Synopsis

The purpose of this study was to evaluate possible improvements in EPI-based DWI of the head/neck at 3 Tesla using a combination of readout-segmented EPI and dynamic shimming. We assessed ADC quantification in an anthropomorphic phantom and evaluated the presence of geometric distortions, signal losses, ghosting artifacts, and overall image quality in both, phantom and in-vivo data from 10 volunteers. We found that combining integrated shimming with readout-segmented EPI significantly improves images quality of EPI based DWI of the head/neck at 3 Tesla compared to the single techniques alone or conventional single-shot EPI.

Purpose

Methods

The present study consisted of a phantom experiment and of volunteer measurements.

All MR acquisitions were performed on a clinical 3 Tesla MR scanner (Magnetom Skyra, 3 T, Siemens Healthineers, Erlangen, Germany). The following sequence parameters were used for both, the phantom as well as the volunteer study: matrix size, 128; FoV [mm] 260; slice thickness [mm], 5; flip angle [°], 90; TR [ms], 5600. TE [ms] and pixel bandwidth [Hz/px] were 67/67/56/56 and 1325/1325/770/770 for sEPI/iEPI/rsEPI/irsEPI respectively.

For the phantom experiments, an anthropomorphic phantom of the head and neck region was constructed by modeling a cast mold and filling it with a 3% agar solution. In addition, 5 plastic tubes were placed within the phantom containing air and sucrose solutions of different concentrations yielding different diffusivities. The phantom was examined using the DWI sequences described above (Figure 1).

For volunteer studies, 10 healthy volunteers (5 male, 5 females) were examined using the DWI sequences described above.

ADC values within the phantom compartments were measured and compared between the different sequences.

For phantom and volunteer measurements, the presence of geometric distortions, signal losses, ghosting artifacts as well as overall image quality were visually assessed on a 4-point scale by two radiologists in consensus. On the 4-point scale, 1 being the best possible outcome of the assessed category while 4 being the worst. In addition, failure of fat saturation was assessed in volunteer data.

Results

Quantification of ADC within the phantom compartments was comparable using the different sequence technologies without significant variations (Figure 2A).

The combination of integrated shimming and readout-segmented EPI yielded significantly better overall image quality compared to sEPI, iEPI and rsEPI in phantom data as well as volunteer measurements (Figures 2B). Markedly reduced geometric distortions, signal loss and better fat saturation was observed using irsEPI (Figure 3).

Using irsEPI significantly improves image quality and reduces artifacts caused by magnetic field inhomogeneities in EPI based DWI of the head and neck region at 3 Tesla compared to alternative techniques. The clinical utility of this novel technique has to be further evaluated in patient studies.

Conclusion

Acknowledgements

References

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