Superparamagnetic Iron Oxide Tracer Research Articles

Abstract PO5-20-01: SENTINOT2- Use of superparamagnetic iron oxide tracer to avoid unnecessary sentinel lymph node biopsies

Abstract Background/Purpose: The use of superparamagnetic nanoparticles of iron oxide tracers (Magtrace) and electromagnetometers (SentiMag) for the detection of sentinel lymph nodes (SLN) during breast cancer surgery has been demonstrated to be noninferior to traditional radioisotope (RI) and blue dye detection, with additional safety benefits. Previous work has shown that transcutaneous detection of SLN with Magtrace/Sentimag is possible for over 30 days. Because of the safety, efficacy, and long detection window of Magtrace, we aim to investigate the use of Magtrace to prevent unnecessary SLN biopsies (SLNB) in breast cancer surgery. SLNB are commonly performed during breast conserving surgeries (BCS) or mastectomy for patients with a preoperative diagnosis of ductal carcinoma in-situ (DCIS). Because metastasis is not expected in patients diagnosed with DCIS, SLNB may be unnecessary and potentially harmful. However, in 15-25% of cases, unexpected invasive carcinoma is found during the post-surgical histopathological analysis of the resected breast tissue. For these cases, if SLNB are forgone during the initial surgery, SLNB during a second (delayed) procedure is the usual standard of care to evaluate SLN for metastasis. However, potential changes to lymphatic drainage following the initial resection may affect tracer localization to SLN. Consequently, we aim to compare SLN detection rates during delayed SLNB with Magtrace administered prior to initial BCS or mastectomy and subsequent RI tracer administered prior to delayed SLNB. Methods: SENTINOT2 is an ongoing international trial with BCM as the sole US site. For eligible patients with a preoperative diagnosis of DCIS, Magtrace will be administered prior to BCS or mastectomy. If invasive carcinoma is found from the post-surgical histopathological analysis, patients will receive delayed SLNB within 4 weeks of their initial surgery. Prior to delayed SLNB, patients will be randomized into two groups differing in the order of modality used for SLN detection (Magtrace or RI). Subjects with the following conditions will be excluded from the study: hypersensitivity to Magtrace, iron overload disease, pregnancy, and lactation. The total expected accrual for this study is 538 subjects globally and 50 subjects at BCM. Results: Currently, 19 patients have been enrolled in SENTINOT2. The subject population is 11% Asian, 26% Black/African American, and 47% Caucasian with non-Hispanic ethnicity. 5% of subjects identified as Hispanic Caucasian and 11% of subjects declined to report their race or ethnicity. 79% of patients had mastectomies, while 21% had BCS. After post-surgical histopathological analysis, 21% (4/19) patients were determined to have invasive carcinoma and received delayed SLNB. 50% (2/4) of these patients were randomized to have Magtrace as their first SLN detection modality (Mag-RI) while the other 50% (2/4) had RI as their first SLN detection modality (RI-Mag). Table 1 shows comparable SLN detection rates between Magtrace and RI for patients who received delayed SLNB. Only 1/4 patients showed SLN metastasis. For this patient, the positive SLN was successfully detected by both modalities. Conclusion: Magtrace has shown potential in delayed SLN detection and the use of Magtrace has prevented 79% (15/19) of enrolled patients from receiving unnecessary SLNB. Table 1. Number of Lymph Nodes (LN) Detected by Magtrace/Radioisotope, Biopsied and Positive for Metastasis Citation Format: Mary Bajomo, Ivan Marin, Jessica Montalvan, Margarita Riojas-Barrett, Logan Healy, Elizabeth Bonefas, Stacey Carter, Alastair Thompson. SENTINOT2- Use of superparamagnetic iron oxide tracer to avoid unnecessary sentinel lymph node biopsies [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-20-01.

Clinical Longevity of Preoperative Injection of Superparamagnetic Iron Oxide Nanoparticles for Delayed Sentinel Lymph Node Biopsy.

