Digital Radiography

Wall Thickness Determination in Digital Radiography, T. Wawrzinek, U. Zscherpel, C. Bellon, COFREND Congress on NDT, Nantes 1997, conference proceedings, vol. l,pp. 79-83... 

The GAMMASCAN 1500 HR is a combined system for two-dimensional (2D-CT) and three-dimensional (3D-CT) computed tomography, as well as digital radiography (DR). The system is equipped with two separate detector systems for the fan-beam and cone-beam CT. The sire of the objects is limited to a height of four meters, maximum diameters of 1.5 meters and a weight of up to 15 tons. The turntable which carries the test samples can be moved along and across the beam direction ( X- and Y- direction). The radiation source and the detector systems can be moved in Z- direction, both, simultaneously and independently. 

In case of some samples besides the cross sectional CT-slice also a projectional image is of interest. In these cases the test mode Digital Radiography (DR) is applied. In the DR-mode the object is not turned, but scanned horizontally and vertically. Again the very high dynamic of the detector and the mechanical accuracy of the complete system are of large benefit to the image quality. 

In order to prepare the system for 3D-CT, it is not enough to integrate a second detector array. Besides this special attention has to be paid to the computer hardware, the synchronisation between object movement and the data read out as well as to the collimator of the LINAC. The collimator has been built with 4 tungsten blocks which can be moved individually m order to shape different sht sizes for 2D-CT as well as different cone angles for 3D-CT or digital radiography. 

Whereas scintillation screens can be used to directly view x-rays passing through the body, the dose to a patient is too high. Instead, scintillation screens are combined with video cameras or electronic intensifier tubes and video cameras. This detection scheme is used in digital radiography where digital x-ray images are recorded, and fluoroscopy where temporal processes are to be followed. 

Digital Radiography. In this technique, the traditional film is replaced by a linear array of detectors and the X-ray beam is Collimated into a fan beam. The object is moved perpendicularly to the detector array, and the attenuated radiation is sampled digitally by the detectors. Data are processed by stored infoimation in the computer s memory to yield a two-dimensional image of the part being inspected. 

Rubenstein. E.. E,B. Hughes. L.E. Cambell, and et al. Synchrotron Radiation and Its Application to Digital Subtraction Angiography," Conf. On Digital Radiography, 314, 42, Bellingham. WA, 1981. 

Greene R, Schaefer CM, Oliver LC. 1991. Improved detection of asbestos-related pleural plaques with digital radiography. Ann NY Acad Sci 643(12) 90-96. 

Yancev. R. N., and Mitchell, C. R. (1994), Nondestructive evaluation of composites u.sing digital radiography and computed tomography. Proc. of the Conf. on NDE Applied to Process Control of Composite Fabrication. Oct. 1994. pp. 111 114. 

Loo L-N, Doi K, Metz CE (1985) Investigation of basic imaging properties in digital radiography. 4. Effect of unsharp masking on the detectability of simple patterns. Med Phys 12 209-214... 

Bragdon C.R., H. Malchau, S.L. Larson, et al. 2002. Validation of digital radiography, for use with radiostereometric analysis (RSA) using a dynamic phantom wear model. Transactions of the 48th Orthopedic Research Society 27 1020. 

Hgure 4 Construction of the flat-panel detector. The X-ray sensitive layer consists of cesium iodide (Csl). The amorphous silicon sensor array comprises 3000 x 3000 pixels. (Reproduced with permission from Hamers S and Freyschmidt J (1998) Digital radiography with an electronic flat-panel detector First clinical experience in skeletal diagnostics. Medicamundi 42 2-6 Medicamundi.)... 

Clinical Indications 5 Comparison Views 5 Digital Radiography and PACS Radiation Dose and Protection Paediatric Service Provision 6... 

A total of 29 additional cylindrical silicon nitride tensile specimens have been received for inspection with the CT system. Initial inspection will be done utilizing digital radiography. Any sample showing any type of discontinuity will be further evaluated with one or more CT slices through the longitudinal center of the sample. 

Siewerdsen JH, Jaffray DA (2001) Cone-beam computed tomography with a flat-panel imager Magnitude and effects of X-ray scatter. Med Phys 28 220-231 Siewerdsen JH, Daly MJ, Bakhtiar B, et al. (2006) A simple, direct method for X-ray scatter estimation and correction in digital radiography and cone-beam CT. Med Phys 33 187-197... 

Future Trends in Digital Radiography and Computed Imaging 97... 

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