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Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [18F]FDG Micro-PET/MR Imaging
Published on: July 1, 2021
Quantitative analysis of image metrics for reduced and standard dose pediatric 18F-FDG PET/MRI examinations
Pietro Zucchetta1, Marco Branchini2, Alessandra Zorz2
11 Nuclear Medicine Unit, Department of Medicine DIMED, University-Hospital of Padova , Padova , Italy.
Objective::
The study performs a comprehensive analysis of image metrics to objectively support the reduction of injected activity in pediatric oncology 18F-FDG PET/MR (18F-fludeoxyglucose PET/MR) examinations. Contrast-to-Noise Ratio (CNR), Normalized Noise (NN), tumor burden, and standardized uptake value (SUV) parameters stability were investigated to robustly define the acceptable reduced activity level that preserves the clinical utility of images, considering different PET applications.
Methods::
21 PET/MRI examinations performed on a 3-Tesla Biograph mMR scanner were analyzed. Tracer activity reduction was stimulated by decreasing the count statistics of the original list-mode data (3 MBq kg-1). In addition to the already studied SUV metrics and subjective scoring on lesion detectability, a thorough analysis of CNR, NN, Metabolic Tumor Volume (MTV), and Total Lesion Glycolysis (TLG) was performed.
Results::
SUVmax and SUVmean increased more than 5% only in 0.6 MBq kg-1 reconstructed images (+10% and +9%, respectively), while SUVpeak was almost unaffected (average variations < 2%). The quantified CNR, NN, MTV, and TLG behavior with the decrease of the injected activity clearly defines 1.5 MBq kg-1 as a threshold of activity after which the quality of the image degrades. Subjective and objective analyses yielded consistent results. All 56 lesions were detected until activity of 1.2 MBq kg-1, whereas five lesions were missed on the 0.6 MBq kg-1 image. Perceived image quality (IQ) decreased in Lower Tracer Activity (LTA) images but remained acceptable until 1.5 MBq kg-1.
Conclusion::
Results about the stability of image metrics beyond the semi-quantitative SUV parameters and subjective analysis, rigorously proves the feasibility of the reduction of injected activity to 1.5 MBqkg-1 for pediatric patients aged between 7 and 17 years.
Advances In Knowledge::
This is the first report on the quantitative evaluation of the effect of activity reduction on image quality in pediatric PET/MR. The findings offer objective corroboration to the feasibility of a significant dose reduction without consequences on clinical image reading and tumor burden metrics.
Insights
Reducing injected activity in pediatric 18F-FDG PET/MR scans to 1.5 MBq/kg is feasible. This dose reduction maintains image quality and clinical utility for pediatric oncology patients, as supported by objective image metric analysis.
Area of Science:
- Nuclear Medicine
- Radiochemistry
- Medical Imaging
Background:
- Pediatric oncology relies on 18F-FDG PET/MR for diagnosis and monitoring.
- Reducing injected activity in PET/MR scans is desirable to minimize radiation dose to pediatric patients.
- Objective image quality metrics are needed to validate reduced activity levels.
Purpose of the Study:
- To objectively evaluate the impact of reduced injected activity on image quality in pediatric 18F-FDG PET/MR examinations.
- To determine a safe and clinically useful threshold for reduced tracer activity in pediatric oncology patients.
- To support dose reduction strategies without compromising diagnostic accuracy.
Main Methods:
- Analysis of 21 pediatric PET/MR examinations using a 3-Tesla Biograph mMR scanner.
- Simulated tracer activity reduction by decreasing count statistics from original list-mode data (starting at 3 MBq/kg).
- Quantitative assessment of Contrast-to-Noise Ratio (CNR), Normalized Noise (NN), Metabolic Tumor Volume (MTV), and Total Lesion Glycolysis (TLG), alongside SUV metrics and subjective lesion detectability.
Main Results:
- SUVmax and SUVmean increased >5% only at 0.6 MBq/kg, while SUVpeak remained largely unaffected (<2% variation).
- CNR, NN, MTV, and TLG behavior indicated 1.5 MBq/kg as a threshold for image quality degradation.
- All lesions were detected down to 1.2 MBq/kg; however, five lesions were missed at 0.6 MBq/kg. Perceived image quality remained acceptable until 1.5 MBq/kg.
Conclusions:
- The study demonstrates the feasibility of reducing injected 18F-FDG activity to 1.5 MBq/kg in pediatric patients (7-17 years) undergoing PET/MR.
- Quantitative analysis of image metrics confirms that this reduction level preserves clinical utility and diagnostic accuracy.
- These findings provide objective evidence supporting significant dose reduction in pediatric oncology PET/MR imaging.
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