Resonance Imaging System Research Articles

SAFIR-I: Design and Performance of a High-Rate Preclinical PET Insert for MRI.

(1) Background: Small Animal Fast Insert for MRI detector I (SAFIR-I) is a preclinical Positron Emission Tomography (PET) insert for the Bruker BioSpec 70/30 Ultra Shield Refrigerated (USR) preclinical 7 Magnetic Resonance Imaging (MRI) system. It is designed explicitly for high-rate kinetic studies in mice and rats with injected activities reaching 500 , enabling truly simultaneous quantitative PET and Magnetic Resonance (MR) imaging with time frames of a few seconds in length. (2) Methods: SAFIR-I has an axial field of view of and an inner diameter of 114 . It employs Lutetium Yttrium OxyorthoSilicate (LYSO) crystals and Multi Pixel Photon Counter (MPPC) arrays. The Position-Energy-Timing Application Specific Integrated Circuit, version 6, Single Ended (PETA6SE) digitizes the MPPC signals and provides time stamps and energy information. (3) Results: SAFIR-I is MR-compatible. The system’s Coincidence Resolving Time (CRT) and energy resolution are between and Full Width at Half Maximum (FWHM) at low activity and and FWHM at 550 , respectively. The peak sensitivity is ∼. The excellent performance facilitated the successful execution of first in vivo rat studies beyond 300 . Based on features visible in the acquired images, we estimate the spatial resolution to be ∼2 in the center of the Field Of View (FOV). (4) Conclusion: The SAFIR-I PET insert provides excellent performance, permitting simultaneous in vivo small animal PET/MR image acquisitions with time frames of a few seconds in length at activities of up to 500 .

Image-guided confirmation of a precision pull-through procedure during laparoscopically assisted anorectoplasty in an open MRI operating theater: first application in an infantile case with anorectal malformation

BackgroundImage-guided surgery with an open magnetic resonance imaging (MRI) system is applied for brain tumors in the neurosurgery field, but has rarely been reported in pediatric surgery. We report our initial experience of intraoperative confirmation of precision rectal pull-through during laparoscopically assisted anorectoplasty (LAARP) in an open MRI operating theater for pediatric patients with anorectal malformation (ARM).Case presentationA 3.0 kg term male neonate was delivered with anorectal malformation. An invertogram revealed the intermediate type. Transverse colostomy was made on the left upper abdomen. The recto-bulbar urethral fistula (RBUF) was diagnosed by a distal colostogram and voiding cystourethrogram. LAARP was planned at 6 months of age. Because this was the first procedure in which the pediatric abdomen had been scanned in an open MRI operating theater in our institution, we scanned his pelvic floor under sedation 3 weeks before the operation using the open MRI system in our operation room. We performed the operation with 4 trocars. The peritoneal reflection was carefully incised and the rectum was dissected. The RBUF was resected. The center of the muscle complex was detected at the perineal skin with an electrical nerve stimulator, and a 7-mm longitudinal skin incision was made on the perineal lesion for anoplasty. The muscle complex and the pubo-rectal sling were confirmed laparoscopically using a 3.5-mm bipolar forceps connected to the electrical nerve stimulator. Anoplasty was performed between the rectal stump and perineal skin. After anoplasty, the patient was scanned with open MRI under general anesthesia. We attached the quadrature-detection (QD) head coil around the patient’s pelvis and inserted him in the gantry. A 0.45-T open MRI clearly revealed that the pulled through rectum was located in the center of the muscle complex on T2-weighted images. The postoperative course was uneventful. Oral intake was started on post-operative day 1. Postoperative dynamic urography showed no complication (e.g., leakage or residual fistula).ConclusionsWe successfully performed LAARP for ARM, with intraoperative confirmation of precision rectal pull-through in an open MRI operating theater. Further cases are required to evaluate the application of open MRI systems in pediatric surgery.

Utility of Real-time CT/MRI-US Automatic Fusion System Based on Vascular Matching in Percutaneous Radiofrequency Ablation for Hepatocellular Carcinomas: A Prospective Study.

