Accuracy and precision of zero-echo-time, single- and multi-atlas attenuation correction for dynamic [11C]PE2I PET-MR brain imaging

Abstract

Background A valid photon attenuation correction (AC) method is instrumental for obtaining quantitatively correct PET images. Integrated PET/MR systems provide no direct information on attenuation, and novel methods for MR-based AC (MRAC) are still under investigation. Evaluations of various AC methods have mainly focused on static brain PET acquisitions. In this study, we determined the validity of three MRAC methods in a dynamic PET/MR study of the brain. Methods Nine participants underwent dynamic brain PET/MR scanning using the dopamine transporter radioligand [11C]PE2I. Three MRAC methods were evaluated: single-atlas (Atlas), multi-atlas (MaxProb) and zero-echo-time (ZTE). The 68Ge-transmission data from a previous stand-alone PET scan was used as reference method. Parametric relative delivery (R1) images and binding potential (BPND) maps were generated using cerebellar grey matter as reference region. Evaluation was based on bias in MRAC maps, accuracy and precision of [11C]PE2I BPND and R1 estimates, and [11C]PE2I time-activity curves. BPND was examined for striatal regions and R1 in clusters of regions across the brain. Results For BPND, ZTE-MRAC showed the highest accuracy (bias < 2%) in striatal regions. Atlas-MRAC exhibited a significant bias in caudate nucleus (− 12%) while MaxProb-MRAC revealed a substantial, non-significant bias in the putamen (9%). R1 estimates had a marginal bias for all MRAC methods (− 1.0–3.2%). MaxProb-MRAC showed the largest intersubject variability for both R1 and BPND. Standardized uptake values (SUV) of striatal regions displayed the strongest average bias for ZTE-MRAC (~ 10%), although constant over time and with the smallest intersubject variability. Atlas-MRAC had highest variation in bias over time (+10 to − 10%), followed by MaxProb-MRAC (+5 to − 5%), but MaxProb showed the lowest mean bias. For the cerebellum, MaxProb-MRAC showed the highest variability while bias was constant over time for Atlas- and ZTE-MRAC. Conclusions Both Maxprob- and ZTE-MRAC performed better than Atlas-MRAC when using a 68Ge transmission scan as reference method. Overall, ZTE-MRAC showed the highest precision and accuracy in outcome parameters of dynamic [11C]PE2I PET analysis with use of kinetic modelling.

Deep-learning-based attenuation correction in dynamic [15O]H2O studies using PET/MRI in healthy volunteers

“…15 Merida et al studied two atlas-based AC methods in PET/MRI studies using the specific serotonin 5-HT1A antagonist [ 18 F]MPPF, and found a performance of the multi-atlas method similar to CTAC, but also a temporal shift of the bias due to an interaction of the spatial tracer-distribution heterogeneity variation over time with the degree of accuracy of the attenuation maps using the single-atlas method. More recently, two independent PET studies on the GE SIGNA platform comparing atlas based methods and zero-echo-time (ZTE) AC using either dynamic [ 11 C] PE2I 14 or [ 18 F]FE-PE2I 30 with either CTAC or 68 Getransmission AC as reference, respectively. Both studies agree on the inferiority of atlas-based methods and a low average ZTE AC bias of striatal binding potential (BP ND ) < 2% using cerebellum as reference.…”

“…However, they diverge regarding the absolute bias, which in one study is 10% in the striatum. 14 This bias can be partially explained by the use of 68Getransmission AC instead of CTAC but remains as a point of concern primarily in the combination of quantitative data derived from different PET system, as any absolute biases will impact quantification directly when using an external reference, such as an AIF. 31 Compared to the findings in previous studies, both RESOLUTE and DeepUTE seem to provide an overall lower bias when using CTAC as the reference standard for PET attenuation, and we did not find the aforementioned temporal variation of the bias in any of the studied regions during the [ 15 O]H 2 O PET studies.…”

“…However, they diverge regarding the absolute bias, which in one study is 10% in the striatum. 14 This bias can be partially explained by the use of 68Ge-transmission AC instead of CTAC but remains as a point of concern primarily in the combination of quantitative data derived from different PET system, as any absolute biases will impact quantification directly when using an external reference, such as an AIF. 31 …”

“…While both approaches showed acceptable results in the evaluation of static PET examinations, both studies showed a temporal variation of the performance during the dynamic PET scan that was attributed to the interaction of the spatial tracer-distribution heterogeneity variation over time and the degree of accuracy of the attenuation maps. 13,14 Similarly, Mansur et al described a temporal bias variation of a single-atlas method in dynamic [ 11 C]Cimbi-36 PET/MRI brain studies. 15 Fixed and known biases of the AC method lead to inaccurate, though potentially precise, measurements that can be corrected for, while temporal variation of the performance of an AC method in dynamic PET scans leads to unpredictable effects in studies using dynamic kinetic modelling.…”

“…While both approaches showed acceptable results in the evaluation of static PET examinations, both studies showed a temporal variation of the performance during the dynamic PET scan that was attributed to the interaction of the spatial tracer-distribution heterogeneity variation over time and the degree of accuracy of the attenuation maps. 13 , 14 Similarly, Mansur et al. described a temporal bias variation of a single-atlas method in dynamic [ 11 C]Cimbi-36 PET/MRI brain studies.…”