ICRP Publication 111 - Application of the Commission's recommendations to the protection of people living in long-term contaminated areas after a nuclear accident or a radiation emergency

In this report, the Commission provides guidance for the protection of people living in long-term contaminated areas resulting from either a nuclear accident or a radiation emergency. The report considers the effects of such events on the affected population. This includes the pathways of human exposure, the types of exposed populations, and the characteristics of exposures. Although the focus is on radiation protection considerations, the report also recognises the complexity of post-accident situations, which cannot be managed without addressing all the affected domains of daily life, i.e. environmental, health, economic, social, psychological, cultural, ethical, political, etc. The report explains how the 2007 Recommendations apply to this type of existing exposure situation, including consideration of the justification and optimisation of protection strategies, and the introduction and application of a reference level to drive the optimisation process. The report also considers practical aspects of the implementation of protection strategies, both by authorities and the affected population. It emphasises the effectiveness of directly involving the affected population and local professionals in the management of the situation, and the responsibility of authorities at both national and local levels to create the conditions and provide the means favouring the involvement and empowerment of the population. The role of radiation monitoring, health surveillance, and the management of contaminated foodstuffs and other commodities is described in this perspective. The Annex summarises past experience of longterm contaminated areas resulting from radiation emergencies and nuclear accidents, including radiological criteria followed in carrying out remediation measures.

Code-division-multiplexed electrical impedance tomography spectroscopy

Electrical impedance tomography uses multiple impedance measurements to image the internal conductivity of an object, such as the human body. Code-division multiplexing is proposed as a new method that can provide simultaneous impedance measurements of the multiple channels. Code division provides clear advantages of a wide frequency range at reduced cost and reduced complexity of sources. A potential drawback is the lack of perfectly orthogonal code sets. This caused an increase of 0.62% in root-mean-square spectral error when two codes were used to record two impedance channels simultaneously on a low-pass filter network. The method described provides images and spectra which are equivalent to the conventional time-multiplexed method, with increases in frequency resolution and measurement speed which may be of benefit in some applications of electrical impedance tomography spectroscopy.

An electrode addressing protocol for imaging brain function with electrical impedance tomography using a 16-channel semi-parallel system

Electrical impedance tomography of brain function poses special problems because applied current is diverted by the resistive skull. In the past, image resolution was maximized with the use of an electrode addressing protocol with widely spaced drive electrode pairs and use of a multiplexer so that many electrode pairs could be flexibly addressed. The purpose of this study was to develop and test an electrode protocol for a 16-channel semi-parallel system which uses parallel recording channels with fixed wiring, the Kyung Hee University (KHU) Mk1. Ten protocols were tested, all addressing pairs of electrodes for recording or current drive, based on recording with a spiral, spiral with suboccipital electrodes (spiral s-o) and zig-zag configurations, and combinations of current injection from electrode pairs at 180 degrees , 120 degrees and 60 degrees . These were compared by assessing the image reconstruction quality of five simulated perturbations in a homogenous model of the human head and of four epileptic foci in an anatomically realistic model in the presence of realistic noise, in terms of localization error, resolution, image distortion and sensitivity in the region of interest. The spiral s-o with current injection at 180 degrees + 120 degrees + 60 degrees gave the best image quality and permitted reconstruction with a localization error of less than 10% of the head diameter. This encourages the view that it might be possible to obtain satisfactory images of focal abnormalities in the human brain with 16 scalp electrodes and improved instrumentation avoiding multiplexers on recording circuits.

A review of errors in multi-frequency EIT instrumentation

Multi-frequency electrical impedance tomography (MFEIT) was proposed over 10 years ago as a potential spectroscopic impedance imaging method. At least seven systems have been developed for imaging the lung, heart, breast and brain, yet none has yet achieved clinical acceptance. While the absolute impedance varies considerably between different tissues, the changes in the spectrum due to physiological changes are expected to be quite small, especially when measured through a volume. This places substantial requirements on the MFEIT instrumentation to maintain a flat system frequency response over a broad frequency range (dc-MHz). In this work, the EIT measurement problem is described from a multi-frequency perspective. Solutions to the common problems are considered from recent MFEIT systems, and the debate over four-terminal or two-terminal (multiple source) architecture is revisited. An analysis of the sources of MFEIT errors identifies the major sources of error as stray capacitance and common-mode voltages which lead to a load dependence in the frequency response of MFEIT systems. A system that employs active electrodes appears to be the most able to cope with these errors (Li et al 1996). A distributed system with digitization at the electrode is suggested as a next step in MFEIT system development.

