Predicting Peri-Operative Cardiorespiratory Adverse Events in Children with Idiopathic Pulmonary Arterial Hypertension Undergoing Cardiac Catheterization Using Echocardiography: A Cohort Study

General anesthesia in children with idiopathic pulmonary arterial hypertension (PAH) carries an increased risk of peri-operative cardiorespiratory complications though risk stratifying individual children pre-operatively remains difficult. We report the incidence and echocardiographic risk factors for adverse events in children with PAH undergoing general anesthesia for cardiac catheterization. Echocardiographic, hemodynamic, and adverse event data from consecutive PAH patients are reported. A multivariable predictive model was developed from echocardiographic variables identified by Bayesian univariable logistic regression. Model performance was reported by area under the curve for receiver operating characteristics (AUCroc) and precision/recall (AUCpr) and a pre-operative scoring system derived (0-100). Ninety-three children underwent 158 cardiac catheterizations with mean age 8.8 ± 4.6 years. Adverse events (n = 42) occurred in 15 patients (16%) during 16 catheterizations (10%) including cardiopulmonary resuscitation (n = 5, 3%), electrocardiographic changes (n = 3, 2%), significant hypotension (n = 2, 1%), stridor (n = 1, 1%), and death (n = 2, 1%). A multivariable model (age, right ventricular dysfunction, and dilatation, pulmonary and tricuspid regurgitation severity, and maximal velocity) was highly predictive of adverse events (AUCroc 0.86, 95% CI 0.75 to 1.00; AUCpr 0.68, 95% CI 0.50 to 0.91; baseline AUCpr 0.10). Pre-operative risk scores were higher in those who had a subsequent adverse event (median 47, IQR 43 to 53) than in those who did not (median 23, IQR 15 to 33). Pre-operative echocardiography informs the risk of peri-operative adverse events and may therefore be useful both for consent and multi-disciplinary care planning.

1197The development and validation of a novel transcatheter microwave renal denervation system

Background

Clinical studies of transcatheter radiofrequency renal denervation for treating hypertension have been hampered by the lack of consistent denervation efficacy. Microwave energy is well suited to renal denervation due to its capacity to spare vascular structures due to cooling from adjacent blood flow while enabling deep perivascular heating.

Purpose

We aimed to: 1) develop a transcatheter microwave system capable of safely delivering deep and circumferential perivascular renal nerve ablation, and 2) demonstrate the feasibility, short-term efficacy and safety of transcatheter microwave renal denervation.

Method

A novel 7F transcatheter microwave denervation system was designed, built, and iteratively prototyped in vitro and in 15 sheep. A histological grading system for microwave induced renal arterial and renal nerve injury was devised. The microwave denervation system was validated in an additional 9 sheep, which underwent unilateral renal denervation. Up to 2 microwave ablations were delivered to each artery with maximum power at 100–110W for 480s. Sheep were euthanised at 2–3 weeks post procedure. Gross microscopic histological examination as well as renal tissue norepinephrine content was analysed.

Results

Catheter deployment and ablation was successful in all 19 targeted vessel segments and ablation produced substantial circumferential perivascular injury; median ablation lesion area >395 (IQR 251–437) mm2, depth 17.1 (IQR 15.8–18.4) mm, length 16 (IQR 12–20) mm, without collateral visceral injury. Limiting power to 100W minimised arterial injury, while maintaining a deep circumferential perivascular ablation. At microwave ablation sites, a total of 292 nerve fascicles were identified, median distance from the renal artery of 4.2mm (IQR 2.1–8.8mm), of which 249 (85%) had sustained thermal injury with 128/249 (51%) showing grade 3–4 (moderate to severe) injury. Microwave denervation reduced median functional sympathetic nerve surface area at the renal hilum on anti-tyrosine hydroxylase staining by 100% (IQR 87%-100%), p=0.0039, and median renal cortical norepinephrine content by 83% (IQR 76%–92%), p=0.0078, compared to the paired control kidney.

Conclusion

Transcatheter microwave ablation can produce deep circumferential perivascular ablations over a long segment of the renal artery without significant arterial or collateral visceral injury to provide effective renal denervation. Clinical translation may enable more consistent and complete transcatheter renal denervation and antihypertensive efficacy.

Acknowledgement/Funding

University of Sydney; Western Sydney Local health District; National Health and Medical Research Council of Australia; National Heart Foundation (Au)

A randomized study of autologous bone marrow-derived stem cells in pediatric cardiomyopathy

BACKGROUND

Bone marrow mononuclear cell fraction has been used as therapy for dilated cardiomyopathy in adults. Although case series are reported, there are no randomized controlled studies in children.

