Aortic valve imaging using 18F-sodium fluoride: impact of triple motion correction

BACKGROUND: Current (18)F-NaF assessments of aortic valve microcalcification using (18)F-NaF PET/CT are based on evaluations of end-diastolic or cardiac motion-corrected (ECG-MC) images, which are affected by both patient and respiratory motion. We aimed to test the impact of employing a triple motion correction technique (3 × MC), including cardiorespiratory and gross patient motion, on quantitative and qualitative measurements. MATERIALS AND METHODS: Fourteen patients with aortic stenosis underwent two repeat 30-min PET aortic valve scans within (29 ± 24) days. We considered three different image reconstruction protocols; an end-diastolic reconstruction protocol (standard) utilizing 25% of the acquired data, an ECG-gated (four ECG gates) reconstruction (ECG-MC), and a triple motion-corrected (3 × MC) dataset which corrects for both cardiorespiratory and patient motion. All datasets were compared to aortic valve calcification scores (AVCS), using the Agatston method, obtained from CT scans using correlation plots. We report SUV(max) values measured in the aortic valve and maximum target-to-background ratios (TBR(max)) values after correcting for blood pool activity. RESULTS: Compared to standard and ECG-MC reconstructions, increases in both SUV(max) and TBR(max) were observed following 3 × MC (SUV(max): Standard = 2.8 ± 0.7, ECG-MC = 2.6 ± 0.6, and 3 × MC = 3.3 ± 0.9; TBR(max): Standard = 2.7 ± 0.7, ECG-MC = 2.5 ± 0.6, and 3 × MC = 3.3 ± 1.2, all p values ≤ 0.05). 3 × MC had improved correlations (R(2) value) to the AVCS when compared to the standard methods (SUV(max): Standard = 0.10, ECG-MC = 0.10, and 3 × MC = 0.20; TBR(max): Standard = 0.20, ECG-MC = 0.28, and 3 × MC = 0.46). CONCLUSION: 3 × MC improves the correlation between the AVCS and SUV(max) and TBR(max) and should be considered in PET studies of aortic valves using (18)F-NaF. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40658-022-00433-7

Triple-gated motion and blood pool clearance corrections improve reproducibility of coronary 18F-NaF PET

PurposeTo improve the test-retest reproducibility of coronary plaque 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) uptake measurements.MethodsWe recruited 20 patients with coronary artery disease who underwent repeated hybrid PET/CT angiography (CTA) imaging within 3 weeks. All patients had 30-min PET acquisition and CTA during a single imaging session. Five PET image-sets with progressive motion correction were reconstructed: (i) a static dataset (no-MC), (ii) end-diastolic PET (standard), (iii) cardiac motion corrected (MC), (iv) combined cardiac and gross patient motion corrected (2 × MC) and, (v) cardiorespiratory and gross patient motion corrected (3 × MC). In addition to motion correction, all datasets were corrected for variations in the background activities which are introduced by variations in the injection-to-scan delays (background blood pool clearance correction, BC). Test-retest reproducibility of PET target-to-background ratio (TBR) was assessed by Bland-Altman analysis and coefficient of reproducibility.ResultsA total of 47 unique coronary lesions were identified on CTA. Motion correction in combination with BC improved the PET TBR test-retest reproducibility for all lesions (coefficient of reproducibility: standard = 0.437, no-MC = 0.345 (27% improvement), standard + BC = 0.365 (20% improvement), no-MC + BC = 0.341 (27% improvement), MC + BC = 0.288 (52% improvement), 2 × MC + BC = 0.278 (57% improvement) and 3 × C + BC = 0.254 (72% improvement), all p < 0.001). Importantly, in a sub-analysis of 18F-NaF-avid lesions with gross patient motion > 10 mm following corrections, reproducibility was improved by 133% (coefficient of reproducibility: standard = 0.745, 3 × MC = 0.320).ConclusionJoint corrections for cardiac, respiratory, and gross patient motion in combination with background blood pool corrections markedly improve test-retest reproducibility of coronary 18F-NaF PET

