Table 2.

Results of regular protocol variation by multi-level analysis.

				systematic difference
				oblique aortic - transverse aortic		pulmonary - transverse aortic
	slope		P	(cm/s)	P	(cm/s)	P
Gradient Speed	-0.54	cm/s	0.01	0.38	0.25	1.37	< 0.01
Partial Echo	-0.93	cm/s	0.02	0.52	0.47	2.34	< 0.01
Bandwidth	0.002	cm/s/ Hz/pix	< 0.01	0.63	0.09	1.69	< 0.01
Venc	0.0003	cm/s/ cm/s	0.59	0.77	0.09	1.79	< 0.01
Slice Thickness	0.03	cm/s/ mm	0.07	0.76	0.03	1.85	< 0.01
average				0.61		1.8

Graphs corresponding to the data are shown in Figure 2. Some slopes (increase of velocity offset per change of protocol parameter) were significant, but in every case this effect was specific to just one of the three scanner-types (gradient speed, partial echo) or not large enough to be of use (bandwidth). Oblique aortic slices showed systematic 0.61 cm/s higher offset than transverse aortic slices but this difference was not always significant. Pulmonary slices showed systematic 1.8 cm/s higher offset than transverse aortic slices.