Infection Imaging: Focus on New Tracers?

Abstract

Infections account for relevant morbidity and mortality, especially if the cardiovascular system is affected. Clinical manifestations are often unspecific, resulting in a challenging diagnostic work-up. The use of molecular imaging methods, namely [ 18 F]FDG PET and leukocyte scintigraphy, is increasingly recognized in recently published international guidelines. However, these 2 established methods focus on the host's immune response to the pathogen and are therefore virtually unable to differentiate infection from inflammation. Targeting the microorganism responsible for the infection directly with novel imaging agents is a promising strategy to overcome these limitations. In this review, we discuss clinically approved [ 18 F]FDG PET with its advantages and limitations in cardiovascular infections, followed by new PET-based approaches for the detection of cardiovascular infections by bacteria-specific molecular imaging methods. A multitude of different targeting options has already been preclinically evaluated, but most still lack clinical translation. We give an overview not only on promising tracer candidates for noninvasive molecular imaging of infections but also on issues hampering clinical translation.

18F-labelled gentiobiose as potential PET-radiotracer for specific bacterial imaging: precursor synthesis, radiolabelling and in vitro evaluation

“…However, this imaging approach is not directed at the bacteria, but rather at the immune response as [ 18 F]FDG-PET visualizes the uptake of radiolabelled glucose by activated immune cells due to their increased glucose metabolism. The lack of differentiation between a sterile inflammation and an infection has driven many new radiotracer developments in recent years [4,5]. Various strategies are available to exclusively address bacteria, ranging from targeting carbohydrate uptake and metabolism, to siderophore-mediated iron uptake [6,7,8].…”

The Evolution of Cardiac Nuclear Imaging

“…Quantification of treatment effects (15) Detection of cardiotoxicity of antitumor therapy Systems-based approach toward tumor-heart crosstalk (16) Gross visualization of cardiac inflammation Dissection of specific immune mechanisms as precursors of remodeling (17) Detection of late contractile failure Quantification of early fibrotic activity (18) Host response to infection Direct detection of pathogens (19) SPECT PET (13)(14)(15)(16)(17)(18)(19) Single modality Multimodality approach (13)(14)(15)(16)(17)(18)(19) Diagnosis of disease Biomarkers for guidance of therapy (13)(14)(15)(16)(17)(18)(19)…”

A novel radiolabelled salmochelin derivative for bacteria-specific PET imaging: synthesis, radiolabelling and evaluation

“…Besides using bacterial cell wall components like d -amino acids or the bacteria specific uptake of complex carbohydrates PET radiotracers targeting the bacteria-specific iron transport system are a possible way. 4…”