To prospectively evaluate the technical success rate of real-time computed tomography/magnetic resonance imaging and ultrasound (CT/MRI-US) automatic fusion system and the long-term therapeutic efficacy of radiofrequency ablation (RFA) guided by automatic fusion in hepatocellular carcinoma (HCC) patients. 139 patients with 151 HCCs were prospectively enrolled for RFA guided by an automatic CT/MRI-US fusion system (PercuNav system, Philips, the Netherlands). Automatic fusion imaging, based on vascular segmentation and registration, was performed by sonographic sweeping at the intercostal plane. The fusion quality, tumor localization confidence and technical feasibility were recorded before and after fusion using a scoring system. Technical success rate of the RFA procedure and local tumor progression (LTP) were assessed during follow-up. Analysis of technical success and LTP was performed using generalized estimating equations and Cox proportional hazard regression analysis. The success rate of the fusion system was 82.7% (115/139) per patient. The mean sonographic scan time for fusion was 154.4 ± 108.4s. In patients with successful fusion, the score indicating tumor localization confidence (2.2 ± 0.8 vs. 2.7 ± 0.9) and technical feasibility (2.6 ± 0.8 vs. 3.4 ± 0.7) increased after fusion (p < 0.001). The technical success rate of the RFA procedure was 96.8% (120/124) per tumor in patients with successful fusion, including poorly localized tumors. LTP rates were 8.6%, 12.2% and 15.2% at 1, 2 and 3years. The CT/MRI-US automatic fusion system showed a high success rate for image registration and facilitated better feasibility and a high technical success rate of RFA in HCCs, even with poor localization on US. Level 3b, Nonrandomized prospective study.

Integrin \u03b1v\u03b26-targeted MR molecular imaging of breast cancer in a xenograft mouse model

BackgroundThe motif RXDLXXL-based nanoprobes allow specific imaging of integrin αvβ6, a protein overexpressed during tumorigenesis and tumor progression of various tumors. We applied a novel RXDLXXL-coupled cyclic arginine-glycine-aspartate (RGD) nonapeptide conjugated with ultrasmall superparamagnetic iron oxide nanoparticles (referred to as cFK-9-USPIO) for the application of integrin αvβ6-targeted magnetic resonance (MR) molecular imaging for breast cancer.MethodsA novel MR-targeted nanoprobe, cFK-9-USPIO, was synthesized by conjugating integrin αvβ6-targeted peptide cFK-9 to N-amino (−NH2)-modified USPIO nanoparticles via a dehydration esterification reaction. Integrin αvβ6-positive mouse breast cancer (4 T1) and integrin αvβ6 negative human embryonic kidney 293 (HEK293) cell lines were incubated with cFK-9-AbFlour 647 (blocking group) or cFK-9-USPIO (experimental group), and subsequently imaged using laser scanning confocal microscopy (LSCM) and 3.0 Tesla magnetic resonance imaging (MRI) system. The affinity of cFK-9 targeting αvβ6 was analyzed by calculating the mean fluorescent intensity in cells, and the nanoparticle targeting effect was measured by the reduction of T2 values in an in vitro MRI. The in vivo MRI capability of cFK-9-USPIO was investigated in 4 T1 xenograft mouse models. Binding of the targeted nanoparticles to αvβ6-positive 4 T1 tumors was determined by ex vivo histopathology.ResultsIn vitro laser scanning confocal microscopy (LSCM) imaging showed that the difference in fluorescence intensity between the targeting and blocking groups of 4 T1 cells was significantly greater than that in HEK293 cells (P < 0.05). The in vitro MRI demonstrated a more remarkable T2 reduction in 4 T1 cells than in HEK293 cells (P < 0.001). The in vivo MRI of 4 T1 xenograft tumor-bearing nude mice showed significant T2 reduction in tumors compared to controls. Prussian blue staining further confirmed that αvβ6 integrin-targeted nanoparticles were specifically accumulated in 4 T1 tumors and notably fewer nanoparticles were detected in 4 T1 tumors of mice injected with control USPIO and HEK293 tumors of mice administered cFK-9-USPIO.ConclusionsIntegrin αvβ6-targeted nanoparticles have great potential for use in the detection of αvβ6-overexpressed breast cancer with MR molecular imaging.

