Characterization of a parallel-beam CCD optical-CT apparatus for 3D radiation dosimetry
Characterization of a parallel-beam CCD optical-CT apparatus for 3D radiation dosimetry
复制标题
DOI：
10.1088/0031-9155/52/13/003
复制
发表时间：
2007-07-07
影响因子：
3.5
通讯作者：
Doran, Simon J.
中科院分区：
文献类型：
--
作者：
Krstajic, Nikola;Doran, Simon J.
光学衰减的3D测量在生物医学的重要性的各种领域中是感兴趣的，包括分光光度法、光学投影层析成像（OPT）和3D辐射剂量计的分析。准确、精确和经济的光密度（OD）3D测量是使3D辐射剂量计能够在临床中更广泛使用的关键一步。在过去的二十年里，聚合物凝胶和凝胶，以及不基于凝胶的剂量计已经被表征用于3D剂量测定。另一个问题是最佳读出方法的验证。已经提出了许多不同的成像模式（磁共振成像（MRI）、光学CT、X射线CT和超声）用于从3D剂量计读出信息。到目前为止，只有MRI和基于激光的光学CT已经详细描述。本文介绍了一些初步的步骤，我们已经建立了电荷耦合器件（CCD）为基础的光学CT作为一个可行的替代MRI读出的三维辐射剂量计。基于CCD的光学CT相对于传统的基于激光的光学CT的主要优点是速度提高至少一个数量级，而如果相机本身足够便宜，则其架构的简单性将使其比MRI和基于激光的光学CT更便宜。具体来说，我们使用高质量测试目标研究光学计量的以下方面：（i）吸光度测量的校准和质量以及3D剂量测定的相机要求;（ii）单个投影的调制传递函数（MTF）;（iii）投影和重建域中的信噪比（SNR）;（iv）投影域中的失真、景深（DOF）和远心度。主要结果如下：（1）在吸光度为0.3 ~ 1.6的范围内，均匀投影的吸光度信噪比优于120：1（比200好：1对于具有测试目标的λ = 1.0至3.5和新的吸光度范围扩展方法），（ii）空间分辨率被示出为在最差0.5mm（并且通常比这更好），其中相关联的DOF为8 cm，iii）重建域中的均匀体模的SNR高于80：1（一个标准偏差），（iv）该装置是远心的并且没有失真。最后，示出了样品扫描和PRESAGETM剂量计扫描的重建，证明了该装置的能力。
3D measurement of optical attenuation is of interest in a variety of fields of biomedical importance, including spectrophotometry, optical projection tomography ( OPT) and analysis of 3D radiation dosimeters. Accurate, precise and economical 3D measurements of optical density ( OD) are a crucial step in enabling 3D radiation dosimeters to enter wider use in clinics. Polymer gels and Fricke gels, as well as dosimeters not based around gels, have been characterized for 3D dosimetry over the last two decades. A separate problem is the verification of the best readout method. A number of different imaging modalities ( magnetic resonance imaging ( MRI), optical CT, x-ray CT and ultrasound) have been suggested for the readout of information from 3D dosimeters. To date only MRI and laser-based optical CT have been characterized in detail. This paper describes some initial steps we have taken in establishing charge coupled device (CCD)-based optical CT as a viable alternative to MRI for readout of 3D radiation dosimeters. The main advantage of CCD-based optical CT over traditional laser-based optical CT is a speed increase of at least an order of magnitude, while the simplicity of its architecture would lend itself to cheaper implementation than both MRI and laser-based optical CT if the camera itself were inexpensive enough. Specifically, we study the following aspects of optical metrology, using high quality test targets: (i) calibration and quality of absorbance measurements and the camera requirements for 3D dosimetry; ( ii) the modulation transfer function ( MTF) of individual projections; ( iii) signal-to-noise ratio (SNR) in the projection and reconstruction domains; ( iv) distortion in the projection domain, depth-of-field (DOF) and telecentricity. The principal results for our current apparatus are as follows: ( i) SNR of optical absorbance in projections is better than 120: 1 for uniform phantoms in absorbance range 0.3 to 1.6 (and better than 200: 1 for absorbances 1.0 to 3.5 with the test target and a novel absorbance range extension method), ( ii) the spatial resolution is shown to be at worst 0.5 mm ( and often better than this) with an associated DOF of 8 cm, iii) the SNR of uniform phantoms in reconstruction domain is above 80: 1 ( one standard deviation) over an absorbance dynamic range of 0.3 to 1.6, (iv) the apparatus is telecentric and without distortion. Finally, a sample scan and reconstruction of a scan of a PRESAGE (TM) dosimeter are shown, demonstrating the capabilities of the apparatus.