Anna Turco

Impact of CT-based Attenuation Correction on the Registration Between Dual-gated Cardiac PET and High-Resolution CT

A high-resolution CT (HRCT) used as anatomical prior information during PET reconstruction can enhance the quality of a corresponding low-resolution PET image, provided that it is accurately registered to the PET dataset of interest. In this work, the impact of different PET/CT attenuation correction (AC) protocols on the registration between a dual-gated cardiac 18F-FDG PET image and an HRCT image is investigated. The aim is to explore the impact of AC on PET-to-HRCT registration, and to identify the AC strategy that yields the best alignment between the left-ventricles in the PET and the HRCT images for subsequent partial volume correction. Simulations were performed using XCAT phantoms. Shallow breathing and a regular beating pattern were simulated and both noise-free and noisy data were evaluated. Respiratory motion during the acquisition of the CT used for attenuation correction strongly affected the dual-gated PET reconstructions, resulting in artefacts and quantification errors in the PET image and poor PET-to-HRCT registration accuracy. The blurring introduced by the beating heart, on the other hand, proved to have a negligible effect on PET-CT registration. Dual-gated PET images reconstructed without attenuation correction could be well registered to the HRCT if a good initial alignment between the starting images was provided. A commercially available strategy to deal with an AC CT that is acquired in the wrong respiratory phase was also evaluated, and yielded not only enhanced quantitative accuracy but also accurate PET-to-HRCT registration. The effect of a high level of noise, as present in a dual-gated cardiac PET study, was also investigated. Registrations proved to be sensitive to noise, but noise is not a major limiting factor for PET-to-HRCT registration. A selection of the investigated attenuation correction procedures was also evaluated using cardiac PET/CT data measured in sheep. The PET-to-HRCT registration performance confirmed the XCAT-based predictions.

Lesion quantification and detection in myocardial 18F-FDG PET using edge-preserving priors and anatomical information from CT and MRI: a simulation study

BackgroundThe limited spatial resolution of the clinical PET scanners results in image blurring and does not allow for accurate quantification of very thin or small structures (known as partial volume effect). In cardiac imaging, clinically relevant questions, e.g. to accurately define the extent or the residual metabolic activity of scarred myocardial tissue, could benefit from partial volume correction (PVC) techniques.The use of high-resolution anatomical information for improved reconstruction of the PET datasets has been successfully applied in other anatomical regions. However, several concerns linked to the use of any kind of anatomical information for PVC on cardiac datasets arise. The moving nature of the heart, coupled with the possibly non-simultaneous acquisition of the anatomical and the activity datasets, is likely to introduce discrepancies between the PET and the anatomical image, that in turn might mislead lesion quantification and detection. Non-anatomical (edge-preserving) priors could represent a viable alternative for PVC in this case.In this work, we investigate and compare the regularizing effect of different anatomical and non-anatomical priors applied during maximum-a-posteriori (MAP) reconstruction of cardiac PET datasets. The focus of this paper is on accurate quantification and lesion detection in myocardial 18F-FDG PET.MethodsSimulated datasets, obtained with the XCAT software, are reconstructed with different algorithms and are quantitatively analysed.ResultsThe results of this simulation study show a superiority of the anatomical prior when an ideal, perfectly matching anatomy is used. The anatomical information must clearly differentiate between normal and scarred myocardial tissue for the PVC to be successful. In case of mismatched or missing anatomical information, the quality of the anatomy-based MAP reconstructions decreases, affecting both overall image quality and lesion quantification. The edge-preserving priors produce reconstructions with good noise properties and recovery of activity, with the advantage of not relying on an external, additional scan for anatomy.ConclusionsThe performance of edge-preserving priors is acceptable but inferior to those of a well-applied anatomical prior that differentiates between lesion and normal tissue, in the detection and quantification of a lesion in the reconstructed images. When considering bull’s eye plots, all of the tested MAP algorithms produced comparable results.

