On the utilization of the adjoint method in microwave tomography.

In microwave imaging, the adjoint method is widely used for the efficient calculation of the update direction, which is then used to update the unknown model parameter. However, the utilization and the formulation of the adjoint method differ significantly depending on the imaging scenario and the applied optimization algorithm. Because of the problem-specific nature of the adjoint formulations, the dissimilarities between the adjoint calculations may be overlooked. Here, we have classified the adjoint method formulations into two groups: the direct and indirect methods. The direct method involves calculating the derivative of the cost function, whereas, in the indirect method, the derivative of the predicted data is calculated. In this review, the direct and indirect adjoint methods are presented, compared, and discussed. The formulations are explicitly derived using the two-dimensional wave equation in frequency and time domains. Finite-difference time-domain simulations are conducted to show the different uses of the adjoint methods for both single source-multiple receiver, and multiple transceiver scenarios. This study demonstrated that an appropriate adjoint method selection is significant to achieve improved computational efficiency for the applied optimization algorithm.

DEQ-MPI: A Deep Equilibrium Reconstruction With Learned Consistency for Magnetic Particle Imaging.

Magnetic particle imaging (MPI) offers unparalleled contrast and resolution for tracing magnetic nanoparticles. A common imaging procedure calibrates a system matrix (SM) that is used to reconstruct data from subsequent scans. The ill-posed reconstruction problem can be solved by simultaneously enforcing data consistency based on the SM and regularizing the solution based on an image prior. Traditional hand-crafted priors cannot capture the complex attributes of MPI images, whereas recent MPI methods based on learned priors can suffer from extensive inference times or limited generalization performance. Here, we introduce a novel physics-driven method for MPI reconstruction based on a deep equilibrium model with learned data consistency (DEQ-MPI). DEQ-MPI reconstructs images by augmenting neural networks into an iterative optimization, as inspired by unrolling methods in deep learning. Yet, conventional unrolling methods are computationally restricted to few iterations resulting in non-convergent solutions, and they use hand-crafted consistency measures that can yield suboptimal capture of the data distribution. DEQ-MPI instead trains an implicit mapping to maximize the quality of a convergent solution, and it incorporates a learned consistency measure to better account for the data distribution. Demonstrations on simulated and experimental data indicate that DEQ-MPI achieves superior image quality and competitive inference time to state-of-the-art MPI reconstruction methods.

Water-Based Route for Dopamine and Reduced Graphene Oxide Aerogel Production.

Water pollution caused by domestic waste oil and accidents with oil/organic spill needs immediate remediation, as such a pollution causes serious threats to health and the environment. Development of absorbent materials for the treatment of oil-polluted waters in a green and energy-efficient manner is highly desired. In this study, a green and simple strategy is proposed to prepare aerogels by hydrothermal reaction of graphene oxide (GO) dispersions using dopamine (DOPA) as the cross-linker. Concentrations of GO and DOPA were changed to determine their effects on absorption capacities. Aerogels produced had low densities ranging from 2.90 to 4.34 mg/cm3. Various organics, diesel oil, and sunflower oil were used to evaluate the absorption capacity of aerogels. It was observed that even with a mild thermal reduction at 150 °C, aerogels exhibited very high absorption capacities of up to 445 mg/mg. The produced aerogels showed high reusability (80%) and structural stability even after 10 absorption/desorption cycles. They possess great potential in oil/organic removal and water treatment based on their high absorption capacities and performances in separating organics/liquids from water.

Retrospective Analysis of Serology and Radiology Results in Patients with Suspected Cystic Echinococcosis Through 3 Years Period

