Clinical Magnetic Resonance System Research Articles

AAPM Task Group 334: A guidance document to using radiotherapy immobilization devices and accessories in an MR environment.

Use of magnetic resonance (MR) imaging in radiation therapy has increased substantially in recent years as more radiotherapy centers are having MR simulators installed, requesting more time on clinical diagnostic MR systems, or even treating with combination MR linear accelerator (MR-linac) systems. With this increased use, to ensure the most accurate integration of images into radiotherapy (RT), RT immobilization devices and accessories must be able to be used safely in the MR environment and produce minimal perturbations. The determination of the safety profile and considerations often falls to the medical physicist or other support staff members who at a minimum should be a Level 2 personnel as per the ACR. The purpose of this guidance document will be to help guide the user in making determinations on MR Safety labeling (i.e., MR Safe, Conditional, or Unsafe) including standard testing, and verification of image quality, when using RT immobilization devices and accessories in an MR environment.

Noninvasive 3-Dimensional 1 H-Magnetic Resonance Spectroscopic Imaging of Human Brain Glucose and Neurotransmitter Metabolism Using Deuterium Labeling at 3T : Feasibility and Interscanner Reproducibility.

Noninvasive, affordable, and reliable mapping of brain glucose metabolism is of critical interest for clinical research and routine application as metabolic impairment is linked to numerous pathologies, for example, cancer, dementia, and depression. A novel approach to map glucose metabolism noninvasively in the human brain has been presented recently on ultrahigh-field magnetic resonance (MR) scanners (≥7T) using indirect detection of deuterium-labeled glucose and downstream metabolites such as glutamate, glutamine, and lactate. The aim of this study was to demonstrate the feasibility to noninvasively detect deuterium-labeled downstream glucose metabolites indirectly in the human brain via 3-dimensional (3D) proton ( 1 H) MR spectroscopic imaging on a clinical 3T MR scanner without additional hardware. This prospective, institutional review board-approved study was performed in 7 healthy volunteers (mean age, 31 ± 4 years, 5 men/2 women) after obtaining written informed consent. After overnight fasting and oral deuterium-labeled glucose administration, 3D metabolic maps were acquired every ∼4 minutes with ∼0.24 mL isotropic spatial resolution using real-time motion-, shim-, and frequency-corrected echo-less 3D 1 H-MR spectroscopic Imaging on a clinical routine 3T MR system. To test the interscanner reproducibility of the method, subjects were remeasured on a similar 3T MR system. Time courses were analyzed using linear regression and nonparametric statistical tests. Deuterium-labeled glucose and downstream metabolites were detected indirectly via their respective signal decrease in dynamic 1 H MR spectra due to exchange of labeled and unlabeled molecules. Sixty-five minutes after deuterium-labeled glucose administration, glutamate + glutamine (Glx) signal intensities decreased in gray/white matter (GM/WM) by -1.63 ± 0.3/-1.0 ± 0.3 mM (-13% ± 3%, P = 0.02/-11% ± 3%, P = 0.02), respectively. A moderate to strong negative correlation between Glx and time was observed in GM/WM ( r = -0.64, P < 0.001/ r = -0.54, P < 0.001), with 60% ± 18% ( P = 0.02) steeper slopes in GM versus WM, indicating faster metabolic activity. Other nonlabeled metabolites showed no significant changes. Excellent intrasubject repeatability was observed across scanners for static results at the beginning of the measurement (coefficient of variation 4% ± 4%), whereas differences were observed in individual Glx dynamics, presumably owing to physiological variation of glucose metabolism. Our approach translates deuterium metabolic imaging to widely available clinical routine MR scanners without specialized hardware, offering a safe, affordable, and versatile (other substances than glucose can be labeled) approach for noninvasive imaging of glucose and neurotransmitter metabolism in the human brain.

Fundamentals of Camera-PPG Based Magnetic Resonance Imaging.

In Magnetic Resonance Imaging (MRI), cardiac triggering that synchronizes data acquisition with cardiac contractions is an essential technique for acquiring high-quality images. Triggering is typically based on the Electrocardiogram (ECG) signal (e.g. R-peak). Since ECG acquisition involves extra workflow steps like electrode placement and ECG signals are usually disturbed by magnetic fields in high Magnetic Resonance (MR) systems, we explored camera-based photoplethysmography (PPG) as an alternative. We used the in-bore camera of a clinical MR system to investigate the feasibility and challenges of camera-based cardiac triggering. Data from ECG, finger oximeter and camera were synchronously collected. Compared to finger-PPG, camera-based PPG provides a higher availability of the signal and the PPG marker delay relative to the ECG R-peak is considerably less with a camera monitoring the forehead. The insights obtained in this study provide a basis for an envisioned system-design phase.

