Sub-voxel position identification in Cadmium Zinc Telluride detectors for Low Dose Molecular Breast Imaging

乳腺癌是英国最常见的疾病，直接影响到1/8的女性。癌症治疗在过去的几十年里有了显着的发展，目前有令人难以置信的复杂技术和技术，癌症患者的成功率不断增长。然而，这种治疗成功的一个主要限制因素是癌症诊断的阶段。疾病诊断得越早，治愈的可能性就越大。因此，也需要发展先进的诊断技术。大约一半的筛查年龄的妇女有什么被认为是“乳房X线摄影致密的乳房”。虽然这是一个正常和常见的特征，但它限制了用于检测癌症的可用筛查方法的诊断能力。当对乳腺密度高的乳腺进行检查时，所有常用的诊断技术的能力都是有限的。乳房X光密度高的女性患乳腺癌的风险更高，被发现的机会更低。因此，在筛查乳腺癌时，需要替代方法来提高诊断性能。分子乳腺成像是诊断核医学的一个分支，它利用放射性同位素Tech-99 m获得功能图像并识别乳腺内的病变。放射性同位素被注射到病人体内，在那里它移动到乳房区域，并优先被癌细胞吸收。随着6小时的半衰期，同位素在患者体内衰变，同时发出特征性的141 keV伽马射线。衰变产物离开身体，与物质相互作用，因为它们这样做。位于患者体外的伽马照相机检测放射出的伽马射线，以便处理事件并重建乳腺中放射性核素摄取的图像，这是癌组织的指示。MBI的主要优点是该技术能够在早期检测乳腺癌。然而，与任何成像技术一样，尽管MBI为致密乳房的女性提供了优于其他方式的优势，但它并非没有缺点。与MBI相关的主要缺点是由于源管理而传递到患者的剂量，其显著高于常规乳房X线摄影中传递的典型剂量。最近的研究试图开发方法学，以减少MBI中使用的放射源的活性，从而减少输送给患者的剂量，而不影响系统的灵敏度或特异性。(1)碲锌镉是一种理想的探测器材料，用于MBI主要是由于其良好的位置分辨率。这一特性使探测器对141 keV的γ射线高度敏感，因此可以在不影响图像质量的情况下将较低放射性的同位素注入患者体内。最终的项目目标是开发一种用于MBI的最佳CZT探测器系统。该项目旨在实现探测器系统的最佳位置分辨率，以便将低放射性源注入患者体内。因此减少了输送的剂量，进而减少了与成像模式相关的辐射风险。首先，有必要量化CZT探测器中的电荷共享效应，以使问题的严重性得到理解并最终解决。一个基于Geant 4的仿真研究将有助于算法的发展，其目的是最大限度地提高系统的可获得的位置分辨率。在整个论文中，不同的像素几何形状和准直器设计如何影响系统的位置分辨率将被调查和分析，以确定最终探测器系统的最佳性能。最终系统将B

Breast cancer is the most common form of the disease in the UK, directly affecting 1 in 8women. Cancer treatment has developed significantly over the last few decades such that thereare currently incredibly sophisticated techniques and technologies available with an evergrowing success rate for cancer sufferers. However, a major limiting factor to the success ofsuch treatments is the stage at which the cancer is diagnosed. The earlier the disease isdiagnosed, the greater the probability of treatments working to eradicate the disease. Hence,developments of sophisticated diagnostic techniques are also required.Approximately half of women of screening age have what are considered 'mammographicallydense breasts'. Although this is a normal and common characteristic, it limits the diagnosticabilities of the screening methods available which are used to detect cancer. The abilities of allcommon diagnostic techniques are limited when conducted on breasts that are considered to bemammographically dense. Women with mammographically dense breasts have a higher risk ofdeveloping breast cancer and a lower chance of having it detected. Hence, alternative methodsare required to improve the diagnostic performance when screening for breast cancer.Molecular Breast Imaging is a branch of diagnostic Nuclear Medicine which utilises theradioisotope Tech-99m to obtain functional images and identify lesions within the breast. Theradioisotope is injected into the patient where it moves to the breast region and is preferentiallyup-taken by cancer cells. With a half-life of 6 hours, the isotope decays within the patient,emitting a characteristic 141 keV gamma ray as it does so. The decay products leave the body,interacting with the material in their path as they do so. A gamma camera situated outside thepatient detects the emitted gammas in order to process the events and reconstruct the image ofradionuclide uptake in the breast, which is indicative of cancerous tissue.The main advantage of MBI is the ability of the technique to detect breast cancer at an earlystage. However, as with any imaging technique, although MBI offers good advantages overother modalities for women with dense breasts, it is not without its downfalls. The maindisadvantage associated with MBI is the dose delivered to the patient as a result of the sourceadministered, which is significantly higher than the typical dose delivered in conventionalmammography. More recent studies have sought to develop the methodology in order to reducethe activity of the source used in MBI, in turn reducing the dose delivered to the patient, withoutcompromising the sensitivity or specificity of the system. (1) Cadmium Zinc Telluride is adesirable detector material for use in MBI primarily due to its good position resolution. Thisproperty makes the detector highly sensitive to 141 keV gamma rays and therefore allows for anisotope of lower activity to be administered to patients without compromising the image quality.The ultimate project aim is to develop a CZT detector system optimised for application in MBI.The project seeks to achieve the best possible position resolution of the detector system suchthat a low activity source can be administered to the patient, hence reducing the dose deliveredand, in turn, the radiation risks associated with the imaging modality. Firstly, it is necessary toquantify charge sharing effects in CZT detectors to enable the magnitude of the problem to beunderstood and, ultimately, solved. A Geant4 based simulation study will aid the development ofalgorithms which will aim to maximise the obtainable position resolution of the system.Throughout the thesis, how different pixel geometries and collimator designs affect the positionresolution of the system will be investigated and analysed accordingly in order to determine theoptimal properties of the final detector system. The final system will b