Ultrasound monitoring of microcirculation: An original study from the laboratory bench to the clinic.

OBJECTIVE: Monitoring microcirculation and visualizing microvasculature are critical for providing diagnosis to medical professionals and guiding clinical interventions. Ultrasound provides a medium for monitoring and visualization; however, there are challenges due to the complex microscale geometry of the vasculature and difficulties associated with quantifying perfusion. Here, we studied established and state-of-the-art ultrasonic modalities (using six probes) to compare their detection of slow flow in small microvasculature. METHODS: Five ultrasonic modalities were studied: grayscale, color Doppler, power Doppler, superb microvascular imaging (SMI), and microflow imaging (MFI), using six linear probes across two ultrasound scanners. Image readability was blindly scored by radiologists and quantified for evaluation. Vasculature visualization was investigated both in vitro (resolution and flow characterization) and in vivo (fingertip microvasculature detection). RESULTS: Superb Microvascular Imaging (SMI) and Micro Flow Imaging (MFI) modalities provided superior images when compared with conventional ultrasound imaging modalities both in vitro and in vivo. The choice of probe played a significant difference in detectability. The slowest flow detected (in the lab) was 0.1885 ml/s and small microvasculature of the fingertip were visualized. CONCLUSIONS: Our data demonstrated that SMI and MFI used with vascular probes operating at higher frequencies provided resolutions acceptable for microvasculature visualization, paving the path for future development of ultrasound devices for microcirculation monitoring.

Automatic detection of cotton balls during brain surgery: Where deep learning meets ultrasound imaging to tackle foreign objects.

Cotton balls are a versatile and efficient tool commonly used in neurosurgical procedures to absorb fluids and manipulate delicate tissues. However, the use of cotton balls is accompanied by the risk of accidental retention in the brain after surgery. Retained cotton balls can lead to dangerous immune responses and potential complications, such as adhesions and textilomas. In a previous study, we showed that ultrasound can be safely used to detect cotton balls in the operating area due to the distinct acoustic properties of cotton compared with the acoustic properties of surrounding tissue. In this study, we enhance the experimental setup using a 3D-printed custom depth box and a Butterfly IQ handheld ultrasound probe. Cotton balls were placed in variety of positions to evaluate size and depth detectability limits. Recorded images were then analyzed using a novel algorithm that implements recently released YOLOv4, a state-of-the-art, real-time object recognition system. As per the radiologists' opinion, the algorithm was able to detect the cotton ball correctly 61% of the time, at approximately 32 FPS. The algorithm could accurately detect cotton balls up to 5mm in diameter, which corresponds to the size of surgical balls used by neurosurgeons, making the algorithm a promising candidate for regular intraoperative use.

DESIGN OF AN ULTRASOUND PROBE HOLDER TO MINIMIZE MOTION ARTIFACT DURING SONOGRAPHY.

Standard diagnostic ultrasound imaging procedures heavily rely on the human operator for image acquisition. This may lead to unnecessary artifacts in the images, since involuntary hand movement is unavoidable. Certain surgical procedures also involve "jump" movement of the subject on the operating table, further exacerbating image quality. In this study, we attempt to mitigate the problem by designing an ultrasound probe holder using 3D printing. This holder would potentially be light enough to attach to surgical retractors, thus eliminating operator intervention and relative motion between the probe and the patient.

DESIGN AND FABRICATION OF A FOCUSED ULTRASOUND DEVICE FOR MINIMALLY-INVASIVE NEUROSURGERY: REPORTING A SECOND, MINIATURIZED AND MR-COMPATIBLE PROTOTYPE WITH STEERING CAPABILITIES.

Many surgeons are faced with inoperable or only partially operable brain lesions, such as tumors. Even when surgery is feasible, patient outcome is greatly affected by blood loss or infection. This has led many physicians toward non- or minimally-invasive surgery, which demands specialized toolkits. Focused ultrasound has great potential for assisting in such procedures due to its ability to focus a few cm away from the surface of the transducer. In a prior study, we developed a focused ultrasound prototype that could fit within a BrainPath trocar, specifically made for minimally invasive brain surgery. Here, we present the design and fabrication of a second prototype that reduces size, is MR-compatible, and has electronic steering capabilities.

A MINIATURE LASER SPECKLE CONTRAST IMAGER FOR MONITORING OF THE NEURO-MODULATORY EFFECT OF TRANSCRANIAL FOCUSED ULTRASOUND STIMULATION.

Transcranial focused ultrasound stimulation is a neuromodulation technique that is capable of exciting or suppressing the neural network. Such neuro-modulatory effects enable the treatment of brain diseases non-invasively, such as treating stroke. The neuro-modulatory effect on cerebral hemodynamics has been monitored using laser speckle contrast imaging in animal studies. However, the bulky size and stationary nature of the imaging system constrains the application of this imaging technique on research that requires the animal to have different body positions or to be awake. We present the design of a system that combines a miniature microscope for laser speckle contrast imaging and transcranial focused ultrasound stimulation, as well as, test its capability to monitor cerebral hemodynamics during stimulation and compare the result with a benchtop imaging system.