Data was analysed using SPSS (22.0) and Excel (2013).
Tests for normality were conducted using the Shapiro-Wilk test.
A paired samples t–test was conducted; this was performed to compare the mean ER between FTC and the corrected ATCM and the mean ER between FTC and the uncorrected ATCM.
The uncorrected ATCM data has been included to enable clinically relevant comparisons to be made between FTC and ATCM approaches,
whilst the corrected ATCM data has been included to enable fair comparison of dose and risk data by normalising the tube currents between these modes as described in the methodology
Tube Current
Comparison of FTC and corrected ATCM
A comparison of the FTC and ATCM mathematically corrected data demonstrated no statistically significant differences between FTC and ATCM for either gender within any of the age groups for 100 mA/low dose+,
200mA/low dose,
250mA/standard or 400 mA/high quality (p>0.05).
When comparing FTC and ATCM at a normalised tube current of 300 mA (Figure 3),
the mean ER for FTC was significantly lower than the mean ER for the corrected ATCM among females and males in all age groups (p<0.05).
These differences were most noticeable in the younger age groups,
for example the lifetime ER for a 20 year old female was 76.322±17.692 relative to 82.656±20.137case/106,
for FTC and ATCM,
respectively.
Comparison of FTC and uncorrected ATCM
The data presented here compares the ER associated with FTC across a tube current range of 100-400mA to the uncorrected ATCM data with a tube current range of 49-440 mA (Figure 4).
The mean ER for ATCM was significantly higher than FTC for all age groups and both genders (p=0.000).
The average increase in ER by using ATCM over FTC was 21% and 20% for females and males respectively.
Pitch Factor
Comparison of FTC and corrected ATCM
When using the detail (0.688) pitch factor,
the mean abdominal ER for FTC tended to be higher than mean ER for the corrected ATCM data in all age groups and both genders,
however no statistically significant differences were observed (P>0.05) (Figure 5). For example the ER for a 20 year old female was 82.877±34.450 relative to 80.576±38.633 case/106,
for FTC and ATCM,
respectively.
When the standard (0.938) pitch factor was used,
there were no differences between the mean ER between FTC and the corrected ATCM for males and females or within any age group (p>0.05).
When the pitch factor was increased to 1.438 (fast),
the mean ER for FTC was considerably lower than mean ER for the corrected ATCM data across all age groups and was observed for both genders (p<0.05).
For example for a 20 year old female the ER was 48.901±18.876 relative to 55.964±16.714 case/106 for FTC and ATCM,
respectively.
These observed differences equated to an 11-13% lower mean ER for the FTC relative to the ATCM technique.
Comparison of FTC and uncorrected ATCM
When comparing the FTC and ATCM for the different pitch factors using the uncorrected ATCM data (Figure 6 ),
the mean ER was higher for the ATCM than FTC technique for all ages and both genders (p<0.05).
This equates to an increase in mean ER by 17% (female) and 16% (male) when using the ATCM technique over FTC.
For example,
for a 20 year old female the ER was 82.877±34.450 relative to 99.263±50.684 case/106 for FTC and ATCM,
respectively.
Detector Configuration
Comparison of FTC and corrected ATCM
(Figure 7) illustrates average ER from FTC and the corrected ATCM data for each age group and gender,
when using detector configuration 0.5×16mm.
For both male and female groups,
the mean effective risk for FTC was substantially lower than mean ER corrected from ATCM in any age group (p<0.05).
For example for a 20 year old female the ER was 68.493±34.031 relative to 72.781±33.805 case/106,
for FTC and ATCM,
respectively.
For a 20 year old male the ER was 59.926±30.175 relative to 63.254±29.556 case/106,
for FTC and ATCM,
respectively.
When the detector configuration increased to 1.0×16mm or 2.0×16mm no differences between the mean abdominal ER for FTC or ATCM were observed for either gender within any of the respective age groups (P>0.05).
Comparison of FTC and uncorrected ATCM
(Figure 8) shows the comparison of the mean ER between FTC and the uncorrected ATCM data.
The mean ER was higher for the ATCM than FTC technique for all ages and both genders and significant across all three different detector configurations (P<0.05).
This was comparable with an average increase in ER by 23% for males and females as a result of using ATCM over FTC.
For example for a 20 year old female the ER was 68.493 ± 34.031 relative to 89.220±44.845 case/106,
for FTC and ATCM,
respectively.