Diagnosis of ductal carcinoma in situ (DCIS) represents about 25% of newly diagnosed breast cancers. There is debate about the benefit of sentinel lymph node biopsy (SLNB) for further staging and guidance of therapy in patients with DCIS. Current guidelines recommend SLNB for patients undergoing breast-conserving therapy (BCT) for DCIS. Utilizing superparamagnetic iron oxide (SPIO) nanoparticles as a tracer may allow for a delayed SLNB (d-SLNB), typically within a month of injection. We present our experience with a patient who due to complications from surgery could not complete her d-SLNB for 165days. The SPIO tracer remained active in the lymph node and remained clinically useful for this five and a half month gap from time of injection. Further study is needed to determine the clinical longevity of SPIO in a lymph node.

Avoiding unnecessary sentinel lymph node biopsy with the use of superparamagnetic iron oxide mapping agents (Magtrace®) in breast surgery.

Superparamagnetic iron oxide (SPIO) (Magtrace®) is a non-radioactive liquid tracer that can stay in the sentinel lymph nodes for 30 days. Injection of SPIO at time of primary breast surgery where upfront sentinel lymph node biopsy (SLNB) is not immediately indicated allows for a return to theatre if pathology then identifies invasive disease. SLNB is associated with paraesthesia, pain, seroma formation and lymphoedema risk. Hence, our study aims to assess the use of SPIO to avoid upfront SLNB in breast surgery for ductal carcinoma in situ (DCIS) and prophylaxis. Retrospective single-centre study of consecutive patients who underwent injection of SPIO tracer at time of primary breast surgery to avoid upfront SLNB at Chris O'Brien Lifehouse, Sydney, NSW, Australia over a 10-month period. SPIO was injected 38 times, with 34 at time of mastectomy and four cases at time of wide local excision. The indication for surgery was DCIS in 18 cases, risk reduction in 17 cases and other indications in three patients. Six cases (15.8%) required delayed SLNB (D-SLNB) due to the finding of invasive disease on post-operative histopathology. All patients who underwent D-SLNB had nodes successfully localized with SPIO. In our cohort, 84.2% of cases were able to avoid upfront SLNB, and hence avoid the associated complications of SLNB. SPIO injection was successful in localizing the SLN in all cases at time of surgery for D-SLNB. This technique was safe with few associated complications.

Impact of low dose superparamagnetic iron oxide tracer for sentinel node biopsy in breast conserving treatment on susceptibility artefacts on magnetic resonance imaging and contrast enhanced mammography

BackgroundResidual particles of superparamagnetic iron oxide (SPIO) tracer, used for sentinel node biopsy, cause susceptibility artefacts on breast Magnetic Resonance Imaging (MRI). We investigated the impact of these artefacts on the imaging quality of MRI and explored whether contrast-enhanced mammography (CEM) could be an alternative in the follow-up of breast cancer patients. Materials and methodsData on patients’ characteristics, injection site, presence, size (mm) of artefacts on full-field digital mammography (FFDM)/CEM, MRI after 1 ml SPIO was recorded. Image quality scored by two breast radiologists using a 4-point Likert system: 0: no artefacts 1: good diagnostic quality 2: impaired but still readable 3: hampered clinical assessment. Continuous variables reported as means and standard deviations (SD), categorical variables as count and percentage. ResultsOn FFDM/CEM, performed 13 months postoperatively, no iron SPIO particles were detected, with a Likert score of 0. In all MRI (100%) images, executed at 16.6 months after SPIO injection, susceptibility artefacts at the injection sites i.e., retroareolair and lateral quadrant were observed with a mean size of 41.9 ± 9.8 mm (SD) by observer 1, and 44.8 ± 12.5 mm (SD) by observer 2, independent of the injection site. Both observers scored a Likert score of 2: locally impaired on all MRI images and sequences. ConclusionsEven 1 ml SPIO tracer used for sentinel node procedure impairs the evaluation of breast MRI at the tracer injection site beyond one year of follow-up. No impairment was observed on FFDM/CEM, suggesting that CEM might be a reliable alternative to breast MRI if required.