METHODS

We designed a randomized, crossover, controlled pilot study to determine safety and feasibility of intracoronary stem cell therapy in children. The primary safety end-point was freedom from death and transplantation or any complication that could be considered related to bone marrow injection or anesthesia (e.g., infection, malignancy, anaphylaxis, renal deterioration). Other end-points were magnetic resonance imaging measurements and N-terminal prohormone brain natriuretic peptide. Participants included 10 children (mean age 7.2 years; range, 2.2-14.1 years; 6 boys) with cardiomyopathy (New York Heart Association/Ross Classification II-IV). Patients were crossed over at 6 months.

RESULTS

The original protocol was completed by 9 patients. The safety end-point was achieved in all. Ratio of the geometric means for treatment effect adjusting for baseline was assessed for end-diastolic and end-systolic volumes (EDV, ESV): 0.93 for EDV (95% confidence interval 0.88-0.99, p = 0.01), indicating EDV was on average 7% lower in patients after stem cell treatment, and 0.90 for ESV (95% confidence interval 0.82-1.00, p = 0.05), indicating ESV was on average 10% lower after stem cell treatment compared with placebo. The primary efficacy end-point ejection fraction was not met.

CONCLUSIONS

Bone marrow mononuclear cell therapy for cardiomyopathy is feasible and safe in children. Left ventricular volumes were significantly reduced 6 months after stem cell injection compared with placebo, which may reflect reverse remodeling.

Is chest CT useful in newborn screened infants with cystic fibrosis at 1 year of age?

Rationale

Sensitive outcome measures applicable in different centres to quantify and track early pulmonary abnormalities in infants with cystic fibrosis (CF) are needed both for clinical care and interventional trials. Chest CT has been advocated as such a measure yet there is no validated scoring system in infants.

Objectives

The objectives of this study were to standardise CT data collection across multiple sites; ascertain the incidence of bronchial dilatation and air trapping in newborn screened (NBS) infants with CF at 1 year; and assess the reproducibility of Brody-II, the most widely used scoring system in children with CF, during infancy.

Methods

A multicentre observational study of early pulmonary lung disease in NBS infants with CF at age 1 year using volume-controlled chest CT performed under general anaesthetic.

Main results

65 infants with NBS-diagnosed CF had chest CT in three centres. Small insignificant variations in lung recruitment manoeuvres but significant centre differences in radiation exposures were found. Despite experienced scorers and prior training, with the exception of air trapping, inter- and intraobserver agreement on Brody-II score was poor to fair (eg, interobserver total score mean (95% CI) κ coefficient: 0.34 (0.20 to 0.49)). Only 7 (11%) infants had a total CT score ≥12 (ie, ≥5% maximum possible) by either scorer.

Conclusions

In NBS infants with CF, CT changes were very mild at 1 year, and assessment of air trapping was the only reproducible outcome. CT is thus of questionable value in infants of this age, unless an improved scoring system for use in mild CF disease can be developed.

A prospective audit of safety issues associated with general anesthesia for pediatric cardiac magnetic resonance imaging

BACKGROUND/OBJECTIVES

Cardiac MRI (CMR) is increasingly used for surgical planning and serial monitoring of children with congenital heart disease (CHD). For small children, general anesthesia (GA) is required. We describe our experience of the safety of GA for pediatric CMR, using data collected prospectively over 3 years.

METHODS

All consecutive infants undergoing GA for CMR at our institution, between November 2005 and May 2008, were included. Informed and written consent to participate in research investigation was acquired from the guardians of every patient prior to CMR. The cardiac anesthetist completed a standardized data collection form during each procedure. Information collected included demographics, diagnosis, surgical history, anesthetic management, significant incidents, and discharge circumstances.

RESULTS

A total of 120 patients with varying cardiac physiology and a range of hemodynamics underwent GA for CMR during the study period. Gas induction was predominantly used, even in those with impaired ventricular function. The majority (71%) of procedures were undertaken without significant incident. Minor adverse incidents were recorded in 32 patients, mild hypotension being most frequent. One major adverse event occurred. A patient with hypoplastic left heart syndrome (HLHS) suffered hypotension then cardiac arrest in the scanner. This patient was successfully resuscitated.

CONCLUSION

Although the majority of cases were safe and without incident, the complication rate in children with CHD receiving a GA for CMR is higher than in the general pediatric population. This reinforces the need for a senior, multidisciplinary team to be involved in the care of these children during imaging.

