Giovanni Calcagnini

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.

Temperature and SAR measurement errors in the evaluation of metallic linear structures heating during MRI using fluoroptic probes.

The purpose of this work is to evaluate the error associated with temperature and SAR measurements using fluoroptic temperature probes on pacemaker (PM) leads during magnetic resonance imaging (MRI). We performed temperature measurements on pacemaker leads, excited with a 25, 64, and 128 MHz current. The PM lead tip heating was measured with a fluoroptic thermometer (Luxtron, Model 3100, USA). Different contact configurations between the pigmented portion of the temperature probe and the PM lead tip were investigated to find the contact position minimizing the temperature and SAR underestimation. A computer model was used to estimate the error made by fluoroptic probes in temperature and SAR measurement. The transversal contact of the pigmented portion of the temperature probe and the PM lead tip minimizes the underestimation for temperature and SAR. This contact position also has the lowest temperature and SAR error. For other contact positions, the maximum temperature error can be as high as -45%, whereas the maximum SAR error can be as high as -54%. MRI heating evaluations with temperature probes should use a contact position minimizing the maximum error, need to be accompanied by a thorough uncertainty budget and the temperature and SAR errors should be specified.

Automated classification of human atrial fibrillation from intraatrial electrograms.

The assessment of the degree of organization and the classification of atrial fibrillation (AF) according to the types defined by Wells usually resorts to the visual inspection of bipolar intraatrial electro‐grams. The focus of this study was to test, seven parameters aimed to quantify the degree of organization of the electrograms, and then to design a final classification scheme based on a multidimensional, minimum‐distance analysis. The following parameters were tested: mean atrial period (AP) and its coefficient of variation (CV); number of points lying at the baseline (NO) and the Shannon entropy (EN) of the amplitude probability density function (APDF); depolarization width (F‐WIDTH); and correlation waveform analysis (CWA) and electrogram bandwidth (BW). The signal database consisted in a set of 160 AF strips of Type I, II, and HI AF, scored by an expert cardiologist (60 Type I, 40 Type II, 60 Type III) and further divided in a training set (60) and a test set (100). Strips were 6 seconds long and were recorded with 5‐mm interspace bipolar catheters from electrically induced (n = 13) and chronic (n = 10) patients. A classification algorithm based on a minimum‐distance (Mahalanobis distance) discriminant analysis was tested. Using a single parameter, the best discriminations were provided by NO, F‐WIDTH, and CV. F‐WIDTH was found strongly inversely correlated to NO (r =−0.90). Of all the two‐parameter combinations, CV‐NO provided the best classification: 92 of WO segments were correctly classified with sensitivity > 90% and specificity > 92%. A further improvement was obtained by including BW as a third parameter (93/100 correctly classified). The use of more than three parameters not only failed to improve, but even degraded the classification.

P-Wave Morphology Assessment by a Gaussian Functions-Based Model in Atrial Fibrillation Patients

Aim of this study was to present a P-wave model, based on a linear combination of Gaussian functions, to quantify morphological aspects of Pwave in patients prone to atrial fibrillation (AF). Five-minute ECG recordings were performed in 25 patients with permanent dual chamber pacemakers. Patients were divided into high-risk and low-risk groups, including patients with and without AF episodes in the last 6 mo preceding the study, respectively. ECG signals were acquired using a 32-lead mapping system for high-resolution biopotential measurement (ActiveTwo, Biosemi, The Netherlands, sample frequency 2 kHz, 24-bit resolution). Up to 8 Gaussian models have been computed for each averaged P-wave extracted from every lead. The P-wave morphology was evaluated by extracting seven parameters. Classical time-domain parameters, based on P-wave duration estimation, have been also estimated. We found that the P-wave morphology can be effectively modeled by a linear combination of Gaussian functions. In addition, the combination of time-domain and morphological parameters extracted from the Gaussian function-based model of the P-wave improves the identification of patients having different risks of developing AF

Evaluation of Electromagnetic Interference of GSM Mobile Phones with Pacemakers Featuring Remote Monitoring Functions

The aim of this study was to evaluate whether global system for mobile communication (GSM) cellular phones can affect the home monitoring (HM) function implemented in last generation pacemakers (PM).

Linear and non-linear analysis of atrial signals and local activation period series during atrial-fibrillation episodes

Linear and non-linear indexes for the characterisation of the dynamics in atrial signals (AS) and local atrial period (LAP) series are assessed in different atrial fibrillation (AF) episodes as defined by Wells. Parameters include the linear index obtained from the cross-correlation function (CCF) between ASs and the non-linear synchronisation (S) index based on the mutual corrected conditional entropy (MCCE). Regularity (R) was computed on single-lead AS. In addition, the level of predictability (LP) and the regularity of LAP series were computed. It was found that the level of synchronisation between ASs decreased passing from type-I to type-II AF when using linear (CCF: 0.90±0.10 against 0.44±0.18; p<0.001) and non-linear (S: 0.22±0.10 against 0.05±0.03; p<0.001) indexes. The regularity index (in normal sinus rhythm (NSR): 0.30±0.08; in AF-I: 0.19±0.10; in AF-II: 0.09±0.02; NSR against AF-I p<0.001; AF-I against AF-II p<0.001) and level of predictability (in NSR: 65±18; in AF-I: 27±13; in AF-II 7±6; NSR against AF-I p<0.001; AF-I against AF-II p<0.001) significantly decreased in the LAP series passing from NSR to AF-II. The proposed parameters succeeded in discriminating the different dynamics which characterised AS and LAP series during different kinds of AF episodes.

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).

Descriptors of wavefront propagation

This article presents two signal processing techniques for the analysis of intracardial electrograins in patients with atrial fibrillation (AF). The first, number of occurrences (NO), is aimed at quantifying the level of organization of the signal. The second, index of synchronization (IS), quantifies the degree of synchrony of electrograms from adjacent atrial sites. The proposed indexes are applied to multielectrode basket catheter recordings in patients with chronic or electrically induced AF

Transient phase locking patterns among respiration, heart rate and blood pressure during cardiorespiratory synchronisation in humans

The interactions between respiration, heart rate and blood pressure variability (HRV, BPV), are considered to be of paramount importance for the study of the functional organisation of the autonomic nervous system (ANS). The aim of the reported study is to detect and classify the intermittent phase locking (PL) phenomena between respiration, HRV and BPV during cardiorespiratory synchronisation experiments, by using the following time-domain techniques: Poincaré maps, recurrence plots, time-space separation plots and frequency tracking locus. The experimental protocol consists of three stages, with normal subjects in paced breathing at 15, 12 and 8 breaths min−1. Transient phenomena of coordination between respiration and the major rhythms of HRV and BPV (low and high frequency, LF and HF) have been detected and classified: no interaction between LF and HF rhythms at 15 breaths min−1; short time intervals of stable 1∶2 frequency and phase synchronisation during the 12 breaths min−1 stage; 1∶1 PL during the 8 breaths min−1 stage. 1∶1 and 1∶2 PL phenomena occurred when the respiration frequency was quite close to the LF frequency or when it was about twice the LF frequency, respectively. The complex organisation of the ANS seems to provoke transient rather than permanent PL phenomena between the co-ordinating components of respiration and cardiovascular variability series.

RESPIRATORY SINUS ARRHYTHMIA AND CARDIOVASCULAR NEURAL REGULATION IN ATHLETES

ABSTRACTStudies using spectral analysis of cardiovascular variability as a noninvasive means for assessing autonomic nervous system activity have provided controversial results in athletes. One reason is that a slow breathing rate-a common feature in athletes-affects spectral estimation because it c