Distortion correction in TSE near titanium implants at 0.55 T using reversed frequency-encoding and model-based...

Area of Science:

• Medical Imaging
• Biomedical Engineering
• Materials Science

Background:

• Imaging metallic implants, such as titanium, presents challenges due to artifacts.
• Existing methods like View Angle Tilting (VAT) and Slice Encoding for Metal Artifact Correction (SEMAC) can introduce blurring.
• Optimizing signal-to-noise ratio (SNR) while minimizing geometric distortion is crucial for diagnostic accuracy.

Purpose of the Study:

• To develop and evaluate a novel imaging method for visualizing tissues near titanium implants at 0.55 Tesla (T).
• The method aims to enhance SNR by utilizing a low readout bandwidth.
• Key objectives include reducing in-plane geometric distortions and artifacts caused by susceptibility effects.

Main Methods:

• Acquisition of Turbo Spin Echo (TSE) data in opposite frequency-encoding directions.
• Model-based iterative reconstruction incorporating Gradient Nonlinearity (GNL) correction for each acquisition.
• Estimation of susceptibility-induced displacement maps and reconstruction of a final image correcting for both GNL and metal-induced distortions.

Main Results:

• The proposed method preserves spatial resolution without the blurring observed in VAT and SEMAC at equivalent bandwidths.
• Reduced off-resonance distortion at low readout bandwidths led to a 1.4-1.6 fold increase in apparent SNR.
• Demonstrated clearer tissue delineation in phantoms and patients with orthopedic implants compared to conventional techniques.

Conclusions:

• The developed GNL and off-resonance distortion correction method effectively images near metal at 0.55T.
• It enables the use of low readout bandwidth for improved SNR without introducing blurring.
• This technique offers a significant advancement for MRI near metallic implants.