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Quantitative and clinical impact of MRI-based attenuation correction methods in [¹⁸F]FDG evaluation of dementia

Silje Kjærnes Øen¹, Thomas Morten Keil², Erik Magnus Berntsen^3,2

¹Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Postbox 8905, N-7491, Trondheim, Norway. silje.k.oen@ntnu.no.

EJNMMI Research

|August 26, 2019

Abstract

Background:

Positron emission tomography/magnetic resonance imaging (PET/MRI) is a promising diagnostic imaging tool for the diagnosis of dementia, as PET can add complementary information to the routine imaging examination with MRI. The purpose of this study was to evaluate the influence of MRI-based attenuation correction (MRAC) on diagnostic assessment of dementia with [¹⁸F]FDG PET. Quantitative differences in both [¹⁸F]FDG uptake and z-scores were calculated for three clinically available (DixonNoBone, DixonBone, UTE) and two research MRAC methods (UCL, DeepUTE) compared to CT-based AC (CTAC). Furthermore, diagnoses based on visual evaluations were made by three nuclear medicine physicians and one neuroradiologist (PET_CT, PET_DeepUTE, PET_DixonBone, PET_UTE, PET_CT + MRI, PET_DixonBone + MRI). In addition, pons and cerebellum were compared as reference regions for normalization.

Results:

The mean absolute difference in z-scores were smallest between MRAC and CTAC with cerebellum as reference region: 0.15 ± 0.11 σ (DeepUTE), 0.15 ± 0.12 σ (UCL), 0.23 ± 0.20 σ (DixonBone), 0.32 ± 0.28 σ (DixonNoBone), and 0.54 ± 0.40 σ (UTE). In the visual evaluation, the diagnoses agreed with PET_CT in 74% (PET_DeepUTE), 67% (PET_DixonBone), and 70% (PET_UTE) of the patients, while PET_CT + MRI agreed with PET_DixonBone + MRI in 89% of the patients.

Conclusion:

The MRAC research methods performed close to that of CTAC in the quantitative evaluation of [¹⁸F]FDG uptake and z-scores. Among the clinically implemented MRAC methods, Dixon_Bone should be preferred for diagnostic assessment of dementia with [¹⁸F]FDG PET/MRI. However, as artifacts occur in Dixon_Bone attenuation maps, they must be visually inspected to assure proper quantification.

Insights

MRI-based attenuation correction (MRAC) methods show promise for dementia diagnosis using [18F]FDG PET/MRI. The DixonBone MRAC method is recommended for clinical use, but requires visual inspection for artifacts to ensure accurate dementia assessment.

Area of Science:

Medical Imaging
Nuclear Medicine
Radiology

Background:

Positron emission tomography/magnetic resonance imaging (PET/MRI) integrates PET's functional data with MRI's anatomical detail.
[18F]FDG PET provides crucial metabolic information for dementia diagnosis, complementing MRI.
Accurate attenuation correction (AC) is vital for quantitative PET imaging within a hybrid PET/MRI framework.

Purpose of the Study:

To evaluate the impact of various MRI-based attenuation correction (MRAC) methods on the diagnostic accuracy of dementia assessment using [18F]FDG PET.
To compare the quantitative differences in [18F]FDG uptake and z-scores between different MRAC techniques and CT-based AC (CTAC).
To assess the diagnostic agreement of visual evaluations performed with different MRAC methods, with and without integrated MRI information.

Main Methods:

Quantitative analysis of [18F]FDG uptake and z-scores using five MRAC methods (DixonNoBone, DixonBone, UTE, UCL, DeepUTE) compared to CTAC.
Visual diagnostic assessment by nuclear medicine physicians and a neuroradiologist using PET/CT and PET/MRI data reconstructed with different MRAC techniques.
Comparison of pons and cerebellum as reference regions for PET data normalization.

Main Results:

MRAC methods, particularly DeepUTE and UCL, demonstrated minimal mean absolute differences in z-scores compared to CTAC when using the cerebellum as a reference region.
Visual diagnoses using PET/MRI with DeepUTE and UTE showed high agreement with PET/CT (74% and 70%, respectively).
Combined PET/CT and MRI visual assessments showed strong concordance (89%) when using DixonBone MRAC.

Conclusions:

Research-based MRAC methods closely approximate CTAC performance in quantitative [18F]FDG PET analysis.
DixonBone MRAC is the preferred clinically available method for dementia diagnosis with [18F]FDG PET/MRI due to its quantitative accuracy.
Visual inspection of DixonBone attenuation maps is crucial to mitigate potential artifacts and ensure reliable quantification for dementia diagnosis.

Read full analysis

Keywords:

Attenuation correction PET/MRI z-scores, dementia

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