3D ultrasound to quantify lateral hip displacement in children with cerebral palsy: a validation study.

AIM: To assess the validity of a new index, lateral head coverage (LHC), for describing hip dysplasia in a population of children with cerebral palsy (CP). METHOD: LHC is derived from 3D ultrasound assessment. Twenty-two children (15 males, seven females; age 4-15y) with CP undergoing routine hip surveillance were recruited prospectively for the study. Each participant had both a planar radiograph acquired as part of their routine care and a 3D ultrasound assessment within 2 months. Reimer's migration percentage (RMP) and LHC were measured by the same assessor, and the correlation between them calculated using Pearson's correlation coefficient. The repeatability of LHC was investigated with three assessors, analysing each of 10 images three times. Inter- and intra-assessor variation was quantified using intraclass correlation coefficients. RESULTS: LHC was strongly correlated with RMP (Spearman's rank correlation coefficient=-0.86, p<0.001). LHC had similar inter-assessor reliability to that reported for RMP (intraclass correlation coefficient=0.97 and intra-assessor intraclass correlation coefficient=0.98). INTERPRETATION: This is an initial validation of the use of 3D ultrasound in monitoring hip development in children with CP. LHC is comparable with RMP in estimating hip dysplasia with similar levels of reliability that are reported for RMP.

Personal exposure to static and time-varying magnetic fields during MRI procedures in clinical practice in the UK.

BACKGROUND: MRI has developed into one of the most important medical diagnostic imaging modalities, but it exposes staff to static magnetic fields (SMF) when present in the vicinity of the MR system, and to radiofrequency and switched gradient electromagnetic fields if they are present during image acquisition. We measured exposure to SMF and motion-induced time-varying magnetic fields (TVMF) in MRI staff in clinical practice in the UK to enable extensive assessment of personal exposure levels and variability, which enables comparison to other countries. METHODS: 8 MRI facilities across National Health Service sites in England, Wales and Scotland were included, and staff randomly selected during the days when measurements were performed were invited to wear a personal MRI-compatible dosimeter and keep a diary to record all procedures and tasks performed during the measured shift. RESULTS: 98 participants, primarily radiographers (71%) but also other healthcare staff, anaesthetists and other medical staff were included, resulting in 149 measurements. Average geometric mean peak SMF and TVMF exposures were 448 mT (range 20-2891) and 1083 mT/s (9-12 355 mT/s), and were highest for radiographers (GM=559 mT and GM=734 mT/s). Time-weighted exposures to SMF and TVMF (GM=16 mT (range 5-64) and GM=14 mT/s (range 9-105)) and exposed-time-weighted exposures to SMF and TVMF (GM=27 mT (range 11-89) and GM=17 mT/s (range 9-124)) were overall relative low-primarily because staff were not in the MRI suite for most of their shifts-and did not differ significantly between occupations. CONCLUSIONS: These results are comparable to the few data available from the UK but they differ from recent data collected in the Netherlands, indicating that UK staff are exposed for shorter periods but to higher levels. These data indicate that exposure to SMF and TVMF from MRI scanners cannot be extrapolated across countries.

Design, operation, and safety of single-room interventional MRI suites: practical experience from two centers.

The design and operation of a facility in which a magnetic resonance imaging (MRI) scanner is incorporated into a room used for surgical or endovascular cardiac interventions presents several challenges. MR safety must be maintained in the presence of a much wider variety of equipment than is found in a diagnostic unit, and of staff unfamiliar with the MRI environment, without compromising the safety and practicality of the interventional procedure. Both the MR-guided cardiac interventional unit at Kings College London and the intraoperative imaging suite at the National Hospital for Neurology and Neurosurgery are single-room interventional facilities incorporating 1.5 T cylindrical-bore MRI scanners. The two units employ similar strategies to maintain MR safety, both in original design and day-to-day operational workflows, and between them over a decade of incident-free practice has been accumulated. This article outlines these strategies, highlighting both similarities and differences between the units, as well as some lessons learned and resulting procedural changes made in both units since installation.

