1D imaging of a superparamagnetic iron oxide nanoparticle distribution by a single-sided FFL magnetic particle imaging scanner

Single-Sided Magnetic Particle Imaging Device With Offset Field Based Spatial Encoding

Single-sided Magnetic Particle Imaging (MPI) devices enable easy imaging of areas outside the MPI device, allowing objects of any size to be imaged and improving clinical applicability. However, current single-sided MPI devices face challenges in generating high-gradient selection fields and experience a decrease in gradient strength with increasing detection depth, which limits the detection depth and resolution. We introduce a novel spatial encoding method. This method combines high-frequency alternating excitation fields with variable offset fields, leveraging the inherent characteristic of single-sided MPI devices where the magnetic field strength attenuates with distance. Consequently, the harmonic signals of particle responses at different spatial positions vary. By manipulating multiple offset fields, we correlate the nonlinear harmonic responses of magnetic particles with spatial position data. In this work, we employed an image reconstruction using a system matrix approach, which takes into account the spatial distribution of the magnetic field during the movement of the device within the field of view. Our proposed encoding approach eliminates the need for the classical selection field and directly links the spatial resolution to the strength and spatial distribution of the magnetic field, thus reducing the dependency of resolution on selection field gradients strength. We have demonstrated the feasibility of the proposed method through simulations and phantom measurements.

Tomographic Magnetic Particle Imaging With a Single-Sided Field-Free Line Scanner

OBJECTIVE

Magnetic Particle Imaging (MPI) is a biomedical imaging modality that shows promise in enhancing clinical imaging capabilities. While there are current efforts to expand MPI hardware to enable whole-body and head imaging, this comes at a significant cost in terms of complexity and expense.

METHODS

A single-sided scanner can offer greater accessibility to the scanning area, as all hardware is located on one side of the device's surface, however, at the price of the limited penetration depth. Despite this, a single-sided device could serve as an open geometry preclinical scanner and a clinical instrument for local screening and procedures. The original single-sided device was introduced for a field-free point encoding gradient, which may limit its practical characteristics.

RESULTS

We developed a field-free line single-sided device that has improved imaging characteristics, which is beneficial for preclinical applications and potential clinical translation.

CONCLUSION

We demonstrated full tomographic imaging capabilities with the prototype of a single-sided MPI scanner and characterized the imaging performance of our imaging system.

SIGNIFICANCE

MPI has the potential to image various human body regions, particularly for breast cancer diagnosis. Our research tackles the crucial aspect of scalability in the emerging MPI technique.

A Novel Hand-Held Multi-Color Magnetic Particle Imaging Device Based on Rapid Frequency Conversion

OBJECTIVE

Multi-color Magnetic Particle Imaging (MPI) technology offers high sensitivity and non-invasive imaging capabilities. It can simultaneously image multiple superparamagnetic iron oxide nanoparticles (SPIOs), facilitating more precise detection of multiple molecular markers in vivo. However, the fixed drive frequency of existing hand-held MPI devices makes it difficult to fully match the nonlinear magnetic response of different SPIOs, affecting the effect of multi-color imaging.

METHODS

We designed a novel hand-held rapid frequency conversion based multi-color MPI (RFC-MPI) device. This device adjusts the drive frequency based on magnetic response at different frequencies, effectively expanding the system matrix information and thereby improving spatial resolution and multi-color imaging capabilities simultaneously.

RESULTS

The device achieved a spatial resolution of 27 mm and an imaging speed of 1 frame/s. The scanning depth is 8 mm. It was used to scan a 22 cm × 22 cm area of a human-shaped phantom, verifying its potential for scanning humans. The ability of the device to quantify SPIOs was validated using mice breast tumors. The quantitative accuracy was determined to be 96.58%.

CONCLUSION

Due to its innovative structural design and rapid frequency conversion method, the RFC-MPI device exhibits excellent in vivo imaging performance. Both simulation and phantom experiments have verified the effectiveness of the proposed method.

SIGNIFICANCE

The hand-held RFC-MPI device can effectively improve the spatial resolution and quantitative accuracy of multi-color MPI, laying the foundation for future clinical applications.

