Phantom Experiments Research Articles

T2*-weighted imaging for detection of intracranial silicone oil in MRI obtained with motion correction sequences

Abstract Background For magnetic resonance imaging (MRI) findings of intracranial silicone oil migration, little has been described about images obtained with motion correction sequences such as MultiVane XD (Philips Healthcare) that provides high resolution diagnostic images even with severe patient motion. We report a case with intracranial silicone oil migration in which MRI was obtained with MultiVane XD and T2*-weighted imaging (T2*WI) was found the most useful in detecting intracranial silicone oil. Case presentation A 77-year-old female with a history of eye surgery using silicone oil referred to our hospital due to conscious disturbance. Head computed tomography demonstrated multiple intracranial masses whose signal density was similar to that in the operated eyeball and the tentative diagnosis of intracranial silicone oil migration was made. MRI was performed with MultiVane XD due to the significant patient’s restlessness, and among all sequences including T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), fluid-attenuated inversion recovery (FLAIR) and T2*WI, only T2*WI detected intracranial silicone oil. In contrast, another MRI obtained previously with conventional turbo spin-echo detected intracranial silicone oil not only in T2*WI but also in T1WI, T2WI and FLAIR. Phantom experiment revealed that chemical shift artifact played an important role in discriminating silicone oil from artificial cerebrospinal fluid, which attenuated in MultiVane XD. However, T2*WI still showed good discrimination of silicone oil even using MultiVane XD because of susceptibility artifacts. Conclusion T2*WI was the best sequence to detect intracranial silicone oil in MRI obtained with motion correction sequences because of its ability to depict the susceptibility artifacts.

A 60-channel high-density flexible receive array for pediatric abdominal MRI.

Conventional MRI coils offer suboptimal parallel imaging performance for young children. Our goal was to enhance imaging acceleration by dedicated, flexible high-density coil design for pediatric patients at 3T. We design, construct, and evaluate a highly flexible small loop array. Key design notes include full-wave simulation and analysis of the dual-turn loop, miniature feedboard allocation at the loop center, and cable management. Phantom experiments and adult and pediatric volunteer case studies were conducted to evaluate the small loop array imaging performance compared to commercial reference coils. Dual-turn loop configuration forms higher preamp decoupling impedance than the same size single-turn, supporting a flexible form factor that requires a wide range of critical overlap. Both phantom and in-vivo studies demonstrate superior parallel imaging performance or high spatial resolution imaging using the small loop, compared to commercial reference coils. A dedicated high-density coil array with a minimum inter-component interference layout design allows a flexible form factor and higher imaging accelerations. Phantom and in-vivo volunteer case studies demonstrate promising results in improving efficiency for pediatric patients in routine clinical imaging procedures.

Rapid and quantitative CEST-MRI sequence using water presaturation.

Despite the significant potential for in vivo metabolic imaging in preclinical and clinical applications, CEST MRI suffers from long scan time and inaccurate quantification. This study aims to suppress the contaminations among signals under different frequencies, which could shorten the TR and thereby facilitate CEST imaging acceleration and quantification. A novel sequence is proposed by applying a water-presaturation (WPS) module at the beginning of each TR. WPS CEST quickly knocks down the residual signal from previous TRs so that the magnetization of all TRs recovers from zero, which aligns well with the formula of quasi-steady-state theorem and enables accurate quantification within shorter TR. WPS CEST was assessed by simulations, creatine phantom, and healthy human brain scans at 3 T. In simulation and phantom experiment, WPS CEST allows accurate estimation of exchange rate (ksw) using omega plot and using shorter delay time (Td) and saturation time (Ts) (e.g., 1 s/1 s) compared with the conventional CEST. Simulations further showed that WPS CEST could obtain consistent spin-lock relaxation (R1ρ) values over varied Tds and Tss. Six human scans indicated that R1ρ collected from conventional sequences showed significant differences between two groups with Td and Ts of (1 s/1 s) and (2 s/2 s) (amide: 1.721 ± 0.051 s-1 vs. 1.622 ± 0.050 s-1, p = 0.001; nuclear Overhauser enhancement: 1.792 ± 0.046 s-1 vs. 1.687 ± 0.053 s-1, p = 0.004), whereas WPS CEST scans using these 2 Td/Ts values obtained the same mean R1ρ (amide: 1.616 ± 0.053 s-1 vs. 1.616 ± 0.048 s-1, p = 0.862; nuclear Overhauser enhancement: 1.688 ± 0.064 s-1 vs. 1.684 ± 0.054 s-1, p = 0.544). WPS CEST demonstrated accurate quantitation within shorter TR compared with conventional sequences, and thereby may allow rapid quantitative CEST scans in various situations.

