A METHOD AND APPARATUS TO MEASURE PATIENT BORE TEMPERATURE IN MAGNETIC RESONANCE IMAGING (MRI)
Publication Date: 2015-Jul-23
The IP.com Prior Art Database
A method and apparatus to measure patient bore temperature in an MRI system is disclosed. The apparatus comprises distributed optical sensor on a patient bore surface of the MRI system to acquire temperature data including, peak temperature and average temperature on patient bore surface within required time. The temperature data is used for maintaining temperature and specific absorption rate (SAR) within regulatory limits. Peak temperature is used and compared with regulatory limit (i.e. 41⁰C) and average patient bore temperature is used along with room temperature for updating SAR in real time. The distributed optical sensor uses an optical time domain reflectometry (OTDR) technique.
The present disclosure relates generally to magnetic resonance imaging (MRI) and more particularly to a method and apparatus to measure patient bore temperature in an MRI system.
An MRI system comprises a magnet, and radiofrequency (RF) transmitter, a receiver coil, a gradient coil and a computer. The magnet generates a stable and homogeneous magnetic field. The RF transmitter coil creates an RF field referred to as b1 field and transmits an RF signal into body part of a patient being imaged. The receiver coil receives the returning RF signals. The gradient coil provides spatial localization of the returning RF signals. The computer controls the MRI system and reconstructs image acquired.
The space in which the patient located during a scan is referred to as a patient bore. As shown in Figure 1, the patient bore has a surface comprising a body coil. During scan, the gradient coil, the RF shield and the body coil generate heat, which gets transferred to the surface of the patient bore. Therefore, the temperature of the surface of the patient bore is a safety matter under regulations. Peak temperature of the surface is to be maintained below 41⁰C to prevent burn injuries to the patient. SAR should not exceed regulatory limit which is also in turn related to average temperature of the surface of the patient.
To meet these two regulatory requirements, conventional techniques monitor the temperature using a temperature sensor, for example, a thermistor at a point on the surface of the patient bore. However, since the hot spot is not a fixed point due to different sequences, relationship between sensor point temperature and hot spot temperature is experimentally acquired. If temperature exceeds limit which is defined based on experimental data, the MRI system is configured to stop scanning to protect the patient.
However, building a correlation between senor point temperature and hot spot temperature remains a challenge. Figure 2 shows an example of temperature distribution in the patient bore.
For SAR control, it is hard to get average patient bore surface temperature within required time. Conventional techniques use worst case scenarios to predict patient bore surface temperature. This limits system capability and increases requirements for patient bore cooling.
One conventional technique monitors temperature in at least one location of an electromagnetic coil assembly by passing a light through a non-magnetic optical fiber inserted into sheath that is wound with the electrical winding. Such conventional technique allows monitoring temperature distribution on gradient coil with electrical winding. However, this technique does not provide monitoring patient bore temperature, peak temperature control and SAR control.
It would be desirable to have a method and apparatus to measure patient bore surface temperature of MRI sy...