Northern Ireland Regional Medical Physics Agency

Belfast, United Kingdom

Northern Ireland Regional Medical Physics Agency

Belfast, United Kingdom
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Mackenzie A.,Royal Surrey County Hospital | Workman A.,Northern Ireland Regional Medical Physics Agency | Dance D.R.,Royal Surrey County Hospital | Dance D.R.,University of Surrey | And 4 more authors.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

Comparing the clinical performance of digital mammography technologies is challenging. The aim of this work is to develop and test a methodology for adjusting mammographic images taken on a given imaging system to simulate their appearance as if taken on a different system. Such methodology would be very useful for a wide range of system performance and design studies using both phantom and clinical images. The process involves changing the image blurring in accordance with the measured modulation transfer functions and adding noise (electronic, quantum and structure). The method has been tested by adapting flat field images acquired using an amorphous selenium detector and a computed radiography (CR) detector to different dose levels and comparing the resultant simulated NPSs with directly measured NPSs. For the detectors used in this work the NPSs at different dose levels are well predicted. This could be a powerful tool for studies of clinical image quality. © 2010 Springer-Verlag.


Yip M.,University of Surrey | Zanca F.,University Hospitals Gasthuisberg | MacKenzie A.,Royal Surrey County Hospital | Workman A.,Northern Ireland Regional Medical Physics Agency | And 5 more authors.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

The purpose of this study is to evaluate the effect of simulated dose reduction using CDMAM and mastectomy images acquired on two digital mammography systems. High dose images have been artificially degraded to reduced dose levels by systematically adding filtered noise. Automated scoring has been carried out on the degraded CDMAM images and on experimental CDMAM images, taken at the same corresponding reduced doses. Contrast-detail curves were derived for both, at all doses, and compared. Relative difference in the contrast-detail curves was approximately 5% overall for all four doses. For the mastectomy images noise power spectra were obtained and the ratio of experimental to synthetic low dose NPS profiles averaged for all doses at 1.04. The largest differences in the NPS profiles were found at the high spatial frequencies, corresponding with the differences in the small discs in the contrast-detail curves. © 2010 Springer-Verlag.


Hanna G.G.,Queen's University of Belfast | Hanna G.G.,Belfast City Hospital | McAleese J.,Belfast City Hospital | Carson K.J.,Northern Ireland Regional Medical Physics Agency | And 11 more authors.
International Journal of Radiation Oncology Biology Physics | Year: 2010

Purpose: Positron emission tomography (PET), in addition to computed tomography (CT), has an effect in target volume definition for radical radiotherapy (RT) for non-small-cell lung cancer (NSCLC). In previously PET-CT staged patients with NSCLC, we assessed the effect of using an additional planning PET-CT scan for gross tumor volume (GTV) definition. Methods and Materials: A total of 28 patients with Stage IA-IIIB NSCLC were enrolled. All patients had undergone staging PET-CT to ensure suitability for radical RT. Of the 28 patients, 14 received induction chemotherapy. In place of a RT planning CT scan, patients underwent scanning on a PET-CT scanner. In a virtual planning study, four oncologists independently delineated the GTV on the CT scan alone and then on the PET-CT scan. Intraobserver and interobserver variability were assessed using the concordance index (CI), and the results were compared using the Wilcoxon signed ranks test. Results: PET-CT improved the CI between observers when defining the GTV using the PET-CT images compared with using CT alone for matched cases (median CI, 0.57 for CT and 0.64 for PET-CT, p = .032). The median of the mean percentage of volume change from GTVCT to GTVFUSED was -5.21% for the induction chemotherapy group and 18.88% for the RT-alone group. Using the Mann-Whitney U test, this was significantly different (p = .001). Conclusion: PET-CT RT planning scan, in addition to a staging PET-CT scan, reduces interobserver variability in GTV definition for NSCLC. The GTV size with PET-CT compared with CT in the RT-alone group increased and was reduced in the induction chemotherapy group. © 2010 Elsevier Inc. All rights reserved.


