Subjectively Reported Effects Experienced in an Actively Shielded 7T MRI: A Large-Scale Study.

BACKGROUND: Ultrahigh-field (UHF) MRI advances towards clinical use. Patient compliance is generally high, but few large-scale studies have investigated the effects experienced in 7T MRI systems, especially considering peripheral nerve stimulation (PNS) and caregiving. PURPOSE: To evaluate the quantity, the intensity, and subjective experiences from short-term effects, focusing on the levels of comfort and compliance of subjects. STUDY TYPE: Prospective. POPULATION: In all, 954 consecutive MRIs in 801 subjects for 3 years. FIELD STRENGTH: 7T. ASSESSMENT: After the 7T examination, a questionnaire was used to collect data. STATISTICAL TESTS: Descriptive statistics, Spearman's rank correlation, Mann-Whitney U-test, and t-test. RESULTS: The majority (63%) of subjects agreed that the MRI experience was comfortable and 93% would be willing to undergo future 7T MRI as a patient (5% undecided) and 82% for research purposes (12% undecided). The most common short-term effects experienced were dizziness (81%), inconsistent movement (68%), PNS (63%), headache (40%), nausea (32%), metallic taste (12%), and light flashes (8%). Of the subjects who reported having PNS (n = 603), 44% experienced PNS as "not uncomfortable at all," 45% as "little or very little uncomfortable," and 11% as "moderate to very much uncomfortable." Scanner room temperature was experienced more comfortable before (78%) than during (58%) examinations, and the noise level was acceptable by 90% of subjects. Anxiety before the examination was reported by 43%. Patients differed from healthy volunteers regarding an experience of headache, metallic taste, dizziness, or anxiety. Room for improvement was pointed out after 117 examinations concerning given information (n = 73), communication and sound system (n = 35), or nursing care (n = 15). DATA CONCLUSION: Subjectively reported effects occur in actively shielded 7T MRI and include physiological responses and individual psychological issues. Although leaving room for improvement, few subjects experienced these effects being so uncomfortable that they would lead to aversion to future UHF examinations. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 5 J. Magn. Reson. Imaging 2020;52:1265-1276.

Valid Exposure Protocols Needed in Magnetic Resonance Imaging Genotoxic Research.

Several in vitro and in vivo studies have investigated if a magnetic resonance imaging (MRI) examination can cause DNA damage in human blood cells. However, the electromagnetic field (EMF) exposure that the cells received in the MR scanner was not sufficiently described. The first studies looking into this could be regarded as hypothesis-generating studies. However, for further exploration into the role of MRI exposure on DNA integrity, the exposure itself cannot be ignored. The lack of sufficient method descriptions makes the early experiments difficult, if not impossible, to repeat. The golden rule in all experimental work is that a study should be repeatable by someone with the right knowledge and equipment, and this is simply not the case with many of the recent studies on MRI and genotoxicity. Here we discuss what is lacking in previous studies, and how we think the next generation of in vitro and in vivo studies on MRI and genotoxicity should be performed. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

Swedish national survey on MR safety compared with CT: a false sense of security?

OBJECTIVES: The objectives were to survey MR safety incidents in Sweden during a 12-month period, to assess severity scores, and to evaluate the confidence of MR personnel in incident-reporting mechanisms. METHOD: Data were collected within a web-based questionnaire on safety in clinical MR environments with CT for comparison. Data reported MR and CT safety incidents (human injury, material damage, and close calls), incident severity, and confidence of participants in incident-reporting systems. RESULTS: The study population consisted of 529 eligible participants. Participants reported 200 MR and 156 CT safety incidents. Among MR incidents, 16% were given the highest potential severity score. More MR workers (73%) than CT workers (50%) were confident in being aware of any incident occurring at their workplace. However, 69% MR workers (83% for CT) were not aware of reported incidents at their hospitals. CONCLUSION: Safety incidents resulting in human injury, material damage, and close calls in clinical MR environments do occur. According to national risk assessment recommendations, risk level is high. Results indicated that MR personnel tend to a false sense of security, as a high proportion of staff members were sure that they would have been aware of any incident occurring in their own department, while in reality, incidents did occur without their knowledge. We conclude that false sense of security exists for MR. KEY POINTS: • Safety incidents in clinical MR environments still result in human injury and material damage. • Severity level of MR incidents-assessed using Swedish national risk assessment recommendations-is high. • Confidence of MR personnel in incident-reporting mechanisms is high, but reflects a false sense of security, as a high proportion of staff is unaware of reported incidents in the same workplace.

