Keywords:
Paediatric, CT, Radiation effects, Radiation safety, Kv imaging
Authors:
T. Oku1, T. Masuda1, N. Imada2, Y. Matsumoto1, M. yoshida1, Y. yamashita1; 1Hiroshima/JP, 2Hiroshima /JP
DOI:
10.26044/ecr2019/C-2995
Conclusion
As we know,
using lower tube voltage,
it is necessary to select the optimal bowtie filter.
Our results show that the radiation dose at 80 kVp in all bowtie filters was significantly higher than at 100 kVp,
120 kVp,
and 140 kVp.
And it shows that the radiation dose at small bowtie filter in all tube voltages was significantly higher than at middle bowtie filter and large bowtie filter.
If bowtie filter's material is the same,
the small bowtie filter is thin than the other bowtie filter from ISO-center to 5 cm.
And it is thought that the shape becomes thick from 5 cm to 16 cm.
Therefore,
when small bowtie filter is used for children with a body width of 10 cm or less,
there is a possibility that the dose to be exposed may increase as compared to other bowtie filters.
In the image quality evaluation,
the radiation dose of the large bowtie filter was low and there was no significant difference in the SD value.
The radiation dose of middle bowtie filter is significantly higher,
and I think that it should not be used in pediatric CT examination.
By using large bowtie filter in pediatric CT examination it is possible to inspect the young patient safely at a lower dose than the recommended condition by the equipment manufacturers.
Bowtie filters are designed to reduce the intensity of incident x-rays toward the periphery of the body in the axial plane.
This results in stronger-intensity x-rays in the center of the body and weaker-intensity x-rays in the peripheral regions.
And this corresponds to the attenuation levels in an oval-shaped human body.
However,
Toth7) reported that bowtie filters are ineffective in children.
In addition,
Toth7) documented that variations in the radiation dose and image quality were greater when small,
rather than medium or large bowtie filters were applied.
But from our study the situation may be changing.
Our study though has limitations.
Our studies were performed on a single CT scanner model from a single manufacturer.
The relationship among the tube voltage,
image noise,
radiation dose,
and phantom size may depend to some degree on the CT scanner specifications that may vary among manufacturers.
In conclusion,
we clarified that the relationship between bowtie filters and the tube voltage may be progressing at pediatric CT.