Operating Manual

117116
AFNOR IQI’s
The AFNOR-type IQI’s originate in
France. They consist of metal step
wedges of the same material as the
object to be examined. The thick-
ness of the steps increases in arith-
metical progression. Each step has
one or more holes with a diameter
equal to the thickness of that step.
There are various models of step
wedges. The most common types
are rectangular with square steps
measuring 15x15 mm and hexagonal with triangular steps measuring 14mm.
See figure 4-13.
Steps thinner than 0.8 mm, have two holes of the same diameter. For a step to be regarded
as visible, all the holes in that particular step must be clearly seen on the film.
The French standard AFNOR NF A04.304 includes an addendum, which defines the
“index of visibility”.
For each radiograph a record is made of:
1. the number of visible holes (a)
2. the number of holes (b) of a diameter equal to or greater than 5 % of the
material thickness being radiographed.
The index of visibility N is given by the formula: N = a-b.
The value of N may be positive, zero or negative.
Image quality improves as the value of N increases.
Duplex IQIs
Fig. 4-13. French AFNOR IQIs
Duplex IQI’s are described in norm EN 462-5. The duplex IQI consists of a number of
pairs (“duplex”) of wires or thin strips made of platinum or tungsten, of increasingly
smaller size and diminishing distances for each pair.
Figure 5-13 shows such an IQI made up of pairs of wires.
The duplex IQI has been in existence for decades but is no longer current in conventio-
nal film radiography because of their high cost and limited possibilities of application.
It is, however, increasingly used in digital radiography, because it is perfectly suited to
determine contrast and (un)sharpness.
13.4 Position of the IQI
To be of any value in checking the factors defining sharpness and quality, the IQI must
be placed on the source side of the specimen. If the source side is not accessible, the IQI
is placed on the film side. In the latter position visibility is no longer an indication of
geometric unsharpness, but still a check on the developing process and radiation
energy used.
13.5 IQI sensitivity values
It is important to realise that any IQI acceptance-value must be based on a particular
type of IQI and the thickness of the object being examined. When IQI sensitivity is
expressed in a percentage of object thickness, a lower recorded value indicates a higher
radiographic sensitivity, hence better image quality.
Fig. 5-13. Duplex wire IQI