Magnetic Resonance Imaging Device Research Articles

Farklı Polimikrogiri Paternlerinin Manyetik Rezonans Görüntüleme Bulguları

Aim: Polymicrogyria is a developmental cortical malformation, characterized by very small and prominent curling sulci that cause irregular vision at cortical surface and at the junction of cortex and white matter. In this study, magnetic resonance imaging findings of patients who have different polymicrogyria patterns were presented. Method: Eight women and 1 men, total 9 patients, whom were prediagnosed as motor mental retardation or different epilepsy types between 2008 and 2011 were enrolled in this study. All petients were radiologically imaged by 1,5 Tesla Magnetic Resonance Imaging device. Results: Bilateral perisylvian and bilateral parasagittal parieto-occipital polymicrogyria which were common types, detected in two patients. Rare types were detected in seven patients which were as follows; the left temporal common polymicrogyria, polymicrogyria from the left parasagittal, parietally, elongates to posterosuperior perisylvian cortical surfaces, left closed lip schizencephaly and in the neighborhood of perisylvian surface and schizencephaly line and with the parietooccipital polymicrogyria parietooccipital sulcus in the right and parasagittal occipital polymicrogyria, open-lipped on the left and closed lipped on the right schizencephaly and adjacent cortical surfaces with perisylvian polymicrogyria at the right, parasagittal paracingulate polymicrogyria, encephalocele sac at the anterior to the right frontal region with polymicrogyria elongates from adjacent cortical surfaces of forntal lob to insular cortex. Conclusion: As one of the most common types of developmental cortical malformations, polymicrogyria can be seen in patients who are presented with clinical findings, such as epilepsy, mental motor retardation and spasticity and polymicrogyria may present in very different types. MRI is an effective imaging technique in patients presenting with cortical developmental malformations such as polymicrogyria

High-intensity therapeutic ultrasound: metrological requirements versus clinical usage

High-intensity therapeutic ultrasound (HITU) is an appealing non-invasive, non-ionizing therapeutic modality with a wide range of tissue interactions ranging from transient permeabilization of cell membranes to thermal ablation. The ability to guide and monitor the treatment with an associated ultrasonic or magnetic resonance imaging device has resulted in a dramatic rise in the clinical use of therapeutic ultrasound in the past two decades. Nevertheless, the range of clinical applications and the number of patients treated has grown at a much higher pace than the definition of standards. In this paper the metrological requirements of the therapeutic beams are reviewed and are compared with the current clinical use of image-guided HITU mostly based on a practical approach. Liver therapy, a particularly challenging clinical application, is discussed to highlight the differences between some complex clinical situations and the experimental conditions of the metrological characterization of ultrasonic transducers.

A study of the standard brain in Japanese children: Morphological comparison with the MNI template

Functional magnetic resonance imaging (MRI) studies involve normalization so that the brains of different subjects can be described using the same coordinate system. However, standard brain templates, including the Montreal Neurological Institute (MNI) template that is most frequently used at present, were created based on the brains of Western adults. Because morphological characteristics of the brain differ by race and ethnicity and between adults and children, errors are likely to occur when data from the brains of non-Western individuals are processed using these templates. Therefore, this study was conducted to collect basic data for the creation of a Japanese pediatric standard brain. Participants in this study were 45 healthy children (contributing 65 brain images) between the ages of 6 and 9years, who had nothing notable in their perinatal and other histories and neurological findings, had normal physical findings and cognitive function, exhibited no behavioral abnormalities, and provided analyzable MR images. 3D-T1-weighted images were obtained using a 1.5-T MRI device, and images from each child were adjusted to the reference image by affine transformation using SPM8. The lengths were measured and compared with those of the MNI template. The Western adult standard brain and the Japanese pediatric standard brain obtained in this study differed greatly in size, particularly along the anteroposterior diameter and in height, suggesting that the correction rates are high, and that errors are likely to occur in the normalization of pediatric brain images. We propose that the use of the Japanese pediatric standard brain created in this study will improve the accuracy of identification of brain regions in functional brain imaging studies involving children.

