Related Experiment Videos
Combined effects of magnetization transfer and gadolinium in cranial MR imaging and MR angiography
V P Mathews1, A D Elster, J C King
1Department of Radiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157-1088.
Abstract:
Magnetization transfer (MT) imaging is an MR technique in which image contrast is altered by applying RF pulses that saturate a restricted pool of hydrogen protons associated with cell membranes, proteins, and other macromolecules. Protons in this restricted pool, unlike those in tissue-free water, are not visible on MR due to their short T2 relaxation times. However, these restricted protons modulate the observed signal from free water by dipolar and chemical exchange interactions. In MT imaging, specifically tailored RF pulses are applied to saturate selectively the restricted macromolecular pool. This saturation is "transferred" to the free protons, causing their signal amplitude to decrease [1]. Increased signal intensity due to T1 shortening caused by gadolinium administration does not depend upon macromolecular interactions and is not appreciably suppressed by MT pulses (Fig. 1). Consequently, MT pulses act synergistically with gadolinium to increase the visibility of enhancing lesions by preferentially suppressing nonenhancing background tissue [2]. The purpose of this paper is to demonstrate the principles underlying the synergistic effects of MT saturation and paramagnetic contrast agents and to illustrate these effects in clinical MR imaging and MR angiography.
Insights
Magnetization transfer (MT) imaging uses RF pulses to suppress background tissue signals. This technique synergizes with gadolinium contrast agents, enhancing lesion visibility in MR imaging.
Area of Science:
- Magnetic Resonance Imaging
- Biophysics
Background:
- Magnetization transfer (MT) imaging is an MRI technique that alters image contrast by saturating macromolecule-associated protons.
- These saturated protons interact with free water protons, reducing the observed MR signal.
- Restricted protons, though not directly visible due to short T2 relaxation, influence free water signals via dipolar and chemical exchange.
Purpose of the Study:
- To demonstrate the principles of synergistic effects between MT saturation and paramagnetic contrast agents.
- To illustrate these synergistic effects in clinical Magnetic Resonance (MR) imaging and MR angiography.
Main Methods:
- Application of specifically tailored radiofrequency (RF) pulses to selectively saturate the restricted macromolecular proton pool.
- Utilizing gadolinium-based contrast agents to shorten T1 relaxation times.
- Observing the preferential suppression of nonenhancing background tissue by MT pulses.
Main Results:
- MT pulses preferentially suppress nonenhancing background tissue signals.
- Gadolinium administration increases signal intensity via T1 shortening, independent of macromolecular interactions.
- MT pulses synergize with gadolinium to enhance the visibility of enhancing lesions by suppressing background tissue.
Conclusions:
- MT saturation and gadolinium contrast agents act synergistically to improve lesion conspicuity in MR imaging.
- This synergistic effect enhances the detection of enhancing lesions by reducing background signal.
- The principles demonstrated are applicable to clinical MR imaging and MR angiography.