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MR-based field-of-view extension in MR/PET: B0 homogenization using gradient enhancement (HUGE)
Jan O Blumhagen1, Ralf Ladebeck, Matthias Fenchel
1Magnetic Resonance, Healthcare Sector, Siemens AG, Erlangen, Germany; Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland.
Abstract:
In whole-body MR/PET, the human attenuation correction can be based on the MR data. However, an MR-based field-of-view (FoV) is limited due to physical restrictions such as B0 inhomogeneities and gradient nonlinearities. Therefore, for large patients, the MR image and the attenuation map might be truncated and the attenuation correction might be biased. The aim of this work is to explore extending the MR FoV through B0 homogenization using gradient enhancement in which an optimal readout gradient field is determined to locally compensate B0 inhomogeneities and gradient nonlinearities. A spin-echo-based sequence was developed that computes an optimal gradient for certain regions of interest, for example, the patient's arms. A significant distortion reduction was achieved outside the normal MR-based FoV. This FoV extension was achieved without any hardware modifications. In-plane distortions in a transaxially extended FoV of up to 600 mm were analyzed in phantom studies. In vivo measurements of the patient's arms lying outside the normal specified FoV were compared with and without the use of B0 homogenization using gradient enhancement. In summary, we designed a sequence that provides data for reducing the image distortions due to B0 inhomogeneities and gradient nonlinearities and used the data to extend the MR FoV.
Insights
This study developed a new gradient enhancement technique to expand the magnetic resonance imaging (MRI) field-of-view (FoV) for whole-body MR/PET scans. This method improves attenuation correction accuracy by reducing distortions without hardware changes.
Area of Science:
- Medical Imaging
- Magnetic Resonance Imaging (MRI)
- Positron Emission Tomography (PET)
Background:
- Whole-body MR/PET attenuation correction often relies on MRI data.
- Limited MRI field-of-view (FoV) due to B0 inhomogeneities and gradient nonlinearities can cause truncated images and biased attenuation correction, especially for larger patients.
- This limitation impacts the accuracy of combined MR/PET imaging.
Purpose of the Study:
- To explore extending the MRI FoV using B0 homogenization via gradient enhancement.
- To compensate for B0 inhomogeneities and gradient nonlinearities to improve attenuation correction.
- To enable more accurate whole-body MR/PET imaging for all patient sizes.
Main Methods:
- Developed a spin-echo-based sequence to compute optimal readout gradients for specific regions of interest.
- Implemented B0 homogenization using gradient enhancement to locally compensate for field distortions.
- Analyzed in-plane distortions in phantom studies with an extended transaxial FoV up to 600 mm.
- Compared in vivo measurements of patient arms with and without the technique.
Main Results:
- Achieved significant distortion reduction outside the standard MRI-based FoV.
- Demonstrated successful FoV extension without requiring hardware modifications.
- Phantom studies confirmed reduced in-plane distortions in the extended FoV.
- In vivo measurements showed improved data quality for regions previously outside the FoV.
Conclusions:
- The designed sequence effectively reduces image distortions caused by B0 inhomogeneities and gradient nonlinearities.
- Gradient enhancement successfully extends the MRI FoV, improving potential for accurate whole-body MR/PET attenuation correction.
- This non-invasive method enhances the applicability of MR/PET imaging for a wider range of patients.