Head-mounted active noise control system and its application to reducing MRI noise

We propose an active noise control (ANC) system for reducing periodic noise generated in a high magnetic field such as noise generated from magnetic resonance imaging (MRI) devices (MRI noise). The proposed ANC system utilizes optical microphones and piezoelectric loudspeakers and consists of a head-mounted structure to control noise near the user's ears. Moreover, internal model control (IMC)-based feedback ANC is employed because the MRI noise includes some periodic components and is predictable. Our experimental results demonstrate that the proposed ANC system (head-mounted structure) can significantly reduce MRI noise by approximately 30 dB in a high field in an actual MRI room even if the imaging mode changes frequently.

Consciousness Studies and a Transformation of the Western Worldview

The emerging field of consciousness studies offers the perspective we need to make our global human community sustainable.

In vitro assessment of factors affecting the apparent diffusion coefficient of Jurkat cells using bio-phantoms.

It is well known that many tumor tissues show lower apparent diffusion coefficient (ADC) values, and that several factors are involved in the reduction of ADC values. The aim of this study was to clarify how much each factor contributes to decreases in ADC values. We investigate the roles of cell density, extracellular space, intracellular factors, apoptosis and necrosis in ADC values using bio-phantoms. The ADC values of bio-phantoms, in which Jurkat cells were encapsulated by gellan gum, were measured by a 1.5-Tesla magnetic resonance imaging device with constant diffusion time of 30sec. Heating at 42℃ was used to induce apoptosis while heating at 48℃ was used to induce necrosis. Cell death after heating was evaluated by flow cytometric analysis and electron microscopy. The ADC values of bio-phantoms including non-heated cells decreased linearly with increases in cell density, and showed a steep decline when the distance between cells became less than 3μm. The analysis of ADC values of cells after destruction of cellular structures by sonication suggested that approximately two-thirds of the ADC values of cells originate from their cellular structures. The ADC values of bio-phantoms including necrotic cells increased while those including apoptotic cells decreased. This study quantitatively clarified the role of the cellular factors and the extracellular space in determining the ADC values produced by tumor cells. The intermediate diffusion time of 30msec might be optimal to distinguish between apoptosis and necrosis.

Case-study magnetic resonance imaging and acoustic investigation of the effects of vocal warm-up on two voice professionals

Vocal warm-up (WU)-related changes were studied in one male musical singer and one female speech trainer. They sustained vowels before and after WU in a magnetic resonance imaging (MRI) device. Acoustic recordings were made in a studio. The vocal tract area increased after WU, a formant cluster appeared between 2 and 4.5 kHz, and SPL increased. Evidence of larynx lowering was only found for the male. The pharyngeal inlet over the epilaryngeal outlet ratio (Aph/Ae) increased by 10%–28%, being 3–4 for the male and 5–7 for the female. The results seem to represent different voice training traditions. A singer's formant cluster may be achievable without a high Aph/Ae (≥ 6), but limitations of the 2D method should be taken into account.

Discretely Loaded Beam-Type Optical Fiber Tactile Sensor for Tissue Manipulation and Palpation in Minimally Invasive Robotic Surgery

In traditional open surgery, surgeons use their fingertip palpation to investigate the hidden anatomical structures of tissue. However, in the current commercially available minimally invasive robotic surgery (MIRS) systems, while surgical instruments interact with tissues, surgeons do not sense any tactile information. Therefore, tactile sensors are required to be integrated into the tips of surgical instruments to mimic the perception of the surgeon's fingertips. The electrically based tactile sensors that exist at present cannot usually operate under static loading conditions. In addition, they are not compatible with magnetic resonance imaging (MRI) devices. Therefore, this research was aimed at restoring tactile information by developing an MRI compatible optical fiber tactile sensor. The sensor consists of only one single moving part. Thanks to this novel design, the sensor does not require the use of an array of sensors to measure the distributed tactile information. This capability simplifies the integration of the sensor into any suitable space available at the tips of surgical instruments. In addition, the sensor performs under both static and dynamic loading conditions. A theoretical model of the sensor and a finite-element model of the sensor-tissue interaction were developed. To validate the sensor, a prototype of the sensor was fabricated and tested.

