Combined Test Piece.

The STP or CTP is used to ensure that the performance requirements for X-ray machines set out are met and maintained.Some times it is called Combined Test Piece (CTP) .The STP contains samples of organic and inorganic material, materials for resolution and penetration tests.



 SINGLE WIRE RESOLUTION (TEST No.1)

A set of un-insulated tinned copper wires of size 26, 30, 35, 38, 40 and 42 SWG or corresponding AWG wires are placed on Perspex sheet. The wires are laid out in 'S" shaped curves. 

 The wires are placed behind varying thickness of aluminium. A quarter of the length of each wire is uncovered whilst the remaining 3 quarters are covered by 3 wedges of aluminium, corresponding to 4.8mm (3/16"), 7.9mm (5/16") and 11.1mm (7/16") thickness. The minimum requirement is to display 40 SWG wire not covered by step wedge for most of the machines.  Metallic marker should be provided using high-density material, so that SWG numbers in the Display are clearly visible.

 USEFUL PENETRATION (TEST No.2)

Defines what level of details can be seen behind a thickness of known material. The requirement of this test is that the 26 SWG wire is seen under step wedge of 5/16 thickness of Aluminium. 

MULTI ENERGY X-RAY (TEST No. 3)

With multi-energy X-Ray, it should be possible to distinguish between materials of different average atomic number. The use of sugar and salt samples encapsulated on the test piece of CTP will check the material discrimination facility. A different color of sugar and salt on display  indicate that the sugar/salt samples are shown in different color.

 SIMPLE PENETRATION (TEST No. 4)

This test defines what thickness of steel the machine should be able to penetrate. The steel step wedge on the CTP has steps of 2 mm from 20 mm to 40 mm with a lead strip, 1.5mm in thickness to check that the machine is above or below the requirement. The requirement will be different for different KV machines. 

 SPATIAL RESOLUTION (TEST No. 5)

This test defines the ability of the system to distinguish and display objects which are close together. The CTP has copper plate with three sets of gratings (1.0mm, 1.5mm and

2.0mm). Each set consists of a horizontal group and a vertical group. The requirement is that a vertical and horizontal grating can be seen. 

 THIN METAL IMAGING (TEST No. 6)

This is to test the machine‘s ability to image thin metal. This involves a three thin squares of steel of 0.15mm, 0.10mm and 0.05mm thickness placed in row and the requirement is to image steel strip of 0.1 mm thickness.

 THIN ORGANIC IMAGING (TEST No. 7)

This is to test the machine‘s capability for thin organic imaging. The test object incorporates plastic of various thicknesses and the requirement is to image plastic of 1 mm thickness.

 IQI SENSITIVITY (TEST No. 8)

This is to determine the image quality indicator (IQI) sensitivity of the X-ray system. The requirement is to demonstrate 2% IQI sensitivity.

 The CTP must be placed with its longest dimension parallel to the direction of belt.

 The CTP should be placed in the best position for optimum performance.The optimum position of the STP on the belt depends on the x-ray source and detector arrangements, with the aim being to obtain the best result  possible.