Abstract
PurposeThe aim of this study was to evaluate and quantify the effect of improved attenuation correction (AC) including bone segmentation and truncation correction on 18F-Fluordesoxyglucose cardiac positron emission tomography/magnetic resonance (PET/MR) imaging.MethodsPET data of 32 cardiac PET/MR datasets were reconstructed with three different AC-maps (1. Dixon-VIBE only, 2. HUGE truncation correction and bone segmentation, 3. MLAA). The Dixon-VIBE AC-maps served as reference of reconstructed PET data. 17-segment short-axis polar plots of the left ventricle were analyzed regarding the impact of each of the three AC methods on PET quantification in cardiac PET/MR imaging. Non-AC PET images were segmented to specify the amount of truncation in the Dixon-VIBE AC-map serving as a reference. All AC-maps were evaluated for artifacts.ResultsUsing HUGE + bone AC results in a homogeneous gain of ca. 6% and for MLAA 8% of PET signal distribution across the myocardium of the left ventricle over all patients compared to Dixon-VIBE AC only. Maximal relative differences up to 18% were observed in segment 17 (apex). The body volume truncation of -12.7 ± 7.1% compared to the segmented non-AC PET images using the Dixon-VIBE AC method was reduced to -1.9 ± 3.9% using HUGE and 7.8 ± 8.3% using MLAA. In each patient, a systematic overestimation in AC-map volume was observed when applying MLAA. Quantitative impact of artifacts showed regional differences up to 6% within single segments of the myocardium.ConclusionsImproved AC including bone segmentation and truncation correction in cardiac PET/MR imaging is important to ensure best possible diagnostic quality and PET quantification. The results exhibited an overestimation of AC-map volume using MLAA, while HUGE resulted in a more realistic body contouring. Incorporation of bone segmentation into the Dixon-VIBE AC-map resulted in homogeneous gain in PET signal distribution across the myocardium. The majority of observed AC-map artifacts did not significantly affect the quantitative assessment of the myocardium.
Highlights
The integration of positron emission tomography (PET) and magnetic resonance (MR) imaging into one positron emission tomography/magnetic resonance (PET/MR) hybrid system [1] [2] has shown great potential in various cardiovascular applications with regard to evaluation of cardiac viability and function and diagnosis of tumor or inflammation [3] [4] [5] [6] [7].Technical challenges remain applying PET/MR to the cardiovascular system [8] [9] [10] [11] [12]
Using HUGE + bone Attenuation correction (AC) results in a homogeneous gain of ca. 6% and for maximum likelihood estimation of activity and attenuation (MLAA) 8% of PET signal distribution across the myocardium of the left ventricle over all patients compared to Dixon-VIBE AC only
The body volume truncation of -12.7 ± 7.1% compared to the segmented non-AC PET images using the Dixon-VIBE AC method was reduced to -1.9 ± 3.9% using HUGE and 7.8 ± 8.3% using MLAA
Summary
The integration of positron emission tomography (PET) and magnetic resonance (MR) imaging into one PET/MR hybrid system [1] [2] has shown great potential in various cardiovascular applications with regard to evaluation of cardiac viability and function and diagnosis of tumor or inflammation [3] [4] [5] [6] [7].Technical challenges remain applying PET/MR to the cardiovascular system [8] [9] [10] [11] [12]. The established MR-based methods of creating AC-maps have certain limitations compared to computer tomography (CT) based AC [16], e.g. the substitution of bone as soft tissue, which may lead to a systematical underestimation in PET signal [17]. Another constraint of MR-based AC is the limitation of the MR field-of-view (FOV) to a diameter of about 50 cm due to hardware restrictions such as B0 inhomogeneities and gradient nonlinearities. A fully MR-based approach for truncation correction is HUGE (B0 Homogenization Using Gradient Enhancement), which optimizes the readout gradient to locally compensate the B0 inhomogeneities, and the truncations [23] [24] [25]
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