MRI Room Research Articles

Brain activity and perceived exertion during cycling exercise: an fMRI study

Background/aimCurrently, the equipment and techniques available to assess brain function during dynamic exercise are limited, which has restricted our knowledge of how the brain regulates exercise. This study assessed the...

Sound source measurement of magnetic resonance imaging driving sound for feedforward active noise control system

We proposed the active noise control (ANC) system reduce the loud MRI sound. It was important for performance improvement of the system. Therefore, we estimated the sound source of MRI driving sound. The position of the sound source of MRI driving sound was between the center and the edge in the gantry of MRI equipment. MRI equipment is important for the medical inspection, which gets the tomography of the body without x-ray. The patient of the MRI inspection needs to use the ear protector because the MRI equipment generated the loud sound, which the sound pressure level was around 100 dB. Here, our study was to make good acoustical environment using the ANC system for the MRI patient. The ANC system used the feedforward type because the MRI driving sound have unsteady pulsed sound. We made the ANC system using non-magnetic devices, ear protectors, and optical microphones. Because the MRI room had high magnetic environment. We measured the sound source of MRI driving sound to set the reference microphone. In this case, we showed the reduction effect of the ANC system of the sound by the computer simulation. As a result, the system reduced the MRI driving sound by around 50 dB.

2P1-G10 fMRI対応マスタスレーブシステムを用いた体外離脱体験への誘導(感覚・運動・計測(3))

This paper introduces an fMRI-compatible master-slave system which enables users to perform both the stroking and tapping their own back on the bed in MRI room. Also, the application to neuroscience experiment is challenged, actually conducting an OBE experiment in normal environment using the prototype. The experimental results imply that the proposed method can be a promising new approach for the study on human body ownership.

Design of a Teleoperated Needle Steering System for MRI-guided Prostate Interventions.

Accurate needle placement plays a key role in success of prostate biopsy and brachytherapy. During percutaneous interventions, the prostate gland rotates and deforms which may cause significant target displacement. In these cases straight needle trajectory is not sufficient for precise targeting. Although needle spinning and fast insertion may be helpful, they do not entirely resolve the issue. We propose robot-assisted bevel-tip needle steering under MRI guidance as a potential solution to compensate for the target displacement. MRI is chosen for its superior soft tissue contrast in prostate imaging. Due to the confined workspace of the MRI scanner and the requirement for the clinician to be present inside the MRI room during the procedure, we designed a MRI-compatible 2-DOF haptic device to command the needle steering slave robot which operates inside the scanner. The needle steering slave robot was designed to be integrated with a previously developed pneumatically actuated transperineal robot for MRI-guided prostate needle placement. We describe design challenges and present the conceptual design of the master and slave robots and the associated controller.

Initial Results of Simultaneous PET/MRI Experiments with an MRI-Compatible Silicon Photomultiplier PET Scanner

The most investigated semiconductor photosensor for MRI-compatible PET detectors is the avalanche photodiode (APD). However, the silicon photomultiplier (SiPM), also called the Geiger-mode APD, is gaining attention in the development of the next generation of PET/MRI systems because the SiPM has much better performance than the APD. We have developed an MRI-compatible PET system based on multichannel SiPM arrays to allow simultaneous PET/MRI. The SiPM PET scanner consists of 12 detector modules with a ring diameter of 13.6 cm and an axial extent of 3.2 cm. In each detector module, 4 multichannel SiPM arrays (with 4 × 4 channels arranged in a 2 × 2 array to yield 8 × 8 channels) were coupled with 20 × 18 Lu(1.9)Gd(0.1)SiO(5):Ce crystals (each crystal is 1.5 × 1.5 × 7 mm) and mounted on a charge division network for multiplexing 64 signals into 4 position signals. Each detector module was enclosed in a shielding box to reduce interference between the PET and MRI scanners, and the temperature inside the box was monitored for correction of the temperature-dependent gain variation of the SiPM. The PET detector signal was routed to the outside of the MRI room and processed with a field programmable gate array-based data acquisition system. MRI compatibility tests and simultaneous PET/MRI acquisitions were performed inside a 3-T clinical MRI system with 4-cm loop receiver coils that were built into the SiPM PET scanner. Interference between the imaging systems was investigated, and phantom and mouse experiments were performed. No radiofrequency interference on the PET signal or degradation in the energy spectrum and flood map was shown during simultaneous PET/MRI. The quality of the MRI scans acquired with and without the operating PET showed only slight degradation. The results of phantom and mouse experiments confirmed the feasibility of this system for simultaneous PET/MRI. Simultaneous PET/MRI was possible with a multichannel SiPM-based PET scanner, with no radiofrequency interference on PET signals or images and only slight degradation of the MRI scans.

