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. 2008 Aug;34(8):1307-16.
doi: 10.1016/j.ultrasmedbio.2008.01.007. Epub 2008 Mar 28.

Three-dimensional electrode displacement elastography using the Siemens C7F2 fourSight four-dimensional ultrasound transducer

Shyam Bharat  1 , Ted G Fisher, Tomy Varghese, Timothy J Hall, Jingfeng Jiang, Ernest L Madsen, James A Zagzebski, Fred T Lee Jr
Affiliations

Three-dimensional electrode displacement elastography using the Siemens C7F2 fourSight four-dimensional ultrasound transducer

Shyam Bharat et al. Ultrasound Med Biol. 2008 Aug.

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 (e.g., radio-frequency 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 article, we present a method for three-dimensional (3D) elastographic reconstruction from volumetric data acquired using the C7F2 fourSight four-dimensional ultrasound transducer, provided by Siemens Medical Solutions USA, Inc. (Issaquah, WA, USA). 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 radio-frequency ablation. Postprocessing is done on the acquired raw radio-frequency 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.

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Figures

Figure 1
Figure 1
Schematic diagram of the single-spherical inclusion phantom with an electrode embedded in the inclusion. The ultrasound transducer is placed adjacent to the electrode. The dotted line represents one plane of the 3D sector volume imaged by the transducer.
Figure 2
Figure 2
(a) Photograph of the C7F2 fourSight 4D ultrasound transducer (Siemens Medical Solutions, USA, Inc.). This curvilinear transducer contains a 192-element array that can be mechanically rotated to scan a sector volume of the target. (b) Illustration of the geometry of the set-up for imaging the TM phantom. The transducer is placed adjacent to the electrode and held firmly in place by a clamp (not in picture). (c) Schematic of the 3D data acquisition sequence. The dotted lines represent the different planes imaged by the transducer. Starting at one end, the transducer elements are mechanically ‘rocked’ at pre-specified angular increments to step through the entire sector volume, acquiring a 2D frame of data at each position.
Figure 2
Figure 2
(a) Photograph of the C7F2 fourSight 4D ultrasound transducer (Siemens Medical Solutions, USA, Inc.). This curvilinear transducer contains a 192-element array that can be mechanically rotated to scan a sector volume of the target. (b) Illustration of the geometry of the set-up for imaging the TM phantom. The transducer is placed adjacent to the electrode and held firmly in place by a clamp (not in picture). (c) Schematic of the 3D data acquisition sequence. The dotted lines represent the different planes imaged by the transducer. Starting at one end, the transducer elements are mechanically ‘rocked’ at pre-specified angular increments to step through the entire sector volume, acquiring a 2D frame of data at each position.
Figure 2
Figure 2
(a) Photograph of the C7F2 fourSight 4D ultrasound transducer (Siemens Medical Solutions, USA, Inc.). This curvilinear transducer contains a 192-element array that can be mechanically rotated to scan a sector volume of the target. (b) Illustration of the geometry of the set-up for imaging the TM phantom. The transducer is placed adjacent to the electrode and held firmly in place by a clamp (not in picture). (c) Schematic of the 3D data acquisition sequence. The dotted lines represent the different planes imaged by the transducer. Starting at one end, the transducer elements are mechanically ‘rocked’ at pre-specified angular increments to step through the entire sector volume, acquiring a 2D frame of data at each position.
Figure 3
Figure 3
(a) The picture shows liver tissue encased in a gelatin block after an RF ablation procedure using a Valleylab Cool-tip™ ablation electrode. (b) Illustration of the placement of the transducer for acquiring 3D data on the liver encased in the gelatin block. The top end of the RF electrode is clamped to a holder attached to a stepper motor, to provide precise displacements.
Figure 3
Figure 3
(a) The picture shows liver tissue encased in a gelatin block after an RF ablation procedure using a Valleylab Cool-tip™ ablation electrode. (b) Illustration of the placement of the transducer for acquiring 3D data on the liver encased in the gelatin block. The top end of the RF electrode is clamped to a holder attached to a stepper motor, to provide precise displacements.
Figure 4
Figure 4
(a) B-mode image of the central plane of the inclusion. (b) Corresponding strain image, in which the inclusion is depicted as a circular dark region in the center. The decorrelation (halo-like appearance) around the inclusion serves to delineate the inclusion from the background.
Figure 4
Figure 4
(a) B-mode image of the central plane of the inclusion. (b) Corresponding strain image, in which the inclusion is depicted as a circular dark region in the center. The decorrelation (halo-like appearance) around the inclusion serves to delineate the inclusion from the background.
Figure 5
Figure 5
Elastogram showing strain artifacts within the inclusion, arising from the motion of the RF electrode. The ROI shows the image pixels used to correct for these artifacts using the procedure described in the text.
Figure 6
Figure 6
3D surface rendering of the inclusion obtained by stacking together segmented versions of 2D strain images of all the planes of the TM phantom scanned by the transducer.
Figure 7
Figure 7
(a) B-mode image of approximately the central plane of the thermal lesion contained in the liver which is encased in the gelatin block. (b) Corresponding strain image, in which the lesion corresponds to the dark region surrounded by a halo.
Figure 7
Figure 7
(a) B-mode image of approximately the central plane of the thermal lesion contained in the liver which is encased in the gelatin block. (b) Corresponding strain image, in which the lesion corresponds to the dark region surrounded by a halo.
Figure 8
Figure 8
Elastogram showing strain artifacts within the lesion, arising from the motion of the RF electrode. The ROI shows the image pixels used to correct for these artifacts using the procedure described in the text.
Figure 9
Figure 9
Overlay of the lesion boundaries (from the strain image) on the corresponding B-mode image, illustrating the poor contrast on the B-mode image. Also note that the gas bubbles on the B-mode image do not correspond to the exact location of the lesion.
Figure 10
Figure 10
(a) 3D surface rendering of the lesion obtained by stacking together segmented versions of 2D strain images of all the planes of the liver tissue in the gelatin block scanned by the transducer. (b) Variation in the size of lesion depiction on successive strain images as we step through the 3D data set in the elevational direction.
Figure 10
Figure 10
(a) 3D surface rendering of the lesion obtained by stacking together segmented versions of 2D strain images of all the planes of the liver tissue in the gelatin block scanned by the transducer. (b) Variation in the size of lesion depiction on successive strain images as we step through the 3D data set in the elevational direction.
See this image and copyright information in PMC

References

    1. Bharat S, Madsen EL, Zagzebski JA, Varghese T. Radiofrequency Electrode Displacement Elastography - A Phantom Study. 4th International Conference on the Ultrasonic Measurement and Imaging of Tissue Elasticity; Austin, TX. 2005.
    1. Bharat S, Varghese T. Contrast-transfer improvement for electrode displacement elastography. Physics in Medicine and Biology. 2006;51:6403–6418. - PubMed
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