OBJECTIVE: Cystic echinococcosis (CE), caused by the larval stage of Echinococcus granulosus sensu latu, is one of the neglected zoonotic infectious diseases and Türkiye is among the endemic countries. This study was designed to analyze serology results for patients who were diagnosed as CE by clinical symptoms and radiological methods over a three-year period. METHODS: Sera were analyzed for Anti-E. granulosus IgG by a chemiluminescence immunoassay (CLIA) (HYDATIDOSIS VIRCLIA® IgG MONOTEST, Vircell) using the VIRCLIA® (CLIA; Vircell, Granada, Spain) and results processed by the dedicated software. Cut-off for a positive test was ≥1.1 index value. Echinococcal cysts were detected based on ultrasonography, computed tomography, and magnetic resonance imaging. RESULTS: A total of 244 sera were analyzed from 109 patients, during three-year-period from January 2018 to December 2020. Anti-E. granulosus IgG was ordered twice in 89 patients, three times in 15 patients, four times in four patients, and five times in one patient. CLIA test was positive among 41 of 109 (37.6%) patients in whom 32 (76%) had only hepatic involvement, whereas in 5 (12%) hepatic and pulmonary involvement were coexisted. The mean age of seropositive patients was 39.8 (6-75±2.72) and 61.9% of them (n=26) were female. Time intervals between sequential test orders varied from 1 day to 33 months. Eight seropositive patients turned out to be negative, and one of 66 seronegative patients became seropositive. Positive test results were converted to negative in the case of therapy or cyst inactivity. CONCLUSION: We may conclude that CLIA could be used as a complementary tool for CE patient follow-up.

TranSMS: Transformers for Super-Resolution Calibration in Magnetic Particle Imaging.

Magnetic particle imaging (MPI) offers exceptional contrast for magnetic nanoparticles (MNP) at high spatio-temporal resolution. A common procedure in MPI starts with a calibration scan to measure the system matrix (SM), which is then used to set up an inverse problem to reconstruct images of the MNP distribution during subsequent scans. This calibration enables the reconstruction to sensitively account for various system imperfections. Yet time-consuming SM measurements have to be repeated under notable changes in system properties. Here, we introduce a novel deep learning approach for accelerated MPI calibration based on Transformers for SM super-resolution (TranSMS). Low-resolution SM measurements are performed using large MNP samples for improved signal-to-noise ratio efficiency, and the high-resolution SM is super-resolved via model-based deep learning. TranSMS leverages a vision transformer module to capture contextual relationships in low-resolution input images, a dense convolutional module for localizing high-resolution image features, and a data-consistency module to ensure measurement fidelity. Demonstrations on simulated and experimental data indicate that TranSMS significantly improves SM recovery and MPI reconstruction for up to 64-fold acceleration in two-dimensional imaging.

The effect of immunization with inactivated SARS-CoV-2 vaccine (CoronaVac) and/or SARS-CoV-2 infection on antibody levels, plasmablasts, long-lived-plasma-cells, and IFN-γ release by natural killer cells.

OBJECTIVES: We evaluated the antibody response, natural killer cell response and B cell phenotypes in healthcare workers (HCW) who are vaccinated with two doses of CoronaVac with or without documented SARS-CoV-2 infection and unvaccinated HCWs with SARS-CoV-2 infection. METHODS: HCWs were divided into four groups: vaccine only (VO), vaccine after SARS-CoV-2 infection (VAI), SARS-CoV-2 infection only (IO), and SARS-CoV-2 infection after vaccine (IAV). Anti-SARS-CoV-2 spike protein (Anti-S) antibodies were measured by Elecsys Anti-SARS-CoV-2 S ELISA kit. Memory B cells (CD19+CD27+), plasmablast B cells (CD19+CD138+) and long-lived plasma cells (LLPC; CD138+CD19-) were measured by flow cytometry in 74 patients. Interferon gamma (IFN-γ) release by natural killer (NK) cells were measured by NKVue Test (NKMAX, Republic of Korea) in 76 patients. RT-PCR was performed with Bio-speedy® COVID-19 qPCR detection kit, Version 2 (Bioexen LTD, Istanbul, Turkey). RESULTS: The Anti-S antibodies were detectable in all HCWs (n: 224). The median Anti-S titers (BAU/mL) was significantly higher in VAI (620 25-75% 373-1341) compared to VO (136, 25-75% 85-283) and IO (111, 25-75% 54-413, p < 0.01). VAI group had significantly lower percentage of plasmablasts (2.9; 0-8.7) compared to VO (6.8; 3.5-12.0) and IO (9.9; 4.7-47.5, p < 0.01) (n:74). Percentage of LLPCs in groups VO, VAI and IO was similar. There was no difference of IFN-γ levels between the study groups (n: 76). CONCLUSION: The antibody response was similar between uninfected vaccinated HCWs and unvaccinated HCWs who had natural infection. HCWs who had two doses of CoronaVac either before or after the natural SARS-CoV-2 infection elicited significantly higher antibody responses compared to uninfected vaccinated HCWs. The lower percentages of plasmablasts in the VAI group may indicate their migration to lymph nodes and initiation of the germinal center reaction phase. IFN-γ response did not differ among the groups.

