Subjective examination quality
SEQ was best at 40 keV with a small effect size compared to the control group and a large effect size compared to 50 keV, again partially due to paired testing. This might indicate that noise is less important to SEQ than attenuation, although this effect may be specific to CTA [More examinations were rated as 3 (acceptable) or 4 (unacceptable) in the calf arteries than other anatomical levels. In the calf arteries, 7.8% were rated unacceptable in the control group compared to 10.6% and 11.1% in the intervention group at 40 and 50 keV, respectively. This might be due to blooming artefacts at low VMIs in calcified arteries. We did not test this difference statistically, but it may well be clinically significant as the calf and foot are often the areas of interest. The lower performance in distal vessels will have to be addressed by further protocol optimization.Unfortunately, we cannot compare SEQ findings from the calf with objective measurements. We decided against measuring in the calf because it would be difficult to adequately place ROIs in very small and calcified vessels. Although some studies have made the same decision, others have made measurements of arterial attenuation in both calf and foot [