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Biomedical subjects

Frank G Shellock

Publications and source records attributed to Frank G Shellock.

At least 19 recordsLinked to original sources
PubMed2007

Cardiac pacemakers and implantable cardioverter defibrillators: in vitro magnetic resonance imaging evaluation at 1.5-tesla.

RATIONALE AND OBJECTIVES: To evaluate the effect of Magnetic Resonance Imaging (MRI) performed at 1.5-Tesla on current generation pacemakers and ICDs to identify safe parameters for MRI examinations. METHODS: Pacemakers (Identity ADx XL DR+ 5386 and Identity ADx DR + 5380 generators; 1688T/52-cm atrial and ventricular leads) and ICDs (Atlas + V-243, Epic + V-236, and Epic + HF V-350 generators; Riata 1581/65-cm and QuickSite 1056K/75-cm leads; St. Jude Medical, Sylmar, California, USA) were evaluated for magnetic field interactions. MRI-related heating was assessed using various levels of RF power (SARs) and conditions that included scans on different body regions. Functional aspects of the devices were evaluated immediately before and after MRI procedures utilizing nine different pulse sequences. Induced currents were measured using a custom built system. RESULTS: Magnetic field interactions will not create a hazard for these pacemakers and ICDs. All scans of the "head" and "lumbar" regions resulted in temperature changes < or =0.5 degrees C at SARs ranging from 2.0 to 3.0-W/kg. For the "chest" area, temperature increases ranged from 0.4 degrees C to 3.6 degrees C at an SAR of 2.0-W/kg. No memory corruption, hardware changes, or changes in device parameters were seen. Magnetic field gradients have a low likelihood of inducing currents that would stimulate the heart. CONCLUSIONS: No hazardous magnetic field interactions or physiologically significant heating occurred for certain conditions. There was no permanent effect on device function. By following specific conditions, these pacemakers and ICDs may be safe for patients scanned at 1.5-Tesla.

Defibrillators, Implantable↗
PubMed2007

MR in patients with pacemakers and ICDs: Defining the issues.

There has been great controversy related to performance of magnetic resonance imaging in patients with pacemakers and implantable cardiac defibrillators. Recent questions have been raised regarding whether contraindications are absolute or relative. Although there are theoretical as well as documented issues relating to device malfunction, data suggest that scanning patients with devices may be feasible when important clinical questions need to be addressed by following strict guidelines. Advanced knowledge and understanding of electrophysiologic as well as magnetic resonance imaging-related issues, and a multidisciplinary, collaborative approach is required to further define the role of MR in patients with pacemakers and implantable cardiac defibrillators.

Artifacts↗
PubMed2006

Safety characteristics of gadobenate dimeglumine: clinical experience from intra- and interindividual comparison studies with gadopentetate dimeglumine.

PURPOSE: To evaluate the safety and tolerability of gadobenate dimeglumine (Gd-BOPTA) relative to that of gadopentetate dimeglumine (Gd-DTPA) in patients and volunteers undergoing MRI for various clinical conditions. MATERIALS AND METHODS: A total of 924 subjects were enrolled in 10 clinical trials in which Gd-BOPTA was compared with Gd-DTPA. Of these subjects, 893 were patients with known or suspected disease and 31 were healthy adult volunteers. Of the 893 patients, 174 were pediatric subjects (aged two days to 17 years) referred for MRI of the brain or spine. Safety evaluations included monitoring vital signs, laboratory values, and adverse events (AE). RESULTS: The rate of AE in adults was similar between the two agents (Gd-BOPTA: 51/561, 9.1%; Gd-DTPA: 33/472, 7.0%; P = 0.22). In parallel-group studies in which subjects were randomized to either agent, the rate of AE was 10.9% for Gd-BOPTA and 7.9% for Gd-DTPA (P = 0.21). In the subset of subjects receiving both agents in intraindividual crossover trials, the rate of AE was 8.0% for Gd-BOPTA and 8.5% for Gd-DTPA (P = 0.84). Results of other safety assessments (laboratory tests, vital signs) were similar for the two agents. CONCLUSION: The safety profile of Gd-BOPTA is similar to Gd-DTPA in patients and volunteers. Both compounds are equally well-tolerated in patients with various disease states undergoing MRI.

