Visual demonstration of aliasing in planar nuclear medicine imaging: The importance of correct collimator selection by nuclear medicine practitioners

Aliasing artefact is an imaging distortion phenomenon experienced in a wide variety of medical imaging modalities. This case report illustrates its occurrence during planar gamma camera nuclear medicine imaging under non-clinical conditions using experimental incorrect selection of collimators. In accordance with provision of an optimal service, nuclear medicine practitioners are recommended to have sufficient technical expertise along with knowledge of gamma camera operation. The purpose, construction and interaction of collimators used during planar imaging are presented herein with specific regards to the aliasing phenomenon. Furthermore, this case report recommends the careful planning of worklists to avoid frequent collimator changes to reduce the risk of human error.     

医用电子直线加速器多叶准直器的维护与故障检修

本文首先简要介绍了多叶准直器的原理与组成,然后说明了多叶准直器具体的维护方法,同时就在日常的工作中容易出现的问题一一列举说明;最后,对经常出现的故障给出了一系列解决方法。     

西门子多角度双探头SPECT工作原理及探头维修一例

SPECT是进行骨癌转移检查的重要设备,主要介绍西门子公司的Signature系列varible angle双探头SPECT的简单工作原理和探头检修。     

The determination of phantom and collimator scatter components of the output of megavoltage photon beams: measurement of the collimator scatter part with a beam-coaxial narrow cylindrical phantom

The separation of the total scatter correction factor S_{c, p} in a collimator scatter component, S_c, and a phantom scatter component, S_p, has proven to be an useful concept in megavoltage photon beam dose calculations in situations which differ from the standard treatment geometry. A clinically applicable method to determine S_c is described. Measurements are carried out with an ionization chamber, placed at a depth beyond the range of contaminant electrons, in a narrow cylindrical polystyrene phantom with a diameter of 4 cm of which the axis coincides with the beam axis. S_{c, p} is measured in a full-scatter phantom and S_p can be derived from S_{c, p} and S_c. In order to obtain a reliable separation, i.e. excluding the influence of contaminant electrons, measurements of S_{c, p} have been carried out at depths of 5 cm for photon beams with a quality index (QI) up to and including 0.75 and a depth of 10 cm with QI larger than 0.75. These depths are in accordance with recommendations given in recent dosimetry protocols. The consistency of the method was checked by comparing calculated and measured values of S_{c, p} for a set of blocked fields for a range of photon beam energies from ⁶⁰Co up to 25 MV showing a maximum deviation of 2%. The method can easily be implemented in existing procedures for the calculation of the number of monitor units to deliver a specified dose to a target volume.     

铅铛块与多叶准直器在固定野三维适形放射治疗中应用的研究

目的在多固定野三维适形放射治疗中,为科学、准确、有效地使用铅挡块与多叶准直器提供重要依据;以便较好地处理好肿瘤组织和周围正常组织间的剂量关系,使肿瘤得到最大限度的局部控制而周围正常组织和器官的放射性损伤最小,提高疗效。方法分析比较多固定野三维适形放射治疗中铅挡块与MLC的适形度、漏射剂量率、不规则靶区边缘1cm处剂量率、物理半影、质量保证和质量控制、CT扫描方向肿瘤计划靶区大小不是MLC叶片整数倍、每次治疗时间等。结果在多固定野三维适形放射治疗中,铅挡块与多叶准直器各有优缺点。结论该研究成果可用于指导多固定野三维适形放射治疗中,铅挡块与多叶准直器的选择使用。     

不同准直器对大病灶中心剂量和周围脑组织受照容积影响的研究

为了比较１８ｍｍ准直器与１４ｍｍ准直器对大病灶中心剂量和周围脑组织受照容积的影响，选择３７例使用１８ｍｍ准直器已作过伽玛刀治疗的病人，计算其２０％等剂量曲线所包含的体积，然后在周边剂量和等中心数不变的情况下，重新用１４ｍｍ准直器进行剂量计划计算。结果显示：（１）新的中心剂量明显高于原中心剂远（Ｐ＜０．００１）；（２）与原２０％等剂量曲线剂量相同的新等剂量曲线所包含的体积比原体积明显减少（Ｐ＜０．００１）。说明使用１４ｍｍ准直器治疗大病灶时，尽管中心剂量提高，但周围脑组织受照射的范围比使用１８ｍｍ准直器时显著减少。     

准直器角度对胸上段食管癌容积旋转调强放疗剂量的影响

目的 研究不同准直器角度对胸上段食管癌病例的剂量影响。方法 选择8例胸上段食管癌病例作为研究对象,每个病例设计准直器角度为0°、5°、10°、15°、20°、25°、30°、35°、40°和45°的10个容积旋转调强放疗（VMAT）计划,比较不同角度下的靶区和危及器官各剂量参数以及总机器跳数。结果 通过比较10组不同准直器角度计划的各项指标结果,选取整体表现最佳的20°组和临床上使用较多的0°及45°组进行分析,显示正常组织全肺V₁₀、V₁₅和V₃₀差异有统计学意义（F=5.328、8.033、28.424,P < 0.05）,脊髓D_max和总机器跳数MU差异有统计学意义（F=9.608、4.464,P < 0.05）。其他指标差异无统计学意义（P > 0.05）。结论 在胸上段食管癌VMAT计划设计时,选择合适的准直器角度可以保证靶区剂量分布,减少危及器官受量,能更好地保护正常组织,并提高治疗效率。     

西门子SOMATOM Spirit双层螺旋CT准直器的维修调节方法

介绍一例西门子SOMATOM Spirit双层螺旋CT在运行中准直器故障,对维修中对准直器的维修调节方法进行总结。     

西门子Sensationl6CT图像伪影形成与检修

通过介绍西门子Sensationl6CT像伪影检修基本方法、基本步骤,排除伪影故障一般方法及一些技巧,了解多层面CT成像的基本结构、基本原理,图像伪影的形成原因。利用仪器自带的软件进行校正,分段检测各部位配件状态,查出不良部件,采取相应的措施排除故障。充分地应用好检修软件,能快速全面地查出各种原因形成的伪影,准确地查出故障部位并排除故障。