Tomoelastography Explained

Tomoelastography (from ancient Greek τόμος tomos, “slice” and elastography – imaging of viscoelastic properties) is a medical imaging technique that provides quantitative maps of the mechanical properties of biological soft tissues with high spatial resolution (called elastograms). It is an advancement of elastography[1] [2] [3] in that it generates unmasked maps of stiffness and viscosity across the entire field of view that can be captured with a given imaging modality. Medical ultrasound and magnetic resonance imaging (MRI) are the most commonly used imaging modalities for elastography. Classical elastography only measures stiffness in a limited region, such as at a depth of 6 cm in the liver or in a selected liver lobe, and thus cannot provide an overview of the adjacent tissues or organs. Tomoelastography, on the other hand, is a radiological imaging method that allows estimation of quantitative mechanical parameters of all organs and structures in the field of view.[4] Moreover, tomoelastography does not rely on a single, specific imaging modality. While it has been introduced and is mostly performed using magnetic resonance elastography (MRE), tomoelastography can be extended to other imaging techniques as well.

Tomoelastography requires external driver systems, which can efficiently generate shear waves throughout the entire field of view including tissues deep within the body. Multiple drivers can be combined such that waves propagate from the surface into the body from different directions to enable full illumination of larger regions with shear waves. Tomoelastography often employs mechanical vibrations at several driving frequencies for multifrequency wave analysis in order to stabilize inverse problem solutions for viscoelasticity reconstructions. A standard way of multifrequency viscoelasticity reconstruction is based on phase gradient analysis of plane waves[5] whereas other methods employ solutions of the Helmholtz equation.[6] [7] [8] The feasibility of tomoelastography was first demonstrated in the human abdomen using multifrequency MRE, where it was possible for the first time to display stiffness values (quantified as shear wave speed in m/s) across the entire axial MRI slice. Although the elastograms are quantitative maps, tomoelastography images, like other radiological images, are often presented in standard gray-scale which gives more perceptual contrast to the subtle nuances than the color-scale.

Applications

Currently, most applications of tomoelastography are based on MRI, which is why tomoelastography is often referred to as an advanced MRE technique. Multifrequency-MRE based tomoelastography has been used for the diagnosis of diffuse liver disease,[9] [10] [11] renal diseases such as renal allograft dysfunction,[12] lupus nephritis,[13] and immunoglobulin A nephropathy (IgAN).[14] In addition, tomoelastography has been used for cancer imaging. In the liver, viscoelastic parameters of lesions less than 1 cm in diameter could be quantified for diagnostic purposes.[15] Pancreatic cancer has been shown to be abnormally stiff compared to surrounding tissue, resulting in a large tumor contrast in elastograms.[16] [17] In the prostate, tomoelastography has been able to distinguish cancer from benign lesions.[18]