Correlation of Treponemal Chemiluminescent Microparticle Immunoassay Screening Test Signal Strength Values With Reactivity of Confirmatory Testing.

BACKGROUND: Automated chemiluminescent microparticle immunoassays (CMIAs) are the most common first step at high-volume laboratories for syphilis screening. If the initial screening test is reactive, 1 more treponemal test is required, resulting in increased cost. In this multicenter study, we aimed to determine the correlation between the CMIA signal-to-cutoff ratio (S/Co) and the confirmatory tests to reduce unnecessary confirmatory testing. METHODS: Eight hospitals from 5 provinces participated in this study. All laboratories used Architect Syphilis TP CMIA (Abbott Diagnostics, Abbott Park, IL) for initial screening. Treponema pallidum hemagglutination (TPHA), rapid plasma reagin (RPR), and fluorescent treponemal antibody absorption (FTA-ABS) were used as confirmatory tests according to the reverse or European Centre for Disease Prevention and Control algorithms. A receiver operating characteristic analysis was used to determine the optimal S/Co ratio to predict the confirmation results. RESULTS: We evaluated 129,346 serum samples screened by CMIA between January 2018 and December 2020. A total of 2468 samples were reactive; 2247 (91%) of them were confirmed to be positive and 221 (9%) were negative. Of the 2468 reactive specimens, 1747 (70.8%) had an S/Co ratio ≥10.4. When the S/Co ratios were ≥7.2 and ≥10.4, the specificity values were determined to be 95% and 100%, respectively. In a subgroup of 75 CMIA-positive patients, FTA-ABS was performed and 62 were positive. Among these FTA-ABS-positive patients, 24 had an S/Co ratio <10.4, and negative TPHA and RPR. CONCLUSIONS: We propose a potentially cost-effective reverse screening algorithm with a treponemal CMIA S/Co ratio ≥10.4, obviating the need for secondary treponemal testing in about 71% of the screening-reactive samples. This would substantially reduce the confirmatory testing volume and laboratory expenses. However, in high-risk group patients with CMIA positive results, S/Co ratio <10.4, and negative TPHA and RPR, FTA-ABS may be used for confirmation.

Clinical Profile and Outcomes of Primary Immunodeficiency and Malignancy in Childhood at a Tertiary Oncology Center in Developing Country.

Primary immune deficiencies are a group of heterogenous genetic disorders characterized by frequent infections, autoimmunity and malignancy. In this study, we aimed to evaluate clinical characteristics, outcomes of children with malignancy developed on background of primary immunodeficiency and compare survival rates of patients between malignant lymphoma with primary immunodeficiency and without immunodeficiency from tertiary oncology center in a developing country. A total 23 patients with primary immunodeficiency and malignancy were evaluated retrospectively. A total of 26 malignancies (first or second) in 23 patients were determined. The median age at the time of the first malignancy was 8 years (ranges 2-18 years) with increased male ratio (M/F:14/9). Non-Hodgkin lymphoma (n = 17; 65%) was the most common malignancy, followed by Hodgkin lymphoma (n = 5), anaplastic ependymoma (n = 1), spinal glioblastoma multiforme (n = 1), retinoblastoma (n = 1) and intracranial hemangiopericytoma (n = 1). The median follow-up time of patients was 25 months (ranges between 1 and 189 months). The 5-year overall survival rate of patients with malignant lymphoma associated with primary immunodeficiency (41%) were lower than immunocompetent patients with malignant lymphoma (80%) (p = 0.000). The 5-year overall survival of patients was diagnosed between 2021 and 2013 years (62%) was higher than previous years (22%) (p = 0.03). In conclusion, non-Hodgkin lymphomas were the most common histopathologic type in patients with malignancy associated with primary immunodeficiency in the present study. The survival of patients with malignant lymphoma associated with primary immunodeficiency has improved in recent years, yet it is still lower than immunocompetent patients with lymphoma and new targeted drugs are required for better survival rates.

