B₁-corrected breast T₁ mapping at ultralow field.

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging
• Biophysics

Background:

• Accurate T1 mapping is crucial for quantitative MRI in various tissues.
• B1 field inhomogeneity poses a significant challenge for T1 mapping accuracy, especially in ultralow-field (ULF) MRI.
• Developing bias-free T1 mapping methods is essential for reliable diagnostic applications.

Purpose of the Study:

• To develop an efficient T1 mapping approach for ultralow-field (ULF) MRI that corrects for B1 inhomogeneity.
• To determine the T1 values of breast tissues at 6.5 mT without fat suppression.
• To validate the developed T1 mapping method in vitro and in vivo.

Main Methods:

• A variable flip angle approach was employed for simultaneous T1 and B1 mapping.
• B1 maps were used to correct T1 maps, improving accuracy.
• The method was validated using copper sulphate phantoms and a breast phantom, followed by in vivo scans of healthy volunteers.

Main Results:

• T1 map measurements in phantoms showed less than 13% deviation from reference T1 values.
• For reference T1 values greater than 50 ms, the deviation was less than 6%.
• In vivo T1 maps of breast tissue in healthy volunteers at 6.5 mT showed 25th to 75th percentiles ranging from 79 to 243 ms.

Conclusions:

• The variable flip angle method is effective for simultaneous B1 and T1 mapping at ULF.
• This approach enables efficient and accurate in vivo T1 mapping in ULF MRI.
• The study provides reference T1 values for breast tissue at 6.5 mT.