Dual-Modal Multi-Aperture Photoacoustic and Ultrasound Imaging for Guiding Minimally Invasive Surgery

Project summary:  Many minimally invasive procedures such as nerve blocks, tumour biopsy, and fetal interventions, are performed under ultrasound guidance because of its real-time imaging capability, low-cost, and high accessibility. However, visualisation of the procedure target (such as nerves, and tumours), and the invasive medical devices (such as metallic needles) with currently clinical ultrasound imaging systems can be challenging. Ultrasound images suffer from limited spatial resolution, restricted field of view, and low soft-tissue contrast.  

  

This project aims to address these limitations by developing a dual-modal photoacoustic and ultrasound imaging system using multiple synchronised ultrasound transducer arrays that can provide functional, molecular and anatomical information of tissue in real-time with improved spatial resolution and extended field of view for guiding minimally invasive procedures.  

 
Project description:

Ultrasound (US) imaging is widely used for guiding many minimally invasive procedures including peripheral nerve blocks, tumour biopsy, central catheter placement in neonates and sampling of amniotic fluid during pregnancy. However, critical tissue targets (such as nerves, and tumour tissue), and invasive medical devices used during these procedures, (such as medical needles and catheters), are often difficult to visualise and sometimes even invisible on ultrasound images. This is because current clinical US imaging systems have several prominent limitations including the limited resolution and field of view due to the small aperture of the hand-held ultrasound probe, and the inherently insufficient soft tissue contrast.  Loss of visibility of critical tissue structures and medical devices can lead to life-threatening complications.  

 

Photoacoustic (PA) imaging is an emerging biomedical imaging modality that is based on the excitation of ultrasound waves from tissue chromophores with pulsed or modulated light. PA imaging thus inherits advantages from both ultrasound imaging and optical imaging, capable of providing distinct spectroscopic contrast from tissue with high spatial resolution and penetration depths. PA imaging can be readily combined with ultrasound imaging by sharing the same ultrasound probe to provide complementary information, with PA imaging highlighting the critical tissue structures (such as nerves, blood vessels, and tumours), and ultrasound imaging providing patient anatomy as demonstrated in pre-clinical studies as part of a Wellcome/EPSRC funded project GIFT-Surg [1-2].  

 

Recently, the feasibility of coherent ultrasound imaging with multiple transducers has been demonstrated, showing significant improvements in resolution, sensitivity, and field of view compared to conventional single-transducer ultrasound imaging [3-4]. A prototype coherent multi-transducer US imaging system has been developed by the supervisors’ team in a Wellcome/EPSRC funded project iFIND. Similarly, PA imaging could also benefit from the coherent use of multiple ultrasound transducers. Such a system will add flexibility to the US receiver locations in practice, improve the signal-to-noise ratio, and enhance resolution.    

 

This project aims to develop a dual-modal multi-aperture PA and US imaging system that will address some of the current limitations of US and PA imaging for guiding minimally invasive procedures. This will be achieved by the following three main tasks: 

 

1. Development of a dual-modal PA and US imaging system with a single ultrasound probe (Year 1). This involves the integration of PA excitation light source into an ultrasound imaging system. The ultrasound transmission and receiving sequences will be programmed to accommodate the two modalities. 

1. Development of a multi-aperture PA and US imaging system and image reconstruction algorithms (Years 2-3).   

1. Validation of the imaging system on tissue-mimicking phantoms and human volunteers (Year 3-4).  

 

References 

[1] Xia W, et al. Sensors. 2018 May;18(5):1394. 

[2] Xia W, et al. J. Biomed. Opt. 2015 Aug;20(8):086005. 

[3] Peralta L, et al. IEEE TUFFC, 2019, 66(8), 1316-1330.  

[4] Peralta L, et al. Applied Sciences. 2020 Jan;10(21):7655. 

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