Magnetic Resonance Imaging and Cardiac Devices: How Safe Is Safe Enough?

Nazarian and colleagues' report in this issue represents the largest published experience to date of MRI in patients with standard, contemporary cardiac rhythm management devices. The editorialists...

Paranasal Sinus Mucosal Hypertrophy in Experienced Divers

Due to the increasing popularity in recreational diving long-term health consequences of this sport have aroused interest in the diving community. Although not as important as dysbaric osteonecrosis, ischemic brain lesions, or neurophysiological symptoms, paranasal sinus mucosal hypertrophy (PSMH) has also been discussed as being more prevalent among divers. In this study, we used magnetic resonance imaging (MRI) to compare asymptomatic divers with control subjects for PSMH. We enrolled 79 male divers (34.0 +/- 5.7 yr) and 79 nondiving age- and sex-matched controls (33.8 +/- 6.1 yr). We used a questionnaire to elicit diving history. Divers with a history of sinus barotrauma, subjects with a history of chronic sinusitis or nasal allergies, and those with retention cysts, nasal polyps, or mastoiditis were excluded. T1-, T2-weighted axial and coronal images of the paranasal sinuses were taken with a 1.5-T MRI device. The threshold for PSMH was defined as mucosal thickness above 3 mm. MRI revealed PSMH in 33 (41.8%) divers and 18 (22.8%) controls. There were no significant differences between the groups with respect to age, smoking history, or alcohol consumption. PSMH identified in divers did not show an association with age or diving history. The higher rate of PSMH identified in divers suggests that diving may cause changes in the paranasal sinus mucosa.

Preclinical multimodality phantom design for quality assurance of tumor size measurement

BackgroundEvaluation of changes in tumor size from images acquired by ultrasound (US), computed tomography (CT) or magnetic resonance imaging (MRI) is a common measure of cancer chemotherapy efficacy. Tumor size measurement based on either the World Health Organization (WHO) criteria or the Response Evaluation Criteria in Solid Tumors (RECIST) is the only imaging biomarker for anti-cancer drug testing presently approved by the United States Food and Drug Administration (FDA). The aim of this paper was to design and test a quality assurance phantom with the capability of monitoring tumor size changes with multiple preclinical imaging scanners (US, CT and MRI) in order to facilitate preclinical anti-cancer drug testing.MethodsThree phantoms (Gammex/UTHSCSA Mark 1, Gammex/UTHSCSA Mark 2 and UTHSCSA multimodality tumor measurement phantom) containing tumor-simulating test objects were designed and constructed. All three phantoms were scanned in US, CT and MRI devices. The size of test objects in the phantoms was measured from the US, CT and MRI images. RECIST, WHO and volume analyses were performed.ResultsThe smaller phantom size, simplified design and better test object CT contrast of the UTHSCSA multimodality tumor measurement phantom allowed scanning of the phantom in preclinical US, CT and MRI scanners compared with only limited preclinical scanning capability of Mark 1 and Mark 2 phantoms. For all imaging modalities, RECIST and WHO errors were reduced for UTHSCSA multimodality tumor measurement phantom (≤1.69 ± 0.33%) compared with both Mark 1 (≤ -7.56 ± 6.52%) and Mark 2 (≤ 5.66 ± 1.41%) phantoms. For the UTHSCSA multimodality tumor measurement phantom, measured tumor volumes were highly correlated with NIST traceable design volumes for US (R2 = 1.000, p < 0.0001), CT (R2 = 0.9999, p < 0.0001) and MRI (R2 = 0.9998, p < 0.0001).ConclusionsThe UTHSCSA multimodality tumor measurement phantom described in this study can potentially be a useful quality assurance tool for verifying radiologic assessment of tumor size change during preclinical anti-cancer therapy testing with multiple imaging modalities.

