title: Elastographic measurement of the area and volume of thermal lesions resulting from radiofrequency ablation: pathologic correlation.
abstract: OBJECTIVE
  Elastography is a promising tool for visualizing the zone of necrosis in liver tissue resulting from radiofrequency tumor ablation. Because heat-ablated tissues are stiffer than normal untreated tissue, elastography may prove useful for following up patients who undergo radiofrequency ablative therapy. We sought to report the initial evaluations of the reliability of elastography for delineating thermal lesion boundaries in liver tissue by comparing lesion dimensions determined by elastography with the findings at whole-mount pathology.
  
  
  METHODS
  Radiofrequency ablation was performed in vitro on liver tissue specimens encased in gelatin phantoms. The imaging plane for elastography was perpendicular to the axis of the radiofrequency electrode so that the ablated region was around the center of the plane. To obtain three-dimensional visualization of thermal lesions, we reconstructed the lesions from multiple elastograms by linearly translating the elastographic scanning plane. Pathology photographs were obtained in the same image plane used for elastography by slicing through the gelatin and tissue phantom using external markers. We used digitized gross pathology photographs obtained at a specified slice thickness to compute the areas and volumes of the lesions. These measurements were then compared to the measurements obtained from the elastograms.
  
  
  RESULTS
  In a sample of 40 thermal lesions, we obtained a correlation between in vitro elastographic and pathologic measurements of r = 0.9371 (p < 0.00001) for area estimates and r = 0.979 (p < 0.00001) for volume estimates.
  
  
  CONCLUSIONS
  We found excellent correlation between the measurements of the dimensions, areas, and volumes of thermal lesions that were based on elastographic images and the measurements that were based on digitized pathologic images. When compared with digitized pathologic measurements, elastographic measurements showed a tendency to slightly underestimate both the areas and volumes of lesions. Nevertheless, elastography is a reliable technique for delineating thermal lesions resulting from radiofrequency ablation.
authors.affiliation: Department of Medical Physics, The University of Wisconsin-Madison, 1530 Medical Sciences Center, 1300 University Ave., Madison, WI 53706, USA.
authors.forename: Tomy
authors.initials: T
authors.lastname: Varghese
authors.forename: Udomchai
authors.initials: U
authors.lastname: Techavipoo
authors.forename: Wu
authors.initials: W
authors.lastname: Liu
authors.forename: James A
authors.initials: JA
authors.lastname: Zagzebski
authors.forename: Quan
authors.initials: Q
authors.lastname: Chen
authors.forename: Gary
authors.initials: G
authors.lastname: Frank
authors.forename: Fred T
authors.initials: FT
authors.lastname: Lee
mesh_terms: D000818:Animals; D017115:Catheter Ablation / Q000009:adverse effects*; D004195:Disease Models, Animal; D004548:Elasticity; D005240:Feasibility Studies; D066298:In Vitro Techniques; D008099:Liver / Q000293:injuries* / Q000473:pathology* / Q000503:physiopathology; D009336:Necrosis; D011183:Postoperative Complications; D015203:Reproducibility of Results; D013552:Swine; D015599:Trauma Severity Indices