Hybrid Imaging of the Autonomic Cardiac Nervous System

Cardiac autonomic innervation is an integrative part of the physiology of the heart. This chapter reveals an overview of SPECT and PET application in cardiac sympathetic nervous system imaging in various cardiovascular diseases, including acquisition techniques and data analysis.</p

Large Vessel Vasculitis

2-[18F] fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) has become part of the worldwide standard of care in oncology. For a decade, this functional imaging tool has also demonstrated important diagnostic results in inflammatory diseases, especially in large vessel vasculitis (LVV). Since clinical PET imaging is increasingly used in these two conditions, this chapter aims to assist imaging specialists and clinicians by getting acquainted with the PET imaging procedures and the current status in clinical practice for LVV. General background information, PET technical considerations (including patient preparation, imaging protocols, scoring methodology), diagnostic and prognostic performance, and response monitoring will be addressed, in line with recent international expert-based recommendations.Also, in the era of personalized medicine, new hybrid technologies such as PET/MR and PET radiotracers will be discussed.</sub

Long Axial Field-of-View PET for Ultra-Low-Dose Imaging of Non-Hodgkin Lymphoma during Pregnancy

Generally, positron emission tomography imaging is not often performed in the case of pregnant patients. The careful weighing of the risks of radiation exposure to the fetus and benefits for cancer staging and the swift onset of treatment for the mother complicates decision making in clinical practice. In oncology, the most commonly used PET radiotracer is 2-deoxy-2-[fluorine-18] fluoro-D-glucose (18F-FDG), a glucose analog which has established roles in the daily routines for, among other applications, initial diagnosis, staging, (radiation) therapy planning, and response monitoring. The introduction of long axial Field-of-View (LAFOV) PET systems allows for PET imaging with a reduced level of injected 18F-FDG activity while maintaining the image quality. Here, we discuss the first reported case of a pregnant patient diagnosed with follicular lymphoma using LAFOV PET imaging for the staging and therapy selection. The acquired PET images show diagnostic quality images with clearly distinguishable areas of lymphadenopathy, even with only 34 MBq of injected 18F-FDG activity, leading to a considerable decrease in the level of radiation exposure to the fetus

Quantitative analysis of aortic Na[¹⁸F]F uptake in macrocalcifications and microcalcifications in PET/CT scans

Background: Currently, computed tomography (CT) is used for risk profiling of (asymptomatic) individuals by calculating coronary artery calcium scores. Although this score is a strong predictor of major adverse cardiovascular events, this method has limitations. Sodium [18F]fluoride (Na[18F]F) positron emission tomography (PET) has shown promise as an early marker for atherosclerotic progression. However, evidence on Na[18F]F as a marker for high-risk plaques is limited, particularly on its presentation in clinical PET/CT. Besides, the relationship between microcalcifications visualized by Na[18F]F PET and macrocalcifications detectable on CT is unknown. Purpose: To establish a match/mismatch score in the aorta between macrocalcified plaque content on CT and microcalcification Na[18F]F PET uptake. Methods: Na[18F]F-PET/CT scans acquired in our centre in 2019–2020 were retrospectively collected. The aorta of each low-dose CT was manually segmented. Background measurements were placed in the superior vena cava. The vertebrae were automatically segmented using an open-source convolutional neural network, dilated with 10 mm, and subtracted from the aortic mask. Per patient, calcium and Na[18F]F-hotspot masks were retrieved using an in-house developed algorithm. Three match/mismatch analyses were performed: a population analysis, a per slice analysis, and an overlap score. To generate a population image of calcium and Na[18F]F hotspot distribution, all aortic masks were aligned. Then, a heatmap of calcium HU and Na[18F]F-uptake on the surface was obtained by outward projection of HU and uptake values from the centerline. In each slice of the aortic wall of each patient, the calcium mass score and target-to-bloodpool ratios (TBR) were calculated within the calcium masks, in the aortic wall except the calcium masks, and in the aortic wall in slices without calcium. For the overlap score, three volumes were identified in the calcium and Na[18F]F masks: volume of PET (PET+/CT-), volume of CT (PET-/CT+), and overlapping volumes (PET+/CT+). A Spearman's correlation analysis with Bonferroni correction was performed on the population image, assessing the correlation between all HU and Na[18F]F vertex values. In the per slice analysis, a paired Wilcoxon signed-rank test was used to compare TBR values within each slice, while an ANOVA with post-hoc Kruskal–Wallis test was employed to compare TBR values between slices. p-values &lt; 0.05 were considered significant. Results: In total, 186 Na[18F]F-PET/CT scans were included. A moderate positive exponential correlation was observed between total aortic calcium mass and total aortic TBR (r = 0.68, p &lt; 0.001). A strong positive correlation (r = 0.77, p &lt; 0.0001) was observed between CT values and Na[18F]F values on the population image. Significantly higher TBR values were found outside calcium masks than inside calcium masks (p &lt; 0.0001). TBR values in slices where no calcium was present, were significantly lower compared with outside calcium and inside calcium (both p &lt; 0.0001). On average, only 3.7% of the mask volumes were overlapping. Conclusions: Na[18F]F-uptake in the aorta behaves similarly to macrocalcification detectable on CT. Na[18F]F-uptake values are also moderately correlated to calcium mass scores (match). Higher uptake values were found just outside macrocalcification masks instead of inside the macrocalcification masks (mismatch). Also, only a small percentage of the Na[18F]F-uptake volumes overlapped with the calcium volumes (mismatch).</p