Analysis of resting noise characteristics of three EIT systems in order to compare suitability for time difference imaging with scalp electrodes during epileptic seizures

Electrical impedance tomography measurements in clinical applications are limited by an undesired noise component. We have investigated the noise in three systems suitable for imaging epileptic seizures, the UCH Mark1b, UCH Mark2.5 and KHU Mark1 16 channel, at applied frequencies in three steps from 1 to 100 kHz, by varying load impedance, single terminal or multiplexed measurements, and in test objects of increasing complexity from a resistor to a saline filled tank and human volunteer. The noise was white, and increased from about 0.03% rms on the resistor to 0.08% on the human; it increased with load but was independent of use of the multiplexer. The KHU Mark1 delivered the best performance with noise spectra of about 0.02%, which could be further reduced by averaging to a level where reliable imaging of changes of about 0.1% estimated during epileptic seizures appears plausible.

Risk of cardiac catheterization under anaesthesia in children with pulmonary hypertension

BACKGROUND

Children with primary pulmonary hypertension (PHT) are a high-risk group who require assessment by cardiac catheterization under anaesthesia. Complications, including death, have occurred during anaesthesia in these patients, but the true risk has not been quantified.

METHODS

The clinical records of children with PHT undergoing general anaesthesia for pulmonary vascular resistance studies were reviewed retrospectively. Data collected included pre-catheter measures of severity of disease, details of clinical management, and complications occurring within 24 h of the start of anaesthesia.

RESULTS

During the past 5 yr, 75 consecutive patients were catheterized and usable records were available in 70. The age range was 0.1-18 yr (mean 7.1). Four children required external cardiac massage [6% (95% confident limits 1-11%)] and one of these died. Of the four, two had an arrhythmia related to the mechanical effects of catheterization, one was hypotensive during anaesthesia and the other had fatal cardiac failure in recovery. All four had severe PHT as judged by echocardiographic estimation of tricuspid regurgitant jet velocity>4 m s-1.

CONCLUSIONS

Resuscitation or death occurred in 6% of cases. Any associated risk factors could not be determined because the number of complications was too small. Risks may be highest in children with severe idiopathic PHT and symptoms of chest pain, syncope, or dizziness.

Prognostic significance of serial magnetic resonance spectroscopies over the course of radiation therapy for patients with malignant glioma

BACKGROUND

The standard treatment of high grade gliomas (HGG) involves maximal neuro-surgical debulking, followed by post-operative radiotherapy, with or without concurrent chemotherapy, depending on histologic grade. Despite this aggressive strategy, there are few long-term survivors. Proton magnetic resonance spectroscopy (MRS) is a non-invasive imaging method that can monitor metabolic changes in brain tumours. To date there is little data concerning the prognostic significance of the evolving spectral alterations during a course of radiotherapy.

MATERIALS

We report herein a prospective study of patients with HGGs undergoing post-operative radiotherapy. Fourteen consecutively eligible patients with a confirmed histologic diagnosis of malignant glioma and completion of all required MRS imaging were included in this study. All patients had MRS imaging prior to radiotherapy, at week 4 of radiotherapy, and 2 months post-treatment. T1 and T2 weighted images as well as post-gadolinium multi-voxel proton MRS images were obtained. Normalized (tumour metabolite/normal brain metabolite) levels of choline, NAA, creatine, lipid and lactate were calculated. Kaplan-Meier (KM) curves of progression-free and overall survival were constructed based on the evolving patterns of metabolite changes over the course of the images.

RESULTS

The mean tumour choline/NAA ratio decreased over the course of therapy, with a reduction observed between the baseline and post-radiotherapy studies (1.91 vs. 1.29, P=0.049). A similar decrease was identified with the mean normalized choline ratio, with a highly significant difference observed between the baseline and post-radiation images (1.61 vs. 0.96, P=0.001). Patients who exhibited more than 40% decrease in normalized choline between the week 4 and post-radiotherapy studies were associated with unfavourable survival (logrank test, P=0.003) and disease progression (logrank test, P=0.012). The Lactate/NAA ratio at the 4th week of radiotherapy and the change in normalized choline/creatine between baseline and week 4 of radiotherapy were also predictive of outcome suggesting the possibility of adaptive, response-based radiation treatment. Patients with two or more poor prognostic MRS indices had a significantly shorter progression-free survival compared with those with zero or one poor indices, with 15% and 68% at 1 year, respectively (logrank test, P=0.045).

CONCLUSION

The evolving pattern of spectral changes over the course of radiotherapy, in particular those associated with choline-containing compounds, appears to be prognostic of tumour response and outcome. Based on our data, a decision point may exist in the mid course of radical radiotherapy, at which time consideration of the choline levels could indicate the extent of radiotherapeutic response, thus allowing for individualized treatment modification.

Design and calibration of a compact multi-frequency EIT system for acute stroke imaging

A new, compact UCLH Mk 2.5 EIT system has been developed and calibrated for EIT imaging of the head. Improvements include increased input and output impedances, increased bandwidth and improved CMRR (80 dB) and linearity over frequencies and load (0.2% on a single channel, +/-0.7% on a saline tank over 20 Hz-256 kHz and 10-65 Omega). The accuracy of the system is sufficient to image severe acute stroke according to the specification from recent detailed anatomical modelling (Horesh et al 2005 3rd European Medical and Biological Engineering Conference EMBEC'05). A preliminary human study has validated the main specifications of the modelling, the range of trans-impedance from the head (8-70 Omega) using a 32 electrode, 258 combination protocol and contact impedances of 300 Omega to 2.7 kOmega over 20 Hz to 256 kHz.

