Freehand Ultrasound Elasticity Imaging in Liver Surgery

Study Procedures This is a prospective cohort study. Data will be collected from patients who have signed an informed consent form and are undergoing open, laparoscopic, or percutaneous RFA or MWA as their treatment for liver tumors. Their images will be assembled and correlated according to their IOUS characteristics plus processed strain images. Below is the description of how each aim will be accomplished.

Aim-1: Ultrasound Elasticity Imaging Acquisition. USEI data (both raw US data and B-mode data) will be recorded during standard operative ultrasound imaging used to guide thermal ablative therapy in the operating room. Images will be acquired before, during, and after RFA or MWA therapy. Raw data acquisition will be conducted using a Siemens Antares US scanner (Siemens Medical Solutions USA, Inc. Ultrasound Division, Issaquah, WA) with an ultrasound research interface (URI) to access raw US data. A Siemens VF 10-5 linear array will be used to acquire data using manual handling. Typically, the ultrasound probe is tracked and spatially registered with the coordinate frame of the of the CT images, so the pixels of the B-mode images are known in the coordinate frame of the CT volume. Thus if one localizes the target anatomy in the B-mode images, then the position of the target is automatically known with respect to the CT volume for validation of the performance of the elastography. The tracking beams are standard B-mode pulses (6.67 MHz center frequency, F/1.5 focal configuration, apodized, pulse repetition frequency (PRF) of 10.6 KHz, with a pulse length of 0.3μs). This US device is one of the standard machines available for clinical US.

We will track the ultrasound probe with an Electro-Magnetic (EM) tracker. The tracker has small sensors that can be attached to the ultrasound probe under the sterile cover of the ultrasound probe, and therefore the sensor is not exposed. Also, the tracker has a 'transmitter' that is flat and is placed underneath the patient below a soft cushion. The sensor is attached to the ultrasound probe prior to the surgery and hencethe probe will remain sterile. The transmitter is flat and will be placed under a soft cushion so that it does not cause any pressure effects on patient.

In both cases (raw data and B-mode), the freehand acquisition should allow for palpation (manual compression within few millimeters). Risks and discomforts are negligible: Interventional ultrasound is FDA-approved, and we will use only the data resulting from standard of care use of clinically certified equipment. The maximum length of a data recording session will be 1-2 minutes during standard ultrasound acquisition. We will acquire cine sequences for five defined periods: 1) tumor imaging before probe placement; 2) immediately after probe placement; 3) near completion during ablation; 4) two minutes following ablation with probe in place; and 5) after removing the ablator probe.