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1.
Clin Ter ; 175(3): 146-153, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38767071

RESUMO

Background: AneurysmFlow (Phillips Healthcare) is the flow measurement tool, utilizing an optical flow-based algorithm from DSA, lacks sufficient published studies. This study aimed to assess the significance of flow velocity changes and the Mean Aneurysm Flow Amplitude (MAFA) ratio in evaluating outcomes following flow-diverting treatments. Methods: Between June 2021 and October 2022, 41 patients with 42 aneurysms underwent FDS treatment with AneurysmFlow measu-rement at the Bach Mai Radiology Center. Results: The tool achieved a 90.5% success rate in 38 out of 42 patients. Most aneurysms (89.5%) were small to medium-sized (<10 mm), and a decrease in flow velocity post-stent deployment was ob-served in 78.9% of cases. Conversely, 21.1% showed increased flow, mainly in aneurysms smaller than 5 mm. No significant association was found between flow changes or MAFA ratio and aneurysm size characteristics. Twenty-two patients (59.5%) underwent re-examination at 6 months, revealing no correlation in MAFA ratio between completely and incompletely occluded aneurysms. Conclusions: Our current investigation, primarily centered on small and medium-sized aneurysms, did not uncover any link between quantitative flow changes assessed using the AneurysmFlow software and the occlusion status of aneurysms at the 6-month follow-up post-flow diverter treatment. Larger case series with extended follow-up imaging are necessary to further explore these findings.


Assuntos
Hemodinâmica , Stents , Humanos , Feminino , Masculino , Pessoa de Meia-Idade , Idoso , Procedimentos Endovasculares/métodos , Aneurisma Intracraniano/cirurgia , Aneurisma Intracraniano/fisiopatologia , Velocidade do Fluxo Sanguíneo , Angiografia Digital , Algoritmos , Estudos Retrospectivos , Adulto , Resultado do Tratamento , Idoso de 80 Anos ou mais
2.
Int J Oral Implantol (Berl) ; 17(1): 89-100, 2024 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-38501401

RESUMO

PURPOSE: To establish consensus-driven guidelines that could support the clinical decision-making process for implant-supported rehabilitation of the posterior atrophic maxilla and ultimately improve long-term treatment outcomes and patient satisfaction. MATERIALS AND METHODS: A total of 33 participants were enrolled (18 active members of the Italian Academy of Osseointegration and 15 international experts). Based on the available evidence, the development group discussed and proposed an initial list of 20 statements, which were later evalu-ated by all participants. After the forms were completed, the responses were sent for blinded ana-lysis. In most cases, when a consensus was not reached, the statements were rephrased and sent to the participants for another round of evaluation. Three rounds were planned. RESULTS: After the first round of voting, participants came close to reaching a consensus on six statements, but no consensus was achieved for the other fourteen. Following this, nineteen statements were rephrased and sent to participants again for the second round of voting, after which a consensus was reached for six statements and almost reached for three statements, but no consensus was achieved for the other ten. All 13 statements upon which no consensus was reached were rephrased and included in the third round. After this round, a consensus was achieved for an additional nine statements and almost achieved for three statements, but no consensus was reached for the remaining statement. CONCLUSION: This Delphi consensus highlights the importance of accurate preoperative planning, taking into consideration the maxillomandibular relationship to meet the functional and aesthetic requirements of the final restoration. Emphasis is placed on the role played by the sinus bony walls and floor in providing essential elements for bone formation, and on evaluation of bucco-palatal sinus width for choosing between lateral and transcrestal sinus floor elevation. Tilted and trans-sinus implants are considered viable options, whereas caution is advised when placing pterygoid implants. Zygomatic implants are seen as a potential option in specific cases, such as for completely edentulous elderly or oncological patients, for whom conventional alternatives are unsuitable.


