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X-ray for non-invasive food quality control


Key words X-ray, density, non-invasive, composition, volume, mass, attenuation
Latest version 2010/12/20
Completed by IRTA

How does it work?

Primary objective Non-invasive technology to control quality and physical-chemical parameters of food material.
Working principle The main working principle is the attenuation of incoming X-ray by matter. In a material of inhomogeneous density such as food products, X-ray will be attenuated in different manners. High density material like bones will attenuate more than soft tissues such as fat or lean meat.

The x-ray intensity is decreasing with the material thickness dependent on the X-ray mass attenuation coefficient (this value is constant for any incident x-ray). If an X-ray source (normally a Coolidge tube) is placed on one side, with an X-ray detector on the opposite side and the food products in the middle, the attenuation of the X-ray in this material can be detected. By image analysis the 2D or 3D distribution of the densities in the material is obtained. This is the basic principle of the equipment for X-ray inspection, dual X-ray absorption (DEXA) or Computed Tomography (CT). The differences between these three technologies will be the complexity and power of the X-ray source and of the X-ray detectors, the movement of the materials to be scanned and the sophistication of the computer tools and algorithms to reconstruct images.

X-ray inspection is a simple equipment with a low X-ray source and cheap detectors. It can run automatically. DEXA is a more sophisticated machine with a computer tools to reconstruct and analyse images, but operations can be automated with a proper PLC program. Computed Tomography is only used as medical equipment with a good X-ray source and expensive X-ray detectors connected with a sophisticate computer tools to reconstruct 3D images. In addition computer programs are needed to analyse the images.

2 1 1 x-ray pierre picouet.JPG

Pic. 2D CT density images of a pig loin with attenuation factors for fat, lean and bone equivalent at 60kV and 100kV © Pierre Picouet

Additional effects With the X-ray source used, on the non-invasive equipments, no ionisation effect is created inside the product and products cannot be considered to have been irradiated. Precautions have to be taken only for the operator especially when a CT is used.
Important process parameters intensity of the X-ray source, voltage applied to the X-ray source, sensibility of the X-ray detectors, movement of the product, reconstruct algorithm
Important product parameters density (only works on food products with inhomogeneous density)

What can it be used for?

Products Meat products, fruit and vegetable, frozen food, products with different densities.
Operations Quality control
Solutions for short comings
  • Non-invasive methods to determine mainly foreign bodies (metal, glass, bones…) and chemical composition (fat, lean, salt…) inside the product and not only on the surface (optical methods).

What can it NOT be used for?

Products The technology is useless for product of homogeneous density.
Operations X-ray can have an impact on operators, especially for equipment like the Computed Tomography (CT). CT equipment has to be located in a special room with biological protection (lead walls) according with national legislation.
Other limitations One of the major limitations for X-ray equipment is the lifetime of the X-ray source. For X-ray inspection and DEXA technology the replacement cost of such device is acceptable for CT operation cost of maintenance and X-ray source are incompatible with an industrial use. Investment costs might also limit the application.
Risks or hazards Depending on the intensity of the X-ray, a biological shield may be necessary in the operating room. Before installation a consultation with national authorities is required.


Maturity In food industry, X-ray inspection systems are used commonly for detection of dense materials (glass, metals, bones …). DEXA system is also in use in the industry to determine fat content in meat products (hamburgers for example). CT is a medical equipment and no industrial equipment application is known at present.
Modularity /Implementation X-ray inspection system and DEXA can be easily inserted in a production line; CT equipment installation is submitted to specific regulation and has a high maintenance cost. ForCT skilled personel is needed.
Consumer aspects No aspects to be considered.
Legal aspects X-ray inspection system and DEXA have a low X-ray source and are accepted as a control tool. CT has a more powerful X-ray source and needs to follow regulation on medical X-ray systems.
Environmental aspects Biological hazard for the use of CT.

Further Information

Institutes IRTA, Wageningen UR - FBR
Companies Sartorius, Jacobsen, AIS, Smiths Detection, Siemens, General Electric, Philips, Hitachi, FOSS
References 1. Allen, P. & Leymaster, K.A. (1985). Machine error in X-ray computer tomography and its relevance to prediction of in vivo body composition. Livestock Production Science 13, 382-398

2. Clarke R. (2004). On-Line Measurement of Meat Composition, Encyclopedia of Meat Sciences, pp 935-941

3. Edwards M. (2004). Detecting foreign bodies in food Woodhead Publishing in Food Science and Technology (ISBN 1 85573 729 9)

4. Fulladosa E., Santos E., Picouet P. & Gou P. (2010). Salt and water content prediction by Computed Tomography in dry-cured hams. Journal of Food Engineering 96(1), 80-85

5. Hansen P.W., Tholl I., Christensen C., Jehg H.C., Borg J., Nielsen O., Østergaard B., Nygaard J. & Andersen O. (2003). Batch accuracy of on-line fat determination. Meat Science 64, 141–147

6. Judas M., Hoereth, R. & Dobrowolski, A. (2006). Computed tomography as an analytical method for pig carcasses. Fleischwirtschaft 86(12), 102-105

7. Mitchell A.D., Solomon M. B. & Rumsey T.S. (1997). Composition Analysis of Beef Rib Sections by Dual-energy X-ray Absorptiometryt, Meat Science, Vol. 47, No. l/2, 115-124

8. Pietrobelli A., Wang Z., Formic C. & Heymsfield S.B. (1996). Dual-energy X-ray absorptiometry: fat estimation errors due to variation in soft tissue hydration.

9. Vestergaard, C., Risum, J. & Adler-Nissen, J. (2004). Quantification of salt concentrations in cured pork by computed tomography. Meat Science 69, 107-113

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Created by Hte irta on 9 February 2012, at 11:16