Applications of advanced and dual energy computed tomography in proton therapy

This thesis focuses on advanced reconstruction methods and Dual Energy (DE) Computed Tomography (CT) applications for proton therapy, aiming at improving patient positioning and investigating approaches to deal with metal artifacts. To tackle the first goal, an algorithm for post-processing input DE images has been developed. The outputs are tumor- and bone-canceled images, which help in recognising structures in patient body. We proved that positioning error is substantially reduced using contrast enhanced images, thus suggesting the potential of such application. If positioning plays a key role in the delivery, even more important is the quality of planning CT. For that, modern CT scanners offer possibility to tackle challenging cases, like treatment of tumors close to metal implants. Possible approaches for dealing with artifacts introduced by such rods have been investigated experimentally at Paul Scherrer Institut (Switzerland), simulating several treatment plans on an anthropomorphic phantom. In particular, we examined the cases in which none, manual or Iterative Metal Artifact Reduction (iMAR) algorithm were used to correct the artifacts, using both Filtered Back Projection and Sinogram Affirmed Iterative Reconstruction as image reconstruction techniques. Moreover, direct stopping power calculation from DE images with iMAR has also been considered as alternative approach. Delivered dose measured with Gafchromic EBT3 films was compared with the one calculated in Treatment Planning System. Residual positioning errors, daily machine dependent uncertainties and film quenching have been taken into account in the analyses. Although plans with multiple fields seemed more robust than single field, results showed in general better agreement between prescribed and delivered dose when using iMAR, especially if combined with DE approach. Thus, we proved the potential of these advanced algorithms in improving dosimetry for plans in presence of metal implants

Automated shape analysis and visualization of the human back.

Spinal and back deformities can lead to pain and discomfort, disrupting productivity, and may require prolonged treatment. The conventional method of assessing and monitoring tile de-formity using radiographs has known radiation hazards. An alternative approach for monitoring the deformity is to base the assessment on the shape of back surface. Though three-dimensional data acquisition methods exist, techniques to extract relevant information for clinical use have not been widely developed. Thi's thesis presentsthe content and progression of research into automated analysis and visu-alization of three-dimensional laser scans of the human back. Using mathematical shape analysis, methods have been developed to compute stable curvature of the back surface and to detect the anatomic landmarks from the curvature maps. Compared with manual palpation, the landmarks have been detected to within accuracy of 1.15mm and precision of 0.8111m.Based on the detected spinous process landmarks, the back midline which is the closest surface approximation of the spine, has been derived using constrained polynomial fitting and statistical techniques. Three-dimensional geometric measurementsbasedon the midline were then corn-puted to quantify the deformity. Visualization plays a crucial role in back shape analysis since it enables the exploration of back deformities without the need for physical manipulation of the subject. In the third phase,various visualization techniques have been developed, namely, continuous and discrete colour maps, contour maps and three-dimensional views. In the last phase of the research,a software system has been developed for automating the tasks involved in analysing, visualizing and quantifying of the back shape. The novel aspectsof this research lie in the development of effective noise smoothing methods for stable curvature computation; improved shape analysis and landmark detection algorithm; effective techniques for visualizing the shape of the back; derivation of the back midline using constrained polynomials and computation of three dimensional surface measurements.

Hearing pathways in the Yangtze finless porpoise, Neophocaena asiaeorientalis asiaeorientalis

© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Experimental Biology 217 (2014): 444-452, doi:10.1242/​jeb.093773.How an animal receives sound may influence its use of sound. While ‘jaw hearing’ is well supported for odontocetes, work examining how sound is received across the head has been limited to a few representative species. The substantial variation in jaw and head morphology among odontocetes suggests variation in sound reception. Here, we address how a divergent subspecies, the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) hears low-, mid- and high-frequency tones, as well as broadband clicks, comparing sounds presented at different locations across the head. Hearing was measured using auditory evoked potentials (AEPs). Click and tone stimuli (8, 54 and 120 kHz) were presented at nine locations on the head and body using a suction-cup transducer. Threshold differences were compared between frequencies and locations, and referenced to the underlying anatomy using computed tomography (CT) imaging of deceased animals of the same subspecies. The best hearing locations with minimum thresholds were found adjacent to a mandibular fat pad and overlaying the auditory bulla. Mean thresholds were not substantially different at locations from the rostrum tip to the ear (11.6 dB). This contrasts with tests with bottlenose dolphins and beluga whales, in which 30–40 dB threshold differences were found across the animals' heads. Response latencies increased with decreasing response amplitudes, which suggests that latency and sensitivity are interrelated when considering sound reception across the odontocete head. The results suggest that there are differences among odontocetes in the anatomy related to receiving sound, and porpoises may have relatively less acoustic ‘shadowing’.The work was funded by the Office of Naval Research, a Mellon Joint Initiatives Award, the Knowledge Innovation Program of Chinese Academy of Sciences [grant no. KSCX2-EW-Z-4] and the National Natural Science Foundation of China [grant no. 31170501]

