Control of SAR Values in MR Imaging
In a method for imaging a body part of a patient particularly in relation to DBS where conductive elements can reduce a safe SAR level, the power in the RF pulses being delivered to the RF transmit coil is measured in real time by a unit associated with the FR transmit coil and is used to stop the supply of RF pulses to the RF coil in the event that the power exceeds a predetermined safe limit. As signal can also be transmitted to the MR control unit to shut off the imaging sequence.
1 . A method for imaging a body part of a patient comprising:
operating an MR magnet with gradient coil of an MR imaging system to generate a variable magnetic field to be applied to the patient;
operating an RF transmit coil arrangement of an MR imaging system for supplying RF pulses to an RF transmit coil in a transmit stage to be applied through the RF transmit coil to the patient to be imaged such that the patient generates an MR signal in response to the magnetic field and the RF signal applied;
acquiring the MR signal in a receive stage;
processing the MR signal by which an image is generated;
measuring the power in the RF pulses being delivered to the RF transmit coil in real time;
and stopping the supply of RF pulses to the RF coil in the event that the power exceeds a predetermined safe limit.
2 . The method according to claim 1 wherein SAR (Watts/kg) being delivered to the patient in real time is measured.
3 . The method according to claim 1 wherein the stopping of the RF pulses acts to ensure the safety of a transmit coil which is independent of patient loading and use.
4 . The method according to claim 1 wherein the RF pulses are stopped by disconnecting the RF coil.
5 . The method according to claim 1 wherein the RF pulses are stopped by supplying a signal to the MR imaging system.
6 . The method according to claim 1 wherein the safe limit is determined including parameters of the patient.
7 . The method according to claim 1 wherein the power is measured at a measurement unit associated with the RF transmit coil and separate from the MR imaging system.
8 . The method according to claim 7 wherein the safe limit is determined including parameters of the patient and the parameters are input manually into the measurement unit.
9 . The method according to claim 7 wherein the safe limit is determined including parameters of the patient and the parameters are obtained from the MR imaging system.
10 . The method according to claim 1 wherein the power is measured by continually measuring instantaneous transmitted power which is integrated to calculate the average power delivered to the patient.
11 . The method according to claim 1 wherein the power is measured by detecting transmitted power through a directional coupler in a lead to the RF transmit coil.
12 . The method according to claim 11 wherein a sampling coil is located at the RF transmit coil and is used in addition to the directional coupler to detect the actual RF power applied.
13 . The method according to claim 12 wherein the power is measured also by detecting reflected power signal from a bi-directional coupler in a lead to the RF transmit coil.
14 . The method according to claim 1 wherein the power is measured at a controller which contains a microprocessor and driver circuitry to turn off an RF Switch to the RF transmit coil.
15 . The method according to claim 1 wherein the power is measured by detecting reflected power signal from a bi-directional coupler in a lead to the RF transmit coil.
16 . The method according to claim 15 wherein a sampling coil is located at the RF transmit coil and is used in addition to the bi-directional coupler to detect the actual RF power applied.
17 . The method according to claim 1 wherein a sampling coil is located at the RF transmit coil and is used to detect the actual RF power applied.