EP-4741863-A1 - FIBER OPTIC MEASUREMENT OF PASSIVE SHIM ELEMENT TEMPERATURE

EP4741863A1EP 4741863 A1EP4741863 A1EP 4741863A1EP-4741863-A1

Abstract

Disclosed herein is a passive shim system (100) for a magnetic resonance imaging system (400). The passive shim system comprises a mounting system (106) for mechanically receiving and positioning multiple passive shim elements (112). The passive shim system comprises multiple fiber optic temperature sensors (110) configured for optically measuring sensor specific temperature data (126). The multiple fiber optic temperature sensors are thermally coupled to the mounting system and/or the multiple passive shim elements. The passive shim system comprises a controller (114) comprising a local memory (120) and a local computational system (116). The local memory stores local machine executable instructions (124). Execution of the local machine executable instructions causes the local computational system to repeatedly: control (300) the multiple fiber optic temperature sensors to measure the sensor specific temperature data, and provide (302) the sensor specific temperature data.

Inventors

LIPS, OLIVER
VOGTMEIER, GEREON
WEISS, STEFFEN

Assignees

Koninklijke Philips N.V.

Dates

Publication Date: 20260513
Application Date: 20241107

Claims (15)

A passive shim system (100) for a magnetic resonance imaging system (400), comprising: - a mounting system (106) for mechanically receiving and positioning multiple passive shim elements (112); - multiple fiber optic temperature sensors (110) configured for optically measuring sensor specific temperature data (126), wherein the multiple fiber optic temperature sensors are thermally coupled to the mounting system and/or the multiple passive shim elements; and - a controller (114) comprising a local memory (120) and a local computational system (116), wherein the local memory stores local machine executable instructions (124), wherein execution of the local machine executable instructions causes the local computational system to repeatedly: - control (300) the multiple fiber optic temperature sensors to measure the sensor specific temperature data, and - provide (302) the sensor specific temperature data.
The passive shim system of claim 1, wherein the mounting system comprises multiple shim pockets (128) configured for receiving one or more of the multiple passive shim elements, wherein the multiple fiber optic temperature sensors are configured such that when the one or more of the multiple passive shim elements is placed into one of the multiple shim pockets there is a direct thermal coupling between the one or more of the multiple passive shim elements and one of the multiple fiber optic temperature sensors.
A main magnet (102) configured for generating a main magnetic field, wherein the main magnet incorporates the passive shim system of claim 1 or 2, wherein the passive shim system is configured for magnetically shimming the main magnetic field.
A magnetic resonance imaging system (400) incorporating the main magnet (102) of claim 3, wherein the magnetic resonance imaging system comprises: - a system memory (436) storing system machine executable instructions (440) and pulse sequence commands (442); - a system computational system (430), wherein execution of the system machine executable instructions causes the system computational system to: - acquire (500) k-space data (444) by controlling the magnetic resonance imaging system with the pulse sequence commands; - repeatedly (502) acquire the sensor specific temperature data at least during the acquisition of the k-space data using the passive shim system; and - monitor (504) a status of the magnetic resonance imaging system using the repeatedly acquired sensor specific temperature data.
The magnetic resonance imaging system of claim 4, wherein monitoring the status of the magnetic resonance imaging system comprises producing a warning signal if the repeatedly acquired sensor specific temperature data is outside of a predetermined temperature range or has a temperature pattern that deviates from a pulse sequence specific temperature pattern.
The magnetic resonance imaging system of claim 5, wherein execution of the system machine executable instructions further causes the system computational system to perform any one of the following if the warning signal is produced: trigger a visual warning, trigger a text warning on a user interface, cause an audible warning, trigger a service request, cancel the acquisition of the k-space data, restrict the execution of pulse sequence commands, selectively restrict the execution of individual members of a library of pulse sequence commands, and combinations thereof.
The magnetic resonance imaging system of any one of claims 4, 5, or 6, wherein the system memory further stores a magnetic parameter model (446) configured for outputting modification parameters in response to receiving the sensor specific temperature data as input, wherein execution of the system machine executable instructions further causes the system computational system to: - receive starting magnetic parameters descriptive of a starting field map of the main magnetic field; - receive the modification parameters in response to inputting the sensor specific temperature data into the magnetic parameter model; and - provide updated parameters using the starting parameters and the modification parameters.
The magnetic resonance imaging system of claim 7, wherein execution of the system machine executable instructions further causes the computational system to generate a magnet alarm signal if the updated parameters are outside of a predetermined parameter range.
The magnetic resonance imaging system of claim 7 or 8, wherein the magnetic resonance imaging system comprises an active magnetic field shimming system (410), wherein execution of the system machine executable instructions further causes the system computational system to adjust the active magnetic field shimming system using the updated parameters or the modification parameters.
The magnetic resonance imaging system of claim 9, wherein execution of the system machine executable instructions further causes the system computational system to: - repeatedly provide the updated parameters during the execution during execution of the pulse sequence commands and/or before execution of subsequent pulse sequence commands; and - perform further adjustment of the active magnetic field shimming system after the updated parameters or the modification parameters are provided.
The magnetic resonance imaging system of any one of claims 7 through 10, wherein any one of the following: - the starting parameters are starting magnetic field map, the modification parameters are a modification of the main magnetic field, and the updated parameters are updated magnetic field map, the magnetic parameter model is a magnetic field model; and - the starting parameters are starting magnetic shim settings, the modification parameters are changes in the magnetic shim settings, and the updated parameters are updated magnetic shim settings.
The magnetic resonance imaging system of any one of claims 7 through 11, wherein the magnetic parameter model is any one of the following: a neural network, an analytical model, and a random forest regressor.
The magnetic resonance imaging system of claim 12, wherein the magnetic parameter model is a random forest regressor, wherein the starting magnetic field map of the main magnetic field is descriptive of the main magnetic field without a subject, wherein the random forest regressor is configured to predict changes in the main magnetic field using subject metadata, wherein execution of the system machine executable instructions further causes the system computational system to receive the subject metadata, wherein the modification of the main magnetic field is received in response to inputting the sensor specific temperature data and the subject metadata into the magnetic parameter model.
A method of using magnetic resonance imaging system (400), wherein the method comprises: - acquiring (500) k-space data (444) by controlling the magnetic resonance imaging system with pulse sequence commands (442); - repeatedly acquire (502) sensor specific temperature data (126) at least during the acquisition of the k-space data, wherein the sensor specific temperature data is acquired optically using multiple fiber optic temperature sensors (110) that are thermally coupled to passive shim elements (100); and - monitoring (504) a status of the magnetic resonance imaging system using the repeatedly acquired sensor specific temperature data.
A computer program comprising system machine executable instructions (440) for execution by a system computational system (430), wherein execution of the system machine executable instructions causes the system computational system to perform the method according to claim 14.

