Introduction: In patients with myocardial infarction (MI), regional left ventricular contractile function has important prognostic value. Displacement ENcoding with Stimulated Echoes (DENSE) is an MRI technique which has been developed to allow quantitative assessment of myocardial strain. To date, much of the research performed with DENSE has been methods development, and its application in a routine clinical setting has been incompletely investigated. The purpose of the research presented within this thesis was to investigate variations in strain within the healthy heart, and then to assess the in vivo performance of DENSE strain imaging in acute and chronic myocardial infarction (MI). Methods: 80 healthy subjects (M:F = 40:40, age 43 +/- 17 years) were recruited from the community. 50 male patients (age 56 +/- 10 years) were recruited from the clinical service and scanned within 7 days of myocardial infarction (“acute MI”), and invited to return for a follow-up scan after 6 months (“chronic MI”). MR imaging was performed on a 1.5T Siemens Avanto scanner, using an imaging protocol which included DENSE, cine, late gadolinium enhancement (LGE, patients only) and T2-weighted imaging acquired from left ventricular (LV) short-axis slices in both basal and mid-ventricular positions, which were divided into 6 segments for analysis. The percentage of LGE and T2 hyperenhancement within each segment were calculated, and the area at risk (acute MI) and myocardial salvage index (chronic MI) were determined. DENSE images were analysed to obtain values for strain parameters relating to circumferential strain (Ecc). Strain measurements obtained from healthy subjects were used to investigate the variations in Ecc with age, gender, slice position and myocardial segment. Strain measurements obtained from MI patients were used to investigate the relationships between Ecc and the extent of myocardial infarction, area at risk and/or salvage, and to determine whether DENSE strain measurements are informative in acute and chronic MI. Results: Comparison of DENSE strain measurements in healthy subjects revealed statistically significant differences between males and females, and between measurements obtained from basal and mid-ventricular short-axis slice positions. These differences must be taken into account to allow appropriate analysis of DENSE data in patients. DENSE was found to be informative in both acute and chronic MI. At both time points, strain measurements can be used to distinguish between myocardial segments with 0%, <50% and >50% infarction. There is the potential for the development of reference ranges which could be applied to strain measurements from future MI patients to allow assessment of the extent of infarction. In acute MI, four additional applications were identified: i) comparison with references ranges, established from strain measurements in healthy subjects, can be used to identify the presence of infarction with high specificity and moderate to high sensitivity, ii) peak Ecc can be used to distinguish between segments categorised as remote and adjacent, iii) strain measurements in the acute setting may provide prognostic information relating to the potential progression or recovery of contractile abnormalities in the chronic setting, iv) peak Ecc may allow a preliminary assessment of LV ejection fraction. Sensitivity for the detection of injured but non-infarcted segments was low. In chronic MI, two additional applications were identified: i) strain recovery can be detected in infarcted myocardial segments, and also in non-infarcted segments which are located adjacent to infarcted segments, which could improve identification of changes in contractile function compared to conventional qualitative analysis of cine imaging, ii) strain measurements can be used to distinguish between segments in which the extent of infarction has increased and those in which it has decreased. The relationships with myocardial salvage index were not found to be informative. Conclusions: DENSE images were successfully acquired and analysed from both healthy subjects and patients with myocardial infarction, which indicates that the technique is feasible in different clinical settings. DENSE strain measurements were found to be informative in both acute and chronic MI, and can provide insight into the presence and extent of infarction and the progression or recovery of contractile abnormalities.