One-step preparation of hierarchical superparamagnetic iron oxide/graphene composites via hydrothermal method

In this paper, graphene/magnetite composites with hierarchical Fe3O4 structures were synthesized via a one-step hydrothermal method. The size of Fe3O4 nanocrystals and nanocrystal clusters can easily be controlled by altering reaction time and the starting mixed solvent ratio, respectively. Raman measurements evidenced that graphene oxide was simultaneously reduced to graphene during the deposition of magnetite particles. The deposition of Fe3O4 nanocrystals and nanocrystal clusters impedes graphene to restore the graphite structure. The composites showed a high crystallinity of magnetite and a considerable saturation magnetization. Furthermore, the acrylate modified Fe3O4 makes the composites water-dispersible and can effectively load polyfluorene polyelectrolyte via electrostatic force. The high magnetism, excellent water dispersibility and strong photoluminescence make these composites ideal candidates for various important applications such as magnetic resonance imaging, bioseparation, bioimaging, and optical devices fabrication.

WE‐C(SAM)‐211‐01: Physics of MR Safety

Magnetic resonance imaging (MRI) is a non‐invasive and non‐ionizing imaging modality that has an excellent track record for safety in its capacity as a diagnostic imaging device for over 20 years. MRI devices utilize a strong static magnetic field to polarize a sample, radiofrequency pulsed magnetic fields to excite the sample, and rapidly switched magnetic field gradients to spatially and temporally modulate the magnetization in the sample for image encoding. Because of their potential interaction with biological tissue as well as with medical implants or ancillary objects in the room, each of these fields presents a unique potential risk to the patient, staff or family members in the MRI environment that must be mitigated via education and constant vigilance.Additionally, innovations in MRI design and use can significantly impact safety considerations in and around the suite. MRI is no longer exclusively confined to a diagnostic imaging environment as its use as a treatment planning, interventional or intra‐operative imaging device expands. In addition to the safety challenges associated with performing procedures in these unique environments, technological advancements also constantly engage a re‐evaluation of MRI safety principles as they apply to monitoring of patients and objects in the MR suite. The use of higher field strengths as well as innovative bore designs which impact the spatial magnetic field gradients, such as wide or short bore magnets, may interact more strongly with implants or objects previously regarded as safe for use in the MRI environment. More powerful gradient systems invite much more rapid or higher resolution imaging acquisitions, which can increase the energy imparted to the patient or implant as well as push the limits of acoustic noise and peripheral nerve stimulation.The purpose of this continuing education review is to provide an overview for the Medical Physicist of the underlying physics which motivate many of the safety concerns associated with operating in the MRI environment. The primary intent is to provide additional perspective to, and promote a better understanding of, the current safety guidelines and recommendations as well as aid in addressing safety questions and concerns related to developing, operating and working in an MRI suite.Learning Objectives:1. Understand the major safety risks associated with MRI from a physics perspective2. Understand the potential impact MRI technology may have on safety considerations3. Review current FDA MR safety guidelines

Micrometer scale resolution of materials by stray-field Magnetic Resonance Imaging

As Magnetic Resonance Imaging devices are becoming more and more powerful, resolutions as small as 10 μm can now be obtained. But, this is only possible when systems with slow transverse relaxation rates, like living tissues, are investigated. In this case, the time available for gradients space-encoding is long, and high k values can be reached in the Fourier domain. However, numerous materials have fast relaxation rates, thus limiting the spatial resolution to a few hundreds of microns. The Stray Field Imaging technique has solved this problem by using a very high (typically 5000 G/cm) static gradient. Consequently, the trajectory in k space is accelerated and it is possible, in principle, to reach a micrometer resolution in a few hundreds of microseconds. Most of the time, however, only resolutions in the millimeter range can be achieved due to mispositioning of the sample within the static magnetic field. Here, we show that by finely mapping the magnetic field and precisely positioning the sample, it is possible with a standard spectrometer to reach a micrometer resolution even on very fast relaxing materials.

