Impact of Bayesian penalized likelihood reconstruction on quantitative and qualitative aspects for pulmonary nodule detection in digital 2-[18F]FDG-PET/CT

To evaluate the impact of block sequential regularized expectation maximization (BSREM) reconstruction on quantitative and qualitative aspects of 2-[18F]FDG-avid pulmonary nodules compared to conventional ordered subset expectation maximization (OSEM) reconstruction method. Ninety-one patients with 144 2-[18F]FDG-avid pulmonary nodules (all ≤ 20 mm) undergoing PET/CT for oncological (re-)staging were retrospectively included. Quantitative parameters in BSREM and OSEM (including point spread function modelling) were measured, including maximum standardized uptake value (SUVmax). Nodule conspicuity in BSREM and OSEM images was evaluated by two readers. Wilcoxon matched pairs signed-rank test was used to compare quantitative and qualitative parameters in BSREM and OSEM. Pulmonary nodule SUVmax was significantly higher in BSREM images compared to OSEM images [BSREM 5.4 (1.2–20.7), OSEM 3.6 (0.7–17.4); p = 0.0001]. In a size-based analysis, the relative increase in SUVmax was more pronounced in smaller nodules (≤ 7 mm) as compared to larger nodules (8–10 mm, or > 10 mm). Lesion conspicuity was higher in BSREM than in OSEM (p < 0.0001). BSREM reconstruction results in a significant increase in SUVmax and a significantly improved conspicuity of small 2-[18F]FDG-avid pulmonary nodules compared to OSEM reconstruction. Digital 2-[18F]FDG-PET/CT reading may be enhanced with BSREM as small lesion conspicuity is improved

Development of clinical simultaneous SPECT/MRI

There is increasing clinical use of combined positron emission tomography (PET) and magnetic resonance imaging (MRI) but to date there has been no clinical system developed capable of simultaneous single photon emission computed tomography (SPECT) and MRI. There has been development of preclinical systems, but there are several challenges faced by researchers who are developing a clinical prototype including the need for the system to be compact and stationary with MRI-compatible components. The limited work in this area is described with specific reference to the Integrated SPECT/MRI for Enhanced stratification in Radio-chemo Therapy (INSERT) project, which is at an advanced stage of developing a clinical prototype. Issues of SPECT/MRI compatibility are outlined and the clinical appeal of such a system is discussed, especially in the management of brain tumour treatment

Implementation and characterisation of radiation detectors based on SIPM for medical imaging

In the last decades, medical imaging techniques have revolutionized medicine facilitating the work to the clinicians, favouring the earlier diagnosis of diseases such as cancer, and reducing the time required for surgical procedures. Among these techniques, one of the most promising is Positron Emission Tomography (PET) due to its constant evolution, the functional information it provides and the possibility of combining it with other structural techniques such as CT or MRI. Recently, new generations of PET detectors have been developed leaving behind the conventionally used photomultiplier tubes (PMTs) for the state-of-the-art digital silicone photomultipliers (d-SiPM). In this work, the last generation of radiation detectors, Philips Digital Photon Counting’s (PDPC) d-SiPMs, was studied and characterized. These detectors are used in the commercial Philips Vereos time-of-flight PET/CT scanner, as well as in the Hyperion-IID preclinical PET scanner. The main objective of this work was to learn how to operate this new system in optimum conditions for small-animal imaging, how to design a precise centre of gravity (COG) algorithm for the localization of the scintillator pixels in a scintillator array, and to characterize the energy and spatial resolutions obtained with this PDPC module. Different COG algorithms were tested, and the final one was designed in such a way that only valid events were considered. This algorithm focuses on the main pixel of each event and the eight pixels surrounding it, discarding scatter and noise as much as possible. The energy resolution was measured by studying the full width half maximum (FWHM) of the photopeak, whereas the spatial resolution was measured by computing the valley-to-peak ratio (V/P) and the resolvability index (RI) of a profile taken from the flood field images acquired. In this project, we used a 30×30 scintillator matrix of LYSO crystals of 1.3×1.3×12 mm3, coupled to a 50×50×2 mm3 light guide in order to spread the scintillation photons among 36 of the 64 die sensors integrated in the PDPC DPC 3200-22 module. A study of how the temperature affects the performance of the system and which acquisition parameters, light guide and time window gives better results was performed. As a final check, we compared the initial and final images obtained, considering their spatial and energy resolution.Ingeniería Biomédic

The clinical utilities of multi-pinhole single photon emission computed tomography

Single photon emission computed tomography (SPECT) is an important imaging modality for various applications in nuclear medicine. The use of multi-pinhole (MPH) collimators can provide superior resolution-sensitivity trade-off when imaging small field-of-view compared to conventional parallel-hole and fan-beam collimators. Besides the very successful application in small animal imaging, there has been a resurgence of the use of MPH collimators for clinical cardiac and brain studies, as well as other small field-of-view applications. This article reviews the basic principles of MPH collimators and introduces currently available and proposed clinical MPH SPECT systems

Absorbed dose maps of patients submitted to 68Ga-PSMA-11 PET/CT

Although nuclear medicine (NM) procedures are highly effective diagnostic tools, they have been contributing significantly, together with other medical diagnostic and therapeutic methodologies, to the increase in exposure to ionizing radiation in recent years. There is an urgent need to opti mize NM techniques, to maintain diagnostic quality at a minimum possible radiation absorbed dose. 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomog raphy (68Ga-PSMA-11 PET/CT) imaging has rapidly gained notoriety in the NM field and, at the same time, personalized dosimetry studies using voxel-based methods have been performed. This study aimed to calculate the absorbed dose at the voxel level in the kidneys, liver, spleen, and red bone marrow, compare the results with other studies and draw conclusions regarding the safety of using 68Ga-PSMA-11 in NM clinics. Whole-body PET/CT images from six patients were acquired after a single 68Ga-PSMA 11 injection. After registration of the CT and PET images, the target organs were manually seg mented in the CT and resampled to the PET voxel size. Voxel S-values were computed for spe cific tissues using the Monte-Carlo N-Particle transport 6.1 code. The absorbed dose rates were obtained by convolution of the PET activity images with the specific S-values of each tissue. A time integral was then applied to each distribution to account for all 68Ga decay. Statistical dose values were computed and compared with the available literature. Considering all the patients included in this study, the kidneys received the highest radi ation, with a mean overall absorbed dose of 0.0561 mGy/MBq and a median overall absorbed dose of 0.0499 mGy/MBq. In contrast, the red bone marrow received the lowest absorbed dose values (mean dose: 0.0015 mGy/MBq, median dose: 0.0013 mGy/MBq). The present study showed lower dosimetry values than the literature, resulting in deviations ranging from -38.1% (in the liver) to -91.3% (in the red bone marrow). The present study employs a voxel-based approach, which considers a non-uniform bio distribution of the radiopharmaceutical in the organs and leads to dosimetry estimates closer to the real ones. The reasonable low absorbed doses in the four organs herein studied is an argument in favor of using 68Ga-PSMA-11 in NM clinics. In the Future Work chapter, a more specific dynamic NM imaging methodology, taking into consideration the radiopharmaceutical pharma cokinetics, is presented