Improved PET/MRI accuracy by use of static transmission source in empirically derived hardware attenuation correction

BackgroundAccurate quantification of radioactivity, measured by an integrated positron emission tomography (PET) and magnetic resonance imaging (MRI) system, is still a challenge. One aspect of such a challenge is to correct for the hardware attenuation, such as the patient table and radio frequency (RF) resonators. For PET/MRI systems, computed tomography (CT) is commonly used to produce hardware attenuation correction (AC) maps, by converting Hounsfield units (HU) to a linear attenuation coefficients (LAC) map at the PET energy level 511 keV, using a bilinear model. The model does not address beam hardening, nor higher density materials, which can lead to inaccurate corrections.PurposeIn this study, we introduce a transmission-based (TX-based) AC technique with a static Germanium-68 (Ge-68) transmission source to generate hardware AC maps using the PET/MRI system itself, without the need for PET or medical CT scanners. The AC TX-based maps were generated for a homogeneous cylinder, made of acrylic as a validator. The technique thereafter was applied to the patient table and posterior part of an RF-phased array used in cardiovascular PET/MRI imaging. The proposed TX-based, and the CT-based, hardware maps were used in reconstructing PET images of one cardiac patient, and the results were analysed and compared.ResultsThe LAC derived by the TX-based method for the acrylic cylinder is estimated to be 0.10851 ± 0.00380 cm−1 compared to the 0.10698 ± 0.00321 cm−1 theoretical value reported in the literature. The PET photon counts were reduced by 8.7 ± 1.1% with the patient table, at the region used in cardiac scans, while the CT-based map, used for correction, over-estimated counts by 4.3 ± 1.3%. Reconstructed in vivo images using TX-based AC hardware maps have shown 4.1 ± 0.9% mean difference compared to those reconstructed images using CT-based AC.ConclusionsThe LAC of the acrylic cylinder measurements using the TX-based technique was in agreement with those in the literature confirming the validity of the technique. The over-estimation of photon counts caused by the CT-based model used for the patient table was improved by the TX-based technique. Therefore, TX-based AC of hardware using the PET/MRI system itself is possible and can produce more accurate images when compared to the CT-based hardware AC in cardiac PET images.

Temporal Changes in In Vivo Glutamate Signal during Demyelination and Remyelination in the Corpus Callosum: A Glutamate-Weighted Chemical Exchange Saturation Transfer Imaging Study.

Background: Glutamate-weighted chemical exchange saturation transfer (GluCEST) is a useful imaging tool that can be used to detect changes in glutamate levels in vivo and could also be helpful in the diagnosis of brain myelin changes. We investigated glutamate level changes in the cerebral white matter of a rat model of cuprizone-administered demyelination and remyelination using GluCEST. Method: We used a 7 T pre-clinical magnetic resonance imaging (MRI) system. The rats were divided into the normal control (CTRL), cuprizone-administered demyelination (CPZDM), and remyelination (CPZRM) groups. GluCEST data were analyzed using the conventional magnetization transfer ratio asymmetry in the corpus callosum. Immunohistochemistry and transmission electron microscopy analyses were also performed to investigate the myelinated axon changes in each group. Results: The quantified GluCEST signals differed significantly between the CPZDM and CTRL groups (−7.25 ± 1.42% vs. −2.84 ± 1.30%; p = 0.001). The increased GluCEST signals in the CPZDM group decreased after remyelination (−6.52 ± 1.95% in CPZRM) to levels that did not differ significantly from those in the CTRL group (p = 0.734). Conclusion: The apparent temporal signal changes in GluCEST imaging during demyelination and remyelination demonstrated the potential usefulness of GluCEST imaging as a tool to monitor the myelination process.

