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Chemical shift misregistration artefact

A water-containing organ surrounded by fat. Because fat and water precess about 3.5 ppm apart, the fat signal is mis-mapped along the frequency-encode direction, producing a bright band where fat overlaps water on one edge and a dark band (signal void) on the opposite edge. Bands appear only along the frequency-encode axis, not the phase-encode axis, and worsen at higher field strength and lower receiver bandwidth.

Chemical shift artefact (type 1 misregistration) A water-containing organ surrounded by fat. Because fat and water precess about 3.5 ppm apart, the fat signal is mis-mapped along the frequency-encode direction, producing a bright band where fat overlaps water on one edge and a dark band (signal void) on the opposite edge. Bands appear only along the frequency-encode axis, not the phase-encode axis, and worsen at higher field strength and lower receiver bandwidth. Chemical shift artefact (type 1 misregistration) Fat and water precess at slightly different frequencies, so fat is mis-mapped along the readout axis. perinephric fat renal parenchyma frequency-encode (readout) direction phase-encode — no shift bright band — fat displaced over water dark band — signal void (not enhancement) Same paired banding outlines the kidneys and orbital fat around the optic nerve. Why it happens fat–water shift ≈ 3.5 ppm ≈ 220 Hz at 1.5 T · 440 Hz at 3 T Δx = Δf ÷ (γ · G_read) = Δf ÷ bandwidth per pixel Worse when field strength B₀ is higher receiver bandwidth is lower Reduced by higher receiver bandwidth smaller FOV → higher BW/pixel fat suppression (STIR) Dixon separates fat/water but does not fix this misregistration.
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