Ahlam Issa

Ahlam Issa

PGSB Fellow
Al Quds University & RWTH Aachen University

Department: Medical Imaging  

Faculty: Faculty of Health Professions 

Specialization: Nuclear imaging and Neuroscience studies

Accurate Specialization: PET Dead Time correction for the Brain PET insert UHF MRI

Palestinian supervisor:  Dr. Hussein AlMasri  

Palestinian Supervisor affiliation:  Medical Imaging/ Faculty of Health Professions/ Al Quds University

Degree aims: PhD

FZJ Supervisor: Dr Christoph Lerche 

Center in Juelich: Full Name with abbreviaion: Institut für Neurowissenschaften und Medizin / INM-4

Affiliated University in Germany: RWTH Aachen University

Department: Doctoral Studies

Faculty: Medical 

The mission research period : from – to (1/11/2018-30/10/2021)

Title of  Research: Characterization of event counts and detector  block-wise counts for dead time correction improvement in  Siemens 3T MRI/Brain PET scanner. 

Research Purpose: PET is a neuroimaging method used to measure the metabolic process in the brain, which has an unrivaled capacity to track the radioactive tracer of the human brain in vivo using radiolabeled biomarkers. By the time, fMRI became available after the PET. However, the shift from PET studies to fMRI was driven by the fact that fMRI is non-invasive and has better spatial resolution than PET. So the integration of PET and MRI is considered as one of the most important technologies of choice in the future researches. This research involves the methodology for the in vivo receptor imaging of the brain function in humans with PET scan and the combination with, especially Ultra High Field (UHF) magnetic resonance imaging (MRI). The main objective of this research is to deliver the best possible conditions for the analysis of the imaging data of PET- UHF-MR imaging and the development of software algorithms and correction methods for high-quality image reconstruction. Molecular imaging with positron emission tomography (PET)is used to provide images of brain function by visualizing the distribution of pharmacologically active substances.The motivation of this work includes creating new strategies to improve image quantitation accuracy,simulation, and modeling of PET systems, in particular for dead time correction. All components in the PET detector system contribute to dead time losses, e.g. the scintillator, the digitization electronic,in some cases the photodetector, and others. Dead time losses affect the quantitation of PET images in many important applications, especially when high doses and/or dynamic acquisitions are used. If left uncorrected, dead time losses distort the measured time activity curves (TAC) and quantities derived from the TAC, e.g. distribution volume, binding potential, and others. Furthermore, inappropriate correction invalidates any assumptions regarding the Poisson nature of the input signals and may lead to reconstruction and quantification biases.

Main outputs/results: In the case of the patient measurement, the single counts of the 192 blocks depend strongly on the angular and axial block position in the PET scanner. The highest single counts were found in those blocks close to the radioactivity sources, especially in the first ring of the PET scanner. Therefore, global dead time correction is an insufficient and independent dead-time correction for each individual detector block is needed to achieve accuracy in quantitative imaging.

Main Impact: During this project, signal processing methods and data correction (dead time estimation & correction/random estimation and correction, improvement of scatter correction) methods have to be implanted into the PET data acquisition system. Impact on PET image quality should be studied based on simulations and phantom measurements. In this distinctive development, UHF-MRI-compatible Brain PET insert is expected to offer a 3- to 4-fold increase in effective sensitivity and a markedly improved and more homogeneous spatial image resolution of 1.5–2.5 mm by using the latest detector- and production technology, as well as an improved system design.

Sharing Conferences: The INM & ICS Retreat 2019. Abstract sent for the Poster session. July 11-15, 2019.  Forschungszentrum Jülich GmbH/Germany . 2- EANM20- October 22 - 30, 2020.  Vienna-Austria. For the Corona pandemic, this time is going as a virtual conference. Abstract sent for the oral presentation  session. https://eanm20.eanm.org/.

Publication: Working on the first manuscript