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

To develop a method for imaging near titanium implants at 0.55 T, which enables the use of a low readout bandwidth for higher SNR while reducing in-plane geometric distortions.

A pair of turbo spin echo (TSE) data with opposite frequency-encoding directions is acquired. For each frequency direction, a gradient nonlinearity (GNL)-corrected image is reconstructed with a model-based iterative reconstruction incorporating GNL. A susceptibility-induced displacement map along the readout direction is estimated from two GNL-corrected images. A single final image is reconstructed with the model-based reconstruction incorporating both GNL and metal-induced displacement fields using both k-space acquisitions. The proposed method is compared against TSE with view angle tilting (VAT) and slice encoding for metal artifact correction (SEMAC).

The proposed reconstruction method maintains spatial resolution compared to current correction techniques. Unlike image-domain correction, VAT, and SEMAC, it does not introduce spatial blurring at equivalent bandwidths. It is feasible to reduce distortion due to off-resonance at a low readout bandwidth, resulting in higher apparent SNR (1.4-1.6-fold) without blurring under current imaging settings. In phantoms, and in patients with total hip arthroplasty and spinal fusion, the proposed method provides clearer delineation of tissues compared to conventional methods.

The proposed GNL and off-resonance distortion correction method for imaging near metal at 0.55 T enables the use of low readout bandwidth, providing SNR improvements without the blurring typically associated with low-bandwidth VAT.