An Automated Method for Quality Control in MRI Systems: Methods and Considerations

Objective: The purpose of this study was to develop an automated method for performing quality control (QC) tests in magnetic resonance imaging (MRI) systems, investigate the effect of different definitions of QC parameters and its sensitivity with respect to variations in regions of interest (ROI) positioning, and validate the reliability of the automated method by comparison with results from manual evaluations. Materials and Methods: Magnetic Resonance imaging MRI used for acceptance and routine QC tests from five MRI systems were selected. All QC tests were performed using the American College of Radiology (ACR) MRI accreditation phantom. The only selection criterion was that in the same QC test, images from two identical sequential sequences should be available. The study was focused on four QC parameters: percent signal ghosting (PSG), percent image uniformity (PIU), signal-to-noise ratio (SNR), and SNR uniformity (SNRU), whose values are calculated using the mean signal and the standard deviation of ROIs defined within the phantom image or in the background. The variability of manual ROIs placement was emulated by the software using random variables that follow appropriate normal distributions. Results: Twenty-one paired sequences were employed. The automated test results for PIU were in good agreement with manual results. However, the PSG values were found to vary depending on the selection of ROIs with respect to the phantom. The values of SNR and SNRU also vary significantly, depending on the combination of the two out of the four standard rectangular ROIs. Furthermore, the methodology used for SNR and SNRU calculation also had significant effect on the results. Conclusions: The automated method standardizes the position of ROIs with respect to the ACR phantom image and allows for reproducible QC results.

Quantitative and Qualitative Improvement of Low-Count [68Ga]Citrate and [90Y]Microspheres PET Image Reconstructions Using Block Sequential Regularized Expectation Maximization Algorithm.

There are several important positron emission tomography (PET) imaging scenarios that require imaging with very low photon statistics, for which both quantitative accuracy and visual quality should not be neglected. For example, PET imaging with the low photon statistics is closely related to active efforts to significantly reduce radiation exposure from radiopharmaceuticals. We investigated two examples of low-count PET imaging: (a) imaging [90Y]microsphere radioembolization that suffers the very small positron emission fraction of Y-90's decay processes, and (b) cancer imaging with [68Ga]citrate with uptake time of 3-4 half-lives, necessary for visualizing tumors. In particular, we investigated a type of penalized likelihood reconstruction algorithm, block sequential regularized expectation maximization (BSREM), for improving both image quality and quantitative accuracy of these low-count PET imaging cases. The NEMA/IEC Body phantom filled with aqueous solution of Y-90 or Ga-68 was scanned to mimic the low-count scenarios of corresponding patient data acquisitions on a time-of-flight (TOF) PET/magnetic resonance imaging system. Contrast recovery, background variation, and signal-to-noise ratio were evaluated in different sets of count densities using both conventional TOF ordered subset expectation (TOF-OSEM) and TOF-BSREM algorithms. The regularization parameter, beta, in BSREM that controls the tradeoff between image noise and resolution was evaluated to find a value for improved confidence in image interpretation. Visual quality assessment of the images obtained from patients administered with [68Ga]citrate (n = 6) was performed. We also made preliminary visual image quality assessment for one patient with [90Y]microspheres. In Y-90 imaging, the effect of 511-keV energy window selection for minimizing the number of random events was also evaluated. Quantitatively, phantom images reconstructed with TOF-BSREM showed improved contrast recovery, background variation, and signal-to-noise ratio values over images reconstructed with TOF-OSEM. Both phantom and patient studies of delayed imaging of [68Ga]citrate show that TOF-BSREM with beta = 500 gives the best tradeoff between image noise and image resolution based on visual assessment by the readers. The NEMA-IQ phantom study with [90Y]microspheres shows that the narrow energy window (460-562keV) recovers activity concentrations in small spheres better than the regular energy window (425-650keV) with the beta value of 2000 using the TOF-BSREM algorithm. For the images obtained from patients with [68Ga]citrate using TOF-BSREM with beta = 500, the visual analogue scale (VAS) was improved by 17% and the Likert score was increased by 1 point on average, both in comparison to corresponding scores for images reconstructed using TOF-OSEM. Our investigation shows that the TOF-BSREM algorithm improves the image quality and quantitative accuracy in low-count PET imaging scenarios. However, the beta value in this algorithm needed to be adjusted for each radiopharmaceutical and counting statistics at the time of scans.

