Technical assessment of a cone-beam CT scanner for otolaryngology imaging: Image quality, dose, and technique protocols
Technical assessment of a cone-beam CT scanner for otolaryngology imaging: Image quality, dose, and technique protocols
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DOI：
10.1118/1.4736805
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发表时间：
2012-08-01
期刊：
影响因子：
3.8
通讯作者：
Siewerdsen, J. H.
中科院分区：
文献类型：
--
作者：
Xu, J.;Reh, D. D.;Siewerdsen, J. H.
目的：随着专用于各种成像专业的锥束CT（CBCT）系统的激增，以成像物理学为基础的技术评估对于确保图像质量和辐射剂量的量化、理解和合理性非常重要。本文涉及一种新型CBCT扫描仪（CS 9300，Carestream Health，罗切斯特，纽约州）的技术评估，该扫描仪专用于耳鼻咽喉头颈外科（OHNS）中耳和鼻窦的成像。结果指导评估的技术协议，以尽量减少辐射剂量的方式足以OHNS imaging tasks.Methods：技术评估的重点是成像性能和辐射剂量的七个技术协议由制造商推荐：三个窦协议和四个耳（颞骨）协议。使用AAPM任务组第111号报告改编的技术测量绝对剂量，包括三个堆叠的16 cm直径丙烯酸圆柱体（CTDI体模）和一个0.6 cm（3）Farmer电离室，以测量中心和外周剂量。中心剂量（Do）也被测量为在主辐射场内和超出主辐射场的纵向位置（z）的函数，以评估例如对颈部的场外剂量。在市售质量保证体模（CATPHAN模块CTP 404，The Phantom Laboratory，格林威治，NY）和带有软组织模拟塑料插件的定制体模（Gammex RMI，麦迪逊，WI）中评估了信噪比（SDNR）和Hounsfield单位（HU）准确度。空间分辨率进行了评估定性（线对图案，CATPHAN模块CTP 528）和定量（调制传递函数，MTF，用线体模测量）。成像性能有关的各种OHNS成像任务进行了定性评估，使用拟人幻影由两个有经验的OHNS specialists.Results评价：技术评估的动机各种修改的医生指定的协议，以提供减少辐射剂量，而不影响相关的任务为基础的成像性能。修订后的方案产生的D-o范围为2.9-5.7 mGy，与原始技术图表相比，剂量减少了30%。在距离射野边缘约8 cm处，射野外剂量与D-o的10%相似。软组织对比分辨率相当有限（水脑SDNR类似于0.4-0.7），而高对比性能相当好（CATPHAN中聚苯乙烯插入物的SDNR类似于2-4）。扫描仪未证明（或声称提供）准确的HU，并且CT数存在系统误差，可能通过进一步校准解决。在线对体模中评估的空间分辨率类似于10-16 1 p/cm，MTF超过10%，类似于20 1 p/cm。专家读者的定性评估建议有限的软组织的能见度，但优秀的高对比度（骨）可视化与各向同性的空间分辨率适合一个广泛的频谱相关的窦和颞骨imaging tasks.Conclusions：CBCT扫描仪提供的空间和对比度分辨率适合可视化的高对比度形态窦，颌面，耳科成像应用。严格的技术评估指导技术方案的修订，以减少辐射剂量，同时保持足够的图像质量，以执行相关成像任务。该扫描仪似乎非常适合高对比度鼻窦和颞骨成像的剂量相当于或低于传统的头部诊断CT报告。(C)2012年美国医学物理学家协会。[http：//dx.doi.org/10.1118/1.4736805]
Purpose: As cone-beam CT (CBCT) systems dedicated to various imaging specialties proliferate, technical assessment grounded in imaging physics is important to ensuring that image quality and radiation dose are quantified, understood, and justified. This paper involves technical assessment of a new CBCT scanner (CS 9300, Carestream Health, Rochester, NY) dedicated to imaging of the ear and sinuses for applications in otolaryngology-head and neck surgery (OHNS). The results guided evaluation of technique protocols to minimize radiation dose in a manner sufficient for OHNS imaging tasks.Methods: The technical assessment focused on the imaging performance and radiation dose for each of seven technique protocols recommended by the manufacturer: three sinus protocols and four ear (temporal bone) protocols. Absolute dose was measured using techniques adapted from AAPM Task Group Report No. 111, involving three stacked 16 cm diameter acrylic cylinders (CTDI phantoms) and a 0.6 cm(3) Farmer ionization chamber to measure central and peripheral dose. The central dose (Do) was also measured as a function of longitudinal position (z) within and beyond the primary radiation field to assess, for example, out-of-field dose to the neck. Signal-difference-to-noise ratio (SDNR) and Hounsfield unit (HU) accuracy were assessed in a commercially available quality assurance phantom (CATPHAN module CTP404, The Phantom Laboratory, Greenwich, NY) and a custom phantom with soft-tissue-simulating plastic inserts (Gammex RMI, Madison, WI). Spatial resolution was assessed both qualitatively (a line-pair pattern, CATPHAN module CTP528) and quantitatively (modulation transfer function, MTF, measured with a wire phantom). Imaging performance pertinent to various OHNS imaging tasks was qualitatively assessed using an anthropomorphic phantom as evaluated by two experienced OHNS specialists.Results: The technical assessment motivated a variety of modifications to the manufacturer-specified protocols to provide reduced radiation dose without compromising pertinent task-based imaging performance. The revised protocols yielded D-o ranging 2.9-5.7 mGy, representing a similar to 30% reduction in dose from the original technique chart. Out-of-field dose was similar to 10% of D-o at a distance of similar to 8 cm from the field edge. Soft-tissue contrast resolution was fairly limited (water-brain SDNR similar to 0.4-0.7) while high-contrast performance was reasonably good (SDNR similar to 2-4 for a polystyrene insert in the CATPHAN). The scanner does not demonstrate (or claim to provide) accurate HU and exhibits a systematic error in CT number that could potentially be addressed by further calibration. The spatial resolution is similar to 10-16 1p/cm as assessed in a line-pair phantom, with MTF exceeding 10% out to similar to 20 1p/cm. Qualitative assessment by expert readers suggested limited soft-tissue visibility but excellent high-contrast (bone) visualization with isotropic spatial resolution suitable to a broad spectrum of pertinent sinus and temporal bone imaging tasks.Conclusions: The CBCT scanner provided spatial and contrast resolution suitable to visualization of high-contrast morphology in sinus, maxillofacial, and otologic imaging applications. Rigorous technical assessment guided revision of technique protocols to reduce radiation dose while maintaining image quality sufficient for pertinent imaging tasks. The scanner appears well suited to high-contrast sinus and temporal bone imaging at doses comparable to or less than that reported for conventional diagnostic CT of the head. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4736805]