Biomedical subjects

Frank G Shellock

Publications and source records attributed to Frank G Shellock.

At least 37 records · Page 2Linked to original sources

PubMed2004

Evaluation of specific absorption rate as a dosimeter of MRI-related implant heating.

PURPOSE: To compare the magnetic resonance imaging (MRI)-related heating per unit of whole body averaged specific absorption rate (SAR) of a conductive implant exposed to two different 1.5-Tesla/64 MHz MR systems. MATERIALS AND METHODS: Temperature changes at the electrode contacts of a deep brain stimulation lead were measured using fluoroptic thermometry. The leads were placed in a typical surgical implant configuration within a gel-filled phantom of the human head and torso. MRI was performed using two different transmit/receive body coils on two different generation 1.5-Tesla MR systems from the same manufacturer. Temperature changes were normalized to whole body averaged SAR values and compared between the two scanners. RESULTS: Depending on the landmark location, the normalized temperature change for the implant was significantly higher on one MR system compared to the other (P < 0.001). CONCLUSION: The findings revealed marked differences across two MR systems in the level of radiofrequency (RF)-induced temperature changes per unit of whole body SAR for a conductive implant. Thus, these data suggest that using SAR to guide MR safety recommendations for neurostimulation systems or other similar implants across different MR systems is unreliable and, therefore, potentially dangerous. Better, more universal, measures are required in order to ensure patient safety.

Body Temperature↗

PubMed2004

Neurostimulation system used for deep brain stimulation (DBS): MR safety issues and implications of failing to follow safety recommendations.

The use of magnetic resonance imaging (MRI) in patients with neurostimulation systems used for deep brain stimulation requires the utmost care, and no individual should undergo an MR examination in the absence of empirical evidence that the procedure can be performed safely. The risks of performing MRI in patients with neurostimulators include those associated with heating, magnetic field interactions, induced currents, and the functional disruption of these devices. The exact safety recommendations for the particular neurostimulation system with regard to the pulse generator, leads, electrodes, operational conditions for the device, the positioning of these components, and the MR system conditions must be carefully followed for MRI. As highlighted by 2 recent accidents, the failure to strictly follow safety recommendations (eg, use a 1.5-T MR system with a send/receive head radiofrequency coil only; limit the specific absorption rate to 0.4 W/kg; etc.) may result in serious, temporary, or permanent injury to the patient including the possibility of transient dystonia, paralysis, coma, or even death.

Brain Diseases↗

PubMed2004

Implantable microstimulator: magnetic resonance safety at 1.5 Tesla.

RATIONALE AND OBJECTIVE: Ex vivo testing is necessary to characterize implants to determine if it is safe for the patient to undergo a magnetic resonance imaging (MRI) examination. Therefore, the objective of this study was to evaluate MR safety for an implantable microstimulator in association with a 1.5 Tesla MR system. METHODS: A microstimulator (RF BION, Alfred E. Mann Foundation for Scientific Research, Valencia, CA) was evaluated for magnetic field interactions and MRI-related heating. The functional aspects of this implant were assessed immediately before and after exposure to MRI (15 different pulse sequences). Artifacts were also characterized. RESULTS: Magnetic field interactions exhibited by the microstimulator will not pose a hazard after a suitable postimplantation period has elapsed. Temperature changes will not pose a risk. The function of the microstimulator was unaffected by MRI. Artifacts will only create a problem if the area of interest is in proximity to this implant (largest artifact area: T1-weighted spin echo, 2291 mm2; gradient echo, 3310 mm2). CONCLUSION: The overall findings indicated that it is safe for a patient with the microstimulator to undergo MRI at 1.5 Tesla by following specific safety guidelines described herein.

Artifacts↗

PubMed2004

Identification of wrist and metacarpophalangeal joint erosions using a portable magnetic resonance imaging system compared to conventional radiographs.