Adolescent↗
PubMed2006

Cardiac pacemaker: in vitro assessment at 1.5 T.

BACKGROUND: In vitro testing is used to determine safe parameters before performing magnetic resonance imaging (MRI) on a patient with an implant. Therefore, the objective of this study was to evaluate a cardiac pacemaker using a 1.5-T magnetic resonance (MR) system. METHODS: A modern cardiac pacemaker (INSIGNIA I PLUS, Model 1298, and FINELINE II, Model 4471, pacing leads; Guidant Corporation, St Paul, MN) was evaluated for magnetic field interactions at 1.5 T. Magnetic resonance imaging-related heating was assessed using 3 different 1.5-T scanners operating at various levels of radio-frequency power and imaging conditions. Functional aspects of the pacemaker were evaluated immediately before and after MRI (9 different pulse sequences). Artifacts were also characterized. RESULTS: Magnetic field interactions for the pacemaker were minor. Temperature changes measured in vitro were at levels that are not expected to pose a risk for specific MR conditions (< 4.0 degrees C). The function of the pacemaker was unaffected by MRI. Artifacts were minor for the leads and relatively large for the implantable pulse generator. CONCLUSION: The findings indicated that this pacemaker exhibited acceptable safety features relative to the use of a 1.5-T MR system. If induced currents do not occur for this device, it may be safe for a patient to undergo MRI by following specific conditions. The results are specific to the pacemaker tested, the MR systems, and conditions used in this evaluation.

Artifacts↗
PubMed2006

Safety of gadobenate dimeglumine (MultiHance): Summary of findings from clinical studies and postmarketing surveillance.

OBJECTIVES: Prospective studies and retrospective analyses were undertaken to evaluate the clinical safety of gadobenate dimeglumine (MultiHance) and to assess tolerability in special populations. MATERIALS AND METHODS: A total of 3092 subjects received MultiHance in 79 clinical trials. Data from comparisons with other contrast agents and studies in children, subjects with hepatic or renal impairment, or subjects with coronary artery disease were reviewed. Postmarketing safety surveillance data after more than 1.5 million applications were also evaluated. RESULTS: In total, 413 of 2982 (14%) adult subjects receiving MultiHance reported at least one adverse event (AE) definitely or potentially related to MultiHance, an incidence that was similar to that observed with placebo (21/127, 17%) or active controls (59/723, 8%). In crossover studies, 23 of 287 (8%) subjects receiving MultiHance experienced AE compared with 25 of 295 (9%) receiving gadopentetate dimeglumine (Magnevist). No increased AE rate was observed in children and no worsening of renal or liver function was observed in subjects with hepatic or renal impairment. No detrimental effect on cardiac electrophysiology could be observed from a retrospective analysis of ECG parameters in more than 1000 patients and healthy volunteers. The AE reporting rate from postmarketing safety surveillance of MultiHance was 0.05%. Serious AEs were rarely reported and included dyspnea, nausea, urticaria, hypotension, and anaphylactoid reactions. CONCLUSIONS: MultiHance appears to be well tolerated in adults and children and in subjects with impaired liver or kidney function or coronary artery disease. In controlled trials, MultiHance demonstrated a similar safety profile to that of Magnevist.

Adolescent↗
PubMed2005

Septal repair implants: evaluation of magnetic resonance imaging safety at 3 T.

