Comparison of image quality and depiction of microscopic fat at 2-D and 3-D T1-Weighted (T1W) chemical shift (dual-echo) MRI for evaluation of adrenal adenomas

Objective To compare image quality and detection of microscopic fat in adrenal adenomas imaged with 2-D and 3-D chemical shift imaging (CSI) and, to derive parameters which best match 2-D and 3-D-CSI. Methods This two-phase, retrospective, and phantom + prospective study was IRB approved. First, a retrospective assessment of 50 consecutive adrenal adenomas imaged at 1.5 T with 2-D (TR minimum, Flip Angle [FA] 70 degrees, TE 2.2/4.4 ms.) and 3-D (TR minimum, FA 10 degrees, TE 2.2/4.4 ms.] CSI was performed. Second, phantom (varied fat: water concentration) experiments guided a prospective assessment of 12 consecutive adrenal adenomas imaged at 1.5 T with 3-D CSI (FA 10 degrees, 18 degrees). Two blinded radiologists independently evaluated: image quality, signal intensity (SI) cancellation (5-point Likert scale), and CSI-index ([SI.In.Phase-SI.Opposed.Phase/SI.In.Phase]*100). Results 2-D-CSI yielded higher image quality (p < 0.001) and, subjectively (p < 0.001) and quantitatively (p < 0.001) had more SI cancellation from microscopic fat. Proportion of adenomas with no detectable microscopic fat (3-D; 26-36% subjectively, 18-24% quantitatively [CSI-index < 16.5%] versus 2-D; 20-22% subjectively, 6-8% quantitatively) differed (p = 0.008-0.08 subjectively, 0.008-0.03 quantitatively) by CSI technique. Phantom experiments indicated 18 degrees FA 3-D-CSI compared favorably to 70 degrees 2-D-CSI for fat detection between 5% and 50%. In vivo, there was no differences in subjective or quantitative SI cancellation comparing 18 degrees 3D-CSI and 2D-CSI (p = 0.16-0.56 and 0.73-0.60). Greater SI cancellation occurred with 18 degrees 3D compared to 10 degrees 3D-CSI evaluated subjectively (p = 0.003-0.01). Conclusion 2-D CSI has subjectively higher image quality and shows more signal intensity loss from microscopic fat in adrenal adenomas compared to 10 degrees flip angle 3-D-CSI. Increasing the 3-D flip angle to 18 degrees more closely matches depiction of microscopic fat to 2-D-CSI at 1.5 T.