Short-term effects experienced during examinations in an actively shielded 7 T MR.

The objective of this study was to evaluate occurrence and strength of short-term effects experienced by study participants in an actively shielded (AS) 7 tesla (7 T) magnetic resonance (MR) scanner, to compare results with earlier reports on passively shielded (PS) 7 T MR scanners, and to outline possible healthcare strategies to improve patient compliance. Study participants (n = 124) completed a web-based questionnaire directly after being examined in an AS 7 T MR (n = 154 examinations). Most frequently experienced short-term effects were dizziness (84%) and inconsistent movement (70%), especially while moving into or out of the magnet. Peripheral nerve stimulation (PNS)-twitching-was experienced in 67% of research examinations and showed a dependence between strength of twitches and recorded predicted PNS values. Of the participants, 74% experienced noise levels as acceptable and the majority experienced body and room temperature as comfortable. Of the study participants, 95% felt well-informed and felt they had had good contact with the staff before the examination. Willingness to undergo a future 7 T examination was high (>90%). Our study concludes short-term effects are often experienced during examinations in an AS 7 T MR, leaving room for improvement in nursing care strategies to increase patient compliance. Bioelectromagnetics. 2019;9999:XX-XX. © 2019 The Authors. Bioelectromagnetics Published by Wiley Periodicals, Inc.

EMF exposure variation among MRI sequences from pediatric examination protocols.

The magnetic resonance imaging (MRI) exposure environment is unique due to the mixture and intensity of magnetic fields involved. Current safety regulations are based on well-known acute effects of heating and neuroexcitation while the scientific grounds for possible long-term effects from MRI exposure are lacking. Epidemiological research requires careful exposure characterization, and as a first step toward improved exposure assessment we set out to characterize the MRI-patient exposure environment. Seven MRI sequences were run on a 3-Tesla scanner while the radiofrequency and gradient magnetic fields were measured inside the scanner bore. The sequences were compared in terms of 14 different exposure parameters. To study within-sequence variability, we varied sequence settings such as flip angle and slice thickness one at a time, to determine if they had any impact on exposure endpoints. There were significant differences between two or more sequences for all fourteen exposure parameters. Within-sequence differences were up to 60% of the corresponding between-sequence differences, and a 5-8 fold exposure increase was caused by variations in flip angle, slice spacing, and field of view. MRI exposure is therefore not only sequence-specific but also patient- and examination occurrence-specific, a complexity that requires careful consideration for an MRI exposure assessment in epidemiological studies to be meaningful. Bioelectromagnetics. 40:3-15, 2019. © 2018 The Authors. Bioelectromagnetics Published by Wiley Periodicals, Inc.

Phantom digit somatotopy: a functional magnetic resonance imaging study in forearm amputees.

Forearm amputees often experience non-painful sensations in their phantom when the amputation stump is touched. Cutaneous stimulation of specific stump areas may be perceived as stimulation of specific phantom fingers (stump hand map). The neuronal basis of referred phantom limb sensations is unknown. We used functional magnetic resonance imaging to demonstrate a somatotopic map of the phantom fingers in the hand region of the primary somatosensory cortex after tactile stump stimulation. The location and extent of phantom finger activation in the primary somatosensory cortex corresponded well to the location of normal fingers in a reference population. Stimulation of the stump hand map resulted in an increased bilateral activation of the primary somatosensory cortex compared with stimulation of forearm regions outside the stump hand map. Increased activation was also seen in contralateral posterior parietal cortex and premotor cortex. Ipsilateral primary somatosensory cortex activation might represent a compensatory mechanism and activation of the non-primary fronto-parietal areas might correspond to awareness of the phantom limb, which is enhanced when experiencing the referred sensations. It is concluded that phantom sensation elicited by stimulation of stump hand map areas is associated with activation of finger-specific somatotopical representations in the primary somatosensory cortex. This suggests that the primary somatosensory cortex could be a neural substrate of non-painful phantom sensations. The stump hand map phenomenon might be useful in the development of prosthetic hand devices.

