurate in the diagnostic work-up of large vessel vasculitis (LVV). While a visual interpretation is currently considered adequate, several attempts have been made to integrate it with a semiquantitative evaluation. In this regard, there is the need to validate current or new thresholds for the semiquantitative parameters on long-axial field of view (LAFOV) scanners. METHODS: We retrospectively evaluated 100 patients (50 with LVV and 50 controls) who underwent [18F]FDG LAFOV PET/CT. Semiquantitative parameters (SUVmax and SUVmean) were calculated for large vessels in 3 districts (supra-aortic [SA], thoracic aorta [TA], and infra-aortic [IA]). Values were also normalized to liver activity (SUVmax/L-SUVmax, and SUVmax/L-SUVmean). RESULTS: Of the 50 patients diagnosed with LVV, SA vessels were affected in 38 (76%), TA in 42 (84%) and IA vessels in 26 (52%). To-liver normalized values had higher diagnostic accuracy than non-normalized values (AUC always ≥ 0.90 vs. 0.74-0.89). For the SA vessels, best thresholds were 0.66 for SUVmax/L-SUVmax and 0.88 for SUVmax/L-SUVmean; for the TA, 1.0 for SUVmax/L-SUVmax and 1.30 for SUVmax/L-SUVmean; finally, for IA vessels, the best threshold was 0.83 for SUVmax/L-SUVmax and 1.11 for SUVmax/L-SUVmean. CONCLUSION: LAFOV [18F]FDG-PET/CT is accurate in the diagnostic workup of LVV, but different threshold in semi-quantitative parameters than reported in literature for standard scanners should be considered.

Cholecystitis induced by Yttrium-90 radioembolization of advanced liver tumors: prospective evaluation of a management algorithm in 197 consecutive patients.

BACKGROUND: Cholecystitis is a rare but dolorous complication after Y90-radioembolization of liver malignancies. PURPOSE: To decide the occlusion of the cystic artery (CA) to prevent cholecystitis after Y90 radioembolization using an algorithm. MATERIAL AND METHODS: In 130 patients, the gallbladder was at risk of embolization as the right liver lobe was targeted. Precautionary measures (e.g. coil occlusion of the cystic artery) were decided by enhancement of the gallbladder in pre-treatment Tc99m-MAA SPECT/CT and performed directly before Y90 radioembolization. In non-enhancing cases, the CA was left open. The outcome was determined by clinical symptoms of acute or chronic cholecystitis as well as imaging and laboratory parameters. Findings were additionally classified according to the Tokyo Guidelines of acute cholecystitis. RESULTS: Only 16 patients demonstrated enhancement of the gallbladder in Tc99m-MAA SPECT/CT. Including additional indications from angiographic findings, prophylactic measures were scheduled in 22 patients (standard of care). Thus, 121 patients were at risk of non-target embolization to the gallbladder during Y90 microsphere administration (investigative arm). Four cases (3.0%) of cholecystitis occurred by clinical presentation: two patients with onset of acute symptoms within 48 h after Y90 radioembolization ("embolic cholecystitis") and two patients with late onset of symptoms ("radiogenic cholecystitis"). The incidence of cholecystitis was not significantly more frequent without indication of precautionary measures (investigative cohort 2.9% vs. standard of care 4.7%; P = 0.53). CONCLUSION: The overall incidence of cholecystitis after Y90 radioembolization is low. Determination of cystic artery intervention using Tc99m-MAA SPECT/CT successfully balances the incidence of symptomatic cholecystitis with unnecessary vessel occlusion.