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Keywords:
Radioprotection / Radiation dose, Musculoskeletal spine, Computer applications, Conventional radiography, Computer Applications-General, Radiation safety
Authors:
E. Davey, A. England; Manchester/UK
DOI:
10.1594/ecr2015/B-1019
Results
Image quality
Total (weighted) image quality scores for both the AP and PA projections,
for each kVp increment,
are presented in Table 1 and Figure 1.
An image quality score of 48 was considered equal to the reference image after weighting factors were applied.
Table 1. Image quality scores for the AP and PA projection.
|
kVp |
AP Projection
|
PA Projection
|
Mean |
SD |
% change from reference |
Mean |
SD |
% change from reference |
75 |
|
|
|
41.6 |
1.1 |
-13.3 |
80 |
58.2 |
5.8 |
+21.3 |
45.4 |
5.8 |
-5.4 |
85 |
52.4 |
7.7 |
+9.2 |
40.2 |
3.5 |
-16.3 |
90 |
51.0 |
5.7 |
+6.3 |
38.2 |
5.0 |
-20.4 |
95 |
46.0 |
4.3 |
-4.2 |
37.2 |
0.8 |
-22.5 |
100 |
42.2 |
5.9 |
-12.1 |
34.8 |
3.3 |
-27.5 |
105 |
33.2 |
0.8 |
-30.8 |
28.0 |
2.1 |
-41.7 |
110 |
28.2 |
3.1 |
-41.3 |
25.4 |
2.6 |
-47.1 |
SD,
standard deviation.
A score of 48 is equivocal to the reference image (AP 75 kVp) |
The reliability of individual image quality scores between raters must be considered. The ICC value for the five students was 0.85 (95% confidence interval,
0.72 to 0.94). An ICC value of 0.85,
according to Rosner (2011),
indicates very good reproducibility.
Magnification
The transverse diameter of the L3 vertebral body was 25 mm and 27 mm for AP and PA projections,
respectively. As a result the PA projection demonstrated a magnification factor of 1.08 times greater than the AP.
Dosimetry
From an evaluation of the dosimetry calculations (Figures 2 – 5) it is evident that the PA projection results in a significantly reduced effective dose for all tube potentials studied. The mean ED reduction was 19.8% (range,
17.9 to 22.8%). As expected a trend was noted where kVp increases the ED for both orientations was seen to progressively decrease.
Individual organ/tissue doses were compared by kVp and between the AP and PA projections. It was evident (Figure 3A) that the PA projection reduced the absorbed dose to the stomach by a maximum 74.0% at 75 kVp and a minimum of 66.9% at 110 kVp. It was also clear that the PA projection reduced the absorbed dose to the colon (Figure 3B). The maximum dose reduction (68.3%) was seen at 70 kVp with a minimum dose reduction of 56.6% seen at 110 kVp. The PA projection also reduced the absorbed dose to the remainder tissues (Figure 3C). The maximum reduction in absorbed dose was again experienced at 75 kVp (36.0%) with a minimum reduction of 29.3% at 110 kVp.
With respect to gonadal dose,
the PA projection also reduced the absorbed dose to the testes by a maximum of 24.7% at 70 kVp a minimum of 8.7% at 80 kVp. The absorbed dose to the testes appears to increase with an increase in tube potential (Figure 4A). The PA projection resulted in a reduction in the absorbed dose to the ovaries of 22.8% at 70 kVp (maximum) and 3.7% at 110 kVp (minimum) (Figure 4B).
Figure 5 demonstrates the relative (percentage) absorbed dose reduction to the stomach,
colon,
remainder tissues,
ovaries and testes across each kVp.
Figure 5 clearly indicates that the most significant dose reduction is to the stomach,
followed by the colon and remainder tissues.