Specialized implants are used for transcatheter closure of septal defects, including atrial and ventricular septal defects, and patent foramen ovale. These metallic devices may pose a risk to patients undergoing magnetic resonance imaging (MRI) procedures especially if performed at 3 T. Therefore, this investigation evaluated MRI safety at 3 T for septal repair implants (CardioSEAL Septal Repair Implant and STARFlex Septal Repair Implant, NMT Medical, Boston, MA, USA) by characterizing magnetic field interactions, heating and artifacts. These implants exhibited minor magnetic field interactions; heating was not excessive (+0.5 degrees C); and artifacts will only create a problem if the area of interest is in the same area as or near these devices. Thus, the findings indicated that it would be safe for a patient with these implants to undergo MRI at 3 T or lower. Importantly, because of the minor magnetic field interactions, MRI may be performed immediately after implantation.

Alloys↗
PubMed2005

Simple design changes to wires to substantially reduce MRI-induced heating at 1.5 T: implications for implanted leads.

Reductions in MRI-induced heating at 1.5 T resulting from a simple design change to coiled wires were investigated. MRI-induced heating was assessed for two different coiled wire forms (length, 26 cm): (1) multi-filar coiled wire form and (2) multi-filar coiled wire form having a different coiled pitch, providing an air gap spacing between adjacent five-filar coil loops. Each wire had an electrode and was insulated to create a lead, similar to that which would be used for a medical implant. The wire forms were placed in a gelled-saline-filled head/torso phantom and imaged at 1.5 T [whole-body average specific absorption rate (SAR), 1.79 W/kg]. Fluoroptic thermometry probes were used to measure temperatures at the distal ends of the wires. The experiments demonstrated a substantial reduction in MRI-induced heating for the modified wire compared to the unmodified wire (i.e., 10.5 degrees C difference observed in one experiment and 26 degrees C difference in another). These findings have important implications for MRI-induced heating of leads used for medical implants.

Electric Wiring↗
PubMed2005

Neurostimulation systems: assessment of magnetic field interactions associated with 1.5- and 3-Tesla MR systems.

PURPOSE: To evaluate magnetic field interactions at 1.5- and 3-Tesla for implantable pulse generators (IPGs) and radiofrequency (RF) receivers used for implantable neurostimulation systems. MATERIALS AND METHODS: Measurements of magnetically induced displacement force and torque were determined for 10 devices (seven IPGs, three RF receivers) used for neurostimulation systems. Displacement force and torque were assessed at various positions in 1.5- and 3-Tesla MR systems using standardized techniques. RESULTS: Four IPGs exhibited force ratios (magnetic attraction force/device weight) greater than 1.0, with the overall magnitude of the force ratio increasing significantly when comparing the 1.5-Tesla to the 3-Tesla MR system. Of the seven IPGs tested, one exhibited a torque ratio (magnetic induced torque/product of the device weight and length) greater than 1.0. The RF receivers displayed relatively strong magnetic field interactions at both 1.5- and 3-Tesla, exhibiting force and torque ratios greater than 1.0. CONCLUSIONS: The neurostimulation implants tested exhibited varying degrees of magnetic field interactions, with four of the seven IPGs and the three RF receivers exhibiting at least one MR-induced force or torque value greater than the effect of gravity. These findings have important implications for patients with these implants who are referred for MRI examinations.

Deep Brain Stimulation↗
PubMed2005

Effects of coil dimensions and field polarization on RF heating inside a head phantom.