Methodology and Tools for Quality Control of Magnetic Resonance Imaging Devices

The quality control process for magnetic resonance imaging (MRI) devices in inpatient settings is discussed. Monitoring systems were designed at the Scientific-Practical Center for Medical Radiology. Methodology and special software for MRI quality control were tested in some hospitals of Moscow.

Active Noise Control System for Reducing MR Noise

We propose an active noise control (ANC) system for reducing periodic noise generated in a high magnetic field such as noise generated from magnetic resonance imaging (MRI) devices (MR noise). The proposed ANC system utilizes optical microphones and piezoelectric loudspeakers, because specific acoustic equipment is required to overcome the high-field problem, and consists of a head-mounted structure to control noise near the user's ears and to compensate for the low output of the piezoelectric loudspeaker. Moreover, internal model control (IMC)-based feedback ANC is employed because the MR noise includes some periodic components and is predictable. Our experimental results demonstrate that the proposed ANC system (head-mounted structure) can significantly reduce MR noise by approximately 30dB in a high field in an actual MRI room even if the imaging mode changes frequently.

The Role of PET with 13N-Ammonia and 18F-FDG in the Assessment of Myocardial Perfusion and Metabolism in Patients with Recent AMI and Intracoronary Stem Cell Injection

Over the last decade, the effects of stem cell therapy on cardiac repair after acute myocardial infarction (AMI) have been investigated with different imaging techniques. We evaluated a new imaging approach using (13)N-ammonia and (18)F-FDG PET for a combined analysis of cardiac perfusion, metabolism, and function in patients treated with intracoronary injection of endothelial progenitors or with conventional therapy for AMI. A total of 15 patients were randomly assigned to 3 groups based on different treatments (group A: bone marrow-derived stem cells; group B: peripheral blood-derived stem cells; group C: standard therapy alone). The number of scarred and viable segments, along with the infarct size and the extent of the viable area, were determined on a 9-segment (13)N-ammonia/(18)F-FDG PET polar map. Myocardial blood flow (MBF) was calculated for each segment on the ammonia polar map, whereas a global evaluation of left ventricular function was obtained by estimating left ventricular ejection fraction (LVEF) and end-diastolic volume, both derived from electrocardiography-gated (18)F-FDG images. Both intragroup and intergroup comparative analyses of the mean values of each parameter were performed at baseline and 3, 6, and 12 mo after AMI. During follow-up, major cardiac events were also registered. A significant decrease (P < 0.05) in the number of scarred segments and infarct size was observed in group A, along with an increase in MBF (P < 0.05) and a mild improvement in cardiac function. Lack of infarct size shrinkage in group B was associated with a marked impairment of MBF (P = 0.01) and cardiac dysfunction. Ambiguous changes in infarct size, MBF, and LVEF were found in group C. No differences in number of viable segments or in extent of viable area were found among the groups. At clinical follow-up, no major cardiac events occurred in group A patients, whereas 2 patients of group B experienced in-stent occlusion and one patient of group C received a transplant for heart failure. Our data suggest that a single nuclear imaging technique accurately analyzes changes in myocardial perfusion and metabolism occurring after stem cell transplantation.

