Taking pictures of cancer provides really important insights into the nature of the disease, helping us formulate treatment plans. It can tell us the size and location of a tumour, and, nowadays, newer methods can provide functional information. Because of that, a lot of work has been done to advance our technology for cancer imaging. But it all started with X-ray.

The first use of X-rays in medicine goes back over 100 years, to a scientist named Wilhelm Röntgen, who discovered a new kind of radiation. He called this new radiation “X radiation”, which stood for unknown radiation. Although we know a lot more about X-rays nowadays, the name has stuck. In the past, to take a radiograph, you’d place a patient between a source of X-rays and a film. The film has chemical properties that allow it to be altered as X-rays hit it. Then, you’d pass X-rays through a patient to the film. As they pass through different tissues, some of them are absorbed. Tissues in our bodies absorb different quantities of X-rays, so, as the remaining rays pass through, those differences show up on the film. This would give you a nice picture contrasting hard tissues that absorb a lot of radiation, like bone, with softer tissues. Now, instead of films, we use digital sensors that help us reconstruct images.

To get around that, CT scans were developed. “Computed Tomography”, or CT scans, take X-ray images in multiple planes, and then use advanced computer systems to reconstruct those 2D images into a three-dimensional structure. This technique can help us locate tumours, but also gives us a lot of information about tumour volume and size. That’s important information because it can help inform treatment regimens. For example, brachytherapy is a treatment that uses a small source of radiation that’s implanted into, or next to, the tumour. But the size of the tumour is a limiting factor here. If tumours are too large, brachytherapy isn’t a viable option, so knowing the volume of the tumour can be enormously helpful.

Ultrasound is another kind of imaging technique that can give us a lot of information about the structure and function inside someone’s body. Unlike X-rays, ultrasound uses sound waves. As a concept, ultrasound works almost opposite to X-rays. For X-rays, radiation is passed through a patient and detected on the other side. For an ultrasound image, a probe is placed in direct contact with someone’s skin and sound waves are propagated into their tissue. But, instead of collecting waves that pass through a person, we collect sound that is reflected to the probe. Similarly to X-ray, we rely on the properties of different tissues to reflect sound differently.

There are a lot of advantages to ultrasound over other imaging techniques. For one, it doesn’t expose anyone to radiation, which is an enormous benefit. It’s also much more affordable, quicker, and can be made portable. Ultrasound can also be done continuously, which can give us functional information! Other imaging techniques are usually a specific snapshot in time. That’s not a bad thing, but it limits the amount of information we can get from a single picture. If we take ultrasound photos in rapid succession, which we can’t do with most other techniques, we can obtain functional information like blood flow or a fetal heartbeat!

Although both X-rays and ultrasound provide a lot of information, both struggle with taking really clear pictures at depth. X-rays rely on the absorption of radiation, but a lot of softer tissue doesn’t absorb that much radiation, so we don’t get a really clear picture of most internal organs. Ultrasound can struggle with things like bone or air getting in the way, which interferes with the image quality. To get the clearest picture, the standard today is magnetic resonance imaging, also referred to as MRI. MRIs are deeply complex, but are absolutely fascinating. MRIs use enormous magnets to generate magnetic fields. These fields quite literally align the atoms in our bodies. Once they’re all aligned, we excite the atoms with radio waves. As they return from their excited state back to normal, they release energy, which is what we actually detect. So, MRI maps out the location of specific atoms throughout our body, which is used to recreate pictures of organs. This gives us really clear pictures of our deepest organs, a wealth of structural information.

Now, we can take advantage of this for treating patients, too! Having a picture of a tumour is great, it tells us how big it is, and its general location. But our bodies move. Tumours don’t always stay in the same place. That’s a problem for some of our treatment options. Radiation therapy, the use of radiation to kill cancer, also kills healthy cells. Because of the movement of a tumour, we often have to overestimate the tumour size. That means more healthy tissue is being irradiated because we don’t know the precise location of a tumour. One device that helps get around this is the MRI-LINAC.

This means we could track the precise location of a tumour as someone goes for radiation therapy. Because of this, we can reduce the total exposed area, keep the beam directly on the tumour, and preserve more healthy tissue.

Firstly, it’s important to define what “functional information” means. Functional information gives us details about more than just purely structure and shape. That includes blood flow, which ultrasound can do, but it can also include details on a cellular level. That’s where nuclear medicine comes in. Nuclear medicine includes SPECT and PET. Both use radioactive elements, called radionuclides, that are put into a person’s body. As the radioactive material decays, they emit particles that we can detect. This can be used for structural information and functional information. For example, SPECT can be used with certain radioactive materials that aggregate at specific anatomical sites, such as the bone. So, if a cancer is growing on the bones, either from a primary cancer or one that has spread there, it will uptake more of the radionuclide and will give a brighter picture.

With PET, we can attach these radioactive materials to specific molecules. By picking the right molecule, we can target a radionuclide specifically to cancer cells and get information about that cancer.

That tells us not only where the cancer is and how big it is, but how fast it’s using sugar for energy, which could tell us how aggressive it is. Additionally, because these radionuclides are free-flowing throughout the body, we can see a cancer even if it has spread! That’s an enormous advantage over conventional imaging techniques.

Imaging in cancer has been around for over a hundred years. Starting with X-rays, it has become a fundamental part of diagnosis and treatment. Knowing the location and size of a tumour can help inform decisions for treatment plans to obtain the best possible outcome. Early imaging techniques only provided structural information and were limited to diagnostic purposes. They also struggled with location, only being able to image one point at a time. Now, we can use techniques like ultrasound and nuclear medicine to get functional information. Some techniques can also give us information about cancer throughout the entire body, at one time! On top of that, the purpose of imaging has expanded into direct use during treatment, too. The development of the MRI-LINAC has led to better tumour targeting, reduced radiation exposure, and better overall outcomes.

I hope you learned a little something this week, but next week we’re getting a bit darker as we talk about the cancer cells’ black market!

If you missed last week’s letter, you can read “It’s In Your Jeans” to learn a little more about the role our clothes play in cancer protection and exposure.