Three-Dimensional Electrode Displacement Elastography Using the Siemens C7F2 fourSight Four-Dimensional Ultrasound Transducer

Abstract

Because ablation therapy alters the elastic modulus of tissues, emerging strain imaging methods may enable clinicians for the first time to have readily available, cost effective, real-time guidance to identify the location and boundaries of thermal lesions. Electrode displacement elastography is a method of strain imaging tailored specifically to ultrasound-guided electrode-based ablative therapies (eg. radiofrequency ablation). Here tissue deformation is achieved by applying minute perturbations to the unconstrained end of the treatment electrode, resulting in localized motion around the end of the electrode embedded in tissue. In this paper, we present a method for 3D elastographic reconstruction from volumetric data acquired using the C7F2 fourSight 4D ultrasound transducer, provided by Siemens Medical Solutions. Lesion reconstruction is demonstrated for a spherical inclusion centered in a tissue-mimicking phantom, which simulates a thermal lesion embedded in a normal tissue background. Elastographic reconstruction is also performed for a thermal lesion created in vitro in canine liver using radiofrequency ablation. Post-processing is done on the acquired raw radiofrequency data to form surface-rendered 3D elastograms of the inclusion. Elastographic volume estimates of the inclusion compare reasonably well with the actual known inclusion volume, with 3D electrode displacement elastography slightly underestimating the true inclusion volume.

Electrode displacement strain imaging of thermally‐ablated liver tissue in an in vivo animal model

“…These results also demonstrate the need for 3D strain imaging for complete tracking and measurement of the lesion volume. 29 Volume imaging of the ablation zone will reduce errors associated with area measurements. 29 The other limitations of this study include the use of a high transducer center frequency, which is not feasible for imaging human patients during a percutaneous procedure.…”

“…29 Volume imaging of the ablation zone will reduce errors associated with area measurements. 29 The other limitations of this study include the use of a high transducer center frequency, which is not feasible for imaging human patients during a percutaneous procedure. Ultrasound imaging was performed using an open-chest preparation with the transducer placed directly on the liver surface.…”

“…For two thermal ablations, it was necessary to replace the needle artifact using uniformly distributed random numbers corresponding to strains between 0% and 0.2% in order to achieve proper automated segmentation. 29 In the gross-pathology photographs of the corresponding ultrasound imaging plane ͑marked on the liver surface͒, the extent of the ablation zone was delineated manually, based on the transition between white and pink tissue regions. The ultrasound scan plane was identified by marking the position of the linear-array transducer on the liver surface.…”

Ultrasound applications to medicine part i: physical principles.

“…There is also Physiotherapy utilization [55] as the treatment of cervical pain [56] [57], its use in surgical and medical instruments (20 to 60 kHz) for dissection, ablation [58] [59], fragmentation and removal of biological tissue [60], activation of transplanted organs [61], biopsies [62] [63], vacuum biopsies [64], orthodontics [65], in obstetrics [66] and ambulatory gynecology [67] [68], pediatric anesthesia [69], forensic examinations [70] or simply to disinfect medical instruments [71].…”

A New Method for the Acquisition of Ultrasonic Strain Image Volumes

“…There is no change in axial compression while recording each volume, but a small change in compression is applied between them. This compression can be achieved in a laboratory setting using an external fixture to compress the scanning subject [1,8,10,15,20,22] or, in the case of ablation imaging, by controlled movement of the ablation electrode [2]. More practically, the probe movement can be applied by hand [26].…”