Deterioration of radiofrequency (RF) inhomogeneity with increasing static magnetic field in magnetic resonance imaging (MRI) is one of the fundamental challenges preventing their clinical rendition and posing safety hazards. Variation in RF coil designs could help redistribute RF energy absorption over the imaged object. This work is intended to determine experimentally the difference in RF heating produced within a human head phantom by in situ measurement of RF inhomogeneity as a function of coil design utilized at 8 T. The heating patterns of 1/4 wavelength (long) and 1/8 wavelength 11-cm (short) transverse electromagnetic (TEM) coils loaded with a homogeneous human head phantom at 340 MHz were evaluated. In addition, different transmit/receive (T/R) configurations were used in search for the possibility of "hot-spot" formation. Fluoroptic thermometry was used to measure temperatures in multiple positions in a head phantom made of ground turkey breast for RF powers corresponding to a specific absorption rate (SAR) of 4.0 W/kg for 10 min. Numerical simulations were performed to study the general RF power deposition patterns in phantoms at 340 MHz including the effects of field polarization. The temperature increases varied from 0 to 0.8 degrees C for the long RF coil, while the short RF coil produced a maximum temperature change of 0.5 degrees C. Similar to ultra high-field electromagnetic simulations, these measurements revealed low peripheral and high deep-tissue heating at 8 T. The findings indicated that the largest temperature changes for both cases were less than 1 degrees C. While these results showed an increase in localized heating due to RF pulses at 8 T, they highlight that RF inhomogeneity could be redistributed using different RF coil designs through which the hot spots could be made cooler.

Equipment Safety↗
PubMed2005

Bilateral neurostimulation systems used for deep brain stimulation: in vitro study of MRI-related heating at 1.5 T and implications for clinical imaging of the brain.

Deep brain stimulation (DBS) is used increasingly in the field of movement disorders. The implanted electrodes create not only a prior risk to patient safety during MRI, but also a unique opportunity in the collection of functional MRI data conditioned by direct neural stimulation. We evaluated MRI-related heating for bilateral neurostimulation systems used for DBS with an emphasis on assessing clinically relevant imaging parameters. Magnetic resonance imaging was performed using transmit body radiofrequency (RF) coil and receive-only head RF coil at various specific absorption rates (SARs) of RF power. In vitro testing was performed using a gel-filled phantom with temperatures recorded at the electrode tips. Each DBS electrode was positioned with a single extension loop around each pulse generator and a single loop at the "head" end of the phantom. Various pulse sequences were used for MRI including fast spin-echo, echo-planar imaging, magnetization transfer contrast and gradient-echo techniques. The MRI sequences had calculated whole-body averaged SARs and local head SARs ranging from 0.1 to 1.6 W/kg and 0.1 to 3.2 W/kg, respectively. Temperature elevations of less than 1.0 degrees C were found with the fast spin-echo, magnetization transfer contrast, gradient-echo and echo-planar clinical imaging sequences. Using the highest SAR levels, whole-body averaged, 1.6 W/kg, local exposed-body, 3.2 W/kg, and local head, 2.9 W/kg, the temperature increase was 2.1 degrees C. These results showed that temperature elevations associated with clinical sequences were within an acceptable physiologically safe range for the MR conditions used in this evaluation, especially for the use of relatively low SAR levels. Notably, these findings are highly specific to the neurostimulation systems, device positioning technique, MR system and imaging conditions used in this investigation.

Deep Brain Stimulation↗
PubMed2005

Drug eluting coronary stent: in vitro evaluation of magnet resonance safety at 3 Tesla.

PURPOSE: To evaluate MR safety at 3 Tesla for a drug eluting coronary stent. METHODS: A drug eluting coronary stent (Endeavor, cobalt alloy, Medtronic Vascular, Santa Rosa, CA) was evaluated for magnetic field interactions, heating, and artifacts at 3 Tesla. MRI-related heating was assessed with the stent in a gelled saline-filled phantom using a transmit/received RF body coil with a whole body averaged SAR of 2.0 W/kg. Artifacts were characterized using T1-weighted, spin echo, and gradient echo pulse sequences. RESULTS: The stent exhibited minor magnetic field interactions that will not cause migration. Heating was not substantial (+0.5 degrees C). Artifacts may create a problem if the area of interest is in the same area or close to the stent (e.g., for a T1-weighted, spin echo pulse sequence, within approximately 16 mm; for a gradient echo pulse sequence, within approximately 23 mm). Conclusion. The findings indicated that it would be safe for a patient with this cobalt alloy-based, drug-eluting coronary stent to undergo MRI at 3 Tesla or less. Importantly, because of the relative lack of magnetic field interactions, MRI may be performed immediately after implantation.