OBJECTIVE: To compare magnetic resonance (MR) images obtained using a portable MR system to radiographs for identifying bone erosions in the wrists and metacarpophalangeal (MCP) joints of patients with inflammatory arthropathy. METHODS: MR imaging and radiographs were performed in wrists (n = 227) and 2nd and 3rd MCP (n = 188) of 132 patients with inflammatory arthritis to identify erosions. MR imaging was performed using a portable MR system. Findings per body location and per patient were calculated and compared. Additionally, intraobserver and interobserver reliabilities were calculated. RESULTS: MR imaging identified bony erosions in 125 (95%) patients and in 315 (78%) body locations. By comparison, radiographs identified erosions in 78 (59%; p < 0.05) patients and in 156 (39%; p < 0.05) body locations. Intraobserver reliability (K = 0.564) and interobserver reliability (K = 0.429) exhibited moderate agreement, with reader agreement in 80% of the joints scored. CONCLUSION: There was superior sensitivity to bone damage using the portable MR system compared to radiographs of the wrists and MCP joints, suggesting that this scanner is extremely promising for assessment of inflammatory arthritis.

Adult↗

PubMed2003

Knees of Ironman triathletes: magnetic resonance imaging assessment of older (>35 years old) competitors.

PURPOSE: To use magnetic resonance imaging (MRI) to evaluate the knees of older (>35 years old), competitive Ironman triathletes to determine the prevalence of abnormal findings. MATERIALS AND METHODS: The knees of 29 Ironman triathletes (20 men, 9 women; age range, 35-66 years old) were studied by MRI. The findings were analyzed collectively and categorized into group I (N = 13), subjects without prior knee injuries and symptoms, and group II (N = 16), subjects with prior knee injuries and/or current symptoms. RESULTS: Ten percent of the knees had ligamentous abnormalities, but the prevalence was not statistically different comparing group I to group II. Fifty-five percent had abnormal menisci. The overall prevalence of abnormal menisci was significantly higher in group II (69%) than in group I (38%, P < 0.05). Cartilage abnormalities were found in 21% of the triathletes with a higher prevalence in group II (31%) than in group I (8%, P < 0.05). Twenty-one percent (6/29) of the knees had bone contusions, with a higher prevalence in group II (31%) than in group I (8%, P < 0.05). CONCLUSION: In general, the spectrum of abnormal MRI findings of the knee was no greater than age-related changes previously reported for other athletic populations and nonathletes. These results have important implications for the diagnostic use of MRI of the knee in this high-endurance, athletic population.

Adult↗

PubMed2003

8.0-Tesla human MR system: temperature changes associated with radiofrequency-induced heating of a head phantom.

PURPOSE: To investigate if the heat induced in biological tissues by typical radio frequency (RF) energy associated with an 8.0-Tesla magnetic resonance (MR) system causes excessive temperature changes. MATERIALS AND METHODS: Fluoroptic thermometry was used to measure temperatures in multiple positions in a head phantom made of ground turkey breast. A series of experiments were conducted with measurements obtained at RF power levels ranging from a specific absorption rate (SAR) of up to 4.0 W/kg for 10 minutes. RESULTS: The highest temperature increases were up to 0.7 degrees C. An inhomogeneous heating pattern was observed. In general, the deep regions within the phantom registered higher temperature increases compared to the peripheral sites. CONCLUSION: The expectation of an inhomogeneous RF distribution in ultra high field systems (> 4 T) was confirmed. At a frequency of 340 MHz and in-tissue RF wave length of about 10 cm, the RF inhomogeneity was measured to create higher temperatures in deeper regions of a human head phantom compared to peripheral tissues. Our results agree with the computational electromagnetic calculations for such frequencies. Importantly, these experiments indicated that there were no regions of heating that exceeded the current FDA guidelines.

Head↗

PubMed2003

Functional assessment of the joints using kinematic magnetic resonance imaging.

Kinematic magnetic resonance imaging (MRI) techniques were developed in recognition of the fact that certain pathologic conditions that affect the joints are position dependent or associated with stress or "loaded" conditions. Information obtained using kinematic MRI procedures often serves to definitively identify and characterize the underlying abnormality or to supplement the findings acquired with standard MRI techniques. To date, kinematic MRI methods have been applied to evaluate virtually every articulation. This article presents information for kinematic MRI applications applied to the temporomandibular and patellofemoral joints, with a discussion of the normal kinematics and pathokinematics seen using these unique imaging procedures. Other kinematic MRI procedures applied to the ankle, wrist, cervical spine, shoulder, and lumbar spine are briefly discussed.