PET Quantification in PET/CT and PET/MR

Positronenemissionstomographie (PET) ist eine hoch sensitive Bildgebungsmethode zur nicht-invasive Untersuchungen biologischer Prozesse im Patienten. Die für eine PET Untersuchung verwendeten Systeme existieren als reine „stand-alone“ PET-Systeme und als kombinierte Bildgebungssysteme mit Computed Tomography (CT) oder Magnetresonanz (MR) Systemen. Einer der größten Vorteile der PET ist die Quantifizierbarkeit der Tracer Verteilung im Patienten. Für diese Quantifizierung benötigt es allerdings Korrekturen der PET Daten wie Beispielsweise Schwächungs- und Streukorrekturen oder Korrekturen eventueller Patientenbewegungen. Schwächungs- und Streukorrekturen basieren in reinen PET Systemen üblicherweise auf Transmissionsmessungen, und in kombinierten Systemen auf den anatomischen Bildgebungsverfahren. Hier werden aus den CT bzw. die MR Daten die Schwächungs- und Streueigenschafen der untersuchten Patienten geschätzt, wobei diese Schätzungen oft durch Bildgebungsartefakte negative beeinflusst werden. Bewegungskorrekturen werden generell eher selten angewendet, wobei routinemäßig nur Herz Untersuchungen (Gating mittels Elektrokardiogramm) oder die Atembewegung (Gating mittels externer Markierungen) korrigiert werden. Darüber hinaus beeinflussen weitere Faktoren die Quantifizierbarkeit wie z.B. unterschiedliche Detektorgrößen und Anordnungen in PET-Systeme von verschiedenen Anbietern oder unterschiedlich implementierte Rekonstruktionsalgorithmen. Das Ziel dieser Arbeit ist es, einige dieser Herausforderungen für die Anwendung der PET genauer zu untersuchen und neue Lösungsansätze für auftretende Probleme zu entwickeln. Dafür wurden im ersten Teil dieser Arbeit Standard-Schwächungskorrekturen für Ganz-Körper Untersuchungen in verschieden PET/MR Systemen evaluiert und miteinander Verglichen. Im zweiten Teil wurden die Standard MR basierte Schwächungskorrektur für Herz Untersuchungen genauer untersucht. Dies beinhaltet die Evaluierung der Häufigkeit des Auftretens von Artefakten und Methoden zu deren Kompensation. Im dritten Teil wurde eine auf den PET Daten basierende Bewegungserkennung und Kompensation für Herzuntersuchungen entwickelt. Überdies, wurde im vierten Teil dieser Arbeit evaluiert, ob laufende Studien von einem reinen PET Scanner auf ein PET/MR Gerät übertragen werden können. Zusammengefasst gibt diese Arbeit Einblick in verschiedene Faktoren, welche die quantitative PET-Bildgebung beeinflussen, wobei für einige der gefundenen Probleme Korrekturen entwickelt wurden. Die vorgeschlagenen Korrekturmethoden verbessern die quantitative Genauigkeit mit einfachen Techniken, die in der klinischen Routine umgesetzt werden können.Positron Emission Tomography (PET) is a quantitative imaging modality offering noninvasive assessments of biological processes in patients. PET systems have been introduced as stand-alone systems (PET-only) and as multi-modality imaging systems by combining them with either Computed Tomography (CT) or Magnetic Resonance (MR) imaging systems. PET systems, in general, face some technical challenges that affect the evaluations of the radio-tracer distribution in the patient. For example, corrections for photon attenuation are required to compensate for the photon absorption in the body. In PET-only systems, the attenuation correction maps (ATN-maps) are acquired from transmission scans employing rod sources rotating around the patient, whereas PET/CT systems employ X-ray based ATN maps and PET/MR systems employ segmentations of MR-images to derive the segmented attenuation correction factors. The ATN maps acquired in the multimodality imaging systems (PET/CT and PET/MR) often suffer from image-distortions arising from metallic implants (PET/MR systems) and respiratory motion (PET/CT and PET/MR systems), to mention a few. Motion, introduced by respiration as well as cardiac contractions, also poses the risk of errors in the quantitative assessment in patients undergoing cardiac PET-examinations. The combination of the respiratory translations and the cardiac contractions introduce a series of complex deformations of the heart, which can affect the image quality to such degree that the examination is inconclusive. Cardiac PET-examinations are routinely corrected for the cardiac contraction through gating schemes, while respiratory motion compensation still awaits full adoption. In addition, PET systems from different vendors affect the quantitative assessment of the patients, given implementations of different crystals, attenuation correction methods, and reconstruction algorithms. The goal of this thesis is to address some of these challenges through: evaluations of standard MR-based ATN maps, testing the feasibility of a data-driven respiratory motion detection and compensation technique (DDPB-rMoCo) and the assessment of the quantitative accuracy obtained in two clinical PET-systems. In the first study (P1), we evaluated standard MR-based ATN maps obtained in three whole-body PET/MR systems. The ATN maps implemented in all the systems are ix obtained through segmentations of the dedicated MR-sequences. The number of tissue-classifications and their assigned ATN values vary across the vendors, thus, introducing the risk of biases in the quantitative accuracy across the systems. Here, the effect of the differences in the ATN maps was evaluated for five regions in the thoracic region, lung volumes and projected linear attenuation coefficients (pLAC). Noteworthy intra-subject and inter-system differences were reported for the ATN values obtained in the lungs, liver, spine as well as the mediastinum. Likewise, biases were observed for the lung volumes and the pLAC's. The effect and frequency of artifacts obtained in standard DIXON-based ATN maps acquired for myocardial PET/MR examinations were evaluated in the second paper (P2). The candidate and his colleagues evaluated the frequency and the relative effect of the most common MR-based artifacts including: truncation, respiratory misalignment, as well as susceptibility artifacts arising from metallic implants. The truncation artifacts were corrected using the MLAA-correction algorithm, whereas misalignment artifacts were corrected using a rigid registration of the ATN map and the PET emission data. The susceptibility-like artifacts were corrected using a custom-made region growing algorithm, which fills the misclassified tissue-segmentations with the ATN values from the adjacent tissues. The study revealed artifacts in 95% of all MR-based ATN maps, caused by respiratory misalignments of the PET emission data and the ATN maps and susceptibility artifacts. In the third paper (P3), a data-driven motion detection and compensation technique were evaluated in a cohort of consecutive heart-failure patients. The proposed technique (DDPB-rMoCo) extracted the respiratory signal from the PET-raw data, followed by motion compensation in the listmode-data before image-reconstruction. The DDPB-rMoCo method was compared against a reconstruction of the acquired data, a gated image and a standard motion correction method (the reconstruction transform average (RTA)). In addition, ECG-gated reconstructions were performed for both the acquired and the DDPB-rMoCo data. A total of 3 mathematical and 7 clinical figures of merit, including the coefficient of variation (CoV) in the liver and evaluations of ejection fraction (EF) for the ECG-gated reconstructions. We report significantly reduced noise in the proposed motion compensation, when comparing to the standard gated images, and the RTA technique. Furthermore, significant changes were observed for evaluations of the EF after corrections for the respiratory motion. The fourth paper (P4) included in this thesis evaluates the feasibility of transferring a neuroimaging protocol from a PET-only to a PET/MR system while preserving the quantitative accuracy of the parametric values. This study was initiated to explore the options of continuing longitudinal studies initiated in the PET-only system in a PET/MR system, as the PET-only system in our center faces the end-of-life-cycle. The quantitative accuracy in the two systems was evaluated through analyses of SUV and parametric values in three brain structures, the whole-brain gray matter, the superior parietal lobe and the insula. We reported significant differences in both the SUV and parametric values, with differences exceeding 30% between the two systems. In summary, this thesis addresses some of the pitfalls in quantitative PET-imaging. The correction methods proposed in the papers (P2-P3) improve the quantitative accuracy with simple correction techniques that can be implemented in the clinical routine, while the papers (P1) and (P4) imply the need for careful considerations before starting multi-center trials involving PET systems from different vendors.Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersArbeit an der Bibliothek noch nicht eingelangt - Daten nicht geprüftMedizinische Universität Wien, Diss., 2017(VLID)234753