Multidimensional RF pulse design with consideration of concomitant field effects.

To develop a small-tip multidimensional RF pulse design procedure that incorporates linear time-invariant gradient imperfections and concomitant field effects. This could be particularly important for contemporary low-field MRI systems with high-performance gradients. We developed an extension of the small-tip excitation k-space formalism, where concomitant fields were approximated as a Bloch-Siegert shift in the rotating frame. This was evaluated using realistic simulations of 2D selective excitation at various field strengths (0.2T, 0.55T, 1.5T, 3T, and 7T) with single and parallel transmit. Simulated excitation profiles from the original and extended k-space formalisms were compared. Experimental validations were performed at 0.55T with a single-channel transmit. The extended formalism provides improved 2D excitation profiles in all scenarios simulated, compared against the original formalism. The proposed method corrects the concomitant field effects on 2D selective excitations for B0 > 0.2T when the magnitude of the B0 is far larger than that of nonrotating concomitant fields. Simulation and phantom experiments at 0.55T match well for both original and proposed methods, with the proposed method providing sharper and more accurate excitation profiles at off-isocenter distances up to 15 cm. The impact of the proposed method is greatest in scenarios where concomitant fields are substantial, such as low field strengths and off-isocenter. Concomitant fields can be modeled as a Bloch-Siegert shift in the rotating frame during multidimensional RF pulse design, resulting in improved excitation profiles with sharp edges. This is important to consider for off-isocenter excitations and imaging at low field strengths with strong gradients.

MIRD Pamphlet No. 32: A MIRD Recovery Coefficient Model for Resolution Characterization and Shape-Specific Partial-Volume Correction.

Accurate quantification in emission tomography is essential for internal radiopharmaceutical therapy dosimetry. Mean activity concentration measurements in objects with diameters less than 10 times the full width at half maximum of the imaging system's spatial resolution are significantly affected (>10%) by the partial-volume effect. This study develops a framework for PET and SPECT spatial resolution characterization and proposes 2 MIRD recovery coefficient models-a geometric mean approximation (RECOVER-GM) and an empirical model (RECOVER-EM)-that provide shape-specific partial-volume correction (PVC). The models were validated using simulations and phantom experiments, with a comparative PVC test on ellipsoidal phantoms demonstrating that the RECOVER models significantly reduced error in activity quantification by factors of approximately 1.3-5.7 compared with conventional sphere-based corrections. The proposed recovery coefficient models and PVC methodology provide a robust framework for improved region-based PVC, including corrections for nonspherical tumor volumes. This work is part of the ongoing MIRDsoft.org project that aims to enhance accessibility to advanced dosimetry tools for improved disease characterization, treatment planning, and radiopharmaceutical therapy dosimetry.

Effectiveness of fat suppression methods and influence on proton-resonance frequency shift (PRFS) MR thermometry.

