Analysis of 18FDG PET/CT Imaging as a Tool for Studying Mycobacterium tuberculosis Infection and Treatment in Non-human Primates

Summary

Here, we present a protocol to describe the analysis of ¹⁸F-FDG PET/CT imaging in non-human primates that have been infected with M. tuberculosis to study disease process, drug treatment, and disease reactivation.

Abstract

Mycobacterium tuberculosis remains the number one infectious agent in the world today. With the emergence of antibiotic resistant strains, new clinically relevant methods are needed that evaluate the disease process and screen for potential antibiotic and vaccine treatments. Positron Emission Tomography/Computed Tomography (PET/CT) has been established as a valuable tool for studying a number of afflictions such as cancer, Alzheimer's disease, and inflammation/infection. Outlined here are a number of strategies that have been employed to evaluate PET/CT images in cynomolgus macaques that are infected intrabronchially with low doses of M. tuberculosis. Through evaluation of lesion size on CT and uptake of ¹⁸F-fluorodeoxyglucose (FDG) in lesions and lymph nodes in PET images, these described methods show that PET/CT imaging can predict future development of active versus latent disease and the propensity for reactivation from a latent state of infection. Additionally, by analyzing the overall level of lung inflammation, these methods determine antibiotic efficacy of drugs against M. tuberculosis in the most clinically relevant existing animal model. These image analysis methods are some of the most powerful tools in the arsenal against this disease as not only can they evaluate a number of characteristics of infection and drug treatment, but they are also directly translatable to a clinical setting for use in human studies.

Introduction

Mycobacterium tuberculosis has plagued humans for millennia and causes more mortality than any other single infectious agent in the world today. In 2015, there were 10.5 million reported new cases of tuberculosis (TB) globally¹ with the majority of cases emanating from India, Indonesia, China, Nigeria, Pakistan, and South Africa. Estimates place the global death toll from TB at 1.4 million people during that same time period. This value is nearly 25% lower than the death rate 100 years ago. Although drug sensitive TB is treatable, the regimen is lengthy requiring multiple medications and compliance is a concern. The emergence of multi ....

Protocol

All methods outlined in this work have been approved by the University of Pittsburgh Institutional Animal Care and Use Committee. All procedures followed institutional biosafety and radiation safety requirements. CT scanning requires donning lead apron and throat cover. Biosafety Level 3 (BSL3) garb and procedures for working with non-human primates must be followed according to institutional guidelines. All scanning was performed in a BSL3 facility.

1. Animal Infection Procedure

1. Sedate animal with ketamine (10 mg/kg, intramuscular) or telazol (5 - 8 mg/kg, intramuscular) if animal has adverse reactions to ketamine.
2. Us....

Results

Identification and Analysis of Individual Lesions

Individual granulomas can be visualized for number, size, and FDG uptake qualitatively to understand the general scope of the infection process (Figure 1). Using these images, counting granulomas over time is a quantitative measure of disease spread. Figure 2 depicts individual granuloma counts over time in a gr.......

Discussion

Data acquired from PET/CT can be used as surrogate measurements for many aspects of M. tuberculosis infection that would be unobservable without such technology. PET/CT is much more sensitive than X-ray technology, which is often used in macaques studies. PET/CT provides structural, spatial and functional information. The analyses described above have many practical applications such as monitoring disease progression, assessing effectiveness of drug treatment, and providing risk factors for reactivation

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ketamine	Henry Schein	23061	Henry Schein
Telazol	Zoetis	4866	Henry Schein
Cetacaine	Patterson Vet Generics	07-892-6862	Patterson
Sterile saline	Hospira	07-800-9721	Patterson
7H11 agar	BD	283810	BD Biosciences
IV catheter	Surflash	07-806-7659	Patterson
18F-FDG	Zevacor	N/A
Endotracheal tube	Jorgensen Labs Inc	07-887-0284	Patterson
Artificial tears	Patterson Vet Generics	07-888-1663	Patterson
Isoflurane	Zoetis	07-806-3204	Patterson
Neurologica Ceretom CT	Samsung Neurologica	N/A
Siemens Focus 220 microPET	Siemens Molecular Imaging Systems	N/A
Inveon Research Software	Siemens Molecular Imaging Systems	N/A
OsiriX	Pixmeo	N/A