Medically reviewed by Susan Kerrigan, MD and Marianne Madsen
A new form of imaging technique may be about to change the way doctors can examine soft tissues in the body.
Until now, if you wanted to scan soft tissues, you would use either an ultrasound or an MRI to give you the images you needed. In the same way, if you wanted to get an image of dense materials like bones, you would get an x-ray. Now researchers at Tohoku University in Japan have devised a method to use x-rays to also give doctors information about soft tissues by combining it with elastography.
Elastography
Elastography is a non-invasive medical imaging technique that helps doctors determine the stiffness of tissues, organs, and other structures in your body. The technique is commonly used in ultrasounds or MRIs to measure how quickly vibrations move through an organ. A computer will then use the data to create images that show the stiffness of the tissue or organ.
Until recently, studies have suggested that using elastography with x-ray imaging was theoretically possible, but the results from Japan are the first time we have seen it working in a real-world context.
The difference between Ultrasound, MRI, and X-Ray
Ultrasound imaging works by beaming ultrasonic sound waves into your body via a transducer, which are then reflected back to the transducer creating electrical signals that are sent to the ultrasound scanner. The scanner then calculates, using the speed of sound and the time it takes for each wave to be echoed. This information is then used to create a two-dimensional non-static image of tissues and organs. Sound waves pass through stiffer, unhealthier tissue faster than they do softer, healthier ones, so this allows the doctor to see where the harder tissues are.
MRI scans work in a similar way to ultrasounds. They use powerful magnets to force protons in your tissues to align with the magnetic field. A radiofrequency current is then sent through your body which causes the protons to strain against the magnetic field. When the current is turned off, MRI sensors will then record how long it takes for the protons in different tissues to realign with the magnetic field. A computer transforms this information into images. How long it takes the protons to realign will tell your doctor about the stiffness of the tissues.
X-rays are a form of electromagnetic radiation where rays travel through the body and become absorbed by different tissues in varying amounts depending on their density and atomic number. As calcium in your bones and teeth have a higher atomic density than most tissues, they absorb the rays more readily, giving them the white contrast you typically see on a radiograph. Soft tissues such as fat and muscle, which usually have a lower atomic density, will appear in shades of gray or black as the x-rays travel more easily through them. This means they are harder to see on an x-ray image.
X-Ray Elastography
The researchers at Tohoku University have now developed a technique where elastography can work with x-rays in the same way they do with MRIs and ultrasounds. The team tested their technique using several samples of polyacrylamide gel, some of which contained harder particles of zirconium dioxide to test their technique. Vibrations were then sent through the samples while X-ray images were taken. The results show that the technique was able to differentiate between the harder zirconium dioxide particles and the softer polyacrylamide gel, showing how x-ray elastography could be used for soft tissue imaging. This is a significant breakthrough as x-rays offer significantly greater image resolution compared to ultrasound and are quicker and cheaper than MRIs.
Wataru Yahiro, the lead researcher of the study and an associate professor at the Institute of Multidisciplinary Research for Advanced Materials (IMRAM) of Tohoku University, believes this breakthrough is not only about being able to identify stiffened tissues more clearly but also when they can be identified. He explains, “This greater precision doesn’t just mean identification of much smaller or deeper lesions, but, importantly for patients, because smaller lesions can be newer ones, potentially also much earlier on in a disease or condition.”
The next step for the researchers is to further develop the technique so that it can produce 3D images. They would then need to find a way to manufacture x-ray elastography equipment so that the new technique can be used by doctors as part of the diagnostic process.