Assuntos
Implantes Dentários , Levantamento do Assoalho do Seio Maxilar , Humanos , Idoso , Maxila/cirurgia , Levantamento do Assoalho do Seio Maxilar/métodos , Consenso , Técnica Delphi , Estética Dentária , Atrofia/patologia
3.
PLoS One ; 17(12): e0278187, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36490249

RESUMO

The majority of studies that assess magnetic resonance imaging (MRI) induced radiofrequency (RF) heating of the tissue when active electronic implants are present have been performed in horizontal, closed-bore MRI systems. Vertical, open-bore MRI systems have a 90° rotated magnet and a fundamentally different RF coil geometry, thus generating a substantially different RF field distribution inside the body. Little is known about the RF heating of elongated implants such as deep brain stimulation (DBS) devices in this class of scanners. Here, we conducted the first large-scale experimental study investigating whether RF heating was significantly different in a 1.2 T vertical field MRI scanner (Oasis, Fujifilm Healthcare) compared to a 1.5 T horizontal field MRI scanner (Aera, Siemens Healthineers). A commercial DBS device mimicking 30 realistic patient-derived lead trajectories extracted from postoperative computed tomography images of patients who underwent DBS surgery at our institution was implanted in a multi-material, anthropomorphic phantom. RF heating around the DBS lead was measured during four minutes of high-SAR RF exposure. Additionally, we performed electromagnetic simulations with leads of various internal structures to examine this effect on RF heating. When controlling for RMS B1+, the temperature increase around the DBS lead-tip was significantly lower in the vertical scanner compared to the horizontal scanner (0.33 ± 0.24°C vs. 4.19 ± 2.29°C). Electromagnetic simulations demonstrated up to a 17-fold reduction in the maximum of 0.1g-averaged SAR in the tissue surrounding the lead-tip in the vertical scanner compared to the horizontal scanner. Results were consistent across leads with straight and helical internal wires. Radiofrequency heating and power deposition around the DBS lead-tip were substantially lower in the 1.2 T vertical scanner compared to the 1.5 T horizontal scanner. Simulations with different lead structures suggest that the results may extend to leads from other manufacturers.


Assuntos
Estimulação Encefálica Profunda , Humanos , Estimulação Encefálica Profunda/métodos , Ondas de Rádio , Calefação , Imageamento por Ressonância Magnética/métodos , Imagens de Fantasmas , Temperatura Alta
5.
Magn Reson Med ; 87(5): 2464-2480, 2022 05.
Artigo em Inglês | MEDLINE | ID: mdl-34958685

RESUMO

PURPOSE: To evaluate the safety of MRI in patients with fragmented retained leads (FRLs) through numerical simulation and phantom experiments. METHODS: Electromagnetic and thermal simulations were performed to determine the worst-case RF heating of 10 patient-derived FRL models during MRI at 1.5 T and 3 T and at imaging landmarks corresponding to head, chest, and abdomen. RF heating measurements were performed in phantoms implanted with reconstructed FRL models that produced highest heating in numerical simulations. The potential for unintended tissue stimulation was assessed through a conservative estimation of the electric field induced in the tissue due to gradient-induced voltages developed along the length of FRLs. RESULTS: In simulations under conservative approach, RF exposure at B1+ ≤ 2 µT generated cumulative equivalent minutes (CEM)43 < 40 at all imaging landmarks at both 1.5 T and 3 T, indicating no thermal damage for acquisition times (TAs) < 10 min. In experiments, the maximum temperature rise when FRLs were positioned at the location of maximum electric field exposure was measured to be 2.4°C at 3 T and 2.1°C at 1.5 T. Electric fields induced in the tissue due to gradient-induced voltages remained below the threshold for cardiac tissue stimulation in all cases. CONCLUSIONS: Simulation and experimental results indicate that patients with FRLs can be scanned safely at both 1.5 T and 3 T with most clinical pulse sequences.


Assuntos
Imageamento por Ressonância Magnética , Ondas de Rádio , Coração/diagnóstico por imagem , Calefação , Temperatura Alta , Humanos , Imageamento por Ressonância Magnética/efeitos adversos , Imageamento por Ressonância Magnética/métodos , Imagens de Fantasmas
6.
IEEE Trans Electromagn Compat ; 63(5): 1757-1766, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34898696

