Limits...
Simultaneous steering and imaging of magnetic particles using MRI toward delivery of therapeutics

View Article: PubMed Central - PubMed

ABSTRACT

Magnetic resonance navigation (MRN) offers the potential for real-time steering of drug particles and cells to targets throughout the body. In this technique, the magnetic gradients of an MRI scanner perform image-based steering of magnetically-labelled therapeutics through the vasculature and into tumours. A major challenge of current techniques for MRN is that they alternate between pulse sequences for particle imaging and propulsion. Since no propulsion occurs while imaging the particles, this results in a significant reduction in imaging frequency and propulsive force. We report a new approach in which an imaging sequence is designed to simultaneously image and propel particles. This sequence provides a tradeoff between maximum propulsive force and imaging frequency. In our reported example, the sequence can image at 27 Hz while still generating 95% of the force produced by a purely propulsive pulse sequence. We implemented our pulse sequence on a standard clinical scanner using millimetre-scale particles and demonstrated high-speed (74 mm/s) navigation of a multi-branched vascular network phantom. Our study suggests that the magnetic gradient magnitudes previously demonstrated to be sufficient for pure propulsion of micron-scale therapeutics in magnetic resonance targeting (MRT) could also be sufficient for real-time steering of these particles.

No MeSH data available.


Examples of MRI-based projections used for particle localization: (a) 50 Hz, (b) 117 Hz.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5036040&req=5

f2: Examples of MRI-based projections used for particle localization: (a) 50 Hz, (b) 117 Hz.

Mentions: To design a pulse sequence that simultaneously images and propels, we first studied the structure of existing pulse sequences that alternately image and propel (Fig. 1a)2123. In these sequences, positive contrast projections (see Fig. 2) of ferromagnetic material2224 are obtained through a combination of radio frequency (RF) pulses and magnetic gradient pulses (Gx, Gy, Gz) applied in the three directions of the MRI coordinate frame. These magnetic gradients also produce propulsive forces on ferromagnetic material in the corresponding coordinate directions. Since the magnitudes required for imaging are typically small and the pulses are of both positive and negative sign, the imaging gradients produce little propulsive force and in some cases have been designed to exactly cancel14. Following imaging, propulsion is accomplished using gradient pulses of varying amplitude and duration. In the context of standard MRI pulse sequences, the propulsive gradients take the place of spoiler gradients which are traditionally intended to clear the effect of the preceding imaging pulses in preparation for acquiring the next image.


Simultaneous steering and imaging of magnetic particles using MRI toward delivery of therapeutics
Examples of MRI-based projections used for particle localization: (a) 50 Hz, (b) 117 Hz.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036040&req=5

f2: Examples of MRI-based projections used for particle localization: (a) 50 Hz, (b) 117 Hz.
Mentions: To design a pulse sequence that simultaneously images and propels, we first studied the structure of existing pulse sequences that alternately image and propel (Fig. 1a)2123. In these sequences, positive contrast projections (see Fig. 2) of ferromagnetic material2224 are obtained through a combination of radio frequency (RF) pulses and magnetic gradient pulses (Gx, Gy, Gz) applied in the three directions of the MRI coordinate frame. These magnetic gradients also produce propulsive forces on ferromagnetic material in the corresponding coordinate directions. Since the magnitudes required for imaging are typically small and the pulses are of both positive and negative sign, the imaging gradients produce little propulsive force and in some cases have been designed to exactly cancel14. Following imaging, propulsion is accomplished using gradient pulses of varying amplitude and duration. In the context of standard MRI pulse sequences, the propulsive gradients take the place of spoiler gradients which are traditionally intended to clear the effect of the preceding imaging pulses in preparation for acquiring the next image.

View Article: PubMed Central - PubMed

ABSTRACT

Magnetic resonance navigation (MRN) offers the potential for real-time steering of drug particles and cells to targets throughout the body. In this technique, the magnetic gradients of an MRI scanner perform image-based steering of magnetically-labelled therapeutics through the vasculature and into tumours. A major challenge of current techniques for MRN is that they alternate between pulse sequences for particle imaging and propulsion. Since no propulsion occurs while imaging the particles, this results in a significant reduction in imaging frequency and propulsive force. We report a new approach in which an imaging sequence is designed to simultaneously image and propel particles. This sequence provides a tradeoff between maximum propulsive force and imaging frequency. In our reported example, the sequence can image at 27 Hz while still generating 95% of the force produced by a purely propulsive pulse sequence. We implemented our pulse sequence on a standard clinical scanner using millimetre-scale particles and demonstrated high-speed (74 mm/s) navigation of a multi-branched vascular network phantom. Our study suggests that the magnetic gradient magnitudes previously demonstrated to be sufficient for pure propulsion of micron-scale therapeutics in magnetic resonance targeting (MRT) could also be sufficient for real-time steering of these particles.

No MeSH data available.