Body Coil Research Articles

Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor-equipped implants and parallel transmission.

To protect implant carriers in MRI from excessive radiofrequency (RF) heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant-related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (without implant) is ensured by state-of-the-art field simulations and the implant-specific hazard is quantified in situ using physical sensors. The concept is demonstrated by electromagnetic simulations performed on a human voxel model with a simplified spinal-cord implant in an eight-channel pTx body coil at . To integrate implant and native safety, the sensor signal must be calibrated in terms of an established safety metric (e.g., specific absorption rate [SAR]). Virtual experiments show that -field and implant-current sensors are well suited for this purpose, while temperature sensors require some caution, and probes are inadequate. Based on an implant sensor matrix , constructed in situ from sensor readings, and precomputed native SAR limits, a vector space of safe RF excitations is determined where both global (native) and local (implant-related) safety requirements are satisfied. Within this safe-excitation subspace, the solution with the best image quality in terms of magnitude and homogeneity is then found by a straightforward optimization algorithm. In the investigated example, the optimized pTx shim provides a 3-fold higher magnitude compared with circularly polarized excitation for a maximum implant-related temperature increase . To date, sensor-equipped implants interfaced to a pTx scanner exist as demonstrator items in research labs, but commercial devices are not yet within sight. This paper aims to demonstrate the significant benefits of such an approach and how this could impact implant-related RF safety in MRI. Today, the responsibility for safe implant scanning lies with the implant manufacturer and the MRI operator; within the sensor concept, the MRI manufacturer would assume much of the operator's current responsibility.

Investigating Local Receive Arrays in tcMRgFUS System and Their Influence by Passive Antennas: A Simulation Study.

Transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) revolutionizes non-invasive therapy by combining MRI and high-intensity focused ultrasound for precise thermal treatment. MRI scans play an essential role during tcMRgFUS treatment in that they are used to localize the target and monitor temperature. Using the body coil for MRI introduces imaging challenges, notably extremely low signal-to-noise ratio (SNR) and a distinct dark band in 3 Tesla brain images. This study explores the impact of diverse local receive coils on SNR and parallel imaging capabilities in tcMRgFUS. Simulation results underscore the significant SNR enhancement, especially with helmet-shaped coils, crucial for capturing signals from the head's top and sides. Additionally, the study delves into integrating passive antennas to address the dark band issue, revealing a combined improvement in SNR and transmit field recovery. The study demonstrates that even a coil array outside the water bath can enhance SNR. This work offers critical insights into optimizing the imaging quality, improving temperature mapping accuracy, and recovering the transmit field in tcMRgFUS technology, holding potential for refined treatment visualization, targeting precision, and real-time monitoring.

Is Hip Medial Ultrasound More Accurate Than Radiography for Determining the Status of Hip Reduction in Children Treated With a Spica Cast? A Retrospective Diagnostic Accuracy Study.

Is Hip Medial Ultrasound More Accurate Than Radiography for Determining the Status of Hip Reduction in Children Treated With a Spica Cast? A Retrospective Diagnostic Accuracy Study.

Evaluation of a novel 8-channel RX coil for speech production MRI at 0.55T.

Speech production MRI benefits from lower magnetic fields due to reduced off-resonance effects at air-tissue interfaces and from the use of dedicated receiver coils due to higher SNR and parallel imaging capability. Here we present a custom designed upper airway coil for 1H imaging at 0.55 Tesla and evaluate its performance in comparison with a vendor-provided prototype 16-channel head/neck coil. Four adult volunteers were scanned with both custom speech and prototype head-neck coils. We evaluated SNR gains of each of the coils over eleven upper airway volumes-of-interest measured relative to the integrated body coil. We evaluated parallel imaging performance of both coils by computing g-factors for SENSE reconstruction of uniform and variable density Cartesian sampling schemes with R = 2, 3, and 4. The dedicated coil shows approximately 3.5-fold SNR efficiency compared to the head-neck coil. For R = 2 and 3, both uniform and variable density samplings have g-factor values below 1.1 in the upper airway region. For R = 4, g-factor values are higher for both trajectories. The dedicated coil configuration allows for a significant SNR gain over the head-neck coil in the articulators. This, along with favorable g values, makes the coil useful in speech production MRI.