Evaluation of different stimulation and measurement patterns based on internal electrode: application in cardiac impedance tomography

The conductivity distribution around the thorax is altered during the cardiac cycle due to the blood perfusion, heart contraction and lung inflation. Previous studies showed that these bio-impedance changes are appropriate for non-invasive cardiac function imaging using Electrical Impedance Tomography (EIT) techniques. However, the spatial resolution is presently low. One of the main obstacles in cardiac imaging at the heart location is the large impedance variation of the lungs by respiration and muscles on the dorsal and posterior side of the body. In critical care units there is a potential to insert an internal electrode inside the esophagus directly behind the heart in the same plane of the external electrodes. The aim of the present study is to evaluate different current stimulation and measurement patterns with both external and internal electrodes. Analysis is performed with planar arrangement of 16 electrodes for a simulated 3D cylindrical tank and pig thorax model. In our study we evaluated current injection patterns consisting of adjacent, diagonal, trigonometric, and radial to the internal electrode. The performance of these arrangements was assessed using quantitative methods based on distinguishability, sensitivity and GREIT (Graz consensus Reconstruction algorithm for Electrical Impedance Tomography). Our evaluation shows that an internal electrode configuration based on the trigonometric injection patterns has better performance and improves pixel intensity of the small conductivity changes related to heart near 1.7 times in reconstructed images and also shows more stability with different levels of added noise. For the internal electrode, when we combined radial or adjacent injection with trigonometric injection pattern, we found an improvement in amplitude response. However, the combination of diagonal with trigonometric injection pattern deteriorated the shape deformation (correlation coefficient r=0.344) more than combination of radial and trigonometric injection (correlation coefficient r=0.836) for the perturbations in the area close to the center of the cylinder. We also find that trigonometric stimulation pattern performance is degraded in a realistic thorax model with anatomical asymmetry. For that reason we recommend using internal electrodes only for voltage measurements and as a reference electrode during trigonometric stimulation patterns in practical measurements.

Dosimetry study of [I-131] and [I-125]- meta-iodobenz guanidine in a simulating model for neuroblastoma metastasis

The physical properties of I-131 may be suboptimal for the delivery of therapeutic radiation to bone marrow metastases, which are common in the natural history of neuroblastoma. In vitro and preliminary clinical studies have implied improved efficacy of I-125 relative to I-131 in certain clinical situations, although areas of uncertainty remain regarding intratumoral dosimetry. This prompted our study using human neuroblastoma multicellular spheroids as a model of metastasis. 3D dose calculations were made using voxel-based Medical Internal Radiation Dosimetry (MIRD) and dose-point-kernel (DPK) techniques. Dose distributions for I-131 and I-125 labeled mIBG were calculated for spheroids (metastases) of various sizes from 0.01 cm to 3 cm diameter, and the relative dose delivered to the tumors was compared for the same limiting dose to the bone marrow. Based on the same data, arguments were advanced based upon the principles of tumor control probability (TCP) to emphasize the potential theoretical utility of I-125 over I-131 in specific clinical situations. I-125-mIBG can deliver a higher and more uniform dose to tumors compared to I-131 mIBG without increasing the dose to the bone marrow. Depending on the tumor size and biological half-life, the relative dose to tumors of less than 1 mm diameter can increase several-fold. TCP calculations indicate that tumor control increases with increasing administered activity, and that I-125 is more effective than I-131 for tumor diameters of 0.01 cm or less. This study suggests that I-125-mIBG is dosimetrically superior to I-131-mIBG therapy for small bone marrow metastases from neuroblastoma. It is logical to consider adding I-125-mIBG to I-131-mIBG in multi-modality therapy as these two isotopes could be complementary in terms of their cumulative dosimetry.

Monozygotic twins discordant for trisomy 13: counselling and management issues

The diagnosis and management of a heterokaryotypic monochorionic pregnancy, in which one of twins had trisomy 13, is presented. Monozygosity and discordant karyotypes were confirmed by amniocentesis of both the sacs. Radiofrequency ablation of the trisomic twin was successfully performed at 18-weeks gestation and the pregnancy ended at term with the birth of a healthy girl who remains well on follow-up at 12 months of age. We reiterate the importance of early amniocentesis of both the sacs in the presence of discordant fetal abnormalities and consideration of selective fetal termination to optimise the outcome of heterokaryotypic monochorionic twin pregnancies.

Comparison of frequency difference reconstruction algorithms for the detection of acute stroke using EIT in a realistic head-shaped tank

Imaging of acute stroke might be possible using multi-frequency electrical impedance tomography (MFEIT) but requires absolute or frequency difference imaging. Simple linear frequency difference reconstruction has been shown to be ineffective in imaging with a frequency-dependant background conductivity; this has been overcome with a weighted frequency difference approach with correction for the background but this has only been validated for a cylindrical and hemispherical tank. The feasibility of MFEIT for imaging of acute stroke in a realistic head geometry was examined by imaging a potato perturbation against a saline background and a carrot-saline frequency-dependant background conductivity, in a head-shaped tank with the UCLH Mk2.5 MFEIT system. Reconstruction was performed with time difference (TD), frequency difference (FD), FD adjacent (FDA), weighted FD (WFD) and weighted FDA (WFDA) linear algorithms. The perturbation in reconstructed images corresponded to the true position to <9.5% of image diameter with an image SNR of >5.4 for all algorithms in saline but only for TD, WFDA and WFD in the carrot-saline background. No reliable imaging was possible with FD and FDA. This indicates that the WFD approach is also effective for a realistic head geometry and supports its use for human imaging in the future.