Assessing the sentimag system for guiding sentinel node biopsies in patients with breast cancer

ABSTRACT Introduction Sentinel lymph node biopsy for breast cancer is a method to localize and excise the first draining lymph node from an invasive cancer of the breast. The histopathologic evaluation of the sentinel lymph node is used for predicting recurrence and survival and thus, guiding oncologists for treatment-decision making to administer adjuvant therapies. The ability to identify the sentinel node depends on methods to map lymphatic drainage from the breast to the sentinel node and accurately discriminate that node from other non-sentinel lymph nodes of the axilla. Areas Covered This review covers the clinical demand for technologies to assist the surgeon in intraoperative lymphatic mapping to specifically identify the sentinel lymph node in patients with breast cancer. Performance characteristics are reviewed for superparamagnetic iron oxide tracers used in lymphatic mapping compared to other current available technologies for lymphatic mapping. Expert opinion The Magtrace (superparamagnetic iron oxide tracer) Sentimag (handheld magnetic probe) system is an FDA-approved technology for intraoperative lymphatic mapping to facilitate sentinel lymph node biopsy in breast cancer with technologic performance characteristics that are equivalent to 99Technetium-sulfur colloid. Barriers to broader utilization primarily center around the need for nonmetallic devices to be used for the conduct of surgery which would interfere with the paramagnetic method for tracer localization.

Combined use of magnetic seed and tracer in breast conserving surgery with sentinel lymph node biopsy for non-palpable breast lesions: A pilot study describing pitfalls and solutions

BackgroundsTraditionally, breast conserving surgery for non-palpable breast cancer is guided by wire or radioactive seed and radioactive tracer for sentinel lymph node biopsy (SLNB). Alternatively, a stain-less magnetic seed and superparamagnetic iron oxide tracer (SPIO) can be combined as a radioactive-free technique. The aim of this study was to define the pitfalls we encountered during implementation of this combined technique and provide solutions resulting in an instruction manual for a radio-active free procedure. MethodsBetween January and March 2021, seventeen consecutive patients with cN0 non-palpable breast cancer were included. The magnetic seed was placed to localize the lesion and SPIO was used to identify the sentinel lymph node (SLN). A lymphoscintigraphy with Technetium-99m nano colloid was performed concomitantly in all patients as a control procedure for SPIO. Surgical outcomes are reported, including problems with placing and retrieval of the seed and SPIO and corresponding solutions. ResultsSurgical excision was successful with invasive tumor-free margins in all patients. SLN detection was successful in 82% patients when compared to Technetium-99m. The most challenging issue was an overlapping magnetic signal of the seed and SPIO. Solutions are provided in detail. ConclusionsCombined use of magnetic seed and SPIO for wide local excision and SLNB patients with non-palpable breast lesions appeared challenging due to overlapping magnetic signals. After multiple adaptations, the protocol proved to be feasible with an added advantage of eliminating the use of radioisotopes. We described the pitfalls and solutions resulting in an instruction manual for a totally radioactive-free procedure.

An adapted protocol for magnetic localisation of nonpalpable breast cancer lesions and sentinel lymph nodes using a magnetic seed and superparamagnetic iron oxide tracer.

Localisation techniques for nonpalpable breast cancer lesions and sentinel lymph node biopsy (SLNB) are associated with several drawbacks. A complete magnetic technique using magnetic seeds and superparamagnetic iron oxide tracer could be an interesting alternative. This study describes a clear protocol and the results of a combined magnetic approach. From August 2021 to February 2022 40 patients undergoing breast conserving surgery with SLNB were eligible for inclusion. Localisation was performed under ultrasound or stereotactic guidance, 1 week before surgery. Subsequently, 1 ml of tracer was injected at least 4 cm away from the tumour. Technetium-99m (99m Tc) was injected 1 day before surgery as control procedure. Outcomes were SLNB time, a number of nodes detected with magnetic tracer including comparison with 99m Tc, a success rate of malignant lesion detection and pathological margin assessment. In total, 40 procedures were performed on 39 patients. A median of one node was retrieved. Sentinel nodes were retrieved using MagTrace® with a 92.5% detection rate compared to 99m Tc. Wide local excision under magnetic guidance was successful in 35 cases. This paper describes a combined magnetic approach for breast-conserving surgery and SLNB. An adapted protocol is described and could be used for implementation.

