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Method and apparatus to monitor and provide additional safety during quench at MRI-scanner

IP.com Disclosure Number: IPCOM000033834D
Published in the IP.com Journal: Volume 5 Issue 1 (2005-01-25)
Included in the Prior Art Database: 2005-Jan-25
Document File: 2 page(s) / 128K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

An MRI-scanner (Magnetic Resonance Imaging) uses strong magnetic fields for producing images of the investigated objects. The required intensity of the magnetic field is excited by an arrangement of superconductive electromagnets. Concerning MRI-scanner, a quench is a sudden loss of superconductivity in the wire of the magnet. The stored magnetic energy turns into heat, causing the liquid helium to boil off very rapidly. A huge volume of helium gas can be released in a few minutes, and the vent pipe of the apparatus has to be able to carry this flow safely. Quenching of superconducting magnet coils can be hazardous. This occurs when (for some reason) the current-carrying coil turns from the superconducting to the normal state, thereby suddenly changing its resistance from zero to a finite value. Then the tremendous dissipation energy (~I2R) generated in the coils vaporizes the liquid helium, creating large internal pressures within the magnet Dewar (the section that holds the liquefied helium coolant) and a large helium gas outflow from the magnet's pressure relief valves.

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Method and apparatus to monitor and provide additional safety during quench at MRI-scanner

Idea: Sultan Haider, DE-Erlangen; Rainer Kuth, DE-Erlangen; Visvanathan Ramesh,

US-Princeton; Dr. Juergen Simon, DE-Forchheim

An MRI-scanner (Magnetic Resonance Imaging) uses strong magnetic fields for producing images of the investigated objects. The required intensity of the magnetic field is excited by an arrangement of superconductive electromagnets.

Concerning MRI-scanner, a quench is a sudden loss of superconductivity in the wire of the magnet. The stored magnetic energy turns into heat, causing the liquid helium to boil off very rapidly. A huge volume of helium gas can be released in a few minutes, and the vent pipe of the apparatus has to be able to carry this flow safely. Quenching of superconducting magnet coils can be hazardous. This occurs when (for some reason) the current-carrying coil turns from the superconducting to the normal state, thereby suddenly changing its resistance from zero to a finite value. Then the tremendous dissipation energy (~I2R) generated in the coils vaporizes the liquid helium, creating large internal pressures within the magnet Dewar (the section that holds the liquefied helium coolant) and a large helium gas outflow from the magnet's pressure relief valves.

In summary, the main dangers of a quench are

- mechanical failure of the magnet,

- suffocation from the displacement of air by gaseous helium (a much more likely hazard), or

- a skin contact may result in considerable amount of injury (due to extremely low temperature of the helium) of human beings.

In a conventional system, the operator does not get a signal if the quench has happened due to mechanical failure (e.g. during the weekend).

The risks and dangers mentioned above can be handled by establishing a system providing the following features:

- The system monitors and records the quench event and gives an estimation of the danger. A built-in control mechanism uses a multiple camera and sensory system (quench circuit, hall sensor, temperature sensor etc.) along with a data storage unit and input-output system. The camera system registers whether the patient/operator is inside the scanner room (motion/change detection). The camera system recognizes if the scan is performed on a patient or a phantom.

- A helium gas detector verifies the permissible oxygen level in the room.

- In case a quench has happened to the machine prior to the scan, the operator gets the information before he starts the scan.

- The camera system records and sorts the quench process and sends the pictures immediately to the service engineer and/or operator/hospital authority via e.g. internet or by phone (e.g. MMS).

- If the patient/operator is inside the scan...