A 3D MR-acquisition scheme for nonrigid bulk motion correction in simultaneous PET-MR
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Updated: Apr 26, 2026
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Published on: September 19, 2025
Christoph Kolbitsch1, Claudia Prieto1, Charalampos Tsoumpas2
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London SE1 7EH, United Kingdom.
Purpose:
Positron emission tomography (PET) is a highly sensitive medical imaging technique commonly used to detect and assess tumor lesions. Magnetic resonance imaging (MRI) provides high resolution anatomical images with different contrasts and a range of additional information important for cancer diagnosis. Recently, simultaneous PET-MR systems have been released with the promise to provide complementary information from both modalities in a single examination. Due to long scan times, subject nonrigid bulk motion, i.e., changes of the patient's position on the scanner table leading to nonrigid changes of the patient's anatomy, during data acquisition can negatively impair image quality and tracer uptake quantification. A 3D MR-acquisition scheme is proposed to detect and correct for nonrigid bulk motion in simultaneously acquired PET-MR data.
Methods:
A respiratory navigated three dimensional (3D) MR-acquisition with Radial Phase Encoding (RPE) is used to obtain T1- and T2-weighted data with an isotropic resolution of 1.5 mm. Healthy volunteers are asked to move the abdomen two to three times during data acquisition resulting in overall 19 movements at arbitrary time points. The acquisition scheme is used to retrospectively reconstruct dynamic 3D MR images with different temporal resolutions. Nonrigid bulk motion is detected and corrected in this image data. A simultaneous PET acquisition is simulated and the effect of motion correction is assessed on image quality and standardized uptake values (SUV) for lesions with different diameters.
Results:
Six respiratory gated 3D data sets with T1- and T2-weighted contrast have been obtained in healthy volunteers. All bulk motion shifts have successfully been detected and motion fields describing the transformation between the different motion states could be obtained with an accuracy of 1.71 ± 0.29 mm. The PET simulation showed errors of up to 67% in measured SUV due to bulk motion which could be reduced to less than 10% with the proposed motion compensation approach.
Conclusions:
A MR acquisition scheme which yields both high resolution 3D anatomical data and highly accurate nonrigid motion information without an increase in scan time is presented. The proposed method leads to a strong improvement in both MR and PET image quality and ensures an accurate assessment of tracer uptake.
Insights
A new 3D MRI method accurately detects and corrects patient motion during simultaneous PET-MR scans. This improves image quality and ensures accurate tumor uptake quantification, crucial for cancer diagnosis.
Area of Science:
- Medical Imaging
- Radiology
- Biophysics
Background:
- Positron emission tomography (PET) and magnetic resonance imaging (MRI) are vital for cancer diagnosis.
- Simultaneous PET-MR systems offer complementary data but are affected by patient motion.
- Nonrigid bulk motion during scans degrades image quality and quantification accuracy.
Purpose of the Study:
- To present a 3D MR-acquisition scheme for detecting and correcting nonrigid bulk motion in simultaneous PET-MR data.
- To assess the impact of motion correction on PET-MR image quality and tracer uptake quantification.
- To maintain high image resolution and accuracy without increasing scan time.
Main Methods:
- A respiratory-navigated 3D MR-acquisition with Radial Phase Encoding (RPE) was used.
- T1- and T2-weighted data were acquired with 1.5 mm isotropic resolution.
- Simulated PET data was used to evaluate motion correction's effect on Standardized Uptake Values (SUV).
Main Results:
- Successfully detected all bulk motion shifts with motion fields accurate to 1.71 ± 0.29 mm.
- Reduced SUV errors from up to 67% to under 10% with the proposed motion compensation.
- Acquired six respiratory-gated 3D datasets in healthy volunteers.
Conclusions:
- The MR acquisition scheme provides high-resolution 3D anatomical and motion data without increasing scan time.
- The method significantly improves both MR and PET image quality.
- Ensures accurate assessment of tracer uptake for improved cancer diagnosis.
