Stephen Keevil | King's College London (original) (raw)

Papers by Stephen Keevil

Journal of Cardiovascular Magnetic Resonance, Feb 3, 2015

British journal of hospital medicine, Apr 1, 2006

British Journal of Radiology, May 1, 1992

Clinical Radiology, May 1, 1992

The spin-lattice (T1) and spin-spin (T2) relaxation times of liver in 42 normal volunteers (21 ma... more The spin-lattice (T1) and spin-spin (T2) relaxation times of liver in 42 normal volunteers (21 male and 21 female) were measured using a calibrated 0.08 T resistive imager capable of accurate and reproducible relaxometry. T1 was determined using an interleaved gradient echo saturation recovery and inversion recovery technique and T2 using a four-echo Carr-Purcell-Meiboom-Gill sequence. The ranges obtained were T1 = 213 +/- 14 ms and T2 = 66 +/- 5 ms. More specific ranges were obtained for each sex and for younger and older subjects. A small variation in T1 was found between older (greater than 40 years) and younger (less than 40 years) subjects, but no such effect was observed in the case of T2. No significant variations were found when female volunteers were imaged at weekly intervals through the menstrual cycle, when a male volunteer was imaged repeatedly over the course of several months or when male volunteers consumed small quantities of alcohol.

Magnetic Resonance Imaging, 1995

Introduction There is an interest in studying small animals using high field whole body scanners ... more Introduction There is an interest in studying small animals using high field whole body scanners equipped with standard clinical protocols. High quality RF coils are required to achieve micron scale high resolution imaging of small rodents. Cooling of a copper RF coil with liquid nitrogen (LN) will greatly reduce the thermal noise and improves its SNR performance by 2 fold at 77K [1]. However designing a non-magnetic cryostat suitable for in-vivo small animal imaging is not an easy task. The requirements of providing good insulation between the cooled coil and sample, close coupling of coil to sample and providing a suitable platform for monitoring and handling small rodents are the major challenges. In this work, a novel PTFE cryostat design achieves good insulation which provides ease of use and is suitable for small rodents is proposed. A receive only cooled cooper coil is developed for a 3T MR scanner, and its low temperature performance is compared to that at room temperature.

The geko TM device is a single-use, battery- powered, neuromuscular electrostimulation device tha... more The geko TM 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 TM device for eval- uation, and invited the manufacturer, Firstkind Ltd, to submit clinical and economic evidence. King's Technol- ogy Evaluation Centre, an External Assessment Centre (EAC) commissioned by the NICE, independently asses- sed the evidence submitted. The sponsor submitted evi- dence related to the geko TM 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 TM prevents VTE. The sponsor's cost model is based on the assumption that patients with an underlying VTE risk and subsequently t...

Introduction It has been widely reported that substantial signal to noise ratio (SNR) gain can be... more Introduction It has been widely reported that substantial signal to noise ratio (SNR) gain can be achieved through the use of the high-temperature superconducting (HTS) surface coil. Due to its complex and expensive design and construction, computational simulation is an essential design tool [1]. However estimating the likely performance gain of the HTS coil where accurate modelling of important parameters such as loaded Q factor and SNR gain in MR imaging experiments has not yet been reported. Firstly this work reports an FDTD mesh based numerical mouse model which will accurately simulate a realistic loading effect on the HTS coil at 3T. Secondly, techniques are developed to assess the high Q factor and SNR gain, and comparisons are made with that of the room temperature copper coil. Finally MR imaging experiments performed on room temperature copper coils to further validate the accuracy of the developed method.

Radiotherapy and Oncology, 1996

Physics in Medicine and Biology, 1998

Physics in Medicine and Biology, 1990

... field. Our method has been used to characterise volumes of interest of various sizes selected... more ... field. Our method has been used to characterise volumes of interest of various sizes selected using the ISIS technique. Deviations ... UK 0031-9155/90/070821+ 14%03.50 0 1990 IOP Publishing Ltd 82 1 Page 3. S F Keevil et a1 These ...

NMR in Biomedicine, 1992

As clinical applications of MRS grow in number and complexity, there is a need for standardized m... more As clinical applications of MRS grow in number and complexity, there is a need for standardized methods for characterizing the performance of volume selection techniques. The results are presented of a thorough evaluation of a particular implementation of ISIS performed using a procedure which forms the basis of the method adopted by the European Community Concerted Action on MRS and MRI. We have found that ISIS localization is optimal when the volume of interest is slightly smaller than the region we wish to study. Contamination with extraneous signal has little T1 dependence so long as TR > T1, and the detection pulse angle is 90°. However, a poorly optimized detection pulse results in T1‐weighted contamination unless TR > 3T1. In the clinical context, this corresponds to a different degree of contamination for each peak in the spectrum. Adiabatic detection pulses were used in an attempt to overcome this problem without resorting to unacceptable TR values, but these were fou...

The British Journal of Radiology

The Control of Electromagnetic Fields at Work Regulations (2016) implement the requirements of th... more The Control of Electromagnetic Fields at Work Regulations (2016) implement the requirements of the EU Physical Agents (Electromagnetic Fields) Directive 2013 into UK Law. These regulations prohibit exposure of employees to electromagnetic fields above defined Exposure Limit Values (ELVs). However, for MRI work activities there is an exemption from this requirement provided that exposures are reduced to a level that is as low as is reasonably practicable. There are additional requirements for an adequate risk assessment, provision for staff training and monitoring of any health effects. This document provides specific guidance on achieving compliance with the regulations in the MRI setting. Consideration of what level of exposure is ‘reasonable’ is key to the proper application of these regulations. The ELVs, as defined in the regulations, are presented in terms of their relevance to exposures in the MRI-setting, what the direct and indirect effects of exposures are likely to be and ...

Document Version Publisher final version (usually the publisher pdf) Link to publication record i... more Document Version Publisher final version (usually the publisher pdf) Link to publication record in King's Research Portal Citation for published version (APA):

Imaging or tissue biomarker evidence has been in-troduced into the core diagnostic pathway for Al... more Imaging or tissue biomarker evidence has been in-troduced into the core diagnostic pathway for Alzheimer’s disease (AD). PET using 18F-labelled beta-amyloid PET tracers has shown promise for the early diagnosis of AD. However, most studies included only small numbers of par-ticipants and no consensus has been reached as to which ra-diotracer has the highest diagnostic accuracy. First, we per-formed a systematic review of the literature published be-tween 1990 and 2014 for studies exploring the diagnostic accuracy of florbetaben, florbetapir and flutemetamol in AD. The included studies were analysed using the QUADAS as-sessment of methodological quality. A meta-analysis of the sensitivity and specificity reported within each study was per-formed. Pooled values were calculated for each radiotracer and for visual or quantitative analysis by population included.

The Author(s) 2014. This article is published with open access at Springerlink.com Abstract The E... more The Author(s) 2014. This article is published with open access at Springerlink.com Abstract The E-vita open plus is a one-stage endoluminal stent graft system used for treating complex aneurysms and dissections of the thoracic aorta. The National Institute for Health and Care Excellence (NICE), as a part of its Medical Technologies Evaluation Programme (MTEP), selected this device for evaluation and invited the manufacturer, JOTEC GmbH, to submit clinical and economic evidence. King’s Technology Evaluation Centre (KiTEC), an External Assessment Centre (EAC) commissioned by the NICE, independently critiqued the manufacturer’s submissions. The EAC considered that the manufacturer had included most of the relevant evidence for the E-vita open plus, based on international E-vita open registry data for 274 patients, but had provided only limited evidence for the comparators.