WORKSHOP ON QUALITY ASSURANCE IN DIAGNOSTIC RADIOLOGY
Perry Sprawls, Emory University, Atlanta, USA
Slavik Tabakov, King's College London, UK
ABSTRACT
The increased awareness that medicine delivers 90% of people’s
exposure to man-made radiation led to number of measures being taken all over the world.
The present Workshop in Sofia (14/10/2000) is one of these activities, endorsed by the
International Organization for Medical Physics (IOMP).
The new EC Euratom Directive 97/43 emphasizes the role of the medical
physicist in the process of minimizing and optimizing of patient dose. One of the most
important activities in X-ray Diagnostic Radiology directly linked with the patient dose,
is performance of effective Quality Assurance (QA) programs in hospitals and Quality
Control (QC) surveys of the respective medical technology.
The aim of Quality Control (QC) is to ensure continuing production of
diagnostic images with optimium quality, using minimum necessary dose to the patient. QC
should include checks and test measurements on all parts of the X-ray imaging system at
intervals not exceeding one year. In the UK practice the X-ray radiographic equipment
(X-ray tube and generator) is tested at least once per year and Fluoroscopic equipment -
twice per year.
The main parameters to be monitored during the routine QC of
Radiography include: Dose consistency ; Dose variation with mA; Dose variation with kV; kV
consistency; kV accuracy; kV variation with mA; Timer consistency; Timer accuracy; Beam
filtration (HVL); Beam alignment; Focal Spot size; Leakage radiation, etc.
The fluoroscopic image quality is tested using special test objects,
allowing assessment of the geometrical size and distortions; limiting spatial resolution;
noise and contrast resolution. The diagram, representing the minimal contrast to
distinguish an object with a certain size (Contrast-Detail Diagram) is a valuable QC
measure and is considered a measure for overall image quality.
Detailed explanations and examples of all useful protocols and
procedures for QC in Radiography and Fluoroscopy are available in the EMERALD Medical
Physics Training Scheme (Workbook and CD-ROM) - www.emerald2.net
The testing of contrast, resolution and noise and of the mammogram
follows precise protocols, and requires special attention due to the very radio-sensitive
anatomical object and high requirements to the image quality. The assessment of risk takes
all these factors into consideration. The QC in mammography is based on different type of
QC equipment and test objects.
QC of the film processing is of extreme importance, as it determines
the final image quality. This is of extreme importance in mammography. The parameters to
be tested include not only the X-ray film and Developing system, but also the entire
environment of the X-ray laboratory.
12 – 14 October 2000, Sofia, Bulgaria