An APTw/CEST-MRI technique to obtain water-only Z-spectra in the presence of fat is described. Water-fat separation in CEST is complicated by partial saturation of spectral fat components. Here, the saturation frequency-dependent water-fat phases are calculated using a multi-peak saturation model. A Z-spectrum acquisition with a single echo-shift is combined with a reference acquisition (S0) using 3 echo-shifts for water-fraction and B0-mapping. A B0-corrected, water-only Z-spectrum is obtained by complex rotations and weighted subtraction according to the water-fat phase. Volunteer examinations at 3T are shown (breast and abdominal). The single echo-shift technique offers a time-efficient means for water-fat separation in APTw/CEST-MRI.
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