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PET/MRI for Oncologic Brain Imaging: A Comparison of Standard MR-Based Attenuation Corrections with a Model-Based
Ivo Rausch1, Lucas Rischka2, Claes N Ladefoged3
1Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
Abstract:
The aim of this study was to compare attenuation-correction (AC) approaches for PET/MRI in clinical neurooncology. Methods: Forty-nine PET/MRI brain scans were included: brain tumor studies using 18F-fluoro-ethyl-tyrosine (18F-FET) (n = 31) and 68Ga-DOTANOC (n = 7) and studies of healthy subjects using 18F-FDG (n = 11). For each subject, MR-based AC maps (MR-AC) were acquired using the standard DIXON- and ultrashort echo time (UTE)-based approaches. A third MR-AC was calculated using a model-based, postprocessing approach to account for bone attenuation values (BD, noncommercial prototype software by Siemens Healthcare). As a reference, AC maps were derived from patient-specific CT images (CTref). PET data were reconstructed using standard settings after AC with all 4 AC methods. We report changes in diagnosis for all brain tumor patients and the following relative differences values (RDs [%]), with regards to AC-CTref: for 18F-FET (A)-SUVs as well as volumes of interest (VOIs) defined by a 70% threshold of all segmented lesions and lesion-to-background ratios; for 68Ga-DOTANOC (B)-SUVs as well as VOIs defined by a 50% threshold for all lesions and the pituitary gland; and for 18F-FDG (C)-RD of SUVs of the whole brain and 10 anatomic regions segmented on MR images. Results: For brain tumor imaging (A and B), the standard PET-based diagnosis was not affected by any of the 3 MR-AC methods. For A, the average RDs of SUVmean were -10%, -4%, and -3% and of the VOIs 1%, 2%, and 7% for DIXON, UTE, and BD, respectively. Lesion-to-background ratios for all MR-AC methods were similar to that of CTref. For B, average RDs of SUVmean were -11%, -11%, and -3% and of the VOIs 1%, -4%, and -3%, respectively. In the case of 18F-FDG PET/MRI (C), RDs for the whole brain were -11%, -8%, and -5% for DIXON, UTE, and BD, respectively. Conclusion: The diagnostic reading of PET/MR patients with brain tumors did not change with the chosen AC method. Quantitative accuracy of SUVs was clinically acceptable for UTE- and BD-AC for group A, whereas for group B BD was in accordance with CTref. Nevertheless, for the quantification of individual lesions large deviations to CTref can be observed independent of the MR-AC method used.
Insights
Comparing attenuation-correction (AC) methods for PET/MRI in neurooncology, this study found that standard diagnoses were unaffected by MR-based AC approaches. Quantitative accuracy varied, with some methods showing clinically acceptable results for specific tracers and patient groups.
Area of Science:
- Neuroimaging
- Radiology
- Medical Physics
Background:
- Accurate attenuation correction (AC) is crucial for quantitative PET/MRI in neurooncology.
- Various MR-based AC (MR-AC) methods exist, each with potential strengths and limitations.
- Comparing these MR-AC techniques against CT-based reference (CTref) is essential for clinical validation.
Purpose of the Study:
- To evaluate and compare different MR-AC techniques for brain PET/MRI.
- To assess the impact of MR-AC methods on diagnostic accuracy and quantitative values (SUVs, VOIs) in neurooncology.
- To determine the clinical acceptability of MR-AC methods compared to CTref.
Main Methods:
- Forty-nine PET/MRI brain scans were analyzed, including 18F-FET, 68Ga-DOTANOC, and 18F-FDG tracers.
- MR-based AC maps were generated using DIXON, ultrashort echo time (UTE), and a bone-attenuation-corrected (BD) prototype.
- PET data were reconstructed using AC from DIXON, UTE, BD, and CTref for comparison.
Main Results:
- No changes in standard PET-based diagnosis for brain tumors were observed with any MR-AC method.
- Quantitative accuracy (SUVmean, VOI) showed varying relative differences compared to CTref across tracers and MR-AC methods.
- Lesion-to-background ratios were similar across all MR-AC methods and CTref.
Conclusions:
- Diagnostic interpretation of brain tumor PET/MRI remains consistent regardless of the AC method used.
- UTE- and BD-AC demonstrated clinically acceptable quantitative accuracy for 18F-FET, while BD aligned with CTref for 68Ga-DOTANOC.
- Significant deviations from CTref in individual lesion quantification can occur with MR-AC methods.
