METHOD AND APPARATUS FOR MEASURING TRANSMISSION AND REFLECTION COEFFICIENT OF MRI SURFACE COILS FOR PHYSIOLOGICAL SIGNAL ACQUISITION
Publication Date: 2017-May-24
The IP.com Prior Art Database
Method for measuring transmission and reflection coefficient comprises utilizing the fact that MRI surface coils consist typically out of multiple coil elements, and impedance information from each coil element may be used to generate more detailed motion model of the cardiac and respiratory motion. Furthermore, since the reflection and transmission coefficient, which are directly linked to impedance variations of each coil, a further detailed motion model may be generated.
The present disclosure relates generally to magnetic resonance imaging (MRI), and more particularly to refinement of data from surface coils used in MRI systems.
In cardiac magnetic resonance imaging (cardiac MRI), the measurement of physiological parametersis essential to trigger the imaging sequence, to monitor the patient or to collect the data for post-processing purposes. The state of the art techniques are navigators or pneumatic belt systems to acquire the respiration phase and electrocardiogram (ECG) or photopletysmography (PPG) for measurement of the cardiac activity.
Respiration information measured with a pneumatic belt or navigator is dependent on the belt position and belt sensitivity and navigator position respectively. Since breathing behavior varies between patients and can change for a patient during a MRI examination, it is usually difficult to obtain a reliable measurement. The problem is particularly more pronounced in pediatric and neonatal imaging, which frequently precludes the use of this technique, either due to the lack of special pediatric equipment (smaller belts), or due the physiological differences of newborns.
Further, for the measurement of heart movement, ECG is generally used to trigger the imaging sequence at the R-peak. However, the reliability often suffers from electromagnetic fields applied during the imaging sequence or by the magnetohydrodynamic effects caused by the blood flow in the static magnetic field. Furthermore, the ECG represents the electrical activity of the heart, rather than the mechanical contraction, which in some diseases can be decoupled from each other. Hence the PPG is a good alternative, however strongly depends on stable sensor placement. Further, the signal is measured at the fingertip and therefore a delay to the heart movement has to be taken into account.
Requiring placement of the respiratory belt on the patient, ECG electrodes and cables extends the patient preparation time, and further affects patient comfort undesirably. An alternative to the described methods exists by multichannel ultra-wideband radar system, which uses multiple transmitters and receivers and reports detailed heart motion profiles. Although this system is MRI compatible, the UWB-Radar needs to be installed as an extra sensor inside the MRI tunnel, which presents an additional burden. A known sensor-less method uses impedance change of the MRI body coil caused by physiological motion at the torso, which causes a shift of the resonance frequency, which in turn leads to alteration of the coil impedance at this frequency. Respiratory and cardio-physiologic motion measured with this technique however is not spatially resolved and might be affected by motion of other body parts. Localized measurements with single loop surface coils show that cardio-physiologic motion c...