To evaluate the effectiveness of fat suppression techniques experimentally and illustrate their influence on the accuracy of PRFS MR-thermometry. The residual magnitudes of the main fat peaks are measured using a water-fat decomposition algorithm in an oil phantom and in vivo in swine bone marrow, either with spectral fat saturation (FS), water excitation (WE) or fast water excitation (FWE), as implemented on 1.5 T whole-body clinical MRIs. Thermometry experiments in tissue-mimicking oil-water phantoms (10 and 30 % fat) allow determining temperature errors in PRFS MR-thermometry with no fat suppression, FS and WE, compared against reference fiber optic thermometry. WE attenuates the signal of the main methylene fat peak more than FS (2 % and 22 % amplitude attenuation in the oil phantom, respectively), while the olefinic and glycerol peaks surrounding the water peak remain unaltered with both FS and WE. Within the 37 °C to 60 °C temperature range explored, FS and WE strongly attenuate temperature errors compared to PRFS without fat suppression. The residual fat signal after FS and WE leads to errors in PRFS thermometry, that increase with the fat content and oscillate with TE and temperature. In our tests limited to a single MR provider, fat suppression with WE appears to suppress fat signal more effectively. We propose a protocol to quantify the remaining fraction of each spectral fat peak after fat suppression. In PRFS thermometry, despite spectral fat suppression, the remnant fat signal leads to temperature underestimation or overestimation depending on TE, fat fraction and temperature range. Fat suppression techniques should be evaluated specifically for quantitative MRI methods such as PRFS thermometry.

Simultaneous acquisition of water, fat and velocity images using a phase-contrast 3p-Dixon method.

Phase-contrast MRI (2D PC-MRI) and Dixon techniques share the characteristic that the difference in frequency between water and fat, as well as the velocity, are encoded in the phase of the MR signal. We propose to take advantage of this characteristic to obtain both sets of images simultaneously. Such an acquisition will improve efficiency by obtaining both types of images in the same scan and will provide co-registered images of water-fat species and velocity images. This, in turn, will correct fat artifacts due to chemical shift in PC-MRI based measurements. This study presents a novel PC multi-echo (PCME-MRI) sequence jointly with a 3-point (3p-) Dixon pipeline that enables reconstruction of water, fat, and velocity images simultaneously. The proposed 3p-Dixon approach preserves the phase information of water-fat images, while velocity images are obtained from the resulting water components. Numerical phantom tests and 2D MR axial images of the neck acquired in 12 healthy volunteers demonstrated the feasibility of the PC 3p-Dixon method, showing comparable performance to standard techniques. In volunteers the median and range MAE comparing PC 3p-Dixon, and standard 3p-Dixon fat fraction were 0.06 and [0.03, 0.09]. The median and range of velocity for PC 3p-Dixon were 6.15 ml and [3.86, 7.21]ml, compared to 6.43 ml and [4.62, 8.27]ml obtained by 2D PC-MRI. Numerical phantom experiments and acquisitions from healthy volunteers showed promising results in fat fraction and velocity estimation of PC 3p-Dixon compared with standard 3p-Dixon and 2D PC-MRI, obtaining both data sets in similar times as standard 3p Dixon.

Implicit neural representation-based method for metal-induced beam hardening artifact reduction in X-ray CT imaging.

In X-ray computed tomography (CT), metal-induced beam hardening artifacts arise from the complex interactions between polychromatic X-ray beams and metallic objects, leading to degraded image quality and impeding accurate diagnosis. A previously proposed metal-induced beam hardening correction (MBHC) method provides a theoretical framework for addressing nonlinear artifacts through mathematical analysis, with its effectiveness demonstrated by numerical simulations and phantom experiments. However, in practical applications, this method relies on precise segmentation of highly attenuating materials and parameter estimations, which limit its ability to fully correct artifacts caused by the intricate interactions between metals and other dense materials, such as bone orteeth. This study aims to develop a parameter-free MBHC method that eliminates the need for accurate segmentation and parameter estimations, thereby addressing the limitations of the original MBHCapproach. The proposed method employs implicit neural representations (INR) to generate two tomographic images: one representing the monochromatic attenuation distribution at a specific energy level, and another capturing the nonlinear beam hardening effects caused by the polychromatic nature of X-ray beams. A loss function drives the generation of these images, where the predicted projection data is nonlinearly modeled by the combination of the two images. This approach eliminates the need for geometric and parameter estimation of metals, providing a more generalizedsolution. Numerical and phantom experiments demonstrates that the proposed method effectively reduces beam hardening artifacts caused by interactions between highly attenuating materials such as metals, bone, and teeth. Additionally, the proposed INR-based method demonstrates potential in addressing challenges related to data insufficiencies, such as photon starvation and truncated fields of view in CTimaging. The proposed generalized MBHC method provides high-quality image reconstructions without requiring parameter estimations and segmentations, offering a robust solution for reducing metal-induced beam hardening artifacts in CT imaging.