Artifacts↗
PubMed2005

Reduction of magnetic resonance imaging-related heating in deep brain stimulation leads using a lead management device.

OBJECTIVE: To evaluate the ability of a lead management device to reduce magnetic resonance imaging (MRI)-related heating of deep brain stimulation (DBS) leads and thereby to decrease the risks of exposing patients with these implants to MRI procedures. METHODS: Experiments were performed using the Activa series (Medtronic, Inc., Minneapolis, MN) DBS systems in an in vitro, gelled-saline head and torso phantom. Temperature change was recorded using fluoroptic thermometry during MRI performed using a transmit-and-receive radiofrequency body coil at 1.5 T and a transmit-and-receive radiofrequency head coil at 3 T. A cranial model placed in the phantom was used to test a custom-designed burr hole device that permitted the placement of small-diameter, concentric loops around the burr hole at the DBS lead as it exited the cranium. RESULTS: A total of 41 scans were performed, with absolute temperature changes ranging from 0.8 to 10.3 degrees C. Depending on the MRI system tested and the side of the phantom on which the hardware was placed, loop placement resulted in reductions in temperature rise of 41 to 74%. The effect was linearly related to the number of loops formed (P < 0.01) over the range tested (0-2.75 loops). CONCLUSION: Small, concentric loops placed around the burr hole seem to reduce MRI-related heating for these implants. Although the mechanism is still not fully understood, a device such as that used in the present study could permit a wider range of clinical scanning sequences to be used at 1.5 and 3 T in patients with DBS implants, in addition to increasing the margin of safety for the patient.

Deep Brain Stimulation↗
PubMed2005

Permanent neurological deficit related to magnetic resonance imaging in a patient with implanted deep brain stimulation electrodes for Parkinson's disease: case report.

OBJECTIVE AND IMPORTANCE: Deep brain stimulation (DBS) is an accepted treatment for patients with Parkinson's disease refractory to medication. The efficacy of this therapy has led to increasing numbers of patients receiving DBS implants. Importantly, physicians caring for patients with implantable neurostimulators must be aware of treatment guidelines for these patients, including the use of therapeutic ultrasound, diathermy, and imaging studies such as magnetic resonance imaging (MRI). CLINICAL PRESENTATION: We describe a case of serious, permanent neurological injury secondary to a radiofrequency lesion produced by heating of a DBS electrode associated with MRI of the lumbar spine in a patient with Parkinson's disease. INTERVENTION: MRI may be performed safely in patients with DBS devices only by following the specific guidelines of the manufacturer. The generalization of these conditions to other neurostimulation system positioning schemes, other scanners, and other imaging scenarios can lead to significant patient injuries. CONCLUSION: To prevent catastrophic incidents, the manufacturer's guidelines should be followed carefully because they are known to result in the safe performance of MRI examinations of patients with neurostimulation systems used for DBS.

Brain Injuries↗
PubMed2005

Detachable coil for cerebral aneurysms: in vitro evaluation of magnetic field interactions, heating, and artifacts at 3T.

A detachable coil was assessed for magnetic field interactions, heating (body RF coil, SAR of 2.0-W/kg), and artifacts at 3-Tesla. The coil showed no magnetic field interactions and heating was negligible (+0.3 degrees C). Therefore, this coil is safe for a patient undergoing MR imaging at 3T or less. While artifacts may impair the ability to properly visualize anatomy in proximity to this implant, careful selection of imaging parameters can mitigate this problem.

Artifacts↗
PubMed2004

MR procedures: biologic effects, safety, and patient care.