Intramuscular fat in ambulant young adults with bilateral spastic cerebral palsy.

BACKGROUND: It is known that individuals with bilateral spastic cerebral palsy (BSCP) have small and weak muscles. However, no studies to date have investigated intramuscular fat infiltration in this group. The objective of this study is to determine whether adults with BSCP have greater adiposity in and around their skeletal muscles than their typically developing (TD) peers as this may have significant functional and cardio-metabolic implications for this patient group. METHODS: 10 young adults with BSCP (7 male, mean age 22.5 years, Gross Motor Function Classification System (GMFCS) levels I-III), and 10 TD young adults (6 male, mean age 22.8 years) took part in this study. 11 cm sections of the left leg of all subjects were imaged using multi-echo gradient echo chemical shift imaging (mDixon). Percentage intermuscular fat (IMAT), intramuscular fat (IntraMF) and a subcutaneous fat to muscle volume ratio (SF/M) were calculated. RESULTS: IntraMF was higher with BSCP for all muscles (p = 0.001-0.013) and was significantly different between GMFCS levels (p < 0.001), with GMFCS level III having the highest IntraMF content. IMAT was also higher with BSCP p < 0.001). No significant difference was observed in SF/M between groups. CONCLUSION: Young adults with BSCP have increased intermuscular and intramuscular fat compared to their TD peers. The relationship between these findings and potential cardio-metabolic and functional sequelae are yet to be investigated.

Physics and medicine: a historical perspective.

Nowadays, the term medical physics usually refers to the work of physicists employed in hospitals, who are concerned mainly with medical applications of radiation, diagnostic imaging, and clinical measurement. This involvement in clinical work began barely 100 years ago, but the relation between physics and medicine has a much longer history. In this report, I have traced this history from the earliest recorded period, when physical agents such as heat and light began to be used to diagnose and treat disease. Later, great polymaths such as Leonardo da Vinci and Alhazen used physical principles to begin the quest to understand the function of the body. After the scientific revolution in the 17th century, early medical physicists developed a purely mechanistic approach to physiology, whereas others applied ideas derived from physics in an effort to comprehend the nature of life itself. These early investigations led directly to the development of specialties such as electrophysiology, biomechanics, and ophthalmology. Physics-based medical technology developed rapidly during the 19th century, but it was the revolutionary discoveries about radiation and radioactivity at the end of the century that ushered in a new era of radiation-based medical diagnosis and treatment, thereby giving rise to the modern medical physics profession. Subsequent developments in imaging in particular have revolutionised the practice of medicine. We now stand on the brink of a new revolution in post-genomic personalised medicine, with physics-based techniques again at the forefront. As before, these techniques are often the unpredictable fruits of earlier investment in basic physics research.

Positive visualization of implanted devices with susceptibility gradient mapping using the original resolution.

In magnetic resonance imaging, implantable devices are usually visualized with a negative contrast. Recently, positive contrast techniques have been proposed, such as susceptibility gradient mapping (SGM). However, SGM reduces the spatial resolution making positive visualization of small structures difficult. Here, a development of SGM using the original resolution (SUMO) is presented. For this, a filter is applied in k-space and the signal amplitude is analyzed in the image domain to determine quantitatively the susceptibility gradient for each pixel. It is shown in simulations and experiments that SUMO results in a better visualization of small structures in comparison to SGM. SUMO is applied to patient datasets for visualization of stent and prostate brachytherapy seeds. In addition, SUMO also provides quantitative information about the number of prostate brachytherapy seeds. The method might be extended to application for visualization of other interventional devices, and, like SGM, it might also be used to visualize magnetically labelled cells.

Non-invasive detection and quantification of human foetal brain lactate in utero by magnetic resonance spectroscopy.

