QUALITY CRITERIA IMPLEMENTION AND AUDIT GUIDELINES

The quality criteria are designed to be easily applied in practice in any x-ray department without the need for special equipment apart from that needed for measuring or estimating the dose to the patient. They are intended to provide a demonstrably achievable standard of good practice both in terms of a satisfactory level of image quality and an acceptably low radiation dose to the patient.

However, the quality criteria will only be of real benefit to an x-ray department if they allow inadequate levels of performance to be readily identified and corrected. The impact of applying the quality criteria in a particular x-ray department in terms of the level of improvement in performance achieved, can only be properly assessed through a correctly structured process of medical audit.

The essential components of the medical audit process can be summarised as:

  Set standards
  Check compliance
  Correct bad practice
  Set new standards
  Repeat

The quality criteria essentially provide the initial "standards" for image quality and patient dose audit: a special case of "medical" audit.

More detailed steps in the audit process specific to this special case are:

1. Choose type of CT examination and CT equipment to audit.
2.

Take random sample of at least 10 standard-sized patients (60-80 kg).

3.

Perform chosen type of CT examination on each patient using the established techniques.

4.

Record all the technique and equipment parameters for each examination. (See example of a questionnaire in Appendix I to this chapter for relevant details to be recorded).

5.

Record the CTDIW and DLP for each examination using the methods described in Appendix I of Chapter 1. Compare the mean value for the sample of at least 10 standard-sized patients with the corresponding reference dose listed in the quality criteria.

6.

At least two observers check compliance of each CT examination with the image criteria independently. Appendix II to this chapter contains examples of image criteria assessment forms for the 5 types of examination evaluated in a pilot trial of quality criteria. As well as providing a system for scoring compliance with the image criteria and the visibility of important image details, these forms also include a system for scoring more general aspects of the image, such as noise, spatial resolution and diagnostic acceptability. Similar forms can be elaborated for other types of examinations for which quality criteria are provided in the guidelines.

To help in judging these image features, both during this audit process and more generally at any time, x-ray departments should consider having available a set of "ideal" hard copies of examinations in which all quality aspects are optimised and against which any other examination, can be directly visually compared. It is essential, of course, that the "ideal" examinations can be produced with a dose to the patient below the corresponding diagnostic reference value.

7.

Identify where the standard (image quality or dose criteria) are being not met.

8.

Investigate the cause(s) of any persistent non-compliance with the criteria. The "Examples of Good Radiographic Technique" may be useful to help identify those aspects of the established technique or equipment which are responsible for non- compliance.

9.

Take corrective action by changing techniques or equipment in a manner likely to remedy the occurrence of non-compliance.

10.

After a short period of using the revised techniques or equipment, repeat steps 2-7.

11.

If no improvement, repeat steps 8-10.

12.

If initial standards (quality criteria) are now being met in full, consider improving standards, for example, by setting lower reference doses in line with the optimisation principle ALARA (As Low as Reasonably Achievable).

To help establish a more uniform and more widespread level of performance in diagnostic radiology, it would be desirable to extend the audit process to include independent observers, external to the x-ray department being audited, and progressively to apply the process to larger groupings than individual x-ray departments.