Development and validation of two novel x-ray filters in computed tomography with focus on fluence modulation for region-of-interest imaging

Die Röntgen-Computertomographie (CT) hat sich zu einem zentralen Element der klinischen Bildgebung entwickelt. Sie liefert Schichtbilder, die sich durch eine hohe zeitliche und räumliche Auflösung bei sehr kurzen Aufnahmezeiten auszeichnen. Allerdings verwendet die CT zur Bildaufnahme ionisierende Röntgenstrahlung, die ein potenzielles Gesundheitsrisiko für den Patienten darstellt. Über die Jahre wurden viele Maßnahmen ergriffen, um die Strahlendosis zu reduzieren. Ein Ansatz ist die dynamische Vorfilterung des Röntgenstrahls, um die Abschwächung der Röntgenstrahlung durch den Patienten, die über die Projektionen und die Fächerstrahlbreite variiert, zu kompensieren. Bowtie-Filter moderner CT Systeme nach dem Stand der Technik sind jedoch statische Vollkörper und können sich nicht an die individuelle Patientenschwächung anpassen. Eine Lösung für patienten- und aufgabenspezifische CT Bildgebung ist die Modulation des Fluenzbereichs (FFM) unter Verwendung eines dynamischen Strahlabschwächers (DBA). DBAs ermöglichen es, die Röntgenfluenz während der Datenaufnahme anzupassen. Existierende DBA-Konzepte zeigen jedoch grundsätzliche Schwachstellen (z.B. zu groß oder zu langsam), die eine Realisierung in klinischen CT Systemen ausschließen. In dieser Thesis wurden zwei grundlegend neue DBA-Konzepte entwickelt, um die mangelnde Flexibilität derzeitiger Bowtie-Filter und die Einschränkungen bisheriger DBA-Ansätze zu überwinden. Der lamellenbasierte DBA (sbDBA) besteht aus einer Anordnung von stark röntgenabsorbierenden Lamellen. Je nach Verkippung des sbDBA verändert sich die Transmission durch den sbDBA – vergleichbar mit Jalousien. Auch der artverwandte, z-ausgerichtete sbDBA (z-sbDBA) besitzt Absorptionslamellen zur FFM, verwendet jedoch eine überarbeitete Strukturierung und eine einfachere Mechanik. Ausgehend von einfachen Skizzen wurden reale Prototypen des sbDBA und des z-sbDBA gebaut und in ein klinisches CT System integriert. Im ersten Teil dieser Arbeit wurden das modifizierte CT System und Monte-Carlo Simulationen, die dieses CT System nachbilden, verwendet, um die DBAs zu untersuchen. In Versuchsmessungen konnten beide DBAs verschiedene Transmissionprofile erzeugen und somit FFM – die Hauptfunktion eines DBA – realisieren. Während der sbDBA auch die Verschiebung der Maximaltransmission erlaubte, wurden mit dem z-sbDBA geeignetere Verläufe der Transmissionsprofile erzielt. Ein Vergleich spektraler Abhängigkeit der Transmission und DBA-induzierter Streustrahlung zeigte bemerkenswerte Vorteile gegenüber herkömmlichen Bowtie-Filtern. Obwohl einzelne Ringartefakte in ersten Bildrekonstruktionen Herausforderung hinsichtlich der mechanischen Stabilität der DBAs aufzeigten, war die Bildqualität insgesamt vielversprechend. Im zweiten Teil wurde das Potenzial für Zielvolumen (ROI) Bildgebung untersucht, bei der nur ein bestimmter Bereich mit hoher Qualität dargestellt und im umliegenden Gewebe die Dosis minimiert wird. Zunächst wurde hierzu ein Optimierungskriterium entwickelt, mit dem die Kippbewegungen der DBAs hinsichtlich eines diagnostischen Ziels optimiert werden. Dabei soll die Patientendosis minimiert und die Bildqualität innerhalb der ROI maximiert werden. Die erzeugten DBA-Trajektorien passten die emittierte Röntgenfluenz an die Geometrie der ROI an. Anschließend wurden verschiedene FFM-Konfigurationen, einschließlich Röhrenstrommodulation und zweier Bowtie-Filter, mit den DBAs bezüglich ihrer Dosiseffizienz bei ROI-Bildgebung verglichen. Es zeigte sich, dass die DBAs die Röntgenstrahlung effizienter einsetzten als Bowtie-Filter moderner CT Systeme: Bei Verwendung der DBAs konnten die ROIs bei gleichbleibender Bildqualität mit bis zu 30 % (z-sbDBA) bzw. 60 % (sbDBA) weniger Dosis im Vergleich zu einem typischen Bowtie-Filter dargestellt werden. In dieser Arbeit wurden zwei neuartige DBA-Konzepte entwickelt und in ein klinisches CT System installiert. Diese DBAs wurden hinsichtlich FFM erfolgreich validiert und zeigten bei ROI-Bildgebung erhebliches Dosiseinsparpotential