An evaluation of quality assurance guidelines comparing the American College of Radiology and American Association of Physicists in Medicine task group 284 for magnetic resonance simulation.

PurposeThe purpose of this study was to evaluate similarities and differences in quality assurance (QA) guidelines for a conventional diagnostic magnetic resonance (MR) system and a MR simulator (MR‐SIM) system used for radiotherapy.MethodsIn this study, we compared QA testing guidelines from the American College of Radiology (ACR) MR Quality Control (MR QC) Manual to the QA section of the American Association of Physicists in Medicine (AAPM) Task Group 284 report (TG‐284). Differences and similarities were identified in testing scope, frequency, and tolerances. QA testing results from an ACR accredited clinical diagnostic MR system following ACR MR QC instructions were then evaluated using TG‐284 tolerances.ResultsFive tests from the ACR MR QC Manual were not included in TG‐284. Five new tests were identified for MR‐SIM systems in TG‐284 and pertained exclusively to the external laser positioning system of MR‐SIM systems. “Low‐contrast object detectability” (LCD), “table motion smoothness and accuracy,” “transmitter gain,” and “geometric accuracy” tests differed between the two QA guides. Tighter tolerances were required in TG‐284 for “table motion smoothness and accuracy” and “low contrast object detectability.” “Transmitter gain” tolerance was dependent on initial baseline measurements, and TG‐284 required that geometric accuracy be tested over a larger field of view than the ACR testing method. All tests from the ACR MR QC Manual for a conventional MR system passed ACR tolerances. The T2‐weighted image acquired with ACR sequences failed the 40‐spoke requirement from TG‐284, transmitter gain was at the 5% tolerance of TG‐284, and geometric accuracy could not be evaluated because of required equipment differences. Table motion passed both TG‐284 and ACR required tolerances.ConclusionOur study evaluated QA guidelines for an MR‐SIM and demonstrated the additional QA requirements of a clinical diagnostic MR system to be used as an MR‐SIM in radiotherapy as recommended by TG‐284.

Ceramic resonators for targeted clinical magnetic resonance imaging of the breast

Currently, human magnetic resonance (MR) examinations are becoming highly specialized with a pre-defined and often relatively small target in the body. Conventionally, clinical MR equipment is designed to be universal that compromises its efficiency for small targets. Here, we present a concept for targeted clinical magnetic resonance imaging (MRI), which can be directly integrated into the existing clinical MR systems, and demonstrate its feasibility for breast imaging. The concept comprises spatial redistribution and passive focusing of the radiofrequency magnetic flux with the aid of an artificial resonator to maximize the efficiency of a conventional MR system for the area of interest. The approach offers the prospect of a targeted MRI and brings novel opportunities for high quality specialized MR examinations within any existing MR system.

Multicompartment magnetic resonance fingerprinting

Magnetic resonance fingerprinting (MRF) is a technique for quantitative estimation of spin-relaxation parameters from magnetic-resonance data. Most current MRF approaches assume that only one tissue is present in each voxel, which neglects intravoxel structure, and may lead to artifacts in the recovered parameter maps at boundaries between tissues. In this work, we propose a multicompartment MRF model that accounts for the presence of multiple tissues per voxel. The model is fit to the data by iteratively solving a sparse linear inverse problem at each voxel, in order to express the measured magnetization signal as a linear combination of a few elements in a precomputed fingerprint dictionary. Thresholding-based methods commonly used for sparse recovery and compressed sensing do not perform well in this setting due to the high local coherence of the dictionary. Instead, we solve this challenging sparse-recovery problem by applying reweighted--norm regularization, implemented using an efficient interior-point method. The proposed approach is validated with simulated data at different noise levels and undersampling factors, as well as with a controlled phantom-imaging experiment on a clinical magnetic-resonance system.

In Vivo Molecular Characterization of Abdominal Aortic Aneurysms Using Fibrin-Specific Magnetic Resonance Imaging.