OBJECTIVE: To assess the feasibility of foetal cerebral lactate detection and quantification by proton magnetic resonance spectroscopy ((1)H-MRS) in pregnancies at increased risk of cerebral hypoxia, using a clinical 1.5 T magnetic resonance imaging (MRI) system. METHOD: Localised (1)H-MRS was performed in four patients with pregnancies in their third trimester complicated by intrauterine growth restriction (IUGR). A long echo time (TE) of 288 ms was used to maximise detection and conspicuity of the lactate methyl resonance, together with a short TE MRS acquisition to check for the presence of lipid contamination. Individual peaks in the resulting spectra were measured, corrected for relaxation and referenced to the unsuppressed water signal to provide metabolite concentrations. RESULTS: A resonance peak consistent with the presence of lactate was observed in all cases. In one subject, this was confounded by the identification of significant lipid contamination in the short TE MRS acquisition. The range of measured lactate concentrations was 2.0-3.3 mmol/kg and compared well with preterm neonatal MRS studies. CONCLUSION: The non-invasive detection and quantification of foetal cerebral lactate by MRS is achievable on a clinical 1.5 T MRI system.

Comparison of combined x-ray radiography and magnetic resonance (XMR) imaging-versus computed tomography-based dosimetry for the evaluation of permanent prostate brachytherapy implants.

PURPOSE: To present a method for the dosimetric analysis of permanent prostate brachytherapy implants using a combination of stereoscopic X-ray radiography and magnetic resonance (MR) imaging (XMR) in an XMR facility, and to compare the clinical results between XMR- and computed tomography (CT)-based dosimetry. METHODS AND MATERIALS: Patients who had received nonstranded iodine-125 permanent prostate brachytherapy implants underwent XMR and CT imaging 4 weeks later. Four observers outlined the prostate gland on both sets of images. Dose-volume histograms (DVHs) were derived, and agreement was compared among the observers and between the modalities. RESULTS: A total of 30 patients were evaluated. Inherent XMR registration based on prior calibration and optical tracking required a further automatic seed registration step that revealed a median root mean square registration error of 4.2 mm (range, 1.6-11.4). The observers agreed significantly more closely on prostate base and apex positions as well as outlining contours on the MR images than on those from CT. Coefficients of variation were significantly higher for observed prostate volumes, D90, and V100 parameters on CT-based dosimetry as opposed to XMR. The XMR-based dosimetry showed little agreement with that from CT for all observers, with D90 95% limits of agreement ranges of 65, 118, 79, and 73 Gy for Observers 1, 2, 3, and 4, respectively. CONCLUSIONS: The study results showed that XMR-based dosimetry offers an alternative to other imaging modalities and registration methods with the advantages of MR-based prostate delineation and confident three-dimensional reconstruction of the implant. The XMR-derived dose-volume histograms differ from the CT-derived values and demonstrate less interobserver variability.

Evaluating the Diagnostic Accuracy of Reflectance Confocal Microscopy to Diagnose Skin Cancer: Protocol for a Prospective, Multicenter Study.

BACKGROUND: In the United Kingdom, 350,000 patients per year are referred to hospital clinics with suspicious moles, and approximately half undergo a biopsy to identify the 5%-10% who require further treatment. If cancer cannot be ruled out clinically and on the basis of biopsy results, the lesion is surgically removed. One type of precancerous mole, called lentigo maligna, is particularly challenging to delineate and treat. Reflectance confocal microscopy (VivaScope, Caliber Imaging & Diagnostics) is an imaging technique that can supplement dermoscopy in identifying whether a clinically suspicious mole is malignant and can better assess lentigo maligna margins for excision. It allows clinicians to visualize the skin lesion to a depth of 200 microns with subcellular resolution, described as quasi-histological, and therefore better guide more accurate diagnoses. OBJECTIVE: The aim of this paper is to describe a prospective, single blinded, multicenter study to examine patients with clinically suspicious moles or lentigo maligna to determine whether confocal microscopy can both reduce the number of unnecessary biopsies of moles and more accurately guide the surgical excision margins of lentigo maligna. METHODS: This study will prospectively recruit adults into the following two cohorts: diagnostic accuracy and margin delineation. The diagnostic accuracy cohort will assess people with clinically suspicious lesions suspected of being diagnosed with melanoma and having an equivocal finding on dermoscopy or persistent clinical suspicion despite normal dermoscopy. Diagnostic accuracy will include the sensitivity and specificity of VivaScope in comparison with the histological diagnosis as the gold standard for patients. The margin delineation cohort will assess the ability of VivaScope to accurately delineate the margins of lentigo maligna compared with that of dermoscopy alone using margins taken during Mohs micrographic surgery as the gold standard. The primary study outcomes will be the diagnostic accuracy of VivaScope for the first cohort of patients and margin agreement between VivaScope and the final pathology report for the second cohort of patients. RESULTS: Funding for this proposed research is being secured. CONCLUSIONS: The outcomes of the proposed study will indicate how many biopsies of nonmelanoma lesions, which are potentially unnecessary, could be prevented. This would reduce patient anxiety and cost to the National Health Service (NHS) in the United Kingdom. Improved margin delineation of lentigo maligna could also improve the surgical clearance rates and decrease overall cost. The results would demonstrate whether the adoption of VivaScope would potentially benefit patients and the NHS. REGISTERED REPORT IDENTIFIER: RR1-10.2196/9296.