im Vergleich zu heutiger FFM-Technik. Die vielversprechenden Ergebnisse bilden eine Grundlage für zukünftige Dosisreduktionen und ebnen den Weg für ROI-Bildgebung in der CT Diagnostik.X-ray computed tomography (CT) imaging has become a workhorse of today’s clinical imaging. It provides cross-sectional diagnostic images featuring high temporal and spatial resolution at very short acquisition times. However, CT images are acquired using x-rays, which bears a potential health detriment to the patient due to ionization radiation. Over the decades, many efforts have been undertaken to reduce the radiation burden. One approach is to employ dynamic pre-filtration of the x-ray beam to compensate for the patient’s x-ray attenuation that changes across the projections and the fan beam angle. State-of-the-art bowtie filters in clinical CT systems, however, are static and therefore cannot adapt to patient attenuation individually. A solution for patient- and task-specific CT imaging is fluence field modulation (FFM) by employing a dynamic beam attenuator (DBA). DBAs are capable of adapting the x-ray fluence during the data acquisition. Existing DBA concepts, however, suffer from inherent limitations (e.g., too large or too slow) that preclude an implementation in clinical CT systems. In this thesis, two fundamentally new DBA concepts were developed to overcome the lack of flexibility of present bowtie filters and the pitfalls of previous DBA approaches. The sheet-based DBA (sbDBA) was composed of an array of highly x-ray attenuating sheets. Depending on the way the sbDBA was tilted, the transmission through the sbDBA changed – comparable to Persian blinds. Likewise, the z-aligned sbDBA (z-sbDBA) employed attenuation sheets for FFM, although it used a revised structuring and simplified mechanics. Starting from simple sketches, physical prototypes of the sbDBA and the z-sbDBA were built and integrated into a clinical CT system. In the first part of this thesis, the DBAs were investigated using the modified CT system and Monte Carlo simulations mimicking this CT system. In experimental measurements, both DBAs were able to realize a wide range of transmission profiles and therefore successfully demonstrated their feasibility of FFM — the key function of a DBA. While the sbDBA allowed to shape the transmission profiles more flexibly by shifting the peak transmission also laterally, the z-sbDBA realized more suitable shapes. A comparison regarding the spectral dependency of the transmission and attenuator-induced scatter revealed remarkable advantages over conventional bowtie filters. Although ring artifacts in first-time image reconstructions unveiled challenges concerning the mechanical reliability of the DBAs, the overall image quality was promising. In the second part, the potential for region-of-interest (ROI) imaging, where only a specific region is imaged at high quality while the dose is minimized in surrounding tissue, was explored. In the first step, an optimization objective was developed to optimize the angular movements of the DBA regarding a given imaging task. The optimization aims at minimizing the patient dose and maximizing the image quality inside the ROI. The optimized DBA movements reasonably adapted the emitted x-ray fluence to the geometry of the ROI. In the second step, different FFM configurations, including tube current modulation and different bowtie filters, were compared with the DBAs regarding their dose efficiency in ROI imaging. The DBAs were shown to exploit the x-ray radiation more efficiently than the bowtie filters of modern CT systems: using the DBAs, the ROIs were imaged with up to 30 % (z-sbDBA) or 60 % (sbDBA) less radiation dose compared to a typical bowtie filter while maintaining the image quality in the ROI. In conclusion, two novel DBA concepts were developed and installed into a clinical CT system. These DBAs were successfully validated regarding FFM and demonstrated a remarkable dose saving potential in ROI imaging compared to state-of-the-art FFM technology. The promising results give rise for future radiation dose reductions and pave the way to ROI imaging in diagnostic CT