Development and Experimental Testing of Microstrip Patch Antenna-Inspired RF Probes for 14 T MRI Scanners

Radio frequency (RF) probes for ultrahigh-field magnetic resonance imaging (MRI) systems were developed from structures inspired by microstrip patch antennas. The patch structures provide an alternative to conventional surface coils. We show that these structures, operating as resonators, can produce strong magnetic fields, which act as B1 fields in MRI studies. The addition of high permittivity inserts to the patch substrate was beneficial for increasing B1 field uniformity. It was also shown by simulations that two vis-a-vis placed identical patches fed with 180° phase difference could produce uniform B1 field in the space between patches and could be used as volume RF probes. This possibility was confirmed by experiments with fabricated prototypes in the VARIAN 14.1 T MRI scanner. We further show that the B1 uniformity is enhanced over larger volume with properly profiled substrates of higher permittivity, along with smaller radiation losses. These probes were found competitive and even advantageous in comparison with birdcage coils because of better stability of their Q-factors at loading by lossy phantoms. Thus, patch-based probes offer a viable alternative to RF probes for ultrahigh field MRI.

Development of a Symmetric Echo-Planar Spectroscopy Imaging Framework for Hyperpolarized 13C Imaging in a Clinical PET/MR Scanner.

Here, we developed a symmetric echo-planar spectroscopic imaging (EPSI) sequence for hyperpolarized 13C imaging on a clinical hybrid positron emission tomography/magnetic resonance imaging system. The pulse sequence uses parallel reconstruction pipelines to separately reconstruct data from odd-and-even gradient echoes to reduce artifacts from gradient imbalances. The ramp-sampled data in the spatiotemporal frequency space are regridded to compensate for the chemical-shift displacements. Unaliasing of nonoverlapping peaks outside of the sampled spectral width was performed to double the effective spectral width. The sequence was compared with conventional phase-encoded chemical-shift imaging (CSI) in phantoms, and it was evaluated in a canine cancer patient with ameloblastoma after injection of hyperpolarized [1-13C]pyruvate. The relative signal-to-noise ratio of EPSI with respect to CSI was 0.88, which is consistent with the decrease in sampling efficiency due to ramp sampling. Data regridding in the spatiotemporal frequency space significantly reduced spatial blurring compared with direct fast Fourier transform. EPSI captured the spatial distributions of both metabolites and their temporal dynamics in vivo with an in-plane spatial resolution of 5 × 9 mm2 and a temporal resolution of 3 seconds. Significantly higher spatial and temporal resolution for delineating anatomical structures in vivo was achieved for EPSI metabolic maps than for CSI maps, which suffered spatiotemporal blurring. The EPSI sequence showed promising results in terms of short acquisition time and sufficient spectral bandwidth of 500 Hz, allowing to adjust the trade-off between signal-to-noise ratio and encoding speed.

Impact of time-of-flight PET on quantification accuracy and lesion detection in simultaneous 18F-choline PET/MRI for prostate cancer