RESUMO

Interaction of an active electronic implant such as a deep brain stimulation (DBS) system and MRI RF fields can induce excessive tissue heating, limiting MRI accessibility. Efforts to quantify RF heating mostly rely on electromagnetic (EM) simulations to assess individualized specific absorption rate (SAR), but such simulations require extensive computational resources. Here, we investigate if a predictive model using machine learning (ML) can predict the local SAR in the tissue around tips of implanted leads from the distribution of the tangential component of the MRI incident electric field, Etan. A dataset of 260 unique patient-derived and artificial DBS lead trajectories was constructed, and the 1 g-averaged SAR, 1gSARmax, at the lead-tip during 1.5 T MRI was determined by EM simulations. Etan values along each lead's trajectory and the simulated SAR values were used to train and test the ML algorithm. The resulting predictions of the ML algorithm indicated that the distribution of Etan could effectively predict 1gSARmax at the DBS lead-tip (R = 0.82). Our results indicate that ML has the potential to provide a fast method for predicting MR-induced power absorption in the tissue around tips of implanted leads such as those in active electronic medical devices.

7.
Annu Int Conf IEEE Eng Med Biol Soc ; 2021: 4204-4208, 2021 11.
Artigo em Inglês | MEDLINE | ID: mdl-34892151

RESUMO

The number of patients with active implantable medical devices continues to rise in the United States and around the world. It is estimated that 50-75% of patients with conductive implants will need magnetic resonance imaging (MRI) in their lifetime. A major risk of performing MRI in patients with elongated conductive implants is the radiofrequency (RF) heating of the tissue surrounding the implant's tip due to the antenna effect. Currently, applying full-wave electromagnetic simulation is the standard way to predict the interaction of MRI RF fields with the human body in the presence of conductive implants; however, these simulations are notoriously extensive in terms of memory requirement and computational time. Here we present a proof-of-concept simulation study to demonstrate the feasibility of applying machine learning to predict MRI-induced power deposition in the tissue surrounding conductive wires. We generated 600 clinically relevant trajectories of leads as observed in patients with cardiac conductive implants and trained a feedforward neural network to predict the 1g-averaged SAR at the lead tips knowing only the background field of MRI RF coil and coordinates of points along the lead trajectory. Training of the network was completed in 11.54 seconds and predictions were made within a second with R2 = 0.87 and Root Mean Squared Error (RMSE) = 14.5 W/kg. Our results suggest that machine learning could provide a promising approach for safety assessment of MRI in patients with conductive leads.Clinical Relevance- Machine learning can potentially allow real-time assessment of MRI RF safety in patients with conductive leads when only the knowledge of lead's trajectory (image-based) and MRI RF coil features (vendor-specific) are in hand.


Assuntos
Calefação , Temperatura Alta , Humanos , Aprendizado de Máquina , Imageamento por Ressonância Magnética , Imagens de Fantasmas
8.
Annu Int Conf IEEE Eng Med Biol Soc ; 2021: 4982-4985, 2021 11.
Artigo em Inglês | MEDLINE | ID: mdl-34892326

RESUMO

Magnetic Resonance Imaging (MRI) access remains conditional to patients with conductive medical implants, as RF heating generated around the implant during scanning may cause tissue burns. Experiments have been traditionally used to assess this heating, but they are time-consuming and expensive, and in many cases cannot faithfully replicate the in-vivo scenario. Alternatively, ISO TS 10974 outlines a four-tier RF heating assessment approach based on a combination of experiments and full-wave electromagnetic (EM) simulations with varying degrees of complexity. From these, Tier 4 approach relies entirely on EM simulations. There are, however, very few studies validating such numerical models against direct thermal measurements. In this work, we evaluated the agreement between simulated and measured RF heating around wire implants during RF exposure at 63.6 MHz (proton imaging at 1.5 T). Heating was assessed around wire implants with 25 unique trajectories within an ASTM phantom. The root mean square percentage error (RMSPE) of simulated vs. measured RF heating remained <1.6% despite the wide range of observed heating (0.2 °C-53 °C). Our results suggest that good agreement can be achieved between experiments and simulations as long as important experimental features such as characteristics of the MRI RF coil, implant's geometry, position, and trajectory, as well as electric and thermal properties of gel are closely mimicked in simulations.Clinical Relevance- This work validates the application of full-wave EM simulations for modeling and predicting RF heating of conductive wires in an MRI environment, providing researchers with a validated tool to assess MRI safety in patients with implants.