Dose optimization in diagnostic radiology

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree for the Doctor of Philosophy. Johannesburg 2012Medical X-ray imaging is nowadays ubiquitous in healthcare. International studies have shown that patient doses during both diagnostic X-ray examinations and fluoroscopically guided procedures from one clinic to another can vary by a factor of up to 100. Such a variation in patient doses offers an opportunity for dose – image quality optimization. Given this background, every radiology clinic which wants to use X-ray imaging ethically and efficiently should have in place ways of optimizing the patient dose – image quality relationship. One generally accepted tool in the optimization process is diagnostic reference levels (DRLs). Currently in South Africa there are no established DRLs and there is no systematic patient dose data collection by the either the national regulator or any competent authority. The main purpose of this thesis was to quantify patient doses for patients undergoing diagnostic examinations and fluoroscopically guided procedures, educate radiation workers on typical patient doses, develop effective methods in quality control of radiographic and fluoroscopic equipment and evaluate radiographer familiarity with digital radiography technology within the context of a typical university teaching South African hospital. The present thesis comprises of seven studies, all carried out at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH), formerly Johannesburg Hospital: Study I: In this investigation the luminance level of X-ray viewing boxes and ambient lighting levels in reporting rooms were measured as a quality assurance procedure and compared with the recommended values by the Directorate of Radiation Control (DRC) of South Africa, European Commission (EC) and Nordic Radiation Protection Co-operation (NORDIC). Results from this investigation showed that the mean average luminance was 1027 cd m-2 and 3284 cd m-2 at the Division of Radiology and Division of Radiation Oncology respectively. The Division of Radiation Oncology had an average viewing box uniformity 7.14% compared to 27.32% at the Division of Radiology. The average ambient lighting was found to be 66 lux for both Divisions. The radiograph viewing conditions variably comply with guidelines. The radiographic imaging chain can only be as strong as its weakest link, thus this study underscores the need of implementing quality control and quality assurance standards in radiographic image viewing. Based on the practical experience of this investigation it is recommended that the DRC test criteria be adopted, in light of the varied recommendations worldwide. Study II: This study aimed to develop, implement and evaluate a software program which can be used in a radiology quality control program. A Microsoft Excel™ based software program was developed for use in quality control: tests data collection, analysis and archiving of the tests done on general radiography equipment, fluoroscopy equipment and film processors. Validation of the software application in terms of usability, user-friendliness was done by an experienced radiographer. This software provides an easier and efficient way of recording quality control data, analysis and archiving. Study III: This study retrospectively analyzed the radiation doses delivered to patients undergoing fluoroscopy guided procedures in terms of the skin dose1 and the kerma-area product readings. A total of three hundred and thirty one fluoroscopically guided procedures were analyzed. In agreement with other published studies, a weak correlation was shown between skin dose and screening time, while a poor correlation was shown between KAP reading and screening time. There was a wide spread in the radiation doses registered for any one given type of examination, which shows that there is room for dose optimization. From the lessons drawn from this study it is practically feasible to record the KAP, fluoroscopy time and number of images routinely. The usefulness and potential use of KAP meters with regards to dose optimization in radiology was confirmed. Study IV: This investigation aimed to assess the feasibility of fabricating in-house the clinical dosimetry radiology phantoms. A total of six patient dose assessment phantoms were fabricated of which four phantoms were as per American National Standards Institute (ANSI) specifications and the other two as per Centre for Devices and Radiological Health (CDRH) specifications. This study proved that the phantoms can be fabricated cost-effectively in-house in a hospital with a mechanical engineering workshop using materials which are locally available. In addition, this study determined radiation doses received by patients undergoing six general radiography examinations. The feasibility of both direct and indirect methods of patient dosimetry was studied. Patient dosimetry based on indirect measurements was the method of choice. Patient data and technical parameters related to the X-ray examinations were collected. The study involved the following examinations: chest posterior-anterior (PA), chest lateral (LAT), pelvis anterior-posterior (AP), abdomen AP, lumbar spine AP and thoracic spine AP. Entrance surface air kerma was calculated based on the X-ray tube 1 See Section 8.3 on the use of the term skin dose output of the unit used and the exposure parameters used for the actual examination. Based on the mean entrance surface air kerma (ESAK) values from the individual rooms, the following DRLs were established: 0.10 mGy for chest PA, 0.22 mGy for chest LAT, 2.98 mGy for pelvis AP, 4.19 mGy for abdomen AP, 5.30 mGy for lumbar spine AP and 3.28 mGy for thoracic spine AP. The calculated mean ESAK values were compared with previously published mean values from other countries. For the first time, a baseline for potential dose reference levels (DRLs) in South Africa was established for the selected examinations. The results of this snapshot audit serve as a benchmark for future dose optimization attempts in South Africa. Feasible and practical dose saving measures are presented and discussed based on the experience of the present patient dose audit carried out. Study V: A replica of the CDRAD phantom was successfully fabricated in-house for use as an image quality test object. It has been shown that the phantom when fabricated in-house is inexpensive and can be made from materials that are readily available locally. Furthermore the utility of the replica phantom as both an acceptance testing and routine quality control tool has been demonstrated. The replica phantom proved effective for purpose and user-friendly. Study VI: The purpose of this study was to assess radiographer familiarity and preferences with digital radiography and thereafter make recommendations in line with the migration from screen film to digital radiography in South Africa. A questionnaire was designed to collect data from either qualified or student radiographers from four teaching hospitals. From the four teaching hospitals there were a total of 205 potential respondents. Among other things, responses regarding experiences and preferences with digital radiography, quality control procedures, patient dose, advantages and disadvantages of digital radiography were sought. The information collected was based on self-reporting by the participants. Sixty-three out of 205 (31 %) radiographers from all the four radiology centres responded to the circulated questionnaire. The participants of this survey showed familiarity with digital radiography and have embraced this relatively new technology as shown by the fact that they can identify both its advantages and disadvantages as applied to clinical practice. However, there are minimal quality control procedures specific to digital radiography being undertaken and there is need for formal education, continuing education and manufacturer training with respect to quality control as institutions make the transition from conventional screen film radiology to digital radiology. Study VII: An investigation into the amount of scattered radiation from the couch during under-couch procedures was carried out. Of dosimetric concern are the forward scattered photons from the couch which contribute in principle to patient dose. Measurement of the amount of scattered radiation off the patient couch was accomplished by using an ionization chamber. The results of the investigation showed that for field size of dimensions, 10 cm * 10 cm, the scatter contribution is approximately 12 % of the total radiation reaching the patient surface. In addition the scatter contribution varies by ±2% across field sizes ranging from 8 cm * 8 cm to 20 cm * 20 cm, with the 10 cm * 10 cm field size taken as a reference field. This study underscores the need to account for the forward scattered radiation so as to improve the accuracy of clinical patient dosimetry. Programs of continuing education and training of radiological personnel in appropriate radiological technique need be actively implemented in order to maintain a high level of awareness of the factors that determine the diagnostic quality and dose to the patients. In line with efforts to optimize dose from diagnostic radiography examinations it is recommended that national DRLs be established in South Africa for the most frequent examinations in general radiography and fluoroscopy. It is recommended that the South African national regulator endeavour to implement or facilitate implementation of a national patient dose database. In summary, this thesis indicates the possibility of dose reduction in diagnostic radiology through optimization of radiographic process