Importance of Blood Glucose Management Before 18F-FDG PET/CT in 322 Patients with Bacteremia of Unknown Origin

We investigated the effects of blood glucose levels on the performance of 18F-FDG PET/CT for detecting an infection focus in patients with bacteremia. Methods: A total of 322 consecutive patients with bacteremia who underwent 18F-FDG PET/CT between 2010 and 2021 were included. Logistic regression analysis was performed to evaluate the association between finding a true-positive infection focus on 18FFDG PET/CT and blood glucose level, type of diabetes, and use of hypoglycemic medication. C-reactive protein, leukocyte count, duration of antibiotic treatment, and type of isolated bacteria were considered as well. Results: Blood glucose level (odds ratio, 0.76 per unit increase; P=,0.001) was significantly and independently associated with 18F-FDG PET/CT outcome. In patients with a blood glucose level between 3.0 and 7.9mmol/L (54-142mg/dL), the true-positive detection rate of 18F-FDG PET/CT varied between 61% and 65%, whereas in patients with a blood glucose level between 8.0 and 10.9mmol/L (144-196mg/dL), the true-positive detection rate decreased to 30%- 38%. In patients with a blood glucose level greater than 11.0mmol/L (200mg/dL), the true-positive detection rate was 17%. In addition to C-reactive protein (odds ratio, 1.004 per point increase; P = 0.009), no other variables were independently associated with 18F-FDG PET/CT outcome. Conclusion: In patients with moderate to severe hyperglycemia, 18F-FDG PET/CT was much less likely to identify the focus of infection than in normoglycemic patients. Although current guidelines recommend postponing 18F-FDG PET/CT only in cases of severe hyperglycemia with glucose levels greater than 11mmol/L (200mg/dL), a lower blood glucose threshold seems to be more appropriate in patients with bacteremia of unknown origin and other infectious diseases.</p

Prosthetic Valve Endocarditis

Prosthetic valve infective endocarditis (PVE) is associated with high morbidity and mortality. With the increasing number of prostheses implanted every year, the incidence of PVE is expected to rise. The diagnosis of PVE is challenging as blood cultures are often negative and the sensitivity of echocardiography is suboptimal in the presence of prosthetic valves. In 2015, the European Society of Cardiology introduced 18F-fluorodeoxyglucose–positron emission tomography/computed tomography (FDG-PET/CT) as a major criterion for the diagnosis of PVE, based on its ability to identify valve infection and to detect septic emboli. In addition, FDG-PET/CT can detect PVE portal of entry, which may lead to change in management. This chapter will discuss the epidemiology and clinical presentations of PVE. In addition, the role of FDG-PET/CT in PVE as well as optimal imaging protocols will be reviewed.</p