99mTc-labeled superparamagnetic iron oxide nanoparticles for multimodality SPECT/MRI of sentinel lymph nodes.

UNLABELLED: The purpose of this study was to develop multimodality SPECT/MRI contrast agents for sentinel lymph node (SLN) mapping in vivo. METHODS: Nanoparticles with a solid iron oxide core and a polyethylene glycol coating were labeled with (99m)Tc. The labeling efficiency was determined with instant thin-layer chromatography and magnetic separation. The stability of the radiolabeled superparamagnetic iron oxide nanoparticles (SPIONs) was verified in both sterile water and human serum at room temperature 6 and 24 h after labeling. Five Wistar rats were injected subcutaneously in the right hind paw with (99m)Tc-SPIONs (25-50 MBq, ∼0.2 mg of Fe) and sacrificed 4 h after injection. Two animals were imaged with SPECT/MRI. All 5 rats were dissected; the lymph nodes, liver, kidneys, spleen, and hind paw containing the injection site were removed and weighed; and activity in the samples was measured. The microdistribution within the lymph nodes was studied with digital autoradiography. RESULTS: The efficiency of labeling of the SPIONs was 99% 6 h after labeling in both water and human serum. The labeling yield was 98% in water and 97% in human serum 24 h after labeling. The SLN could be identified in vivo with SPECT/MRI. The accumulation of (99m)Tc-SPIONs (as the percentage injected dose/g [%ID/g]) in the SLN was 100 %ID/g, whereas in the liver and spleen it was less than 2 %ID/g. Digital autoradiography images revealed a nonhomogeneous distribution of (99m)Tc-SPIONs within the lymph nodes; nanoparticles were found in the cortical, subcapsular, and medullary sinuses. CONCLUSION: This study revealed the feasibility of labeling SPIONs with (99m)Tc. The accumulation of (99m)Tc-SPIONs in lymph nodes after subcutaneous injection in animals, verified by SPECT/MRI, is encouraging for applications in breast cancer and malignant melanoma.

Can resting-state functional MRI serve as a complement to task-based mapping of sensorimotor function? A test-retest reliability study in healthy volunteers.

PURPOSE: To investigate if resting-state functional MRI (fMRI) reliably can serve as a complement to task-based fMRI for presurgical mapping of the sensorimotor cortex. MATERIALS AND METHODS: Functional data were obtained in 10 healthy volunteers using a 3 Tesla MRI system. Each subject performed five bilateral finger tapping experiments interleaved with five resting-state experiments. Following preprocessing, data from eight volunteers were further analyzed with the general linear model (finger tapping data) and independent component analysis (rest data). Test-retest reliability estimates (hit rate and false alarm rate) for resting-state fMRI activation of the sensorimotor network were compared with the reliability estimates for task-evoked activation of the sensorimotor cortex. The reliability estimates constituted a receiver operating characteristics curve from which the area under the curve (AUC) was calculated. Statistical testing was performed to compare the two groups with respect to reliability. RESULTS: The AUC was generally higher for the task experiments, although median AUC was not significantly different on a group level. Also, the two groups showed comparable levels of within-group variance. CONCLUSION: Test-retest reliability was comparable between resting-state measurements and task-based fMRI, suggesting that presurgical mapping of functional networks can be a supplement to task-based fMRI in cases where patient status excludes task-based fMRI.

fMRI memory assessment in healthy subjects: a new approach to view lateralization data at an individual level.

