J. Scuffham - Academia.edu (original) (raw)
Papers by J. Scuffham
Journal of Instrumentation, 2014
A new "paraboloidal" model of Mercury's magnetospheric magnetic field is developed... more A new "paraboloidal" model of Mercury's magnetospheric magnetic field is developed based upon terrestrial model using similar formulations. The model describes Mercury's dipole field, the magnetopause currents driven by the solar wind, and the tail current system including the currents in the tail current sheet and their closure currents at the magnetopause. The effect of the interplanetary magnetic field is modelled as partially penetrating into the magnetosphere. The goals of the present paper are: 1) to develop an easily usable, yet robust model of Mercury's magnetospheric magnetic field; and 2) to produce an improved "unified" determination of Mercury's magnetic dipole moment which fits the measurements taken during both Mariner 10's first and third flybys. This result is a Mercury dipole moment of 270 nT RM3, which is intermediate between the various estimates produced by previous models. In preparation for the up-coming Mercury fly-bys by the MESSENGER mission this new paraboloidal model is used to predict the configuration of this miniature magnetosphere under average and extreme solar wind conditions.
Small pixel Cd(Zn)Te detectors often suffer from inter-pixel variations in gain, resulting in shi... more Small pixel Cd(Zn)Te detectors often suffer from inter-pixel variations in gain, resulting in shifts in the individual energy spectra. These gain variations are mainly caused by inclusions and defects within the crystal structure, which affect the charge transport within the material causing a decrease in the signal pulse height. In imaging applications, spectra are commonly integrated over a particular peak of interest. This means that the individual pixels must be accurately calibrated to ensure that the same portion of the spectrum is integrated in every pixel. The development of large-area detectors with fine pixel pitch necessitates automated algorithms for this spectral calibration, due to the very large number of pixels. Algorithms for automatic spectral calibration require accurate determination of characteristic x-ray or photopeak positions on a pixelwise basis. In this study, we compare two peak searching spectral calibration algorithms for a small-pixel CdTe detector in gamma spectroscopic imaging. The first algorithm uses rigid search ranges to identify peaks in each pixel spectrum, based on the average peak positions across all pixels. The second algorithm scales the search ranges on the basis of the position of the highest-energy peak relative to the average across all pixels. In test spectra acquired with Tc-99m, we found that the rigid search algorithm failed to correctly identify the target calibraton peaks in up to 4% of pixels. In contrast, the scaled search algorithm failed in only 0.16% of pixels. Failures in the scaled search algorithm were attributed to the presence of noise events above the main photopeak, and possible non-linearities in the spectral response in a small number of pixels. We conclude that a peak searching algorithm based on scaling known peak spacings is simple to implement and performs well for the spectral calibration of pixellated radiation detectors.
Nuclear Medicine Communications, 2011
Background Treatment of inoperable hepatocellular carcinoma or secondary metastases by radioembol... more Background Treatment of inoperable hepatocellular carcinoma or secondary metastases by radioembolization using yttrium-90 ( 90 Y) microspheres is a promising method for the treatment of unresectable liver metastases. A pretreatment scintigraphy planar scan using 99m Tc-labelled macroaggregated albumin ( 99m Tc-MAA) injected directly into the hepatic artery is carried out to assess the degree of portal shunting of blood between the liver and the lungs. The quantitative results of this scan are used to modulate the activity of therapeutic 90 Y microspheres injected into the patient to limit the radiation dose received by the lungs. The presence of scattered events in the MAA lung shunt scan leads to an overestimation of the true shunting ratio, which in turn leads to the administered therapeutic activity being lowered unnecessarily to comply with the protocols of radiation protection. Overall, this may impact the efficacy of treatment.
Clinical Nuclear Medicine, 2013
Lipoma arborescens (LA) in the knee is a benign intra-articular lipomatous proliferation of the s... more Lipoma arborescens (LA) in the knee is a benign intra-articular lipomatous proliferation of the synovial membrane, and data on treatment of LA by radionuclide therapy is sparse. We present a rare case of bilateral LA in the knees successfully treated with injection of Y-citrate colloid. We assessed the biodistribution of the radiopharmaceutical through the use of SPECT/CT imaging. Our images show slight redistribution of the radiocolloid in the knee joint, whereas most of the radioactivity remains localized around the LA. MRI scans confirmed the efficacy of this treatment, with a significant reduction in LA volume after 6 months.
Advances in Space Research, 2006
Two new missions will arrive at Mercury within the next decade. Interest in this enigmatic planet... more Two new missions will arrive at Mercury within the next decade. Interest in this enigmatic planet has therefore been revived in the magnetospheric community, and new models of MercuryÕs magnetic field are demanded. In the past, there have been several attempts to model the magnetosphere of Mercury based on simply scaling models of the EarthÕs magnetosphere. Although these scaled models have enjoyed many successes, their global magnetic configurations are determined by measurements made at the Earth, not at Mercury. In this paper, we develop a new empirical model of the Hermean field which is constrained wherever possible by the Mariner 10 dataset. We also explore the response of the model to upstream solar wind conditions. Data-based empirical models are an invaluable tool in magnetospheric physics at the Earth, and will doubtless prove to be just as useful at Mercury. The model developed here is generally applicable, and can be used to fit a much larger spacecraft dataset when it becomes available.