Biomechanical Phenomena↗

PubMed2003

Cardiac pacemakers, ICDs, and loop recorder: evaluation of translational attraction using conventional ("long-bore") and "short-bore" 1.5- and 3.0-Tesla MR systems.

PURPOSE: To evaluate magnet-related translational attraction for cardiac pacemakers, ICDs, and an insertable loop recorder in association with exposure to "long-bore" and "short-bore" 1.5- and 3.0-Tesla MR systems. MATERIALS AND METHODS: Fourteen cardiac pacemakers, four ICDs, and one insertable loop recorder were evaluated for translational attraction using deflection angle tests performed at the points of the highest spatial gradients for long-bore and short-bore 1.5- and 3.0-Tesla MR systems according to ASTM guidelines. RESULTS: Deflection angles ranged from 9-90 degrees for the long-bore and from 11-90 degrees for the short-bore 1.5-T MR system. Deflection angles ranged from 23-90 degrees for the long-bore and from 34-90 degrees for the short-bore 3.0-T MR system. Three of the cardiovascular implants exhibited deflection angles > or = 45 degrees (i.e., indicating that they are potentially unsafe for patients) on the long-bore and short-bore 1.5-T MR systems. Eight implants exhibited deflection angles > or = 45 degrees on the long-bore 3.0-T MR system, while 14 exhibited deflection angles > or = 45 degrees on the short-bore 3.0-T MR system. In general, deflection angles for these cardiovascular implants were significantly (p < 0.01) higher on 1.5- and 3.0-Tesla short-bore compared to the long-bore MR systems. CONCLUSIONS: Several of the cardiovascular implants that underwent evaluation may be problematic for patients undergoing MR procedures using 1.5- and 3.0-T MR systems because of risks associated with magnet-related movements. Obviously, additional MR safety issues must also be considered for these implants.

Cardiovascular Diseases↗

PubMed2003

Patellofemoral kinematics during weight-bearing and non-weight-bearing knee extension in persons with lateral subluxation of the patella: a preliminary study.

STUDY DESIGN: Single-group, repeated-measures design. OBJECTIVE: To compare patellofemoral joint kinematics during weight-bearing and non-weight-bearing knee extension in persons with lateral subluxation of the patella. BACKGROUND: The only previous study to quantify differences in patellofemoral joint kinematics during weight-bearing and non-weight-bearing tasks was limited in that static loading conditions were utilized. Differences in patellofemoral joint kinematics between weight-bearing and non-weight-bearing conditions have not been quantified during dynamic movement. METHODS AND MEASURES: Six females with a diagnosis of patellofemoral pain and lateral subluxation of the patella participated. Using kinematic magnetic resonance imaging, axial images of the patellofemoral joint were obtained as subjects extended their knee from 45 degrees to 0 degrees during non-weight-bearing (5% body weight resistance) and weight-bearing (unilateral squat) conditions. Measurements of patellofemoral joint relationships (medial/lateral patellar displacement and patellar tilt), as well as femur and patella rotations relative to an external reference system (ie, the image field of view), were obtained at 3 degrees increments during knee extension. RESULTS: During non-weight-bearing knee extension, lateral patellar displacement was more pronounced than during the weight-bearing condition between 30 degrees and 12 degrees of knee extension, with statistical significance being reached at 27 degrees, 24 degrees, and 21 degrees. No differences in lateral patellar tilt were observed between conditions (P = .065). During the weight-bearing condition, internal femoral rotation was significantly greater than during the non-weight-bearing condition as the knee extended from 18 degrees to 0 degrees. During the non-weight-bearing condition, the amount of lateral patellar rotation was significantly greater than during the weight-bearing condition throughout the range of motion tested. CONCLUSIONS: The results of this study demonstrated that lateral patellar displacement was more pronounced during non-weight-bearing knee extension compared to weight-bearing knee extension in persons with lateral patellar subluxation. In addition, the results of this investigation suggest that the patellofemoral joint kinematics during non-weight-bearing could be characterized as the patella rotating on the femur, while the patellofemoral joint kinematics during the weight-bearing condition could be characterized as the femur rotating underneath the patella.

Adolescent↗

PubMed2003

Aneurysm clips: evaluation of magnetic field interactions and translational attraction by use of "long-bore" and "short-bore" 3.0-T MR imaging systems.

