Testing Digitome® with Computed Radiography Collin Epstein, Dr. Dan Boye Davidson College, Davidson, NC 28035, USA

Acknowledgements We would like to thank John Burke of the NDE Program at Central Piedmont Community College, Harper Campus, for his guidance and help in using CPCC’s x-ray vault and CareStream Industrex HPX-1 CR system. Thanks also to Ryan Kozlowski ‘16 and Alex Demopoulos ‘17 for their work on this project.

Volumetric Imaging Method Digitome Volumetric Technology constructs a view from several 2D x-radiographs acquired through transmission from multiple perspectives. Views are reconstructed from the exam images and presented giving a 3D volumetric reconstruction of the object.

Digitome® is a registered trademark of Digitome Corporation.

Abstract Digitome® is a 3D, volumetric program that uses 8-16 x-radiographs taken from different perspectives of an object or volume of interest to compute a 2D planar view of any level, angle or orientation. Previously, Digitome® exams have been generated using digital radiography (DR) plates because of the importance of precision alignment between the object and the plate when computing exams. We demonstrate that computed radiography (CR) plates can be used to obtain Digitome® exams of comparable quality to those taken with DR plates. Furthermore, we examine how CR enables us to take higher resolution exams than are generally available with DR plates.

Exam Object

Radiography Method Comparison CR and DR are both methods of 2D radiography that yield digitized radiographs. CR uses a phosphor plate that must be inserted into a reader after every x-ray exposure. The reader uploads the image data to a computer and wipes the phosphor plate clean. The plate can then capture another radiograph (Fig. 2). The required movement of the plate between each radiograph makes retaining precise knowledge of the orientation of the object to the plate very difficult. Since Digitome® exams require precise alignment data, it has previously been nearly impossible to compile clear, coherent Digitome® exams using CR. The CR plate we used was read with step size corresponding to a pixel size of 50 microns. DR uses a digital plate that is directly connected to a computer. After x-ray exposure, data is uploaded and the plate is ready for another radiograph without having been moved. (Fig. 3) Since the plate remains stationary between each radiographs, we can maintain precise alignment between the object and the plate. Until now, DR has been the primary method for obtaining Digitome® exams. The DR plate we used has a pixel size of 127 microns.

Fig 2: Illustration of Computer Radiography (CR). Plate is removed and inserted into the reader between radiographs. Fig 3: Digital Radiography (DR). Plate remains stationary between radiographs.

Registration and Alignment To solve the alignment problem with CR, we built a cassette to hold the phosphor plate in a constant position relative to the exam object in each radiograph and inserted the plate into the reader in the same location as best we could. Since the phosphor plates are printed with a serial number, we can use the serial numbers in each radiograph to assess the alignment precision we achieved. The images below are sums of the exam source images before and after registration correction. The pre-correction image (Fig. 5) is blurrier, indicating less precise alignment. Using Qingzong Tseng’s registration correction plug-in ‘Align Slices in Stack’ for ImageJ in Fiji, we achieved more precise alignment, as seen in the sharper after-correction image (Fig. 6).

Fig. 5 (above): Plate registration number, sum of exam images before alignment correction. Note blurring around the edges.

Fig 6 (above): Plate registration number, sum of exam images after alignment correction. Sharper edges indicate superior image alignment.

Fig. 8 (above): Image correction data. Correction is on order of pixels. Small changes, but noticeably increases image clarity.

Fig. 7 (left): Example exam source radiograph. Observe serial number on right side. Sample area outlined in red.

Comparison of Exam Results Digital Radiography Computed Radiography CR Aligned

Fig. 1: Illustration of Digitome Volumetric Technology exam

Fig. 9: DR exam slice Fig. 10: CR exam slice Fig. 11: aligned CR exam slice

While the DR exam is the most clearly defined, the aligned CR exam is comparable in quality. Observe the concealed paperclip within the tube. Note the increase in image quality achieved with source radiograph alignment.

Sub-pixel Resolution A unique feature of Digitome® is that compiled exams can achieve greater resolution than that of the individual source radiographs that comprise the exam. Below, we compare a magnified view of the plate registration number in a source radiograph with a similarly-sized exam view of the same registration number in a compiled exam. Note the visible pixels in the radiograph, compared to the lack thereof in the exam image. Further, we graph a plot profile of the same region of the two images, the top line of the leftmost ‘3’. Observe the smoother curve and greater number of points in the exam plot compared to the radiograph plot. Digitome® exams achieve resolution greater than that of the plates that capture the source images. Since CR has a small pixel size smaller than DR, using CR enables Digitome® exams to detect and resolve very small details in objects.

Fig. 12 (above): Source radiograph serial number. Points have straight edges. Fig. 13 (above): Compiled exam serial number. Points are smooth and rounded.

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Fig. 14 (above): Plot profile of source radiograph. Region is top of first ‘3’. Observe number of measured points.

Fig. 15 (above): Plot profile of source radiograph. Region is top of first ‘3’. Notice smoother plot and greater number of points compared to radiograph plot.

Conclusions •  Digitome® exams using CR are possible! •  CR exams are comparable in quality and clarity to

DR exams. •  CR exams require minimal alignment correction,

though correction noticeably improves exam. •  Digitome® exams achieve sub-pixel resolution,

resolution that is higher than that of the deviceused to record source radiographs.

•  Since CR plates can be read with greater resolution than DR plates can record, Digitome®

exams can potentially achieve very high resolution.

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Citations •  S c h i n d e l i n , J . ; R u e d e n , C . T . & H i n e r , M . C . e t a l . ( 2 0 1 5 ) , "

The ImageJ ecosystem: An open platform for biomedical image analysis", Molecular Reproduction and Development, PMID 26153368 (on Google Scholar).

•  S c h i n d e l i n , J . ; A r g a n d a - C a r r e r a s , I . & F r i s e , E . e t a l . ( 2 0 1 2 ) , "Fiji: an open-source platform for biological-image analysis", Nature methods 9(7): 676-682, PMID 22743772 (on Google Scholar).

•  ‘Align Slices in Stack’ plugin for Fiji by Qingzong Tseng