1,720,973 research outputs found
Exact solution to the inverse Womersley problem for pulsatile flows in cylindrical vessels, with application to magnetic particle targeting
No full textAn exact solution to the inverse Womersley problem was derived for the fully-developed, laminar pulsatile flow of a viscous Newtonian fluid, within a circular cylindrical vessel with rigid walls. In particular, given an arbitrary, time-periodic flow rate, the axisymmetric velocity profile was obtained by means of two neat and computable maps relating the corresponding Fourier coefficients. The study of such an inverse problem is motivated by the fact that flow rate is the main physical quantity which can be actually measured in many practical situations. The hypothesis of a fully-developed flow was deliberately introduced, in order to obtain an analytical solution (otherwise hardly achievable). Despite the intrinsic simplifications associated with the adopted position (which restrict the applicability of our results to 3D finite-length complex domains, and non-Newtonian fluids), the obtained solution provides a benchmark – and at the same time an approximation – for the inverse problem of pulsatile flows, it may serve as a debugging tool for more ambitious numerical approaches based on realistic data, and can also be used as an improved source of boundary data. As expected, the main advantage of our analytical solutions (compared to fully numerical approaches) resides in computational efficiency; this was quantitatively assessed through numerical tests. Moreover, the proposed solution was applied in the context of magnetic particle targeting, to highlight some peculiar effects on particle trajectories and capture efficiency due to pulsatility. Such a transport problem is increasingly drawing the attention of an interdisciplinary community, ranging from physicians to biomedical engineers, physicists and roboticists, thanks to its potential for targeted therapy, up to remote guidance of intravascular devices. More in general, the obtained benchmark solution holds potential for effectively exploitation in an interdisciplinary context
Removing vascular obstructions: a challenge, yet an opportunity for interventional microdevices
No full textQualitative assessment of thermal effects in high intensity ultrasound thrombolysis experiments
No full textObjective
High Intensity Focused Ultrasounds (HIFU) demonstrated the ability to destroy blood clots without addiction of
thrombolytic drugs. However, the involved physical principles are yet unclear, thus slowing a translation to clinical
application. It is agreed that thermal effects must be avoided; however it is hard to directly measure the temperature
because of the dynamics of the procedures.
Methods
We demonstrated the possibility to break human blood clots in an in-vitro system. We used a commercial HIFU
transducer (Precision Acoustics) with focus dimensions (previously mapped) of 2.2mm and 23mm (-6dB focal radius
and length). Acoustic parameters were: frequency 1MHz, pulse length 450μs, duty cycle (d.c.) 10%, output power 65W,
therapy duration (t.d.) 120s.
Results
We used long segments of porcine clots (similar acoustic properties of human thrombi but easier to produce) to evaluate
the presence of thermal effects, by varying the duty cycle of the sonication protocol. The following parameters were
adopted in order to maintain the same amount of delivered energy: A. d.c. 100% t.d. 20s; B. d.c. 50% t.d. 40s; C. d.c.
10% (same as thrombolysis experiments) t.d. 200s; D. d.c. 0% (control).
After sonication, porcine clots were cut in correspondence of the produced lesion and were observed under a digital
microscope (HiroxKH7700, magnification 20x). The following features were observed:
A. evidence of necrotic tissue, surface erosion and internal holes;
B. moderate necrosis and surface erosion;
C. presence of surface erosion, no evidence of thermal lesions;
D. homogeneous and uniform surface.
Conclusions
The absence of visible thermal lesions enforces the hypothesis of mechanical effects in HIFU thrombolysis. Inertial
cavitation should play an important role in the phenomenon and must be detected and quantified, and possibly enhanced
by microbubbles. We implemented a system which detects acoustic emission of collapsing bubbles (i.e. broadband
noise at high frequencies) in order to assess the influence of this phenomenon in thrombolysis
Inertial cavitation detection during in-vitro sonothrombolysis
Full text linkBackground
Cardiovascular diseases are the leading cause of death worldwide; a prompt intervention is needed to restore
blood flow. Sonothrombolysis with or without addiction of thrombolytic drugs seems to be a promising
solution, thanks to the non-invasiveness, precision and quickness of its action. Mechanical effects, rather
than thermal, are employed. Even if the mechanisms involved are not completely understood, acoustic
cavitation is credited to play a significant role.
Materials and Methods
An experimental setup to detect acoustic cavitation during in-vitro sonothrombolysis tests has been
developed. A Passive Cavitation Detector (PCD), able to record pressure fluctuation of oscillating bubbles, is
mounted confocally to a 1MHz focused ultrasound transducer. Confocality has been verified by a 0.2mm
needle hydrophone to map the pressure fields of both devices. A LDPE tube containing the thrombus is
placed at the foci thanks to a 3 axis positioning frame. A constant flow of 2ml/min is established.
To detect inertial cavitation (broadband emission with an increase in white noise) , the original signal from
the PCD has been filtered analogically at 5MHz in order to remove harmonic frequencies which could
saturate the acquisition system.
Results
In-vitro sonothrombolysis tests have been carried out on human blood clots. Clots were exposed for two
minutes to an acoustic field of 65W (focal length 25mm, focal diameter 3mm), with pulse length of 450μs
and a duty cycle of 1:10. Acquisition of PCD signal was synchronized with the burst; two windows per
second at a sampling frequency of 40MHz were acquired. Power spectral density was calculated in the 5-12MHz band, with digital notch filters at the super-harmonic frequencies, in order to quantify the cavitation
dose. Figure on the left shows the results of two tests with the same acoustic parameters. Blue line refers to a
test in which there was no evidence of thrombolysis. When complete thrombus disruption took place a
temporal correlation between thrombolysis inception and the increment of white noise can be observed (red
line).