BACKGROUND AND PURPOSE: The use of 3.0-T MR systems is increasing worldwide. We evaluated magnetic field interactions and translational attraction for 32 aneurysm clips in association with exposure to "long-bore" and "short-bore" 3.0-T MR imaging systems. METHODS: Thirty-two different aneurysm clips were evaluated in this investigation. Each aneurysm clip was qualitatively evaluated for magnetic field interactions and quantitatively assessed for translational attraction by using the deflection angle test. The deflection angle tests were performed at the points of the highest spatial gradients for long-bore and short-bore 3.0-T MR imaging systems. RESULTS: Seventeen of the 32 aneurysm clips showed positive magnetic field interactions. Deflection angles for the aneurysm clips were significantly (P <.001) higher on the short-bore (range, 0-18 degrees) compared with those recorded on the long-bore (range, 0-16 degrees) 3.0-T MR imaging system. Aneurysm clips made from commercially pure titanium and titanium alloy displayed no translational attraction (n = 15), whereas those made from stainless steel alloy, Phynox, and Elgiloy displayed positive deflection angles (n = 17). CONCLUSION: The 32 different aneurysm clips passed (angle <45 degrees) the deflection angle test by using the long- and short-bore 3.0-T MR imaging systems, indicating that they are safe for patients and other persons in these MR environments (ie, immediate area of MR imaging systems). However, only clips made from the titanium and titanium alloy are entirely safe for patients undergoing MR imaging procedures because of the total lack of magnetic field interactions. The remaining clips require characterization of magnetic field-induced torque. Because of possible differences in the points of the highest spatial gradients for different 3.0-T MR imaging systems, the results are specific to the imaging units and bore designs used in this investigation.

Contraindications↗

PubMed2002

Magnetic resonance imaging and permanent cosmetics (tattoos): survey of complications and adverse events.

PURPOSE: To use a survey to determine the incidence of complications and adverse events in individuals with permanent cosmetics (e.g., tattooed eyeliner, eyebrows, lips, cheeks, etc.) who underwent magnetic resonance (MR) imaging. MATERIALS AND METHODS: A questionnaire was distributed to clients of cosmetic tattoo technicians. This survey asked study subjects for demographic data, information about their tattoos, and for their experiences during MR imaging procedures. RESULTS: Data obtained from 1032 surveys were tabulated. One hundred thirty-five (13.1%) study subjects underwent MR imaging after having permanent cosmetics applied. Of these, only two individuals (1.5%) experienced problems associated with MR imaging. One subject reported a sensation of "slight tingling" and the other subject reported a sensation of "burning"; both sensations were transient in nature. CONCLUSION: Based on these findings and information in the peer-reviewed literature, it appears that MR imaging may be performed in patients with permanent cosmetics without any serious soft tissue reactions or adverse events. Therefore, the presence of permanent cosmetics should not prevent a patient from undergoing MR imaging.

Artifacts↗

PubMed2002

Neurostimulation systems for deep brain stimulation: in vitro evaluation of magnetic resonance imaging-related heating at 1.5 tesla.

PURPOSE: To assess magnetic resonance imaging (MRI)-related heating for a neurostimulation system (Activa Tremor Control System, Medtronic, Minneapolis, MN) used for chronic deep brain stimulation (DBS). MATERIALS AND METHODS: Different configurations were evaluated for bilateral neurostimulators (Soletra Model 7426), extensions, and leads to assess worst-case and clinically relevant positioning scenarios. In vitro testing was performed using a 1.5-T/64-MHz MR system and a gel-filled phantom designed to approximate the head and upper torso of a human subject. MRI was conducted using the transmit/receive body and transmit/receive head radio frequency (RF) coils. Various levels of RF energy were applied with the transmit/receive body (whole-body averaged specific absorption rate (SAR); range, 0.98-3.90 W/kg) and transmit/receive head (whole-body averaged SAR; range, 0.07-0.24 W/kg) coils. A fluoroptic thermometry system was used to record temperatures at multiple locations before (1 minute) and during (15 minutes) MRI. RESULTS: Using the body RF coil, the highest temperature changes ranged from 2.5 degrees-25.3 degrees C. Using the head RF coil, the highest temperature changes ranged from 2.3 degrees-7.1 degrees C.Thus, these findings indicated that substantial heating occurs under certain conditions, while others produce relatively minor, physiologically inconsequential temperature increases. CONCLUSION: The temperature increases were dependent on the type of RF coil, level of SAR used, and how the lead wires were positioned. Notably, the use of clinically relevant positioning techniques for the neurostimulation system and low SARs commonly used for imaging the brain generated little heating. Based on this information, MR safety guidelines are provided. These observations are restricted to the tested neurostimulation system.