BackgroundAccurate attenuation correction (AC) is an inherent problem of positron emission tomography magnetic resonance imaging (PET/MRI) systems. Simulation studies showed that time-of-flight (TOF) detectors can reduce PET quantification errors in MRI-based AC. However, its impact on lesion detection in a clinical setting with 18F-choline has not yet been evaluated. Therefore, we compared TOF and non-TOF 18F-choline PET for absolute and relative difference in standard uptake values (SUV) and investigated the detection rate of metastases in prostate cancer patients.ResultsNon-TOF SUV was significantly lower compared to TOF in all osseous structures, except the skull, in primary lesions of the prostate, and in pelvic nodal and osseous metastasis. Concerning lymph node metastases, both experienced readers detected 16/19 (84%) on TOF PET, whereas on non-TOF PET readers 1 and 2 detected 11 (58%), and 14 (73%), respectively. With TOF PET readers 1 and 2 detected 14/15 (93%) and 11/15 (73%) bone metastases, respectively, whereas detection rate with non-TOF PET was 73% (11/15) for reader 1 and 53% (8/15) for reader 2. The interreader agreement was good for osseous metastasis detection on TOF (kappa 0.636, 95% confidence interval [CI] 0.453–0.810) and moderate on non-TOF (kappa = 0.600, CI 0.438–0.780).ConclusionTOF reconstruction for 18F-choline PET/MRI shows higher SUV measurements compared to non-TOF reconstructions in physiological osseous structures as well as pelvic malignancies. Our results suggest that addition of TOF information has a positive impact on lesion detection rate for lymph node and bone metastasis in prostate cancer patients.

Design and Manufacture of Half-Size 3-T High-Temperature Superconducting Magnet for MRI

A new high-temperature superconducting (HTS) application project supported by the New Energy and Industrial Technology Development Organization (NEDO) started in July 2016. One of the targets of this project is to demonstrate the half-size of whole-body magnetic resonance imaging (MRI) system using HTS magnets with REBCO conductors. In the first phase of this project (FY2016–FY2018), a three-tesla magnet with an active shield will be manufactured. The room-temperature bore of the magnet is 480 mm in diameter. The magnet will be cooled down to lower than 20 K with a G-M refrigerator and the MR imaging will be performed to evaluate the magnetic field uniformity and stability. The design of the half-size 3-T coil has been finished: it consists of 220 single-pancake coils, and it has an inner diameter of 560 mm, an outer diameter of 1200 mm, and an axial length of 1000 mm. The rated current is 148 A and the stored energy at the rated excitation is 1.58 MJ. The designed magnetic field homogeneity is 1.7 ppm (250 mm DSV) which is adequate for MR imaging. Furthermore, the fringe field is suppressed by active shielding technology. The number of 53 single-pancake coils was manufactured in FY2016, and the yield rate was about 95%.

Validation of LYSO Scintillators Coupled to SensL C-Series SiPM's Detectors

Simulation and experimental procedures, using Na-22 sources, were carried out in order to examine the spatial resolution of a preclinical positron emission tomographymagnetic resonance imaging (PETMRI) system, due to the innovative use of Silicon Photomultiplier (SiPM) detectors coupled with doubled jaw layer lutetium yttrium oxyorthosilicate (LYSO) crystals. Optical properties of LYSO scintillation crystals were examined, and the optimal crystal configuration was determined. Noise-equivalent count rate curves were analyzed in order to determine the stability of the PET system. The highest resolution in the 511-keV photopeak was measured as 10.84 for 27.5 V, and in the 1274-keV photopeak, the best resolution was recorded as 12.75 again for 27.5 V. Moreover, simulation and experimental images of the SiPM, for 1.2-mm and 1.68-mm pixel pitch size, were compared, showing that for 27.5 V of bias voltage, the spatial resolution is better, while the gain and the noise is low. However, for 29V, the gain is better, but there is more noise.

Quench analysis of 1.5 T superconducting MRI magnet

A national project on indigenous development of whole body 1.5 T superconducting magnetic resonance imaging (MRI) system has been initiated by Meity Govt. of India. This MRI magnet will have multi-coil solenoidal structure to be operated at a current density of 140 A/mm2. The total stored magnetic energy will be 4.5 MJ. This high stored energy of the magnet makes it crucial to design an efficient quench protection system for the magnet to prevent any damage due to either localized temperature rise or any voltage arcing during the quench. This paper presents the details of the quench characteristics of the MRI magnet simulated using OPERA. The transient thermal mapping of the magnet is also discussed in detail in the paper. A comparison has been made of the quench behavior of the magnet using different types of quench protection systems.

