MR Coil Attenuation Correction in Hybrid PET/MR Imaging
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Solution Overview
Problem
Current PET/MR hybrid systems face challenges in correcting for attenuation caused by MR coils and accessories, leading to degraded image quality due to the presence of metals and materials not accounted for in existing conversion algorithms.
Innovation Solution
A system and method for generating and storing unique attenuation correction map templates for each MR coil and accessory, using transmission data to create accurate templates that can be recalled and applied during scans, allowing for precise correction of attenuation in nuclear images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If MR coils and accessories are present in the PET scanner field of view, then high-resolution MR images of different body parts can be obtained, but attenuation of PET radiation occurs leading to degraded PET image quality
Solution Approach 1:
The system performs preliminary scanning of the MR coil and accessories using a transmission source before the actual PET scan to generate an attenuation correction map template. This template is then applied during PET image reconstruction to compensate for the attenuation caused by the coil materials, thereby resolving the contradiction between having the coil present for MR imaging and maintaining PET image quality.
Solution Approach 2:
The patent introduces an intermediary attenuation correction map template that mediates between the MR coil presence and PET image quality. The template, generated from transmission data and stored in a library, serves as a corrective layer that accounts for coil attenuation without requiring removal of the coil, thus enabling both high-resolution MR imaging and accurate PET imaging.
2Productivity
If standard CT-to-PET attenuation conversion algorithms are used, then attenuation correction can be applied for human tissues, but accurate correction for metallic and non-biological materials in MR coils cannot be achieved
Solution Approach 1:
The system segments the attenuation correction process into two parts: a patient-specific attenuation map generated from MR images, and a pre-generated coil attenuation correction map template stored in a library. The template library contains pre-characterized attenuation properties of different coil materials and configurations, allowing accurate correction for metallic and non-biological materials without compromising overall correction efficiency.
Solution Approach 2:
The patent changes the approach from using standard CT-to-PET conversion algorithms to using empirically measured transmission data from the actual coil materials. By scanning the coil with a transmission source and measuring actual attenuation parameters, the system creates accurate correction templates that reflect the true attenuation properties of metallic and non-biological materials at 511 keV PET energy.
3Measurement precision
If attenuation correction templates are generated for each unique MR coil configuration, then accurate correction can be achieved, but system complexity and template library requirements increase
Solution Approach 1:
The system creates universal attenuation correction templates that can be applied to multiple coil types and configurations. By categorizing coils into standard types (e.g., head coils, body coils, surface coils) and generating representative templates for each category, the library serves multiple functions across different imaging scenarios, reducing overall system complexity while maintaining correction accuracy for various coil configurations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Significantly improves PET image quality by accurately accounting for attenuation caused by MR coils and accessories, enabling the use of MR coils within PET gantries and generating diagnostic-quality MR image data correctly registered with PET images.
Implementation Method 1
transmission data acquired during a nuclear scan of the accessory
Data Source
AI summary
Nuclear image data generated by a multimodal imaging device, such as a combined position emission tomography (PET)/magnetic resonance (MR) scanner (12, 14), is attenuation-corrected with a combined patient-specific attenuation correction (AC) map and an AC map template (70) for an MR coil (72) that is present in both the nuclear and MR scanning procedures. A template library (46) contains templates for each of a plurality of MR coils and other accessories. Each template is generated on one of two manners. The coil may be imaged inside the PET scanner 14 with the transmission source 16 (e.g., Ge-68 or Cs-137). A transmission image 48 is reconstructed using the known algorithms and may be used as the AC template directly. Alternatively, the template can be generated by creating a global histogram of the transmission image and identifying segments of the coil or other accessory. An average linear attenuation coefficient (LAC) value is determined from the distribution of the histogram. The coil or other accessory is imaged using a high resolution CT scan, and the CT image is segmented and assigned the computed LAC values determined from the distribution of the histogram to create the AC map template for the coil.