Brain↗

PubMed2002

Assessment of patellofemoral relationships using kinematic MRI: comparison between qualitative and quantitative methods.

PURPOSE: To compare the level of agreement between quantitative and qualitative methods in determining patellofemoral relationships, since controversy exists regarding the use of quantitative vs. qualitative criteria to interpret images of the patellofemoral joint (PFJ) obtained using kinematic magnetic resonance (MR) imaging. MATERIALS AND METHODS: One hundred twenty mid-patellar axial plane images obtained using kinematic MR imaging from fifteen subjects were randomly selected for analysis. MR images represented various knee flexion angles ranging from 0 to 60 degrees. Quantitative analysis (bisect offset and patellar tilt angle) was performed by two examiners using a computer-assisted software program. Based on data from previously published literature, MR images were characterized as demonstrating normal, medial, or lateral patellar subluxation, and/or normal, medial, or lateral tilt. Using similar categories, two different examiners experienced in reading MR images of the PFJ then applied qualitative criteria to the same images. RESULTS: The average agreement between the quantitative and qualitative assessments of horizontal patellar displacement and patellar tilt ranged from poor to moderate (Kappa coefficient values of 0.27 and 0.45, respectively). Quantitative and qualitative techniques demonstrated acceptable intra- and inter-observer reliability. CONCLUSION: These findings indicate that the use of quantitative criteria does not compare well to qualitative criteria in the analysis of kinematic MR images of the PFJ. One explanation for this discrepancy relates to the fundamental difference between the techniques. That is, quantitative measurements are based on the use of osseous landmarks, while the qualitative assessments tend to rely on a description of patellofemoral relationships based on joint surfaces.

Adult↗

PubMed2002

Magnetic resonance safety testing of a newly-developed fiber-optic cardiac pacing lead.

PURPOSE: To assess magnetic resonance (MR) safety for a newly developed, fiber-optic cardiac pacing lead. MATERIALS AND METHODS: MR safety was assessed for the fiber-optic cardiac pacing lead by evaluating magnetic field interactions and heating. Translational attraction and torque were evaluated using a 1.5-Tesla MR system and previously described, standardized techniques. MR imaging-related heating was assessed using a 1.5-Tesla MR system and a transmit/receive, body radiofrequency (RF) coil with the fiber-optic lead positioned to simulate an in vivo condition in a saline-filled phantom. The phantom had dimensions similar to a human subject's torso and head. A fluoroptic thermometry system was used to record temperatures on and near the electrodes of the fiber-optic pacing lead at five-second intervals immediately before and during 20 minutes of MR imaging performed at a whole-body-averaged specific absorption rate (SAR) of 1.5 W/kg. Temperatures were also recorded from a reference site during this experiment. RESULTS: Magnetic field interactions for the fiber-optic lead were minimal (deflection angle, 23 degrees; torque, +2). The highest temperature change recorded for the fiber-optic cardiac pacing lead and reference site was +0.8 degrees C. CONCLUSION: The minor magnetic field interactions and relative lack of heating for the fiber-optic pacing lead indicate that it should be safe for patients with this device to undergo MR imaging procedures using MR systems operating at 1.5-T or less and at a whole-body-averaged SARs up to 1.5 W/kg.

Electrodes↗

PubMed2002

Magnetic resonance safety update 2002: implants and devices.

The preservation of a safe magnetic resonance (MR) environment requires constant vigilance by MR healthcare professionals, particularly with regard to the management of patients with metallic biomedical implants or devices. The variety and complexity of implants and devices constantly changes, requiring continuous attention and diligence with regard to obtaining the most current and accurate information about these objects relative to the MR environment. This review article discusses MR safety and MR compatibility issues and presents important information for a variety of implants and devices, with an emphasis on those objects that have recently undergone evaluation or that require additional consideration because of existing controversy or confusion.