We have developed a pixellated high energy X-ray detector instrument to be used in a variety of i... more We have developed a pixellated high energy X-ray detector instrument to be used in a variety of imaging applications. The instrument consists of either a Cadmium Zinc Telluride or Cadmium Telluride (Cd(Zn)Te) detector bump-bonded to a large area ASIC and packaged with a high performance data acquisition system. The 80 by 80 pixels each of 250 µm by 250 µm
Journal of Instrumentation, 2014
A new "paraboloidal" model of Mercury's magnetospheric magnetic field is developed... more A new "paraboloidal" model of Mercury's magnetospheric magnetic field is developed based upon terrestrial model using similar formulations. The model describes Mercury's dipole field, the magnetopause currents driven by the solar wind, and the tail current system including the currents in the tail current sheet and their closure currents at the magnetopause. The effect of the interplanetary magnetic field is modelled as partially penetrating into the magnetosphere. The goals of the present paper are: 1) to develop an easily usable, yet robust model of Mercury's magnetospheric magnetic field; and 2) to produce an improved "unified" determination of Mercury's magnetic dipole moment which fits the measurements taken during both Mariner 10's first and third flybys. This result is a Mercury dipole moment of 270 nT RM3, which is intermediate between the various estimates produced by previous models. In preparation for the up-coming Mercury fly-bys by the MESSENGER mission this new paraboloidal model is used to predict the configuration of this miniature magnetosphere under average and extreme solar wind conditions.
Small pixel Cd(Zn)Te detectors often suffer from inter-pixel variations in gain, resulting in shi... more Small pixel Cd(Zn)Te detectors often suffer from inter-pixel variations in gain, resulting in shifts in the individual energy spectra. These gain variations are mainly caused by inclusions and defects within the crystal structure, which affect the charge transport within the material causing a decrease in the signal pulse height. In imaging applications, spectra are commonly integrated over a particular peak of interest. This means that the individual pixels must be accurately calibrated to ensure that the same portion of the spectrum is integrated in every pixel. The development of large-area detectors with fine pixel pitch necessitates automated algorithms for this spectral calibration, due to the very large number of pixels. Algorithms for automatic spectral calibration require accurate determination of characteristic x-ray or photopeak positions on a pixelwise basis. In this study, we compare two peak searching spectral calibration algorithms for a small-pixel CdTe detector in gamma spectroscopic imaging. The first algorithm uses rigid search ranges to identify peaks in each pixel spectrum, based on the average peak positions across all pixels. The second algorithm scales the search ranges on the basis of the position of the highest-energy peak relative to the average across all pixels. In test spectra acquired with Tc-99m, we found that the rigid search algorithm failed to correctly identify the target calibraton peaks in up to 4% of pixels. In contrast, the scaled search algorithm failed in only 0.16% of pixels. Failures in the scaled search algorithm were attributed to the presence of noise events above the main photopeak, and possible non-linearities in the spectral response in a small number of pixels. We conclude that a peak searching algorithm based on scaling known peak spacings is simple to implement and performs well for the spectral calibration of pixellated radiation detectors.
Nuclear Medicine Communications, 2011
Background Treatment of inoperable hepatocellular carcinoma or secondary metastases by radioembol... more Background Treatment of inoperable hepatocellular carcinoma or secondary metastases by radioembolization using yttrium-90 ( 90 Y) microspheres is a promising method for the treatment of unresectable liver metastases. A pretreatment scintigraphy planar scan using 99m Tc-labelled macroaggregated albumin ( 99m Tc-MAA) injected directly into the hepatic artery is carried out to assess the degree of portal shunting of blood between the liver and the lungs. The quantitative results of this scan are used to modulate the activity of therapeutic 90 Y microspheres injected into the patient to limit the radiation dose received by the lungs. The presence of scattered events in the MAA lung shunt scan leads to an overestimation of the true shunting ratio, which in turn leads to the administered therapeutic activity being lowered unnecessarily to comply with the protocols of radiation protection. Overall, this may impact the efficacy of treatment.
Clinical Nuclear Medicine, 2013
Lipoma arborescens (LA) in the knee is a benign intra-articular lipomatous proliferation of the s... more Lipoma arborescens (LA) in the knee is a benign intra-articular lipomatous proliferation of the synovial membrane, and data on treatment of LA by radionuclide therapy is sparse. We present a rare case of bilateral LA in the knees successfully treated with injection of Y-citrate colloid. We assessed the biodistribution of the radiopharmaceutical through the use of SPECT/CT imaging. Our images show slight redistribution of the radiocolloid in the knee joint, whereas most of the radioactivity remains localized around the LA. MRI scans confirmed the efficacy of this treatment, with a significant reduction in LA volume after 6 months.
Advances in Space Research, 2006
Two new missions will arrive at Mercury within the next decade. Interest in this enigmatic planet... more Two new missions will arrive at Mercury within the next decade. Interest in this enigmatic planet has therefore been revived in the magnetospheric community, and new models of MercuryÕs magnetic field are demanded. In the past, there have been several attempts to model the magnetosphere of Mercury based on simply scaling models of the EarthÕs magnetosphere. Although these scaled models have enjoyed many successes, their global magnetic configurations are determined by measurements made at the Earth, not at Mercury. In this paper, we develop a new empirical model of the Hermean field which is constrained wherever possible by the Mariner 10 dataset. We also explore the response of the model to upstream solar wind conditions. Data-based empirical models are an invaluable tool in magnetospheric physics at the Earth, and will doubtless prove to be just as useful at Mercury. The model developed here is generally applicable, and can be used to fit a much larger spacecraft dataset when it becomes available.
We have developed a pixellated high energy X-ray detector instrument to be used in a variety of i... more We have developed a pixellated high energy X-ray detector instrument to be used in a variety of imaging applications. The instrument consists of either a Cadmium Zinc Telluride or Cadmium Telluride (Cd(Zn)Te) detector bump-bonded to a large area ASIC and packaged with a high performance data acquisition system. The 80 by 80 pixels each of 250 µm by 250 µm