Conclusion
The proposed setup demonstrated the ability to detect inertial cavitation while performing in-vitro
sonothrombolysis tests; a correlation between thrombolysis inception and increment of white noise was
found. Statistically significant analysis will be performed in order to verify this correlation, thus allowing the
optimization of sonothrombolysis parameters and protocols in order to enhance cavitational effects
Speed of sound in rubber-based materials for ultrasonic phantoms
No full textPurpose: In this work we provide measurements of speed of sound (SoS) and acoustic impedance (Z) of some doped/non-doped rubber-based materials dedicated to the development of ultrasound phantoms. These data are expected to be useful for speeding-up the preparation of multi-organ phantoms which show similar echogenicity to real tissues. Methods: Different silicones (Ecoflex, Dragon-Skin Medium) and polyurethane rubbers with different liquid (glycerol, commercial detergent, N-propanol) and solid (aluminum oxide, graphene, steel, silicon powder) inclusions were prepared. SoS of materials under investigation was measured in an experimental setup and Z was obtained by multiplying the density and the SoS of each material. Finally, an anatomically realistic liver phantom has been fabricated selecting some of the tested materials. Results: SoS and Z evaluation for different rubber materials and formulations are reported. The presence of liquid additives appears to increase the SoS, while solid inclusions generally reduce the SoS. The ultrasound images of realized custom fabricated heterogeneous liver phantom and a real liver show remarkable similarities. Conclusions: The development of new materials’ formulations and the knowledge of acoustic properties, such as speed of sound and acoustic impedance, could improve and speed-up the development of phantoms for simulations of ultrasound medical procedures
Development and Testing of a System for Controlled Ultrasound Hyperthermia Treatment With a Phantom Device
Full text linkHyperthermia is the process of raising tissue temperatures in the range 40 degrees C-45 degrees C for a prolonged time (up to hours). Unlike in ablation therapy, raising the temperature to such levels does not cause necrosis of the tissue but has been postulated to sensitize the tissue for radiotherapy. The ability to maintain a certain temperature in a target region is key to a hyperthermia delivery system. The aim of this work was to design and characterize a heat delivery system for ultrasound hyperthermia able to generate a uniform power deposition pattern in the target region with a closed-loop control, which would maintain the defined temperature over a defined period. The hyperthermia delivery system presented herein is a flexible design with the ability to strictly control the induced temperature rise with a feedback loop. The system can be reproduced elsewhere with relative ease and is adaptable for various tumor sizes/locations and for other temperature elevation applications, such as ablation therapy. The system was fully characterized and tested on a newly designed custom-built phantom with controlled acoustic and thermal properties and containing embedded thermocouples. Additionally, a layer of thermochromic material was fixed above the thermocouples, and the recorded temperature increase was compared to the red, green, and blue (RGB) color change in the material. The transducer characterization allowed for input voltage to output power curves to be generated, thus allowing for the comparison of power deposition to temperature increase in the phantom. Additionally, the transducer characterization generated a field map of the symmetric field. The system was capable of increasing the temperature of the target area by 6 degrees C above body temperature and maintains the temperature to within +/- 0.5 degrees C over a defined period. The increase in temperature correlated with the RGB image analysis of the thermochromic material. The results of this work have the potential to contribute toward increasing confidence in the delivery of hyperthermia treatment to superficial tumors. The developed system could potentially be used for phantom or small animal proof-of-principle studies. The developed phantom test device may be used for testing other hyperthermia systems
The FUTURA platform: a new approach merging non-invasive ultrasound therapy with surgical robotics
No full text
Low invasive therapy under robotic guidance in the vascular district: a case study
No full textIntegration between surgery and robotics leads to new paradigms in clinical field. Innovative robotic solutions represent the enabling technology for highly targeted therapeutic actions, such as operating in the cardiovascular system. In this framework, the authors present a robotic platform for the treatment of vascular obstructions. It integrates a system for locomotion and navigation based on magnetic dragging and ultrasound tracking and a therapeutic module which involves mechanical attack to the obstruction by means of high intensity focused ultrasound. The system overview and the technical and theoretical instruments for developing the overall platform were illustrated; preliminary results, together with future planned works, are reported in order to demonstrate the feasibility of the proposed approach
Combination of US hyperthermia and radiotherapy on a preclinical glioblastoma model
Full text linkIn this work the effect of combining ultrasound (US) hyperthermia (HT) with radiotherapy (RT) was investigated. The treatment was applied to a GBM xenograft nude mouse model obtained by injecting 2×106 U87 luc+ cells. The combined treatment group received 6 Gy and HT at 43∘ for 8 min. The ultrasound field was generated by a closed-loop computationally controlled system, consisting of a High Intensity Focused Ultrasound (HIFU) transducer with centre frequency 3.57 MHz, a power amplifier, a function generator and a MATLAB controller. A mechanical cone adaptor has been designed to use the HIFU beam at a pre-defined post-focal distance. Two thermocouples were placed between the mechanical cone and the mice skin to measure and control the temperature during the HT treatment. Radiotherapy was carried out by using a dedicated small animal image guided radiotherapy system. Measurements of tumor volume performed with a caliper showed good tumor control for the RT-HT group with respect to the RT or control groups for up to 21 days after treatment. The mean value of the normalized (before therapy) tumor volume was almost equal to 0.5 for two weeks after treatment with an increase to 1.5 at sacrifice. The control and HT groups showed a higher value of about 1.5 during the first two weeks and 3.5 at the end of the follow-up period. We concluded that the use of HT as a radiosensitizer can improve the outcome for glioblastoma treatments
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