Myocardial creep-induced misalignment artifacts in PET/MR myocardial perfusion imaging

Elia Von Felten,Georgios Benetos,Catherine Gebhard,Tobias A Fuchs,Dimitri Patriki,Aju P Pazhenkottil,Christoph Gräni,Dominik C Benz,Ronny R Buechel,Adam Bakula,Georgios P Rampidis,Andreas A Giannopoulos,Philipp A Kaufmann

doi:10.1007/s00259-020-04956-y

Abstract

PurposeMisalignment between positron emission tomography (PET) datasets and attenuation correction (AC) maps is a potential source of artifacts in myocardial perfusion imaging (MPI). We assessed the impact of adenosine on the alignment of AC maps derived from magnetic resonance (MR) and PET datasets during MPI on a hybrid PET/MR scanner.MethodsTwenty-eight volunteers underwent adenosine stress and rest 13N-ammonia MPI on a PET/MR. We acquired Dixon sequences for the creation of MRAC maps. After reconstruction of the original non-shifted PET images, we examined MRAC and PET datasets for cardiac spatial misalignment and, if necessary, reconstructed a second set of shifted PET images after manually adjusting co-registration. Summed rest, stress, and difference scores (SRS, SSS, and SDS) were compared between shifted and non-shifted PET images. Additionally, we measured the amount of cranial movement of the heart (i.e., myocardial creep) after termination of adenosine infusion.ResultsRealignment was necessary for 25 (89.3%) stress and 12 (42.9%) rest PET datasets. Median SRS, SSS, and SDS of the non-shifted images were 6 (IQR = 4–7), 12 (IQR = 7–18), and 8 (IQR = 2–11), respectively, and of the shifted images 2 (IQR = 1–6), 4 (IQR = 7–18), and 1 (IQR = 0–2), respectively. All three scores were significantly higher in non-shifted versus shifted images (all p < 0.05). The difference in SDS correlated moderately but significantly with the amount of myocardial creep (r = 0.541, p = 0.005).ConclusionMisalignment of MRAC and PET datasets commonly occurs during adenosine stress MPI on a hybrid PET/MR device, potentially leading to an increase in false-positive findings. Our results suggest that myocardial creep may substantially account for this and prompt for a careful review and correction of PET/MRAC data.

Highlights

When combined and fully integrated positron emission tomography (PET)/magnetic resonance (MR) devices have become commercially available, the calculation of accurate attenuation correction (AC) maps was found to be a significant challenge for PET/MR imaging
We found that misalignment between MR acquisition for attenuation correction (MRAC) maps and PET datasets is a common finding during PET/MR myocardial perfusion imaging (MPI) using adenosine stress and is causing misalignment artifacts in a substantial proportion of patients
We found that the presence and extent of reversible perfusion defects, which were unmasked by MRAC shifting, interrelate with the adenosine-dependent myocardial creep

Summary

Introduction

When combined and fully integrated positron emission tomography (PET)/magnetic resonance (MR) devices have become commercially available, the calculation of accurate attenuation correction (AC) maps was found to be a significant challenge for PET/MR imaging. It is well known that vasodilators may cause a change in respiratory levels with the diaphragm, and subsequently the heart shifting to a more caudal position during stress followed by a gradual cranial movement once the vasodilator stimulus is terminated. This phenomenon, termed myocardial creep, has been described recently for PET MPI [6,7,8] but was initially observed in single-photon emission tomography (SPECT) MPI after physical stress [9]. The protocols and the techniques of PET MPI using a PET/CT scanner differ fundamentally from PET/MR, myocardial creep may potentially trigger cardiac misalignment in a hybrid PET/MR scanner as well

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