The Control of Electromagnetic Fields at Work Regulations 2016 and medical MRI.

This short commentary provides the MRI community in the UK with practical advice on the impact of the Control of Electromagnetic Fields at Work Regulations 2016 in clinical and research settings. The regulations are the UK implementation of the European Union Physical Agents (Electromagnetic Fields) Directive, which has been the subject of much discussion and concern over the past 13 years. However, thanks to concessions achieved through negotiation, and sensible and proportionate transposition into UK law by the Health and Safety Executive, the negative consequences that were foreseen have been averted. MRI activities are exempt from the occupational exposure limits contained in the regulations, subject to meeting certain conditions. The commentary gives advice on compliance with these conditions and on how to satisfy the other requirements of the regulations, all of which are either already required under existing legislation or represent good MR safety practice.

Spatial localization in nuclear magnetic resonance spectroscopy.

The ability to select a discrete region within the body for signal acquisition is a fundamental requirement of in vivo NMR spectroscopy. Ideally, it should be possible to tailor the selected volume to coincide exactly with the lesion or tissue of interest, without loss of signal from within this volume or contamination with extraneous signals. Many techniques have been developed over the past 25 years employing a combination of RF coil properties, static magnetic field gradients and pulse sequence design in an attempt to meet these goals. This review presents a comprehensive survey of these techniques, their various advantages and disadvantages, and implications for clinical applications. Particular emphasis is placed on the reliability of the techniques in terms of signal loss, contamination and the effect of nuclear relaxation and J-coupling. The survey includes techniques based on RF coil and pulse design alone, those using static magnetic field gradients, and magnetic resonance spectroscopic imaging. Although there is an emphasis on techniques currently in widespread use (PRESS, STEAM, ISIS and MRSI), the review also includes earlier techniques, in order to provide historical context, and techniques that are promising for future use in clinical and biomedical applications.

Selecting a CT scanner for cardiac imaging: the heart of the matter.

Coronary angiography to assess the presence and degree of arterial stenosis is an examination now routinely performed on CT scanners. Although developments in CT technology over recent years have made great strides in improving the diagnostic accuracy of this technique, patients with certain characteristics can still be "difficult to image". The various groups will benefit from different technological enhancements depending on the type of challenge they present. Good temporal and spatial resolution, wide longitudinal (z-axis) detector coverage and high X-ray output are the key requirements of a successful CT coronary angiography (CTCA) scan. The requirement for optimal patient dose is a given. The different scanner models recommended for CTCA all excel in different aspects. The specification data presented here for these scanners and the explanation of the impact of the different features should help in making a more informed decision when selecting a scanner for CTCA.

Cardiac catheterisation guided by MRI in children and adults with congenital heart disease.