A pathway towards a two-dimensional, bore-mounted, volume body coil concept for ultra high-field magnetic resonance imaging.

Lack of a body-sized, bore-mounted, radiofrequency (RF) body coil for ultrahigh field (UHF) magnetic resonance imaging (MRI) is one of the major drawbacks of UHF, hampering the clinical potential of the technology. Transmit field (B1 ) nonuniformity and low specific absorption rate (SAR) efficiencies in UHF MRI are two challenges to be overcome. To address these problems, and ultimately provide a pathway for the full clinical potential of the modality, we have designed and simulated two-dimensional cylindrical high-pass ladder (2D c-HPL) architectures for clinical bore-size dimensions, and demonstrated a simplified proof of concept with a head-sized prototype at 7T. A new dispersion relation has been derived and electromagnetic simulations were used to verify coil modes. The coefficient of variation (CV) for brain, cerebellum, heart, and prostate tissues after B1 + shimming in silico is reported and compared with previous works. Three prototypes were designed in simulation: a head-sized, body-sized, and long body-sized coil. The head-sized coil showed a CV of 12.3%, a B1 + efficiency of 1.33 μT/√W, and a SAR efficiency of 2.14 μT/√(W/kg) for brain simulations. The body-sized 2D c-HPL coil was compared with same-sized transverse electromagnetic (TEM) and birdcage coils in silico with a four-port circularly polarized mode excitation. Improved B1 + uniformity (26.9%) and SAR efficiency (16% and 50% better than birdcage and TEM coils, respectively) in spherical phantoms was observed. We achieved a CV of 12.3%, 4.9%, 16.7%, and 2.8% for the brain, cerebellum, heart, and prostate, respectively. Preliminary imaging results for the head-sized coil show good agreement between simulation and experiment. Extending the 1D birdcage coil concept to 2D c-HPLs provides improved B1 + uniformity and SAR efficiency.

Comparison of SNR Assessment Techniques for Routine Multi-Element RF Coil QC Testing

In the UK, the Institute of Physics and Engineering in Medicine (IPEM) provides guidance to Medical Physics departments on appropriate Quality Control (QC) tests to evaluate MRI scanners used in routine clinical practice. The method recommended for the rigorous annual assessment of the SNR produced by RF coils uses a sequence and regions of interest (ROIs) recommended by IPEM, and calculates SNR through a subtraction calculation (IPEM recommended Method). This method was compared to alternative methods proposed by NessAiver at the 2019 American Association of Physicists in Medicine meeting in their talk on RF coil testing. Comparisons were completed for sequences and regions of interest (ROIs) recommended by IPEM and NessAiver. Testing was performed at 1.5 T using the scanner’s integrated body coil and at 3.0 T using a peripheral Head/Neck coil. Calculation of SNR using the mean of the background noise, assessed using the NessAiver recommended sequence and ROIs (NessAiver Noise-Average Method), typically offered the lowest variability in SNR results. Additionally, the SNR results produced by the IPEM Recommended Method were less repeatable than those from the NessAiver Noise-Average Method (p<0.001). Furthermore, the significance level to which a simulated reduction in SNR could be detected using the IPEM Recommended Method (p<0.001) was less than with the NessAiver Noise-Average Method (p≥0.0031). Finally, when comparing the test duration of each method, use of the NessAiver Noise-Average Method results in a 90% reduction in acquisition time per SNR result, when compared to the IPEM Recommended Method.

