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

improved in various ways. Faster imaging <strong>with</strong>out time requirement for film processing
provides efficiency by a 30% increase in patient throughput [15]. This is big advantage
in developing countries because for example in Cameroon the physician density is <strong>with</strong>
0.19 per 1000 inhabitants only 5% <strong>of</strong> the density in Germany (3.531%) [16]. Additionally,
the digital storage <strong>of</strong> patient data, examinations and diagnoses leads to a further
improvement <strong>of</strong> the workflow. This is especially a benefit because <strong>of</strong> the insufficient
organization in Cameroon [4]. Due to the digital storage, material costs can be reduced
additionally. It is expected that the reduction in film costs results in an over 40%
reduction <strong>of</strong> the total examination costs [14]. Thus, digital imaging is a starting point
for refurbishing dose reduced radiology systems by economic retooling. Thereby, great
benefits are assumed for patients and radiologists in developing nations.
b) X-Ray Tubes and Generators
X-ray tubes and generator are components <strong>of</strong> X-ray systems which are already wellengineered.
Hence, there is no big potential for further improvements. Additionally, it
has to be taken into account that these hardware components are well-matched which
makes retooling challenging and uneconomical [17].
c) Collimation <strong>of</strong> X-Ray Beam
Pre-patient collimators are positioned between X-ray source and patient to define the
X-ray beam coverage and shape to avoid unnecessary radiation dose. Retooling and refurbishing
<strong>of</strong> collimators is again challenging as discussed in the previous section [17].
d) X-Ray Beam Filtration
X-ray beam filter attenuates and “hardens” the absorption spectrum resulting in an efficient
penetration <strong>of</strong> the X-ray beams through the patient. “S<strong>of</strong>t X-rays”, i.e. radiation
<strong>with</strong> low energy and a high chance <strong>of</strong> being absorbed <strong>with</strong>in the patient are decreased.
X-ray filters <strong>of</strong> aluminum or cooper selectively remove these s<strong>of</strong>t X-rays which never
reach the detectors and therefore do not contribute to the image and thus decrease radiation
dose. Especially for thinner patients, like common in developing nations, prefiltration
can be <strong>of</strong> notable advantage [17].
e) Detector Efficiency
The detector is one <strong>of</strong> the most important components <strong>of</strong> the dose performance <strong>of</strong> a
X-ray system. Two dose-relevant characteristics <strong>of</strong> a detector are quantum detection
efficiency and geometrical efficiency, which together describe the effectiveness <strong>of</strong> the
detector on converting incident X-ray energy into signals referred to as dose efficiency.
The geometric efficiency describes the relation between active detector area and total
detector area while the detector efficiency describes the amount <strong>of</strong> the X-rays reaching
the detector and are indeed absorbed and translated into signal for the image.
Table 1 gives an overview <strong>of</strong> the detector development for digital X-ray units and CT
systems. Over the last decades gas detectors, scintillation detectors and direct conver-
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