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

Fundamentals of Materials Science

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

Background: Scaling and root planing (SRP) are the bases of non-surgical therapy in the treatment of periodontitis. However, results from this therapy are often unpredictable and dependable from many different factors.

Objectives:  The aim of this systematic review was to evaluate the effectiveness of the adjunctive use of systemic antimicrobials with scaling and root planing (SRP) vs. SRP alone in the treatment of chronic (CP) or aggressive periodontitis (AgP).

Search strategy:  Use of computerized databases, namely MEDLINE, the Cochrane Oral Health Group Specialty Trials Register and EMBASE; reference lists from relevant articles were hand-searched; and a hand-search of selected journals until April 2001.

Selection criteria:  Studies were selected if they were designed as controlled clinical trials in which systemically healthy patients with either AgP or CP were treated with SRP plus systemic antimicrobials in comparison with SRP alone or with placebo, for a minimum of 6 months. Main outcome measures were clinical attachment level (CAL) change and probing pocket depth (PPD) change.

Data collection and analysis:  Two reviewers extracted independently information regarding quality and study characteristics, in duplicate. Kappa scores determined their agreement. Main results were collected and grouped by drug, disease and PPD category. For the quantitative data synthesis, the data was pooled (when mean differences and standard errors were available), and either a Fixed Effects or Random Effects meta-analysis was used for the analysis.

Results:  After an initial selection, 158 papers were identified by the manual and electronic searches; 25 papers were eligible for inclusion. Their quality assessment showed that randomization and allocation concealment methods were seldom reported and blindness was usually not defined clearly. In general, selected studies showed high variability and lack of relevant information for an adequate assessment. Overall, SRP plus systemic antimicrobial groups demonstrated better results in CAL and PPD change than SRP alone or with placebo groups. Only limited meta-analyses could be performed, due to the difficulties in pooling the studies and the lack of appropriate data. This analysis showed a statistically significant additional benefit for spiramycin (PPD change) and amoxicillin/metronidazole (CAL change) in deep pockets.

Conclusion:  Systemic antimicrobials in conjunction with SRP, can offer an additional benefit over SRP alone in the treatment of periodontitis, in terms of CAL and PPD change, and reduced risk of additional CAL loss. However, differences in study methodology and lack of data precluded an adequate and complete pooling of data for a more comprehensive analyses. It was difficult to establish definitive conclusions, although patients with deep pockets, progressive or ‘active’ disease, or specific microbiological profile, can benefit more from this adjunctive therapy.

A systematic review on the effect of systemic antimicrobials as an adjunct to scaling and root planing in periodontitis patients.

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.

A digital subtraction technique for dental radiography

The use of a cephalostat to stabilize projection geometry for subtraction radiography was investigated. Six replicate repositionings of patients within a cephalostat indicated that the mean angular disparity between repositioning was 0.33 ± 0.10 degrees. Subtraction images produced from films of a phantom with artificial periodontal defects exposed using the cephalostat or stent technique were compared. There was no significant difference in the standard deviations of the gray level histograms obtained using the two methods. However, the ability of 10 investigators to detect the presence or absence of simulated periodontal lesions was superior from subtraction radiographs produced from cephalostat-based images when compared to stent-based images (p < .02). Sets of radiographs taken of 6 patients on the same day or 3 months apart indicate that the cephalometric technique may be used to stabilize projection geometry.

Extraoral control of geometry for digital subtraction radiography.

The influence of differences in imaging geometry on the detection of small periodontal bone lesions was studied when using a digital subtraction technique. The results were compared with those from conventional radiographs. Reference radiographs were obtained on human mandibular jaws before small lesions were made in the marginal alveolar bone. Subsequent radiographs were taken with the same imaging projection as well as with changes of the angulation in either vertical, or horizontal direction, or both. 10 dentists served as observers, who compared the conventional radiographs taken before and after the lesions were made, and registered the presence or absence of lesions using a diagnostic rating scale. The conventional radiographs were digitized, and subtraction images made. These images were interpreted by the same observers. For each observer, image modality and projection, the resulting rates of true positive and false positive diagnoses were plotted on a graph. The area under the curve, obtained by connecting the paired values of true positive and false positive results associated with the different diagnostic ratings, was used as a measure of diagnostic accuracy. Statistically significant differences could be demonstrated between the results obtained from the subtraction images, whether produced from identical or non-identical pairs of conventional radiographs, and the results from the conventional radiographs obtained under ideal conditions.

Influence of variations in projection geometry on the detectability of periodontal bone lesions. A comparison between subtraction radiography and conventional radiographic technique.

X‐ray image subtraction as a basis for assessment of periodontal changes

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.

Richard L. Webber

Papers

A digital subtraction technique for dental radiography

Extraoral control of geometry for digital subtraction radiography.

Influence of variations in projection geometry on the detectability of periodontal bone lesions. A comparison between subtraction radiography and conventional radiographic technique.

X‐ray image subtraction as a basis for assessment of periodontal changes

Computer Correction of Projective Distortions in Dental Radiographs