High Resolution Active Pixel Sensor X-Ray Detectors for Digital Breast Tomosynthesis

Current large area x-ray detectors for digital breast tomosynthesis (DBT) are based on the amorphous silicon (a-Si:H) passive pixel sensor (PPS) technology. However, PPS detectors suffer from a limited resolution and high electronic noise. In this dissertation, we propose high resolution large area active pixel sensor (APS) x-ray detectors based on the complementary metal-oxide-semiconductor (CMOS) and amorphous In-Sn-Zn-O (a-ITZO) thin-film transistor (TFT) technologies to improve the imager resolution and noise properties. We evaluated the two-dimensional (2D) x-ray imaging performance as measured by the modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) for both 75 µm (Dexela 2923 MAM) and 50 µm pixel pitch (DynAMITe) CMOS APS x-ray detectors. Excellent imaging performance (DQE in the range of 0.7 – 0.3) has been achieved over the entire spatial frequency range (0 – 6.7 mm-1) at low air kerma below 10 µGy using the 75 µm pixel pitch Dexela 2923 MAM detector. The 50 μm pixel pitch DyAMITe detector has further extended the spatial resolution of the detector to 10 mm-1 with a low electronic noise of 150 e-. Also, a 2D cascaded system analysis model has been developed to describe the signal and noise transfer for the CMOS APS x-ray imaging systems. We also implemented three-dimensional (3D) cascaded system analysis to simulated the 3D MTF, NPS and DQE characteristics using DBT radiation conditions and acquisition geometries. The 3D cascaded system analysis for the DynAMITe detector was integrated with an object task function, a medical imaging display model, and the human eye contrast sensitivity function to calculate the detectability index and area under the ROC curve (AUC). It has been demonstrated that the display pixel pitch and zoom factor should be optimized to improve the AUC for detecting high contrast objects such as microcalcifications. Also, detector electronic noise of smaller than 300 e- and a high display maximum luminance (>1000 cd/cm2) are desirable to distinguish microcalcifications of 150 µm or smaller in size. For low contrast object detection, a medical imaging display with a minimum of 12 bits gray levels is needed to realize accurate luminance levels. A wide projection angle range (≥ ±30°) combined with the image gray level magnification could improve the detectability for low contrast objects especially when the anatomical background noise is high. CMOS APS x-ray detectors demonstrate both a high pixel resolution and low electronic noise, but are challenging to be fabricated in a large detector size greater than the wafer scale. Alternatively, current-mode APS (C-APS) based on a-ITZO TFTs was proposed for DBT due to the high gain, low noise, and capability to realize a large detector area. Specifically, we fabricated a-ITZO TFTs and achieved a high field-effect mobility of >30 cm2/Vs. We have also evaluated the electrical performance of a 50 µm pixel pitch a-ITZO TFT C-APS combined with an a-Si:H p+-i-n+ photodiode using SPICE simulation. The proposed C-APS circuit demonstrates a high charge gain of 885 with data line loadings considered. A pixel circuit layout and fabrication process have also been suggested. Finally, noise analysis has been applied to the a-ITZO TFT C-APS. A low electronic noise of around 239 e- has been established. The research presented in this thesis indicates that APS x-ray detectors based on both CMOS and a-ITZO TFT technologies are promising for next generation DBT systems.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136983/1/zhaocm_1.pd