Partial volume correction of doubly-gated cardiac datasets using anatomical and edge-preserving priors

Positron emission tomography (PET) images suffer from partial volume (PV) effects due to the poor spatial resolution of the PET system. In cardiac imaging, additional blurring is caused by the breathing motion and the beating of the heart. Dual gating of the cardiac datasets is one possible approach to remove the motion blur [1], but it dramatically reduces the statistics of the dataset and leads to extremely noisy reconstructions (still to be corrected for PV).

Validation of anatomy-enhanced cardiac FDG-PET imaging: An ex vivo sheep study

PET images suffer from partial volume effects (PVE) due to the poor spatial resolution of the PET system. Anatomy-enhanced PET reconstruction allows to restore such loss of resolution in PET images and attempt to reveal more accurately the actual tracer distribution [1] [4].

Registration between respiratory-gated PET/CT and high-resolution CT with XCAT simulations: Evaluation and optimization for subsequent PVC

Registration of a high-resolution CT (HRCT) to a low-resolution PET has been shown to enable enhanced PET image quality. The CT can be used as prior information for partial volume correction (PVC) during reconstruction, provided that it is accurately registered to the PET dataset of interest. By means of simulations using an XCAT phantom, this work analyzes the impact of different attenuation correction protocols on HRCT to PET registration. The focus of this work is on cardiac images with only respiratory motion taken into account, with the aim of optimally aligning the left-ventricular region in PET and HRCT. Shallow breathing was simulated and so far only noise-less data were evaluated. Also, a comparison to registration results from a deep breathing phantom has been performed. As expected, results speak in favour of using an ideal, perfectly matching attenuation correction map (ACM). However, when using an average or a single respiratory phase ACM accurate alignment can still be achieved. Registration of non-attenuation-corrected images requires further investigation, as it seems to be strongly dependent on the initial alignment of PET and CT.

Papillary muscles contribute significantly more to left ventricular work in dilated hearts

Aims Left ventricular (LV) dilatation results in increased sphericity and affects position and orientation of papillary muscles (PMs), which may influence their performed work. The aim of this study was to assess the contribution of PM to LV function and its changes with dilatation. Methods and results Fifteen sheep were investigated. Ten animals were subjected to 8 weeks of rapid (180 bpm) pacing, inducing LV dilatation. Five animals served as controls. High-resolution gated computed tomography was performed to assess LV volumes, left ventricular ejection fraction (LVEF), global longitudinal strain (GLS), sphericity index, and PM angle, width and fractional shortening. 18F-fluorodeoxyglucose positron emission tomography (PET) was used to measure glucose metabolism as surrogate of regional myocardial work. Spatial resolution of PET images was maximized by electrocardiogram- and respiratory-gating. 18F-fluorodeoxyglucose uptake was measured in PM and compared with remaining left ventricular myocardium (MYO) to obtain a PM/MYO ratio. Animals with dilated heart had a more spherical left ventricle, with reduced LVEF (P < 0.0001) and GLS (P < 0.0001). In dilated hearts, PET analysis revealed a higher contribution of both PM to LV myocardial work (P < 0.0001); and PM angle towards LV wall correlated with PM work, together with PM width and the LV sphericity index. Sphericity index and posterior PM angle were strongest determinants of posterior PM/MYO ratio (R2 = 0.754; P < 0.0001), while anterior PM/MYO was mostly determined by sphericity index and the PM width (R2 = 0.805; P < 0.0001). Conclusion In dilated hearts, PM contribute relatively more to LV myocardial work. We hypothesize that this is caused by the more cross-sectional orientation of the subvalvular apparatus, which leads to a higher stress on the PM compared with the spherical LV walls. The reduced cross-sectional area of the PM may further explain their increased stress.

