Theranostics 2018; 8(13):3691-3692. doi:10.7150/thno.27454


Take a Deep Breath - Monitoring of Inhaled Nanoparticles with Magnetic Particle Imaging

Franz Wegner1 Corresponding address, Thorsten M. Buzug2, Joerg Barkhausen1

1. Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Ratzeburger Allee 160, 23562 Lübeck, Germany
2. Institute of Medical Engineering, University of Lübeck, Building 64, Ratzeburger Allee 160, 23562 Lübeck, Germany

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Wegner F, Buzug TM, Barkhausen J. Take a Deep Breath - Monitoring of Inhaled Nanoparticles with Magnetic Particle Imaging. Theranostics 2018; 8(13):3691-3692. doi:10.7150/thno.27454. Available from

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Magnetic Particle Imaging (MPI) is a new imaging modality based on the visualization of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) using magnetic fields. The potential of MPI was recently evaluated in numerous ex vivo and in vivo studies and the technique can now be considered as an established preclinical imaging modality with a promising perspective of clinical applications.

Keywords: Magnetic Particle Imaging, Nanoparticles, Preclinical Imaging, Clinical Imaging


More than 10 years ago Magnetic Particle Imaging (MPI) emerged as a completely new imaging modality. The basic principle of MPI - the visualization of the spatial distribution of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) using oscillating magnetic fields - was first described by Gleich and Weizenecker in 2005 [1]. The technique provides a high temporal and spatial resolution combined with a high sensitivity and due to its electro-magnetic properties, the MPI signal penetrates tissue unrestrictedly. MPI acquires quantitative, hot-spot images with positive contrast similar to PET and SPECT, except that MPI avoids the use of radiochemicals. The sensitivity of MPI to an optimal iron oxide contrast agent is predicted to be two to three orders of magnitude greater than that of MRI. Furthermore, MPI is much faster than MRI, because the signal can be detected immediately after the excitation, whereas the MRI signal (echo) occurs after a considerable waiting time in the range of 1 to 100 ms. MPI therefore opens the way to new radiation-free applications in real-time imaging, molecular diagnostics and therapy-monitoring.

Especially the field of cardiovascular imaging was intensely evaluated in several proof-of-principle studies in the last decade. The quantification of stenosis, vascular flow-measurements and MPI-guided catheter interventions have been successfully performed in several preclinical studies [2-5]. Safety limits of interventional devices were evaluated and recently first real-time experiments were published [6-9]. Additionally, the detection of bleeding and ischemic events were taken into account in small animal studies [10-12].

As cardiovascular applications take advantage of the high temporal resolution of MPI, it is the excellent sensitivity which predisposes MPI for molecular imaging applications. Graeser et al. recently demonstrated a detection limit of 5 ng iron in MPI using a gradiometric receive coil [13]. In 2009, first preclinical experiments on MPI guided sentinel lymph node biopsies have been published [14]. Additionally, it is possible to load erythrocytes with SPIOs [16] and Zheng et al. depicted neuronal cells for 87 days in rat brains [17]. Furthermore, stem cells [15,18] as well as cancer cells [19] can be tracked by MPI. Another interesting application is the conjugation of SPIONs with molecules, which bind to specific cell surfaces. Thus, the conjugation of lactoferrin with SPIONs to detect glioma cells is an impressive example for a new approach of MPI based cancer imaging [20].

In this issue of Theranostics an excellent article titled “In Vivo Tracking and Quantification of Inhaled Aerosol using Magnetic Particle Imaging towards Inhaled Therapeutic Monitoring” was published by Tay et al. [21]. In a well-designed and innovative study the authors showed that inhaled nanoparticles can be visualized by MPI in mice with accuracy comparable to radiolabeled aerosols. The inhalation parameters such as aerosol particle size have major impact on the particle distribution, and due to quantitative MPI measurements the described method can be applied for MPI-based drug monitoring. This concept was first described in the article and the authors validated their results by means of fluorescence imaging. Another interesting aspect of the study is the in vivo visualization of the mucociliary clearance. The clearance pathway of SPIONs in mice was shown for 13 days and the transport function of the alveolar cells was successfully demonstrated with MPI. Last but not least, the authors addressed potential safety concerns and pointed out options for human applications.

Taken together with recent results from Zhou et al. [22], demonstrating the possibility of lung perfusion imaging with MPI, the authors completed the proof of concept of an MPI-based perfusion-ventilation mapping [21]. Perfusion-ventilation mapping is widely used in clinical routine for the diagnosis of pulmonary embolism and the preoperative evaluation of the lungs. Without the use of ionizing radiation, MPI may overcome important disadvantages of nuclear medicine techniques.

In conclusion, the article by Tay et al. shows the huge potential of MPI for basic research in a very illustrative way. The quantitative in vivo visualization of inhaled particle aerosols as well as SPION labeled drugs combined with the analysis of the mucociliary clearance provides an effective tool for the investigation of numerous scientific questions.


