A magnetic resonance imaging scan, or “MRI scan” is a medical procedure that uses magnetic fields and radio waves to produce images of the patient’s internal organs. The acronym MRI stands for Magnetic Resonance Imaging. It produces detailed pictures of organs in the body without using radiation. This is an advantage over other imaging techniques such as X-ray, CT scan and PET scan.
The MRI machine itself is composed of very strong magnets with electromagnetic coils that produce radio waves or microwaves to be used for imaging. The MRI pictures are the result of the magnetic relationship between hydrogen atoms in water located in human tissues. Water molecules have chemical properties that cause them to align themselves in a “North” and “South” pole direction with the use of an outside energy source.
A strong magnetic field can control this polarity. The combination of radio waves with the strong magnet then disrupts the water molecules’ alignment, producing faint signals that are collected by receivers. These signals are used to create images on a monitor for viewing by a doctor.
The MRI scanner contains a large magnet and a system of powerful coils and radio transmitters and receivers, housed in the tightly enclosed space of the scan room. A cylindrical magnet producing a constant magnetic field is surrounded by three sets of coils that produce magnetic pulses to create images on computer monitors.
The magnets used for this are not just an average magnet that you can buy at any store. This is something much more powerful and must be handled by trained technicians.
The MRI machine has a cooling system to keep the superconducting magnet cold enough to produce images, as well as make sure there is no loss of electrical current within the coils. The coils are made of copper which are cooled by liquid helium. The cooling system is composed of a compressor, pump, cold box, and heat exchanger.
The MRI scanner uses helium as the coolant for the superconducting magnet because it has one of the lowest boiling points (-452°F/-269°C at sea level). Any gas other than helium would expand too much when cooled to become a liquid. Helium won’t turn into a gas unless it is warmed above 4 degrees above absolute zero (-269°C). No electricity is needed to keep the helium refrigerated because of its low boiling point.
The MRI machine’s cooling system also includes an automatic pressure control device, electrical supply, and interlock and alarm systems. The cooling system manages the refrigeration to maintain a temperature between -452°F to -269°C. This is what keeps the superconducting magnet cold enough to produce images, as well as make sure there is no loss of electrical current within the coils.
The safety features in an MRI machine’s cooling system work hand-in-hand with other safety features and procedures of the MRI machine to prevent medical personnel and patients from coming into harm’s way.
In a nutshell, this is how the cooling system in an MRI machine works. Engineering Experts can help ensure that these machines are used safely.