Design and Control of a 1-DOF MRI Compatible Pneumatically Actuated Robot with Long Transmission Lines.

This paper presents the design and control of an MRI-compatible 1-DOF needle driver robot and its precise position control using pneumatic actuation with long transmission lines. MRI provides superior image quality compared to other imaging modalities such as CT or ultrasound, but imposes severe limitations on the material and actuator choice (to prevent image distortion) due to its strong magnetic field. We are primarily interested in developing a pneumatically actuated breast biopsy robot with a large force bandwidth and precise targeting capability during radio-frequency ablation (RFA) of breast tumor, and exploring the possibility of using long pneumatic transmission lines from outside the MRI room to the device in the magnet to prevent any image distortion whatsoever. This paper presents a model of the entire pneumatic system. The pneumatic lines are approximated by a first order system with time delay, because its dynamics are governed by the telegraph equation with varying coefficients and boundary conditions, which cannot be solved precisely. The slow response of long pneumatic lines and valve subsystems make position control challenging. This is further compounded by the presence of non-uniform friction in the device. Sliding mode control (SMC) was adopted, where friction was treated as an uncertainty term to drive the system onto the sliding surface. Three different controllers were designed, developed, and evaluated to achieve precise position control of the RFA probe. Experimental results revealed that all SMCs gave satisfactory performance with long transmission lines. We also performed several experiments with a 3-DOF fiber-optic force sensor attached to the needle driver to evaluate the performance of the device in the MRI under continuous imaging.

FMRI brain mapping during motion capture and FES induced motor tasks: Signal to noise ratio assessment

Functional Electrical Stimulation (FES) is a well known clinical rehabilitation procedure, however the neural mechanisms that underlie this treatment at Central Nervous System (CNS) level are still not completely understood. Functional magnetic resonance imaging (fMRI) is a suitable tool to investigate effects of rehabilitative treatments on brain plasticity. Moreover, monitoring the effective executed movement is needed to correctly interpret activation maps, most of all in neurological patients where required motor tasks could be only partially accomplished. The proposed experimental set-up includes a 1.5 T fMRI scanner, a motion capture system to acquire kinematic data, and an electro-stimulation device. The introduction of metallic devices and of stimulation current in the MRI room could affect fMRI acquisitions so as to prevent a reliable activation maps analysis. What we are interested in is that the Blood Oxygenation Level Dependent (BOLD) signal, marker of neural activity, could be detected within a given experimental condition and set-up. In this paper we assess temporal Signal to Noise Ratio (SNR) as image quality index. BOLD signal change is about 1–2% as revealed by a 1.5 T scanner. This work demonstrates that, with this innovative set-up, in the main cortical sensorimotor regions 1% BOLD signal change can be detected at least in the 93% of the sub-volumes, and almost 100% of the sub-volumes are suitable for 2% signal change detection. The integrated experimental set-up will therefore allows to detect FES induced movements fMRI maps simultaneously with kinematic acquisitions so as to investigate FES-based rehabilitation treatments contribution at CNS level.

