Digital x-ray tomosynthesis is a technique for producing slice images using conventional x-ray systems. It is a refinement of conventional geometric tomography, which has been known since the 1930s. In conventional geometric tomography, the x-ray tube and image receptor move in synchrony on opposite sides of the patient to produce a plane of structures in sharp focus at the plane containing the fulcrum of the motion; all other structures above and below the fulcrum plane are blurred and thus less visible in the resulting image. Tomosynthesis improves upon conventional geometric tomography in that it allows an arbitrary number of in-focus planes to be generated retrospectively from a sequence of projection radiographs that are acquired during a single motion of the x-ray tube. By shifting and adding these projection radiographs, specific planes may be reconstructed. This topical review describes the various reconstruction algorithms used to produce tomosynthesis images, as well as approaches used to minimize the residual blur from out-of-plane structures. Historical background and mathematical details are given for the various approaches described. Approaches for optimizing the tomosynthesis image are given. Applications of tomosynthesis to various clinical tasks, including angiography, chest imaging, mammography, dental imaging and orthopaedic imaging, are also described.

https://iopscience.iop.org/article/10.1088/0031-9155/48/19/R01/pdf

Digital x-ray tomosynthesis: current state of the art and clinical potential

https://www.endoexperience.com/documents/Pulprevasc-retrospectivestudyHargreavesetal2009.pdf

A Retrospective Evaluation of Radiographic Outcomes in Immature Teeth With Necrotic Root Canal Systems Treated With Regenerative Endodontic Procedures

Three algorithms for breast tomosynthesis reconstruction were compared in this paper, including (1) a back-projection (BP) algorithm (equivalent to the shift-and-add algorithm), (2) a Feldkamp filtered back-projection (FBP) algorithm, and (3) an iterative Maximum Likelihood (ML) algorithm. Our breast tomosynthesis system acquires 11 low-dose projections over a 50 degree angular range using an a-Si (CsI:Tl) flat-panel detector. The detector was stationary during the acquisition. Quality metrics such as signal difference to noise ratio (SDNR) and artifact spread function (ASF) were used for quantitative evaluation of tomosynthesis reconstructions. The results of the quantitative evaluation were in good agreement with the results of the qualitative assessment. In patient imaging, the superimposed breast tissues observed in two-dimensional (2D) mammograms were separated in tomosynthesis reconstructions by all three algorithms. It was shown in both phantom imaging and patient imaging that the BP algorithm provided the best SDNR for low-contrast masses but the conspicuity of the feature details was limited by interplane artifacts; the FBP algorithm provided the highest edge sharpness for microcalcifications but the quality of masses was poor; the information of both the masses and the microcalcifications were well restored with balanced quality by the ML algorithm, superior to the results from the other two algorithms.

A comparison of reconstruction algorithms for breast tomosynthesis.

De novo bone induction by recombinant human bone morphogenetic protein-2 (rhBMP-2) in maxillary sinus floor augmentation

The physical characteristics of a clinical prototype amorphous silicon-based flat panel imager for full-breast digital mammography have been investigated. The imager employs a thin thalliumdoped CsI scintillator on an amorphous silicon matrix of detector elements with a pixel pitch of 100 μm. Objective criteria such as modulation transfer function(MTF),noise power spectrum, detective quantum efficiency (DQE), and noise equivalent quanta were employed for this evaluation. The presampling MTF was found to be 0.73, 0.42, and 0.28 at 2, 4, and 5 cycles/mm, respectively. The measured DQE of the current prototype utilizing a 28 kVp, Mo–Mo spectrum beam hardened with 4.5 cm Lucite is ∼55% at close to zero spatial frequency at an exposure of 32.8 mR, and decreases to ∼40% at a low exposure of 1.3 mR. Detector element nonuniformity and electronic gain variations were not significant after appropriate calibration and software corrections. The response of the imager was linear and did not exhibit signal saturation under tested exposure conditions.

Full breast digital mammography with an amorphous silicon‐based flat panel detector: Physical characteristics of a clinical prototype

Distortions in radiographic images caused by changes in shape and position of the film relative to the x-ray beam can result in registration artifacts which interfere with interpretation of subtracted images.A warping transformation is described which maps known points of reference in one image into homologous points in another. The corrected image pair can then be superimposed and subtracted with significantly-reduced differences in registration to facilitate the detection of localized changes of diagnostic interest.

Computer Correction of Projective Distortions in Dental Radiographs

Tomosynthetic reconstructions suffer from the disadvantage that blurred images of object detail lying outside the plane of interest are superimposed over the desired image of structures in the tomosynthetic plane. It is proposed to selectively reduce these undesired superimpositions by a constrained iterative restoration method, suitably generalized to permit simultaneous deconvolution of multiple planes. Sufficient conditions are derived ensuring the convergence of the iterations to the exact solution in the absence of noise and constraints. Although in practice the restoration process must be left incomplete because of inescapable noise and quantization artifacts, the experimental results demonstrate that for reasons of stability the convergence conditions derived for the noise-free, unconstrained case should be satisfied. In order to establish a basis for a formal stopping criterion of the iteration procedure, the buildup of noise in the sequence of iterative restorations arising from white noise in the original radiographs is investigated theoretically and experimentally. This results in the derivation of an approximation to the limiting noise variance in the reconstructions which is verified experimentally.

Restoration of Digital Multiplane Tomosynthesis by a Constrained Iteration Method

Computerized tomosynthesis of dental tissues

Tomosynthesis and iterative restoration can be applied in dentistry to increase the information about the three-dimensional relationship of dental structures. In order to have a tool that facilitates the study of tomosynthesis and other image enhancement procedures, a flexible program was developed that effectively integrates multiple data management and image processing capabilities. A choice can be made to perform one or more of the image processing options provided in the program. In addition, options are provided to delete intermediate results that are no longer necessary for economy of space, and print a list of images that are produced by the command procedure. The program has been found to be a helpful tool in studying the effects of various parameters in tomosynthesis and iterative restoration, and facilitates analyses essential to the construction of dedicated hardware for specific diagnostic applications.

A procedure for reconstruction and enhancement of tomosynthetic images.

Two methods were studied of estimating automatically the relative volume of local lesions in digital subtractions radiographs. The first method approximates the projected, lesion area by an equivalent circular area, and the second by an equivalent polygonal area. Lesion volume is estimated in both methods as equivalent area times the average gray-level difference between the detected area and the surrounding background. Regression results of the estimated relative volume versus the calibrated size of lesions induced in dry human mandibles showed the polygonal approximation to be superior. This method also permitted successful monitoring of bone remodelling during the healing process of surgically induced lesions in dogs. The quantitative results, as well as the examples from in vivo lesions demonstrate feasibility and clinically relavance of the methodology.

R.A.J. Groenhuis

Papers

Computer Correction of Projective Distortions in Dental Radiographs

Restoration of Digital Multiplane Tomosynthesis by a Constrained Iteration Method

Computerized tomosynthesis of dental tissues

A procedure for reconstruction and enhancement of tomosynthetic images.

Automated Estimation Of Lesion Size