Hanna G.G.,Queen's University of Belfast | Hanna G.G.,Belfast City Hospital | Carson K.J.,Royal Victoria Hospital | Lynch T.,Belfast City Hospital | And 9 more authors.
International Journal of Radiation Oncology Biology Physics | Year: 2010

Purpose: 18F-Fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) has benefits in target volume (TV) definition in radiotherapy treatment planning (RTP) for non-small-cell lung cancer (NSCLC); however, an optimal protocol for TV delineation has not been determined. We investigate volumetric and positional variation in gross tumor volume (GTV) delineation using a planning PET/CT among three radiation oncologists and a PET radiologist. Methods and Materials: RTP PET/CT scans were performed on 28 NSCLC patients (Stage IA-IIIB) of which 14 patients received prior induction chemotherapy. Three radiation oncologists and one PET radiologist working with a fourth radiation oncologist independently delineated the GTV on CT alone (GTVCT) and on fused PET/CT images (GTV PETCT). The mean percentage volume change (PVC) between GTV CT and GTVPETCT for the radiation oncologists and the PVC between GTVCT and GTVPETCT for the PET radiologist were compared using the Wilcoxon signed-rank test. Concordance index (CI) was used to assess both positional and volume change between GTVCT and GTV PETCT in a single measurement. Results: For all patients, a significant difference in PVC from GTVCT to GTVPETCT exists between the radiation oncologist (median, 5.9%), and the PET radiologist (median, -0.4%, p = 0.001). However, no significant difference in median concordance index (comparing GTVCT and GTVFUSED for individual cases) was observed (PET radiologist = 0.73; radiation oncologists = 0.66; p = 0.088). Conclusions: Percentage volume changes from GTVCT to GTVPETCT were lower for the PET radiologist than for the radiation oncologists, suggesting a lower impact of PET/CT in TV delineation for the PET radiologist than for the oncologists. Guidelines are needed to standardize the use of PET/CT for TV delineation in RTP. © 2010 Elsevier Inc.


Hamilton P.,Queen's University of Belfast | Lockhart C.J.,Queen's University of Belfast | McCann A.J.,Northern Ireland Regional Medical Physics Agency | Agnew C.E.,Northern Ireland Regional Medical Physics Agency | And 5 more authors.
QJM | Year: 2011

Background: Flow-mediated dilatation (FMD) of the brachial artery is commonly measured as a surrogate marker of endothelial function. Its measurement is, however, technically demanding and reports regarding its reproducibility have not always been favourable. Aim: Two Type I diabetes and control group comparator studies were conducted to assess the reproducibility of FMD and to analyse blood flow data normally discarded during FMD measurement. Design: The studies were sequential and differed only with regard to operator and ultrasound machine. Seventy-two subjects with diabetes and 71 controls were studied in total. Methods: Subjects had FMD measured conventionally. Blood velocity waveforms were averaged over 10 pulses post forearm ischaemia and their component frequencies analysed using the wavelet transform, a mathematical tool for waveform analysis. The component frequencies were grouped into 11 bands to facilitate analysis. Results: Subjects were well-matched between studies. In Study 1, FMD was significantly impaired in subjects with Type I diabetes vs. controls (median 4.35%, interquartile range 3.10-4.80 vs. 6.50, 4.79-9.42, P < 0.001). No differences were detected between groups in Study 2, however. However, analysis of blood velocity waveforms yielded significant differences between groups in two frequency bands in each study. Conclusions: This report highlights concerns over the reproducibility of FMD measures. Further work is required to fully elucidate the role of analysing velocity waveforms after forearm ischaemia. © The Author 2011. Published by Oxford University Press on behalf of the Association of Physicians. All rights reserved.


