Total 80 studies. Age: pre-split bolus (49, median 47), split bolus (62, median 52). Gender was equal in both groups (M:F = 29:11). Number of image data sets (pre-split bolus = 8-12, split bolus = 2).
There was no significant difference in the dose length product (radiation dose equivalent) between the conventional and split bolus techniques (Figure 6).
There was higher enhancement / attenuation of the abdominal aorta, common iliac artery, portal vein, IVC above renal vein and spleen (p<0.05) using the split bolus technique. There was higher enhancement / attenuation of the abdominal aorta, common iliac artery, portal vein, IVC above renal vein and spleen (p<0.05) using the split bolus technique, (figure 7).
There was good agreement between the 4 observers (ICC 0.664 for standard protocol and ICC 0.949 for split bolus) (Figure 8). There was no statistical significance of the overall IQ of the chest in the two protocols. The IQ scores were statistically higher in the abdomen and pelvis, spleen and kidneys with the split bolus protocol.
Discussion
Our institutional experience of the split bolus protocol for blunt trauma shows that the technique for single pass split bolus CT scanning has a higher overall clinical image quality, compared to the conventional arterial chest and portal venous abdomen and pelvis CT protocol, despite the conventional protocol demonstrating significantly better renal attenuation. This is comparable to previous studies 3,4.
There was no significant difference in the radiation exposure on our cohort of patients. This could be explained by the conventional protocol covered arterial chest up to the superior margin of liver and portal venous abdomen and pelvis; hence only limited overlap of scanned area performed. Biphasic/ dual phase CT can be considered as a complete work up as it has better overall diagnostic performance, than single phase CT. However, this is at the cost of doubling radiation exposure to the abdomen.
The number of image data sets to review dropped from 8-12 in the conventional protocol to 2 in the split bolus protocol. Although not evaluated in this study, this would extrapolate to time saved in reporting.
Limitations
The patient’s BMI is unknown, although the Camp Bastion contrast wheel is a weight based tool. This may affect liver parenchymal enhancement. The fixed delay contrast injection may result in variable arterial enhancement values depending on patient circulation, however is more practical and less error prone.