A Clinical and Experimental Comparison of Time of Flight PET/MRI and PET/CT Systems

Daniela E Oprea-Lager,Adriaan A Lammertsma,Reindert J A Van Moorselaar,Otto S Hoekstra,Ronald Boellaard,Alfons J M Van Den Eertwegh,Maqsood Yaqub,Indra C Pieters,Rinze Reinhard

doi:10.1007/s11307-015-0826-8

Abstract

PurposeThe purpose of the study was to compare image quality and quantitative accuracy of positron emission tomography/magnetic resonance imaging (PET/MRI) and PET/computed tomography (PET/CT) systems with time of flight PET gantries, using phantom and clinical studies.ProceduresIdentical phantom experiments were performed on both systems. Calibration, uniformity, and standardized uptake value (SUV) recovery were measured. A clinical PET/CT versus PET/MRI comparison was performed using [18F]fluoromethylcholine ([18F]FCH).ResultsCalibration accuracy and image uniformity were comparable between systems. SUV recovery met EANM/EARL requirements on both scanners. Thirty-four lesions with comparable PET image quality were identified. Lesional SUVmax differences of 4 ± 26 % between PET/MRI and PET/CT data were observed (R 2 = 0.79, slope = 1.02). In healthy tissues, PET/MRI-derived SUVs were 16 ± 11 % lower than on PET/CT (R 2 = 0.98, slope = 0.86).ConclusionPET/MRI and PET/CT showed comparable performance with respect to calibration accuracy, image uniformity, and SUV recovery. [18F]FCH uptake values for both healthy tissues and lesions corresponded reasonably well between MR- and CT-based systems, but only in regions free of MR-based attenuation artifacts.Electronic supplementary materialThe online version of this article (doi:10.1007/s11307-015-0826-8) contains supplementary material, which is available to authorized users.

Highlights

Multimodality imaging has improved patient care over the past decade
positron emission tomography/computed tomography (PET/CT) was rapidly incorporated into routine clinical practice, positron emission tomography/magnetic resonance imaging (PET/MRI) faces a number of technical challenges
The performance in body mode showed slight differences between the systems with a stable performance for PET/CT, whereas for PET/MRI, the calibration offsets were less than 10 % with activity concentration ranging from 2 to 20 kBq·ml−1

Summary

Introduction

Multimodality imaging has improved patient care over the past decade. Non-invasive, integrated positron emission tomography/computed tomography (PET/CT)D.E. PET photomultiplier tubes (PMTs), which are needed to convert and amplify the signal from scintillation crystals into an electronic signal [6], do not function properly in a strong magnetic field. Solutions to this have included physically separating PET and MRI units [5] or using avalanche photodiodes (APDs), which in contrast to PMTs are not affected by the magnetic field [7]. APDs, have poorer timing resolution than PMTs and they have no TOF capability [8]. Silicon PMTs (SiPMTs) have been described as a possible alternative to conventional PMTs, combining good energy and timing resolution with the ability to decode arrays of scintillator elements [9]

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