Technegas, A Universal Technique for Lung Imaging in Nuclear Medicine: Technology, Physicochemical Properties, and Clinical Applications

Abstract

Technegas was developed in Australia as an imaging radioaerosol in the late 1980s and is now commercialized by Cyclomedica, Pty Ltd. for diagnosing pulmonary embolism (PE). Technegas is produced by heating technetium-99m in a carbon crucible for a few seconds at high temperatures (2750 °C) to generate technetium-carbon nanoparticles with a gas-like behaviour. The submicron particulates formed allow easy diffusion to the lung periphery when inhaled. Technegas has been used for diagnosis in over 4.4 m patients across 60 countries and now offers exciting opportunities in areas outside of PE, including asthma and chronic obstructive pulmonary disease (COPD). The Technegas generation process and the physicochemical attributes of the aerosol have been studied over the past 30 years in parallel with the advancement in different analytical methodologies. Thus, it is now well established that the Technegas aerosol has a radioactivity aerodynamic diameter of <500 nm and is composed of agglomerated nanoparticles. With a plethora of literature studying different aspects of Technegas, this review focuses on a historical evaluation of the different methodologies' findings over the years that provides insight into a scientific consensus of this technology. Also, we briefly discuss recent clinical innovations using Technegas and a brief history of Technegas patents.

Keywords: Pertechnegas; Technegas particles; argon; lung imaging/ventilation; particle size; pulmonary embolism; radioactive aerosol; technetium-99m-pertechnetate.

Figure 1

Photograph of (A) TechnegasPlus Technegas^® generator, (B) Cyclopharm Patient Administration Set (PAS), and (C) Pulmotec^® empty crucible. (Courtesy of Cyclomedica.)

Figure 2

Global registration of Technegas as of August 2022 (blue areas on the map) and cumulative publication record as a function of year (PubMed Technegas).

Figure 3

Principles for the operation of Technegas generator for lung imaging. (A) Contacts (blue arrows) and collection tray (orange arrow), (B) Pulmotec^® graphite crucible (green arrow), (C) start simmering button (yellow arrow), (D) burn stage, (E) inhalation stage using patient administration set (black arrow). (Inset courtesy of Cyclomedica.)

Figure 4

Macroscopic process of Technegas generation process at the crucible level.

Figure 5

A schematic illustration represents the proposed Technegas production mechanism. Modified from the original study of potassium pertechnetate. Reprinted/adapted from Ref. [7].

Figure 6

Technegas particle transmission electron microscopy images as obtained through the years using different techniques or methods. (A) Primary particles (left), agglomerate (middle), and particles in the gas stream (right) [18,19]; (B) particles in the gas stream (left and right) [20]; (C) cluster of particles precipitated in liquid. Reprinted/adapted from [7]; (D) primary hexagonal particles agglomerated in clusters (left, red hexagon and red arrows) and NaCl crystals in aerosolized nanoparticles (right) [21]. Reprinted/adapted with permission from Refs. [18,19,20,21]; 1993, 1994, 1995, 2021, Springer Nature.

Figure 7

Photograph of a parallel diffusion battery connected to a Technegas generator. Reprinted/adapted with permission from Ref. [17]. 1989, Wolters Kluwer Health, Inc.

Figure 8

A schematic of the operating principles of the ELPI and particle size distributions on each stage from calibration data. Reprinted/adapted with permission from Ref. [26]. 2014, Elsevier.

Figure 9

Aerodynamic size distributions (cumulative) of Technegas aerosol using an ELPI and gamma counter. Reprinted/adapted with permission from Ref. [27]. 2013, Elsevier.

Figure 10

Structure of (A) buckminsterfullerene molecule, C60, metallofullerenes, (B) endohedral, (C) exohedral.

Figure 11

(a) A 63-year-old male with a 10-h history of right-sided pleuritic chest pain. V/Q SPECT showed multiple asymmetric wedge-shaped perfusion defects in reference to PE. (b) A 37-year-old male who presented with a swollen leg and chest pain. SPECT showed multiple asymmetric wedge-shaped perfusion defects in reference to PE. (c) A 31-year-old female who presented with shortness of breath, pleuritic chest pain, and two episodes of haemoptysis. V/Q SPECT showed a single subsegmental asymmetric perfusion defect in the left lung. Computed tomography pulmonary angiography performed the next day showed no PE, but lingular atelectasis, pericardial thickening, and a small pericardial effusion. Reprinted/adapted with permission from Ref. [35]. 2014, Elsevier.

Figure 12

(A) A 45-year-old healthy male. Technegas SPECT images show homogeneous distribution in whole lung. (B) A 65-year-old male with mild emphysema. Technegas SPECT images show heterogeneous distribution in whole lung. (C) A 63-year-old male with severe emphysema. Technegas SPECT images show heterogeneous distribution of cold and hot spots throughout peripheral lung field. Reprinted/adapted with permission from Ref. [36]. 2002, Springer Nature.

Figure 13

Advantages and disadvantages of Technegas compared to xenon scans. Reprinted/adapted with permission from Ref. [9]. 1988, John Wiley and Sons.