Evaluation of early-onset cardiotoxic effects of anthracyclines used during the treatment of childhood acute lymphoblastic leukemia by speckle-tracking echocardiography.

OBJECTIVE: Anthracyclines are widely used in the treatment of acute lymphoblastic leukemia (ALL). However, cardiotoxicity is the most critical side effect that requires dose limitation. It is thought to occur at first exposure, but the clinical presentation may occur years later. In this study, we aimed to determine the time of initial damage and cardiotoxicity that develops in children with ALL. METHODS: In this prospective study, 13 patients with newly diagnosed intermediate-risk precursor B cell ALL treated with the ALL-IC BFM 2009 protocol were included. Conventional echocardiography, tissue Doppler imaging (TDI), and speckle-tracking echocardiography (STE) were performed in all the patients before chemotherapy, after completing the induction phase, and at the end of the reinduction phase. RESULTS: The mean age of the patients was 7.8±4.6 (3.1-16.3) years. Myocardial velocity during systole (Sm) determined by TDI at the interventricular septum significantly decreased during the induction phase. Despite a decrease in STE parameters, a statistically significant reduction was determined in the global longitudinal strain rate at both left and right ventricles at the end of the induction. Nevertheless, a statistically significant increase was observed among the conventional echocardiographic findings in the left ventricular end-diastolic diameter at the end of the reinduction. CONCLUSION: During the treatment of ALL, subclinical anthracycline-associated cardiotoxicity develops in the early stages of treatment. The findings detected by TDI and STE could be missed by conventional echocardiography. We recommend evaluating patients with these newly developed techniques to detect subclinical cardiotoxicity at an early stage and starting appropriate therapy on time.

A Simulation Study for Three Dimensional Tomographic Field Free Line Magnetic Particle Imaging.

Magnetic Particle Imaging (MPI) is an emerging modality that images the magnetic nanoparticle distribution inside the body. The method is based on the non-linear response of the magnetic nanoparticles to an applied magnetic field. In this study, we present simulation results for three-dimensional (3D) tomographic imaging using an open-bore MPI system that can electronically scan a field free line (FFL). A field of view with 26×26×10 mm3 volume is imaged with a relatively low gradient field of 0.5 T/m. Imaging results for two 3D phantoms are presented: a letter phantom and a vessel phantom with stenosis regions. Using the system-matrix based reconstruction approach, the images were obtained with the Algebraic reconstruction technique (ART) and alternating direction method of multipliers (ADMM) methods. The stenosis regions were visually recognizable in high SNR conditions with ADMM. The effect of low gradient strength became prominent with increasing noise level, resulting in interlayer coupling artifacts.Clinical relevance- Magnetic Particle Imaging (MPI) is a new tracer-based imaging modality with high-spatiotemporal resolution. MPI can map quantitative distribution of super-paramagnetic iron oxide nanoparticles introduced inside the body. A field free line scanning MPI system with an open configuration can enable imaging of human-size volumes for interventional operations. In this study, we present simulation results for an FFL scanning open MPI system configuration to scan 3D field of view volume electronically. We analyze 3D imaging performance for various SNR levels at a low gradient value of 0.5 T/m that is relevant for clinical-size systems.

Interaction Structures in Psychodynamic Psychotherapy for Adolescents.

Despite advances in psychotherapy research showing an evidence-base for psychodynamic psychotherapy (PDT) in adolescents, developmentally specific treatment characteristics are under-researched. We aimed to identify interaction structures (IS: reciprocal patterns of in-session interactions involving therapist interventions, patient behaviors, and the therapeutic relationship) and assess associations between IS and outcome. The study cohort comprised 43 adolescents (Mage = 13.02 years) with nonclinical, internalizing, and comorbid internalizing-externalizing problems in PDT. A total of 123 sessions from different treatment phases were rated based on the Adolescent Psychotherapy Q-Set (APQ). Outcome was assessed with the Brief Problem Monitor-Youth (BPM-Y) administered repeatedly over the treatment course. Principal component analysis of APQ items resulted in five IS, named "Negative Therapeutic Alliance", "Demanding Patient, Accommodating Therapist", "Emotionally Distant Resistant Patient", "Inexpressive Patient, Inviting Therapist", and "Exploratory Psychodynamic Technique" (EPT). Multilevel modeling analyses with Bayesian Markov chain Monte Carlo (MCMC) estimations indicated a two-way interaction effect between EPT and problem levels at baseline such that patients with lower problems at baseline showed good outcome in the context of EPT, whereas an inverse relationship was found for patients with higher problems. Findings provide empirical evidence for characteristic components of PDT for adolescents and preliminary answers about who benefits from psychodynamic techniques.

