Cortical Bone Assessment Using Ultrasonic Guided Waves: A Reproducibility Study in a Healthy Population

The idea of the research is to develop a clinical device for cortical bone measurements using ultrasound so it can be portable, at least transportable, and non-ionizing. The measurement principle is based on ultrasonic guided waves, both frequency depends on both materials and geometry of cortical bone. The current gold standard for bone assessment is DXA, the X-ray bone densitometry.

It provides a bone mineralosity. It's very useful, but has some limitation. First, it requires a dedicated room.

Its ability for discrimination is only moderate, and then it's not widely available in many parts of the world, like Latin American, in particular in the public health system. You can use other device for bone assessment like MRI or QCT, but they are larger and even less available. Finally, it appears that ultrasound is a very interesting and promising alternative.

The first challenge is to find useful clinical parameters. In this study, we have two kind of parameters, preparation velocity, which are very easy, a robust measure, but not so easy to interpret. And we have also cortical thickness and porosity, which are more easy to interpret in term of quality and quantity of bone, but less easy to measure.

And then the second challenge is to measure this parameter in a very precise and reliable way.Why? We want to measure very small difference between patients. For the next step, our lab will focus on the design on the next generation of the device, which will be hopefully very portable, thanks to the advance of electronics.

We will also incorporate new clinical parameters issued from artificial intelligence and machine learning. And finally, we will also focus on different fragility fracture sites, in particular for hip fracture, with the idea to improve the prevention and the following of patients. To begin, arrange the electric insulation transformer electronic module and laptop side by side on a large table, ensuring sufficient space in front of these parts to place the participant's forearm.

Plug the electric insulation transformer into the room's domestic power source using a dedicated cable. Connect the electronic module to the electric insulation transformer with a dedicated power cable. Press the on button on the transformer to power the module, then turn on the electronic module.

Next, connect the laptop to the module using the dedicated USB cable to enable the transmission of digitized signals to the computer. If the laptop requires power, connect its power cable to the electric insulation transformer. Attach the ultrasonic probe to the module using the dedicated cable slot located on the module's front side.

Place the pedal switch on the floor near the operator's feet, ensuring easy access during measurement. Connect the pedal switch to the laptop using a USB cable. To begin, invite the participant to sit in front of the operator with their naked forearm resting on the table in front of the bidirectional axial transmission ultrasonic device.

Measure the radius length using a ruler from the radial styloid to the elbow. Divide the length by three. Then mark the measurement site one third of the distal radius using a pen.

Click on the human machine interface or HMI icon on the laptop. In the pop-up window, add the participant's data, including anonymized ID, laterality, measured site, operator's ID, and gender. Next, apply eco-graphic gel to the front side of the ultrasonic probe and to the marked measurement site on the participant's forearm to ensure ultrasonic wave propagation.

Place the probe in contact with the forearm, aligning its center with the mark. After placing the probe in contact with the marked location on the forearm of the participant, click on the START button located at the bottom right corner of the HMI software. Observe the velocities of the first arriving signal, or VFOS parameter value, displayed in the interface, which updates every 0.5 seconds.

Slowly adjust the probe position to achieve a vFAS parameter value within the normal range of 3800 to 4200 meters per second. Next, adjust the probe position while observing the bidirectional value displayed in a specific case of the interface. Apply gentle pressure to one side of the probe to reduce the absolute angle value to less than 2 degrees, ensuring better parallelism between the probe and the bone surface.

Adjust the probe position while observing the VA0 parameter value to displayed on the interface. Then aim for a value within the normal range of 1, 500 to 1, 900 meters per second, ensuring that the VA0 variation between successive calculations is less than 40 meters per second. In case of difficulty, refer to the guided wave image spectra in the right column of the interface.

Confirm that the upper spectrum appears as a continuous line with a slope representing the VA0 value. Next, observe the inverse problem image, which appears automatically once the vFAS and VA0 velocities and angle values stabilize. Confirm that the image contains one maximum indicated with a clear pixel and one or several secondary maxima indicated with a different color.

The three missing quality parameters, max, diff, and low K are automatically calculated in real time. Slowly adjust the probe position while observing the inverse problem image maxima. Aim to find the highest possible first maximum and the lowest possible secondary maximum using the corresponding cases on the interface.

In case of difficulty, observe the guided wave spectrum image in the right column of the interface. Ensure the lower part of the spectrum has continuous lines representing high phase velocity modes with the parameter quality, low K, as high as possible. Once an acceptable inverse problem image is achieved, stabilize the probe position and ensure no significant changes between successive calculations.

Once a stable position is achieved, press the pedal switch with the foot to start a series of 10 acquisitions. After the series ends, observe the means and standard deviations of the parameters of interest. If the standard deviations are below fixed thresholds, accept the series.

Otherwise, reject it. After pressing the STOP option, verify that the final values are automatically reported in the PDF generated. Verify the second precise report generated using exact wave guide model values for the inverse problem calculations instead of approximated values used in the first automatic report.

Compare the automatic and precise reports to ensure consistency. Remove inconsistent series that are not automatically eliminated to finalize the dataset.