Advances in Quantitative Analysis of 18F-Sodium Fluoride Coronary Imaging

18F-sodium fluoride (18F-NaF) positron emission tomography (PET) has emerged as a promising noninvasive imaging tool for the assessment of active calcification processes in coronary artery disease. 18F-NaF uptake colocalizes to high-risk and ruptured atherosclerotic plaques. Most recently, 18F-NaF coronary uptake was shown to be a robust and independent predictor of myocardial infarction in patients with advanced coronary artery disease. In this review, we provide an overview of the advances in coronary 18F-NaF imaging. In particular, we discuss the recently developed and validated motion correction techniques which address heart contractions, tidal breathing, and patient repositioning during the prolonged PET acquisitions. Additionally, we discuss a novel quantification approach—the coronary microcalcification activity (which has been inspired by the widely employed method in oncology total active tumor volume measurement). This new method provides a single number encompassing 18F-NaF activity within the entire coronary vasculature rather than just information regarding a single area of most intense tracer uptake

Quantitative PET/MR imaging of lung cancer in the presence of artifacts in the MR-based attenuation correction maps

Background - Positron emission tomography (PET)/magnetic resonance (MR) imaging may become increasingly important for assessing tumor therapy response. A prerequisite for quantitative PET/MR imaging is reliable and repeatable MR-based attenuation correction (AC). Purpose - To investigate the frequency and test–retest reproducibility of artifacts in MR-AC maps in a lung cancer patient cohort and to study the impact of artifact corrections on PET-based tumor quantification. Material and Methods - Twenty-five lung cancer patients underwent single-day, test–retest, 18F-fluorodeoxyglucose (FDG) PET/MR imaging. The acquired MR-AC maps were inspected for truncation, susceptibility, and tissue inversion artifacts. An anatomy-based bone template and a PET-based estimation of truncated arms were employed, while susceptibility artifacts were corrected manually. We report the frequencies of artifacts and the relative difference (RD) on standardized uptake value (SUV) based quantification in PET images reconstructed with the corrected AC maps. Results - Truncation artifacts were found in all 50 acquisitions (100%), while susceptibility and tissue inversion artifacts were observed in six (12%) and 26 (52%) of the scans, respectively. The RD in lung tumor SUV was  Conclusion - The absence of bone and truncation artifacts have limited effect on the PET quantification of lung lesions. In contrast, susceptibility artifacts caused significant and inconsistent underestimations of the lung tumor SUVs, between test–retest scans. This may have clinical implications for patients undergoing serial imaging for tumor therapy response assessment