Medical imaging has become a significant source of

Medical imaging has become a
significant source of radiation exposure. In the developed nations, the
contribution from medical imaging can be greater19. In the United
States, medical radiation exposure is reported to have exceeded natural back
ground radiation from environment. If we leave this upward trend unchecked, we
will take a risk of increase in malignant disease in the future. Prevention of
further expansion of medical radiation exposure is necessary. Growth of medical
radiation exposure is largely attributable to the increase in the number of CT
examinations20.

Since children are more sensitive
to radiation and at a relatively greater risk of carcinogenesis than are
adults, it is even more important to avoid unnecessary radiation exposure in
this group than in the adult population17. An optimal CT radiation
dose in MDCT studies can be achieved by modifying the acquisition parameters,
using the automatic exposure control, and adjusting acquisition parameters for
patient size or iterative reconstruction. Kritsaneepaiboon S et al17
retrospectively did a study to compare the multidetector CT(MDCT) radiation
doses between default settings(phase 1) and a revised dose reduction
protocol(phase 2) and to determine whether the diagnostic confidence can be
maintained with imaging quality made under the revised protocol in paediatric
head, chest and abdominal CT studies. They found that paediatric CT radiation
doses can be significantly reduced from manufacturer’s default protocol while
still maintaining anatomical delineation, diagnostic confidence and overall
imaging quality.

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Ledenius21 et al used
computer-simulated images that were based on existing patient examinations
(retrospective material) and studied several different tube currents per patient,
i.e. paired data.  They did a
study to investigate the effect of tube current on diagnostic image quality in
paediatric cerebral multidetector CT (MDCT) images in order to identify the
minimum radiation dose required to reproduce acceptable levels of different
diagnostic image qualities. Their ages ranged from newborn to 15 years. Three
experienced radiologists blindly and randomly assessed the resulting images
from two different levels of the brain with regard to reproduction of
structures and overall image quality. Final data were evaluated using the
non-parametric statistical approach of inter-scale concordance. The minimum
value of tube current–time product (mAs) required to reproduce an image of
sufficient diagnostic quality was established in relation to the age of the patient.
The corresponding CT dose index values by volume (CTDIvol (mGy))
were also established. In conclusion, acceptable reproduction of low
contrast structures was possible at CTDIvol values down to 20 mGy
(patients 1–5 years old).

We studied 100 patients divided in three
age groups. It is important to use patients of similar size and developmental
stage when assessing the effect of a dose reduction, as the image quality at a
constant radiation dose is dependent on the patient attenuation.
This study was limited by only using two observers
who were experienced radiologists in the field21. The results may
have been different if less experienced radiologists had participated in the
study. Reductions in radiation dose should therefore be implemented with care,
using a safety margin and supervision for a period of time. There is a risk of
bias in assessing the overall impression of image quality, as radiologists tend
to recognise and favour their old settings.
The age distribution of patients in this study was
representative of patients within our paediatric department and surgery
department. The majority of patients (between 5 years and 10 years old) are at
an active age, resulting in an increased number of accident-related injuries.
Among the younger children (under 1 year old), pathology is often suspected at
birth, resulting in a scarcity of patients between 6 months and 1 year old.

Follow-up MDCT examinations of
shunt-treated hydrocephalus patients are common in paediatric patients, with
the ventricles being of special interest21. These patients are
repeatedly scanned during an extended period of time, leading to relatively
high accumulated patient doses22. Protocols especially designed for
hydrocephalus follow-up examinations were already in use prior to this study,
with the radiation doses being up to 50% lower than those in the standard
protocols. The images produced at these radiation doses agree relatively well
with the results of this study as regards the minimum tube current–time product
required to reproduce the ventricles acceptably for patients older than 1 year.

In our study tube current was
reduced approximately by 15%. The anatomic delineation, diagnostic confidence
and overall image quality showed no significant difference between normal
radiation protocol and reduced radiation protocol (Figure 1a & b). Based on the results of this study, the tube
currents in our standard protocols for patients aged between 1 and 10 years of
age can be lowered by approximately 15%.

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