Electromagnetic Fields↗

PubMed2002

Biomedical implants and devices: assessment of magnetic field interactions with a 3.0-Tesla MR system.

PURPOSE: To evaluate magnetic field interactions for 109 different biomedical implants and devices in association with exposure to a 3.0-Tesla magnetic resonance (MR) system. MATERIALS AND METHODS: A total of 109 implants and devices (aneurysm clips, 32; clips, fasteners, and staples, 10; coils and stents, 10; heart valve prostheses and annuloplasty rings, 12; orthopedic implants, five; suture materials, 13; vascular access ports and accessories, 13; miscellaneous implants and devices, 14) were tested for magnetic field interactions at 3.0-Tesla using previously-described, standardized techniques to assess magnetic field translational attraction and torque. RESULTS: The deflection angles and torque measurements ranged, respectively, from 0 to 16 degrees and 0 to +2 for the aneurysm clips; 0 to 90 degrees and 0 to +4 for the clips, fasteners, and staples; 0 to 47 degrees and 0 to +4 for the coils and stents; 0 to 4 degrees and 0 to +1 for the heart valve prostheses and annuloplasty rings; 0 to 12 degrees and 0 to +2 for the orthopedic implants; 0 to 13 degrees and 0 to +2 for the suture materials; 0 to 52 degrees and 0 to +4 for the vascular access ports and accessories; and 0 to 28 degrees and 0 to +3 for the miscellaneous implants and devices. CONCLUSION: Of the 109 implants and devices assessed for magnetic field interactions at 3.0-Tesla, four (4%) are potentially unsafe based on deflection angle criteria. The implications of these results for patients undergoing MR procedures at 3.0-Tesla is discussed. Notably, these results are specific to the 3.0-Tesla MR system used for this evaluation.

Biocompatible Materials↗

PubMed2002

Radiofrequency energy induced heating of bovine capsular tissue: in vitro assessment of newly developed, temperature-controlled monopolar and bipolar radiofrequency electrodes.

This in vitro investigation characterized temperature changes associated with radiofrequency (RF) energy induced heating of bovine capsular tissue using newly developed, temperature-controlled monopolar (Vulcan RF system and Vulcan, TAC-S Electrothermal Probe) and bipolar (VAPR II RF system and VAPR TC RF electrode) RF systems and electrodes. Bovine capsular tissue samples were placed in a saline bath maintained at room temperature. Both RF generators were used at settings of 75 degrees C and 40 W. The RF electrodes were placed in stationary positions on the tissue samples and activated for 1- to 10-s. A fluoroptic thermometry system was utilized to record temperatures at the RF electrode-tissue interface at 1-s intervals. The results indicated that the mean tissue temperatures for the monopolar RF electrode tended to be higher than those produced by the bipolar RF electrode, especially during the 2- to 10-s RF delivery time intervals (P<0.05). Notably, during the 2- to 10-s time intervals the monopolar RF electrode produced mean tissue temperatures that exceeded the set temperature of 75 degrees C (range of differences +1.2 to +15.7 degrees C highest mean temperature 90.7 degrees C). By comparison, the bipolar RF electrode maintained tissue temperatures relatively close to the set temperature(range of differences -3.2 to +2.7 degrees C; highest mean temperature 77.7 degrees C). These findings provide basic temperature profiles for the two new temperature-controlled RF devices.

Animals↗

PubMed2002

In-office MR imaging.

The development of new metal alloys, along with more innovative magnet technology, has permitted the construction of smaller magnets for magnetic resonance (MR) systems, which, in turn, has allowed development of MR imaging systems designed to be physically smaller than conventional whole-body MR imaging systems. These specialized devices are commonly referred to as "niche," "dedicated," or "extremity" MR imaging systems. Performing MR imaging procedures with this type of system offers distinct advantages that include reduced overall costs, more convenient installation and siting, and greater patient comfort and safety. Importantly, these critical features permit extremity MR imaging systems to be readily utilized in an "in-office" setting. This article will provide an overview of the technical aspects and clinical applications for extremity MR imaging systems, present patient management issues, and discuss the economic and practical considerations of the use of extremity MR imaging systems in an in-office environment.

Adipose Tissue↗