Assuntos
Calefação , Temperatura Alta , Humanos , Imageamento por Ressonância Magnética , Imagens de Fantasmas , Ondas de Rádio
9.
Annu Int Conf IEEE Eng Med Biol Soc ; 2021: 4986-4989, 2021 11.
Artigo em Inglês | MEDLINE | ID: mdl-34892327

RESUMO

Patients with cardiovascular implantable electronic devices (CIEDs) are often prevented from receiving magnetic resonance imaging (MRI) due to risks associated with radiofrequency (RF) heating of tissue around the implanted leads. Although MR-conditional CIEDs are available, the safety labeling of such devices does not extend to patients with fragmented retained leads (FRLs), where segments of the leads are left in the tissue after the original device is extracted. Unlike intact and isolated leads of CIEDs, FRLs are often bare conductive lead fragments in direct contact with the tissue. No experimental work has been reported that assess RF heating of FRL during MRI thus far. In this work, we performed phantom experiments to measure RF heating of 4 patient-derived FRL models in a gel-based ASTM-like phantom during RF exposure at 64 MHz (proton imaging at 1.5 T) and 123 MHz (proton imaging at 3 T). We found FRL models to generate negligible temperature rise in the gel (∆T<1.84 °C) during a 10-minute scan at both 1.5 T and 3 T. These results are in agreement with previous simulation studies and suggest MRI may be performed safely in patients with fragmented retained leads.


Assuntos
Calefação , Ondas de Rádio , Coração , Humanos , Imageamento por Ressonância Magnética , Imagens de Fantasmas , Ondas de Rádio/efeitos adversos
10.
World J Urol ; 39(7): 2363-2374, 2021 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-33948694

RESUMO

PURPOSE: To summarize the current evidence and the reasons to go for thulium-based anatomical endoscopic enucleation of the prostate (AEEP). METHODS: This review discusses the available literature on thulium-based AEEP. RESULTS: Thulium lasers operate at a wavelength between 1940 and 2013 nm. This wavelength, which has a low penetration depth in water, allows to perform smooth cuts in the prostatic tissue and allows urologists to perform various procedures: resection, vaporization, enucleation, or vapoenucleation of the prostate. Depending on the type of thulium laser, it can be used either in a continuous, or pulsed mode. CONCLUSION: In recent years, an increasing amount of evidence has described the thulium laser as a minimally invasive and size-independent treatment option for benign prostatic enlargement with excellent long-term results.


Assuntos
Endoscopia , Lasers de Estado Sólido/uso terapêutico , Prostatectomia/métodos , Hiperplasia Prostática/cirurgia , Túlio/uso terapêutico , Humanos , Masculino
12.
J Am Chem Soc ; 143(1): 137-141, 2021 01 13.
Artigo em Inglês | MEDLINE | ID: mdl-33375792

RESUMO

In aqueous solution, biological decarboxylation reactions proceed irreversibly to completion, whereas the reverse carboxylation processes are typically powered by the hydrolysis of ATP. The exchange of the carboxylate of ring-substituted arylacetates with isotope-labeled CO2 in polar aprotic solvents reported recently suggests a dramatic change in the partition of reaction pathways. Yet, there is little experimental data pertinent to the kinetic barriers for protonation and thermodynamic data on CO2 capture by the carbanions of decarboxylation reactions. Employing a combined quantum mechanical and molecular mechanical simulation approach, we investigated the decarboxylation reactions of a series of organic carboxylate compounds in aqueous and in dimethylformamide solutions, revealing that the reverse carboxylation barriers in solution are fully induced by solvent effects. A linear Bell-Evans-Polanyi relationship was found between the rates of decarboxylation and the Gibbs energies of reaction, indicating diminishing recombination barriers in DMF. In contrast, protonation of the carbanions by the DMF solvent has large free energy barriers, rendering the competing exchange of isotope-labeled CO2 reversible in DMF. The finding of an intricate interplay of carbanion stability and solute-solvent interaction in decarboxylation and carboxylation could be useful to designing novel materials for CO2 capture.


