Diagnostic equipment

Chapter 11 Diagnostic equipment





KEY POINTS








IMAGING TABLES


The majority of imaging tables utilised within general diagnostic departments have to meet a number of key requirements to ensure patient safety and the provision of optimal image quality. Modern imaging tables are designed to minimise unnecessary strain on practitioners during examinations and provide security and comfort for patients (Fig. 11.2). The availability of a variable height feature permits easy transfer of patients, whether they are walking, in a chair or on a stretcher. A wide range of movement is available, usually via foot control switches situated at the base of the table, and this prevents the need to move the patient around on a draw sheet and minimises injury to the practitioner. Controls positioned at either side of the imaging table also provide a universal approach to transferring and positioning patients.



Most modern imaging tables are designed using low attenuation materials, such as carbon fibre, which have the advantages of being lightweight and strong to accommodate the weight of the heavy individuals, typically up to 450 kg.1 Using materials such as carbon fibre also absorbs less of the primary beam and reduces radiation dose when undertaking grid work. Carbon fibre is also warm to the touch and has rounded edges to prevent physical damage to patients and staff and the build up of electrostatic charge.


All modern imaging tables should encompass a good range of longitudinal and transverse travel and possess a floating top design to minimise physical strain upon the practitioner. Such designs may aid in the ability to undertake prompt and effective examinations; however, the distance between the patient and cassette unit is increased and appropriate measures need to be taken to ensure object magnification and image unsharpness does not occur. This is normally compensated by increasing the source–image distance (SID) when undertaking examinations requiring an oscillating grid mechanism. The practitioner also needs to ensure the various table and X-ray tube interlocks are observed during such examinations; all manufacturers use colour coding to indicate X-ray tube functions.


Modern imaging tables also accommodate direct capture imaging plates, which are linked to a monitor and computer unit for a near instantaneous display. The advent of digital imaging has redefined clinical practice in terms of patient positioning and appropriate use of a DR system. Traditional systems employ integrated conventional cassette units, which also act as a scatter minimisation unit. Such systems are also linked to automatic exposure devices (AED). The use of the AED has become a routine aspect of clinical work. There are normally three AED chambers integrated into the tabletop mechanism. Selection of the appropriate chamber(s) is facilitated by pre-set protocols with a manual override if the practitioner needs to change the programme to provide an optimum image, or if the patient has a metal prosthesis (e.g. hip), affecting the overall quality of the image. The density settings on the control console may be password protected to prevent changes to optimal stored values.2


The use of automatic cassette size sensing (ACSS) techniques ensures the collimation from the light beam diaphragm matches the size of the cassette within the Bucky mechanism. This reduces the area irradiated and produces less scattered radiation, improving image quality as well as limiting radiation dose to the patient and staff. Closer collimation can again be performed, as the diaphragms are not fixed in the position sensed by the ACSS.



TUBE SUPPORTS


Modern general X-ray tubes are supported via a ceiling track mechanism which is able to withstand the rigour and demands of a typical department workload (Fig. 11.3). Most clinical departments utilise ceiling suspended units and employ a ‘cross track’ mechanism to allow the unit to move swiftly over a large floor space. The tube support facilitates movement around the longitudinal, transverse and vertical axes. The telescopic column provides a flexible range of vertical movement and is supported by electromechanical locks. The ceiling in imaging rooms containing a ceiling mounted unit needs to be of a reasonable height, thus permitting the required SID for a range of examinations.



The practitioner is normally provided with colour coded functions on the X-ray tube control unit, which are associated with the same coloured indicators on the ceiling and telescopic support. Some imaging rooms which undertake basic procedures (e.g. chest room) may employ a floor mounted X-ray unit, which is cost effective but



not as flexible as a ceiling mounted system. Such units are limited in their range of movement and the practitioner should take this into consideration when undertaking more complex examinations or with non-ambulant patients. Floor mounted systems are positioned on a track unit which is recessed into the floor and secured to a ceiling track for added stability. This design limits the available floor space and may present health and safety challenges.


The major advantages of a ceiling suspended unit include:







High-tension cables are securely encased in protective flexible piping, which is supported by additional ceiling sockets (Fig. 11.5). This enables the practitioner to safely manoeuvre the X-ray unit without the risk of placing unnecessary stress upon the high-tension cables. The supports for the cables must run freely along the track to prevent any mechanical strain when the X-ray tube is rotated.




CASSETTES AND FILM HOLDERS


Modern imaging departments utilise some form of digital capturing devices (image receptor), such as computed radiography (CR) or DR. This will have some impact upon the working logistics within a general imaging room. However, some departments may still also utilise conventional film screen cassettes to capture a latent image.


Typically, if a department is employing either conventional cassettes or CR technology, there will be a range of image receptor sizes to accommodate various radiographic techniques. All image receptor devices should be stored away from primary and scattered radiation, ideally in an appropriately designed storage holder. Routine quality control assessments of the image capturing devices should also be performed, in particular the routine secondary erasure of unused CR cassettes. Direct capture units (Fig. 11.6) may either be mobile devices or fixed units (e.g. chest imaging unit). Such units are expensive and require proper storage facilities when not employed.



To undertake a range of diagnostic techniques, the modern imaging environment should include various ancillary items. These include cassette holders, foam pads, stationary grid units, sandbags and radiation protection devices (e.g. lead rubber coats). The practitioner is required to utilise a range of skills and knowledge in order to produce optimal quality images. The use of a cassette holder to acquire images may minimise radiation dose to staff or carers.


Cassette holders may take the form of a basic device, such as the example shown in Figure 11.7, and are generally employed for techniques such as lateral horizontal beam hip examinations. However, a modern upright Bucky mechanism with an integrated cassette holder is also a crucial feature in a general imaging room.



Figure 11.8 demonstrates the advantages of a ceiling mounted X-ray unit and upright Bucky unit. The provision of standard interlocks also ensures set geometry for chest examinations, which need to be at a standardised distance of approximately 180 cm SID. This aids in the minimisation of geometric unsharpness for certain examinations.



A variable height facility supported by either manual or electromechanical locks enables the assembly to be moved up and down to examine a range of procedures, from lateral cervical spines to erect standing knees. The cassette support mechanism may then be removed to facilitate AED or Bucky work. The system can also be rotated 90 ° into a horizontal position if required for adapted techniques, such as a lateral elbow in plaster or wrists on patients who may be immobile. Modern upright DR units (Fig. 11.9

Feb 20, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Diagnostic equipment
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