Michele Triventi

Complexity of MRI induced heating on metallic leads: Experimental measurements of 374 configurations

BackgroundMRI induced heating on PM leads is a very complex issue. The widely varying results described in literature suggest that there are many factors that influence the degree of heating and that not always are adequately addressed by existing testing methods.MethodsWe present a wide database of experimental measurements of the heating of metallic wires and PM leads in a 1.5 T RF coil. The aim of these measurements is to systematically quantify the contribution of some potential factors involved in the MRI induced heating: the length and the geometric structure of the lead; the implant location within the body and the lead path; the shape of the phantom used to simulate the human trunk and its relative position inside the RF coil.ResultsWe found that the several factors are the primary influence on heating at the tip. Closer locations of the leads to the edge of the phantom and to the edge of the coil produce maximum heating. The lead length is the other crucial factor, whereas the implant area does not seem to have a major role in the induced temperature increase. Also the lead structure and the geometry of the phantom revealed to be elements that can significantly modify the amount of heating.ConclusionOur findings highlight the factors that have significant effects on MRI induced heating of implanted wires and leads. These factors must be taken into account by those who plan to study or model MRI heating of implants. Also our data should help those who wish to develop guidelines for defining safe medical implants for MRI patients. In addition, our database of the entire set of measurements can help those who wish to validate their numerical models of implants that may be exposed to MRI systems.

In vitro investigation of pacemaker lead heating induced by magnetic resonance imaging: role of implant geometry.

To evaluate the effect of the geometry of implantable pacemakers (PMs) on lead heating induced by magnetic resonance imaging (MRI).

Numerical Model for Estimating RF-Induced Heating on a Pacemaker Implant During MRI: Experimental Validation

MRI may cause tissue heating in patients implanted with pacemakers (PMs) or cardioverters/defibrillators. As a consequence, these patients are often preventatively excluded from MRI investigations. The issue has been studied for several years now, in order to identify the mechanisms involved in heat generation, and define safety conditions by which MRI may be extended to patients with active implants. In this sense, numerical studies not only widen the range of experimental measurements, but also model a realistic patients anatomy on which it is possible to study individually the impact of the many parameters involved. In order to obtain reliable results, however, each and every numerical analysis needs to be validated by experimental evidence. Aim of this paper was to design and validate through experimental measurements, an accurate numerical model, which was able to reproduce the thermal effects induced by a birdcage coil on human tissues containing a metal implant, specifically, a PM. The model was then used to compare the right versus left pectoral implantation of a PM, in terms of power deposited at the lead tip. This numerical model may also be used as reference for validating simpler models in terms of computational effort.

Time-Domain and Morphological Analysis of the P-Wave. Part I: Technical Aspects for Automatic Quantification of P-Wave Features

Introduction: Time‐domain and morphological analysis of P‐wave from surface electrocardiogram has been extensively used to identify patients prone to atrial arrhythmias, especially atrial fibrillation (AF). However, since no standard procedure exists for P‐wave preprocessing, standardization of cut‐off values for P‐wave duration and morphological features is difficult. This study is a methodological investigation of P‐wave preprocessing procedures for automatic time‐domain and morphological analysis.

MRI induced heating of pacemaker leads: effect of temperature probe positioning and pacemaker placement on lead tip heating and local SAR.

The radio frequency field used in magnetic resonance imaging (MRI) procedures leads to temperature and local absorption rate (SAR) increase for patients with implanted pacemakers (PM). In this work a methodological approach for temperature and SAR measurements using fluoroptic probes is presented. Experimental measures show how the position of temperature probes affects the temperature and SAR value measured at the lead tip. The transversal contact between the active portion of the probe and the lead tip is the configuration associated with the highest values for temperature and SAR, whereas other configurations may lead to an underestimation close to 11% and 70% for temperature and SAR, respectively. In addition measurements were performed on a human-shaped phantom inside a real MRI system, in order to investigate the effect of the PM placement and of the lead geometry on heating and local SAR

Impact of capped and uncapped abandoned leads on the heating of an MR‐conditional pacemaker implant

To assess the risk of radiofrequency (RF) ‐induced heating in patients with MR‐conditional pacemaker (PM) systems, in the presence of another lead abandoned from a previous implant.

Role of the lead structure in MRI-induced heating: In vitro measurements on 30 commercial pacemaker/defibrillator leads.

MRI‐induced heating on endocardial leads is a serious concern for the safety of patients with implantable pacemakers or cardioverter‐defibrillator. The lead heating depends on many factors and its amount is largely variable. In this study, we investigated the role of those structural properties of the lead that are reported on the accompanying documents of the device: ( 1 ) fixation modality (active vs. passive); ( 2 ) number of electrodes (unipolar vs. bipolar); ( 3 ) length; ( 4 ) tip surface; and ( 5 ) tip and ring resistance. In vitro temperature and specific absorption rate measurements on 30 leads (27 pacemakers, three implantable cardioverter‐defibrillator leads) exposed to the radiofrequency field typical of a 1.5 T MRI scanner are presented. The data show that each lead has its own attitude to radiofrequency‐induced heating and that the information that is available in the accompanying documents of the pacemaker is not sufficient to explain such attitude. Even if combined with that of the implant geometry, this information is still not sufficient to estimate the amount of heating due to the exposure to the radiofrequency field during MRI examination. Magn Reson Med, 2011.

Effect of high-pass filtering on ECG signal on the analysis of patients prone to atrial fibrillation

The aim of this study was to assess the effect of filtering techniques on the time-domain analysis of the ECG. Multi-lead ECG recordings obtained from chronic atrial fibrillation (AF) patients after successful external cardioversion have been acquired. Several high-pass filtering techniques and three cut-off frequency values were used: Bessel and Butterworth four-pole and two-pole bidirectional and unidirectional filters, at 0.01, 0.05 and 0.5 Hz low cut-off frequency. As a reference, a beat-by-beat linear piecewise interpolation was used to remove baseline wander, on each P-wave. Results show that ECG filtering affects the estimation of P-wave duration in a manner that depends upon the type of filter used: particularly, the bidirectional filters caused negligible variation of P-wave duration, while unidirectional ones provoked an increase higher than 8%.

RFID in healthcare environment: electromagnetic compatibility regulatory issues

Several wireless technology applications (RFID, WiFi, GSM, GPRS) have been developed to improve patient care, reaching a significant success and diffusion in healthcare. Given the potential development of such a technology, care must be paid on the potential risks deriving from the use of wireless device in healthcare, among which one of the most important is the electromagnetic interference with medical devices. The analysis of the regulatory issues concerning the electromagnetic compatibility of medical devices is essential to evaluate if and how the application of the current standards allows an effective control of the possible risks associated to the electromagnetic interference on medical devices.

SMS-based platform for cardiovascular tele-monitoring

The focus of this paper is to describe a fully automatic platform to transmit, using the SMS service, medical data collected at home. The overall platform has two main components: a central server for SMS receiving (Central Receiving Unit, CRU) and the remote sending data collection and transmitting units (Home Transmitting Unit, HTU). HTU is connected to commercial meters of arterial pressure and blood glucose, and to a stepcounter. The CRU is located in a clinical center and acts also as a server for the database housing and for the users applications (data display, trend visualizations, alarms). Five platforms (CRU+5HTU) have been realized and given to patients. During a cumulative monitoring period of 251 days, there were 175 data transfer sessions, a mean of 35 plusmn 20 per patient. The stability of the telemonitoring system and the mean percentage of successful encoding of the transmitted data were 100%.