Comparison of SARS-COV-2 antibody assays in PCR negative and PCR positive Turkish patients.

BACKGROUND: To the Editor, Serology may offer valuable information during COVID-19 pandemic; however, published papers mainly reported the results of symptomatic patients having positive RT-PCR on upper respiratory tract specimens [1]. More studies are needed to address whether asymptomatic patients, or patients with chest imaging compatible with COVID-19 but negative RT-PCR, have different antibody response that could influence assays performances. We wanted to share our data from Turkey where 4,323,596 COVID-19 cases were detected out of 44,087,628 PCR tests by April 20, 2021 but there are only a couple of published studies about serodiagnosis of the infection. DISCUSSION: The authors have no funding source for the study. The authors have no conflicts of interest to declare.

A Generalized Split-Step Angular Spectrum Method for Efficient Simulation of Wave Propagation in Heterogeneous Media.

Angular spectrum (AS) methods enable efficient calculation of wave propagation from one plane to another inside homogeneous media. For wave propagation in heterogeneous media such as biological tissues, AS methods cannot be applied directly. Split-stepping techniques decompose the heterogeneous domain into homogeneous and perturbation parts, and provide a solution for forward wave propagation by propagating the incident wave in both frequency-space and frequency-wavenumber domains. Recently, a split-step hybrid angular spectrum (HAS) method was proposed for plane wave propagation of focused ultrasound beams. In this study, we extend these methods to enable simulation of acoustic pressure field for an arbitrary source distribution, by decomposing the source and reflection spectra into orthogonal propagation direction components, propagating each component separately, and summing all components to get the total field. We show that our method can efficiently simulate the pressure field of arbitrary sources in heterogeneous media. The accuracy of the method was analyzed comparing the resultant pressure field with pseudospectral time domain (PSTD) solution for breast tomography and hemispherical transcranial-focused ultrasound simulation models. Eighty times acceleration was achieved for a 3-D breast simulation model compared to PSTD solution with 0.005 normalized root mean-squared difference (NRMSD) between two solutions. For the hemispherical phased array, aberrations due to skull were accurately calculated in a single simulation run as evidenced by the resultant-focused ultrasound beam simulations, which had 0.001 NRMSD with 40 times acceleration factor compared to the PSTD method.

Evaluation of phenotypic tests for detection of carbapenemases: New modifications with new interpretation.

INTRODUCTION: The emergence and spread of carbapenemase-producing Enterobacterales (CPE) is a worldwide public health threat. Rapid and accurate detection of CPE is essential to prevent their dissemination within health care settings. The aim of this study was to evaluate the performance of CIM, mCIM and mCIM with ammonium bicarbonate (mCIM-A) methods by using different interpretation criteria for detection of carbapenemases. METHODS: One hundred and fifty-three Klebsiella pneumoniae isolates previously characterized by molecular tests, including 133 carbapenemase producers and 20 non-carbapenemase producers, were collected in this study. CIM and mCIM tests were performed as described previously. mCIM-A by adding 50 mM ammonium bicarbonate to the bacterial suspension prepared in tryptic soy broth. The inhibition zone diameter of around meropenem disc was measured and interpreted as positive according to i) Pierce and colleagues (<19 mm), ii) EUCAST meropenem susceptibility breakpoint (<22). RESULTS: CIM, although seems to be good for carbapenemases other than OXA-48-like and NDM, is not satisfactory (42.3% and 83.4%, respectively) for those enzymes with any of the interpretation criteria. OXA-48-like and NDM were detected with a better performance (88.7% and 92.8, respectively) with mCIM when results were interpreted according to <22 mm zone diameter for OXA-48-like and NDM. The best results were obtained with mCIM-A using <22 mm criteria without any difference in the results of other enzymes and negative strains. CONCLUSIONS: mCIM-A method interpreted with <22 mm meropenem zone diameter seems to be preferable compared to CIM and mCIM. mCIM-A is simple and useful tool for identification of CPEs in clinical microbiology laboratories.