1. Gleich B, Weizenecker J. Tomographic imaging using the nonlinear response of magnetic particles. Nature. 2005;435:1214-17

2. Haegele J, Rahmer J, Gleich B, Borgert J, Wojtczyk H, Panagiotopoulos N. et al. Magnetic particle imaging: visualization of instruments for cardiovascular intervention. Radiology. 2012;265:933-8

3. Vaalma S, Rahmer J, Panagiotopoulos N, Duschka RL, Borgert J, Barkhausen J. et al. Magnetic particle imaging (MPI): experimental quantification of vascular stenosis using stationary stenosis phantoms. PLoS One. 2017;12:e0168902

4. Herz S, Vogel P, Kampf T, Ruckert MA, Veldhoen S, Behr VC. et al. Magnetic particle imaging for quantification of vascular stenoses: a phantom study. IEEE Trans Med Imaging. 2017;37:61-7

5. Kaul MG, Salamon J, Knopp T, Ittrich H, Adam G, Weller H. et al. Magnetic particle imaging for in vivo blood flow velocity measurements in mice. Phys Med Biol. 2018;63:064001

6. Duschka RL, Wojtczyk H, Panagiotopoulos N, Haegele J, Bringout G, Buzug TM. et al. Safety measurements for heating of instruments for cardiovascular interventions in magnetic particle imaging (MPI) - first experiences. J Healthc Eng. 2014;5:79-93

7. Salamon J, Hofmann M, Jung C, Kaul MG, Werner F, Them K. et al. Magnetic particle/magnetic resonance imaging: in-vitro MPI-guided real time catheter tracking and 4D angioplasty using a road map and blood pool tracer approach. PLoS One. 2016;11:e0156899

8. Herz S, Vogel P, Dietrich P, Kampf T, Rückert MA, Kickuth R. et al. Magnetic particle imaging guided real-time percutaneous transluminal angioplasty in a phantom model. Cardiovasc Intervent Radiol. doi: 10.1007/s00270-018-1955-7.

9. Wegner F, Friedrich T, Panagiotopoulos N, Vaalma S, Goltz JP, Vogt FM. et al. First heating measurements of endovascular stents in magnetic particle imaging. Phys Med Biol. 2018;63:045005

10. Ludewig P, Gdaniec N, Sedlacik J, Forkert ND, Szwargulski P, Graeser M. et al. Magnetic particle imaging for real-time perfusion imaging in acute stroke. ACS Nano. 2017;11:10480-8

11. Yu EY, Chandrasekharan P, Berzon R, Tay ZW, Zhou XY, Khandhar AP. et al. Magnetic particle imaging for highly sensitive, quantitative, and safe in vivo gut bleed detection in a murine model. ACS Nano. 2017;11:12067-76

12. Orendorff R, Peck AJ, Zheng B, Shirazi SN, Matthew Ferguson R, Khandhar AP. et al. First in vivo traumatic brain injury imaging via magnetic particle imaging. Phys Med Biol. 2017;62:3501-9

13. Graeser M, Knopp T, Szwargulski P, Friedrich T, von Gladiss A, Kaul M. et al. Towards picogram detection of superparamagnetic iron-oxide particles using a gradiometric receive coil. Sci Rep. 2017;7:6872

14. Ruhland B, Baumann K, Knopp T, Sattel T, Biederer S, Lüdtke-Buzug K. et al. Magnetic particle imaging with superparamagnetic nanoparticles for sentinel lymph node detection in breast cancer. Geburtshilfe Frauenheilkd. 2009;69:A096

15. Bulte JWM, Walczak P, Janowski M, Krishnan KM, Arami H, Halkola A. et al. Quantitative “hot spot” imaging of transplanted stem cells using superparamagnetic tracers and magnetic particle imaging (MPI). Tomography. 2015;1:91-7

16. Antonelli A, Sfara C, Rahmer J, Gleich B, Borgert J, Magnani M. Red blood cells as carriers in magnetic particle imaging. Biomed Tech (Berl). 2013;58:517-25

17. Zheng B, Vazin T, Goodwill PW, Conway A, Verma A, Saritas EU. et al. Magnetic particle Imaging tracks the long-term fate of in vivo neural cell implants with high image contrast. Sci Rep. 2015;5:14055

18. Zheng B, von See MP, Yu E, Gunel B, Lu K, Vazin T. et al. Quantitative magnetic particle imaging monitors the transplantation, biodistribution, and clearance of stem cells in vivo. Theranostics. 2016;6:291-301

19. Lindemann A, Lüdtke-Buzug K, Fräderich BM, Gräfe K, Pries R, Wollenberg B. Biological impact of superparamagnetic iron oxide nanoparticles for magnetic particle imaging of head and neck cancer cells. Int J Nanomedicine. 2014;9:5025-40

20. Tomitaka A, Arami H, Gandhi S, Krishnan KM. Lactoferrin conjugated iron oxide nanoparticles for targeting brain glioma cells in magnetic particle imaging. Nanoscale. 2015;7:16890-8

21. Tay ZW, Chandrasekharan P, Zhou XY, Yu E, Zheng B, Conolly S. In vivo tracking and quantification of inhaled aerosol using magnetic particle imaging towards inhaled therapeutic monitoring. Theranostics. 2018;8(13):3676-3687 doi:10.7150/thno.26608

22. Zhou XY, Jeffris KE, Yu EY, Zheng B, Goodwill PW, Nahid P. et al. First in vivo magnetic particle imaging of lung perfusion in rats. Phys Med Biol. 2017;62:3510-22

Author contact

Corresponding address Corresponding author: Franz Wegner (franz.wegnerde)

Received 2018-5-24
Accepted 2018-5-26
Published 2018-6-11