BACKGROUND: Fluoroscopically guided cardiac catheterisation is an essential tool for diagnosis and treatment of congenital heart disease. Drawbacks include poor soft tissue visualisation and exposure to radiation. We describe the first 16 cases of a novel method of cardiac catheterisation guided by MRI with radiographic support. METHODS: In our cardiac catheterisation laboratory, we combine magnetic resonance and radiographic imaging facilities. We used MRI to measure flow and morphology, and real-time MRI sequences to visualise balloon angiographic catheters. 12 patients underwent diagnostic cardiac catheterisation, two had interventional cardiac catheterisations, and for two patients, MRI was used to plan radiofrequency ablation for treatment of tachyarrhythmias. FINDINGS: In 14 patients, some or all of the cardiac catheterisation was guided by MRI. In two patients undergoing radiofrequency ablation, catheters were manipulated with use of fluoroscopic guidance and outcome was assessed with MRI. All patients received lower amounts of radiation than controls. There was some discrepancy between pulmonary vascular resistance calculated by flow derived from MRI and the traditional Fick method. We were able to superimpose fluoroscopic images of electro physiology electrode catheters on the three dimensional MRI of the cardiac anatomy. INTERPRETATION: We have shown that cardiac catheterisation guided by MRI is safe and practical in a clinical setting, allows better soft tissue visualisation, provides more pertinent physiological information, and results in lower radiation exposure than do fluoroscopically guided procedures. MRI guidance could become the method of choice for diagnostic cardiac catheterisation in patients with congenital heart disease, and an important tool in interventional cardiac catheterisation and radiofrequency ablation.

Impact of electromagnetic field exposure limits in Europe: is the future of interventional MRI safe?

The European Union (EU) has recently introduced a directive that aims to protect workers from adverse effects of exposure to electromagnetic fields. All countries within the EU are required to incorporate this directive into their national law by 2008. This legislation applies to all types of occupational exposure to electromagnetic fields with frequencies from 0 Hz to 300 GHz. It has dramatic implications for interventional magnetic resonance (MR) imaging, because workers who are close to the MR scanner while scanning is taking place are exposed at levels substantially above the exposure limits. This is especially the case for time-varying magnetic fields in the 110 Hz-5 kHz range, which includes the field from the imaging gradients. In this article, the scientific evidence on which the limits are based is brought into question. It is concluded that an urgent review of the directive is required and that more research, especially at MR gradient frequencies, is needed.

The geko™ electro-stimulation device for venous thromboembolism prophylaxis: a NICE medical technology guidance.

The geko™ device is a single-use, battery-powered, neuromuscular electrostimulation device that aims to reduce the risk of venous thromboembolism (VTE). The National Institute for Health and Care Excellence (NICE) selected the geko™ device for evaluation, and invited the manufacturer, Firstkind Ltd, to submit clinical and economic evidence. King's Technology Evaluation Centre, an External Assessment Centre (EAC) commissioned by the NICE, independently assessed the evidence submitted. The sponsor submitted evidence related to the geko™ device and, in addition, included studies of other related devices as further clinical evidence to support a link between increased blood flow and VTE prophylaxis. The EAC assessed this evidence, conducted its own systematic review and concluded that there is currently limited direct evidence that geko™ prevents VTE. The sponsor's cost model is based on the assumption that patients with an underlying VTE risk and subsequently treated with geko™ will experience a reduction in their baseline risk. The EAC assessed this cost model but questioned the validity of some model assumptions. Using the EACs revised cost model, the cost savings for geko™ prophylaxis against a 'no prophylaxis' strategy were estimated as £197 per patient. Following a second public consultation, taking into account a change in the original draft recommendations, the NICE medical technologies guidance MTG19 was issued in June 2014. This recommended the adoption of the geko™ for use in people with a high risk of VTE and when other mechanical/pharmacological methods of prophylaxis are impractical or contraindicated in selected patients within the National Health Service in England.

Simultaneous PET and NMR.

