MRI Pulse Sequences for Liver Fibrosis Relaxometry
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Solution Overview
Problem
Current MRI techniques for detecting liver fibrosis, particularly in early stages, are not reliable due to challenges in performing T1rho and T2 relaxometry in human liver tissue, which is rich in blood vessels, leading to elevated relaxation parameter values and spatial misregistration artifacts.
Innovation Solution
The development of pulse sequences for MRI that include magnetization preparation and fast spin echo or turbo spin echo imaging, with optimized flip angles and echo times for blood and fat suppression, allowing for breath-hold single slice T1rho and T2 relaxometry with reduced spatial misregistration and motion-related artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MRI pulse sequences are used for liver imaging, then anatomical structures can be visualized, but blood signal contamination elevates relaxation parameter values and reduces measurement precision
Solution Approach 1:
The patent applies magnetization preparation pulses (inversion recovery or saturation pulses) before the main imaging sequence to pre-suppress blood signal. This preliminary action ensures that when the actual imaging is performed, the blood signal is already suppressed, preventing contamination of the relaxation parameter measurements and improving measurement precision.
Solution Approach 2:
The patent extracts or removes the harmful blood signal from the measurement by using selective suppression techniques. Through magnetization preparation tailored to blood's specific relaxation characteristics, the blood signal is effectively removed or nullified from the combined tissue-blood signal, leaving only the liver tissue signal for accurate relaxometry.
2Measurement precision
If long-duration spin-lock pulses are used for T1rho measurement, then accurate T1rho quantification is achieved, but patient motion and spatial misregistration artifacts increase
Solution Approach 1:
The patent performs magnetization preparation and blood suppression before the spin-lock sequence, establishing the desired magnetization state in advance. This allows the actual imaging to be completed more efficiently during a breath-hold, reducing the time window for motion artifacts while maintaining T1rho measurement accuracy through the pre-prepared magnetization state.
Solution Approach 2:
The patent uses periodic breath-hold instructions to patients during the imaging sequence, creating periodic pauses in respiratory motion that coincide with data acquisition windows. This periodic action reduces motion-related artifacts while allowing sufficient time for accurate T1rho measurement.
3Adaptability or versatility
If multiple imaging sequences are acquired for T1rho and T2 relaxometry, then comprehensive diagnostic information is obtained, but spatial misregistration between images increases
Solution Approach 1:
The patent merges T1rho and T2 relaxometry measurements into a single integrated pulse sequence or performs them sequentially during one breath-hold. This combining approach ensures that both relaxation parameters are measured from the same anatomical position and temporal window, eliminating spatial misregistration between separate acquisitions while maintaining comprehensive diagnostic capability.
Solution Approach 2:
The patent designs a universal pulse sequence framework that can perform both T1rho and T2 measurements using the same magnetization preparation and acquisition parameters. This multi-functional approach allows both relaxation parameters to be derived from a single imaging protocol, ensuring spatial consistency while providing comprehensive diagnostic information.
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
The proposed pulse sequences enable accurate and reliable breath-hold single slice T1rho and T2 relaxometry with effective blood signal suppression, improving image quality and reducing artifacts, thus enhancing the detection of liver fibrosis.
Implementation Method 1
a patient is placed in a strong longitudinal magnetic field that aligns nuclear spins of atoms in the patient's body, producing a net magnetization vector
Implementation Method 2
Radio frequency (RF) pulses with magnetic field components transverse to the longitudinal field and frequencies tuned to the Larmor frequency of an isotope of interest are applied. These pulses can flip spins into a higher energy state, resulting in a transverse component to the magnetization vector
Implementation Method 3
As these spins return to the ground state, responsive signals from the patient's body can be detected. Based on the response to the RF pulses, characteristics of the magnetization can be measured. Commonly used measurements include the spin-lattice relaxation time (T1), measurement of which is typically based on recovery of the longitudinal component of the magnetization vector
Implementation Method 4
the spin-spin relaxation time (T2), measurement of which is typically based on decay of the transverse component of the magnetization vector
Implementation Method 5
For T1rho measurement, a long-duration low-power RF pulse, referred to as a spin-lock pulse, is applied to lock the magnetization around an effective magnetic field
Data Source
AI summary
Pulse sequences for an MRI apparatus can provide improved quantitative relaxometry in liver and other tissues. Relaxation parameters such as T1rho or T2 (or both at once) can be measured. The pulse sequence can include a magnetization preparation pulse sequence and an acquisition pulse sequence including a fast spin echo (FSE) pulse sequence. Flip angles and echo time for the FSE pulse sequence can be chosen to optimize image quality without affecting the quantification of a relaxation parameter. Additional pulse sequences, e.g., for enhanced blood suppression and/or fat suppression can be incorporated. The acquisition pulse sequence can have a duration that allows data for a single slice image to be acquired during a breath-hold.