Evaluation of two commercial methods for rapid detection of the carbapenemase-producing Klebsiella pneumoniae.

In this study, we evaluated the performance of the two commercial methods (Rapidec Carba NP and NG-Test Carba-5) for the rapid detection of carbapenemase-producing Klebsiella pneumoniae. A total of 224 Klebsiella pneumoniae strains previously characterized for carbapenemase genes by polymerase chain reaction were included in the study. The strain collection included 30 non-carbapenemase producers, 85 OXA-48-like, 59 NDM, 14 IMP, 7 KPC, 7 VIM, 19 OXA-48-like plus NDM, and 3 KPC plus NDM producers. Rapidec Carba NP and NG-Test Carba 5 was performed according to the manufacturer's instructions. NG-Test Carba 5 correctly detected all carbapenemase-producing K. pneumoniae, however, Rapidec Carba NP failed to detect 41% of OXA-48-like producers even with extended incubation time. The overall sensitivity and specificity were 81,9% and 100% for Rapidec Carba NP, 100% and 100% for NG-Test Carba 5, respectively. Both tests seem to be fast and reliable for the detection of carbapenemase-producing K. pneumoniae especially for microbiology laboratories where molecular tests cannot be performed. However, Rapidec Carba NP with weak hydrolysis activity for OXA-48 like might be used in regions where OXA-48 is not prevalent. The additional advantage of NG-Test Carba 5 is that it specifically detects carbapenemases giving way to threat-related infections with an effective drug such as ceftazidime-avibactam or meropenem- vaborbactam.

Tomographic Field Free Line Magnetic Particle Imaging With an Open-Sided Scanner Configuration.

Superparamagnetic iron oxide nanoparticles (SPIONs) have a high potential for use in clinical diagnostic and therapeutic applications. In vivo distribution of SPIONs can be imaged with the Magnetic Particle Imaging (MPI) method, which uses an inhomogeneous magnetic field with a field free region (FFR). The spatial distribution of the SPIONs are obtained by scanning the FFR inside the field of view (FOV) and sensing SPION related magnetic field disturbance. MPI magnets can be configured to generate a field free point (FFP), or a field free line (FFL) to scan the FOV. FFL scanners provide more sensitivity, and are also more suitable for scanning large regions compared to FFP scanners. Interventional procedures will benefit greatly from FFL based open magnet configurations. Here, we present the first open-sided MPI system that can electronically scan the FOV with an FFL to generate tomographic MPI images. Magnetic field measurements show that FFL can be rotated electronically in the horizontal plane and translated in three dimensions to generate 3D MPI images. Using the developed scanner, we obtained 2D images of dot and cylinder phantoms with varying iron concentrations between 11 [Formula: see text]/ml and 770 [Formula: see text]/ml. We used a measurement based system matrix image reconstruction method that minimizes l1 -norm and total variation in the images. Furthermore, we present 2D imaging results of two 4 mm-diameter vessel phantoms with 0% and 75% stenosis. The experiments show high quality imaging results with a resolution down to 2.5 mm for a relatively low gradient field of 0.6 T/m.

Fast System Calibration With Coded Calibration Scenes for Magnetic Particle Imaging.

Magnetic particle imaging (MPI) is a relatively new medical imaging modality, which detects the nonlinear response of magnetic nanoparticles (MNPs) that are exposed to external magnetic fields. The system matrix (SM) method for MPI image reconstruction requires a time consuming system calibration scan prior to image acquisition, where a single MNP sample is measured at each voxel position in the field-of-view (FOV). The scanned sample has the maximum size of a voxel so that the calibration measurements have relatively poor signal-to-noise ratio (SNR). In this paper, we present the coded calibration scene (CCS) framework, where we place multiple MNP samples inside the FOV in a random or pseudo-random fashion. Taking advantage of the sparsity of the SM, we reconstruct the SM by solving a convex optimization problem with alternating direction method of multipliers using CCS measurements. We analyze the effects of filling rate, number of measurements, and SNR on the SM reconstruction using simulations and demonstrate different implementations of CCS for practical realization. We also compare the imaging performance of the proposed framework with that of a standard compressed sensing SM reconstruction that utilizes a subset of calibration measurements from a single MNP sample. The results show that CCS significantly reduces calibration time while increasing both the SM reconstruction and image reconstruction performances.