Sol-gel derived bioactive glasses are promising candidates for bone regeneration, where bone is a natural nanocomposite of collagen (organic polymer) and hydroxyapatite (inorganic mineral) with a complex hierarchical structure and excellent mechanical properties. Solid-state NMR is a sensitive probe and offers atomic-level information on the structure of sol-gel derived bioactive glasses. In this thesis, a multinuclear solid state NMR approach, as part of an extensive study, has been applied to a key range of sol-gel derived materials related to novel nanocomposites to act as tissue scaffolds. The nanostructure evolution of sol-gel derived bioactive glasses 70S30C (70 mol% SiO2 and 30 mol% CaO) was characterised by 29Si, 1H and 13C CP MAS NMR. Calcium was found to be incorporated into the silica network during the stabilisation stage and to increases its disorder. The inhomogeneity found within 70S30C bioactive glass monoliths showed that the calcium concentration was higher in the outer region of the monolith caused by the way calcium only enters into the structure after breakbown of the nitrate. Trimethylsilylation reaction mechanisms used to tailor the nanoporosity of sol-gel derived 70S30C bioactive glass was also studied. The 29Si NMR results showed that the modification processes affected the atomic scale structure of the glass, such as Qn structure and network connectivity. 1H and 13C NMR was used to follow the loss of hydroxyls and organic groups directly. The study was extended to 58S (60 mol% SiO2, 36 mol% CaO, 4 mol% P2O5) systems and compared for two synthesis routes: inorganic and alkoxide. Via the inorganic route high temperatures were needed for calcium incorporation, while via alkoxide route calcium was found to be incorporated at low temperatures. Reactive surface Ca ions were involved in the formation of different types of carbonates for the two routes. The addition of P2O5 to the silica-calcium oxide system results in a scavenging of calcium ions by phosphate groups to give orthophosphate and pyrophosphate units. Solid-state NMR of new organic-inorganic hybrid scaffolds, class II, in the silicagelatin and silica-calcium oxide-poly(γ-glutamic acid) (γ-PGA) systems indicates that 3- glycidoxypropyltrimethoxysilane (GPTMS) provides a covalent link between the organic and inorganic networks and increased the inorganic condensation. 1H-1H intra- and intermolecular proximities have been identified using 1H DQ (double-quantum) CRAMPS (combined rotation and multiple pulse spectroscopy) techniques. 13C NMR results indicate that an efficient promotion of epoxide ring opening of GPTMS was reached by either gelatin or γ-PGA. 43Ca NMR identified different calcium environments in the hybrid systems. The last part of this thesis is focused on the comparison studies in the mechanism of apatite growth on both melt-derived (Bioglass®) and sol-gel derived (TheraGlass®) bioactive glass surfaces. By using a combination of 1H, 13C, 31P, 29Si and 23Na, using one and two dimensional NMR spectroscopy, the inhibitive effects of serum proteins in the mechanism of the apatite growth was revealed. The solid-state NMR experimental data support the hydroxycarbonate apatite formation mechanism proposed by Hench. Apatite formation takes place from the largely amorphous phosphate ions initially deposited on the glass surface. Serum proteins adsorbed on the glass surface have been found to significantly inhibit the apatite formation. Multiple sodium sites have been identified in Bioglass® composition with the formation of a more ordered local structure on increasing immersion time.

Investigations have been made into the use of a computer based simulation technique (Monte Carlo (MC)) to ionising radiation transport in order to verify the doses delivered during linear accelerator based stereotactic radiotherapy and radiosurgery. Due to the complex nature of the micro multi-leaf collimators (μMLC) used in this these treatments, a bespoke model of the μMLC was developed and combined with standard component modules to represent the remainder of the linear accelerator. Following validation of the above models, investigations were made into the dosimetry of small fields, defined by the μMLC and measured with a variety of detectors. Comparisons of relative output, profiles and depth doses were made against MC simulations, and a series of correction factors determined, to account for detector geometry and the non water equivalence of materials used in semiconductor detectors. An assessment was then made to determine the smallest fields that can be measured with each detector with confidence. Systems were then developed to independently simulate stereotactic treatments and compare doses simulated with those calculated by the treatment planning system (TPS); excellent agreement between TPS calculations and MC simulations was observed. The application of MC methods to determine the most appropriate treatment tactics and calculation algorithms for stereotactic body radiotherapy in the lung was then investigated with recommendations made on the most appropriate calculation algorithms and beam arrangements for the technique. The doses calculated using the type-b or collapsed cone algorithm agreed most closely with the MC simulation. There was little difference observed between plans using more than four beams in the treatment delivery. Treatment techniques using only three beams or less achieved poorer coverage of the tumour with dose, producing lower doses at the periphery of the tumour near the interface with the surrounding lung tissue, compared to using a greater number of beams. Finally, methods of transit dosimetry using Electronic Portal Imaging Devices were investigated for use in cranial stereotactic radiotherapy. Three methods were investigated based on a full MC simulation of the radiation transport through the patient and on to the imager, prediction of the dose based on a TPS calculation and an approximation of the radiological path length of the central axis of the beams to derive an expected dose at the imager plane. The MC method produced the best agreement at the expense of a longer time to acquire the comparison doses compared to the TPS calculation method. The equivalent path length method showed good agreement (within 3.5%) between delivered and predicted doses but at a single point.

