Method for determining the position of a ferromagnetic particle and associated MRI system

Magnetic resonance imaging (MRI) system, comprising:

• a magnet for generating a homogeneous magnetic field B0 in a measurement volume,
• a gradient coil system for generating spatially encoding magnetic field gradients in the measurement volume,
• a radiofrequency excitation and readout coil system for radiating radiofrequency pulses into the measurement volume and for reading the measurement volume, and
• a control device,
• wherein the MRI system is configured to determine a position of a ferromagnetic particle in a liquid matrix,
• wherein the determination comprises:
• applying an MRI measurement sequence to the measurement volume, wherein the measurement sequence comprises a plurality of individual measurements, during each of which there is a spatially encoding gradient switching operation, including an excitation pulse and a signal recording with the MRI system, and wherein the measurement sequence further comprises a multiplicity of measurement blocks, each of which comprises at least one individual measurement and each of which, in a pause of the spatial encoding, comprises an intermediate gradient switched by the MRI system, and
• dimensioning the intermediate gradient such that, over each of the measurement blocks, an initial point of the particle is substantially the same as an end point of the particle,
• wherein the control device is configured to switch the intermediate gradients between the individual measurements of the measurement sequence via the gradient coil system,
• wherein the MRI system is further configured to position the ferromagnetic particle in the liquid matrix
• wherein the positioning comprises:
• switching a positioning gradient with the MRI system, thereby changing the position of the particle, and
• again performing the determination with a fixing gradient as the intermediate gradient, whereby the position of the particle is kept at least substantially constant, and
• wherein said switching step is performed following application of the measurement sequence in said again performing step and until start of the application of the positioning gradient in said switching step, and
• wherein the control device, via the gradient coil system, switches fixing gradients between the end of measurement sequences and application of the positioning gradients.