Non-invasive photo acoustic approach for human bone diagnosis

An NIR-II Probe with High PSMA Affinity Demonstrates an Unexpected Excellent Bone Imaging Ability

(S)-3-(Carboxyformamido)-2-(3-(carboxymethyl)ureido)propanoic acid (EuK) is a known binder toward the prostate-specific membrane agent (PSMA) with strong affinity, making it a popular choice for prostate cancer medicine development. However, during the probe modification, a new EuK-based PSMA tetramer, Bone-1064, was discovered to have an unexpected and intense uptake in bone, which has not yet been reported in any previous studies yet. After administration, Bone-1064 allowed for high contrast visualization of the bone from surrounding tissues with a signal-to-background ratio of 10.22 at 24 h postinjection. In contrast, the tumor had a blurry contour, and the maximum tumor-to-normal-tissue ratio was only 2.22. Further imaging studies revealed that Bone-1064 binds specifically to hydroxyapatite in bone tissues, instead of PSMA. Overall, Bone-1064 is an excellent bone probe with a unique structure that can be used for NIR-II fluorescence imaging in animal models. Meanwhile, this modification study might also inspire further PSMA probe designations.

Photoacoustic Imaging and Characterization of Bone in Medicine: Overview, Applications, and Outlook

Photoacoustic techniques have shown promise in identifying molecular changes in bone tissue and visualizing tissue microstructure. This capability represents significant advantages over gold standards (i.e., dual-energy X-ray absorptiometry) for bone evaluation without requiring ionizing radiation. Instead, photoacoustic imaging uses light to penetrate through bone, followed by acoustic pressure generation, resulting in highly sensitive optical absorption contrast in deep biological tissues. This review covers multiple bone-related photoacoustic imaging contributions to clinical applications, spanning bone cancer, joint pathologies, spinal disorders, osteoporosis, bone-related surgical guidance, consolidation monitoring, and transsphenoidal and transcranial imaging. We also present a summary of photoacoustic-based techniques for characterizing biomechanical properties of bone, including temperature, guided waves, spectral parameters, and spectroscopy. We conclude with a future outlook based on the current state of technological developments, recent achievements, and possible new directions.

Influence of optical transmissivity on signal characteristics of photoacoustic guided waves in long cortical bone

Long cortical bone allows axial transmission of ultrasonic guided waves, which has been utilized for osteoporosis evaluation. Benefiting structural and molecular sensitivity, photoacoustic has been used for tissue composition characterization. However, photoacoustic guided waves (PAGWs) in long cortical bone as well as the influence of optical transmissivity on PAGWs have not been thoroughly investigated. In the study, the influence of optical transmissivity on the signal characteristics of PAGWs was experimentally studied with a 1064 nm pulsed laser ultrasonic system and a tunable laser system (wavelength range: 650-2600 nm). Results show that dispersion curves of PAGWs are not significantly affected by the optical transmissivity; while photoacoustic guided modes and signal spectrum are sensitive to the optical transmissivity in cortical bone. In experiments, the lasers with high transmissivity can emit pure A₀ mode PAGWs at the low frequency, around 22 kHz, in the relatively thick 6.2 mm bone plate; on the contrary, both A₀ and S₀ modes are generated. The slope of power spectrum density (PSD) of PAGWs decreases with the increase of transmissivity, and the decline rate is around -0.229. The study proves the correlation between the signal characteristics of PAGWs and the optical transmissivity, it is helpful for the development of PAGWs in long cortical bone towards the osteoporosis evaluation.

Review of Photoacoustic Imaging for Imaging-Guided Spinal Surgery

This review introduces the current technique of photoacoustic imaging as it is applied in imaging-guided surgery (IGS), which provides the surgeon with image visualization and analysis capabilities during surgery. Numerous imaging techniques have been developed to help surgeons perform complex operations more safely and quickly. Although surgeons typically use these kinds of images to visualize targets hidden by bone and other tissues, it is nonetheless more difficult to perform surgery with static reference images (e.g., computed tomography scans and magnetic resonance images) of internal structures. Photoacoustic imaging could enable real-time visualization of regions of interest during surgery. Several researchers have shown that photoacoustic imaging has potential for the noninvasive diagnosis of various types of tissues, including bone. Previous studies of the surgical application of photoacoustic imaging have focused on cancer surgery, but photoacoustic imaging has also recently attracted interest for spinal surgery, because it could be useful for avoiding pedicle breaches and for choosing an appropriate starting point before drilling or pedicle probe insertion. This review describes the current instruments and clinical applications of photoacoustic imaging. Its primary objective is to provide a comprehensive overview of photoacoustic IGS in spinal surgery.

Photoacoustic imaging of a human vertebra: implications for guiding spinal fusion surgeries

It is well known that there are structural differences between cortical and cancellous bone. However, spinal surgeons currently have no reliable method to non-invasively determine these differences in real-time when choosing the optimal starting point and trajectory to insert pedicle screws and avoid surgical complications associated with breached or weakened bone. This paper explores 3D photoacoustic imaging of a human vertebra to noninvasively differentiate cortical from cancellous bone for this surgical task. We observed that signals from the cortical bone tend to appear as compact, high-amplitude signals, while signals from the cancellous bone have lower amplitudes and are more diffuse. In addition, we discovered that the location of the light source for photoacoustic imaging is a critical parameter that can be adjusted to non-invasively determine the optimal entry point into the pedicle. Once inside the pedicle, statistically significant differences in the contrast and SNR of signals originating from the cancellous core of the pedicle (when compared to signals originating from the surrounding cortical bone) were obtained with laser energies of 0.23-2.08 mJ (p  <  0.05). Similar quantitative differences were observed with an energy of 1.57 mJ at distances  ⩾6 mm from the cortical bone of the pedicle. These quantifiable differences between cortical and cancellous bone (when imaging with an ultrasound probe in direct contact with each bone type) can potentially be used to ensure an optimal trajectory during surgery. Our results are promising for the introduction and development of photoacoustic imaging systems to overcome a wide range of longstanding challenges with spinal surgeries, including challenges with the occurrence of bone breaches due to misplaced pedicle screws.

Dynamic thermal/acoustic response for human bone materials at different energy levels: A diagnosis approach

BACKGROUND

The non-invasive diagnostic approaches have gained high attention in recent years, utilizing high technology sensor systems, including infrared, microwave devices, acoustic transducers, etc. The patient safety, high resolution images, and reliability are among the driving forces toward high technology approaches. The thermal and acoustic responses of the materials may reflect the important research parameters such as penetration depth, power consumption, and temperature change used for the practical models of the system. This paper emphasizes the approach for orthopedic application where the bone densities were considered in simulation to designate the type of human bones.

METHODS

Thermal energy pulses were applied in order to study the penetration depth, the maximum temperature change; spatially and dynamically, and the acoustic pressure distribution over the bone thickness. The study was performed to optimize the amount of energy introduced into the materials that generate the temperature value for high resolution beyond the noise level.

RESULTS

Three different energy pulses were used; 1 J, 3 J and 5 J. The thermal energy applied to the four bone materials, cancellous bone, cortical bone, red bone marrow, and yellow bone marrow were producing relative changes in temperature. The maximum change ranges from 0.5 K to 2 K for the applied pulses. The acoustic pressure also ranges from 210 to 220 dB among the various types of bones.

CONCLUSION

The results obtained from simulation suggest that a practical model utilizing infra-red scanning probe and piezoelectric devices may serve for the orthopedic diagnostic approach. The simulations for multiple layers such as skin interfaced with bone will be reserved for future considerations.