Counterbalancing the use of ultrasound contrast agents by a cavitation-regulated system.

The stochastic behavior of cavitation can lead to major problems of initiation and maintenance of cavitation during sonication, responsible of poor reproducibility of US-induced bioeffects in the context of sonoporation for instance. To overcome these disadvantages, the injection of ultrasound contrast agents as cavitation nuclei ensures fast initiation and lower acoustic intensities required for cavitation activity. More recently, regulated-cavitation devices based on the real-time modulation of the applied acoustic intensity have shown their potential to maintain a stable cavitation state during an ultrasonic shot, in continuous or pulsed wave conditions. In this paper is investigated the interest, in terms of cavitation activity, of using such regulated-cavitation device or injecting ultrasound contrast agents in the sonicated medium. When using fixed applied acoustic intensity, results showed that introducing ultrasound contrast agents increases reproducibility of cavitation activity (coefficient of variation 62% and 22% without and with UCA, respectively). Moreover, the use of the regulated-cavitation device ensures a given cavitation activity (coefficient of variation less 0.4% in presence of UCAs or not). This highlights the interest of controlling cavitation over time to free cavitation-based application from the use of UCAs. Interestingly, during a one minute sonication, while ultrasound contrast agents progressively disappear, the regulated-cavitation device counterbalance their destruction to sustain a stable inertial cavitation activity.

Numerical simulations of particle dynamics in a poststenotic blood vessel region within the scope of extracorporeal ultrasound stenosis treatment.

A numerical model was developed to predict the dynamics of a solid particle in a poststenotic blood vessel region. The flow through a 3D axisymmetric stenosis with 75% reduction in cross-section area was considered for inlet Reynolds numbers of 500 and 1000, which corresponds to typical values for the blood flow in human large arteries. Spherical particles were injected in the flow from the stenosis and tracked using the Discrete Phase Model (DPM) based on a Lagrangian approach. Within the scope of the development of ultrasound thrombolysis methods, the hydrodynamical forces predicted were used to evaluate the residence time of the particle and the minimal ultrasonic intensity required to keep it in the treatment region. For particle sizes larger than 400 µm, the intensity required appeared to be compatible with extracorporeal therapeutic ultrasound.

[Contribution of low-intensity pulsed ultrasounds to bone regeneration]. / Intérêt des ultrasons pulsés de faible intensité dans la stimulation de la régénération osseuse.

A maxillo-facial surgeon manages patients with bone defects due to trauma, malformations or of iatrogenic origin. The surgical management has potentially deleterious effects and its cost for society is increasing. Hence, it is crucial to develop techniques stimulating bone growth, stimulating the regeneration of a fracture or filling bone deficit. Ultrasounds (US), vibrations of the same nature as sound but with frequencies above the highest audible frequency for men (above 20 kHz), are used in many fields, particularly in medicine, usually at frequencies of around 0.5 to 5 MHz (million cycles per second). Their biological effects are not fully understood yet, but it is well known that US have effects on organic tissues when their mechanical energy is converted into thermic energy. These effects induce vasodilation and modification of membrane permeability. Several publications present the benefit of US for the stimulation of bone regeneration after a fracture. We present an overview of current knowledge on the effect of pulsed ultrasound on craniofacial bone regeneration, with study results conducted within Inserm unit U1032 in Lyon, the current reference lab on this issue.

[The impact of low intensity pulsed ultrasound on mouse skull bone osteoblast cultures]. / Ultrasons pulsés de faible intensité (LIPUS): effets sur des cultures d'ostéoblastes crâniens de souris.

INTRODUCTION: Low intensity pulsed ultrasound (LIPUS) is one of the methods used to stimulate bone regeneration. This technique is still not well known or explained. The expression of several proteins (VEGF, IL-8, FGF-ß, IL-1 ß) or genes (ALP and OP) was increased after being exposed to weak ultrasounds, whereas IL-6 and TNF-α were not affected. The purpose of this study was to verify and understand the mechanisms involved in this stimulation, and more specifically to understand if the stimulation concerned only cellular differentiation factors or if it also affected transcription of stem cells into osteoblasts. MATERIALS AND METHODS: Cultures of mouse skull bone osteoblasts were exposed to pulsed ultrasounds of varying intensities during three consecutive days. The effect of this stimulation was assessed by counting cells and determining the number of bone nodules formed. We studied various genes participating in osteoblast proliferation or in the differentiation and transcription of osteoblasts, using reverse transcriptase PCR. RESULTS: The cellular proliferation of osteoblasts was increased after stimulation by low intensity pulsed ultrasound. The expression of various genes involved in differentiation and transcription of stem cells into osteoblasts was increased, especially after stimulating at 100 mW/cm(2). DISCUSSION: Low intensity pulsed ultrasound allows stimulation of bone proliferation in vitro by stimulating osteoblastic differentiation and transcription.