We present a comprehensive and clinically applicable fMRI test-including both a verbal and a visuospatial task-for assessment of hemispheric specific memory in the medial temporal lobe (MTL). fMRI data was collected from 15 healthy right-handed volunteers. Whole-brain activation was analyzed as well as activation in two regions of interest: the MTL and the anterior speech area. Laterality indices (LI) and LI-curves were calculated using the LI toolbox of Wilke and Lidzba, 2007. The fMRI paradigms successfully visualized memory-related activity in the MTL, the verbal memory measure also provided information of language lateralization. Eleven subjects showed left lateralized verbal encoding in the MTL, visuospatial memory activation was divided equally between left and right, and 14/15 subjects had left lateralized language. Lateralization data at the group level were consistent with previous studies, but a variety of activation effects were found at the individual level indicating differences in strategy during verbal and visuospatial processing. Further studies using the presented method are needed to determine its clinical usefulness.

Assessment of spatial BOLD sensitivity variations in fMRI using gradient-echo field maps.

Clinical blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is becoming increasingly valuable in, e.g., presurgical planning, but the commonly used gradient-echo echo-planar imaging (GE-EPI) technique is sometimes hampered by macroscopic field inhomogeneities. This can affect the degree of signal change that will occur in the GE-EPI images as a response to neural activation and the subsequent blood oxygenation changes, i.e., the BOLD sensitivity (BS). In this study, quantitative BS maps were calculated directly from gradient-echo field maps obtainable on most clinical scanners. In order to validate the accuracy of the calculated BS-maps, known shim gradients were applied and field maps and GE-EPI images of a phantom were acquired. Measured GE-EPI image intensity was then compared with the calculated (predicted) image intensity (pII) which was obtained from the field maps using theoretical expressions for image-intensity loss. The validated expressions for pII were used to calculate the corresponding predicted BOLD sensitivity (pBS) maps in healthy volunteers. Since the field map is assumed to be valid throughout an entire fMRI experiment, the influence of subject motion on the pBS maps was also assessed. To demonstrate the usefulness of such maps, pBS was investigated for clinically important functional areas including hippocampus, Broca's area and primary motor cortex. A systematic left/right pBS difference was observed in Broca's area and in the hippocampus, most likely due to magnetic field inhomogeneity of the particular MRI-system used in this study. For all subjects, the hippocampus showed pBS values above unity with a clear anterior-posterior gradient and with an abrupt drop to zero pBS in the anterior parts of hippocampus. It is concluded that GE field maps can be used to accurately predict BOLD sensitivity and that this parameter is useful to assess spatial variations which will influence fMRI experiments.

Dimensionality reduction of fMRI time series data using locally linear embedding.

OBJECTIVE: Data-driven methods for fMRI analysis are useful, for example, when an a priori model of signal variations is unavailable. However, activation sources are typically assumed to be linearly mixed, although non-linear properties of fMRI data, including resting-state data, have been observed. In this work, the non-linear locally linear embedding (LLE) algorithm is introduced for dimensionality reduction of fMRI time series data. MATERIALS AND METHODS: LLE performance was optimised and tested using simulated and volunteer data for task-evoked responses. LLE was compared with principal component analysis (PCA) as a preprocessing step to independent component analysis (ICA). Using an example data set with known non-linear properties, LLE-ICA was compared with PCA-ICA and non-linear PCA-ICA. A resting-state data set was analysed to compare LLE-ICA and PCA-ICA with respect to identifying resting-state networks. RESULTS: LLE consistently found task-related components as well as known resting-state networks, and the algorithm compared well to PCA. The non-linear example data set demonstrated that LLE, unlike PCA, can separate non-linearly modulated sources in a low-dimensional subspace. Given the same target dimensionality, LLE also performed better than non-linear PCA. CONCLUSION: LLE is promising for fMRI data analysis and has potential advantages compared with PCA in terms of its ability to find non-linear relationships.

A two-compartment gel phantom for optimization and quality assurance in clinical BOLD fMRI.

Clinical applications of blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) depend heavily on robust paradigms, imaging methods and analysis procedures. In this work, as a means to optimize and perform quality assurance of the entire imaging and analysis chain, a phantom that provides a well known and reproducible signal change similar to a block type fMRI experiment is presented. It consists of two gel compartments with slightly different T2 that dynamically enter and leave the imaged volume. The homogeneous gel in combination with a cylindrical geometry results in a well-defined T*2 difference causing a signal difference between the two compartments in T*2-weighted MR images. From time series data obtained with the phantom, maps of percent signal change (PSC) and t-values are calculated. As an example of image parameter optimisation, the phantom is demonstrated to be useful for accurate determination of the influence of echo time (TE) on BOLD fMRI results, taking the t-value as a measure of sensitivity. In addition, the phantom is proposed as a tool for quality assurance (QA) since reproducible time series and t-maps are obtained in a series of independent repeat experiments. The phantom is relatively simple to build and can therefore be used by any clinical fMRI center.

