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.

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.

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.

Deep Learned Super Resolution of System Matrices for Magnetic Particle Imaging.

Magnetic Particle Imaging (MPI) is a new imaging technique that allows high resolution & high frame-rate imaging of magnetic nanoparticles (MNP). It relies on the nonlinear response of MNPs under a magnetic field. The imaging process can be modeled linearly, and then image reconstruction can be case as an inverse problem using a measured system matrix (SM). However, this calibration measurement is time consuming so it reduces practicality. In this study, we proposed a novel method for accelerating the SM calibration based on joint super-resolution (SR) and denoising of sensitivty maps (i.e., rows of SM). The proposed method is based on a deep convolutional neural network (CNN) architecture with residual-dense blocks. Model training was performed using noisy SM measurements simulated for varying MNP size and gradient strengths. Comparisons were performed against conventional low-resolution SM calibration, noisy high-resolution SM calibration, and bicubic upsampling of low-resolution SM. We show that the proposed method improves high-resolution SM recovery, and in turn leads to improved resolution and quality in subsequently reconstructed MPI images.

Fractal analysis as a useful predictor for determining osseointegration of dental implant? A retrospective study.

PURPOSE: The present study aimed at evaluating the effectiveness of fractal analysis on determining the osseointegration of dental implants. MATERIAL AND METHODS: In a single center, retrospective clinical trial, patients with dental implants in the mandibular premolar/molar region, ASA I-II and < 65-year-old patients were included. Orthopantomograph (OPG) were taken before implant surgery (t0), within a week of surgery (t1), and 1 (t2) and 2 (t3) months after surgery, respectively. Three regions of interest (ROIs) from mesial, distal, and apical sites of the implants were chosen and fractal analysis (FA) was conducted with the box-counting algorithm using White and Rudolph's method. RESULTS: A total of 39 patients 19 women and 20 men, with a mean age of 52.2 years (52.3 and 52.1 years, respectively) were included. The mean, minimum and maximum values of mesial (roi1), distal (roi2), and apical (roi3) surfaces were compared. The fractal dimension (FD) values of t1 were significantly lower compared with t0 as they decreased during the first week. FD values gradually increased after the first week although never exceeded the FD values of t0. Also, difference between mean FD values of t0 and t3 were found statistically significant (p < 0.05). DISCUSSION: FA is a promising and noninvasive method to predict osseointegration of a dental implant based on dental radiographs, and it can help shorten the total treatment time.

The evaluation of agreement between high-frequency ultrasonography and research diagnostic criteria for the diagnosis of temporomandibular joint internal derangements.

AIM: The aim of this study is to compare the diagnosis of patients with temporomandibular joint (TMJ) internal derangements which had been diagnosed using Research Diagnostic Criteria/Temporomandibular Disorders (RDC/TMD) with the dynamic high resolution sonography findings. SETTINGS AND DESIGN: Axis I section of RDC/TMD form had been applied to participants. Participants were divided into three groups as healthy TMJ, disc displacement with reduction, and disc displacement without reduction. The diagnoses had been compared with the dynamic high-resolution sonography findings. MATERIALS AND METHODS: Twelve of the patients had been treated with laser therapy, whereas 13 patients were treated with stabilization splint. Seventeen patients were treated with anterior repositioning splint (n = 42). After the application of different treatment modalities, the position of the articular disc had been determined with Axis I of RDC/ TMD form and dynamic high-resolution sonography. The findings were compared and statistically analyzed. STATISTICAL ANALYSIS USED: Statistical analyses of data were analyzed with Turcosa Cloud (Turcosa Ltd Co, Turkey). RESULTS: For the right TMJ, pretreatment and posttreatment ultrasonography (USG) diagnoses and RDC/ TMD clinical diagnoses were found similar (κ = 0.125-0.008). No statistically significant relationship was found (P > 0.05). For the left TMJ, pretreatment USG diagnosis and RDC/TMD clinical diagnose were found similar (κ = 0.070). No statistically significant relationship was found (P > 0.05). For the left TMJ, posttreatment USG diagnosis and RDC/TMD clinical diagnose were compared. A statistically significant difference was found (κ = 0.256). A statistically significant relationship was found (P < 0.05). CONCLUSIONS: Axis 1 of RDC/TMD form which is used for the diagnosis of internal derangements and dynamic high resolution sonography was not found in the agreement.

Effect of internal derangements and degenerative bone changes on the minimum thickness of the roof of the glenoid fossa in temporomandibular joint.

OBJECTIVES: The aim of this study is to investigate the effect of internal derangements and degenerative bone changes on the minimum thickness of the roof of the glenoid fossa (RGF). METHODS: MRI and cone beam CT records of temporomandibular joints (TMJ) of 68 patients were evaluated retrospectively in this study. The joints were divided into three groups according to TMJ disc status which had been diagnosed in MRI: normal disc status, anterior disc displacement with reduction, and anterior disc displacement without reduction. Cone beam CT was used to evaluate the degenerative bone changes of TMJ and to measure the minimum thickness of RGF. The joints were categorized as "with osteoarthritis (OA)" or "without OA". The findings of OA were determined as erosion, osteophyte, flattening, sclerosis, and pseudocyst. RESULTS: No significant relationship was found between gender and the thickness of RGF (p > 0.05). RGF was found significantly higher in "with OA" group compared to "without OA" group (p < 0.001). No significant difference was found between disc displacement groups for minimum thickness of RGF (p > 0.005). No significant difference was found between condyles without erosion and condyles with erosion for the minimum thickness of RGF (p = 0.272). In the present study, osteophyte, sclerosis, flattening, and pseudocyst were found to be associated with the minimum thickness of RGF. CONCLUSIONS: Osteophyte, flattening, pseudocyst, and sclerosis have an influence on RGF thickness. The minimum thickness of RGF is not significantly correlated with internal derangements. Erosion is not significantly correlated with RGF thickness. RGF thickness may be unaffected by the early stages of OA.

Masseter muscle thickness and elasticity in periodontitis.

This study aimed to compare the thickness and elasticity of the masseter muscle between patients with gingivitis and patients with periodontitis. A total of 124 patients (63 gingivitis, 61 chronic periodontitis) were recruited at the start of the study, but only 84 patients were declared as final participants. Patients were divided into two groups: (1) patients suffering from gingivitis and (2) those with generalized chronic periodontitis. Clinical (PI, plaque index; GI, gingival index; PD, probing depth; CAL, clinical attachment loss; and BOP, bleeding on probing scores) and ultrasonographic (thickness and elasticity of the masseter muscle) measurements of periodontitis were performed. There were no significant differences in gender, age, body mass index, education status, income level, or marital status between the two groups (P > 0.05). The mean age ± SD for the gingivitis and periodontitis groups was 39.5 ± 10.8 years and 44.8 ± 8.8 years, respectively. There were significant differences between the two groups in the number of PI, GI, PD, CAL, and BOP scores. There were significant differences between the two groups when thickness of masseter during contraction and at rest was taken into account. The gingivitis group had significantly thicker masseter during both contraction and rest. On the other hand, when the elasticity of the masseter was evaluated, there were no significant differences found between the two groups and two sides for each group. Masseter muscle thickness in the periodontitis group was found to be decreased compared with that in the gingivitis group. Furthermore, loss of periodontal tissues due to periodontitis reduces the masticatory ability.