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Noninvasive In Vivo Small Animal MRI and MRS: Basic Experimental Procedures
Published on: October 20, 2009
[Value of new MR techniques in MR-PET]
U I Attenberger1, H H Quick, A Guimaraes
1Institut für klinische Radiologie und Nuklearmedizin, Universitätsmedizin Mannheim, Medizinische Fakultät Mannheim der Universität Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Deutschland, ulrike.attenberger@medma.uni-heidelberg.de.
Abstract:
The unparalleled soft tissue contrast of magnetic resonance imaging (MRI) and the functional information obtainable with 18-F fluorodeoxyglucose positron emission tomography (FDG-PET) render MR-PET well-suited for oncological and psychiatric imaging. The lack of ionizing radiation with MRI also makes MR-PET a promising modality for oncology patients requiring frequent follow-up and pediatric patients. Lessons learned with PET computed tomography (CT) over the last few years do not directly translate to MR-PET. For example, in PET-CT the Hounsfield units derived from CT are used for attenuation correction (AC). As 511 keV photons emitted in PET examinations are attenuated by the patient's body CT data are converted directly to linear attenuation coefficients (LAC); however, proton density measured by MRI is not directly related to the radiodensity or LACs of biological tissue. Thus, direct conversion to LAC data is not possible making AC more challenging in simultaneous MRI-PET scanning. In addition to these constraints simultaneous MRI-PET acquisitions also improve on some solutions to well-known challenges of hybrid imaging techniques, such as limitations in motion correction. This article reports on initial clinical experiences with simultaneously acquired MRI-PET data, focusing on the potential benefits and limitations of MRI with respect to motion correction as well as metal and attenuation correction artefacts.
Insights
Simultaneous magnetic resonance imaging-positron emission tomography (MRI-PET) offers superior soft tissue contrast and functional data for oncology and psychiatric imaging. However, attenuation correction in MR-PET presents unique challenges compared to PET-CT.
Area of Science:
- Advanced medical imaging techniques
- Hybrid imaging modalities
- Radiological sciences
Context:
- Magnetic resonance imaging (MRI) provides excellent soft tissue contrast, while 18-F fluorodeoxyglucose positron emission tomography (FDG-PET) offers functional metabolic information.
- The combination, MR-PET, is advantageous for oncological and psychiatric imaging due to its comprehensive data acquisition.
- MRI's lack of ionizing radiation makes MR-PET suitable for frequent follow-up scans in oncology and for pediatric patients.
Purpose:
- To report initial clinical experiences with simultaneously acquired MRI-PET data.
- To evaluate the potential benefits and limitations of MRI in the context of simultaneous PET scanning.
- To address specific challenges in MR-PET, including motion correction, metal artifacts, and attenuation correction.
Summary:
- Simultaneous MR-PET combines the strengths of MRI and PET, offering unparalleled soft tissue contrast and functional insights.
- Unlike PET-CT, direct attenuation correction (AC) in MR-PET is challenging because MRI proton density does not directly correlate with radiodensity.
- Simultaneous acquisition may offer improved solutions for motion correction in hybrid imaging.
Impact:
- Highlights the unique challenges of attenuation correction in MR-PET, differing from established PET-CT protocols.
- Demonstrates the potential of MR-PET for improved oncological and psychiatric diagnostics and patient monitoring.
- Provides insights into overcoming technical limitations for broader clinical adoption of simultaneous MR-PET.
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