Weighted sum of harmonic signals for direct imaging in magnetic particle imaging

Objective. Magnetic particle imaging (MPI) is a novel radiation-free medical imaging modality that can directly image superparamagnetic iron oxide tracers (SPIOs) with high sensitivity, temporal resolution, and good spatial resolution. The MPI reconstruction task can be formulated mathematically as a Fredholm integral problem, but the concrete inversion is not easily possible because of the particle dynamics or scanner issues. Measurement based system matrix inversion takes these factors into account, but prior measurement and calibration are time consuming. Approach. We proposed a direct imaging method based on the weighted sum of harmonic signals. The harmonic signals with spatial information are obtained by the short-time Fourier transform, and odd harmonic components are selected for recombination and then mapped to the sampling trajectory to image the concentration distribution of SPIOs. In addition, we adopt a normalized-weighted sum of harmonics to improve the resolution of the native image. Main results. The effectiveness of the proposed method is verified by simulation imaging experiments and our in-house scanner-based experiments. Quantitative evaluation results show that compared with traditional methods, the structural similarity improved by 48%, mean square error decreased by 88%, and signal-to-artifact ratio increased by 2.5 times. Significance. The proposed method can rapidly image the concentration distribution of nanoparticles without any prior calibration measurements and reduce the blur of MPI images without deconvolution, which has the potential to be implemented as a multi-patch imaging method in MPI.

Sentinel lymph node mapping with superparamagnetic iron oxide for melanoma: a pilot study in healthy participants to establish an optimal MRI workflow protocol

BackgroundCurrent pre-operative Sentinel Lymph Node (SLN) mapping using dual tracing is associated with drawbacks (radiation exposure, logistic challenges). Superparamagnetic iron oxide (SPIO) is a non-inferior alternative for SLN mapping in breast cancer patients. Limited research has been performed on SPIO use and pre-operative MRI in melanoma patients to identify SLNs. MethodsHealthy participants underwent MRI-scanning pre- and post SPIO-injection during 20 min. Workflow protocols varied in dosage, massage duration, route of administration and injection sites. The first lymph node showing a susceptibility artefact caused by SPIO accumulation was considered as SLN.ResultsArtefacts were identified in 5/6 participants. Two participants received a 0.5 ml subcutaneous injection and 30-s massage, of which one showed an artefact after one hour. Four participants received a 1.0 ml intracutaneous injection and two-minute massage, leading to artefacts in all participants. All SLNs were observed within five minutes, except after lower limb injection (30 min).ConclusionSPIO and pre-operative MRI-scanning seems to be a promising alternative for SLN visualization in melanoma patients. An intracutaneous injection of 1.0 ml SPIO tracer, followed by a two-minute massage seems to be the most effective technique, simplifying the pre-operative pathway. Result will be used in a larger prospective study with melanoma patients.Trial registrationClinicalTrials.gov (NCT05054062) – September 9, 2021.

Superparamagnetic iron oxide: a novel tracer for sentinel lymph node detection in vulvar cancer

ObjectivesSuperparamagnetic techniques for sentinel lymph node (SLNs) biopsy in breast cancer is well recognized but remains novel in the literature in relation to early stage vulvar cancer. The aim of...