References

  1. Lerner RM, Huang SR, Parker KJ. "Sonoelasticity" images derived from ultrasound signals in mechanically vibrated tissues. Ultrasound Med Biol. 16. 3. 231–9. 1990. 1694603. 10.1016/0301-5629(90)90002-t.
  2. Muthupillai R, Ehman RL. Magnetic resonance elastography. Nat Med. 2. 5. 601–3. May 1996. 8616724. 10.1038/nm0596-601. 5140184.
  3. Ingolf Sack: Magnetic resonance elastography from fundamental soft-tissue mechanics to diagnostic imaging. In: Nature Reviews Physics. 5, 2023, S. 25, .
  4. Book: Sack, Ingolf . Principles and Applications of Magnetic Resonance Elastography . John Wiley & Sons, Incorporated . Somerset . 2016 . 978-3-527-34008-8 . 965775099 .
  5. Tzschätzsch H, Guo J, Dittmann F, Hirsch S, Barnhill E, Jöhrens K, Braun J, Sack I. Tomoelastography by multifrequency wave number recovery from time-harmonic propagating shear waves. Med Image Anal. 30. 1–10. May 2016. 26845371. 10.1016/j.media.2016.01.001.
  6. Papazoglou S, Hirsch S, Braun J, Sack I. Multifrequency inversion in magnetic resonance elastography. Phys Med Biol. 57. 8. 2329–46. April 2012. 22460134. 10.1088/0031-9155/57/8/2329. 2012PMB....57.2329P . 25278940 .
  7. Honarvar M, Sahebjavaher R, Sinkus R, Rohling R, Salcudean SE. Curl-Based Finite Element Reconstruction of the Shear Modulus Without Assuming Local Homogeneity: Time Harmonic Case. IEEE Trans Med Imaging. 32. 12. 2189–99. December 2013. 23925367. 10.1109/TMI.2013.2276060. 5807358.
  8. Barnhill E, Davies PJ, Ariyurek C, Fehlner A, Braun J, Sack I. Heterogeneous Multifrequency Direct Inversion (HMDI) for magnetic resonance elastography with application to a clinical brain exam. Med Image Anal. 46. 180–188. May 2018. 29574398. 10.1016/j.media.2018.03.003. 11693/49924. 4964009. free.
  9. Reiter R, Tzschätzsch H, Schwahofer F, Haas M, Bayerl C, Muche M, Klatt D, Majumdar S, Uyanik M, Hamm B, Braun J, Sack I, Asbach P. Diagnostic performance of tomoelastography of the liver and spleen for staging hepatic fibrosis. Eur Radiol. 30. 3. 1719–1729. March 2020. 31712963. 7033143. 10.1007/s00330-019-06471-7.
  10. Marticorena Garcia SR, Althoff CE, Dürr M, Halleck F, Budde K, Grittner U, Burkhardt C, Jöhrens K, Braun J, Fischer T, Hamm B, Sack I, Guo J. Tomoelastography for Longitudinal Monitoring of Viscoelasticity Changes in the Liver and in Renal Allografts after Direct-Acting Antiviral Treatment in 15 Kidney Transplant Recipients with Chronic HCV Infection. J Clin Med. 10. 3. February 2021. 510. 33535495. 7867050. 10.3390/jcm10030510. free.
  11. Hudert CA, Tzschätzsch H, Rudolph B, Bläker H, Loddenkemper C, Müller HP, Henning S, Bufler P, Hamm B, Braun J, Holzhütter HG, Wiegand S, Sack I, Guo J. Tomoelastography for the Evaluation of Pediatric Nonalcoholic Fatty Liver Disease. Invest Radiol. 54. 4. 198–203. April 2019. 30444796. 10.1097/RLI.0000000000000529. 53568878.
  12. Marticorena Garcia SR, Fischer T, Dürr M, Gültekin E, Braun J, Sack I, Guo J. Multifrequency Magnetic Resonance Elastography for the Assessment of Renal Allograft Function. Invest Radiol. 51. 9. 591–5. September 2016. 27504796. 10.1097/RLI.0000000000000271. 34327744.
  13. Marticorena Garcia SR, Grossmann M, Bruns A, Dürr M, Tzschätzsch H, Hamm B, Braun J, Sack I, Guo J. Tomoelastography Paired With T2* Magnetic Resonance Imaging Detects Lupus Nephritis With Normal Renal Function. Invest Radiol. 54. 2. 89–97. February 2019. 30222647. 10.1097/RLI.0000000000000511. 52286012.
  14. Lang ST, Guo J, Bruns A, Dürr M, Braun J, Hamm B, Sack I, Marticorena Garcia SR. Multiparametric Quantitative MRI for the Detection of IgA Nephropathy Using Tomoelastography, DWI, and BOLD Imaging. Invest Radiol. 54. 10. 669–674. October 2019. 31261295. 10.1097/RLI.0000000000000585. 195772720.
  15. Shahryari M, Tzschätzsch H, Guo J, Marticorena Garcia SR, Böning G, Fehrenbach U, Stencel L, Asbach P, Hamm B, Käs JA, Braun J, Denecke T, Sack I. Tomoelastography Distinguishes Noninvasively between Benign and Malignant Liver Lesions. Cancer Res. 79. 22. 5704–5710. November 2019. 31551364. 10.1158/0008-5472.CAN-19-2150. free.
  16. Marticorena Garcia SR, Zhu L, Gültekin E, Schmuck R, Burkhardt C, Bahra M, Geisel D, Shahryari M, Braun J, Hamm B, Jin ZY, Sack I, Guo J. Tomoelastography for Measurement of Tumor Volume Related to Tissue Stiffness in Pancreatic Ductal Adenocarcinomas. Invest Radiol. 55. 12. 769–774. December 2020. 32796197. 10.1097/RLI.0000000000000704. 221133340.
  17. Zhu L, Guo J, Jin Z, Xue H, Dai M, Zhang W, Sun Z, Xu J, Marticorena Garcia SR, Asbach P, Hamm B, Sack I. Distinguishing pancreatic cancer and autoimmune pancreatitis with in vivo tomoelastography. Eur Radiol. 31. 5. 3366–3374. May 2021. 33125553. 10.1007/s00330-020-07420-5. 225994738.
  18. Li M, Guo J, Hu P, Jiang H, Chen J, Hu J, Asbach P, Sack I, Li W. Tomoelastography Based on Multifrequency MR Elastography for Prostate Cancer Detection: Comparison with Multiparametric MRI. Radiology. 299. 2. 362–370. May 2021. 33687285. 10.1148/radiol.2021201852. 232161536 .

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