BackgroundThe incidence of abdominal aortic aneurysms (AAAs) will significantly increase during the next decade. Novel biomarkers, besides diameter, are needed for a better characterization of aneurysms and the estimation of the risk of rupture. Fibrin is a key protein in the formation of focal hematoma associated with the dissection of the aortic wall and the development of larger thrombi during the progression of AAAs. This study evaluated the potential of a fibrin‐specific magnetic resonance (MR) probe for the in vivo characterization of the different stages of AAAs.Methods and Results AAAs spontaneously developed in ApoE−/− mice following the infusion of angiotensin‐II (Ang‐II, 1 μg/kg−1·per minute). An established fibrin‐specific molecular MR probe (EP2104R, 10 μmol/kg−1) was administered after 1 to 4 weeks following Ang‐II infusion (n=8 per group). All imaging experiments were performed on a clinical 3T Achieva MR system with a microscopy coil (Philips Healthcare, Netherlands). The development of AAA‐associated fibrin‐rich hematoma and thrombi was assessed. The high signal generated by the fibrin probe enabled high‐resolution MR imaging for an accurate assessment and quantification of the relative fibrin composition of focal hematoma and thrombi. Contrast‐to‐noise‐ratios (CNRs) and R1‐relaxation rates following the administration of the fibrin probe were in good agreement with ex vivo immunohistomorphometry (R 2=0.83 and 0.85) and gadolinium concentrations determined by inductively coupled plasma mass spectroscopy (R 2=0.78 and 0.72).ConclusionsThe fibrin‐specific molecular MR probe allowed the delineation and quantification of changes in fibrin content in early and advanced AAAs. Fibrin MRI could provide a novel in vivo biomarker to improve the risk stratification of patients with aortic aneurysms.

Toward quantitative fast diffusion kurtosis imaging with b-values chosen in consideration of signal-to-noise ratio and model fidelity.

Diffusion kurtosis (DK) imaging is a variant of conventional diffusion magnetic resonance (MR) imaging that allows assessment of non-Gaussian diffusion. Fast DK imaging expedites the procedure by decreasing both scan time (acquiring the minimally required number of b-values) and computation time (obviating least-square curve fitting). This study aimed to investigate the applicability of fast DK imaging for both cerebral gray matter and white matter as a quantitative method. Seventeen healthy volunteers were recruited and each provided written informed consent before participation. On a 3-Tesla clinical MR system, diffusion imaging was performed with 12 b-values ranging from 0 to 4000 s/mm2 . Diffusion encoding was along three orthogonal directions (slice selection, phase encoding, and frequency encoding) in separate series. Candidate b-values were chosen by first determining the maximum b-value (bmax ) in the context of signal-to-noise ratio and then assessing the model fidelity for all b-value combinations within bmax . Diffusion coefficient (D) and diffusion kurtosis coefficient (K) were derived from these candidates and assessed for their dependence on b-value combination. Our data suggested bmax to be 2200 s/mm2 as a trade-off between the percentage (~80%) of voxels statistically detectable against background and the sensitivity to non-Gaussian diffusion in both gray matter and white matter. The measurement dependence on b-value was observed predominantly in areas with a considerable amount of cerebrospinal fluid. In most gray matter and white matter, b-value combinations do not cause statistical difference in the calculated D and K. For fast DK imaging to be quantitatively applicable in both gray matter and white matter, bmax should be chosen to ensure adequate signal-to-noise ratio in the majority of gray/white matter and the two nonzero b-values should be chosen in consideration of model fidelity to mitigate the dependence of derived indices on b-values.

Antioxidant treatment attenuates lactate production in diabetic nephropathy.