Sequential Scan-Based Single-Dimension Multi-Voxel System Matrix Calibration for Open-Sided Magnetic Particle Imaging

Open-sided magnetic particle imaging (OS-MPI) has garnered significant interest due to its potential for interventional applications. However, the system matrix calibration in OS-MPI using sequential scans is a time-consuming task and susceptible to the low signal-to-noise ratio (SNR) resulting from the small calibration sample size. These challenges have hindered the practical implementation of system matrix-based reconstruction for sequentially scanned OS-MPI. To address these issues, we propose a novel calibration method, named sequen- tial scan-based single-dimension multi-voxel calibration (SS-SDMVC), to efficiently obtain a high-SNR system matrix. This method was implemented in a cylindrical field of view (FOV), where a bar calibration sample parallel to the field-free line (FFL) was shifted along a fixed radial direction. A standard image reconstruction process was also introduced to verify the feasibility of SS-SDMVC. Through simulations, we analyzed the effects of noise levels and scanner imperfections on the SS-SDMVC-based reconstruction and demonstrated its robustness. In experiments, we compared the imaging performance of SS-SDMVC and the sequential scan-based traditional cubic-FOV SMC. The results showed that SS-SDMVC reduced the number of measurements by a factor of 210.94 and achieved higher reconstruction quality. Therefore, SS-SDMVC is expected to improve the reconstruction quality of human- scale or high-gradient FFL MPI scanners.

Implementation of the surface gradiometer receive coils for the improved detection limit and sensitivity in the single-sided MPI scanner

Objective.Magnetic Particle Imaging (MPI) promises to enhance diagnostic capabilities of the existing clinical imaging modalities. Traditional MPI scanners utilize cylindrical bore geometry that prevents scaling up the MPI to accommodate full human subject. Single-sided geometry, on the other hand, has all the hardware located on one side providing an unrestricted imaging volume.Approach.Our single-sided MPI device utilizes a field-free line topology with a single drive coil and a surface receive coil, which is used to detect the nanoparticles. Unlike closed bore systems, single-sided devices cannot adapt well established solenoid gradiometer receive coil, which result in impinging potential sensitivity gain.Main results.In this work we study multiple receive coil configurations with compensation for the purpose of removing feedthrough, whilst preserving the superparamagnetic iron oxide nanoparticle signal. Moreover, we present a compensated surface receive coil design that provides highest sensitivity in the single-sided geometry and demonstrate a new detection limit in a single-sided scanner of 100 ng of iron. In addition, we demonstrate 1D imaging of a sample without use of receive filter recovering signal at fundamental harmonic.Significance.These advancements in the receive chain are crucial for developing a practical MPI scanner with a single-sided geometry.

SPIONs Conjugate Supported Anticancer Drug Doxorubicin's Delivery: Current Status, Challenges, and Prospects

Considerable efforts have been directed towards development of nano-structured carriers to overcome the limitations of anticancer drug, doxorubicin's, delivery to various cancer sites. The drug's severe toxicity to cardio and hepatic systems, low therapeutic outcomes, inappropriate dose-demands, metastatic and general resistance, together with non-selectivity of the drug have led to the development of superparamagnetic iron oxide nanoparticles (SPIONs)-based drug delivery modules. Nano-scale polymeric co-encapsulation of the drug, doxorubicin, with SPIONs, the SPIONs surface end-groups' cappings with small molecular entities, as well as structural modifications of the SPIONs' surface-located functional end-groups, to attach the doxorubicin, have been achieved through chemical bonding by conjugation and cross-linking of natural and synthetic polymers, attachments of SPIONs made directly to the non-polymeric entities, and attachments made through mediation of molecular-spacer as well as non-spacer mediated attachments of several types of chemical entities, together with the physico-chemical bondings of the moieties, e.g., peptides, proteins, antibodies, antigens, aptamers, glycoproteins, and enzymes, etc. to the SPIONs which are capable of targeting multiple kinds of cancerous sites, have provided stable and functional SPIONs-based nano-carriers suitable for the systemic, and in vitro deliveries, together with being suitable for other biomedical/biotechnical applications. Together with the SPIONs inherent properties, and ability to respond to magnetic resonance, fluorescence-directed, dual-module, and molecular-level tumor imaging; as well as multi-modular cancer cell targeting; magnetic-field-inducible drug-elution capacity, and the SPIONs' magnetometry-led feasibility to reach cancer action sites have made sensing, imaging, and drug and other payloads deliveries to cancerous sites for cancer treatment a viable option. Innovations in the preparation of SPIONs-based delivery modules, as biocompatible carriers; development of delivery route modalities; approaches to enhancing their drug delivery-cum-bioavailability have explicitly established the SPIONs' versatility for oncological theranostics and imaging. The current review outlines the development of various SPIONs-based nano-carriers for targeted doxorubicin delivery to different cancer sites through multiple methods, modalities, and materials, wherein high-potential nano-structured platforms have been conceptualized, developed, and tested for, both, in vivo and in vitro conditions. The current state of the knowledge in this arena have provided definite dose-control, site-specificity, stability, transport feasibility, and effective onsite drug de-loading, however, with certain limitations, and these shortcomings have opened the field for further advancements by identifying the bottlenecks, suggestive and plausible remediation, as well as more clear directions for future development.