PET performance evaluation of a pre-clinical SiPM-Based MR-Compatible PET Scanner

We have carried out a PET performance evaluation a silicon photo-multiplier (SiPM) based PET scanner designed for fully simultaneous pre-clinical PET/MR studies. The PET scanner has an inner diameter of 20 cm with an LYSO crystal size of 1.3 by 1.3 by 10 mm. The axial PET field of view (FOV) is 30.2 mm. The PET detector modules, which incorporate SiPMs, have been designed to be MR-compatible allowing them to be located directly within a Philips Achieva 3T MR scanner. The spatial resolution of the system measured using a point source in a non-active background, is just under 2.3 mm full width at half maximum (FWHM) in the transaxial direction when single slice rebinning (SSRB) and 2D filtered back-projection (FBP) is used for reconstruction, and 1.3 mm FWHM when resolution modeling is employed. The system sensitivity is 0.6% for a point source at the center of the FOV. The true coincidence count rate shows no sign of saturating at 30 MBq, at which point the randoms fraction is 8.2%, and the scatter fraction for a rat sized object is approximately 23%. Artifact-free images of phantoms have been obtained using FBP and iterative reconstructions. The performance is currently limited because only one of three axial ring positions is populated with detectors, and due to limitations of the first-generation detector readout ASIC used in the system. The performance of the system as described is sufficient for simultaneous PET-MR imaging of rat-sized animals and large organs within the mouse. This is demonstrated with dynamic PET and MR data acquired simultaneously from a mouse injected with a dual-labeled PET/MR probe

Simultaneous PET–MR acquisition and MR-derived motion fields for correction of non-rigid motion in PET

Positron emission tomography (PET) provides an accurate measurement of radiotracer concentration in vivo, but performance can be limited by subject motion which degrades spatial resolution and quantitative accuracy. This effect may become a limiting factor for PET studies in the body as PET scanner technology improves. In this work, we propose a new approach to address this problem by employing motion information from images measured simultaneously using a magnetic resonance (MR) scanner. The approach is demonstrated using an MR-compatible PET scanner and PET-MR acquisition with a purpose-designed phantom capable of non-rigid deformations. Measured, simultaneously acquired MR data were used to correct for motion in PET, and results were compared with those obtained using motion information from PET images alone. Motion artefacts were significantly reduced and the PET image quality and quantification was significantly improved by the use of MR motion fields, whilst the use of PET-only motion information was less successful. Combined PET-MR acquisitions potentially allow PET motion compensation in whole-body acquisitions without prolonging PET acquisition time or increasing radiation dose. This, to the best of our knowledge, is the first study to demonstrate that simultaneously acquired MR data can be used to estimate and correct for the effects of non-rigid motion in PET

18 Fluorodeoxyglucose positron emission tomography in the prediction of relapse in patients with high-risk, clinical stage I nonseminomatous germ cell tumors: preliminary report of MRC trial TE22 - the NCRI testis tumour clinical study group

Purpose: There are several management options for patients with clinical stage I ( CS1) nonseminomatous germ cell tumors (NSGCT); this study examined whether an (18)fluorodeoxyglucose positron emission tomography ( (18)FDG PET) scan could identify patients without occult metastatic disease for whom surveillance is an attractive option. Methods: High-risk ( lymphovascular invasion positive) patients with CS1 NSGCT underwent 18FDG PET scanning within 8 weeks of orchidectomy or marker normalization. PET-positive patients went off study; PET-negative patients were observed on a surveillance program. The primary outcome measure was the 2-year relapse-free rate ( RFR) in patients with a negative PET scan ( the negative predictive value). Assuming an RFR of 90% to exclude an RFR less than 80% with approximately 90% power, 100 PET-negative patients were required; 135 scanned patients were anticipated. Results: Patients were registered between May 2002 and January 2005, when the trial was stopped by the independent data monitoring committee due to an unacceptably high relapse rate in the PET-negative patients. Of 116 registered patients, 111 underwent PET scans, and 88 ( 79%) were PET-negative ( 61% of preorchidectomy marker-negative patients v 88% of marker-positive patients; P = .002); 87 proceeded to surveillance, and one requested adjuvant chemotherapy. With a median follow-up of 12 months, 33 of 87 patients on surveillance relapsed ( 1-year RFR, 63%; 90% CI, 54% to 72%). Conclusion: Though PET identified some patients with disease not detected by computed tomography scan, the relapse rate among PET negative patients remains high. The results show that 18FDG PET scanning is not sufficiently sensitive to identify patients at low risk of relapse in this setting

High-Resolution and Animal Imaging Instrumentation and Techniques

During the last decade we have observed a growing interest in “in vivo” imaging techniques for small animals. This is due to the necessity of studying biochemical processes at a molecular level for pharmacology, genetic, and pathology investigations. This field of research is usually called “molecular imaging.”Advances in biological understanding have been accompanied by technological advances in instrumentation and techniques and image-reconstruction software, resulting in improved image quality, visibility, and interpretation. The main technological challenge is then the design of systems with high spatial resolution and high sensitivity. This chapter gives a short overview of the state-of-the-art technologies for high-resolution and high-sensitivity molecular imaging techniques, namely, positron emission tomography (PET) and single photon emission computed tomography (SPECT) as well as the basics of small-animal x-ray computed tomography (CT). Multimodality techniques merging molecular information with anatomical details are also introduced. Finally, the new trends in detector technology for other high-resolution applications like breast cancer investigation are presented