What's new in cancer?: Imaging

Wilhelm Conrad Röntgen’s discovery of x-rays in 1895 led to them being immediately used in the practice of medicine and the diagnosis of disease.

X-rays were also being applied to the treatment of cancer within the year. Early radiologists used x-rays for both diagnosis and treatment and that close association means that to this day Consultant Clinical Oncologists in the UK are members of The Royal College of Radiologists.

X-ray based techniques are still important and routinely used, for example in breast screening mammography. However, the most exciting innovations are in non-radiation based techniques. Standard tests like computerised tomography (CT) and magnetic resonance imaging (MRI) scanners continue to improve their resolution (think how home televisions have gone from standard, to HD and now to 5K). These advances have allowed routine testing to have greater sensitivity (to detect smaller cancers) and better specificity (to tell the difference between malignant disease and benign changes).

The vast amount of data these scans produce creates problems for staff to interpret and there are multiple worldwide efforts to harness Artificial intelligence to help with scan reading including lung cancer CT, prostate MRI scans, and mammograms. Nonetheless there is still the need for imaging to go further and faster.

Imaging technologies have historically identified changes in anatomy: is an organ too big? Are there shadows present where there should be none?

But cancer can affect our bodies without changing the size and shape of our component parts. In order to see and monitor cancer we need to be able to detect the activity of the cells – what they are doing - this is the realm of functional and molecular imaging.

MRIs can detect small changes in the magnetic properties of blood dependent on how much deoxyhaemoglobin is present and use this factor to detect brain activity in functional MRI (fMRI). The ability of water to diffuse in and out of cells alters in abnormal tissues and this can be detected in diffusion weighted MRI (dwMRI). These scans can be used to distinguish benign from malignant tissue and have proven to be useful for investigating and diagnosing head and neck cancers and brain tumours. A further extension of these techniques is to study the effects that pharmacological agents have on brain function by analysing changes in blood flow.

Molecular techniques analyse various separate metabolic processes taking place inside tissue. The most widely used of these is Positron Emission Tomography (PET) scanning. PET scanners use radiotracers – safe, injectable chemicals that produce a small temporary and measurable amount of radioactivity. Different radiotracers can be developed for different use dependent on how they are taken up into different tissues. The most widely used tracer is a form of glucose (FDG). All active cells use carbohydrates like glucose in some form.

More active cells use more glucose so take up more of the tracer and are more easily demonstrated on a PET scan. Cancer cells have more active glucose consumption, so a PET scan shows them well (alongside other active tissues such as the heart and brain). This knowledge has contributed to the myth that sugar ‘feeds’ cancer. PET scans are widely used in both cancer diagnosis and in treatment monitoring but new radiotracers are extending their use.

Prostate-specific membrane antigen (PSMA) is a tracer which, as the name suggests, is highly sensitive at detecting prostate cells and is becoming widespread in detection of prostate cancer after treatment. Radiotracers are now in development that have potential to monitor the very specific targets used in modern cancer drug therapies such as immunotherapy where PDL-1, PD-1 and CTLA-4 may all potentially be identified by PET. In breast cancers research has already shown that the oestrogen and HER-2 receptors that are used to select therapies can also be monitored with functional imaging and may have an important role in the future is tracking success of these therapies for individual patients. 

These molecular techniques offer great promise but alongside the exciting research there are practical problems that need to be overcome. The radioactive isotopes used in these scans come from only 6 reactors in the world and that can lead to problems of supply which can affect availability of scans. A current proposal to manufacture isotope in the UK may help with those supply problems in the future.

The research into modern scan technologies is exciting science but for people living with cancer scans may cause different emotions. Waiting for, and then going for a test often may cause stress or anxiety. The worry of waiting for test results is so common it has generated a new word: scanxiety.

The worry is present in up to two-thirds of people attending for cancer scans. 

"I will have regular scans and, on each occasion, will be right on edge for the couple of weeks beforehand. It is just a waiting game between me and the tumour. Who is going to blink first?" Adam Blain, Pearshaped. 

If you are someone you know is struggling with anxiety of waiting for a cancer scan result then you can:

• Call the Macmillan Support Line on 0800 808 00 00 Monday to Friday, 8am to 6pm
• Join our Online Community to connect with those who may be going through a similar experience
• Chat to us online, open 8am to 8pm seven days a week.