Identification of a suitable current waveform for acute stroke imaging

MFEIT (multi-frequency electrical impedance tomography) has the potential to provide a portable non-invasive neuroimaging method ideal for use in acute stroke. Skin perception has not previously occurred in MFEIT with injected frequencies above 2 kHz, but use in brain imaging requires applied current below 100 Hz, which could stimulate cutaneous nerve endings. The purpose of this work was to find the most suitable current pattern that could be employed in MFEIT measurements in the adult head with the UCLH Mk2.5 system, which applies currents from 20 Hz-1.6 MHz. Single frequency current waveforms of 0.28 mA peak-to-peak at 20 Hz-80 Hz were applied to the forearms of three volunteers; although the skin was abraded, none of these were perceived, which agrees with similar studies in the literature. When a full frequency pattern at 20 Hz-1.6 MHz was applied to the forearm or head in four healthy subjects, with the same current amplitude of 0.28 mA for each component, an unpleasant tingling sensation was perceived, due to summation of the applied currents. The sensation was reduced or abolished by attenuation or removal of frequencies below 100 Hz; the optimal compromise was a pattern with absence of 40 Hz, and with 80 and 20 Hz respectively reduced to 75% and 50%.

Factors limiting the application of electrical impedance tomography for identification of regional conductivity changes using scalp electrodes during epileptic seizures in humans

Electrical impedance tomography (EIT) has the potential to produce images during epileptic seizures. This might improve the accuracy of the localization of epileptic foci in patients undergoing presurgical assessment for curative neurosurgery. It has already been shown that impedance increases by up to 22% during induced epileptic seizures in animal models, using cortical or implanted electrodes in controlled experiments. The purpose of this study was to determine if reproducible raw impedance changes and EIT images could be collected during epileptic seizures in patients who were undergoing observation with video-electroencephalography (EEG) telemetry as part of evaluation prior to neurosurgery to resect the region of brain causing the epilepsy. A secondary purpose was to develop an objective method for processing and evaluating data, as seizures arose at unpredictable times from a noisy baseline. Four-terminal impedance measurements from 258 combinations were collected continuously using 32 EEG scalp electrodes in 22 seizure episodes from 7 patients during their presurgical assessment together with the standard EEG recordings. A reliable method for defining the pre-seizure baseline and recording impedance data and EIT images was developed, in which EIT and EEG could be acquired simultaneously after filtering of EIT artefact from the EEG signal. Fluctuations of several per cent over minutes were observed in the baseline between seizures. During seizures, boundary voltage changes diverged with a standard deviation of 1-54% from the baseline. No reproducible changes with the expected time course of some tens of seconds and magnitude of about 0.1% could be reliably measured. This demonstrates that it is feasible to acquire EIT images in parallel with standard EEG during presurgical assessment but, unfortunately, expected EIT changes on the scalp of about 0.1% are swamped by much larger movement and systematic artefact. Nevertheless, EIT has the unique potential to provide invaluable neuroimaging data for this purpose and may still become possible with improvements in electrode design and instrumentation.

Multi-frequency electrical impedance tomography (EIT) of the adult human head: initial findings in brain tumours, arteriovenous malformations and chronic stroke, development of an analysis method and calibration

MFEIT (multi-frequency electrical impedance tomography) could distinguish between ischaemic and haemorrhagic stroke and permit the urgent use of thrombolytic drugs in patients with ischaemic stroke. The purpose of this study was to characterize the UCLH Mk 2 MFEIT system, designed for this purpose, with 32 electrodes and a multiplexed 2 kHz to 1.6 MHz single impedance measuring circuit. Data were collected in seven subjects with brain tumours, arteriovenous malformations or chronic stroke, as these resembled the changes in haemorrhagic or ischaemic stroke. Calibration studies indicated that the reliable bandwidth was only 16-64 kHz because of front-end components placed to permit simultaneous EEG recording. In raw in-phase component data, the SD of 16-64 kHz data for one electrode combination across subjects was 2.45 +/- 0.9%, compared to a largest predicted change of 0.35% estimated using the FEM of the head. Using newly developed methods of examining the most sensitive channels from the FEM, and nonlinear imaging constrained to the known site of the lesion, no reproducible changes between pathologies were observed. This study has identified a specification for accuracy in EITS in acute stroke, identified the size of variability in relation to this in human recordings, and presents new methods for analysis of data. Although no reproducible changes were identified, we hope this will provide a foundation for future studies in this demanding but potentially powerful novel application.