A randomized study comparing different doses of superparamagnetic iron oxide tracer for sentinel lymph node biopsy in breast cancer: The SUNRISE study

IntroductionThe non-radioactive method that uses the magnetic tracer (SPIO/Sienna) has shown to be a feasible technique for the SLN detection in breast cancer patients. The aim of this study is to assess the efficacy of different doses of a new magnetic tracer Sienna XP (Magtrace) compared to Tc-99 m and to evaluate its non-inferiority. MethodsPatients diagnosed with early-stage breast cancer cT1-3 N0, from October 2016 to August 2018 were eligible and consecutively randomized to three different doses of new SPIO used: group 1 (1 mL), group 2 (1.5 mL) and group 3 (2 mL). ResultsA total of 135 patients were included in the study, 45 in each group. Detection of SLNs with the three doses of Sienna XP (1 mL, 1.5 mL and 2 mL) showed non-inferior rates compared to the conventional technique with radiotracer (p = 0.654). Concordance by patients with SLN positive was 100% for all groups.83 (70.3%) patients reported skin staining at one month postoperatively, significantly lower in group 1 (p = 0.042). At 6 months follow up, group 1 remains with significantly lower skin discoloration (p = 0,01). In multivariate analysis, dose of 2 mL showed statistically significant for the skin staining. The majority of patients (70%) felt that skin discoloration does not represent a problem. ConclusionThe use of the Sienna XP magnetic tracer at 1 mL is not inferior to higher doses of magnetic tracer neither is inferior to radiotracer. 1 mL of magnetic tracer resulted in significantly less skin discoloration compared to higher doses.

Detection of the Sentinel Node Using a Magnetic Tracer in Thyroid Cancer. A Technical Pilot Study

IntroductionThere is no standard procedure for the detection of the sentinel node (SN) in thyroid disease. However, the recent detection of the SN using a paramagnetic tracer is proving to be useful in breast cancer and melanoma. The objective was to assess the utility of super paramagnetic iron oxide tracer for the intraoperative detection of the SN in patients with papillary thyroid cancer without nodal involvement in the preoperative study. MethodA single center, prospective pilot study of a class IIa medical device (a paramagnetic tracer). The study included thyroid cancers which were T1–T2 tumors in the cytohistological analysis with a negative preoperative nodal assessment, operated on consecutively during scheduled treatment. For the localization of the SN, an interlesional injection of 2mL of super paramagnetic iron oxide was administered. After 10min, ferromagnetic activity was detected in the adjacent nodes. Once the node had been detected, we proceeded by extracting it for intraoperative analysis. The effectiveness of the procedure for detecting the SN was assessed, with the main variable being whether it was detected or not. ResultsThe project was assessed after the first cases had been carried out. The SN was located in all cases, which was done easily in the first four, but in the fifth case the SN detection was complicated by the interference of the reusable neurostimulation electrodes with the ferromagnetic signal. Intraoperative histology revealed the SN was positive in 80% (n=4) of cases (20% [n=1] were macrometastases and 60% [n=3] micrometastases). Total thyroidectomies were carried out, with central lymph node dissection in 4 of the patients and lateral in one due to the result of the detected SN. The histology showed the carcinoma was papillary, a classic type, in 80% (n=4) and a follicular variant in 20% (n=1). Forty percent (n=2) were multifocal, 40% (n=2) had vascular infiltration, and 60% (n=3) had extrathyroidal extension. Staging determined the application of radioactive iodine therapy (150mCi) in 80% of cases (n=4). ConclusionsA paramagnetic tracer can be useful for detecting the SN and correctly staging papillary carcinoma.

Detección del ganglio centinela mediante trazador paramagnético en el cáncer de tiroides. Estudio piloto técnico