Finite element analysis of gradient z-coil induced eddy currents in a permanent MRI magnet

In permanent magnetic resonance imaging (MRI) systems, pulsed gradient fields induce strong eddy currents in the conducting structures of the magnet body. The gradient field for image encoding is perturbed by these eddy currents leading to MR image distortions. This paper presents a comprehensive finite element (FE) analysis of the eddy current generation in the magnet conductors. In the proposed FE model, the hysteretic characteristics of ferromagnetic materials are considered and a scalar Preisach hysteresis model is employed. The developed FE model was applied to study gradient z-coil induced eddy currents in a 0.5T permanent MRI device. The simulation results demonstrate that the approach could be effectively used to investigate eddy current problems involving ferromagnetic materials. With the knowledge gained from this eddy current model, our next step is to design a passive magnet structure and active gradient coils to reduce the eddy current effects.

Mutual interferences and design principles for mechatronic devices in magnetic resonance imaging

Robotic and mechatronic devices that work compatibly with magnetic resonance imaging (MRI) are applied in diagnostic MRI, image-guided surgery, neurorehabilitation and neuroscience. MRI-compatible mechatronic systems must address the challenges imposed by the scanner's electromagnetic fields. We have developed objective quantitative evaluation criteria for device characteristics needed to formulate design guidelines that ensure MRI-compatibility based on safety, device functionality and image quality. The mutual interferences between an MRI system and mechatronic devices working in its vicinity are modeled and tested. For each interference, the involved components are listed, and a numerical measure for "MRI-compatibility" is proposed. These interferences are categorized into an MRI-compatibility matrix, with each element representing possible interactions between one part of the mechatronic system and one component of the electromagnetic fields. Based on this formulation, design principles for MRI-compatible mechatronic systems are proposed. Furthermore, test methods are developed to examine whether a mechatronic device indeed works without interferences within an MRI system. Finally, the proposed MRI-compatibility criteria and design guidelines have been applied to an actual design process that has been validated by the test procedures. Objective and quantitative MRI-compatibility measures for mechatronic and robotic devices have been established. Applying the proposed design principles, potential problems in safety, device functionality and image quality can be considered in the design phase to ensure that the mechatronic system will fulfill the MRI-compatibility criteria. New guidelines and test procedures for MRI instrument compatibility provide a rational basis for design and evaluation of mechatronic devices in various MRI applications. Designers can apply these criteria and use the tests, so that MRI-compatibility results can accrue to build an experiential database.

Magnetic resonance imaging of the ankle in female ballet dancers en pointe

Ballet dancers require extreme range of motion of the ankle, especially weight-bearing maximum plantar flexion (en pointe). In spite of a high prevalence of foot and ankle injuries in ballet dancers, the anatomy and pathoanatomy of this position have not been sufficiently studied in weight-bearing. Magnetic resonance imaging (MRI) is a beneficial method for such study. To develop an MRI method of evaluating the ankles of female ballet dancers standing en pointe and to assess whether pathological findings from the MR images were associated with ankle pain reported by the subjects. Nine female ballet dancers (age, 21+/-2.9 years; dance experience, 16+/-4.1 years; en pointe dance experience, 7+/-4.9 years) completed an ankle pain visual analog scale questionnaire and underwent T1- and T2-weighted scans using a 0.25 T open MRI device. The ankle was scanned in three positions: supine with full plantar flexion, standing with the ankle in anatomical position, and standing en pointe. Obtaining MR images of the ballet dancers en pointe was successful in spite of limitations imposed by the difficulty of remaining motionless in the en pointe position during scanning. MRI signs of ankle pathology and anatomical variants were observed. Convergence of the posterior edge of the tibial plafond, posterior talus, and superior calcaneus was noted in 100% of cases. Widened anterior joint congruity and synovitis/joint effusion were present in 71% and 67%, respectively. Anterior tibial and/or talar spurs and Stieda's process were each seen in 44%. However, clinical signs did not always correlate with pain reported by the subjects. This study successfully established an ankle imaging technique for ballet dancers en pointe that can be used in the future to assess the relationship between en pointe positioning and ankle pathoanatomy in ballet dancers.