Trolley

The experimental images were acquired on a Lifeguard 50 trolley (Lifeguard trolley range, ArjoHuntleigh, UK) using two different mattresses and will be further discussed with regards to technique in section 4.3.2 below). The Lifeguard trolley ranges are commonly used in clinical practice and are commercially available (see figure 14 for main

components). They are used in the three district hospitals of North Wales and are also used in other hospitals across the UK including Nottingham, Forth Valley and Salford Royal (Briody & Walker, 2013; Thompson, 2012; Stone, 2012). The Lifeguard 50 trolley has a fully radio-translucent mattress trolley top, has an elevating x-ray platform, which can be accessed from both sides of the trolley enabling flexible positioning of image receptors (ArjoHuntleigh, 2014). The Lifeguard trolley can be sold with either a standard 65mm mattress or a thicker foam mattress (Bi-Flex) used to reduce pressure sores as described below:

Standard mattress

The Lifeguard 50 trolley is sold with a standard 65 mm deep mattress pad (see figure 15). This mattress is the mattress available on the x-ray department’s trolleys where this thesis was conducted. The construction of this mattress is not specified by the manufacturer and no previous published work has been conducted to explore the mattress materials and how they differ from general x-ray mattresses that are used on x-ray tabletops (ArjoHuntleigh Healthcare, UK).

Bi-Flex mattress

ArjoHuntleigh’s Healthcare offers an alternative mattress that is compatible with the Lifeguard 50 trolley at additional cost. This mattress is known as the Bi-Flex pressure re- distributing mattress which is double the thickness of the standard mattress (130mm) (see figure 16). This Bi-Flex mattress is required for areas such as the emergency department where patients remain on the trolley for long periods of time. The emergency department would always purchase a Lifeguard trolley with the Bi-flex mattress due to tissue viability concerns (Dawkins, 2012). According to ArjoHuntleigh’ Healthcare UK, this mattress has been developed using two layers of foam, with the base layer made of higher density foam whilst the top layer is made from lower density foam. This mattress construction has resulted in a comfortable and more stable design, which maximises pressure redistribution, thereby reducing the likelihood of pressure ulcers. ArjoHuntleigh Healthcare UK stated that this mattress has been tested for x-ray translucency but this statement was not supported by empirical evidence and therefore cannot be translated into clinical practice (Lifeguard trolley range, ArjoHuntleigh, UK).

Due to the limited manufacturer information regarding the specific materials and density of these two mattresses above (standard and Bi-Flex), a small preliminary experiment was conducted prior to the main experiment in order to discover their attenuating properties. This experiment was carried out in the same x-ray room using the same equipment as for the main experiment whereby the two trolley mattresses (standard and Bi-Flex), the x-ray tabletop mattress and the use of ‘no mattress’ was compared.

The experiment was conducted on the Lifeguard 50 trolley using a 10cm Perspex block to simulate an attenuating dense object (similar to a patient) with the mAs determined from

the given AEC value using no mattress and 66kVp. The AEC in this situation gave an mAs of 4 which was then used throughout this small experiment. Dose measurements were performed at the centre of the image receptor position (which is on an elevated platform) in order to determine detector dose. The measurements were made using an Unfors

Calibartion device (Unifors Equipments US) with the dose measurement taken in microGrays (µGy). Three reading were taken for each measurement and the average calculated. The results were as follows:

 On average, there was a 14% difference in detector dose between no mattress and Bi-Flex mattress (see figure 13)

 On average, there was an 8% difference in detector dose between the x-ray tabletop mattress and Bi-Flex mattress.

 On average, the was a 7% difference in detector dose between both trolley mattress (standard v Bi-Flex)

 On average, there was no % difference in detector dose between x-ray table top mattress and standard mattress

Note* Standard deviation was negligible for the above values and are therefore not visible on figure 13

Figure 13 – figure demonstrating the difference in detector dose between different types of mattresses

Detector dose is the dose received by the image receptor to form the image after absorption and penetration through the patient and other objects in the path of the beam, With this and

16.4 15.44 _15.38 14.29 13 13.5 14 14.5 15 15.5 16 16.5 17

No mattress x-ray tabletop standard Bi-flex

D e te cto r d o se (µ Gy) Type of mattress

the results of the small experiment in mind, it can be seen that the thicker Bi-Flex mattress absorbs more of the primary beam than the other mattresses (Hess & Neitzel, 2012).

For this thesis, both the standard (65mm) and Bi-Flex (130mm) mattresses were used for comparison.

Trolley /mattress support

Mattress

Image Receptor

Image receptor holder platform that can be elevated

Figure 15 - the Lifeguard 50 trolley with the standard 65mm mattress (ArjoHuntleighs Healthcare, UK)

Figure 16 - the Lifeguard 50 trolley with the Bi-Flex pressure redistributing mattress (ArjoHuntleighs Healthcare, UK)