Quantitative Susceptibility Mapping of the Substantia Nigra in Parkinson’s Disease

The purpose of this study was to evaluate the sensitivities of quantitative susceptibility mapping (QSM) and R2* mapping in clinical diagnoses of Parkinson’s disease (PD). QSM images and R2* maps from 29 patients with PD and 25 healthy controls were obtained on a clinical 3T magnetic resonance imaging (MRI) system using a three-dimensional multi-echo gradient-echo sequence. Two-tailed t tests and receiver operating characteristic curves analyses were applied to the mean values of QSM and R2* of the two groups. In the PD group, a two-tailed Pearson correlation analysis was used to investigate the correlations between MRI measures (susceptibility and R2* values) and the Unified Parkinson’s Disease Rating Scale-III (UPDRS-III) score. In the substantia nigra (SN), a significant difference between patients with PD and healthy controls was found on QSM (154.80 ± 43.36 vs. 127.50 ± 21.05 ppb, P = 0.006) but not on R2* mapping. The receiver operating characteristic curves showed that QSM was more sensitive than R2* mapping to distinguish PD patients from healthy controls, with areas under the curve equal to 0.68 and 0.51, respectively. The UPDRS-III motor scores did not correlate with mean susceptibility or R2* values in the PD group. In conclusion, QSM is a more accurate and sensitive method than R2* mapping to detect the pathologic changes in the SN of patients with PD.

Reconfigurable multi‐channel RF crossbar switch matrix for MRI receiver front‐end

In this Letter, a highly reconfigurable crossbar transmission line switch matrix for magnetic resonance imaging (MRI) system is proposed. Unlike the conventional M × N crossbar switch configuration, the proposed structure can manipulate 2M × N matrix without doubling the area occupancy. Also, the proposed structure includes the signal loss-compensation circuitry based on inductor banks to enhance signal-to-noise ratio (SNR). Thus, for any required numbers of input and output channels, the proposed structure can reduce the overall size, the number of required component, and even increase the quality of MR images by SNR enhancement. The proposed structure was implemented and verified at 4-Tesla (170 MHz) MR system through the comparison of RF path loss, SNR and phantom test image qualities.

Simultaneous assay of platelet adhesion at multiple shear rates within a single microfluidic channel

Cardiovascular diseases are currently the major causes of mortality in the world, especially in developed nations. As a predominant one, thrombosis is the platelet aggregation induced by a high shear rate. Platelet aggregation assay can clarify the occurrence mechanism of thrombosis, as well as be used as an important tool in the clinical diagnosis, personalized treatment, and screening of anticoagulants. Thus, relevant studies attracted considerable attention. As an important step in platelet aggregation, platelet adhesion and its detection also attract intensive concern. Thus, some analytical methods have been developed for platelet adhesion assay, and the impact of shear rate is one of the focuses. Compared with other devices, biosensors can give a more accurate result within a shorter time. Furthermore, some biosensors can achieve real-time analysis. However, only one or several shear rates can be tested at the same time, which may decrease the analytical efficiency. Meanwhile, in most cases, only the average platelet adhesion effect within a reactor is detected, and the impact of the distribution of shear rates is improperly neglected. In this study, a microfluidic device with a single channel is designed and fabricated for platelet adhesion assay. When the platelet-rich plasma flows through the collagen-modified sensing surface of the channel bottom, the interaction between platelets and collagen molecules on the entire surface can be simultaneously monitored by using a surface plasmon resonance imaging (SPRi) system. A gradient of the shear rate (0–546 s-1) could be formed within the channel by choosing a suitable depth-to-width ratio (1:5), so platelet adhesion at multiple shear rates could be monitored simultaneously. This method enables the measurement of the adhesion process of unlabeled platelets on the entire sensing surface, in vitro, at multiple shear rates. Such a system can obtain more accurate platelet adhesion result at a given shear rate than traditional methods. Furthermore, in an individual operation, platelet adhesion can be repeatedly tested at multiple points with an equal shear rate, so a much higher analytical efficiency can also be achieved.