The early progression of diabetic nephropathy is notoriously difficult to detect and quantify before the occurrence of substantial histological damage. Recently, hyperpolarized [1-13C]pyruvate has demonstrated increased lactate production in the kidney early after the onset of diabetes, implying increased lactate dehydrogenase activity as a consequence of increased nicotinamide adenine dinucleotide substrate availability due to upregulation of the polyol pathway, i.e., pseudohypoxia. In this study, we investigated the role of oxidative stress in mediating these metabolic alterations using state-of-the-art hyperpolarized magnetic resonance (MR) imaging. Ten-week-old female Wistar rats were randomly divided into three groups: healthy controls, untreated diabetic (streptozotocin treatment to induce insulinopenic diabetes), and diabetic, receiving chronic antioxidant treatment with TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl) via the drinking water. Examinations were performed 2, 3, and 4 wk after the induction of diabetes by using a 3T Clinical MR system equipped with a dual tuned 13C/1H-volume rat coil. The rats received intravenous hyperpolarized [1-13C]pyruvate and were imaged using a slice-selective 13C-IDEAL spiral sequence. Untreated diabetic rats showed increased renal lactate production compared with that shown by the controls. However, chronic TEMPOL treatment significantly attenuated diabetes-induced lactate production. No significant effects of diabetes or TEMPOL were observed on [13C]alanine levels, indicating an intact glucose-alanine cycle, or [13C]bicarbonate, indicating normal flux through the Krebs cycle. In conclusion, this study demonstrates that diabetes-induced pseudohypoxia, as indicated by an increased lactate-to-pyruvate ratio, is significantly attenuated by antioxidant treatment. This demonstrates a pivotal role of oxidative stress in renal metabolic alterations occurring in early diabetes.

3D MR thermometry of frozen tissue: Feasibility and accuracy during cryoablation at 3T

To assess the feasibility and accuracy of 3D ultrashort echo time (UTE) magnetic resonance (MR) thermometry of frozen tissue during cryoablation on a clinical 3T MR system. Ex vivo porcine muscle specimens (n = 4) were imaged during two cycles of 10:3 minutes freeze-thaw on a 3T clinical MR scanner. Continuous MR monitoring was performed using a 3D radial ramp-sampled UTE sequence with a shortest TE of 70 μs. Fiber optic sensors were used for temperature reference. Data of three experiments were used as reference sets. Signal intensity values were normalized to baseline before cooling and related to temperature. Data for subzero temperatures were fit to a monoexponential function. In the separate validation set, the obtained fit was used to generate 3D MR temperature maps of frozen tissue at each imaging timepoint. Statistical analysis was performed to assess accuracy of the MR temperature maps. With 3D UTE imaging, MR signal was measured from frozen tissue down to temperatures as low as -40°C. Temperatures predicted from the MR temperature maps strongly correlated with sensor recorded values (r = 0.977, P < 0.001). Bland-Altman analysis demonstrated a mean difference between MR-estimated temperatures and sensor readings of -1.2 ± 2.7°C with upper and lower limits of agreement of +4.1 and -6.5°C, respectively. 3D MR thermometry of frozen tissue using UTE signal intensity was feasible during cryoablation on a clinical 3T MR system. Down to temperatures as low as -40°C, accuracy of the MR temperature maps was within clinically acceptable limits. J. Magn. Reson. Imaging 2016;44:1572-1579.

Oxygen Mapping within Healthy and Acutely Infarcted Brain Tissue in Humans Using the NMR Relaxation of Lipids: A Proof-Of-Concept Translational Study.

The clinical applicability of brain oxygenation mapping using the MOBILE (Mapping of Oxygen By Imaging Lipids relaxation Enhancement) magnetic resonance (MR) technique was assessed in the clinical setting of normal brain and of acute cerebral ischemia as a founding proof-of-concept translational study. Changes in the oxygenation level within healthy brain tissue can be detected by analyzing the spin-lattice proton relaxation (‘Global T 1 ’ combining water and lipid protons) because of the paramagnetic properties of molecular oxygen. It was hypothesized that selective measurement of the relaxation of the lipid protons (‘Lipids T 1 ’) would result in enhanced sensitivity of pO2 mapping because of higher solubility of oxygen in lipids than in water, and this was demonstrated in pre-clinical models using the MOBILE technique. In the present study, 12 healthy volunteers and eight patients with acute (48–72 hours) brain infarction were examined with the same clinical 3T MR system. Both Lipids R1 (R1 = 1/T1) and Global R1 were significantly different in the infarcted area and the contralateral unaffected brain tissue, with a higher statistical significance for Lipids R1 (median difference: 0.408 s-1; p<0.0001) than for Global R1 (median difference: 0.154 s-1; p = 0.027). Both Lipids R1 and Global R1 values in the unaffected contralateral brain tissue of stroke patients were not significantly different from the R1 values calculated in the brain tissue of healthy volunteers. The main limitations of the present prototypic version of the MOBILE sequence are the long acquisition time (4 min), hampering robustness of data in uncooperative patients, and a 2 mm slice thickness precluding accurate measurements in small infarcts because of partial volume averaging effects.

