Tomosynthesis

Tomosynthesis, also digital tomosynthesis (DTS), is a method for performing high-resolution limited-angle tomography at radiation dose levels comparable with projectional radiography. It has been studied for a variety of clinical applications, including vascular imaging, dental imaging, orthopedic imaging, mammographic imaging, musculoskeletal imaging, and chest imaging.[1]

Tomosynthesis of a lung with chronic fibrosing pulmonary aspergillosis.

History

The concept of tomosynthesis was derived from the work of Ziedses des Plantes, who developed methods of reconstructing an arbitrary number of planes from a set of projections. Though this idea was displaced by the advent of computed tomography, tomosynthesis later gained interest as a low-dose tomographic alternative to CT.[2]

Reconstruction

Tomosynthesis reconstruction algorithms are similar to CT reconstructions, in that they are based on performing an inverse Radon transform. Due to partial data sampling with very few projections, approximation algorithms have to be used. Filtered back projection and iterative, expectation-maximization algorithms have both been used to reconstruct the data.[3]

Reconstruction algorithms for tomosynthesis are different from those of conventional CT because the conventional filtered back projection algorithm requires a complete set of data. Iterative algorithms based upon expectation maximization are most commonly used, but are computationally intensive. Some manufacturers have produced practical systems using off-the-shelf GPUs to perform the reconstruction in a few seconds.

Differences from other imaging modalities

Digital tomosynthesis combines digital image capture and processing with simple tube/detector motion as used in conventional computed tomography (CT). However, though there are some similarities to CT, it is a separate technique. In modern (helical) CT, the source/detector makes at least a complete 180-degree rotation about the subject obtaining a complete set of data from which images may be reconstructed. Digital tomosynthesis, on the other hand, only uses a limited rotation angle (e.g., 15-60 degrees) with a lower number of discrete exposures (e.g., 7-51) than CT. This incomplete set of projections is digitally processed to yield images similar to conventional tomography with a limited depth of field. Because the image processing is digital, a series of slices at different depths and with different thicknesses can be reconstructed from the same acquisition. However, since fewer projections are needed than CT to perform the reconstruction, radiation exposure and cost are both reduced.[4]

Applications

Breast

Tomosynthesis is Food and Drug Administration (FDA) approved for use in breast cancer screening.[5] As of 2016, however, it is unclear if its use in screening normal risk women is beneficial or harmful.[6]

Digital breast tomosynthesis (DBT) can provide a higher diagnostic accuracy compared to conventional mammography. In DBT, like conventional mammography, compression is used to improve image quality and decreases radiation dose. The laminographic imaging technique dates to the 1930s and belongs to the category of geometric or linear tomography.[7]

Because the data acquired are 85 - 160 micron typical resolution, much higher than CT, DBT is unable to offer the narrow slice widths that CT offers (typically 1-1.5 mm). However, the higher resolution detectors permit very high in-plane resolution, even if the Z-axis resolution is less. The primary interest in DBT is in breast imaging, as an extension to mammography, where it offers better detection rates with little extra increase in radiation.[8][9]

Chest

Musculoskeletal imaging

Tomosynthesis has a much more limited depth of field than does CT. For this reason, it likely will not be able to replace CT for the evaluation of the deeper organs of the body. However, since bones are often near the skin, multiple musculoskeletal applications of tomosynthesis have been studied, most of which have mostly been used in research with limited use in everyday practice.

Evaluation of fractures

Tomosynthesis has been compared to both radiography and CT for the evaluation of healing fractures, especially in the presence of hardware. In a study of patients with wrist fractures, digital tomosynthesis was shown to enable detection of more fractures than radiography while simultaneously providing lower metal artifact than radiography.[4]

Evaluation of erosions in rheumatoid arthritis

Tomosynthesis has been compared to digital radiography, with CT as the standard, for the detection of erosions associated with rheumatoid arthritis. The radiation dose of digital tomosynthesis was very close to that of digital radiography. However, tomosynthesis showed sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of 80%, 75%, 78%, 76%, and 80%, compared to digital radiography were 66%, 81%, 74%, 77%, and 71%.[10] The slight benefit digital tomosynthesis in this application may or may not justify the slightly increased cost of the modality compared to digital radiography.

Electronics

Tomosynthesis is also used for x-ray inspection of electronics[11], particularly printed circuit board assemblies and electronic components. Tomosynthesis is usually used where a CT slice is required at high magnification, where conventional CT would not allow the sample to be located close enough to the x-ray source.

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References
  1. Dobbins, James; McAdams, H. Page (Nov 2009). "Chest Tomosynthesis: Technical Principles and Clinical Update". European Journal of Radiology. 72 (2): 244–251. doi:10.1016/j.ejrad.2009.05.054. PMC 3693857. PMID 19616909.
  2. Dobbins JT, 3rd; Godfrey, DJ (7 October 2003). "Digital x-ray tomosynthesis: current state of the art and clinical potential". Physics in Medicine and Biology. 48 (19): R65–106. doi:10.1088/0031-9155/48/19/r01. PMID 14579853.
  3. Sechopoulos, Ioannis (2013). "A review of breast tomosynthesis. Part II. Image reconstruction, processing and analysis, and advanced applications". Medical Physics. 40 (1): 014302. Bibcode:2013MedPh..40a4302S. doi:10.1118/1.4770281. PMC 3548896. PMID 23298127.
  4. Ha, Alice; Lee, Amie; Hippe, Daniel; Chou, Shinn-Huey; Chew, Felix (July 2015). "Digital Tomosynthesis to Evaluate Fracture Healing: Prospective Comparison With Radiography and CT". American Journal of Roentgenology. 205 (1): 136–141. doi:10.2214/AJR.14.13833. PMID 26102392.
  5. "Selenia Dimensions 3D System - P080003, US Food and Drug Administration (FDA), February 11, 2011
  6. Siu, Albert L. (12 January 2016). "Screening for Breast Cancer: U.S. Preventive Services Task Force Recommendation Statement". Annals of Internal Medicine. 164 (4): 279–96. doi:10.7326/M15-2886. PMID 26757170.
  7. Dedicated Computed Tomography of the Breast: Image Processing and Its Impact on Breast Mass Detectability. Qing Xia. 2007. ISBN 0549663193 pp.4
  8. Smith, Andrew P.; Niklason, Loren; Ren, Baorui; Wu, Tao; Ruth, Chris; Jing, Zhenxue (2006). "Lesion Visibility in Low Dose Tomosynthesis". Digital Mammography. Lecture Notes in Computer Science. 4046. pp. 160–166. doi:10.1007/11783237_23. ISBN 978-3-540-35625-7.
  9. Lång, K; Andersson, I; Zackrisson, S (2014). "Breast cancer detection in digital breast tomosynthesis and digital mammography—a side-by-side review of discrepant cases". The British Journal of Radiology. 87 (1040): 20140080. doi:10.1259/bjr.20140080. ISSN 0007-1285. PMC 4112403. PMID 24896197.
  10. Simon, Paolo; Gérard, Laurent; Kaiser, Marie-Joëlle; Ribbens, Clio; Rinkin, Charline; Malaise, Olivier; Malaise, Michecl (August 2016). "Use of Tomosynthesis for Detection of Bone Erosions of the Foot in Patients With Established Rheumatoid Arthritis: Comparison With Radiography and CT". American Journal of Roentgenology. 205 (2): 364–370. doi:10.2214/AJR.14.14120. PMID 26204289.
  11. A Practical Guide to X-ray Inspection Criteria and Common Defect Analysis (Second ed.). 2019. p. 83. ISBN 978-1527233614.
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