The effect of corpus callosum abnormalities on myelin development in the fetal brain using the fast macromolecular proton fraction mapping

INTRODUCTION: There is evidence, indicate early compensatory axonal remodeling connections in the prenatal period, providing a favorable neurological outcome in isolated anomalies of the corpus callosum (CC). Mapping of the macromolecular proton fraction (MPF) is proven method of quantitative determination of myelin, which has been adapted for prenatal studies.OBJECTIVE: To investigate the relationship between CC anomalies and prenatal myelination of the brain using the fast macromolecular proton fraction (MPF) mapping.MATERIALS AND METHODS: Fetal MR imaging were performed on a 1.5 scanner (Achieva, Philips) using a 16-channel body coil. Of 66 fetal brains MRI, 12 studies were selected with MT abnormalities (22.8±2.8, 19–28.5 WG) and 21 without brain pathology (23.1±2.3, 20–29.5 WG). The images were analyzed according to structural MRI data (T2-Ssh and T1-GE, EPI, DWI, MYUR, T2-BFE-DYN) by two experienced radiologists. Fast-3D-MPF scan protocol with the MPF maps reconstruction was carried out according to a specialized protocol (open-source software: https://www.macroatomicmri.org /). Quantitative data were obtained by choosing the region of interest (ROI) in numerous brain structures bilateral (bridge, medulla oblongata, thalamus, cerebellum, and cerebral hemispheres). Statistics: distinctions between the groups and structures were assessed using repeated-measures analysis of covariance (ANCOVA), Pearson correlation analysis.RESULTS: MPF was significantly increased in the CC anomalies group as compared to controls in the medulla (3.26±0.63% vs. 2.75±0.59%, р=0.001) and cerebellum (2.02±0.55% vs. 1.76±0.34%, р=0.006). In hemispheres significant correlation with GA was observed in CC anomalies group (r=0.81, р=0.002), but was absent in controls (r=0.32, р=0.16).CONCLUSION: Primary observed MPF increase in the medulla and cerebellum as well as the dependence of the large hemispheres myelination on gestational age indicates that fetal cerebral matter undergoes early compensatory axonal remodeling in the cases of the interhemispheric connections’ reduction.

Gelatin-Agar Liver Phantom to Simulate Typical Enhancement Patterns of Hepatocellular Carcinoma for MRI

Background: Hepatocellular carcinoma (HCC) is one of the most common cause of cancer-related deaths worldwide. The objective of this study is to detect the various stages of HCC through the utilization of a dynamic liver phantom with MRI. Methods: Three liver phantoms composed of different gelatin concentrations (2.5%wt, 4.0%wt, and 5.0%wt) and fixed agar concentrations were used. The HCC samples consisted of agarose and glycerol and were of varying sizes (0.5,1.0, and 2.0cm). The chemical, mechanical, electrical, and imaging properties of the phantoms were examined. The consistency of T1 and T2 signal intensities over a six-week period was studied. In addition, dynamic contrast-enhanced MRI was used to detect the HCC samples through the Dixon sequence. Results: The gelatin concentration of 5%wt was the most stable in regard to density, exhibited the lowest average compressive strength of 0.22MPa, and had the lowest electrical conductivity over the course of a six-week period. During this time, an increase in the T1 signal intensity was observed as the gelatin concentration in the sample increased. On the contrary, the least change in T1 and T2 was noted in the first sample with the 2.5% wt of gelatin. The HCC samples simulated the typical appearance of HCC, with the minimum sample size the body coil could detect being 1cm. Conclusion: Typical Enhancement patterns of HCC were simulated under MRI.