IntroductionThere is no standard procedure for the detection of the sentinel node (SN) in thyroid disease. However, the recent detection of the SN using a paramagnetic tracer is proving to be useful in breast cancer and melanoma. The objective was to assess the utility of super paramagnetic iron oxide tracer for the intraoperative detection of the SN in patients with papillary thyroid cancer without nodal involvement in the preoperative study. MethodA single center, prospective pilot study of a class IIa medical device (a paramagnetic tracer). The study included thyroid cancers which were T1-T2 tumors in the cytohistological analysis with a negative preoperative nodal assessment, operated on consecutively during scheduled treatment. For the localization of the SN, an interlesional injection of 2mL of super paramagnetic iron oxide was administered. After ten minutes, ferromagnetic activity was detected in the adjacent nodes. Once the node had been detected, we proceeded by extracting it for intraoperative analysis. The effectiveness of the procedure for detecting the SN was assessed, with the main variable being whether it was detected or not. ResultsThe project was assessed after the first cases had been carried out. The SN was located in all cases, which was done easily in the first four, but in the fifth case the SN detection was complicated by the interference of the reusable neurostimulation electrodes with the ferromagnetic signal. Intraoperative histology revealed the SN was positive in 80% (n=4) of cases (20% [n=1] were macrometastases and 60% [n=3] micrometastases). Total thyroidectomies were carried out, with central lymph node dissection in 4 of the patients and lateral in one due to the result of the detected SN. The histology showed the carcinoma was papillary, a classic type, in 80% (n=4) and a follicular variant in 20% (n=1). Forty percent (n=2) were multifocal, 40% (n=2) had vascular infiltration, and 60% (n=3) had extrathyroidal extension. Staging determined the application of radioactive iodine therapy (150mCi) in 80% of cases (n=4). ConclusionsA paramagnetic tracer can be useful for detecting the SN and correctly staging papillary carcinoma.

The accuracy of sentinel lymph node detection with a superparamagnetic iron oxide tracer (Sienna+®) in the setting of surgical breast biopsy

The accuracy of sentinel lymph node detection with a superparamagnetic iron oxide tracer (Sienna+®) in the setting of surgical breast biopsy

SentiDose – A dose optimizing study with a new superparamagnetic iron oxide tracer for sentinel lymph node detection

Background: Superparamagnetic iron oxide (SPIO) is a validated method of detecting sentinel lymph nodes (SN) in axillary staging for breast cancer patients without radioactivity. Several studies have shown non-inferiority compared to radiolabelled colloid and blue dye (Tc/BD). In this study a SPIO tracer (MagtraceTM) was evaluated, which is a new version of the currently available (Sienna+®). A handheld magnetometer (Sentimag®) was used for the detection of magnetically marked nodes. Aim of this prospective, double cohort study is the comparison of 1.5ml SPIO injected intra/perioperatively and 1.0 ml SPIO injected preoperatively (1-7 days) to the formerly assessed performance of Sienna+® (2ml + 3 ml saline) and to Tc/BD. Skin staining will also be compared. Herein, results from the first cohort are presented.

Improvement in breast magnetic resonance imaging after a sentinel procedure for breast cancer with superparamagnetic tracers

The superparamagnetic iron oxide tracer Sienna+® was introduced as an alternative to the radioisotope 99Tc Nanocoll to preoperatively mark sentinel lymph nodes in breast cancer. As previously reported, this tracer causes susceptibility artifacts on magnetic resonance imaging (MRI), potentially hampering the diagnostic performance of follow-up breast MRI. This short report illustrates the temporal development of these artifacts in a patient who was followed up at 6, 12, and 18 months after administration of Sienna+® with MRI systems of different magnetic field strengths (1.5 T and 3.0 T) and using an MRI protocol with sequences optimized for artifact reduction. Although the artifacts were severe and predominant at the higher magnetic strength in the early postoperative period, they diminished over time and the image quality could be further improved by adapting the sequences. These findings indicate the possible use of MRI even after administration of a superparamagnetic tracer for post-treatment monitoring in breast cancer.

