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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.


Image-based position measurement.(a) Particle position versus time as estimated by MRI and high-speed camera for an MRI imaging frequency of 125 Hz. (b) Error in MRI-based position measurement as a function of imaging frequency. RMSE = Root Mean Square Error.
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f4: Image-based position measurement.(a) Particle position versus time as estimated by MRI and high-speed camera for an MRI imaging frequency of 125 Hz. (b) Error in MRI-based position measurement as a function of imaging frequency. RMSE = Root Mean Square Error.

Mentions: With a sinusoidal forcing frequency of 0.5 Hz and a displacement amplitude of 100 mm, the maximum particle velocity in these experiments was about 314 mm/s, which is the same order of magnitude as blood velocity in the ascending aorta (peak and mean velocities of 66 and 11 cm/s25). An example plot for an imaging frequency of 125 Hz is given in Fig. 4(a). As shown in the plot of position error versus imaging frequency in Fig. 4(b), mean position error is slightly larger than particle diameter for frequencies up to 125 Hz. Errors of this size are acceptable for image-based steering as demonstrated in the following section.


Simultaneous steering and imaging of magnetic particles using MRI toward delivery of therapeutics
Image-based position measurement.(a) Particle position versus time as estimated by MRI and high-speed camera for an MRI imaging frequency of 125 Hz. (b) Error in MRI-based position measurement as a function of imaging frequency. RMSE = Root Mean Square Error.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Image-based position measurement.(a) Particle position versus time as estimated by MRI and high-speed camera for an MRI imaging frequency of 125 Hz. (b) Error in MRI-based position measurement as a function of imaging frequency. RMSE = Root Mean Square Error.
Mentions: With a sinusoidal forcing frequency of 0.5 Hz and a displacement amplitude of 100 mm, the maximum particle velocity in these experiments was about 314 mm/s, which is the same order of magnitude as blood velocity in the ascending aorta (peak and mean velocities of 66 and 11 cm/s25). An example plot for an imaging frequency of 125 Hz is given in Fig. 4(a). As shown in the plot of position error versus imaging frequency in Fig. 4(b), mean position error is slightly larger than particle diameter for frequencies up to 125 Hz. Errors of this size are acceptable for image-based steering as demonstrated in the following section.

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.