Related Experiment Video
Updated: Oct 21, 2025
09:30
Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease
Published on: December 18, 2016
19.7K
B1 -gradient-based MRI using frequency-modulated Rabi-encoded echoes.
Efraín Torres1,2, Taylor Froelich1, Paul Wang1,2
1Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
Magnetic Resonance in Medicine
|September 9, 2021
Summary
This study introduces frequency-modulated Rabi-encoded echoes (FREE), a new MRI technique that eliminates the need for pulsed field gradient hardware. FREE enables spatial encoding using radiofrequency fields, potentially reducing MRI costs and improving accessibility.
Area of Science:
- Magnetic Resonance Imaging
- Radiofrequency Physics
- Medical Imaging Technology
Background:
- Conventional MRI relies on pulsed magnetic field gradients (B0) for spatial encoding, adding complexity and cost.
- Existing radiofrequency (RF) imaging methods face limitations due to resonance offset and B1-gradient characteristics.
Purpose of the Study:
- To develop and evaluate a novel RF imaging method for spatial encoding without B0 gradients.
- To reduce the expense and increase the accessibility of MRI by eliminating hardware requirements.
Main Methods:
- Introduced frequency-modulated Rabi-encoded echoes (FREE), an RF imaging technique using adiabatic full passage pulses and a B1 field gradient.
- Implemented Cartesian phase encoding using FREE in a multi-shot double spin-echo sequence.
- Conducted theoretical analysis, computer simulations, and experimental comparisons with conventional MRI on human visual cortex.
Main Results:
- FREE enabled slice-selective 2D imaging of the human brain without a B0 gradient.
- High resolution was achieved in areas with steep B1 gradients, while nonlinear B1 fields caused image distortions.
- Minimal signal loss occurred due to B1 nonlinearities and resonance offset.
Conclusions:
- Frequency-modulated Rabi-encoded echoes (FREE) is a viable method for MRI spatial encoding without B0 gradients.
- Potential for future correction of image distortions using B1 and B0 maps.
- This technique could lead to more accessible and cost-effective MRI.
Related Concept Videos
01:17NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences
1.0K
A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.
1.0K
01:24Magnetic Resonance Imaging
8.1K
Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic fields and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the first MRI scanning device in clinical use by the early 1980s. The early MRI...
8.1K
01:05Atomic Nuclei: Magnetic Resonance
834
The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
834
01:12Double Resonance Techniques: Overview
362
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Spin decoupling is usually achieved by...
362
01:27Imaging Studies IV: Magnetic Resonance Imaging
88
Introduction:Magnetic Resonance Imaging, or MRI, can include a specialized imaging technique of the urinary system known as Magnetic Resonance Urography (MRU). This radiation-free technique uses strong magnetic fields and radio waves to produce detailed images with the help of a computer. MRU is particularly effective for visualizing fluid-filled structures like the kidneys, ureters, and bladder.Applications of MRI in the Genitourinary SystemKidneys and Ureters: MRI detects tumors, cysts,...
88
01:14NMR Spectrometers: Resolution and Error Correction
820
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
820