Incorporating Spatial and Spectral Saturation Modules Into MR Fingerprinting.

In this work, we introduce spatial and chemical saturation options for artefact reduction in magnetic resonance fingerprinting (MRF) and assess their impact on T1 and T2 mapping accuracy. An existing radial MRF pulse sequence was modified to enable spatial and chemical saturation. Phantom experiments were performed to demonstrate flow artefact reduction and evaluate the accuracy of the T1 and T2 maps. As an invivo demonstration, MRF of the prostate was performed on an asymptomatic volunteer using saturation modules to reduce flow-related artefacts. T1, T2 and B1 + maps obtained with and without saturation modules were compared. Application of spatial saturation in prostate MRF reduced streaking artefacts from the femoral vessels. When saturation is enabled T1 accuracy is preserved, and T2 accuracy remains acceptable up to approximately 100 ms. Chemical and spatial saturation can be incorporated into MRF sequences with limited impact on T1 accuracy. Further sequence optimisation may be needed to accurately estimate long T2 components. Spatial saturation modules have potential in prostate MRF applications as a means to reduce flow-related artefacts.

Photon-counting-detector CT outperforms state-of-the-art cone-beam and energy-integrated-detector CT in delineation of dental root canals

This experimental phantom study investigates current standard of care protocols in cone beam computed tomography (CBCT), energy-integrating-detector (EID) CT, and photon-counting-detector (PCD) CT regarding their potential in delineation of dental root canals. Artificial accessory canals (diameters: 1000, 600, 400, 300 and 200 μm) were drilled into three bovine teeth mounted on a bovine rib as a jaw substitute. The phantom was scanned in two dental CBCTs, two EID-CTs and a PCD-CT using standard clinical protocols. Scans from a micro-CT served as reference standard. Spatial resolution was evaluated via line profiles through the canals, whereby visibility compared to surrounding noise and compared to the ground truth were assessed. PCD-CT was able to delineate all artificial canals down to 200 μm diameter. In CBCT and EID-CT canals could only be reliably detected down to 300 μm. Also, PCD-CT showed a considerably smaller width-divergence from the ground trough with 4.4% at 1000 μm and 35.1% at 300 μm compared to CBCT (13.5 and 72.9%) and EID-CT (10.1 and 115.7%). PCD-CT provided superior resolution, accurate size measurement, and enhanced detection of small dental root canals, thereby offering improvements in diagnostic capabilities compared to CBCT and EID-CT systems.

A low-dose CT reconstruction method using sub-pixel anisotropic diffusion.

We present a new low-dose CT reconstruction method using sub-pixel and anisotropic diffusion. The sub-pixel intensity values and their second-order differences were obtained using linear interpolation techniques, and the new gradient information was then embedded into an anisotropic diffusion process, which was introduced into a penalty-weighted least squares model to reduce the noise in low-dose CT projection data. The high-quality CT image was finally reconstructed using the classical filtered back-projection (FBP) algorithm from the estimated data. In the Shepp-Logan phantom experiments, the structural similarity (SSIM) index of the CT image reconstructed by the proposed algorithm, as compared with FBP, PWLS-Gibbs and PWLS-TV algorithms, was increased by 28.13%, 5.49%, and 0.91%, the feature similarity (FSIM) index was increased by 21.08%, 1.78%, and 1.36%, and the root mean square error (RMSE) was reduced by 69.59%, 18.96%, and 3.90%, respectively. In the digital XCAT phantom experiments, the SSIM index of the CT image reconstructed by the proposed algorithm, as compared with FBP, PWLS-Gibbs and PWLS-TV algorithms, was increased by 14.24%, 1.43% and 7.89%, the FSIM index was increased by 9.61%, 1.78% and 5.66%, and the RMSE was reduced by 26.88%, 9.41% and 18.39%, respectively. In clinical experiments, the SSIM index of the image reconstructed using the proposed algorithm was increased by 19.24%, 15.63% and 3.68%, the FSIM index was increased by 4.30%, 2.92% and 0.43%, and the RMSE was reduced by 44.60%, 36.84% and 15.22% in comparison with FBP, PWLS-Gibbs and PWLS-TV algorithms, respectively. The proposed method can effectively reduce the noises and artifacts while maintaining the structural details in low-dose CT images.

