Effects of the Use of Multi-Layer Filter on Radiation Exposure and the Quality of Upper Airway Radiographs Compared to the Traditional Copper Filter
Somphan Klandima MEd*, Anchalee Kruatrachue MD*, Lawan Wongtapradit MD*, Narong Nithipanya MD*, Warangkana Ratanaprakarn MD*
Affiliation : * Department of Radiology, Queen Sirikit National Institute of Child Health, Bangkok, Thailand
Background : The problem of image quality in a large number of upper airway obstructed patients is the superimposition of
the airway over the bone of the spine on the AP view. This problem was resolved by increasing KVp to high KVp technique
and adding extra radiographic filters (copper filter) to reduce the sharpness of the bone and increase the clarity of the airway.
However, this raises a concern that patients might be receiving an unnecessarily higher dose of radiation, as well as the
effectiveness of the invented filter compared to the traditional filter.
Objective : To evaluate the level of radiation dose that patients receive with the use of multi-layer filter compared to non-filter,
and to evaluate the image quality of the upper airways between using the radiographic filter(multi-layer filter) and the
traditional filter (copper filter).
Material and Method: The attenuation curve of both filter materials was first identified. Then, both the filters were tested with
Alderson Rando phantom to determine the appropriate exposure. Using the method described, a new type of filter called the
multi-layer filter for imaging patients was developed. A randomized control trial was then performed to compare the
effectiveness of the newly developed multi-layer filter to the copper filter. The research was conducted in patients with upper
airway obstruction treated at Queen Sirikit National Institute of Child Health from October 2006 to September 2007. A total
of 132 patients were divided into two groups. The experimental group used high kVp technique with multi-layer filter, while the
control group used copper filter. A comparison of film interpretation between the multi-layer filter and the copper filter was
made by a number of radiologists who were blinded to both to the technique and type of filter used.
Results : Patients had less radiation from undergoing the kVp technique with copper filter and multi-layer filter compared to
the conventional technique, where no filter is used. Patients received approximately 65.5% less radiation dose using high kVp
technique with multi-layer filter compared to the conventional technique, and 25.9% less than using the traditional copper
filter. 45% of the radiologists who participated in this study reported that the high kVp technique with multi-layer filter was
better for diagnosing stenosis, or narrowing of the upper airways. 33% reported that, both techniques were equal, while 22%
reported that the traditional copper filter allowed for better details of airway obstruction. These findings showed that the multi-
layered filter was comparable to the copper filter in terms of film interpretation.
Conclusion : Using the multi-layer filter resulted in patients receiving a lower dose of radiation, as well as similar film
interpretation when compared to the traditional copper filter.
Keywords : Upper airway, High KV technique, Multi-layer filter, Copper filter