Assuntos
Dióxido de Carbono/química , Ácidos Carboxílicos/química , Dimetilformamida/química , Água/química , Descarboxilação , Simulação de Dinâmica Molecular , Solventes/química , Termodinâmica
13.
J Magn Reson Imaging ; 53(2): 599-610, 2021 02.
Artigo em Inglês | MEDLINE | ID: mdl-32860322

RESUMO

BACKGROUND: Patients with deep brain stimulation (DBS) implants have limited access to MRI due to safety concerns associated with RF-induced heating. Currently, MRI in these patients is allowed in 1.5T horizontal bore scanners utilizing pulse sequences with reduced power. However, the use of 3T MRI in such patients is increasingly reported based on limited safety assessments. Here we present the results of comprehensive RF heating measurements for two commercially available DBS systems during MRI at 1.5T and 3T. PURPOSE: To assess the effect of imaging landmark, DBS lead configuration, and patient's body composition on RF heating of DBS leads during MRI at 1.5T and 3T. STUDY TYPE: Phantom and ex vivo study. POPULATION/SUBJECTS/PHANTOM/SPECIMEN/ANIMAL MODEL: Gel phantoms and cadaver brain. FIELD STRENGTH/SEQUENCE: 1.5T and 3T, T1 -weighted turbo spin echo. ASSESSMENT: RF heating was measured at the tips of DBS leads implanted in brain-mimicking gel. Image artifact was assessed in a cadaver brain implanted with an isolated DBS lead. STATISTICAL TESTS: Descriptive. RESULTS: We observed substantial fluctuation in RF heating, mainly affected by phantom composition and DBS lead configuration, ranging from 0.14°C to 23.73°C at 1.5T, and from 0.10°C to 7.39°C at 3T. The presence of subcutaneous fat substantially altered RF heating at the electrode tips (3.06°C < ∆T < 19.05° C). Introducing concentric loops in the extracranial portion of the lead at the surgical burr hole reduced RF heating by up to 89% at 1.5T and up to 98% at 3T compared to worst-case heating scenarios. DATA CONCLUSION: Device configuration and patient's body composition substantially altered the RF heating of DBS leads during MRI. Interestingly, certain lead trajectories consistently reduced RF heating and image artifact. Level of Evidence 1 Technical Efficacy Stage 1 J. MAGN. RESON. IMAGING 2021;53:599-610.


Assuntos
Estimulação Encefálica Profunda , Calefação , Artefatos , Composição Corporal , Humanos , Imageamento por Ressonância Magnética , Imagens de Fantasmas
14.
RSC Adv ; 12(2): 698-707, 2021 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-35425141

RESUMO

Cobalt doped magnetite nanoparticles (Co x Fe3-x O4 NPs) are investigated extensively because of their potential hyperthermia application. However, the complex interrelation among chemical compositions and particle size means their correlation with the magnetic and heating properties is not trivial to predict. Here, we prepared Co x Fe3-x O4 NPs (0 ≤ x ≤ 1) to investigate the effects of cobalt content and particle size on their magnetic and heating properties. A detailed analysis of the structural features indicated the similarity between the crystallite and particle sizes as well as their non-monotonic change with the increase of Co content. Magnetic measurements for the Co x Fe3-x O4 NPs (0 ≤ x ≤ 1) showed that the blocking temperature, the saturation magnetization, the coercivity, and the anisotropy constant followed a similar trend with a maximum at x = 0.7. Moreover, 57Fe Mössbauer spectroscopy adequately explained the magnetic behaviour, the anisotropy constant, and saturation magnetization of low Co content samples. Finally, our study shows that the relaxation loss is a primary contributor to the SAR in Co x Fe3-x O4 NPs with low Co contents as well as their potential application in magnetic hyperthermia.

15.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3629-3633, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018788

RESUMO

Deep brain stimulation (DBS) has evolved to an important treatment for several drug-resistant neurological and psychiatric disorders, such as epilepsy, Parkinson's disease, essential tremor and dystonia. Despite general effectiveness of DBS, however, its mechanisms of action are not completely understood. Simulations are commonly used to predict the volume of tissue activated (VTA) around DBS electrodes, which in turn helps interpreting clinical outcomes and understand therapeutic mechanisms. Computational models are commonly used to visualize the extend of volume of activated tissue (VTA) for different stimulation schemes, which in turn helps interpreting and understanding the outcomes. The degree of model complexity, however, can affect the predicted VTA. In this work we investigate the effect of volume conductor model complexity on the predicted VTA, when the VTA is estimated from activation function field metrics. Our results can help clinicians to decide what level of model complexity is suitable for their specific need.