There is currently great interest in combining data from different imaging modalities, either by image registration methods that are performed after the data has been acquired or using new devices that can acquire data from two modalities simultaneously, or near simultaneously. In this paper a small prototype NMR-compatible PET scanner capable of acquiring PET images simultaneously with either NMR images or NMR spectra is described. In an associated paper [1], Pamela Garlick describes some investigations of cardiac metabolism that have been made using this system. One of the main challenges in constructing an NMR-compatible PET scanner is that photomultiplier tubes, which are an essential element of nearly all current PET systems, will not function in a high magnetic field. In collaboration with Simon Cherry and the Crump Institute of Biomedical Imaging at UCLA Medical School, a small (5.4 cm diameter) NMR-compatible PET scanner that will operate within the bore of an NMR magnet has been developed. Long optical fibres are used to transport light from the scintillation crystals that form the detector head to photomultiplier tubes situated in a low magnetic field region several metres from the magnet. This system has been used to perform simultaneous PET and NMR spectroscopy measurements with a 9.4T spectroscopy system, and has also been used to obtain simultaneous PET and MR images in several MRI scanners including a 4.7T small bore animal imaging system. Current efforts in the development of this technology are directed at experimental studies on small animals, both because this is less demanding technically and because it is in this area that applications are likely to appear first. However, there is no reason in principle why human PET-MR would not be feasible. Below, work with the prototype system and the next stage in its development are described, and some of the future possibilities and challenges are discussed.

Lower limb muscle volumes in bilateral spastic cerebral palsy.

AIM: Muscle weakness is a feature of individuals with spastic cerebral palsy (SCP) but there are few reports in the literature of muscle volume in this group. This study compares muscle volumes in adolescents and young adults with SCP with those of their typically developing (TD) peers. DESIGN: Measurements of the volumes of nine major lower limb muscles in 19 independently ambulant subjects with SCP (mean age 14.2 years (sd 2.7), 11 male, GMFCS I (n=5); GMFCS II (n=14)), 19 TD subjects (mean age 16.5 years (sd 3.0), 11 male) were made using magnetic resonance imaging. RESULTS: Lower limb muscles were smaller in the SCP group (p≤0.023 in all muscles) than the TD group with the exception of the vastii (lateralis+intermedius; p=0.868) and gluteus maximus (p=0.056). Average muscle volume deficit was 27.9%. Muscle volume deficits were significantly greater for distal muscles than proximal muscles (p<0.001). CONCLUSIONS: Reduced muscle size in adolescence and the natural history of sarcopenia in adulthood may contribute to the early loss of mobility of adults with SCP.

Bone strength is related to muscle volume in ambulant individuals with bilateral spastic cerebral palsy.

OBJECTIVE: The aim of this study is to investigate how bone strength in the distal femur and proximal tibia are related to local muscle volume in ambulant individuals with bilateral spastic cerebral palsy (CP). METHODS: Twenty-seven participants with CP (mean age: 14.6±2.9years; Gross Motor Function Classification System (GMFCS) levels I-III) and twenty-two typically developing (TD) peers (mean age: 16.7±3.3years) took part in this study. Periosteal and medullary diameter in the distal femur and cortical bone cross-sectional area (CSA) and thickness (CT) in the distal femur and proximal tibia were measured along with nine lower limb muscle volumes using MRI. Additionally, the polar section modulus (Zp) and buckling ratio (BR) were calculated to estimate bone bending strength and compressional bone stability respectively in the distal femur. The relationships of all measured parameters with muscle volume, height, age, body mass, gender, and subject group were investigated using a generalized linear model (GZLM). RESULTS: In the distal femur, Zp was significantly positively related to thigh muscle volume (p=0.007), and height (p=0.026) but not significantly related to subject group (p=0.076) or body mass (p=0.098). BR was not significantly different between groups and was not related to any of the variables tested. Cortical bone CSA was significantly lower in the CP group at both the distal femur (p=0.002) and proximal tibia (p=0.009). It was also positively associated with thigh muscle volume (p<0.001) at the distal femur, and with subject height (p=0.005) at the proximal tibia. CONCLUSIONS: Bending and compressional strength of the femur, estimated from Zp and cortical bone CSA respectively, is associated with reduced thigh muscle volume. Increasing muscle volume by strength training may have a positive effect on bone mechanics in individuals with CP.