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，每8名女性中就有1人直接受到影响。在过去的几十年里，癌症治疗有了显著的发展，目前有了令人难以置信的复杂技术和技术，癌症患者的成功率也在不断提高。然而，这种治疗成功的一个主要限制因素是癌症的诊断阶段。这种疾病越早被诊断出来，治疗根除这种疾病的可能性就越大。因此，还需要发展复杂的诊断技术。大约有一半达到筛查年龄的女性被认为是“乳房密度高”。虽然这是一种正常和常见的特征，但它限制了用于检测癌症的现有筛查方法的诊断能力。所有常见的诊断技术的能力都是有限的，当进行乳房x光检查认为是致密的乳房。乳房x光检查显示乳房致密的女性患乳腺癌的风险更高，被发现的几率更低。因此，需要其他方法来提高乳腺癌筛查的诊断性能。乳房分子成像是诊断性核医学的一个分支，它利用放射性同位素Tech-99m获得功能图像并识别乳房内的病变。放射性同位素被注射到病人体内，然后转移到乳房区域，并优先被癌细胞吸收。这种同位素的半衰期为6小时，在病人体内衰变，同时释放出141 keV的伽马射线。腐烂产物离开身体，与沿途的物质相互作用。位于患者体外的伽马照相机检测发射的伽马，以处理事件并重建乳房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发现乳腺癌。然而，与任何成像技术一样，尽管MBI对致密乳房的女性提供了比其他方式更好的优势，但它也不是没有缺点。与MBI相关的主要缺点是由于给药源而给患者的剂量明显高于常规乳房x光检查的典型剂量。最近的研究试图开发一种方法，以减少MBI中使用的源的活性，从而减少给患者的剂量，同时不影响系统的敏感性或特异性。(1)碲化镉锌具有良好的位置分辨率，是应用于MBI的理想探测器材料。这种特性使探测器对141 keV伽马射线高度敏感，因此允许在不影响图像质量的情况下对患者施用低活性同位素。项目的最终目标是开发一种适合MBI应用的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，以便为患者提供低活度源，从而减少剂量，进而减少与成像方式相关的辐射风险。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得到解决。基于Geant4的仿真研究将有助于开发旨在最大化系统可获得位置分辨率的算法。在整个论文中，将相应地研究和分析不同像素几何形状和准直器设计对系统位置分辨率的影响，以确定最终探测器系统的最佳性能。最终的系统是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