Hybrid gamma camera imaging: translation from bench to bedside

There is increasing interest in the use of small field of view (SFOV) portable gamma cameras in medical imaging. A novel hybrid optical-gamma camera (HGC) has been developed through a collaboration between the Universities of Leicester and Nottingham. This system offers high resolution gamma and optical imaging and shows potential for use at the patient bedside, or in the operating theatre. The aim of this thesis was to translate the HGC technology from in vitro laboratory studies to clinical use in human subjects. Pilot studies were undertaken with the HGC as part of this thesis. Furthermore, efforts have been made to transform the HGC technologies into a new medical device, known as Nebuleye. Initial physical evaluation of the pre-production prototype camera was carried out as part of the device developmental process, highlighting some aspects of the design that require further modification. A complete and rigorous testing scheme to assess the pre-production prototype camera has been developed and successfully implemented. The newly introduced tests enabled the system uniformity, system sensitivity, detector head shielding leakage, optical-gamma image alignment and optical image quality of the hybrid camera to be assessed objectively. This harmonised testing scheme allows characterisation and direct comparison of SFOV gamma cameras. In vitro and in vivo preclinical imaging was undertaken to examine the performance of the SFOV gamma cameras for experimental animal studies. The results of animal study have shown for the first time the feasibility and performance of these SFOV gamma cameras for imaging mice injected with a newly developed 111In labelled hybrid tracer. Further investigations are needed to improve the system resolution and prepare the camera system for combined gamma-near infrared fluorescence imaging in future. A systematic in vitro laboratory assessment method has been established to examine the imaging performance of the SFOV gamma camera in radioguided sentinel lymph node biopsy (SLNB) and radioactive seed localisation procedures for breast cancer surgery. Further preparatory work was undertaken to carry out a pilot clinical trial of the use of the pre-production prototype camera in sentinel node localisation procedures during breast cancer surgery. The clinical study protocol and routine quality control procedures have been established and are suitable for future use. Baseline data on the camera performance assessed using the routine quality control scheme have been obtained. Finally, the capabilities of the SFOV gamma camera were assessed. This has provided baseline data on user feedback and the imaging consequences on operator motion effects, as well as examining the detectability of a range of radionuclides, including 99mTc, 111In, 123I, 125I and 75Se. The first clinical results of the use of the HGC in clinical hybrid optical-gamma imaging in patients administered with 99mTc and 123I labelled radiopharmaceuticals have been reported. This clinical study has demonstrated the feasibility and capability of HGC in various clinical applications performed at the patient bedside, which included patients undergoing bone, thyroid, lacrimal drainage and lymphatic imaging as well as DaTscan studies. In conclusion, the work in this thesis has demonstrated the successful translation of an SFOV hybrid gamma camera for clinical use. This system would be ideally suited for use in the operating theatre for radioguided procedures such as sentinel node detection and tumour localisation. This system also offers potential for use with the new generation of hybrid fluorescent-radionuclide tracers currently under development