Evaluation of Real-Time Cardiovascular Flow MRI Using Compressed Sensing in a Phantom and in Patients With Valvular Disease or Arrhythmia.

Real-time (RT) phase contrast (PC) flow MRI can potentially be used to measure blood flow in arrhythmic patients. Undersampled RT PC has been combined with online compressed sensing (CS) reconstruction (CS RT) enabling clinical use. However, CS RT flow has not been validated in a clinical setting. Evaluate CS RT in phantom and patients. Prospective. Flow phantom (60 cycles/min: N = 10, 120 cycles/min: N = 12), sinus rhythm patients, no regurgitation (N = 20) or suspected aortic regurgitation (N = 10), arrhythmia patients (N = 10). 1.5 T, 2D gated PC, CS RT PC, RT cine with arrhythmia rejection. Phantom experiments tested the accuracy of CS RT cardiac output and peak flow rate at 60 and 120 cycles/min against gated PC. For sinus rhythm patients, cardiac output, peak flow rate, and regurgitation fraction in the ascending aorta and/or pulmonary artery were evaluated against gated PC. Cardiac output in patients with arrythmia was evaluated against RT cine with arrhythmia rejection. Bland Altman, correlation, Mann-Whitney test, Wilcoxon signed-rank test. Cardiac output bias ± SD for CS RT in the phantom was -0.0 ± 0.2 L/min (0.5 ± 3%, P = 0.76) at 60 cycles/min and 0.2 ± 0.3 L/min (4 ± 4%, P = 0.0016) at 120 cycles/min. Correspondingly, peak flow rate bias was -23 ± 6 mL/s (-7 ± 2%, P < 0.0001) and -73 ± 25 mL/s (-23 ± 4%, P < 0.0001). In patients, regurgitant fraction was -4 ± 0.5% (-23 ± 4%, P = 0.0025). Cardiac output bias in patients in sinus rhythm was -0.1 ± 0.5 L/min (-2 ± 10%, P = 0.99) (with regurgitation) and -0.3 ± 0.6 L/min (-5 ± 11%, P = 0.035) (without regurgitation). Peak flow rate bias was -60 ± 31 mL/s (-13 ± 6%, P < 0.0001) (with regurgitation) and -64 ± 32 mL/s (-16 ± 8%, P < 0.0001) (without regurgitation). Cardiac output bias was -0.4 ± 0.6 L/min (-9 ± 11%, P < 0.003) in arrhythmia patients. CS RT flow could potentially serve as a clinical tool for patients with or without valvular disease or arrhythmia, with accurate cardiac output and regurgitation fraction quantification. Accurate flow assessment is important in clinical evaluation of cardiac patients, but in the presence of irregular heart rhythm flow assessment is challenging. We have evaluated a new method using cardiac magnetic resonance imaging and real-time flow for blood flow assessment in cardiac patients. The method was tested against a reference method in a phantom flow model in low and high heart rates, and in cardiac patients with and without irregular heart rhythm and in different vessels. We found the cardiac magnetic resonance imaging real time flow method accurate and therefore promising for clinical implementation. 1 TECHNICAL EFFICACY: Stage 1.

