3D Ultrafast Shear Wave Absolute Vibro-Elastography using a Matrix Array Transducer (2309.00002v1)

Abstract: 3D ultrasound imaging provides more spatial information compared to conventional 2D frames by considering the volumes of data. One of the main bottlenecks of 3D imaging is the long data acquisition time which reduces practicality and can introduce artifacts from unwanted patient or sonographer motion. This paper introduces the first shear wave absolute vibro-elastography (S-WAVE) method with real-time volumetric acquisition using a matrix array transducer. In SWAVE, an external vibration source generates mechanical vibrations inside the tissue. The tissue motion is then estimated and used in solving a wave equation inverse problem to provide the tissue elasticity. A matrix array transducer is used with a Verasonics ultrasound machine and frame rate of 2000 volumes/s to acquire 100 radio frequency (RF) volumes in 0.05 s. Using plane wave (PW) and compounded diverging wave (CDW) imaging methods, we estimate axial, lateral and elevational displacements over 3D volumes. The curl of the displacements is used with local frequency estimation to estimate elasticity in the acquired volumes. Ultrafast acquisition extends substantially the possible S-WAVE excitation frequency range, now up to 800 Hz, enabling new tissue modeling and characterization. The method was validated on three homogeneous liver fibrosis phantoms and on four different inclusions within a heterogeneous phantom. The homogeneous phantom results show less than 8% (PW) and 5% (CDW) difference between the manufacturer values and the corresponding estimated values over a frequency range of 80 Hz to 800 Hz. The estimated elasticity values for the heterogeneous phantom at 400 Hz excitation frequency show average errors of 9% (PW) and 6% (CDW) compared to the provided average values by MRE. Furthermore, both imaging methods were able to detect the inclusions within the elasticity volumes.

• The paper presents a novel 3D ultrafast shear wave elastography method that reduces acquisition time to 0.05 seconds for rapid tissue elasticity estimation.
• It compares Plane Wave and Compounded Diverging Wave sequences, achieving errors under 8% in homogeneous phantoms and under 11% in complex tissues.
• The curl-based reconstruction and GPU optimizations enhance precision, paving the way for improved ultrasound-guided diagnostics and interventions.

Overview of 3D Ultrafast Shear Wave Absolute Vibro-Elastography

The paper presents a novel approach to real-time three-dimensional ultrafast elastography using a matrix array transducer for estimating tissue elasticity. The method, coined 3D Ultrafast Shear Wave Absolute Vibro-Elastography (S-WAVE), is significant in its potential utility for ultrasound-guided interventions, notably in assessing liver fibrosis and other medical procedures requiring precise, real-time imaging.

Methodology and Imaging Sequences

The 3D Ultrafast S-WAVE method utilizes a matrix array transducer coupled with a Verasonics ultrasound machine to acquire volumetric data at an exceptionally high frame rate of 2000 volumes per second. Two imaging sequences are proposed: Plane Wave (PW) and Compounded Diverging Wave (CDW). These sequences allow for the rapid acquisition of 100 radio frequency (RF) volumes within a mere 0.05 seconds. Utilizing a density-based approach, the tissue elasticity is estimated through a curl-based reconstruction method that mitigates issues from compressional wave artifacts.

Numerical Results

The validation involved homogeneous phantoms representative of liver conditions, as well as heterogeneous phantoms containing inclusions of varied elasticity. The experiments demonstrated that the proposed method achieved elasticity estimates with less than 8% deviation for PW and 5% for CDW compared to manufacturer-reported values in homogeneous phantoms. In complex heterogeneous phantoms, the average errors of elasticity estimates were 9% for PW and 6% for CDW, indicating a high concordance against Magnetic Resonance Elastography (MRE) benchmarks. Furthermore, ex vivo testing on bovine liver samples confirmed the feasibility of the method with elasticity results closely aligning with MRE and Acoustic Radiation Force Impulse (ARFI) metrics (less than 11% difference for PW and 9% for CDW).

Theoretical Implications and Future Prospects

The paper introduces important advancements in real-time volumetric imaging capabilities, addressing the limitations of previous 12-second acquisition times to under 0.05 seconds. The reduction in acquisition time is particularly valuable in clinical settings where patient motion and breath-hold requirements pose significant challenges. The extended frequency range up to 800 Hz facilitates a comprehensive tissue characterization, promising broader diagnostic and therapeutic applications.

Moreover, the implementation of a curl-based elasticity reconstruction improves the robustness of estimates against shear wave reflections, a recognized challenge in more conventional elastography techniques. The application of 3D displacement field analysis further enhances the precision of elasticity estimates and sets the stage for extending real-time elasticity imaging to more intricate clinical scenarios.

Given these enhancements, potential future developments may focus on real-time integration within clinical ultrasound systems and further GPU optimizations for displacement estimation. Such advancements could enable more routine usage in diagnosing and monitoring liver fibrosis and potentially other tissues where elasticity serves as a biomarker for disease.

Practical Implications

The practical implications of this technique are profound, with direct applications in point-of-care settings where rapid and reliable tissue characterization is critical. The ability to noninvasively quantify tissue elasticity could guide therapy in oncology and improve the monitoring of thermotherapy or other minimally invasive procedures. The implementation of a small footprint transducer broadens the feasibility of conducting specialized exams in diverse healthcare settings, including resource-limited environments.

In conclusion, the presented 3D Ultrafast S-WAVE method offers a sophisticated framework for real-time elastography, paving the way for significant advancements in ultrasound-guided diagnostics and therapeutic monitoring across various medical fields. The capabilities demonstrated in this paper underscore the method's potential impact as it transitions into clinical practice.