Magnetic particle imaging for in vivo blood flow velocity measurements in mice

Magnetic particle imaging (MPI) is a new imaging technology. It is a potential candidate to be used for angiographic purposes, to study perfusion and cell migration. The aim of this work was to measure velocities of the flowing blood in the inferior vena cava of mice, using MPI, and to evaluate it in comparison with magnetic resonance imaging (MRI). A phantom mimicking the flow within the inferior vena cava with velocities of up to 21 cm s−1 was used for the evaluation of the applied analysis techniques. Time–density and distance–density analyses for bolus tracking were performed to calculate flow velocities. These findings were compared with the calibrated velocities set by a flow pump, and it can be concluded that velocities of up to 21 cm s−1 can be measured by MPI. A time–density analysis using an arrival time estimation algorithm showed the best agreement with the preset velocities. In vivo measurements were performed in healthy FVB mice (n = 10). MRI experiments were performed using phase contrast (PC) for velocity mapping. For MPI measurements, a standardized injection of a superparamagnetic iron oxide tracer was applied. In vivo MPI data were evaluated by a time–density analysis and compared to PC MRI. A Bland–Altman analysis revealed good agreement between the in vivo velocities acquired by MRI of 4.0 ± 1.5 cm s−1 and those measured by MPI of 4.8 ± 1.1 cm s−1. Magnetic particle imaging is a new tool with which to measure and quantify flow velocities. It is fast, radiation-free, and produces 3D images. It therefore offers the potential for vascular imaging.

Multi-Channel Acquisition for Isotropic Resolution in Magnetic Particle Imaging.

Magnetic Particle Imaging (MPI), a molecular imaging modality that images biocompatible superparamagnetic iron oxide tracers, is well-suited for clinical angiography, in vivo cell tracking, cancer detection, and inflammation imaging. MPI is sensitive and quantitative to tracer concentration, with a positive contrast that is not attenuated or corrupted by tissue background. Like other clinical imaging techniques, such as computed tomography, magnetic resonance imaging, and nuclear medicine, MPI can be modeled as a linear and shift-invariant system with a well-defined point spread function (PSF) capturing the system blur. The key difference, as we show here, is that the MPI PSF is highly dependent on scanning parameters and is anisotropic using only a single-imaging trajectory. This anisotropic resolution poses a major challenge for clear and accurate clinical diagnosis. In this paper, we generalize a tensor imaging theory for multidimensional x-space MPI to explore the physical source of this anisotropy, present a multi-channel scanning algorithm to enable isotropic resolution, and experimentally demonstrate isotropic MPI resolution through the construction and the use of two orthogonal excitation and detector coil pairs.

Tracking short-term biodistribution and long-term clearance of SPIO tracers in magnetic particle imaging

Magnetic particle imaging (MPI) is an emerging tracer-based medical imaging modality that images non-radioactive, kidney-safe superparamagnetic iron oxide (SPIO) tracers. MPI offers quantitative, high-contrast and high-SNR images, so MPI has exceptional promise for applications such as cell tracking, angiography, brain perfusion, cancer detection, traumatic brain injury and pulmonary imaging. In assessing MPI’s utility for applications mentioned above, it is important to be able to assess tracer short-term biodistribution as well as long-term clearance from the body. Here, we describe the biodistribution and clearance for two commonly used tracers in MPI: Ferucarbotran (Meito Sangyo Co., Japan) and LS-oo8 (LodeSpin Labs, Seattle, WA). We successfully demonstrate that 3D MPI is able to quantitatively assess short-term biodistribution, as well as long-term tracking and clearance of these tracers in vivo.

First in vivo magnetic particle imaging of lung perfusion in rats

Pulmonary embolism (PE), along with the closely related condition of deep vein thrombosis, affect an estimated 600 000 patients in the US per year. Untreated, PE carries a mortality rate of 30%. Because many patients experience mild or non-specific symptoms, imaging studies are necessary for definitive diagnosis of PE. Iodinated CT pulmonary angiography is recommended for most patients, while nuclear medicine-based ventilation/perfusion (V/Q) scans are reserved for patients in whom the use of iodine is contraindicated. Magnetic particle imaging (MPI) is an emerging tracer imaging modality with high image contrast (no tissue background signal) and sensitivity to superparamagnetic iron oxide (SPIO) tracer. Importantly, unlike CT or nuclear medicine, MPI uses no ionizing radiation. Further, MPI is not derived from magnetic resonance imaging (MRI); MPI directly images SPIO tracers via their strong electronic magnetization, enabling deep imaging of anatomy including within the lungs, which is very challenging with MRI. Here, the first high-contrast in vivo MPI lung perfusion images of rats are shown using a novel lung perfusion agent, MAA-SPIOs.