Food for x ray

BMJ 2004; 329 doi: (Published 07 October 2004) Cite this as: BMJ 2004;329:848
  1. Brian Witcombe, radiologist
  1. Gloucestershire Royal Hospital, Gloucester

    When my black Labrador had a shoulder x ray to help diagnose trouble with a front leg I couldn't interpret the images, and my limitations were underlined when the vet, in telephone conversation with a canine orthopaedist, referred to me, the owner of the patient, as a human radiologist. Immersed in medical matters, we forget too easily not only the veterinary but also the wider potential of radiology. Imaging can be used to detect engineering defects, to investigate mummies, to search for concealed stowaways, or to reveal a masterpiece concealed beneath another painting.

    Our computed tomographic scanner can detect the brown, mushy bits in a banana even when the skin is still yellow. Once, when obsessed with growing vegetables for competition at local gardening shows, I used mammographic techniques to examine my exhibit of peas. I could detect an imperfect row of peas or a miscreant maggot before the judge opened the pod and without disturbing the essential bloom. The commercial value of these latter techniques is yet to be exploited, but foodstuffs undergo radiography more than we think.

    Most ice cream and much packaged food from large manufacturers are x rayed before they are eaten. A few years ago, an ice cream might have had a bit missing because of a hidden air pocket. Now x rays detect any deficiency so neither the customer nor the retailer is short changed, and foreign bodies can be detected. The screening is done automatically by means of computer software, and some 500 items a minute can be scanned by one machine.

    Manufacturers once used metal detectors to examine their products, but cornets wrapped in metal foil proved difficult, so x rays at 80 kVp are now used. The sensitivity of the examination can be varied, and parameters set for radiodensity or density variation from pixel to pixel. There are practical problems: for example, some ice cream cornets may be inappropriately rejected if their chocolate-containing tips overlap in the packaging. As in any diagnostic process, there is a trade off between sensitivity and specificity. In practice a cherry missing from a cake or a 1.5 mm piece of bone or eggshell in a pie or fish product are detected. Twenty thousand chocolate ice cream lollipops a day are examined on one production line, and only a few score are rejected.

    How do I know this? An engineer from a local factory had a venogram and invited me to see x rays being used in another way. He was generous with his time, but there was no free ice cream.


    • We welcome articles up to 600 words on topics such as A memorable patient, A paper that changed my practice, My most unfortunate mistake, or any other piece conveying instruction, pathos, or humour. Please submit the article on Permission is needed from the patient or a relative if an identifiable patient is referred to. We also welcome contributions for “Endpieces,” consisting of quotations of up to 80 words (but most are considerably shorter) from any source, ancient or modern, which have appealed to the reader.

    View Abstract

    Sign in

    Log in through your institution