title: Characterisation of tissue shrinkage during microwave thermal ablation.
abstract: OBJECTIVE
  The aim of this study was to characterise changes in tissue volume during image-guided microwave ablation in order to arrive at a more precise determination of the true ablation zone.
  
  
  METHODS
  The effect of power (20-80 W) and time (1-10 min) on microwave-induced tissue contraction was experimentally evaluated in various-sized cubes of ex vivo liver (10-40 mm ± 2 mm) and muscle (20 and 40 mm ± 2 mm) embedded in agar phantoms (N = 119). Post-ablation linear and volumetric dimensions of the tissue cubes were measured and compared with pre-ablation dimensions. Subsequently, the process of tissue contraction was investigated dynamically during the ablation procedure through real-time X-ray CT scanning.
  
  
  RESULTS
  Overall, substantial shrinkage of 52-74% of initial tissue volume was noted. The shrinkage was non-uniform over time and space, with observed asymmetry favouring the radial (23-43 % range) over the longitudinal (21-29%) direction. Algorithmic relationships for the shrinkage as a function of time were demonstrated. Furthermore, the smallest cubes showed more substantial and faster contraction (28-40% after 1 min), with more considerable volumetric shrinkage (>10%) in muscle than in liver tissue. Additionally, CT imaging demonstrated initial expansion of the tissue volume, lasting in some cases up to 3 min during the microwave ablation procedure, prior to the contraction phenomenon.
  
  
  CONCLUSIONS
  In addition to an asymmetric substantial shrinkage of the ablated tissue volume, an initial expansion phenomenon occurs during MW ablation. Thus, complex modifications of the tissue close to a radiating antenna will likely need to be taken into account for future methods of real-time ablation monitoring.
authors.affiliation: Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome , Italy .
authors.forename: Laura
authors.initials: L
authors.lastname: Farina
authors.forename: Noam
authors.initials: N
authors.lastname: Weiss
authors.forename: Yitzhak
authors.initials: Y
authors.lastname: Nissenbaum
authors.forename: Marta
authors.initials: M
authors.lastname: Cavagnaro
authors.forename: Vanni
authors.initials: V
authors.lastname: Lopresto
authors.forename: Rosanna
authors.initials: R
authors.lastname: Pinto
authors.forename: Nevio
authors.initials: N
authors.lastname: Tosoratti
authors.forename: Claudio
authors.initials: C
authors.lastname: Amabile
authors.forename: Simone
authors.initials: S
authors.lastname: Cassarino
authors.forename: S Nahum
authors.initials: SN
authors.lastname: Goldberg
mesh_terms: D000818:Animals; D002417:Cattle; D008099:Liver / Q000528:radiation effects*; D008872:Microwaves; D009132:Muscles / Q000528:radiation effects*; D019047:Phantoms, Imaging; D014422:Turkeys
keywords: Ex vivo studies; microwave thermal ablation; tissue shrinkage