Deep proximal gradient network for absorption coefficient recovery in photoacoustic tomography

Objective.The optical absorption properties of biological tissues in photoacoustic (PA) tomography are typically quantified by inverting acoustic measurements. Conventional approaches to solving the inverse problem of forward optical models often involve iterative optimization. However, these methods are hindered by several challenges, including high computational demands, the need for regularization, and sensitivity to both the accuracy of the forward model and the completeness of the measurement data. The aim of this study is to introduce a novel learned iterative method for recovering spatially varying optical absorption coefficients (OACs) from PA pressure measurements.Approach.The study introduces a deep learning-based approach that employs the proximal gradient descent mechanism to achieve optical inversion. The proposed framework consists of multiple cascaded structural units, which iteratively update the absorption coefficients through a learning process, unit by unit.Main results.The proposed method was validated through simulations, phantom experiments, andin vivostudies. Comparative analyses demonstrated that the proposed approach outperforms traditional nonlearning and learning-based methods, achieving at least 12.85% improvement in relative errors, 3.50% improvement in peak signal-to-noise ratios, and 3.53% improvement in structural similarity in reconstructing the OAC distribution.Significance.This method significantly improves the accuracy and efficiency of quantitative PA tomography. By addressing key challenges such as computational demand and sensitivity to the accuracy of the forward model and the completeness of the measurement data, the proposed framework offers a more reliable and efficient alternative to traditional methods, with potential applications in medical imaging and diagnostics.

Investigation of identification size of liver tumor by open-ended coaxial probe

The open-ended coaxial probe method is the most commonly used approach for retrieving the dielectric properties of human tissues. This method is also often used to identify cancer because of the difference between the dielectric properties of normal and malignant tissues. This technique not only ensures quick measurement but also has a good identification effect. Although it has the potential to be utilized in tumor surgeries, its clinical application is hindered by the lack of an established identifiable tumor size. In this study, we examine the minimum detectable size of liver tumors by simulation and Mann–Whitney U test. Then, a phantom experiment was conducted to verify the simulation results. For Probes 1, 2, 3, and 4, the smallest cancer tumor detectable size is 0.59, 1.05, 1.85, and 2.95 mm radius, respectively. Furthermore, an evaluation approach for investigating the minimum detectable size of tumors through different probes is proposed. The results showed that the identification sizes were affected by the frequency and size of the probe. Moreover, the minimum detectable size of liver cancer and the crucial factors were investigated in this work.

Enhancement of structural and functional photoacoustic imaging based on a reference-inputted convolutional neural network.

Photoacoustic microscopy has demonstrated outstanding performance in high-resolution functional imaging. However, in the process of photoacoustic imaging, the photoacoustic signals will be polluted by inevitable background noise. Besides, the image quality is compromised due to the biosafety limitation of the laser. The conventional approach to improving image quality, such as increasing laser pulse energy or multiple-times averaging, could result in more health risks and motion artifacts for high exposures to the laser. To overcome this challenge of biosafety and compromised image quality, we propose a reference-inputted convolutional neural network (Ri-Net). The network is trained using the photoacoustic signal and noise datasets from phantom experiments. Evaluation of the trained neural network demonstrates significant signal improvement. Human cuticle microvasculature imaging experiments are also conducted to further assess the performance and practicality of our network. The quantitative results show that we achieved a 2.6-fold improvement in image contrast and a 9.6 dB increase in signal-to-noise ratio. Finally, we apply our network, trained on single-wavelength data, to multi-wavelength functional imaging. The functional imaging of the mouse ear demonstrates the robustness of our method and the potential to capture the oxygen saturation of microvasculature. The Ri-Net enhances photoacoustic microscopy imaging, allowing for more efficient microcirculation assessments in a clinical setting.

Brain temperature mapping based on chemical exchange saturation transfer signal at 2 ppm.