Analysis of partial volume correction on quantification and regional heterogeneity in cardiac PET

Background The partial volume correction (PVC) of cardiac PET datasets using anatomical side information during reconstruction is appealing but not straightforward. Other techniques, which do not make use of additional anatomical information, could be equally effective in improving the reconstructed myocardial activity. Methods Resolution modeling in combination with different noise suppressing priors was evaluated as a means to perform PVC. Anatomical priors based on a high-resolution CT are compared to non-anatomical, edge-preserving priors (relative difference and total variation prior). The study is conducted on ex vivo datasets from ovine hearts. A simulation study additionally clarifies the relationship between prior effectiveness and myocardial wall thickness. Results Simple resolution modeling during data reconstruction resulted in over- and underestimation of activity, which hampers the absolute left ventricular quantification when compared to the ground truth. Both the edge-preserving and the anatomy-based PVC techniques improve the absolute quantification, with comparable results (Student t -test, P = .17). The relative tracer distribution was preserved with any reconstruction technique (repeated ANOVA, P = .98). Conclusions The use of edge-preserving priors emerged as optimal choice for quantification of tracer uptake in the left ventricular wall of the available datasets. Anatomical priors visually outperformed edge-preserving priors when the thinnest structures were of interest.

Young Investigator Award session: Basic Science311Intraventricular flow patterns after percutaneous mitral valve repair with MitraClip implantation312Papillary muscles contribute significantly to shortening of dilated left ventricles313Relationship between cardiac uptake by 99mTc-DPD scintigraphy and left ventricular longitudinal strain in patients with transthyretin-related cardiac amyloidosis314Premature ventricular contraction in resynchronized patients with short atrio-ventricular delay: hemodynamic impact beyond A-wave truncation