[Craniofacial approach for orbital tumors and ultrasonic bone cutting]. / Voies d'abord craniofaciales des tumeurs orbitaires et découpe osseuse ultrasonique.

BACKGROUND: Removal of orbital tumors is a difficult problem. The goal of this study was to evaluate the advantages of the craniofacial approach to remove such tumors and to evaluate ultrasonic bone cutting during the procedure. METHOD: The authors reviewed their experience with 57 tumors of the posterior cavity using lateral craniofacial and frontal transsinus approaches. Orbital osteotomies were performed with mechanical instruments or piezoelectric bone surgery as a minimally invasive surgery. For each case, the quality of bone cutting and soft tissue damage were evaluated. RESULTS: Craniofacial approaches are simple and fast. Under the microscope, they provide a good view of the entire posterior orbital cavity. Using Piezosurgery, the functional results are good with no soft tissue damage. These advantages balance with the increased operative time required by ultrasonic bone cutting. CONCLUSION: This study shows the advantages of craniofacial approaches for removal of posterior orbital tumor. Moreover, the present preliminary report introduces and demonstrates the utility of piezoelectric bone surgery in craniofacial approaches for orbital tumors.

Ultrasonic osteotomy as a new technique in craniomaxillofacial surgery.

Ultrasound osteotomy is a new surgical technique used in dentistry to section hard tissues without damaging adjacent soft tissues. It was hypothesized that this could also be useful in craniofacial and orthognathic surgery. An ultrasonic device was employed in the following craniofacial surgical procedures: 144 Le Fort I osteotomies, 140 palatal expansions after Le Fort I osteotomies and 140 bilateral sagittal osteotomies; 2 Le Fort III osteotomies for treatment of Crouzon syndrome in two patients; 12 cases of unicortical calvarial bone grafting; removal of superior orbital roof in 25 cases of craniofaciostenosis; removal of external wall of the orbit in 10 cases of orbital cavity tumour; removal of anterior and posterior walls of the frontal sinuses in four cases of orbital cavity tumour. Integrity of soft tissues and surgical time were evaluated. Functional results were good without any soft-tissue damage being observed, but the overall operative time was increased. Ultrasound osteotomy is a new technical procedure that is advantageous for bone cutting in multiple situations, with minimal to no damage in adjacent soft tissues such as brain, palatal mucosa and the inferior alveolar nerve.

Distortion product otoacoustic emissions and sensorineural hearing loss.

As other types of otoacoustic emissions, distortion product otoacoustic emissions (DPOAEs) allow the exploration of the active cochlear mechanisms known to take place in the outer hair cell system. Most authors consider that 2f1-f2 DPOAEs are generated in a cochlear region corresponding to the geometric mean (GM) of the primary frequencies. To verify the relevance of this hypothesis in clinical practice, DPOAEs were recorded at seven different frequencies, ranging from 0.5 to 4 kHz, in 81 hearing-impaired patients and in 24 normally hearing subjects. To test the hypothesis that DPOAEs reflect the hearing threshold at the frequency of the GM rather than at the 2f1-f2 frequency, this study compares the 2f1-f2 frequency and the GM of the primaries to the frequency of hearing loss. DPOAEs can be used to explore a large range of frequencies, especially at high frequencies, but responses at low frequencies are less reliable due to noise contamination. Secondly, DPOAEs can be recorded in ears that have a hearing threshold as high as 65 dB HL at the frequency corresponding to the GM of the primaries. Finally, DPOAE recordings show frequency specificity: i.e., hearing loss at a specific frequency correlates best with DPOAEs whose GM of primary frequencies corresponds to the frequency of the hearing loss. However, this frequency specificity is still unsatisfactory and decreases as the levels of primaries increase above 60 dB SPL. Moreover, DPOAE amplitude is too variable to predict hearing loss at a particular frequency, whereas DPOAE threshold allows a correct prediction of abnormal auditory threshold in more than 80% of the cases at frequencies above 1 kHz.