WE-G-217A-09: Phase Imaging Measurement of Static Magnetic Field Homogeneity.

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging (MRI)
• Quality Assurance (QA)

Background:

• The American College of Radiology (ACR) MRI accreditation program mandates annual magnetic field homogeneity (MFH) measurements.
• Current vendor-implemented methods for MFH assessment are often time-consuming and require specialized techniques.
• Existing simpler methods may lack accuracy and precision for reliable MFH evaluation.

Purpose of the Study:

• To propose a robust, time-efficient method for MFH analysis in MRI scanners.
• To develop a practical approach for annual QA that balances speed and accuracy.
• To offer an alternative to time-intensive vendor-specific MFH measurement techniques.

Main Methods:

• Utilized a simple phase mapping acquisition to generate phase images.
• Acquired images in axial, sagittal, and coronal planes to approximate 3D MFH.
• Calculated the standard deviation of phase values within circular regions of interest (ROIs) to estimate MFH for the effective diameter of sample volume (DSV).
• Tested the method on five clinical MRI scanners (1.5T and 3.0T) using manufacturer phantoms and a 2D gradient echo sequence.

Main Results:

• MFH measurements on five scanners were within vendor specifications for the DSV.
• The proposed method demonstrated favorable comparison with vendor planned maintenance records, showing less than 0.1 ppm discrepancy.
• The technique proved effective in assessing MFH across different field strengths and scanner models.

Conclusions:

• The proposed phase mapping method is a reliable and practical approach for regular MFH measurement in MRI QA programs.
• This technique offers an independent verification of vendor-provided MFH measurements.
• The method provides a valuable compromise between efficiency and accuracy for clinical physicists.