The technology used for magnetic resonance (MR) procedures has evolved continuously during the past 20 years, yielding MR systems with stronger static magnetic fields, faster and stronger gradient magnetic fields, and more powerful radiofrequency transmission coils. Most reported cases of MR-related injuries and the few fatalities that have occurred have apparently been the result of failure to follow safety guidelines or of use of inappropriate or outdated information related to the safety aspects of biomedical implants and devices. To prevent accidents in the MR environment, therefore, it is necessary to revise information on biologic effects and safety according to changes that have occurred in MR technology and with regard to current guidelines for biomedical implants and devices. This review provides an overview of and update on MR biologic effects, discusses new or controversial MR safety topics and issues, presents evidence-based guidelines to ensure safety for patients and staff, and describes safety information for various implants and devices that have recently undergone evaluation.

Biophysical Phenomena↗
PubMed2004

Magnetic resonance imaging and cardiac pacemaker safety at 1.5-Tesla.

OBJECTIVES: The study was done to determine whether patients with pacemakers could safely undergo magnetic resonance imaging (MRI) at 1.5-Tesla (T). BACKGROUND: Because of theoretical risks, it is an absolute contraindication for a patient with a pacemaker to undergo MRI. However, there are times when an MRI is needed to provide valuable clinical information. METHODS: Fifty-four patients underwent a total of 62 MRI examinations at 1.5-T. The type of MRI examination was not limited and included cardiac, vascular, and general MRI studies using various whole-body averaged specific absorption rate (SAR) of radiofrequency power. Restrictions were not placed on the type of pacemaker present in the patient. All pacemakers were interrogated immediately before and after MRI scanning, and patients were continuously monitored. Before and after MRI, interrogation was done, and pacing and sensing thresholds, as well as lead impedances, were all measured. RESULTS: A total of 107 leads and 61 pulse generators were evaluated. No adverse events occurred. Forty (37%) of the leads underwent changes, whereas 10 (9.4%) leads underwent a significant change. Only 2 of the 107 (1.9%) leads required a change in programmed output. Threshold changes were unrelated to cardiac chamber, anatomical location, peak SAR, and time from lead implant to the MRI examination. Electrocardiographic changes and patient symptoms were minor and did not require cessation of MRI. CONCLUSIONS: Safety was demonstrated in this series of patients with pacemakers at 1.5-T.

Arrhythmias, Cardiac↗
PubMed2004

Assessment of the rotator cuff and glenoid labrum using an extremity MR system: MR results compared to surgical findings from a multi-center study.

PURPOSE: To conduct a multi-center assessment of the use of a 0.2-T, extremity MR system (E-scan; General Electric Lunar Corp. and Esaote, Genoa, Italy) for identifying tears of the rotator cuff and glenoid labrum. MATERIALS AND METHODS: A retrospective study was performed involving 160 patients (age range, 15-84 years old) from five facilities in the United States, comparing shoulder MR imaging to surgical findings. MR imaging of the shoulder was conducted as follows: shoulder coil; T1-weighted spin echo, coronal-oblique and axial images; short Tau inversion recovery (STIR), coronal-oblique images and axial images; and T2-weighted spin echo, coronal-oblique and sagittal-oblique images. The MR examinations were interpreted in an independent, prospective manner by two radiologists with extensive musculoskeletal MRI experience. Arthroscopic (N = 103) or open surgical (N = 57) procedures were performed within a mean of 53 days after MR imaging. RESULTS: Surgical findings demonstrated rotator cuff tears in 131 patients and labral tears in 60 patients. For the rotator cuff, the sensitivity, specificity, positive predictive value, and negative predictive value were 90%, 93%, 98%, and 68%, respectively. For the labrum, the sensitivity, specificity, positive predictive value, and negative predictive value were 55%, 100%, 100%, and 82%, respectively. CONCLUSIONS: There was good agreement when MR results obtained using the extremity MR system were compared to surgical findings for identifying rotator cuff tears, while the sensitivity of MR imaging for determining labral tears was relatively poor. Nevertheless, these findings were comparable to those reported in the peer-reviewed literature for MR systems operating at mid-, and high-field-strengths.

Adolescent↗