The measurement of radiation dose in radiotherapy is vital in ensuring the accuracy of treatments. As more advanced techniques using protons and ions emerge, they pose challenges to ensure the same level of accuracy of dosimetry is achieved as for conventional X-ray radiotherapy. A relatively new method of particle acceleration using ultra-high intensity lasers and thin metallic targets has sparked a large effort to investigate the possible application of this technology in radiotherapy, which in turn requires accurate methods of dosimetry to be carried out and is the main motivation for this work. Accurate dosimetry was initially performed here using an air ionisation chamber, various models of GafChromic film and a PMMA phantom in 15 and 29 MeV protons and 38 MeV \(\alpha\)-particles from the Birmingham cyclotron. In developing an accurate protocol for absorbed dose-to-water at these relatively low proton energies, new data was generated on the proton energy response of GafChromic films. This enabled accurate dosimetry of a prototype laser-particle source, and provided improvements to a method of spectroscopic measurement in the resultant mixed field of multi-energy protons, electrons and X-rays. Monte Carlo simulations using MCNPX but mainly FLUKA were performed throughout to support and verify experimental measurements.

Many studies have shown that the computed tomography dose index (CTDI100) which is considered to be the main dose descriptor for CT dosimetry fails to provide a realistic reflection of the dose involved in cone beam CT (CBCT) scans. The main reason for this failure is that CTDI100 measurements are performed within standard head and body phantoms made of polymethyl methacrylate (PMMA) that are only 150 cm long, which is less than or similar to beam widths used for CBCT scans. Therefore, much of the scatter that would contribute to the dose received by a patient is not recorded. Several practical approaches have been proposed to overcome drawbacks of the CTDI100. The aim of this project was to investigate the various dose indices based on the approaches proposed. The dose indices studied were: (1) CTDIIEC proposed by the International Electrotechnical Commission (IEC) and based on measuring CTDI100 using a reference beam and the application of a correction factor based on free-in-air CTDI measurements, (2) f(0,150) the cumulative dose measured with a small ionization chamber within the standard PMMA phantoms, (3) f100 (150) the cumulative dose measured in the standard PMMA phantoms with a 100 mm pencil ionization chamber, (4) f(0,∞) proposed by the American Association of Physicists in Medicine (AAPM) TG - 111 and similar to f(0,150), but measured in infinitely long phantoms made of PMMA, polyethylene, and water, (5) f100 (∞) similar to f100 (150), but measured in infinitely long phantoms. The project also aimed to facilitate the use of indices defined in long phantoms through the generation of correction factors that could be applied to measurements in standard phantoms. This project was based on the use of the Monte Carlo (MC) technique. MC EGSnrc-based user codes namely BEAMnrc and DOSXYZnrc were used to simulate the On-Board-Imager (OBI) imaging system mounted on a Varian TrueBeam linear accelerator. The MC model was benchmarked against experimental measurements and good agreement shown. PMMA, polyethylene, and water head and body phantoms of various lengths and diameters were simulated including a new polyethylene phantom named ICRU/AAPM phantom made by the International Commission on Radiation Units and Measurements (ICRU) and AAPM. A wide range of beam widths with different beam qualities were employed. Four scanning protocols using two acquisition modes (full and half), employed in routine clinical practice, were utilized. In addition, organ doses resulting from three CBCT scans (head, thorax, and pelvis) were evaluated in terms of absorbed dose to organs and tissues using MC simulations on the International Commission on Radiological Protection (ICRP) 110 adult male and female reference computational phantoms. The suitability of the dose indices for CBCT dosimetry was investigated by taking three factors into consideration: (1) the efficiency of the approach as a dose descriptor to report CTDI∞, which is close to the dose received by body tissues near to the middle of a CBCT scan of a patient, (2) the simplicity of the application of the approach in the clinical environment in terms of availability of the measuring instruments, simplicity of the technique, and the number of the scans required to accomplish a quality assurance (QA) assessment, i.e. the QA time, and (3) the ability of the approach in providing an evaluation of organ doses resulting from CBCT scans. To facilitate the use of long phantoms, the relationship between f(0,150) and f100 (150) measurements obtained within the standard PMMA phantoms and those for f(0,∞) obtained within longer phantoms of different compositions were studied. Considering the three factors for the dose indices investigated, all the dose indices were found to be comparable, but each index has advantages and disadvantages. Overall, f(0,150) was considered to be the most suitable with f100 (150) providing an alternative for wider beams. Therefore, the dose indices f(0,150) followed by f100 (150) are recommended for practical CBCT dosimetry. In addition, a function called Gx(W)100 was proposed for evaluating the cumulative dose in long phantoms, and correction factors were also provided to avoid the use of long phantoms. The Gx(W)100 function did not vary significantly with tube potential, but the tube potential did influence the correction factors. The use of the Gx(W)100 function is recommended for estimation of f(0,∞) values from f100 (150) measurements taken in the standard PMMA phantoms.