An assessment of cortical function in expert and novice surgeons

Imperial Users onl

CT dose optimization with model based iterative reconstruction

The aim of this thesis is to assess the feasibility of using model-based iterative reconstruction (MBIR) to develop new low-dose CT (computed tomography) protocols in the areas of neck, chest, and abdominal imaging without compromising diagnostic performance. Medical imaging has become the largest source of radiation exposure for humans other than natural background radiation. The availability of and improvements in diagnostic imaging have led to a sevenfold increase in the use of imaging over the past 30 years. This is especially true for CT, with a 7.8% annual increase in the use of CT from 1996 to 2010. The major concern associated with the widespread uptake of CT is the parallel increase in radiation exposure incurred by patients, and while the relationship of diagnostic radiation exposure to a quantifiable risk of cancer induction remains a controversial topic, physicians are beholden to keep radiation doses from diagnostic imaging as low as reasonably possible to limit the risk of radiation-induced cancer. We conducted preliminary phantom and cadaveric studies to examine the performance of MBIR at different radiation dose levels in the thorax and abdomen. Cadavers and phantoms provide a means of safely assessing new technologies and optimizing scan protocols prior to clinical validation. An anthropomorphic torso phantom and 5 human cadavers were scanned at varying radiation dose levels and images reconstructed using three different reconstruction techniques: filtered back projection, hybrid IR and MBIR. MBIR reduced image noise and improved image quality even in CT images acquired with a mean radiation dose reduction of 62%, compared with conventional dose studies reconstructed with hybrid IR, with lower levels of objective image noise, superior diagnostic acceptability and contrast resolution, and comparable subjective image noise and streak artifact scores. We subsequently performed clinical studies with the objectives of assessing MBIR as a tool for image quality improvement and radiation dose reduction in CT, and for the development of new low-dose carotid angiography, chest, and abdominopelvic CT protocols. We developed a low-dose carotid CTA protocol reconstructed with MBIR comparable to a conventional dose CTA protocol in terms of image quality and diagnostic accuracy while enabling a dose reduction of 49.6%. 20 patients were scanned using a split-dose technique with radiation dose divided into a low-dose acquisition reconstructed with MBIR and a conventional dose acquisition reconstructed with hybrid IR. Mean effective dose was significantly lower for the low-dose studies (1.84mSv versus 3.71mSv) and subjective image noise, contrast resolution, and spatial resolution were significantly higher for the low-dose studies. There was excellent agreement for stenosis grading accuracy between low- and conventional dose studies (Cohen κ = 0.806). A modified low-dose CT thorax protocol reconstructed with MBIR was also developed to monitor pulmonary disease progression in patients with cystic fibrosis with our low-dose protocol enabling the acquisition of a full-volume diagnostic quality chest CT at a dose equivalent to that of a chest radiograph (0.09±0.01mSv). Finally, we assessed the feasibility of low-dose abdominopelvic CT performed with MBIR as a radiation dose reduction strategy for imaging patients presenting with acute abdominal pain. A 74.7% mean radiation dose reduction was achieved with scans performed in the peri- and submillisievert range in patients of normal and low BMI, respectively, without compromising diagnostic performance. Dose reduction to the submillisievert range for patients with an elevated BMI was a challenge. The current era is extremely exciting in terms of radiation dose optimization in CT. This thesis is a demonstration of the potential for substantial reductions in radiation exposure, when the benefits of iterative reconstruction are combined with automated tube current modulation and other CT scanner technologies. The combination of all these hardware and software developments is now seeing major benefits for the patient and moving beyond the narrow aim of radiation exposure reduction to a complete change in practice, towards replacement of conventional radiography with low-dose CT, without any penalty for the patient in terms of radiation exposure

Automated visual measurement of body shape in scoliosis.