Magnetic field threshold for accurate electrocardiography in the MRI environment

Although the electrocardiogram is known to be nondiagnostic within the bore of any high-field magnet due to the magnetohydrodynamic effect, there are an increasing number of applications that require accurate electrocardiogram monitoring of a patient inside the MRI room but outside of the magnet bore. Magnetohydrodynamic effects on the ST segment of the electrocardiogram waveform were investigated in six subjects at magnetic field strengths ranging from 6.4 mT to 652 mT at the aortic midarch, and the electrocardiogram was found to be accurate at magnetic fields below 70 mT. This corresponds to a distance of 160 cm from the isocenter and 80 cm from the bore entrance for the 1.5-T MRI system used in this study. These results can be translated to any MRI system, with knowledge of the fringe field. Accurate electrocardiogram monitoring is feasible in close proximity to the MRI magnet, such as during and after pharmacologic or exercise stress, or interventional or surgical procedures performed in the MRI room.

A PVDF Receiver for Ultrasound Monitoring of Transcranial Focused Ultrasound Therapy

Focused ultrasound (FUS) shows great promise for use in the area of transcranial therapy. Currently dependent on MRI for monitoring, transcranial FUS would benefit from a real-time technique to monitor acoustic emissions during therapy. A polyvinylidene fluoride receiver with an active area of 17.8 mm (2) and a film thickness of 110 mum was constructed. A compact preamplifier was designed to fit within the receiver to improve the receiver SNR and allow the long transmission line needed to remove the receiver electronics outside of the MRI room. The receiver was compared with a 0.5 mm commercial needle hydrophone and focused and unfocused piezoceramics. The receiver was found to have a higher sensitivity than the needle hydrophone, a more wideband response than the piezoceramic, and sufficient threshold for detection of microbubble emissions. Sonication of microbubbles directly and through a fragment of human skull demonstrated the ability of the receiver to detect harmonic bubble emissions, and showed potential for use in a larger scale array. Monitoring of disruption of the blood-brain barrier in rats showed functionality in vivo and the ability to detect subharmonic, harmonic, and wideband emissions during therapy. The receiver shows potential for monitoring acoustic emissions during treatments and providing additional parameters to assist treatment planning. Future work will focus on developing a multi-element array for transcranial treatment monitoring.

Audibility of anaesthesia alarms during magnetic resonance imaging: should we be alarmed?

The effects of MRI acoustic noise on anaesthesia safety concerns have not yet been documented. The objectives of this study were to provide subjective and objective evaluations of anaesthesia alarm audibility during MRI and to review the literature to determine whether or not to worry about our results. Following Institutional Review Board's approval, we tested the audibility of four anaesthesia equipment alarms and selected one of them. Additionally, we selected the least audible of three MRI sequences (spin echo) for the study. The evaluations were conducted inside and outside the scanning room in a subjective and objective manner. First, 20 normal hearing consenting adult volunteers rated their audibility of the anaesthesia alarm using a 10-point numerical scale (0 = not audible to 10 = maximum audibility). Second, a sound level meter was used to measure the intensity of acoustic noise (A-weighted scale) under the above-mentioned conditions. Data, expressed as median [interquartile range], were analysed using the Wilcoxon test with P less than 0.05 considered as significant. The subjective audibility scores (inside vs. outside the MRI room) were 9.0 [8.5-10.0] vs. 7 [6.5-8.0]. During MRI scanning, the scores were 6.0 [5.5-7.0] vs. 4.0 [3.5-5.0], respectively (P < 0.001). The sound level measurements were 70 [69-71] vs. 55 [54-57] dB (A). During MRI 91 [91-92] dB (A) vs. 68 [65-69] dB (A) (P < 0.001). The audibility of the anaesthesia alarm is significantly reduced during MRI, particularly outside the scanning room. Consequently, optical alarms and interactive screens (outside the room) must be available without exception.