Shear stress generated by biological fluid flows in vivo plays an important role in the regulation of numerous cellular processes; these include apoptosis, cellular proliferation and differentiation, regulation of metabolism and of inflammatory responses. The effects of shear stress are particularly prevalent in cells of the cardiovascular and skeletal systems due to the haemodynamic and interstitial fluid flows respectively. The limited scope for controlling in vivo shear stress has required the research to be conducted in vitro. Within the thesis, stable cavitation microstreaming was harnessed as a method for mimicking in vivo shear stress with the aim of developing a generic method for stressing cells. Stable cavitation microstreaming is a steady fluid flow generated by the transfer of acoustic energy into a time averaged steady momentum flux as a result of viscous damping in the boundary layer of an oscillating gas bubble. Microstreaming was generated around Expancel encapsulated microbubbles (EMBs) in purpose built microfluidic devices. The devices provided controlled environments for the generation of microstreaming. Important features of the final device include adherence of microbubbles to an internal surface of the device, the minimisation of primary acoustic radiation forces and the ability to perform high throughput biological experiments on adhered cells in the device. The microstreaming flow was characterized by micro particle image velocimetry (μPIV), showing that flows possess good repeatability and controllability. H9c2 cardiomyocytes, adhered opposite to the microbubbles at a separation distance of approximately 150 μm, were stressed with microstreaming and their viability was measured. This was carried out in order to assess the applicability of the device to biomedical research. This research is thought to be the first in depth analysis of the controllability and repeatability of microstreaming in the context of stressing cells. Furthermore, it is thought to be the first demonstration of inflicting controlled cell death by stable cavitation microstreaming at a distance of 150 μm.

Nuclear Magnetic Resonance (NMR) is a phenomenon in which certain nuclei in the presence of a magnetic field and radiofrequency (RF) radiation emit a certain amount of signal at a frequency equal to that of the RF radiation. Proton Magnetic Resonance Spectroscopy (1H-MRS) is an NMR technique capable of measuring the chemical composition, often referred to as metabolites, of the human body non-invasively and in vivo. It is commonly used as a research tool in the investigation of neurological disorders such as multiple sclerosis, brain tumors, stroke, clinical depression, and schizophrenia. Accurate quantification of the metabolites of interest requires a reference standard of known and fixed concentration. Brain tissue water has been previously reported to have a fairly constant and known concentration, and so has been suggested to be a suitable reference concentration in absolute quantitative 1H-MRS of the human brain. In practice, however, it is challenging to measure the actual tissue water concentration; hence, some studies choose to use estimates of tissue water concentration from the literature. These literature values are usually averages from a healthy study group. There are however indications that brain tissue water content could vary widely in certain disease conditions such as in brain tumors and inflammation. In such situations, absolute metabolite quantification using the literature estimates of tissue water content will be inaccurate while the measurement of cerebral water content using the available techniques will be impractical for the patients due to scanning time considerations. It is therefore necessary to develop a technique that can be used to quantify both the reference water and metabolite concentrations, simultaneously without subject tolerance issues. The main objective of this thesis was to investigate the response of water NMR signal from human brain tissue under various measurement conditions using the single-voxel 1H-MRS technique. As part of the investigation, the thesis also focused on the development of methods for the absolute quantification of cerebral water and metabolite concentrations. A standard 1H-MRS water-suppressed acquisition on the General Electric (GE) MR scanner acquires some unsuppressed-water spectra at the beginning of the PRESS pulse sequence. Using the Spectroscopy Analysis by GE (SAGE) software package (version 7), this thesis developed methods to optimise the unsuppressed-water and suppressed-water signals from which, respectively, cerebral water and metabolite concentrations were estimated. The unsuppressed-water signal response characteristics were investigated in experiments at 3 T that involved: 1) variation of the MRS voxel position over a three-dimensional RF field within an eight-channel head coil; 2) measurement of the relaxation times