An optical setup for electric field measurements in MRI with high spatial resolution

Electric field measurements in the magnetic resonance (MR) imaging environment are important to assess potentially dangerous radio-frequency (RF) heating in the vicinity of metallic structures such as coils, implants or catheters. So far, E-field measurements have been performed with dipole antennas that lag of limited spatial resolution and which are difficult to use in the magnet bore as they interfere with the RF transmit field of the MRI system. In this work an electro-optic sensor is presented that utilizes the Pockels effect to measure the E-field in a clinical MR system with high spatial resolution. This sensor consists of dielectric materials only and thus, it only minimally influences the measured E-field distribution. A 10 m long flexible optical fiber connects the small sensor head to a remote processing unit where the optical signal is transformed into an electrical output signal. Spatially resolved qualitative E-field measurements were performed in a 1.5 T clinical MR system in the vicinity of metallic samples and an active tracking catheter with a resolution of up to 1 mm. The near-field pattern of a resonant U-shaped metallic sample was clearly identified and compared with numerical simulations. A more complex field behavior was found for the tracking catheter where strong E-field enhancements were observed at the distal tip and at its proximal part outside the phantom solution. Due to its sub-mm spatial resolution the optical sensor approach provides detailed insight into the complex and difficult to access field distributions close to implants and metallic structures and has turned out to be promising tool for MRI field and safety inspections.

Separate pulmonary artery and vein magnetic resonance angiography by use of an arterial spin labeling method.

A separate pulmonary vein (PV) is difficult to depict with the commonly used bright-blood magnetic resonance angiography method. Until now, no study has described the depiction of peripheral PVs without the artery. Our purpose in this study was to develop an arterial spin labeling (ASL)-based magnetic resonance angiography sequence to depict the pulmonary artery (PA) and vein separately. We developed such a sequence by using two inversion recovery pulses. The first pulse was non-selective, and the second pulse was selective and was applied to the aorta and heart. All studies were conducted on a 1.5-T clinical magnetic resonance system with six different inversion times for seven healthy volunteers. For evaluation, we categorized the inversion times by using visual scoring. Then, we used the magnitude image to evaluate the PA, and we used the real image to evaluate the PV. For the PA, an inversion time of 300 ms had the lowest score (1.43), and the score changed with increasing times; an inversion time of 1,100 ms had the highest score (3.85). For the PV, an inversion time of 300 ms had the highest score (2.68), and the score decreased with increasing times. The results indicated that the PA and vein could be depicted separately by the use of an ASL-based magnetic resonance angiography method. The optimal inversion times for the PV and artery were 300 and 1,100 ms, respectively.

Monitoring the brain metabolites of children with acute encephalopathy caused by the H1N1 virus responsible for the 2009 influenza pandemic: a quantitative in vivo 1H MR spectroscopy study

Background and PurposeInfluenza viral infection, which results in central nervous system dysfunction, is a major cause of acute encephalopathy (AE). The purpose of this study was to investigate the changes in the concentrations of brain metabolites in children with AE using single-voxel magnetic resonance spectroscopy (MRS) and to provide diagnostic information about the relationship between the symptoms of AE and metabolite concentrations. Materials and MethodsThe subjects were 10 children (mean age: 6.2 years; range: 1–13) with AE caused by the novel influenza A virus responsible for the 2009 influenza pandemic. The serial MRS data (TE/TR=30/5000 ms, 3 T) acquired from the basal ganglia (BG) and centrum semiovale (CS) of each patient were categorized into three periods: (1) initial neurological symptom presentation and the start of treatment (n=10), (2) short-term follow-up (n=9) and (3) long-term follow-up (n=3). As controls, the magnetic resonance (MR) spectra of eight age-matched children were also investigated. ResultsIn both regions, the concentrations of the major metabolites (N-acetylaspartate, creatine, choline, myo-inositol, glutamate/glutamine complex and glutamate) only showed minor fluctuations between the three periods. On the other hand, higher levels of taurine (Tau) were observed in the BG during the second period (P=.005), and increased levels of glucose were observed in the CS during the first (P=.005) and second (P=.036) periods. ConclusionsSerial monitoring of brain metabolite changes was carried out with a clinical MR system. The concentrations of major metabolites only displayed very minor fluctuations in response to mild H1N1-related AE. However, a higher Tau concentration was found to be associated with neurological symptoms. Further studies are required to improve our understanding of the detailed activity of Tau in AE.