Don't forget the quench pipe when installing an MRI

An MRI is a useful medical device but it makes a lot of noise. A sound level of 90 dB(A) or more in the MRI room is not unusual. Placing an MRI in an existing hospital means that extra care has to be taken to prevent the noise from the MRI causing nuisance in adjacent rooms. In this paper the situation is discussed in which complaints appeared after the installation of the MRI. First sound measurements were done to see if the sound level in the office above the MRI fulfils the noise ratings. This way it would be clearer if the acoustic measures were doing their job. Whatever the outcome, the hospital wanted to put an end to the complaints. So, more sound measurements were done to establish the cause of the nuisance and to point out what extra measures have to be taken to solve the problem. It turned out that the quench pipe played an important role in this situation.

Magnetic resonance imaging with the Digisonic SP Neurelec cochlear implant

The goal of this study was to evaluate the MR compatibility of the Neurelec Digisonic SP cochlear implant by performing in vitro and in vivo tests. All tests were performed on 1.5 T machine. Torque and force were measured to observe a potential displacement of the internal receiver. Demagnetisation of the internal magnet was monitored inside the MRI scanner and outside the MRI scanner (in the MRI room). Potential-induced voltage on electrodes was measured in vitro, performing the usual MR sequences. Heating around the internal receiver was measured after the same MR sequences. Following in vitro tests, in vivo MR imaging (brain and posterior fossa MRI) was performed to evaluate the induced signal void and geometrical distortion. In vivo test was performed with one volunteer who had a cochlear implant device fixed to the surface of the skin with a bandage. All the in vitro tests were in compliance with standard EN 45502-2-3 relating to Cochlear Implants. In vivo MRI scans demonstrated an image distortion for spin echo sequences of 7 cm maximum around the internal magnet. Magnetic resonance imaging with the Neurelec Digisonic SP cochlear implant is possible with no measurable adverse effects for either the patient or the device. Image artefact around the internal magnet, however, is unavoidable.

Cardiac function and myocardial perfusion immediately following maximal treadmill exercise inside the MRI room.

Treadmill exercise stress testing is an essential tool in the prevention, detection, and treatment of a broad spectrum of cardiovascular disease. After maximal exercise, cardiac images at peak stress are typically acquired using nuclear scintigraphy or echocardiography, both of which have inherent limitations. Although CMR offers superior image quality, the lack of MRI-compatible exercise and monitoring equipment has prevented the realization of treadmill exercise CMR.It is critical to commence imaging as quickly as possible after exercise to capture exercise-induced cardiac wall motion abnormalities. We modified a commercial treadmill such that it could be safely positioned inside the MRI room to minimize the distance between the treadmill and the scan table. We optimized the treadmill exercise CMR protocol in 20 healthy volunteers and successfully imaged cardiac function and myocardial perfusion at peak stress, followed by viability imaging at rest. Imaging commenced an average of 30 seconds after maximal exercise. Real-time cine of seven slices with no breath-hold and no ECG-gating was completed within 45 seconds of exercise, immediately followed by stress perfusion imaging of three short-axis slices which showed an average time to peak enhancement within 57 seconds of exercise. We observed a 3.1-fold increase in cardiac output and a myocardial perfusion reserve index of 1.9, which agree with reported values for healthy subjects at peak stress. This study successfully demonstrates in-room treadmill exercise CMR in healthy volunteers, but confirmation of feasibility in patients with heart disease is still needed.

A single nocturnal exposure to 2-7 millitesla static magnetic fields does not inhibit the excretion of 6-sulfatoxymelatonin in healthy young men.

