System for simultaneous pet/mr imaging

A combined PET/MR system comprising:

• an MR subsystem including a main field magnet which generates a stationary magnetic field through an examination region, a gradient magnetic field system which applies magnetic field gradients across the examination region, and RF system that applies RF excitation pulses to excite resonance in a subject in the examination region and receive magnetic resonance signals from the subject;
• and
• a plurality of PET detector units;
• RF shielding which individually RF shields each PET detector unit;
• wherein the RF shielded PET detector units are mounted in a circumferentially spaced relationship with a gap there between through which the RF excitation pulses and the magnetic resonance signals pass.

A method of combined PET/MR imaging with a PET detector module permanently or removably fixed in an examination region of an MR scanner, the method comprising:

• with the MR scanner, applying an MR imaging sequence including:
• applying magnetic field gradients across the examination region, which applied magnetic field gradients are distorted by the PET detector module,
• inducing magnetic resonance in a subject in the examination region,
• receiving magnetic resonance signals from the subject;
• with a plurality of RF probes which are mounted in a fixed relationship with the PET detector module, measuring magnetic field strength in the examination region during the application of the magnetic field gradients;
• determining the distortions caused in the applied gradient magnetic fields and correcting received magnetic resonance signals in accordance with the determined distortion;
• reconstructing the corrected magnetic resonance signals into an MR image representation.

A combined PET/MR system comprising:

• an MR subsystem including a main field magnet configured to generate a stationary magnetic field through an examination region, a gradient magnetic field system configured to apply magnetic field gradients across the examination region, and an RF system configured to apply RF excitation pulses to excite resonance in a volume of interest in the examination region and to receive magnetic resonance signals from the volume of interest;
• a PET detector module permanently or removably fixed in the examination region configured to detect radiopharmaceuticals in the volume of interest;
• a processor configured to select, based on a current PET detector module location in the examination region, a distortion correction map from a library of distortion correction maps, and to apply the selected distortion correction map to the magnetic resonance signals to correct for distortions in the gradient magnetic fields;
• an MR reconstruction system configured to reconstruct the corrected magnetic resonance signals into an image representation.

A method of combined PET/MR imaging with a PET detector module permanently or removably fixed in an examination region of an MR scanner, the method comprising:

• with the MR scanner, applying an MR imaging sequence including:
• applying magnetic field gradients across the examination region, which applied magnetic field gradients are distorted by the PET detector module,
• inducing magnetic resonance in a volume of interest in the examination region,
• receiving magnetic resonance signals from the volume of interest;
• with a processor, receiving input indicative of a current PET detector module location in the examination region;
• with the processor, selecting, based on the current PET detector module location in the examination region, a distortion correction map from a library of distortion correction maps, and applying the selected distortion correction map to the magnetic resonance signals to correct for distortions in the gradient magnetic fields;
• reconstructing the corrected magnetic resonance signals into an MR image representation.