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.


Maximum average force produced by sequences of Fig. 1 normalized by the maximum possible force that can be produced by the scanner.Experimental data points are denoted by *. Dashed vertical lines separate frequency ranges according to the delay, measured in number of pulse sequences, between when an image is taken and when it is available for modulating propulsive force.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Maximum average force produced by sequences of Fig. 1 normalized by the maximum possible force that can be produced by the scanner.Experimental data points are denoted by *. Dashed vertical lines separate frequency ranges according to the delay, measured in number of pulse sequences, between when an image is taken and when it is available for modulating propulsive force.

Mentions: Predicted and measured maximum average force for the sequence of Fig. 1b are plotted in Fig. 3 normalized by the force associated with a constant maximum gradient of 21 mT/m. The equivalent result for the interleaved imaging and propulsion Fig. 1a is also shown. With alternating imaging and propulsion, the maximum normalized force falls to less than 50% at a control frequency of 27 Hz and reaches zero at about 52 Hz. In contrast, the proposed spin echo sequence provides 95% of the open-loop force at 27 Hz and 63% of open-loop force at 182 Hz.


Simultaneous steering and imaging of magnetic particles using MRI toward delivery of therapeutics
Maximum average force produced by sequences of Fig. 1 normalized by the maximum possible force that can be produced by the scanner.Experimental data points are denoted by *. Dashed vertical lines separate frequency ranges according to the delay, measured in number of pulse sequences, between when an image is taken and when it is available for modulating propulsive force.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Maximum average force produced by sequences of Fig. 1 normalized by the maximum possible force that can be produced by the scanner.Experimental data points are denoted by *. Dashed vertical lines separate frequency ranges according to the delay, measured in number of pulse sequences, between when an image is taken and when it is available for modulating propulsive force.
Mentions: Predicted and measured maximum average force for the sequence of Fig. 1b are plotted in Fig. 3 normalized by the force associated with a constant maximum gradient of 21 mT/m. The equivalent result for the interleaved imaging and propulsion Fig. 1a is also shown. With alternating imaging and propulsion, the maximum normalized force falls to less than 50% at a control frequency of 27 Hz and reaches zero at about 52 Hz. In contrast, the proposed spin echo sequence provides 95% of the open-loop force at 27 Hz and 63% of open-loop force at 182 Hz.

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.