Aspects of Green Hospital Approaches with a Focus on Developing ...

f) Automatic Exposure Control
With the use <strong>of</strong> automatic exposure control (AEC) the brightness <strong>of</strong> an image is controlled
automatically. Thus, the scanner is adjusting the exposure automatically and
stops before overexposure by itself. Illustrated in Figure 5, for smaller patients (Figure
5A), less exposure, less current and therefore less dose is sufficient to obtain the desired
exposure. In contrast, for larger patients (Figure 5B) attenuation is higher and radiation
dose must be increased. Hence, application <strong>of</strong> a single protocol is inherently inefficient.
Especially the failure <strong>of</strong> transfer scanning protocols from developed nation, where the
average patient is much more corpulent than in developing nations has to be avoided.
Therefore, exposure times must be adjusted according to body size, weight and body
circumference. Additionally, exposure also has to be adapted according to medical examinations
[24, 25]. This individualization <strong>of</strong> scanning parameters is important to achieve
high quality images and prevent under- or over-exposure and unnecessary patient dose.
Hence, <strong>with</strong> the use <strong>of</strong> AEC it is also possible for unexpired physicians to get images
<strong>of</strong> high quality <strong>with</strong> low dose. Caused by the opportunity <strong>of</strong> economically retooling this
technique, AEC has potential to be used in developing nations like Cameroon.#
g) Shielding <strong>of</strong> Radiosensitive Organs
Selective protection <strong>of</strong> radiosensitive tissue and organs, such as the breast, eye lenses
and gonads, is particularly relevant for younger population groups like the average population
in Cameroon. Shields made <strong>of</strong> thin sheets <strong>of</strong> flexible latex impregnated <strong>with</strong>
bismuth and shaped to cover the eye lens, thyroid, or breasts can be used, respectively,
during periodontal, skull, cervical spine, or chest radiography exams to reduce the effective
organ dose [27, 28].
B. Computed Tomography (CT)
The following paragraph shows and discusses the results <strong>of</strong> the CT system analysis. It
is divided into three parts; first hardware, followed by system control and concluded by
s<strong>of</strong>tware solutions.
B.1 Hardware – Optimization <strong>of</strong> the CT System
a) X-Ray Beam Filtration
In CT beam hardening filters are implemented like already described for X-ray units and
targets again at ”hardening“ the beam spectra to reduce dose which do not contribute to
the image data. Itoh et al. [29] compared radiation exposure <strong>with</strong> an aluminum filter and
that <strong>with</strong> a conventional filter. The study showed a 17% reduction in patient dose and a
9% decrease in image noise <strong>with</strong> the aluminum filter. For beam shaping in CT additional
bow-tie filters are used. Since the cross-section <strong>of</strong> patients is typically oval in shape,
the attenuation <strong>of</strong> a fan beam in the peripheral region is less than that passing through
the central region. As illustrated in Figure 6: Bow-tie filter or beam-shaping filter mi-
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