Flexible statistical modelling detects clinical functional magnetic resonance imaging activation in partially compliant subjects.

Clinical functional magnetic resonance imaging (fMRI) occasionally fails to detect significant activation, often due to variability in task performance. The present study seeks to test whether a more flexible statistical analysis can better detect activation, by accounting for variance associated with variable compliance to the task over time. Experimental results and simulated data both confirm that even at 80% compliance to the task, such a flexible model outperforms standard statistical analysis when assessed using the extent of activation (experimental data), goodness of fit (experimental data), and area under the operator characteristic curve (simulated data). Furthermore, retrospective examination of 14 clinical fMRI examinations reveals that in patients where the standard statistical approach yields activation, there is a measurable gain in model performance in adopting the flexible statistical model, with little or no penalty in lost sensitivity. This indicates that a flexible model should be considered, particularly for clinical patients who may have difficulty complying fully with the study task.

Magnetic resonance imaging artifacts caused by aneurysm clips and shunt valves: dependence on field strength (1.5 and 3 T) and imaging parameters.

PURPOSE: To evaluate artifact sizes at 3 T compared to at 1.5 T, and to evaluate the influence of scanning parameters with respect to artifact size on a 3-T magnetic resonance imaging (MRI) system. MATERIALS AND METHODS: Two aneurysm clips and five shunt valves were imaged in a water phantom at 1.5 and 3 T. At 3 T the influence of bandwidth (spin echo (SE) images) and echo time (gradient echo (GRE) images) on artifact size (area and extension in two orthogonal directions) was investigated. RESULTS: Artifact sizes increased substantially (typically 5-10 mm) at 3 T, compared to at 1.5 T, for implants entirely made of metallic materials, whereas the increase was the size less prominent (0-5 mm) for implants only partly containing metal. Artifact areas could be altered by changing the bandwidth or the echo time to about the same extent as it was affected by the increased field strength. CONCLUSION: Artifact sizes increase at 3 T, compared to at 1.5 T, depending on the type and composition of the implant, but can be substantially reduced by altering the imaging parameters. Optimization of imaging protocols to minimize artifacts is therefore important at higher field strengths.

Fingersomatotopy in area 3b: an fMRI-study.

BACKGROUND: The primary sensory cortex (S1) in the postcentral gyrus is comprised of four areas that each contain a body map, where the representation of the hand is located with the thumb most laterally, anteriorly and inferiorly and the little finger most medially, posteriorly and superiorly. Previous studies on somatotopy using functional MRI have either used low field strength, have included a small number of subjects or failed to attribute activations to any area within S1. In the present study we included twenty subjects, who were investigated at 3 Tesla (T). We focused specifically on Brodmann area 3b, which neurons have discrete receptive fields with a potentially more clearcut somatotopic organisation. The spatial distribution for all fingers' peak activation was determined and group as well as individual analysis was performed. RESULTS: Activation maps from 18 subjects were of adequate quality; in 17 subjects activations were present for all fingers and these data were further analysed. In the group analysis the thumb was located most laterally, anteriorly and inferiorly with the other fingers sequentially positioned more medially, posteriorly and superiorly. At the individual level this somatotopic relationship was present for the thumb and little finger, with a higher variability for the fingers in between. The Euclidian distance between the first and fifth finger was 17.2 mm, between the first and second finger 10.6 mm and between the remaining fingers on average 6.3 mm. CONCLUSION: Results from the group analysis, that is both the location of the fingers and the Euclidian distances, are well comparable to results from previous studies using a wide range of modalities. On the subject level the spatial localisation of the fingers showed a less stringent somatotopic order so that the location of a finger in a single subject cannot be predicted from the group result.