Brain temperature signifies the thermal homeostasis of the tissue, and may serve as a marker for neuroprotective therapy. Currently, it remains challenging to map the human brain temperature with high spatial resolution. The thermal dependence of chemical exchange saturation transfer (CEST) effects of endogenous labile protons may provide a promising mechanism for the absolute brain temperature imaging. In this study, we aimed to investigate the temperature dependency of the CEST effect of creatine (CrCEST), and contemplate its feasibility for brain temperature mapping. Creatine (Cr) was selected as the endogenous agent to probe the brain temperature. Proof-of-concept phantom experiments were first conducted using a 400 MHz nuclear magnetic resonance (NMR) spectrometer and a 5.0T magnetic resonance (MR) scanner at various temperatures. A multi-pool Lorentzian fitting model was utilized to quantify the apparent chemical shift, amplitude, linewidth, and integral of CrCEST peak at around 2 ppm. Regression analysis was performed to estimate the thermal response of these CrCEST parameters. Finally, the temperature mapping of ex vivo swine brain tissues was conducted based on the CEST signal at 2 ppm (CEST@2ppm). A robust linear correlation between the apparent chemical shift of CrCEST and temperature was identified in the in vitro phantom experiments (+0.005 ppm/℃, P<0.001), based on which temperature maps of phantoms were generated. In the subsequent experiments on ex vivo swine brain tissue, a comparable temperature dependency of the apparent chemical shift of CEST@2ppm peak was found (+0.008 ppm/℃), confirming the utility of this approach for mapping brain temperature. The CEST-based approach proposed in this study suggests a path toward label-free brain thermometry in vivo at high resolution and may be potentially applied in other tissues such as muscle and kidney.

Novel T1 Analysis Method to Address Reduced Measurement Accuracy Due to Irregular Heart Rate Variability in Myocardial T1 Mapping Using Polarity-corrected Inversion Time Preparation

Polarity-corrected inversion time preparation (PCTIP), a myocardial T1 mapping technique, is expected to reduce measurement underestimation in the modified Look-Locker inversion recover method. However, measurement precision is reduced, especially for heart rate variability. We devised an analysis using a recurrence formula to overcome this problem and showed that it improved the measurement accuracy, especially at high heart rates. Therefore, this study aimed to determine the effect of this analysis on the accuracy and precision of T1 measurements for irregular heart rate variability. A PCTIP scan using a 3T MRI scanner was performed in phantom experiment. We generated the simulated R-waves required for electrocardiogram (ECG)-gated acquisition using a signal generator set to 30 combinations. T1 map was generated using the signal train of the PCTIP images by nonlinear curve fitting using conventional and recurrence formulas. Accuracy against reference T1 and precision of heart rate variability were evaluated. To evaluate the fitting accuracy of both analyses, the relative fitting error was calculated. For the longer T1, the fitting error was larger than the short T1, with the conventional analysis showing 10.1±2.0%. The recurrence formula analysis showed a small fitting error less than 1%, which was consistent for all heart rate variability patterns. In the conventional analysis, the accuracy, especially for longer T1, showed a large underestimation of the measurements and poor linearity. However, in the recurrence formula analysis, the accuracy improved at a long T1, and linearity also improved. The Bland-Altman plot showed that it varied greatly depending on the heart rate variability pattern for the longer T1 in the conventional analysis, whereas the recurrence formula analysis suppressed this variation. T1 analysis of PCTIP using the recurrence formula analysis achieved accurate and precise T1 measurements, even for irregular heart rate variability.

A method of enhanced shear wave elastography based on Chirp coded excitation.

Shear Wave Elastography (SWE) is an imaging technique that detects shear waves generated by tissue excited by Acoustic Radiation Force (ARF), and characterizes the mechanical properties of soft tissue by analyzing the propagation velocity of shear wave. ARF induces a change in energy density through the nonlinear propagation of ultrasound waves, which drives the tissue to generate shear waves. However, the amplitude of shear waves generated by ARF is weak, and the shear waves are strongly attenuated in vivo. Furthermore, the shear waves are usually drowned out by noise at deep locations, which presents a challenge in the detection of shear waves and low signal-to-noise ratios. In this paper, we investigate the feasibility of applying the Chirp coded signal for shear wave excitation (Chirp-SWE) in ARF-based shear wave elastography. The use of Chirp coded excitation of push waveforms was employed to enhance the action of ARF, thereby effectively exciting shear waves. Comparative experiments were carried out with conventional sine long pulses (SWE) and the Barker coded signal (Barker-SWE). The analysis of theoretical and simulation results revealed that Chirp-SWE could increase the excitation energy by approximately 10% compared to conventional SWE and Barker-SWE. The results of the elastic phantom experiments demonstrated that the average peak axial particle velocity obtained by Chirp-SWE was approximately 30%-50% higher, which facilitated the formation of a more stable shear wave. Additionally, it exhibited a higher signal-to-noise ratio during elasticity measurements. The in vitro liver experiments further validated the feasibility of implementing Chirp-SWE in tissues. The results demonstrated the feasibility and advantages of Chirp coded excitation of push waveforms in improving shear wave elastography results. It is expected that this will enhance the accuracy and robustness of soft tissue elastography.

Synergistic microwave hyperthermia treatment for subcutaneous deep in situ breast cancer using conformal array antennas and a microwave-thermal-sensitive nanomaterial.

When microwave hyperthermia (MWH) array antenna technology is used to treat breast cancer, how to effectively target and heat deep tumors and reduce thermal damage to healthy tissues is still a challenge in clinical applications. In this study, the synergistic MWH effect of conformal-array antennas (CAA) and a novel microwave-thermal-sensitive nanomaterial (MTSN) was investigated for the treatment of subcutaneous deep in situ breast cancer. At the beginning of the study, the thermal damage score was used to evaluate the therapeutic efficacy of the CAA. It was found that although array antenna technology can achieve effective heating of deep tumors, its damage to healthy tissues is unacceptable. Consequently, we developed a novel MTSN, ZIF-8@HA, whose unique structure significantly enhanced the absorption of MW energy and MW thermal conversion efficiency in the local tumor region. The MW thermal conversion efficiency of ZIF-8@HA achieved was as high as 46.46% in in vivo MW heating experiments. In the phantom that simulates the electromagnetic environment of the human body, the microwave-thermal sensitization (MTS) effect is also significant, and the reduction in the average thermal damage score of healthy tissues by more than 10% was verified through measurements using the coaxial probe method and COMSOL simulations. Cellular experiments confirmed that the combination of ZIF-8@HA and MW irradiation could significantly reduce the survival rate of tumor cells. In addition, cross-tissue MW heating experiments revealed the advantages of ZIF-8@HA combined with the CAA. Finally, phantom experiments confirmed that the synergistic use of the CAA with ZIF-8@HA significantly accelerated the local heating rate of deep tumors, reduced the time required for the tumor region to achieve 100% thermal damage, and effectively minimized the thermal damage to healthy tissues.

High-speed tissue metabolism measurement using a combination of diffuse speckle contrast analysis and near-infrared spectroscopy

This study presents and validates a multimodal optical system combining diffuse speckle contrast analysis (DSCA) and near-infrared spectroscopy (NIRS) with a unique system design for high-speed tMRO2 monitoring. The optical system for simultaneous dual-wavelength illumination and detection by a single camera is constructed using dichroic mirrors without an external trigger device. Phantom experiments and in-vivo arterial occlusion tests are conducted by varying the camera exposure time from 0.5 ms to 10 ms to validate system performance. We analyze and compare the results according to the exposure time to acquire the optimal relative tMRO2 (rtMRO2) signal by dual-exposure time control. The in-vivo experiment confirmed that the relative blood flow (rBF) and tissue oxygenation index (TOI) signals from the two modalities had a trade-off with the camera exposure time. We obtained the optimal rtMRO2 using dual-exposure time control. We conclude that the proposed DSCA/NIRS provides real-time rtMRO2 assessment, which can provide biomarkers for diagnosing vascular diseases.