This thesis describes the content and progression of research into automated non-contact methods for measuring the three-dimensional shape of the human back in scoliosis. Scoliosis is a condition in which the spine becomes distorted and a rib-hump appears on the surface of the back. The research was driven by the needs of the scoliosis clinician and was supported by the Royal Liverpool Children's Hospital, Merseyside. A number of optical methods for measuring back surface shape are considered. Moire contouring and Fourier transform profilometry are investigated through practical research in the laboratory. Stereophotogrammetry, phase stepping profilometry, optical scanning and raster pattern contouring are investigated through consideration of theory and literature review. However, none of these approaches is found to be free from limitations. The main novel content of the work presented in this thesis lies in the research into a new method for reconstructing back shape. A new optical method is proposed in which a modified multi-stripe structured light pattern is projected onto the surface of the back. Image processing operations, specialised for this application, process the image of the pattern to reconstruct three-dimensional shape. Further research demonstrates that the computer reconstruction can be interrogated to measure parameters of clinical significance such as Angle of Trunk Inclination and Standardised Trunk Asymmetry Score. A working clinical system was implemented and tested on scoliosis patients at the hospital. The method is evaluated in terms of technical qualities and as a usable clinical tool and was found to satisfy the criteria for a successful automated system

3D Imaging for Planning of Minimally Invasive Surgical Procedures

Novel minimally invasive surgeries are used for treating cardiovascular diseases and are performed under 2D fluoroscopic guidance with a C-arm system. 3D multidetector row computed tomography (MDCT) images are routinely used for preprocedural planning and postprocedural follow-up. For preprocedural planning, the ability to integrate the MDCT with fluoroscopic images for intraprocedural guidance is of clinical interest. Registration may be facilitated by rotating the C-arm to acquire 3D C-arm CT images. This dissertation describes the development of optimal scan and contrast parameters for C-arm CT in 6 swine. A 5-s ungated C-arm CT acquisition during rapid ventricular pacing with aortic root injection using minimal contrast (36 mL), producing high attenuation (1226), few artifacts (2.0), and measurements similar to those from MDCT (p\u3e0.05) was determined optimal. 3D MDCT and C-arm CT images were registered to overlay the aortic structures from MDCT onto fluoroscopic images for guidance in placing the prosthesis. This work also describes the development of a methodology to develop power equation (R2\u3e0.998) for estimating dose with C-arm CT based on applied tube voltage. Application in 10 patients yielded 5.48┬▒177 2.02 mGy indicating minimal radiation burden. For postprocedural follow-up, combinations of non-contrast, arterial, venous single energy CT (SECT) scans are used to monitor patients at multiple time intervals resulting in high cumulative radiation dose. Employing a single dual-energy CT (DECT) scan to replace two SECT scans can reduce dose. This work focuses on evaluating the feasibility of DECT imaging in the arterial phase. The replacement of non-contrast and arterial SECT acquisitions with one arterial DECT acquisition in 30 patients allowed generation of virtual non-contrast (VNC) images with 31 dose savings. Aortic luminal attenuation in VNC (32┬▒177 2 HU) was similar to true non-contrast images (35┬▒177 4 HU) indicating presence of unattenuated blood. To improve discrimination between c