RANGE ADAPTIVE PROTON THERAPY FOR PROSTATE CANCER

Purpose: The rapid distal falloff of a proton beam allows for sparing of normal tissues distal to the target. However proton beams that aim directly towards critical structures are avoided due to concerns of range uncertainties, such as CT number conversion and anatomy variations. We propose to eliminate range uncertainty and enable prostate treatment with a single anterior beam by detecting the proton’s range at the prostate-rectal interface and adaptively adjusting the range in vivo and in real-time. Materials and Methods: A prototype device, consisting of an endorectal liquid scintillation detector and dual-inverted Lucite wedges for range compensation, was designed to test the feasibility and accuracy of the technique. Liquid scintillation filled volume was fitted with optical fiber and placed inside the rectum of an anthropomorphic pelvic phantom. Photodiode-generated current signal was generated as a function of proton beam distal depth, and the spatial resolution of this technique was calculated by relating the variance in detecting proton spills to its maximum penetration depth. The relative water-equivalent thickness of the wedges was measured in a water phantom and prospectively tested to determine the accuracy of range corrections. Treatment simulation studies were performed to test the potential dosimetric benefit in sparing the rectum. Results: The spatial resolution of the detector in phantom measurement was 0.5 mm. The precision of the range correction was 0.04 mm. The residual margin to ensure CTV coverage was 1.1 mm. The composite distal margin for 95% treatment confidence was 2.4 mm. Planning studies based on a previously estimated 2mm margin (90% treatment confidence) for 27 patients showed a rectal sparing up to 51% at 70 Gy and 57% at 40 Gy relative to IMRT and bilateral proton treatment. Conclusion: We demonstrated the feasibility of our design. Use of this technique allows for proton treatment using a single anterior beam, significantly reducing the rectal dose

Hybrid gamma camera imaging: translation from bench to bedside

There is increasing interest in the use of small field of view (SFOV) portable gamma cameras in medical imaging. A novel hybrid optical-gamma camera (HGC) has been developed through a collaboration between the Universities of Leicester and Nottingham. This system offers high resolution gamma and optical imaging and shows potential for use at the patient bedside, or in the operating theatre. The aim of this thesis was to translate the HGC technology from in vitro laboratory studies to clinical use in human subjects. Pilot studies were undertaken with the HGC as part of this thesis. Furthermore, efforts have been made to transform the HGC technologies into a new medical device, known as Nebuleye. Initial physical evaluation of the pre-production prototype camera was carried out as part of the device developmental process, highlighting some aspects of the design that require further modification. A complete and rigorous testing scheme to assess the pre-production prototype camera has been developed and successfully implemented. The newly introduced tests enabled the system uniformity, system sensitivity, detector head shielding leakage, optical-gamma image alignment and optical image quality of the hybrid camera to be assessed objectively. This harmonised testing scheme allows characterisation and direct comparison of SFOV gamma cameras. In vitro and in vivo preclinical imaging was undertaken to examine the performance of the SFOV gamma cameras for experimental animal studies. The results of animal study have shown for the first time the feasibility and performance of these SFOV gamma cameras for imaging mice injected with a newly developed 111In labelled hybrid tracer. Further investigations are needed to improve the system resolution and prepare the camera system for combined gamma-near infrared fluorescence imaging in future. A systematic in vitro laboratory assessment method has been established to examine the imaging performance of the SFOV gamma camera in radioguided sentinel lymph node biopsy (SLNB) and radioactive seed localisation procedures for breast cancer surgery. Further preparatory work was undertaken to carry out a pilot clinical trial of the use of the pre-production prototype camera in sentinel node localisation procedures during breast cancer surgery. The clinical study protocol and routine quality control procedures have been established and are suitable for future use. Baseline data on the camera performance assessed using the routine quality control scheme have been obtained. Finally, the capabilities of the SFOV gamma camera were assessed. This has provided baseline data on user feedback and the imaging consequences on operator motion effects, as well as examining the detectability of a range of radionuclides, including 99mTc, 111In, 123I, 125I and 75Se. The first clinical results of the use of the HGC in clinical hybrid optical-gamma imaging in patients administered with 99mTc and 123I labelled radiopharmaceuticals have been reported. This clinical study has demonstrated the feasibility and capability of HGC in various clinical applications performed at the patient bedside, which included patients undergoing bone, thyroid, lacrimal drainage and lymphatic imaging as well as DaTscan studies. In conclusion, the work in this thesis has demonstrated the successful translation of an SFOV hybrid gamma camera for clinical use. This system would be ideally suited for use in the operating theatre for radioguided procedures such as sentinel node detection and tumour localisation. This system also offers potential for use with the new generation of hybrid fluorescent-radionuclide tracers currently under development

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium