Localizing infection with a technetium-99m-labeled peptide: initial results

Currently Available Radiopharmaceuticals for Imaging Infection and the Holy Grail

Infection is ubiquitous. However, its management is challenging for both the patients and the health-care providers. Scintigraphic imaging of infection dates back nearly half a century. The advances in our understanding of the pathophysiology of disease at cellular and molecular levels have paved the way to the development of a large number of radiopharmaceuticals for scintigraphic imaging of infection. These include radiolabeling of blood elements such as serum proteins, white blood cells (WBCs), and cytokines, to name a few. Infectious foci have also been imaged using a radiolabeled sugar molecule by taking advantage of increased metabolic activity in the infectious lesions. Literature over the years has well documented that none of the radiopharmaceuticals and associated procedures that facilitate imaging infection are flawless and acceptable without a compromise. As a result, only a few compounds such as 99mTc-hexamethylpropyleneamineoxime, 18F-FDG, the oldest but still considered as a gold standard 111In-oxine, and, yes, even 67Ga-citrate in some countries, have remained in routine clinical practice. Nonetheless, the interest of scientists and physicians to improve the approaches to imaging and to the management of infection is noteworthy. These approaches have paved the way for the development of numerous, innovative radiopharmaceuticals to label autologous WBCs ex vivo or even those that could be injected directly to image infection or inflammation without direct involvement of WBCs. In this review, we briefly describe these agents with their pros and cons and place them together for future reference.

Proximal environment controlling the reactivity between inorganic sulfide and heme-peptide model

Synthesized deuterohemin-peptide, which is lack of the distal protein structure, is used as a heme model to investigate the effects of the proximal environment on the reactivity of inorganic sulfide to heme center.

Rationale for the use of radiolabelled peptides in diagnosis and therapy

Nuclear medicine techniques are becoming more important in imaging oncological and infectious diseases. For metabolic imaging of these diseases, antibody and peptide imaging are currently used. In recent years peptide imaging has become important, therefore the rationale for the use of peptide imaging is described in this article. Criteria for a successful peptide tracer are a high target specificity, a high binding affinity, a long metabolic stability and a high target-to-background ratio. Tracer internalization is also beneficial. For oncological imaging, many tracers are available, most originating from regulatory peptides, but penetrating peptides are also being developed. Peptides for imaging inflammatory and infectious diseases include regulatory peptides, antimicrobial peptides and others. In conclusion, for the imaging of oncological, imflammatory and infectious diseases, many promising peptides are being developed. The ideal peptide probe is characterized by rapid and specific target localization and binding with a high tumour-to-background ratio.

The labeled-leukocyte scan in the study of abdominal abscesses

AIM

The purpose of the present paper was to review the literature over the last 30 years to assess the value of radionuclide imaging, particularly labeled leukocyte scan, as compared to other imaging modalities in the management of abdominal abscesses.

METHODS

A systematic review of the published studies in humans cited in PubMed written in English, French, German, Italian, and Spanish was made.

RESULTS

Ultrasound (US) has lower sensitivity than leukocyte scan (LS), particularly in patients without localizing signs, while CT has higher sensitivity than US, but less than LS. On the other hand, CT had higher specificity than both LS and US.

DISCUSSION

LS is the more sensitive method to localize abdominal abscesses and may guide dedicated US and CT investigations to improve their diagnostic potential. Further diagnostic evolution is expected from the routine use of hybrid SPECT/CT systems.

Biological imaging for the diagnosis of inflammatory conditions

Radiopharmaceuticals used for in vivo imaging of inflammatory conditions can be conveniently classified into six categories according to the different phases in which the inflammatory process develops. The trigger of an inflammatory process is a pathogenic insult (phase I) that causes activation of endothelial cells (phase II); there is then an increase of vascular permeability followed by tissue oedema (phase III). Phase IV is characterised by infiltration of polymorphonuclear cells, and a self-limiting regulatory process called apoptosis is observed (phase V). If the inflammatory process persists, late chronic inflammation takes place (phase VI). In some pathological conditions, such as organ-specific autoimmune diseases, chronic inflammation is present early in the disease. The aim of nuclear medicine in the field of inflammation/infection is to develop noninvasive tools for the in vivo detection of specific cells and tissues. This would allow early diagnosis of initial pathophysiological changes that are undetectable by clinical examination or by other diagnostic tools, and could also be used to evaluate the state of activity of the disease during therapy. These potential applications are of great interest in clinical practice. In this review, we describe the various approaches that have been developed in the last 25 years of experience. Recent advances in the diagnosis of inflammatory processes have led to the development of specific radiopharmaceuticals that are intended to allow specific stage-related diagnosis.