Noninvasive Assessment of Transstenotic Pressure Gradients in Porcine Renal Artery Stenoses by Using Vastly Undersampled Phase-Contrast MR Angiography

To compare noninvasive transstenotic pressure gradient (TSPG) measurements derived from high-spatial- and temporal-resolution four-dimensional magnetic resonance (MR) flow measurements with invasive measurements obtained from endovascular pressure wires with digital subtraction angiographic guidance. After Animal Care and Use Committee approval, bilateral renal artery stenosis (RAS) was created surgically in 12 swine. Respiratory-gated phase-contrast vastly undersampled isotropic projection (VIPR) MR angiography of the renal arteries was performed with a 1.5-T clinical MR system (repetition time, 11.4 msec; echo time [first echo], 3.7 msec; 18,000 projection angles; imaging volume, 260 × 260 × 200 mm; acquired isotropic spatial resolution, 1.0 × 1.0 × 1.0 mm; velocity encoding, 150 cm/sec). Velocities measured with phase-contrast VIPR were used to calculate TSPGs by using Navier-Stokes equations. These were compared with endovascular pressure measurements (mean and peak) performed by using fluoroscopic guidance with regression analysis. In 19 renal arteries with an average stenosis of 62% (range, 0%-87%), there was excellent correlation between the noninvasive TSPG measurement with phase-contrast VIPR and invasive TSPG measurement for mean TSPG (R² = 95.4%) and strong correlation between noninvasive TSPG and invasive TSPG for the peak TSPG measures (R² = 82.6%). The phase-contrast VIPR-derived TSPG measures were slightly lower than the endovascular measurements. In four arteries with severe stenoses and one occlusion (mean, 86%; range, 75%-100%), the residual lumen within the stenosis was too small to determine TSPG with phase-contrast VIPR. The unenhanced MR angiographic technique with phase-contrast VIPR allows for accurate noninvasive assessment of hemodynamic significance in a porcine model of RAS with highly accurate TSPG measurements.

DETERMINATION OF T1 RELAXATION TIME OF NORMAL EQUINE TENDONS USING MAGIC ANGLE MAGNETIC RESONANCE IMAGING

Seven isolated equine front limbs were used to establish the normal T1 relaxation time of equine superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), and suspensory ligament (SL) using magic angle magnetic resonance (MR) imaging. MR imaging of the metacarpi was performed with the limbs positioned at 55° (the magic angle) relative to the main magnetic field. Transverse spin-echo proton density and inversion recovery images were acquired. T1 relaxation time was calculated based on ratios of signal intensity determined from the different pulse sequences. T1 relaxation times for SDFT, DDFT, and SL were 288 (± 17), 244 (± 14), and 349 (± 16) ms, respectively. The difference in T1 values between SDFT, DDFT, and SL was statistically significant. T1 values of equine tendons can be determined with magic angle imaging on a clinical MR system using < 10 min total scan time. The knowledge of the normal range of T1 values may be useful to identify horses with chronic tendinopathy, where based on the human literature, an increased T1 value may be expected.

Safety in magnetic resonance units: an update

The number of anaesthetists who are involved in magnetic resonance (MR) units is increasing. Magnetic resonance systems are becoming more powerful and interventional procedures are now possible. This paper updates information relating to safety terminology, occupational exposure, reactions to gadolinium-based contrast agents and the risk of nephrogenic systemic fibrosis. Magnetic resonance examinations of patients with pacemakers are still generally contra-indicated but have been carried out in specialist centres under strictly controlled conditions. As availability of MR increases, so the education of anaesthetists, who are occasionally required to provide a service, must be considered.Anaesthesia in MR units was first described in the 1980s. Guidelines on the provision of anaesthetic services in MR units were published by the Association of Anaesthetists of Great Britain and Ireland (AAGBI) in 2002 [1]. Since then, the number of hospitals with MR units, and hence the number of patients requiring anaesthesia for MR, has increased. While the issues relating to setting up anaesthetic services in MR have not changed, there have been a number of developments that warrant this update:Safety terminology and guidelines have changed.MR systems utilise higher magnetic-field strengths and more open designs are available.Interventional and intra-operative MR are now routine in some centres.Mobile MR scanners are increasingly used to reduce waiting lists.Although still generally contra-indicated, some patients with pacemakers have been scanned under strictly controlled conditions in specialist centres.‘MR safe’ medical implants are now being produced.New equipment is now available for use in MR.Out-of-hours availability of MR investigations has increased.Reports of allergic reactions to MR contrast media have increased.Gadolinium based contrast agents (Gd-CAs) are associated with a varying degree of risk of nephrogenic systemic fibrosis in patients with impaired renal function.

