Quantification error obtained for the three calibration phantoms and the three test phantoms. The error is plotted as a function of the calibration phantom ROI diameter expressed as a percentage of the phantom physical diameter for the four SPECT-CT systems. The quantification was performed for the uniform part of the contrast (red) or NEMA NU 2–1994 attenuation and scatter correction accuracy (green) phantom and the S phantom (blue) using the conversion factor obtained with the M (triangle), L (square), or XL (diamond) phantom. All reconstructions with 24 iterations and eight subsets. (A) Philips Brightview XCT. (B) General Electric Discovery NM/CT 670. (C) General Electric Hawkeye 4. (D) Siemens Symbia T6.