X-ray-based virtual slicing of TB-infected lungs

Ana Ortega-Gil,Juan José Vaquero,Mario Gonzalez-Arjona,Joaquín Rullas,Arrate Muñoz-Barrutia

doi:10.1038/s41598-019-55986-y

Abstract

Hollow organs such as the lungs pose a considerable challenge for post-mortem imaging in preclinical research owing to their extremely low contrast and high structural complexity. The aim of our study was to enhance the contrast of tuberculosis lesions for their stratification by 3D x-ray–based virtual slicing. Organ samples were taken from five control and five tuberculosis-infected mice. Micro-Computed Tomography (CT) scans of the subjects were acquired in vivo (without contrast agent) and post-mortem (with contrast agent). The proposed contrast-enhancing technique consists of x-ray contrast agent uptake (silver nitrate and iodine) by immersion. To create the histology ground-truth, the CT scan of the paraffin block guided the sectioning towards specific planes of interest. The digitalized histological slides reveal the presence, extent, and appearance of the contrast agents in lung structures and organized aggregates of immune cells. These findings correlate with the contrast-enhanced micro-CT slice. The abnormal densities in the lungs due to tuberculosis disease are concentrated in the right tail of the lung intensity histograms. The increase in the width of the right tail (~376%) indicates a contrast enhancement of the details of the abnormal densities. Postmortem contrast agents enhance the x-ray attenuation in tuberculosis lesions to allow 3D visualization by polychromatic x-ray CT, providing an advantageous tool for virtual slicing of whole lungs. The proposed contrast-enhancing technique combined with computational methods and the diverse micro-CT modalities will open the doors to the stratification of lesion types associated with infectious diseases.

Highlights

Cutting-edge translational research on preclinical models of infectious lung diseases rely on computed tomography (CT) images for the assessment of infection burden and in particular, for the evaluation of new effective antibiotic combinations for tuberculosis (TB) treatment[1,2]
The hypothesis driving this work was that the enhancement of complex lung structures by conventional contrast agents would allow the stratification of tuberculosis lesions by post mortem polychromatic x-ray imaging
To illustrate that the enhancement can be achieved with multiple contrast agents, we present two alternatives targeting the diagnostic x-ray energy range (10 keV, 150 keV)[9,28,29,30].The contrast-enhanced organs are embedded in ethanol and moved to paraffin, which enables longer storage of the biological phantom at room temperature

Summary

Introduction

Cutting-edge translational research on preclinical models of infectious lung diseases rely on computed tomography (CT) images for the assessment of infection burden and in particular, for the evaluation of new effective antibiotic combinations for tuberculosis (TB) treatment[1,2]. The hypothesis driving this work was that the enhancement of complex lung structures by conventional contrast agents would allow the stratification of tuberculosis lesions by post mortem polychromatic x-ray imaging. Postmortem studies benefit from the use of contrast agents, as micro-CT imaging of excised organs (e.g., heart, lung, brain)[11,12] and even whole animals (e.g., chick embryos)[11] allow for 3D non-destructive virtual histology examination. This circumvents the challenges inherent to performing 3D histological reconstruction of the whole organ from serial sections, which is a difficult and laborious procedure. The histological analysis of our samples reveals the distribution of the contrast agent in the lesion subtypes associated with the tuberculosis model under study and the nature of their abnormal x-ray density

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