3D Imaging for Planning of Minimally Invasive Surgical Procedures

Novel minimally invasive surgeries are used for treating cardiovascular diseases and are performed under 2D fluoroscopic guidance with a C-arm system. 3D multidetector row computed tomography (MDCT) images are routinely used for preprocedural planning and postprocedural follow-up. For preprocedural planning, the ability to integrate the MDCT with fluoroscopic images for intraprocedural guidance is of clinical interest. Registration may be facilitated by rotating the C-arm to acquire 3D C-arm CT images. This dissertation describes the development of optimal scan and contrast parameters for C-arm CT in 6 swine. A 5-s ungated C-arm CT acquisition during rapid ventricular pacing with aortic root injection using minimal contrast (36 mL), producing high attenuation (1226), few artifacts (2.0), and measurements similar to those from MDCT (p\u3e0.05) was determined optimal. 3D MDCT and C-arm CT images were registered to overlay the aortic structures from MDCT onto fluoroscopic images for guidance in placing the prosthesis. This work also describes the development of a methodology to develop power equation (R2\u3e0.998) for estimating dose with C-arm CT based on applied tube voltage. Application in 10 patients yielded 5.48┬▒177 2.02 mGy indicating minimal radiation burden. For postprocedural follow-up, combinations of non-contrast, arterial, venous single energy CT (SECT) scans are used to monitor patients at multiple time intervals resulting in high cumulative radiation dose. Employing a single dual-energy CT (DECT) scan to replace two SECT scans can reduce dose. This work focuses on evaluating the feasibility of DECT imaging in the arterial phase. The replacement of non-contrast and arterial SECT acquisitions with one arterial DECT acquisition in 30 patients allowed generation of virtual non-contrast (VNC) images with 31 dose savings. Aortic luminal attenuation in VNC (32┬▒177 2 HU) was similar to true non-contrast images (35┬▒177 4 HU) indicating presence of unattenuated blood. To improve discrimination between c

Dynamic surface topography and its application to the evaluation of adolescent idiopathic scoliosis

Dynamic surface topography is a method to quantify the surface and locations of features acquired from moving and distorting shapes against time. This thesis describes the application of the technique to the potential evaluation of adolescent idiopathic scoliosis patients. Scoliosis or curvature of the spine is one of the major skeletal diseases in adolescents where in the majority of cases the cause is unknown or idiopathic. The progression of the disease occurs in three dimensions with the spine simultaneously curving towards the arms and rotating as it collapses with the first indications usually being changes in body symmetry and back surface shape. Following diagnosis, most children do not exhibit any significant worsening of their condition and are routinely monitored using radiography as frequently as every three months whilst vertebral growth potential remains. In a small number of patients, the lateral curvature can unpredictably worsen requiring, in some cases, surgical intervention to prevent further deterioration and to diminish the deformity. Earlier work by many researchers concentrated on attempting to reduce patient exposure to ionizing radiation by investigating if there was a reliable correlation between progression of the scoliosis and changes in surface topography. The techniques have not gained acceptance as the relational algorithms were found to be insufficiently robust in all cases and measurements acquired from available technologies were prone to artefacts introduced by stance, breathing, 'posture and sway. For many patients the motivation in seeking treatment is for the improvement of their appearance rather than to correct the underlying deformity, so cosmetic concerns and an understanding of the psychosocial and physical impacts of the disease and treatments remain important factors in the clinical decision-making process. In the current environment of evidence based medicine there is a growing need to quantify back surface shape, general body asymmetry and patient capability with the objective of producing an agreed scoring to be used in developing treatment plans and assessing outcomes but to date many clinics continue to rely on qualitative methods to describe cosmetic deformity and ability. The aim of the research was to develop an original, low cost and inherently safe apparatus using well understood video based motion capture technology that overcame the disadvantages of earlier work by simultaneously acquiring multiple samples of back surface shape and the locations of bony landmarks to provide averaged results for a quantitative and reliable analysis of cosmetic defect and physical impairment. 172,650 data samples were acquired from thirty skeletally mature subjects not exhibiting any musculoskeletal disease to define normality limits for Page 2 established morphological measurements and to compare the specificity of the approach with existing single sample techniques. Three novel calculations of back paraspinous volumetric asymmetry were tested of which two were found to be potentially useful clinical indicators of deformity and an index was proposed and tested using simulated data that could offer a single value to describe patient back shape asymmetry. Previous research has found that there is a loss of trunk ranges of motion among postoperative patients that has a direct impact on their quality of life, function and physical capability. Data were acquired from the mature subjects and similar results were observed when compared with published data for preoperative scoliosis patients. This thesis has shown that using averaged tri-dimensional morphological and back shape data combined with measurement of dynamic capability acquired using an inherently safe apparatus have the potential to be clinically useful. The opportunity to routinely and safely quantify the cosmetic defect and trunk ranges of motion of adolescent idiopathic scoliosis patients should stimulate more important research to help improve the quality of life of many affected children throughout the world