Longitudinal Stability of MRI QA up to Two Years on Eight Clinical 1.5 T MR-Linacs

MR-guided radiotherapy on hybrid MR-Linacs exploits the excellent soft-tissue contrast of MRI to deliver daily adaptive precision radiotherapy. Geometric fidelity and long-term stability of MRI components are essential, but their longitudinal performance under daily exposure to scattered ionizing radiation is unknown. We report on longitudinal stability of periodic MRI QA on eight clinical 1.5T MR-Linac systems. We provided measurement instructions for periodic MRI QA and received data from seven different centers within the Elekta MR-Linac consortium, which contributed data over acquisition periods ranging from 3–24 months. We tested B0 and B1 homogeneity using a 37 cm diameter cylindrical phantom, which was measured monthly in axial orientation, supplemented by quarterly sagittal and coronal acquisitions. We report average, standard deviation and peak-to-peak variation (99th-1st percentile) within a region of interest (ROI) of 35 cm diameter. Dependence of B0 on the gantry angle and gradient non-linearity were tested quarterly. We analyzed the longitudinal stability of selected metrics of the vendor-provided periodic image quality tests. We found high temporal stability of B0 and B1 measurements and good agreement between different MR-Linac systems. For all measurements, the standard deviation of B0 within the analyzed ROI was below 0.66/0.33/0.33 ppm for axial/sagittal/coronal orientation. The average standard deviation of the ratio between actual and nominal flip angle was 0.022/0.100/0.088 for axial/sagittal/coronal orientation. Systems exhibited distinctively different gantry angle dependencies of B0, with sensitivities of B0 to the gantry angle differing by factors of up to two between systems. Gradient non-linearity analysis yielded average radii of 172 and 242 mm for which 98% of the phantom markers had deviations below 1 and 2 mm, respectively. All analyzed periodic image quality tests were passed, but major events including a body coil replacement and ramp down were apparent in the time series. Overall we found very similar performance of the tested systems and our results could inform the implementation of MR imaging QA for MR-Linacs. While we found differences of the gantry angle dependence of B0 between systems, the high temporal stability found for all tests is a foundation for stereotactic radiotherapy and multi-center clinical trials involving quantitative MRI.

QUANTIFICATION OF LIVER IRON IN CHRONIC LIVER DISEASE USING 3 TESLA MRI

Aims And Objectives: 1. To assess the feasibility and evaluate the performance of various 3 Tesla MR imaging techniques in the detection and quantication of hepatic iron in patients with chronic liver disease. 2.To understand the scope of liver diseases with respect to iron deposition and to dene a correlation between liver disease and liver iron concentration. Materials And Methods: Present prospective cross-sectional study was carried out during the period of December 2019 to May 2021 in 31 patients with chronic liver disease who underwent MR imaging using 3T MR scanner (General Electric, Signa Pioneer) with a body coil. Liver signal intensity in three different locations were measured. The L/M ratio (signal intensity ratio/SIR) was calculated by dividing mean liver signal intensity by mean muscle signal intensity. The T2* and R2* method was also carried out from the same sequence. The Liver Iron Concentration (LIC) was obtained from R2* and SIR using the DICOM Software MRQuantif. Results: Among the 31 patients studied, 16 of them had serum ferritin ≤464 μg/dL and 15 had Serum Ferritin &gt;464 μg/Dl and 14 of them had TIBC &lt;261 μg/dL and 17 had TIBC ≥261 μg/dL. A statistically signicant (p = &lt;0.001) strong negative correlation was established between Serum Ferritin and T2*and a statistically signicant strong positive correlation was established between TIBC and T2* Considering Liver Iron Concentration, there was a statistically signicant strong positive correlation between LIC and Serum Ferritin, and a statistically signicant strong negative correlation between TIBC and LIC. Conclusion: SIR and T2* MR imaging techniques are feasible in determining and quantifying hepatic iron in patients with chronic liver disease. From our study ndings we could dene a positive correlation between liver disease and liver iron concentration

Synthetic MRI for Radiotherapy Planning for Brain and Prostate Cancers: Phantom Validation and Patient Evaluation.

PurposeWe aimed to evaluate the accuracy of T1 and T2 mappings derived from a multispectral pulse sequence (magnetic resonance image compilation, MAGiC®) on 1.5-T MRI and with conventional sequences [gradient echo with variable flip angle (GRE-VFA) and multi-echo spin echo (ME-SE)] compared to the reference values for the purpose of radiotherapy treatment planning.MethodsThe accuracy of T1 and T2 measurements was evaluated with 2 coils [head and neck unit (HNU) and BODY coils] on phantoms using descriptive statistics and Bland–Altman analysis. The reproducibility and repeatability of T1 and T2 measurements were performed on 15 sessions with the HNU coil. The T1 and T2 synthetic sequences obtained by both methods were evaluated according to quality assurance (QA) requirements for radiotherapy. T1 and T2 in vivo measurements of the brain or prostate tissues of two groups of five subjects were also compared.ResultsThe phantom results showed good agreement (mean bias, 8.4%) between the two measurement methods for T1 values between 490 and 2,385 ms and T2 values between 25 and 400 ms. MAGiC® gave discordant results for T1 values below 220 ms (bias with the reference values, from 38% to 1,620%). T2 measurements were accurately estimated below 400 ms (mean bias, 8.5%) by both methods. The QA assessments are in agreement with the recommendations of imaging for contouring purposes for radiotherapy planning. On patient data of the brain and prostate, the measurements of T1 and T2 by the two quantitative MRI (qMRI) methods were comparable (max difference, <7%).ConclusionThis study shows that the accuracy, reproducibility, and repeatability of the multispectral pulse sequence (MAGiC®) were compatible with its use for radiotherapy treatment planning in a range of values corresponding to soft tissues. Even validated for brain imaging, MAGiC® could potentially be used for prostate qMRI.

Characterization of mesenteric and portal hemodynamics using 4D flow MRI: the effects of meals and diurnal variation.

To determine the variability of blood flow measurements using 4D flow MRI in the portal and mesenteric circulations and to characterize the effects of meal ingestion, time of day, and between-day (diurnal) variations on portal and mesenteric hemodynamics. In this IRB-approved and HIPAA-compliant study, 7 healthy and 7 portal hypertension patients imaged. MRI exams were conducted at 3T using a 32-channel body coil with large volumetric coverage and 1.25-mm isotropic true spatial resolution. Blood flow was quantified (L/min) in the hepatic and splanchnic vasculature. The first MR scan was performed after at least 8h of fasting. Subsequently, subjects ingested 574mL EnSure Plus® orally. A second acquisition was started 20min after the meal ingestion. A third scan was performed before lunch and a fourth acquisition took place 20min after lunch. A fifth scan was performed around 4pm. Finally, subjects returned one week later for a repeat morning visit, with identical conditions as the first visit. In healthy controls significant increase in blood flow was seen in the PV, SMV, SMA, HA, and SCAo in response to breakfast but only the SCAo, SMA, SMV, and PV had a significant response to lunch. In general, patients with cirrhosis showed reduced response to meals compared to that in healthy controls. Additionally, PV flow in patients had the highest value in the afternoon. Effects of meal ingestion, time of day, and between-day variations were characterized using Radial 4D flow MRI in patients with cirrhosis and healthy controls.

Correcting inter-scan motion artifacts in quantitative R1 mapping at 7T.

PurposeInter‐scan motion is a substantial source of error in R1 estimation methods based on multiple volumes, for example, variable flip angle (VFA), and can be expected to increase at 7T where B1 fields are more inhomogeneous. The established correction scheme does not translate to 7T since it requires a body coil reference. Here we introduce two alternatives that outperform the established method. Since they compute relative sensitivities they do not require body coil images.TheoryThe proposed methods use coil‐combined magnitude images to obtain the relative coil sensitivities. The first method efficiently computes the relative sensitivities via a simple ratio; the second by fitting a more sophisticated generative model.Methods R1 maps were computed using the VFA approach. Multiple datasets were acquired at 3T and 7T, with and without motion between the acquisition of the VFA volumes. R1 maps were constructed without correction, with the proposed corrections, and (at 3T) with the previously established correction scheme. The effect of the greater inhomogeneity in the transmit field at 7T was also explored by acquiring B1+ maps at each position.ResultsAt 3T, the proposed methods outperform the baseline method. Inter‐scan motion artifacts were also reduced at 7T. However, at 7T reproducibility only converged on that of the no motion condition if position‐specific transmit field effects were also incorporated.ConclusionThe proposed methods simplify inter‐scan motion correction of R1 maps and are applicable at both 3T and 7T, where a body coil is typically not available. The open‐source code for all methods is made publicly available.

Study on the radiofrequency transparency of electrically floating and ground PET inserts in a 3T clinical MRI system.

The positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system that implements the radiofrequency (RF) built-in body coil of the MRI system as a transmitter is designed to be RF-transparent, as the coil resides outside the RF-shielded PET ring. This approach reduces the design complexities (e.g., large PET ring diameter) related to implementing a transmit coil inside the PET ring. However, achieving the required field transmission into the imaging region of interest (ROI) becomes challenging because of the RF shield of the PET insert. In this study, a modularly RF-shielded PET insert is used to investigate the RF transparency considering two electrical configurations of the RF shield, namely the electrical floating and ground configurations. The purpose is to find the differences, advantages and disadvantages of these two configurations. Eight copper-shielded PET detector modules (intermodular gap: 3mm) were oriented cylindrically with an inner diameter of 234mm. Each PET module included four-layer Lutetium-yttrium oxyorthosilicate scintillation crystal blocks and front-end readout electronics. RF-shielded twisted-pair cables were used to connect the front-end electronics with the power sources and PET data acquisition systems located outside the MRI room. In the ground configuration, both the detector and cable shields were connected to the RF ground of the MRI system. In the floating configuration, only the RF shields of the PET modules were isolated from the RF ground. Experiments were conducted using two cylindrical homogeneous phantoms in a 3T clinical MRI system, in which the built-in body RF coil (a cylindrical volume coil of diameter 700mm and length 540mm) was implemented as a transceiver. For both PET configurations, the RF and MR imaging performances were lower than those for the MRI-only case, and the MRI system provided specific absorption ratio (SAR) values that were almost double. The RF homogeneity and field strength, and the signal-to-noise ratio (SNR) of the MR images were mostly higher for the floating PET configuration than they were for the ground PET configuration. However, for a shorter axial field-of-view (FOV) of 125mm, both configurations offered almost the same performance with high RF homogeneities (e.g., 76±10%). Moreover, for both PET configurations, 56±6% larger RF pulse amplitudes were required for MR imaging purposes. The increased power is mostly absorbed in the conductive shields in the form of shielding RF eddy currents; as a result, the SAR values only in the phantoms were estimated to be close to the MRI-only values. The floating PET configuration showed higher RF transparency under all experimental setups. For a relatively short axial FOV of 125mm, the ground configuration also performed well which indicated that an RF-penetrable PET insert with the conventional design (e.g., the ground configuration) might also become possible. However, some design modifications (e.g., a wider intermodular gap and using the RF receiver coil inside the PET insert) should improve the RF performance to the level of the MRI-only case.

Characterization of a Low-Profile, Flexible, and Acoustically Transparent Receive-Only MRI Coil Array for High Sensitivity MR-Guided Focused Ultrasound.

Magnetic resonance guided focused ultrasound (MRgFUS) is a non-invasive therapeutic modality for neurodegenerative diseases that employs real-time imaging and thermometry monitoring of targeted regions. MRI is used in guidance of ultrasound treatment; however, the MR image quality in current clinical applications is poor when using the vendor built-in body coil. We present an 8-channel, ultra-thin, flexible, and acoustically transparent receive-only head coil design (FUS-Flex) to improve the signal-to-noise ratio (SNR) and thus the quality of MR images during MRgFUS procedures. Acoustic simulations/experiments exhibit transparency of the FUS-Flex coil as high as 97% at 650 kHz. Electromagnetic simulations show a SNR increase of 13× over the body coil. In vivo results show an increase of the SNR over the body coil by a factor of 7.3 with 2× acceleration (equivalent to 11× without acceleration) in the brain of a healthy volunteer, which agrees well with simulation. These preliminary results show that the use of a FUS-Flex coil in MRgFUS surgery can increase MR image quality, which could yield improved focal precision, real-time intraprocedural anatomical imaging, and real-time 3D thermometry mapping.

A single-center experience of magnetic resonance imaging findings of fetal sacrococcygeal teratomas.

Sacrococcygeal teratomas (SCT) are known as rare tumors, but they are the most common tumor in fetuses and newborns. This study aims to present fetal magnetic resonance imaging (MRI) findings of SCT diagnosed prenatally and compare them with that of the prenatal Ultrasound (US) findings. Eleven patients diagnosed as SCT prenatally by US and further assessed by MRI are included. MRI was performed via a 1.5-T magnet with a body coil. The presence, size, content extension, and compressive effects of each mass were determined and correlated with US findings and with postnatal examinations, including surgery and pathology. As complications, the presence of ascites and skin edema or pleural or pericardial effusion was diagnosed as hydrops. The amniotic fluid index was calculated for the assessment of oligo- or polyhydramnios. US findings are found strongly correlated with MRI findings. An agreement on the extent of each mass was observed in eight patients, disagreement in one fetus was an extension of the tumor within the spinal canal recognized only at MR and assessment of intrapelvic-abdominal extension was superior in MRI. There were n = 6 type I, n = 2 type II, n = 1 type III and, n = 2 type IV tumors. MRI was superior to US for detecting displacement of the colon (n = 3), intrapelvic-intraabdominal extension (n = 1), urinary tract complication (n = 2), and intraspinal extension (n = 1). MRI is found to be superior to US especially in the assessment of intrapelvic and intraspinal extension of the tumor, colonic displacement, and complications.

Diagnostic Value of Magnetic Resonance Diffusion-Weighted Imaging Combined with Routine Scanning in Body Tumors.

The aim of this study was to evaluate the value of whole body magnetic resonance diffusion-weighted imaging (WB-DWI) combined with routine scanning in the diagnosis of body tumors. Sixty-three patients with surgically and pathologically confirmed body tumors admitted to our hospital from October 2019 to October 2021 were scanned by WB-DWI using a 1.5TMR body coil. The images were reconstructed by a three-dimensional maximum intensity projection (3D-MIP) and black-white inversion technique. The lesions detected by WB-DWI were all plain MRI, and 35 cases were enhanced MRI. The number of lesions detected by WB-DWI and WB-DWI combined with routine scanning and the number of cases matching diagnosis were compared. The WB-DWI images of tumor lesions were analyzed, and the apparent diffusion coefficient (ADC) of the lesions was measured, and the ADC value of benign and malignant lesions was compared. There were 236 lesions in 63 patients with clinically confirmed tumors. 46 cases were diagnosed by WB-DWI, the diagnostic coincidence rate was 73.0%, and 207 lesions were detected. Fifty-eight cases were diagnosed by WB-DWI combined with routine scanning, the diagnostic coincidence rate was 92.1%, 236 lesions were detected. There were statistically significant differences in the number of lesions detected and the coincidence rate of tumor diagnosis between the two groups (P < 0.05). The average ADC value of malignant tumor ((1.04 ± 0.46) × 10−3 mm2/s) was lower than that of benign tumor ((2.53 ± 0.43) × 10−3 mm2/s), and the difference was statistically significant (P < 0.05). In conclusion, MR whole-body diffusion weighted imaging is safe, efficient, radiation-free, and highly sensitive, which is of great significance in the differential diagnosis of benign and malignant lesions. WB-DWI combined with MR routine scanning can further improve the detection rate of lesions and the coincidence rate of tumor diagnosis.

Agarose and Wax Tissue-Mimicking Phantom for Dynamic Magnetic Resonance Imaging of the Liver

Objectives: Polymer phantoms can be used to simulate the properties of tissues or organs such as the liver during magnetic resonance imaging (MRI). Although there are reports of simulated liver phantoms with hepatocellular carcinoma (HCC); no studies have documented the simulating of the typical dynamic pattern. Aim: The present study aimed to investigate properties of developed phantoms with respect to the stability, including chemical, mechanical, electrical, as well as MRI properties (T1- and T2- signal intensities), in addition to simulating HCC in a dynamic way. Methods: In this study, liver parenchyma of size 23 ×18 ×13 cm was simulated using three different agarose-wax samples (agarose at concentrations of 2.5 wt%, 4.5 wt%, and 6.0 wt%) mixed with a fixed wax concentration of 2.6 wt%.. HCC samples were fabricated using polyurethane and glycerol of various diameters (0.5, 1.0, and 2.0 cm). Results: The results showed that the agarose-wax sample with a concentration of 2.5 wt% was the most stable sample among the other samples (P-value, 0.468) in mechanical and T1 and T2 intensities. It was also noted that the sample at the concentration of 4.5 wt% had the closest density value to human liver with a difference of 7.88%. Moreover, the agarose-wax sample at a concentration of 2.5 wt% had the closest compressibility and conductivity values, and T1-relaxation time compared to the human liver. However, the largest changes in relaxation times were observed in the fifth week of all samples (P-value = 0.047). The typical enhancement pattern for a simulated HCC of a minimum size, which can be measured with MRI, was 1.0 cm, using a body coil, and 0.5 cm using a head coil. Conclusions: The chemical, electrical density, compressive strength, density, and MR imaging properties of the phantom were measured and compared to those of the human body.

Control of the near magnetic field pattern uniformity inside metamaterial-inspired volumetric resonators

In recent years metamaterial-inspired resonators, due to the ability to form desired near field patterns at subwavelength scale, have found application in various practical fields, i.e., magnetic resonance imaging or wireless power transfer. This paper proposes an approach for controlling the near electromagnetic field distribution inside the volumetric metamaterial-inspired structure based on a set of split-ring resonators or materials with high permittivity. We numerically and experimentally demonstrate how to precisely manipulate the near-field pattern’s uniformity by changing the number of resonant elements while maintaining the geometric dimensions of the structure. The effectiveness of the concept was also verified via a magnetic resonance imaging study. The optimized volumetric metamaterial-inspired resonator showed an increase in transmit efficiency and receive performance of the large body coil compared to the commercial dedicated radiofrequency coil.

Performance and safety assessment of an integrated transmit array for body imaging at 7T under consideration of specific absorption rate, tissue temperature, and thermal dose.

In this study, the performance of an integrated body-imaging array for 7T with 32 radiofrequency (RF) channels under consideration of local specific absorption rate (SAR), tissue temperature, and thermal dose limits was evaluated and the imaging performance was compared with a clinical 3 T body coil. Thirty-two transmit elements were placed in three rings between the bore liner and RF shield of the gradient coil. Slice-selective RF pulse optimizations for B1 shimming and spokes were performed for differently oriented slices in the body under consideration of realistic constraints for power and local SAR. To improve the B1+ homogeneity, safety assessments based on temperature and thermal dose were performed to possibly allow for higher input power for the pulse optimization than permissible with SAR limits. The results showed that using two spokes, the 7 T array outperformed the 3 T birdcage in all the considered regions of interest. However, a significantly higher SAR or lower duty cycle at 7T is necessary in some cases to achieve similar B1+ homogeneity as at 3T. The homogeneity in up to 50 cm-long coronal slices can particularly benefit from the high RF shim performance provided by the 32 RF channels. The thermal dose approach increases the allowable input power and the corresponding local SAR, in one example up to 100 W/kg, without limiting the exposure time necessary for an MR examination. In conclusion, the integrated antenna array at 7T enables a clinical workflow for body imaging and comparable imaging performance to a conventional 3 T clinical body coil.