Contactless measurements of liquid sample electrical conductivity for estimating specific absorption rate in MR applications

Specific Absorption Rate (SAR) is the dosimetric parameter currently used as standard in the safety recommendation reports [1] for Magnetic Resonance Imaging (MRI) procedures. With the employment of MR systems with high field strengths (from 3T up to 8T), the study of the potential radiofrequency (RF) effects on the biological tissues due to higher radiofrequency, has a particular relevance [2]. Bottomley et al. [3] described a theoretical method to estimate the radiofrequency power deposition during MR exams, based on the sample geometry, the magnetic field radiofrequency, the MR sequence used (its pulse width, repetition time and flip angle) and, finally, the sample electrical conductivity. In this work we develop a liquid sample dielectric properties measurement system based on the evaluation of the resonance frequency and quality factor of a resonant circuit composed by a home-made coil. The major advantage of this method is the contactless between the liquid sample and the measurement electrode. We perform the measurement at 63.85MHz, corresponding to a 1.5T clinical MR environment, but this method can be used for measurements in the whole RF range, tuning the resonant circuit on the desired frequency

Study for a portable IR sensor to detect the blood temperature during coronary bypass implantation

The objective of this research was to investigate the possibility of using an infrared prototype device for the detection of the blood temperature during a surgical operation for coronary bypass implantation. The correlation between the fluid temperature time behavior and the fluid flow rate was demonstrated. Each blood vessel acts like a thermal wave emitter, so the amount of heat is proportional to the blood flow detected by the IR sensor. The idea was to design a low cost portable device with the advantage that it can be placed near the region of interest. We chose a pyroelectric sensor for its high-quality cost ratio. Because this kind of sensor detects only a variable infrared source, we used an electromechanical chopper for modulating the radiation. It consists of an electronic shutter whose opening speed is controlled by an astable multivibrator. The output signal was analyzed using a dedicated electronic circuit including a bandpass filter and an amplifier; then an acquisition board was employed for capturing and displaying the signal using a PC. Prototype assessment was made with laboratory equipment and in vivo measurements were made during surgical operation on a small pig

Measurement of tissue oxygenation in isolated rat hearts using near infrared spectroscopy

New techniques involving Near Infrared Spectroscopy (NIRS) and imaging are rapidly evolving for a large number of new clinical applications. These techniques, based upon nearinfrared light transmission through biological tissue, aim to monitor the hemoglobin and myoglobin concentration changes due to particular physiological state. Clinical applications regard, for instance, the monitoring of muscles and cerebral oxygenation, functional brain activation studies and heart perfusion research. Recently, some works presented tissue oxygenation studies in beating or arrested isolated porcine hearts. In our work we present the design and realization of a dedicated NIRS system for the myocardial perfusion analysis of isolated, saline solution perfused beating rat hearts; in this case the absence of blood allows for unambiguous measurement of tissue myoglobin oxygenation. The presented prototype is portable, low cost, battery operated and permits the measurement of both oxy and deoxy myoglobin concentration changes during imposed regional or global ischemia and reperfusion

Computational Analysis of a Radiofrequency Knee Coil for Low-Field MRI Using FDTD

Magnetic resonance imaging (MRI) is essential for the diagnosis and treatment of musculoskeletal conditions. Low-field

QRS Complex Separation from Convolutive Mixtures of Biolectrical Signals Acquired by Wearable Systems

Independent component analysis (ICA) has been widely used to remove artefacts from multichannel biomedical signal acquisitions under the hypothesis that there is statistical independence among the original sources. However, the basic ICA model does not take into account the influence on the mixing process of the different paths from the signal sources to the sensors In this study we propose a convolutive mixtures model in order to overcome the limitations of the basic ICA approach. The independent components are estimated in the frequency domain, where the convolutive model can be solved through an instantaneous mixing model. The signals are reconstructed back to the observation space resolving the ICA model ambiguities. Simulations are carried out to optimize of the proposed method for convolutive mixtures of electrocardiographic (ECG) and motion artefacts signals. The algorithm is tested on real ECG signals acquired by wearable systems in order to preserve the QRS complex when the signals are degraded by real life conditions of acquisition

Pancreatitis after percutaneous ethanol injection into HCC: a minireview of the literature

Deaths after percutaneous ethanol injection (PEI) into hepatocellular carcinoma (HCC) may occur within a few hours to a few days following the procedure because of hemoperitoneum and haemorrhage from oesophageal varices or hepatic insufficiency. Pancreatitis has been recently reported as a rare lethal complication of intra-arterial PEI, another modality for treating HCCs. In this minireview, we analyze the literature concerning the development of acute pancreatitis after PEI. Pathogenesis of pancreatitis from opioids and ethanol is also addressed. Treatment with opioids to reduce the patient's abdominal pain after PEI in combination with the PEI itself may lead to direct toxic effects, thus favouring the development of pancreatitis

Biological Effects and Safety in Magnetic Resonance Imaging: A Review

Since the introduction of Magnetic Resonance Imaging (MRI) as a diagnostic technique, the number of people exposed to electromagnetic fields (EMF) has increased dramatically. In this review, based on the results of a pioneer study showing in vitro and in vivo genotoxic effects of MRI scans, we report an updated survey about the effects of non-ionizing EMF employed in MRI, relevant for patients’ and workers’ safety. While the whole data does not confirm a risk hypothesis, it suggests a need for further studies and prudent use in order to avoid unnecessary examinations, according to the precautionary principle

A checklist for assessing the methodological quality of concurrent tES-fMRI studies (ContES checklist): a consensus study and statement

Background: Low intensity transcranial electrical stimulation (tES), including alternating or direct current stimulation (tACS or tDCS), applies weak electrical stimulation to modulate the activity of brain circuits. Integration of tES with concurrent functional magnetic resonance imaging (fMRI) allows for the mapping of neural activity during neuromodulation, supporting causal studies of both brain function and tES effects. Methodological aspects of tES-fMRI studies underpin the results, and reporting them in appropriate detail is required for reproducibility and interpretability. Despite the growing number of published reports, there are no consensus-based checklists for disclosing methodological details of concurrent tES-fMRI studies. Objective: To develop a consensus-based checklist of reporting standards for concurrent tES-fMRI studies to support methodological rigor, transparency, and reproducibility (ContES Checklist). Methods: A two-phase Delphi consensus process was conducted by a steering committee (SC) of 13 members and 49 expert panelists (EP) through the International Network of the tES-fMRI (INTF) Consortium. The process began with a circulation of a preliminary checklist of essential items and additional recommendations, developed by the SC based on a systematic review of 57 concurrent tES-fMRI studies. Contributors were then invited to suggest revisions or additions to the initial checklist. After the revision phase, contributors rated the importance of the 17 essential items and 42 additional recommendations in the final checklist. The state of methodological transparency within the 57 reviewed concurrent tES-fMRI studies was then assessed using the checklist. Results: Experts refined the checklist through the revision and rating phases, leading to a checklist with three categories of essential items and additional recommendations: (1) technological factors, (2) safety and noise tests, and (3) methodological factors. The level of reporting of checklist items varied among the 57 concurrent tES-fMRI papers, ranging from 24% to 76%. On average, 53% of checklist items were reported in a given article. Conclusions: Use of the ContES checklist is expected to enhance the methodological reporting quality of future concurrent tES-fMRI studies, and increase methodological transparency and reproducibility