After posterior lumbar instrumented fusion, radiographic changes suggesting disc degeneration appear homogeneously at several levels cephalad to fusion and seem to be determined by individual characteristics.

Simplified statistical image reconstruction for X-ray CT with beam-hardening artifact compensation. IEEE Transactions on Medical Imaging. [Early access], [8] p.

Objective Dual energy radiography (DER) makes it possible to obtain separate images for soft‐tissue and bony structures (tissue maps) based on the acquisition of two radiographs at different source peak‐kilovoltage values. Current DER studies are based on the weighted subtraction method, which requires either manual tuning or the use of precomputed tables, or on decomposition methods, which make use of a calibration to model soft‐tissue and bone components. In this study, we examined in depth the optimum method to perform this calibration. Methods We used simulations to optimize the calibration protocol and evaluated the effect of the material and size of a calibration phantom composed of two wedges and its positioning in the system. Evaluated materials were water, PMMA and A‐150 as soft‐tissue equivalent, and Teflon, B‐100 and aluminum as bone equivalent, with sizes from 5 to 30 cm. Each material combination was compared with an ideal phantom composed of soft tissue and bone. Our simulation results enabled us to propose four designs that were tested with the NOVA FA X‐ray system with a realistic thorax phantom. Results Calibration based on a very simple and inexpensive phantom with no strict requirements in its placement results in appropriate separation of the spine (a common focus in densitometry studies) and the identification of nodules as small as 6 mm, which have been reported to have a low rate of detection in radiography. Conclusion The proposed method is completely automatic, avoiding the need for a radiology technician with expert knowledge of the protocol, as is the case in densitometry exams. The method provides real mass thickness values, enabling quantitative planar studies instead of relative comparisons.

Purpose: The last decades have seen the consolidation of the Cone-Beam CT (CBCT) technology, which is nowadays widely used for different applications such as micro-CT for small animals, mammography, dentistry, or surgical procedures. Some CBCT systems may suffer mechanical strains due to the heavy load of the X-ray tube. This fact, together with tolerances in the manufacturing process, lead to different types of undesirable effects in the reconstructed image unless they are properly accounted for during the reconstruction. To obtain good quality images, it is necessary to have a complete characterization of the system geometry including the angular position of the gantry, the source-object and detector-object distances, and the position and pose of the detector. These parameters can be obtained through a calibration process done periodically, depending on the stability of the system geometry. To the best of our knowledge, there are no comprehensive works studying the effect of inaccuracies in the geometrical calibration of CBCT systems in a systematic and quantitative way. In this work, we describe the effects of detector misalignments (linear shifts, rotation and inclinations) on the image and define their tolerance as the maximum error that keeps the image free from artifacts.Methods: We used simulations of four phantoms including systematic and random misalignments.Reconstructions of these data with and without errors were compared to identify the artifacts introduced in the reconstructed image and the tolerance on miscalibration deemed to provide acceptable image quality.Results: Visual assessment provided an easy guideline to identify the sources of error by visual inspection of the artifactual images. Systematic errors result in blurring, shape distortion and/or reduction of the axial field of view while random errors produce streaks and blurring in all cases, with a tolerance which is more than twice that of systematic errors. The tolerance corresponding to errors in position of the detector along the tangential direction, i.e., skew (<0.2 degrees) and horizontal shift (<0.4 mm), is tighter than the tolerance to those errors affecting the position along the longitudinal direction or the magnification, i.e., vertical shift (<2 mm), roll (<1.5 degrees), tilt (<2 degrees) and SDD (<3 mm). Conclusion:We present a comprehensive study, based on realistic simulations, of the effects on the reconstructed image quality of errors in the geometrical characterization of a CBCT system and define their tolerance. These results could be used to guide the design of new systems, establishing the mechanical precision that must be achieved, and to help in the definition of an optimal geometrical calibration process. Also, the thorough visual assessment may be valuable to identify the most predominant sources of error based on the effects shown in the reconstructed image.