Fig. 4
From: Developing a novel positronium biomarker for cardiac myxoma imaging
A scheme showing positronium lifetime measurements in cardiac myxoma and adipose tissues. a Photographs of non-fixed cardiac myxoma (CM) and adipose tissue samples. The numbers indicate patient ID (Table 1). Each sectioned tissue has been cut in halves with a 22Na radionuclide placed between and inserted into the aluminum measurement chamber. b The left part of the panel depicts the scheme of the detection system: scintillators (S), photomultipliers (PM), attenuators (A), discriminators (D), coincidence units (C), digitizer, and a data acquisition system (DAQ). The photograph displays a part of the system together with the plastic rod localized between the scintillators. The superimposed scheme indicates an aluminum chamber inserted inside the rod. 22Na (red dot) emits (green arrow) positron (+), which annihilates (predominantly into two photons indicated in blue) with electrons (−) in the tissue. Following the positron emission, 22Na changes into an excited nucleus of 22Ne, which de-excites almost instantly by the emission of the de-excitation photon (indicated in yellow). The PALS detection system, enables the measurement of the positronium lifetime by registering the time of emission of the de-excitation photon (corresponding to the time of positronium formation) and the time of creating the annihilation photons (corresponding to the time of the positronium decay). c For each sample, 1 × 106 coincidences between annihilation and deexcitation gamma quanta have been registered, resulting in the lifetime spectrum (example for the adipose tissue—patient ID 2). The analysis enables the extraction of the mean lifetime and intensities of para-Positronium (green line) and ortho-Positronium (blue line) atoms trapped in the intramolecular voids [42]. The dark yellow, turquoise, and purple lines denote direct annihilation in the source material, direct annihilation in the sample, and the background because of the accidental coincidences, respectively. The spectra are shifted by the delay coming from detection system configuration (~ 5 ns). d Results of the mean ortho-Positronium (o-Ps) lifetime (upper) and intensity (lower panel) for CM (black squares) and mediastinal adipose (red circle) tissues