Quinn C.E.,Queen's University of Belfast | Hamilton P.K.,Queen's University of Belfast | Mccann A.J.,Northern Ireland Regional Medical Physics Agency | Agnew C.E.,Northern Ireland Regional Medical Physics Agency | And 4 more authors.
Microcirculation | Year: 2011

Waveform analysis has been used to assess vascular resistance and predict cardiovascular events. We aimed to identify microvascular abnormalities in patients with IGT using ocular waveform analysis. The effects of pioglitazone were also assessed. Methods: Forty patients with IGT and 24 controls were studied. Doppler velocity recordings were obtained from the central retinal, ophthalmic, and common carotid arteries, and sampled at 200Hz. A discrete wavelet-based analysis method was employed to quantify waveforms. The RI was also determined. Patients with IGT were randomized to pioglitazone or placebo, and measurements were repeated after 12-week treatment. Results: In the ocular waveforms, significant differences in power spectra were observed in frequency band 4 (corresponding to frequencies between 6.25 and 12.50Hz) between groups (p<0.05). No differences in RI occurred. No association was observed between waveform parameters and fasting glucose or insulin resistance. Pioglitazone had no effect on waveform structure, despite significantly reducing insulin resistance, fasting glucose, and triglycerides (p<0.05). Conclusions: Analysis of ocular Doppler flow waveforms using the discrete wavelet transform identified microvascular abnormalities that were not apparent using RI. Pioglitazone improved glucose, insulin sensitivity, and triglycerides without influencing the contour of the waveforms. © 2011 John Wiley & Sons Ltd.


Agnew C.E.,Northern Ireland Regional Medical Physics Agency | Hamilton P.K.,Queen's University of Belfast | McCann A.J.,Northern Ireland Regional Medical Physics Agency | McGivern R.C.,Northern Ireland Regional Medical Physics Agency | McVeigh G.E.,Queen's University of Belfast
Ultrasound in Medicine and Biology | Year: 2015

Wavelet entropy assesses the degree of order or disorder in signals and presents this complex information in a simple metric. Relative wavelet entropy assesses the similarity between the spectral distributions of two signals, again in a simple metric. Wavelet entropy is therefore potentially a very attractive tool for waveform analysis. The ability of this method to track the effects of pharmacologic modulation of vascular function on Doppler blood velocity waveforms was assessed. Waveforms were captured from ophthalmic arteries of 10healthy subjects at baseline, after the administration of glyceryl trinitrate (GTN) and after two doses of NG-nitro-L-arginine-methyl ester (L-NAME) to produce vasodilation and vasoconstriction, respectively. Wavelet entropy had a tendency to decrease from baseline in response to GTN, but significantly increased after the administration of L-NAME (mean: 1.60 ± 0.07 after 0.25 mg/kgand 1.72 ± 0.13 after 0.5 mg/kg vs. 1.50 ± 0.10 at baseline, p<0.05). Relative wavelet entropy had a spectral distribution from increasing doses of L-NAME comparable to baseline, 0.07 ± 0.04 and 0.08 ± 0.03, respectively, whereas GTN had the most dissimilar spectral distribution compared with baseline (0.17 ± 0.08, p= 0.002). Wavelet entropy can detect subtle changes in Doppler bloodvelocity waveform structure in response to nitric-oxide-mediated changes in arteriolar smooth muscle tone. © 2015 World Federation for Ultrasound in Medicine & Biology.


Pinnock R.A.,Northern Ireland Regional Medical Physics Agency | McGivern R.C.,Northern Ireland Regional Medical Physics Agency | Forbes R.,Craigavon Area Hospital | Gibson J.M.,Royal Victoria Hospital
Journal of Neurology | Year: 2010

Since the basal ganglia are thought to have a role in controlling ocular fixation it is expected that patients with parkinsonian conditions would show impaired performance in fixation tasks. Our study examines ocular fixation in patients with a range of parkinsonian conditions (Idiopathic Parkinson's Disease, Multiple System Atrophy and Progressive Supranuclear Palsy). Eye movements were recorded from 44 patients and 50 age matched control subjects during ocular fixation both with and without a visible target. The data for each patient were then characterised in terms of fixation periods and saccadic intrusions (SI). Patient groups exhibited larger and more frequent SI as well as greater displacement from the fixation target. Patients with Progressive Supranuclear Palsy exhibit larger SI than control subjects when fixation targets are visible, this difference is reversed in the absence of a fixation target. Patients with Multiple System Atrophy show increased frequency of SI both with and without a visible target. Our findings show that ocular fixation is impaired in patients with parkinsonian conditions and may prove useful as part of an oculomotor profile to aid with the differentiation of parkinsonian conditions. © 2009 Springer-Verlag.