Detection of temporal lobe seizures and identification of lateralisation from audified EEG

OBJECTIVE

To investigate the accuracy of human listeners in identifying epileptic seizures and seizure lateralisation from audified EEG signals.

METHODS

EEG data from 17 temporal lobe epilepsy patients (9 male, 8 female; aged 23-55) was converted to audio format by 60× time compression. Using a subset of 19% of the data, five auditory participants (2 female, 3 male; aged 23-58) were trained to identify seizures and their lateralisation by listening to audified EEG signals from difference electrodes P3-T5 and P4-T6. Following training, seizure detection performance of the auditory participants was tested using the remaining data.

RESULTS

Allowing a 5s auditory time margin for successful detection, the mean sensitivity of the five auditory participants was 89.6% (SD 8.3%) with a false detection rate of only 0.0068/h (SD 0.0077/h). The mean accuracy of seizure lateralisation identification was 77.6% (SD 7.1%).

CONCLUSIONS

With a limited amount of training, humans can detect seizures and seizure lateralisation from audified EEG signals of electrodes P3-T5 and P4-T6 with accuracy comparable to visual assessment of full EEG traces (21 electrodes) by an expert encephalographer.

SIGNIFICANCE

A more efficient and accurate clinical tool for assessing EEG data based on audification may be developed, which will improve diagnosis and treatment of epilepsy.

Application of machine learning methodology for PET-based definition of lung cancer

We applied a learning methodology framework to assist in the threshold-based segmentation of non-small-cell lung cancer (nsclc) tumours in positron-emission tomography–computed tomography (pet–ct) imaging for use in radiotherapy planning. Gated and standard free-breathing studies of two patients were independently analysed (four studies in total). Each study had a pet–ct and a treatment-planning ct image. The reference gross tumour volume (gtv) was identified by two experienced radiation oncologists who also determined reference standardized uptake value (suv) thresholds that most closely approximated the gtv contour on each slice. A set of uptake distribution-related attributes was calculated for each pet slice. A machine learning algorithm was trained on a subset of the pet slices to cope with slice-to-slice variation in the optimal suv threshold: that is, to predict the most appropriate suv threshold from the calculated attributes for each slice. The algorithm’s performance was evaluated using the remainder of the pet slices. A high degree of geometric similarity was achieved between the areas outlined by the predicted and the reference suv thresholds (Jaccard index exceeding 0.82). No significant difference was found between the gated and the free-breathing results in the same patient. In this preliminary work, we demonstrated the potential applicability of a machine learning methodology as an auxiliary tool for radiation treatment planning in nsclc.

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.

Patient handover from surgery to intensive care: using Formula 1 pit-stop and aviation models to improve safety and quality

BACKGROUND

We aimed to improve the quality and safety of handover of patients from surgery to intensive care using the analogy of a Formula 1 pit stop and expertise from aviation.

METHODS

A prospective intervention study measured the change in performance before and after the implementation of a new handover protocol that was developed through detailed discussions with a Formula 1 racing team and aviation training captains. Fifty (23 before and 27 after) postsurgery patient handovers were observed. Technical errors and information omissions were measured using checklists, and teamwork was scored using a Likert scale. Duration of the handover was also measured.

RESULTS

The mean number of technical errors was reduced from 5.42 (95% CI +/-1.24) to 3.15 (95% CI +/-0.71), the mean number of information handover omissions was reduced from 2.09 (95% CI +/-1.14) to 1.07 (95% CI +/-0.55), and duration of handover was reduced from 10.8 min (95% CI +/-1.6) to 9.4 min (95% CI +/-1.29). Nine out of twenty-three (39%) precondition patients had more than one error in both technical and information handover prior to the new protocol, compared with three out of twnety-seven (11.5%) with the new handover. Regression analysis showed that the number of technical errors were significantly reduced with the new handover (t = -3.63, P < 0.001), and an interaction suggested that teamwork (t = 3.04, P = 0.004) had a different effect with the new handover protocol.

CONCLUSIONS

The introduction of the new handover protocol lead to improvements in all aspects of the handover. Expertise from other industries can be extrapolated to improve patient safety, and in particular, areas of medicine involving the handover of patients or information.

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.