Department of Medical Physics, Institute of Oncology Ljubljana, Zaloška cesta 2, Ljubljana 1000, Slovenia.
Department of Medical Physics, Institute of Oncology Ljubljana, Zaloška cesta 2, Ljubljana 1000, Slovenia.
Phys Med. 2016 Sep;32(9):1072-81. doi: 10.1016/j.ejmp.2016.08.003. Epub 2016 Aug 9.
When comparing different scans of the same radiochromic film, several patterns can be observed. These patterns are caused by different sources of uncertainty, which affect the repeatability of the scanner. The purpose of this work was to study these uncertainties.
The variance of the scanner noise, as a function of the pixel position, was studied for different resolutions. The inter-scan variability of the scanner response was analyzed taking into account spatial discrepancies. Finally, the distance between the position of the same point in different scans was examined.
The variance of noise follows periodical patterns in both axes, causing the grid patterns. These patterns were identified for resolutions of 50, 72 and 96dpi, but not for 150dpi. Specially recognizable is the sinusoidal shape with a period of 8.5mm that is produced with 72dpi. Inter-scan variations of the response caused systematic relative dose deviations larger than 1% in 5% of the red channel images, 9% of the green and 51% of the blue. No systematic deviation larger than 1% was found after applying response corrections. The initial positioning and the speed of the scanner lamp vary between scans.
Three new sources of uncertainty, which influence radiochromic film dosimetry with flatbed scanners, have been identified and analyzed in this work: grid patterns, spatial inter-scan variations and scanning reading repeatability. A novel correction method is proposed, which mitigates spatial inter-scan variations caused by deviations in the autocalibration of the individual Charge Coupled Device detectors.
在比较同一张光致变色胶片的不同扫描时，可以观察到几种模式。这些模式是由不同的不确定来源引起的，这些不确定来源会影响扫描仪的可重复性。本工作的目的是研究这些不确定来源。
研究了不同分辨率下，扫描仪噪声的像素位置函数的方差。考虑到空间差异，分析了扫描仪响应的扫描间可变性。最后，检查了不同扫描中同一位置之间的距离。
噪声方差在两个轴上都呈现周期性模式，导致出现网格图案。这些模式在 50、72 和 96dpi 的分辨率下被识别，但在 150dpi 下没有被识别。特别明显的是，72dpi 产生的正弦形状，其周期为 8.5mm。响应的扫描间变化导致 5%的红色通道图像、9%的绿色通道和 51%的蓝色通道中的相对剂量偏差大于 1%，而在应用响应校正后，没有发现大于 1%的系统偏差。初始定位和扫描仪灯的速度在每次扫描之间都有所不同。
本工作中已经确定并分析了三种新的不确定来源，它们会影响平板扫描仪的光致变色胶片剂量测定：网格图案、扫描间空间变化和扫描读取重复性。提出了一种新的校正方法，可以减轻由于单个电荷耦合器件探测器的自动校准偏差引起的空间扫描间变化。