Assuntos
Estimulação Encefálica Profunda , Doença de Parkinson , Biofísica , Simulação por Computador , Humanos , Modelos Neurológicos , Doença de Parkinson/terapia
16.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 5192-5197, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33019155

RESUMO

Patients with deep brain stimulation (DBS) devices have limited access to magnetic resonance imaging (MRI) due to safety concerns associated with RF heating generated around the implant. The problem of predicting RF heating of conductive leads is complex with a large parameter space and several interplaying factors. Recently however, off-label use of MRI in patients with DBS devices has been reported based on limited safety assessments, raising the concern that potentially dangerous scenarios may have been overlooked. In this work, we present results of a systematic assessment of RF heating of a commercial DBS device during MRI at 1.5T and 3T, taking into account the effect of device configuration, imaging landmark, and patient's body composition. Ninety-six (96) RF heating measurements were performed using anthropomorphic phantoms implanted with a full DBS system. We evaluated eight clinically relevant device configurations, implanted in phantoms with different material compositions, and imaged at three different landmarks (head, shoulder, and lower chest) in 1.5 T and 3T scanners. We observed a substantial fluctuation in the RF heating depending on phantom's composition and device configuration. RF heating in the brain-mimicking gel varied from 0.1°C to 12°C during 1.5 T MRI and from <0.1°C to 4.5°C during 3T MRI. We also observed that certain device configurations consistently reduced RF heating across different phantom compositions, imaging landmarks, and MRI transmit frequencies.


Assuntos
Estimulação Encefálica Profunda , Calefação , Composição Corporal , Humanos , Imageamento por Ressonância Magnética , Próteses e Implantes
17.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 6107-6110, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33019364

RESUMO

Patients with long conductive implants such as deep brain stimulation (DBS) leads are often denied access to magnetic resonance imaging (MRI) exams due to safety concerns associated with radiofrequency (RF) heating of implants. Experimental temperature measurements in tissue-mimicking gel phantoms under MRI RF exposure conditions are common practices to predict in-vivo heating in the tissue surrounding wire implants. Such experiments are both expensive-as they require access to MRI units-and time-consuming due to complex implant setups. Recently, full-wave numerical simulations, which include realistic MRI RF coil models and human phantoms, are suggested as an alternative to experiments. There is however, little literature available on the accuracy of such numerical models against direct thermal measurements. This study aimed to evaluate the agreement between simulations and measurements of temperature rise at the tips of wire implants exposed to RF exposure at 64 MHz (1.5 T) for different implant trajectories typically encountered in patients with DBS leads. Heating was assessed in seven patient-derived lead configurations using both simulations and RF heating measurements during imaging of an anthropomorphic head phantom with implanted wires. We found substantial variation in RF heating as a function of lead trajectory; there was a 9.5-fold and 9-fold increase in temperature rise from ID1 to ID7 during simulations and experimental measurements, respectively. There was a strong correlation (r2 = 0.74) between simulated and measured temperatures for different lead trajectories. The maximum difference between simulated and measured temperature was 0.26 °C with simulations overestimating the temperature rise.


Assuntos
Calefação , Temperatura Alta , Humanos , Imageamento por Ressonância Magnética , Imagens de Fantasmas , Ondas de Rádio
18.
Phys Med Biol ; 65(18): 185007, 2020 09 16.
Artigo em Inglês | MEDLINE | ID: mdl-32756027