of brain tissue water using standard saturation recovery and multi spin-echo MRS techniques; 3) measurement of brain tissue water content in peripheral inflammation; and 4) estimation of the BOLD effect on the water spectral peak. The stability of the MR scanner used for all the investigations was assessed. Over the project period, the worst precision measurements of the scanner (for both water and metabolite signals) were observed to be about 12 % and 26 % in serial phantom and human studies, respectively. The MRI/MRS scanner was therefore found to measure water and metabolite signals with good precision, both in vivo and in vitro. By recording the water NMR signal responses at various locations within the phased-array head coil, RF sensitivity profile (voxel position-dependent) equations of the head coil were obtained. The coordinates of any in vivo voxel could be substituted into an appropriate profile equation to estimate an unsuppressed-water signal area that could be used as a reference signal to quantify brain tissue water content. This novel technique of quantifying cerebral water content is superior to the previous techniques of performing multi-echo unsuppressed-water signal acquisitions. The method does not require extra unsuppressed-water acquisitions, or corrections for variations in the sensitivity of the eight-channel head coil as both the in vivo and reference signals are acquired from the same voxel position. Brain tissue water content was subsequently quantified accurately using the newly developed method of referencing. In frontal brain voxels, the average water content, WC of grey matter, GM was found to be higher than that of white matter, WM (GM/WM WC ± SE = 46.37 ± 2.58/42.86 ± 2.46 mol/kg; p = 0.02); parietal voxels also showed a similar comparison (GM/WM WC ± SE = 37.23 ± 1.70/34.14 ± 2.02 mol/kg; p = 0.03). These findings were consistent with previous reports of cerebral water content. For regions of mixed proportions of grey and white matter tissues, the average water contents of each tissue type considered separately (by voxel segmentation) and together were found to compare with literature estimates. Using data from five voxel positions, average brain tissue water content was observed to be uniformly distributed across the human brain by one-way ANOVA (p = 0.60), and did not vary significantly with gender (p > 0.05) and age (p > 0.05). For the first time, cerebral water content was observed in this thesis to remain fairly constant in psoriatic arthritis, a peripheral inflammatory condition (one-way ANOVA, p = 0.63). Among five brain metabolites quantified in the psoriasis patients, only the mean concentration of creatine, Cr was found to be significantly lower in the frontal grey matter voxels of the patients, PsA compared to healthy controls, HC at baseline (PsA/HC ± SE = 6.34 ± 0.38/7.78 ± 0.38 mM/kg; p = 0.01) and post-TNF-alpha blockade medication (PsA/HC ± SE = 6.69 ± 0.25/7.78 ± 0.38 mM/kg; p = 0.03). None of the metabolite concentrations, including Cr (p = 0.27), changed significantly with medication. The condition of PsA was not observed to affect the mood of the patients, as indicated by their BDI scores. The significant finding of Cr concentration alteration in psoriatic arthritis thus suggests that Cr may not be a reliable denominator in studies of psoriasis that express the metabolite levels as ratios. The T1 and T2 relaxation times of water and the metabolites were measured in the prefrontal grey matter (T1/T2 ± SE = 1574 ± 61/147 ± 6 ms) and bilateral Hippocampi (T1/T2 ± SE; left = 1475 ± 68/178 ± 83 ms, right = 1389 ± 58/273 ± 98 ms). The relaxation time estimates for the metabolites were in agreement with literature values; relaxation times for water however were measured for the first time in those regions and at 3 T. The measured relaxation times were used to correct the water and metabolite signals for relaxation effects during their absolute quantification, and could as well serve the same purpose in future studies. There is increasing interest in the BOLD response of cerebral metabolites and water during tasks. This thesis thus also assessed changes in brain tissue metabolite and water contents while a subject experienced a visual stimulus. In the presence of the visual stimulus, the BOLD effects on the metabolite and water spectral peaks were found to be comparable, as has been observed in previous studies. For the first time, this thesis further investigated the impact of temporal resolution (determined by NEX) on the amount of the BOLD signal acquired from cerebral water and metabolites. In a single visual activation paradigm, the BOLD effect resulted in increased water peak area which differed significantly between NEX values of 2 and 8 (p < 0.01); this observation also was true for NAA and Glu. The findings thus suggest that temporal resolution of the MRS data could result in significant differences in the results of functional MRS studies.