The present study sought to evaluate possible acute effects on 6-sulfatoxymelatonin (aMT6s) excretion, a surrogate for melatonin levels in blood, in volunteers exposed to static magnetic fields with flux densities representative for workers in light metal reduction plants and operators of medical MRI in hospitals. Eleven healthy male volunteers (23-43 years) participated. Urine samples were collected for two consecutive 24 h periods from 22:00 hours day 1 (exposure day) through day 2 (day after exposure) and then for 24 h from 07:00 hours on day 7 (control day). On the day of exposure the subjects slept in the MRI room from 22:00 hours until 07:00 hours next morning, thus receiving a 9 h exposure to the magnetic field (2-7 mT). On the day after exposure and on the control day, they slept at home and otherwise performed their ordinary daily activities. Total daily urine production was collected in four parts: 22:00-07:00 hours, 07:00-11:00 hours, 11:00-18:00 hours, 18:00-22:00 hours, and the volume for each interval was measured and recorded. Samples were transferred to coded bottles and frozen for later RIA analysis of aMT6s. Pairs of values of mean hourly aMT6s excretion, both diurnal and for the four daily intervals, were compared using two-sided Wilcoxon signed ranks test. The day of exposure and the day after exposure were not significantly different from the control day, either for the total diurnal secretion or the interval data. In summary, the study shows no association between a single nocturnal exposure to a static magnetic field of strength 2-7 mT and excretion of aMT6s in urine.

磁気シールドルーム設計のための磁場解析手法の検討

This paper compares various magnetic field analysis techniques for designing a magnetically shielded room. The effectiveness and capability of techniques are discussed with regard to practical considerations such as computation speed and accuracy. The magnetic field analysis techniques studied here include the finite element method using edge elements, the improved integral equation method, and the finite element method using the magnetic vector potential. Both two- and three-dimensional models are examined. The study indicates that all two-dimensional models are faster in computation speed but lower in accuracy than the three-dimensional ones, as expected. The three-dimensional finite element methods are found to be impractical in terms of their computation time. The improved integral equation method proves to be effective for open types of boundary problem such as the shielding effect of an MRI room.

Magnetic Resonance Imaging of the Orbit

Magnetic resonance has twin capabilities. It can provide anatomical (magnetic resonance imaging, MRI) and physiochemical (magnetic resonance spectroscopy) information. Nuclei with an odd mass number, particularly hydrogen in free water, have electromagnetic properties. When placed in a strong static magnetic field and excited by radiofrequency waves of a specific wavelength, these nuclei emit a signal. The MR signal can then be digitized, stored in a computer, and subsequently converted into an image. Factors that affect these images are tissue parameters (T1 and T2 time constants, proton density, and flow) and radiofrequency pulse sequences. Surface coils are useful for improving images of the orbit. The magnet can have a major and potentially dangerous influence on the surrounding environment, and access to the MRI area must be carefully controlled. Shielding of the MRI room prevents external factors from adversely affecting the MRI unit and the images produced.

磁場遮蔽に関する研究

Magnetic shielding is more difficult than radio frequency shielding. Therefore, good shielding effect can hardly be expected using the magnetic shielding method. This fact can easily be seen by comparing the ratio of energy conduction and the stopping power of electric energy and of magnetic energy. For the study of the magnetic shielding effect of an MRI room, measurements of magnetic field strength were made using gaussmeter equipped with a probe. Furthermore, these results were compared with the results of a computer simulation based on the boundary element method. The experimentally obtained results indicated 33 dB, which corresponds to the attenuation of 1/50. Calculated shielding effect by computer simulation was 20.9 dB, which corresponds to an attenuation of about 1/10.

MRI室の遮蔽

During the time of shielding the MRI room, it is necessary to consider shielding of the magnetic field as well as that of electromagnetic wave (radio frequency). In order to reduce these influences as much as posible, we must ensure that there is sufficient distance or install an appropriate shield. This is a report of the results of our experiments which were carried out in the MRI room to evaluate the shielding effect of the magnetic field and electromagnetic waves. Materials used for the shield were a 0.6 mm MT steel plate and 0.036 mm electric copper lief. The method of measurement was proportionate to MIL-STD-285. The effect of the magnetic shield was a 1/50 reduction in the magnetic field intensity, with almost complete shielding of the electromagnetic waves.