A Structure Design Method for Reduction of MRI Acoustic Noise.

The acoustic problem of the split gradient coil is one challenge in a Magnetic Resonance Imaging and Linear Accelerator (MRI-LINAC) system. In this paper, we aimed to develop a scheme to reduce the acoustic noise of the split gradient coil. First, a split gradient assembly with an asymmetric configuration was designed to avoid vibration in same resonant modes for the two assembly cylinders. Next, the outer ends of the split main magnet were constructed using horn structures, which can distribute the acoustic field away from patient region. Finally, a finite element method (FEM) was used to quantitatively evaluate the effectiveness of the above acoustic noise reduction scheme. Simulation results found that the noise could be maximally reduced by 6.9 dB and 5.6 dB inside and outside the central gap of the split MRI system, respectively, by increasing the length of one gradient assembly cylinder by 20 cm. The optimized horn length was observed to be 55 cm, which could reduce noise by up to 7.4 dB and 5.4 dB inside and outside the central gap, respectively. The proposed design could effectively reduce the acoustic noise without any influence on the application of other noise reduction methods.

Emergency personnel and magnetic resonance imaging: is there a risk from clothing and working materials?

The use of Magnetic Resonance Imaging (MRI) systems is on the rise and the number of installed systems is constantly increasing. This raises the possibility for emergency personnel to get in contact with these systems. This study examines the effects of magnetic force on selected working materials and clothes of firefighters and paramedics. This study was conducted as a field study, utilising a 1.5 tesla MRI system. The highest force of attraction can be researched on helmets (30 newton), boots (90 newton) and gloves (17 newton). Moreover, working material can be influenced by eddy currents. Considering the results of this study, boots and helmets must be considered as a risk in MRI examination rooms. Additional trainings for firefighters and paramedics should consider the danger of ferromagnetic objects close to MRI systems and that specific material can become a threat. More research is needed to investigate more material of emergency personnel.

Design of super-elliptical gradient coils based on multiple objective Pareto optimization method

The design of gradient coils for a magnetic resonance imaging (MRI) system is a multiple objective optimization problem, which usually needs to deal with a couple of conflicting design objectives, such as the stored magnetic energy, power consumption, and target linear gradient distribution. These design requirements usually conflict with each other, and there is no unique optimal solution which is capable of minimizing all objectives simultaneously. Therefore, the design of gradient coils needs to be optimized reasonably with the tradeoff among different design objectives. Based on the developable property of the super-elliptical cylindrical surface and the stream function design method, the multiple objective optimization problem is analyzed by using the Pareto optimization method in this paper. The effect of proposed approach is illustrated by using the stream function method and three aforementioned coil design objectives are analyzed. The influences of the stored magnetic energy and power consumption target on linearity of gradient coil and the configuration of coils are analyzed respectively. The suitable sizes of gradient coils are discussed by analyzing the change of the stored magnetic energy. A weighted sum method is employed to produce the optimal Pareto solutions, in which the multiple objective problem reduces into a single objective function through a weighted sum of all objectives. The quantitative relationship of each design requirement is analyzed in the Pareto solution space, where Pareto optimal solutions can be intuitively found by dealing efficiently with the tradeoff among different coil properties. Numerical examples of super-elliptical gradient coil solutions are provided to demonstrate the effectiveness and versatility of the proposed method to design super-elliptical gradient coils with different coil requirements. The optimization results show that there are multiple available solutions in the convex Pareto solution space under the constraints that the linear gradient deviation is less than 5% and the magnetic stored energy and power dissipated are both no more than user-preset values. In the case that the values of summed objective functions are the same, the proposed method can intuitively see the performance of each individual target, thereby conducting to realizing the final design of gradient coils under the different design requirements. With the proposed approach, coil designers can have a reasonable overview of gradient coil design about the achievable performances of some specific properties and the competing or compatible relationships among coils properties. Therefore, a suitable design of the gradient coils for a given requirement of MRI application can be chosen reasonably.