Trajectory analysis for field free line magnetic particle imaging.

PURPOSE: Magnetic particle imaging (MPI) is a relatively new method to image the spatial distribution of magnetic nanoparticle (MNP) tracers administered to the body with high spatial and temporal resolution using an inhomogeneous magnetic field. The spatial information of the MNP's is encoded using a field free point (FFP), or a field free line (FFL), in which the magnetic field vanishes at a point, or on a line, respectively. FFL scanning has the advantage of improved sensitivity compared to FFP scanning as a result of higher signal-to-noise ratio. The trajectory traversed by the FFL or FFP is an important parameter of the MPI system and should be selected to achieve the best imaging quality in minimum scan time, while considering hardware constraints and patient safety. In this study, we analyzed the image quality of different FFL trajectories for a large field of view (FOV) using simulations, to provide a baseline information for FFL scanning MPI system design. METHODS: We simulated a human-sized FFL scanning MPI configuration to image a circular FOV with 160 mm diameter, and compared Radial, Spiral, Uniform Spiral, Flower, and Lissajous trajectories with different trajectory densities scanned by the FFL for constant scan time. We analyzed the system matrices of the trajectories in terms of mutual coherence and homogeneity of the spatial sensitivity. We calculated the maximum electric fields induced on a homogeneous conductive body by the selection field (SF) and the focus field (FF) to compare the trajectories based on the nerve stimulation threshold. The images were obtained using the system matrix reconstruction approach with two different image reconstruction methods. In the first one, we used the conventional image reconstruction method, algebraic reconstruction technique (ART), which gives a regularized least-squares solution. In the second one, we used the state-of-the-art alternating direction method of multipliers (ADMM), which minimizes a weighted sum of the l1 -norm and the total variation (TV) of the images. RESULTS: The Radial and Spiral trajectories resulted in a poor imaging performance at low trajectory densities due to relatively high coherency and poor sensitivity of the measurements, respectively. For ART reconstruction, the highest image quality with the lowest trajectory density was achieved with the Uniform Spiral trajectory. Uniform Spiral, Flower, and Lissajous trajectories yielded comparable performance with ADMM reconstruction. The rotating SF induced higher electric field amplitude compared to the FF. Consequently, maximum allowable gradient at the same trajectory density was greater for the Radial trajectory compared to the other trajectories. CONCLUSIONS: For a large FOV coverage, the Uniform Spiral trajectory offers a good compromise between image quality and imaging time, taking safety and hardware limitations into account. The Radial trajectory, especially using l1 -norm and TV priors in the reconstruction, may be favorable in case the SF induced electric field is higher than that of the FF at the same frequency (e.g., relatively small FOV coverage). In general, ADMM reconstruction resulted in higher contrast and resolution compared to ART, leading to lighter requirements on the density of the trajectory.

Two-dimensional multi-frequency imaging of a tumor inclusion in a homogeneous breast phantom using the harmonic motion Doppler imaging method.

Harmonic motion microwave Doppler imaging (HMMDI) is a novel imaging modality for imaging the coupled electrical and mechanical properties of body tissues. In this paper, we used two experimental systems with different receiver configurations to obtain HMMDI images from tissue-mimicking phantoms at multiple vibration frequencies between 15 Hz and 35 Hz. In the first system, we used a spectrum analyzer to obtain the Doppler data in the frequency domain, while in the second one, we used a homodyne receiver that was designed to acquire time-domain data. The developed phantoms mimicked the elastic and dielectric properties of breast fat tissue, and included a [Formula: see text] mm cylindrical inclusion representing the tumor. A focused ultrasound probe was mechanically scanned in two lateral dimensions to obtain two-dimensional HMMDI images of the phantoms. The inclusions were resolved inside the fat phantom using both experimental setups. The image resolution increased with increasing vibration frequency. The designed receiver showed higher sensitivity than the spectrum analyzer measurements. The results also showed that time-domain data acquisition should be used to fully exploit the potential of the HMMDI method.