Julian Haegele MD, Presenter: Nothing to Disclose

Jurgen Rahmer, Abstract Co-Author: Employee, Koninklijke Philips NV

Robert Lothar Duschka MD, Abstract Co-Author: Nothing to Disclose

Nikolaos Panagiotopoulos, Abstract Co-Author: Nothing to Disclose

Joerg Barkhausen MD, Abstract Co-Author: Nothing to Disclose

Florian Matthias Vogt MD, Abstract Co-Author: Nothing to Disclose

Purpose of this study was to visualize and quantify different vascular stenosis phantoms using Magnetic Particle Imaging (MPI).

Nine standardized stenosis-phantoms featuring a circular lumen of 10 mm diameter were used. Their lumen narrowed conically to 1 mm diameter (99% stenosis), 2 mm (96 %), 3 mm (91 %), 4 mm (84 %), 5 mm (75 %), 6 mm (64 %), 7 mm (51 %), 8 mm (36 %) or 9mm (19 %), respectively. For MPI, the phantoms were filled with a 1% and 5% dilution of Resovist (Bayer Pharma AG), corresponding to 0.28 and 1.4 mg(Fe)/ml Resovist, respectively. Images were acquired using a pre-clinical MPI-demonstrator (Philips Research, Hamburg, Germany, field of view 36 x 36 x 20 mm3, temporal resolution 46 Volumes per second). Imaging was conducted in steady state without flow and during manual movement of the phantoms through the field of view of the MPI-demonstrator. The MPI-signal was used for image reconstruction and also for intensity measurements to quantify the grade of stenosis. For comparison, the same stenosis-phantoms were evaluated with contrast-enhanced CT. Acquisition time for the 3D CT, MRI, and MPI scans was 1.2 s, 60 s, and 21 ms, respectively.

With a resulting spatial resolution of about 3 x 3 x 1 mm3, MPI was able to visualize all residual lumina of the stenoses accurately except for the highest grade stenosis. It was possible to quantify the extent of the stenoses down to 6 mm (64 %) independently of the Resovist concentration and the rate of movement of the stenosis-phantoms through the field of view. Higher grade stenoses were underestimated, the stenosis of 84% was measured as 74 %, 91 % as 79 %, 96 % as 82 % and 99 % as 88 %. CT exhibited the highest spatial resolution, followed by MRI.

Direct quantification of vascular stenoses using MPI is possible in phantoms. Due to the high temporal resolution of the system, visualization and quantification is independent of the movement of the probe, which may be beneficial for future clinical applications where respiratory and cardiac motion occur. With current experimental MPI-systems and available tracer materials, the spatial resolution at high imaging speeds is limited, so that high grade stenoses are underestimated systematically due to a partial volume effect.

Quantification of vascular stenosis using the SPIOs signal intensity may prove beneficial in in vivo cardiovascular imaging using MPI.

Haegele, J, Rahmer, J, Duschka, R, Panagiotopoulos, N, Barkhausen, J, Vogt, F, Magnetic Particle Imaging (MPI): Visualization and Quantification of Vascular Stenosis Phantoms.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14005287.html