MOLLI T1 Mapping Pulse Sequence Heartbeat Synchronization
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Solution Overview
Problem
The Modified Look-Locker Inversion Recovery (MOLLI) method for T1 mapping in magnetic resonance imaging faces challenges such as biased data distribution due to heartbeat-dependent inversion times, leading to degraded measurement accuracy and prolonged breath-hold periods, along with signal attenuation and polarity inversion errors.
Innovation Solution
A magnetic resonance imaging apparatus that executes a pulse sequence with specific collection patterns, including non-read-out periods after inversion pulses, to synchronize with heartbeats and collect MR signals, thereby improving T1 map accuracy and reducing imaging time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the MOLLI method is used to perform T1 mapping by repeating inversion pulses and data collection over multiple heartbeats, then data can be collected at different inversion times, but the inversion time becomes dependent on the number of heartbeats causing biased data distribution and degraded T1 measurement accuracy
Solution Approach 1:
The patent applies dynamics by making the inversion time (TI) values variable and adaptable to different heartbeat conditions. The system dynamically selects from multiple predetermined TI value sets based on the subject's actual heartbeat rate, rather than using fixed TI values that become biased when heartbeat-dependent. This dynamic adaptation ensures accurate T1 measurement across varying physiological conditions.
Solution Approach 2:
The patent changes the parameter of inversion time (TI) from fixed values to multiple selectable predetermined values. By providing a plurality of TI value sets and selecting appropriate values based on heartbeat rate, the system optimizes the inversion timing parameter to prevent data distribution bias and improve measurement accuracy across different cardiac conditions.
2Measurement precision
If the number of inversion pulse applications is increased to collect data at desired inversion times, then more complete data can be obtained, but the imaging time is prolonged causing extended breath-hold periods and increased subject burden
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing multiple sets of inversion time (TI) values before the actual T1 mapping measurement. These predetermined TI value sets are prepared in advance based on different heartbeat rate scenarios, allowing the system to quickly select the most appropriate set without requiring additional inversion pulses or extending the measurement time during the actual scan.
Solution Approach 2:
The patent uses partial action by selecting only the necessary subset of inversion time values from the predetermined sets based on the subject's actual heartbeat rate. Instead of collecting data at all possible inversion times, the system selectively applies only the appropriate TI values needed for accurate measurement under current conditions, reducing unnecessary imaging time and breath-hold duration.
3Measurement precision
If imaging is performed over multiple heartbeats after inversion pulse application, then data can be collected at different inversion times, but the longitudinal magnetization is attenuated by RF pulses during data collection reducing signal quality
Solution Approach 1:
The patent applies periodic action by using the natural periodicity of heartbeats to time the inversion pulses and data collection. The system synchronizes the inversion pulse application and signal acquisition with the cardiac cycle, utilizing the periodic cardiac motion as a reference for optimal imaging timing. This periodic synchronization ensures that data is collected at consistent physiological phases across multiple heartbeats.
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
This approach enables the generation of highly accurate T1 maps with reduced breath-hold duration and improved measurement accuracy across varying heart rates, by optimizing data collection and signal inversion efficiency.
Implementation Method 1
a pulse called an inversion recovery pulse which inverts longitudinal magnetization, is used
Implementation Method 2
magnetic resonance imaging is an imaging method of magnetically exciting atomic nucleus spins of a subject, which is laid in a still magnetic field, using an RF signal of a Larmor frequency and reconstructing an image from an MR signal generated along with the excitation
Implementation Method 3
enables quantitatively imaging a longitudinal relaxation time (T1 value) of a tissue
Data Source
AI summary
According to one embodiment, an MRI apparatus includes sequence control circuitry and processing circuitry. The sequence control circuitry executes a pulse sequence for collecting MR signals in collection timings along a relaxation curve of longitudinal magnetization in synchronization with heartbeats or blood beats. The processing circuitry generate a T1 map representing a distribution of T1 values by using the collected MR signals. The pulse sequence is set so as not to collect any MR signal in at least one heartbeat or blood beat among heartbeats or blood beats included between first and second inversion pulses, and so as to collect an MR signal in a heartbeat or blood beat subsequent to the at least one heartbeat or blood beat in which no MR signal is collected.