An independent multichannel imaging research system for ultrashort echo time imaging on clinical MR systems

AbstractMost clinical magnetic resonance systems do not have access to ultrashort echo time (UTE) imaging. The aim of this project was to develop a fully independent imaging insert for clinical MR systems to provide this new research application without disturbing routine operation. The initial clinical target for the system was improved orthopedic upper limb imaging using ultrashort repeat and echo time acquisitions. Echo times as short as TE = 80 μs were attained for standard 2DFT gradient echo sequences and TE = 25 μs for asymmetrically sampled radial acquisitions using the 160 mm inside diameter symmetrical cylindrical insert gradient set. The spectrometer was able to acquire 32 channels simultaneously with 14 bit resolution at up to 2.5 MS/s and had broadband operation from 250 kHz up to 200 MHz. Only eight active RF channels were constructed and used for this study. Acoustic noise with the insert coil was up to 30 dbA quieter than a whole body gradient system operating at the same gradient strength. The insert provides a useful method of performing UTE imaging using a standard clinical MRI system with no disturbance to normal operation. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 35B: 80–88, 2009

Magnetic resonance microneurography of rabbit sciatic nerve on a 1.5‐T clinical MR system correlated with gross anatomy

This study was performed to investigate the feasibility and accuracy of magnetic resonance (MR) microneurography of the rabbit sciatic nerve on a 1.5-T clinical MR system by correlation with the gross anatomy. The 3D T2-weighted imaging (3D-T2WI), 3D T2-weighted imaging plus spectral presaturation with inversion recovery (SPIR), and T1-weighted imaging (T1WI) of the sciatic nerve in ten rabbits were performed on a 1.5-T MR system. The radiological anatomy of the sciatic nerve was observed and correlated with the gross anatomy. The anterior-posterior diameter of the sciatic nerve trunk was measured on 3D T2WI and on gross anatomy. The T1 and T2 relaxation times were also measured with multiecho spin echo and mixed sequence, respectively. The tibial nerve and peroneal nerve in the sciatic nerve trunk in all ten rabbits could be clearly displayed on T2WI and T2WI. The fine branches of the gastrocnemius nerve, posterior femoral cutaneous nerve, and the posterior gluteal nerve could be clearly depicted on T2WI. The T1 and T2 relaxation times of the sciatic nerves were 915 and 40 ms, respectively. The anterior-posterior diameter of sciatic nerve trunk was measured grossly, and on T2WI was 3.17 +/- 0.21 mm and 3.15 +/- 0.19 mm, respectively. There was no statistically significant difference (t = 0.768, P = 0.462). With the 1.5-T clinical MR system, the microneurography of the sciatic nerve could be revisualized, and the finer structure of the sciatic nerve trunk could be clearly and accurately delineated.

High-Resolution Complementary Spatial Modulation of Magnetization (CSPAMM) Rat Heart Tagging on a 1.5 Tesla Clinical Magnetic Resonance System

The purpose of this study was to assess the feasibility of cardiac magnetic resonance (MR) tagging in rats on a standard clinical 1.5T MR system. Small animal models have been largely used as an experimental model in cardiovascular disease studies but mainly on high field systems (>4T) dedicated to research. Given the larger availability of routine clinical MR systems in centers with active cardiac research programs, it is of great interest to perform small animal imaging on whole-body MR systems of moderate field strength. The feasibility study was performed on 7 rats within 6 to 8 hours after myocardial infarction and 3 normal control rats. Myocardial strain was measured successfully in normal rats using the harmonic phase (ie, HARP) method, and a transmural gradient was demonstrated. In a rat model of acute occlusion/reperfusion, the myocardial circumferential strains were decreased, but the transmural strain gradient was preserved. This study demonstrated the feasibility of cardiac MR tagging in rats with a subendocardial resolution using a clinical 1.5T system.