Donaghy C.,Royal Victoria Hospital | Pinnock R.,Northern Ireland Regional Medical Physics Agency | Abrahams S.,University of Edinburgh | Cardwell C.,Queen's University of Belfast | And 4 more authors.
Journal of Neurology | Year: 2010

Historical studies of eye movements in motor neurone disease (MND) have been conflicting although current findings suggest that eye movement abnormalities relate to frontal lobe impairment. Numerous case reports, however, describe slow saccades and supranuclear gaze palsies in patients with MND often associated with bulbar-onset disease. We performed a study of saccades and smooth pursuit in a large group of patients with MND to examine for any differences between bulbar-onset and spinal-onset patients. Forty-four patients (14 bulbar-onset and 30 spinal-onset patients) and 45 controls were recruited. Reflexive saccades, antisaccades and smooth pursuit were examined using infra-red oculography and all subjects then underwent neuropsychological evaluation. Reflexive saccades were found to be slower in bulbar-onset compared to spinal-onset patients and controls (p = 0.03, p = 0.05). Antisaccade latency (p = 0.01) and antisaccade type 1 errors (p = 0.03, p = 0.04) were increased in patients compared to controls. 'Proportion of time spent in smooth pursuit' and smooth pursuit 'velocity gain' were reduced in patients compared to controls (p = 0.000, p = 0.001). Antisaccade errors and velocity gain correlated with neuropsychological measures sensitive to lesions of the frontal lobes. This is the first study to highlight the presence of slow saccades in bulbar-onset MND. These findings suggest that slow saccades may be due to increased brainstem pathology in bulbar-onset disease that involves burst cell neurons. Furthermore these observations highlight the potential for overlap between bulbar-onset MND and progressive supranuclear palsy (PSP) as both can have a bulbar palsy and slowed saccades. © 2010 Springer-Verlag.


PubMed | Northern Ireland Regional Medical Physics Agency and Queen's University of Belfast
Type: Journal Article | Journal: Ultrasound in medicine & biology | Year: 2015

Wavelet entropy assesses the degree of order or disorder in signals and presents this complex information in a simple metric. Relative wavelet entropy assesses the similarity between the spectral distributions of two signals, again in a simple metric. Wavelet entropy is therefore potentially a very attractive tool for waveform analysis. The ability of this method to track the effects of pharmacologic modulation of vascular function on Doppler blood velocity waveforms was assessed. Waveforms were captured from ophthalmic arteries of 10 healthy subjects at baseline, after the administration of glyceryl trinitrate (GTN) and after two doses of N(G)-nitro-L-arginine-methyl ester (L-NAME) to produce vasodilation and vasoconstriction, respectively. Wavelet entropy had a tendency to decrease from baseline in response to GTN, but significantly increased after the administration of L-NAME (mean: 1.60 0.07 after 0.25 mg/kg and 1.72 0.13 after 0.5 mg/kg vs. 1.50 0.10 at baseline, p < 0.05). Relative wavelet entropy had a spectral distribution from increasing doses of L-NAME comparable to baseline, 0.07 0.04 and 0.08 0.03, respectively, whereas GTN had the most dissimilar spectral distribution compared with baseline (0.17 0.08, p = 0.002). Wavelet entropy can detect subtle changes in Doppler blood velocity waveform structure in response to nitric-oxide-mediated changes in arteriolar smooth muscle tone.

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