Description

FIELD OF THE INVENTION The invention relates to magnetic resonance imaging, in particular to the shimming of the main magnetic field. BACKGROUND OF THE INVENTION Magnetic Resonance Imaging (MRI) is a medical imaging technique that uses a strong magnetic field, often referred to as the main magnetic field or the B0 field, and Radio Frequency (RF) signals to generate detailed images which depict a subject's internal anatomy. The main magnetic field is used to align atomic spins, typically hydrogen protons in the subject. The system then uses RF pulses to manipulate these spins. During relaxation of the atomic spins, they emit radio signals which are then used to reconstruct a magnetic resonance image. The uniformity of the magnetic field affects the quality of the magnetic resonance image. This main magnetic field uniformity can be enhanced or "shimmed" using both active and passive methods. Active shimming involves the use of shimming coils that adjust the field dynamically by controlling the current through the shimming coils. Passive shimming employs strategically placed passive shim elements (i.e., small pieces of ferromagnetic materials) to fine-tune the magnetic field. United State patent application publication US8723523B2 discloses magnetic resonance imaging apparatus includes: a pair of static magnetic field generators separately disposed at the top and bottom of an imaging space in which a subject is placed; a shim magnetic material, disposed on the imaging-space side of each of the pair of static magnetic field generators, for generating a magnetic field to adjust the static magnetic field; a gradient magnetic field generator; a high-frequency magnetic field generator; a temperature sensor for directly or indirectly measuring the temperature of the shim magnetic material; and a controller for controlling the gradient magnetic field generator and the high-frequency magnetic field generator to execute an imaging pulse sequence. The controller determines the inhomogeneity of the static magnetic field from the output of the temperature sensor, considering the change in a magnetic field adjustment parameter due to the temperature change of the shim magnetic material, and causes a warning message to be presented if the determined static magnetic field inhomogeneity has exceeded a predetermined allowable value. SUMMARY OF THE INVENTION The invention provides for a passive shim system, a main magnet, a magnetic resonance imaging system, a method of using a magnetic resonance imaging system and a computer program. Embodiments are given in the dependent claims. In one aspect a passive shim system for a magnetic resonance imaging system is disclosed. The passive shim system comprises a mounting system for mechanically receiving and positioning multiple passive shim elements. The passive shim system further comprises multiple fiber optic temperature sensors that are configured for optically measuring sensor-specific temperature data. The multiple fiber optic temperature sensors are thermally coupled to the mounting system and/or the multiple passive shim elements. The passive shim system further comprises a controller comprising a local memory and a local computational system. The local memory stores local machine-executable instructions. Execution of the local machine-executable instructions causes the local computational system to repeatedly control the multiple fiber optic temperature sensors to measure the sensor-specific temperature data and to provide the sensor-specific temperature data. In another aspect, a main magnet configured for generating a main magnetic field is disclosed. The main magnet incorporates a passive shim system. The passive shim system is configured for magnetically shimming the main magnetic field. In another aspect, a magnetic resonance imaging system incorporating the main magnet and passive shim system is disclosed. The magnetic resonance imaging system comprises a system memory storing system machine-executable instructions and pulse sequence commands. The magnetic resonance imaging system further comprises a system computational system. Execution of the system machine-executable instructions causes the system computational system to acquire k-space data by controlling the magnetic resonance imaging system with the pulse sequence commands. Execution of the system machine-executable instructions further causes the system computational system to repeatedly acquire the sensor-specific temperature data at least during the acquisition of the k-space data during the passive shim system. Execution of the system machine-executable instructions further causes the system computational system to monitor a status of the magnetic resonance imaging system using the repeatedly acquired sensor-specific temperature data. BRIEF DESCRIPTION OF THE DRAWINGS In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which: