Systems that Perform Imaging Using Magnetic Fields and Radio Waves without X-ray Exposure to Patients

MRI Scanners

MRI scanners obtain cross-sectional images of the human body using radio waves and magnetic fields generated by powerful magnets. There is no X-ray exposure, so they can even be used to safely perform examinations of young children. Canon's diagnostic imaging technologies, hidden in the ring-shaped bodies of these scanners, assist with early diagnosis of diseases.

How MRI Scanners Work

MRI scanners comprise five principle components: a superconducting magnet that generates a powerful magnetic field, high-frequency coils that transmit radio waves, gradient coils that alter the magnetic field, receiver coils that catch the radio signals from the patient's body, and a patient table, which places the patient inside the donut-shaped scanner. MRI scanners use magnetic fields, radio waves, and the fact that approximately 70% of the human body is made up of water, which contains hydrogen nuclei, to freely perform vertical, horizontal, and diagonal cross-section imaging of the human body.

Superconducting magnet

The superconducting magnet constantly generates a powerful magnetic field. This field is known as a static magnetic field. Depending on the strength of the magnetic field, an MRI scanner may be classified as a 1.5 tesla scanner, 3 tesla scanner, or the like. This is one of the indicators of the MRI scanner's capabilities.

High frequency coils

These coils emit radio waves that reorient the hydrogen nuclei in the patient's body. To change the orientation of hydrogen nuclei, it is important to impart high frequency radio waves matched to the hydrogen nuclei, causing them to resonate.

Gradient coils

While the superconducting magnet constantly emits a powerful magnetic field, the gradient coils generate magnetic fields only while imaging is in progress. Their purpose is to alter the magnetic field. In a constant, strong magnetic field, it is difficult to identify when the axes of hydrogen nuclei demonstrate their propensity to return. However, gradient coils generate vertical, horizontal, and diagonal magnetic fields, producing changes in the return behavior of the axes of the hydrogen nuclei, which can then be used to obtain accurate position information.

Receiver coils

Receiver coils are worn by the patient to perform imaging of the head, abdomen, and other parts of the body where appropriate, and provide a high level of sensitivity. The data received from the receiver coils are transmitted to the data processing equipment to generate images.

Normally, the hydrogen nuclei in the human body point in different directions. However, if placed in a powerful magnetic field (a static magnetic field), they have a tendency to point in the same direction while spinning at the same frequency. Applying radio waves to the hydrogen nuclei with the same frequency as their own frequency causes them to all change direction simultaneously (this is known as magnetic resonance). If the radio waves are stopped, the orientations of the hydrogen nuclei will go back to their previous state, all pointing in different directions. The tiny amounts of energy generated when their axes turn are caught by the MRI scanner, processed, and used to perform imaging. When the radio waves are stopped, some of the nuclei do not reorient themselves quickly (they move slowly, meaning they might be diseased areas), while others reorient themselves like normal. These differences are indicated through differences in the contrast of the image. Because of this, MRI scanners generally excel at performing imaging for parts of the body with a great deal of water content, such as the brain, spinal cord, and torso. They can also be used to easily visualise blood vessels. However, generally speaking, for parts of the body with little water content or with large amounts of air, such as bones or lungs, X-ray-based imaging equipment, such as a CT scanner, is better suited.

Canon Technologies Used in MRI Scanners

Pianissimo™ Acoustic Noise Reduction Technology

While MRI scanners have the advantage of not requiring X-ray exposure, they also have drawbacks, such as long scan times, the need to use contrast agent, and acoustic noise. To reduce the burden on patients and medical personnel, Canon has been at the forefront of advancing MRI scanner technology to perform MRI imaging faster, more reliably, and more comfortably. Standard MRI testing produces a great deal of acoustic noise, which can make patients uncomfortable or scared. This acoustic noise is caused by the current flowing through the gradient coils inside the large magnet. When this current flows, force is generated in accordance with Fleming's left-hand rule, which causes the gradient coils to vibrate. These vibrations are then conveyed to parts such as the magnet itself and cause the equipment itself to generate acoustic noise. However, with Pianissimo™ , Canon Medical's acoustic noise reduction technology, the gradient coils are vacuum-sealed to reduce the acoustic noise propagation by 90% compared to conventional Canon Medical MRI scanners. This makes examinations quieter and reduces the burden imposed on patients.

Non-contrast MRA Makes It Possible to Perform Blood Vessel Imaging without Using Contrast Agent

Non-contrast MR Angiography (MRA) makes it possible to perform imaging of blood vessels using an MRI scanner, without the use of a contrast agent. Using a contrast agent to observe blood vessels produces clear images, but can also cause side effects including nausea, malaise, and headaches. Canon took the lead in developing non-contrast MRA applications, beginning its development efforts in the 1990s. Since 2006, Canon has incorporated the Time-Spatial Labeling Inversion Pulse (Time-SLIP) non-contrast examination system in all of its MRI scanner models. This system images only the blood vessels you wish to observe. The ability to perform imaging without the use of contrast agent has made it possible for imaging to be used on even more patients.