# 311 Intraventricular flow patterns after percutaneous mitral valve repair with MitraClip implantation {#article-title-2} Background: Percutaneous Mitral valve repair using MitraClip implantation has become a valid alternative for patients with severe mitral regurgitation (MR) and high surgical risk. After mitral valve (MV) replacement with mechanical prosthesis, vortex reversal flow and increase in energy dissipation was observed by Echo-PIV analysis. Aim of the present study was to evaluate if the revised valve anatomy with a generated double or multi-orifice configuration after MitraClip implantation may alter intraventricular flow patterns during diastole. Methods: From May 2015 to April 2016, 13 consecutive patients with severe MR undergoing MitraClip implantation were enrolled. All pts underwent contrast echocardiography before and after the procedure (2±1 days) for Echo-PIV analysis and vortex quantification. Acute procedural success (APS) was defined as successful clip implantation with residual MR grade ≤2+. Following parameters were evaluated by 2D/3D echocardiography: the etiology of MR (functional, ischemic and degenerative), MV anatomic characteristics, tricuspid regurgitation (TR) and pulmonary artery systolic pressure (PASP), LV dimension and function. Following parameters were evaluated by Echo-PIV analysis: vortex area, intensity and geometry, energy dissipation, flow force momentum (φ) and flow force dispersion. Results: Study population was divided in two groups according to the success of the procedure (APS in 7 and failure in 6 pts). No difference in MR etiology and severity, leaflets’ length and valve area was found. Patients with APS presented with a less pre-interventional PASP (28±6 vs 53±11 mmHg, p=0.005). By comparing vortex data before and after the procedure, in all patients vortex area and intensity were significantly lower after MitraClip implantation (0.39±0.07 vs 0.32±0.11; p=0.006 and -0.53±0.1 vs-0.30±0.34; p=0.009), confirmed in both sub-groups analysis. Contrary to what observed after MV replacement with mechanical prosthesis, vortex reversal flow was not detected. Finally, only in APS subgroup, a significant flow force dispersion reduction (50±3.4 vs 45±5; p=0.01) was found. Conclusion: The results of this study showed significant changes in intraventricular flow patterns following MitraClip implantation with different characteristics as compared to patients undergoing surgical MV replacement. A significant reduction of flow turbulence (flow force dispersion) in APS group was found. Further longitudinal studies are necessary to assess the impact of these intraventricular flow patterns on functional outcome. # 312 Papillary muscles contribute significantly to shortening of dilated left ventricles {#article-title-3} Background: Dilated left ventricles (LV) have a more spherical shape and displaced papillary muscles (PM). We hypothesized that this altered geometry may influence the contribution of PM to LV function. We therefore assessed the regional myocardial work by measuring the myocardial glucose uptake by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in an animal model of normal and dilated LVs. Methods: Fifteen animals were included in the study. Ten sheep were subjected to 8 weeks of rapid (180 bpm) pacing to induce LV dilatation. Five sheep served as control. Imaging was performed at a heart rate of 110 bpm. Cardiac magnetic resonance imaging (MRI) was performed in all animals to assess end-diastolic (EDV), end-systolic (ESV) volumes and LV ejection fraction (LVEF). LV sphericity index was defined as mid-ventricular septal-to-lateral width divided by LV length. Mitral regurgitation (MR) was graded visually on the MRI cine images as no (0), minimal (0.5), mild (1), moderate (2), moderate to severe (3), severe (4). ECG- and respiratory gating was used to obtain high resolution PET images. Regional metabolism was measured in the PM and compared to the remaining LV myocardium (MYO) (Figure). Results: Animals subjected to rapid pacing had a higher EDV and ESV compared to controls (105±20 vs. 76±7 ml and 76±16 vs. 41±6 ml, resp., both p<0.01), a lower LVEF (28±5 vs. 46±6 %, p<0.01), a higher MR score (1.6±0.8 vs. 0.2±0.4, p<0.01), and a higher LV sphericity index (0.61±0.03 vs. 0.47±0.02, p<0.01). The ratio of total PM FDG-uptake over total MYO uptake was significantly higher in dilated LVs compared to controls (0.54±0.05 vs. 0.39±0.03, p<0.01). The PM/MYO ratio correlated significantly with LVEF reduction (r=0.79, p<0.01), the MR score (r=0.61, p=0.01), and the LV sphericity index (r=0.86, p<0.01) (Figure). The LV sphericity index remained the strongest determinant of increased PM/MYO ratio after multiple regression analysis (model R²=0.86, p<0.01). Conclusions: Our data show that papillary muscles contribute more to LV shortening in dilated compared to normal hearts. We hypothesize that their higher workload is due to geometric abnormalities in dilated LVs which make papillary muscles work more diametral through the LV and less parallel to the LV wall. The increased contribution of papillary muscles to LV work in dilated hearts may further strengthen the argument of their preservation during MV repair/replacement in DCM. Funding Acknowledgements: KU Leuven research grant (OT/12/084). ![Figure][1] Abstract 312 Figure. # 313 Relationship between cardiac uptake by 99mTc-DPD scintigraphy and left ventricular longitudinal strain in patients with transthyretin-related cardiac amyloidosis {#article-title-4} Background: Pathophysiology of 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid (99mTc-DPD) uptake by scintigraphy in transthyretin-related (TTR) amyloidosis remains unclear. Impact of cardiac uptake on cardiac function is unknown. Purpose: The aim of this study was to explore the relationship between cardiac uptake by 99mTc-DPD scintigraphy and longitudinal myocardial strain assessed by echocardiography. Methods: Forty patients with TTR cardiac amyloidosis underwent 99mTc-DPD scintigraphy and echocardiography with measure of left ventricular segmental and global longitudinal strain (GLS). Cardiac retention was assessed by visual scoring and the heart/whole body (H/B) ratio was calculated by dividing counts in the heart by counts in late whole body images. Results: The mean population age was 79±10 years. Most of the patients (88%) were male. Visual score was 2 and 3 for 6 (15%) and 34 (85%) patients, respectively. Mean H/B ratio was 12±7. Mean left ventricular ejection fraction (LVEF) and GLS were 50±10% and -10±3%, respectively. H/B ratio was correlated with GLS (R = 0.490, P=0.001) but not with LVEF (R=-0,097, P=0.558). Segmental myocardial uptake normalized by H/B ratio was correlated with segmental longitudinal strain (n = 480 segments, R = 0.155, P<0.001). Conclusion: In patients with TTR cardiac amyloidosis, myocardial uptake by 99mTc-DPD scintigraphy is correlated with decrease of myocardial longitudinal strain. On behalf of: Department of Cardiology, Rangueil University Hospital, Toulouse, France. # 314 Premature ventricular contraction in resynchronized patients with short atrio-ventricular delay: hemodynamic impact beyond A-wave truncation {#article-title-5} Introduction: Optimization of atrio-ventricular delay (AVD) is one of the interventions that has been suggested to improve response to resynchronization therapy in heart failure patients. Excessively short AVD leads to A-wave truncation and, consequently, compromises left ventricular (LV) end-diastolic volume. Previous studies of intracardiac flow have suggested that atrial contraction impacts LV flow dynamics beyond its filling by generating a vortex that redirects flow towards the LV outflow tract, minimizing energy dissipation and facilitating initial ejection. In this study we assess the consequences of A-wave truncation on LV flow mechanics through LV flow mapping. Methods: Patients under cardiac resynchronization therapy (CRT) and in sinus rhythm underwent echocardiographic AVD optimization with transmitral flow assessment. Using intracardiac flow mapping, we measured Kinetic Energy Dissipation (KED) with automated software comparing flow direction and velocity in each pixel with its neighbouring points and integrates it into an image displaying energy loss in bright colours compared to dark areas with minimal energy dissipation. We also measured the angle between the longitudinal axis of the LV and the vector of early ejection flow (axis-flow angle, or AFA). Results: 25 patients (67% male, aged 72 ±11.7, LVEF 39.2±10.8) were included in the study. KED and AFA were measured in all patients in optimal AVD (Opt) and short AVD (Opt – 60 ms). Student’s t test showed a significant difference in KED between short (48,76 ± 8,33 J/m*s) and optimal AVD (24,32 ± 8,61 J/m*s, p<0,0001) in early ejection. The Flow – LV-Axis Angle was significantly narrower in short AVD vs. optimal AVD (20,2 ± 1,9° vs. 10,1 ± 1,3°, p<0.01), which implied that flow collided with the mitral valve and mitro-aortic junction before being ejected, with consequent energy dissipation, in short but not in optimal AVD. See Figure 1. Conclusions: Premature ventricular contraction due to short atrio-ventricular delay impacts LV flow dynamics causing higher kinetic energy dissipation due to impaired flow redirection to the LV outflow tract, which adds to the compromise of LV filling due to A wave truncation in explaining poor response to CRT in patients with suboptimal AVD programming. ![Figure][1] Abstract 314 Figure. [1]: pending:yes

Monte Carlo simulation of a dental Positron Emission Tomograph and image reconstruction of scatter and true coincidence events

Detection of inflammation with nuclear medical imaging techniques [1], especially using PET, has an important role because the location of the disease helps the doctor in the choice of the treatment. In dental applications, the proper treatment of the inflammation might save a tooth.

Modular miniPET: A comparison between 10 and 12 detector modules

By means of computer simulations, scatter fraction, spatial resolution and sensitivity of two 10-detector-module small-animal PET (r77-miniPET and r106-miniPET), are analyzed and compared to the performance of the 12-detector-module PET scanner miniPET II [1]. All simulations have been performed with the well validated Geant4 Application for Emission Tomography (GATE) [2]. Sensitivity and scatter fraction speak in favor of the 10-module scanner: a clear improvement in count rate and scatter fraction was found. Moreover, steeper slopes of noise equivalent count rate curves at low levels of activity was found. Spatial resolution instead was found to be better in the 12-module scanner. The encouraging results here presented particularly refer to r77-miniPET: all things considered, the 10-detector design behaves better than miniPET II if there are no gaps between detector modules. Preliminary trials performed with 8 detector modules in a ring are even more encouraging and need further assessment.