RESUMO

Numerical simulations are increasingly employed in safety assessment of high-field magnetic resonance imaging (MRI) in patients with conductive medical implants such as those with deep brain stimulation (DBS) devices. Performing numerical simulations with realistic patient models and implant geometry is the preferred method as it provides the most accurate results; however, in many cases such an approach is infeasible due to limitation of computational resources. The difficulties in reconstructing realistic patient and device models and obtaining accurate electrical properties of tissue have compelled researchers to adopt compromises, either to exceedingly simplify implant structure and geometry, or the complexity of the body model. This study examines the effect of variations in anatomical details of the human body model and implant geometry on predicted values of specific absorption rate (SAR) values during MRI in a patient with a DBS implant. We used a patient-derived model of a fully implanted DBS implant and performed numerical simulations to calculate the maximum SAR during MRI at 1.5T (64 MHz) and 3T (127 MHz). We then assessed the effect of uncertainties in dielectric properties of tissue, complexity of body model, truncation of body/DBS model, and DBS lead geometry on SAR. Our results showed that 40% variation in the conductivity of individual tissues in a heterogeneous body model caused a peak of 7% variation in maximum SAR value at 64 MHz, and 10.6% variation in SAR at 127 MHz. SAR predictions from a homogeneous body model with a conductivity range of [Formula: see text] could cover the full range of SAR variations predicted by the heterogeneous body model. Truncation of body model below the implanted pulse generator changed the predicted SAR by 16% at 1.5T and 32% at 3T while saving 250% and 148% in computational time and memory allocation, respectively. In contrast, variation in DBS lead geometry significantly changed the SAR by up to 51% at 64 MHz and 67% at 127 MHz. These results suggest that the error introduced by simplifying the implant's geometry could negate the benefit of using a realistic body model, should such model be used at the expense of oversimplifying implant geometry.


Assuntos
Simulação por Computador , Estimulação Encefálica Profunda/instrumentação , Condutividade Elétrica , Imageamento por Ressonância Magnética , Próteses e Implantes , Humanos
19.
Urologe A ; 59(5): 544-549, 2020 May.
Artigo em Alemão | MEDLINE | ID: mdl-32274543

RESUMO

The diagnosis and treatment of lower urinary tract symptoms (LUTS) due to benign prostatic enlargement plays an important role in daily urological practice. Therefore, a targeted and resource-saving approach is essential. A rational base-line work-up of our patients provides the necessary information for obtaining the diagnosis and only needs to be expanded in individual cases. In addition to drug therapy, the modification of lifestyle and the possibility of watchful waiting must not be underestimated. Simple measures such as a timed fluid intake, double micturition in the case of residual urine development, but also bladder reconditioning can significantly improve the quality of life of our patients. Regarding surgical treatment, laser procedures have found their way into many departments and have established themselves in daily routine as a reference procedure in addition to transurethral resection of the prostate (TUR-P) and simple open prostatectomy. New, minimally invasive procedures-such as prostatic artery embolization (PAE), the Rezum™- (NxThera Inc., Maple-Grove, MN, USA) or the Aquabeam® (Procept, Redwood City, CA, USA) procedure, but also nonablative procedures such as iTind© (TIND, Medi-Tate, Or Akiva, Israel) or Urolift® (Neotract Inc., Pleasanton, CA, USA)-offer new treatment options to those affected, with the potential to maintain patient's sexual function. As a result, individual risk assessment and advice on the advantages and disadvantages of all available treatment options-even more than today-will be an important part of LUTS treatment. An individual approach, similar to that used in the treatment of oncological disease, will become standard also in the treatment of benign prostatic syndrome.


Assuntos
Embolização Terapêutica , Sintomas do Trato Urinário Inferior/terapia , Guias de Prática Clínica como Assunto , Hiperplasia Prostática/terapia , Ressecção Transuretral da Próstata/normas , Humanos , Sintomas do Trato Urinário Inferior/diagnóstico , Sintomas do Trato Urinário Inferior/fisiopatologia , Masculino , Hiperplasia Prostática/diagnóstico , Hiperplasia Prostática/fisiopatologia , Qualidade de Vida , Ressecção Transuretral da Próstata/efeitos adversos , Resultado do Tratamento
20.
Polymers (Basel) ; 12(2)2020 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-32024248

RESUMO

The aim of this work was to assess the effect of fish gelatin-citric acid nucleophilic substitution and agar-citric acid esterification reactions on the properties of agar/fish gelatin films. Since temperature is an important cross-linking parameter, films were treated at 90 °C and 105 °C and film properties were compared to those of non-cured films. It was observed that temperature favored the aforementioned reactions, which induced physical and morphological changes. In this regard, darker films with a rougher surface were obtained for the films with a higher cross-linking degree. While mechanical properties were slightly modified, the barrier properties were enhanced due to the reactions that occurred. Therefore, these agar/fish gelatin films cross-linked through two different reactions can be considered to be promising materials as active films for different purposes, such as active packaging or pharmaceutical applications.

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