Assessment of MRI safety issues for stainless steel sutures used for microtia reconstruction.

INTRODUCTION: Potential magnetic resonance imaging issues for stainless steel sutures used for microtia reconstruction could be clinically significant for safety and diagnostic yield considerations. Therefore, the purpose of this investigation was to assess magnetic resonance issues (magnetic field interactions, heating, and artifacts) for different types of stainless steel sutures used for microtia reconstruction. METHODS: Small gauge, commonly used stainless steel sutures from four different manufacturers (5/0 Steelex, Aesculap/B, Braun Medical, Inc.; Nagata 38 Gauge Microtia Wire, Bear Medical Corporation; Auricular Reco Wire, Medicon Surgical Inc.; and 5-0 B&S 35 Surgical Steel Suture, Ethicon, Inc.) were tested using standardized ex vivo techniques to assess magnetic field interactions, heating, and artifacts at 3 Tesla. Before testing, the stainless steel sutures were configured in a manner same as that for cartilage reconstruction used to treat microtia. RESULTS: Each stainless steel suture exhibited minor magnetic field interactions at 3 Tesla (translational attraction, deflection angle <10°, and no torque). Heating associated with a whole-body averaged specific absorption rate of 2.9 W/kg was not excessive (highest temperature changes, ≤1.8 °C). Artifacts were relatively minor in relation to the size and shape of each stainless steel suture (artifact size in relation to the size and shape of each stainless steel suture extending ≤5 mm). CONCLUSIONS: The stainless steel sutures that underwent testing do not present additional risks to patients in a 3-Tesla or less magnetic field setting (i.e., magnetic resonance conditional). Artifacts for these sutures may only be an issue within close proximity to the reconstructed ear.

In vitro evaluation of MR imaging issues at 3T for aneurysm clips made from MP35N: Findings and information applied to 155 additional aneurysm clips.

BACKGROUND AND PURPOSE: Aneurysm clips need to be tested at 3T to characterize MR imaging concerns, including magnetic field interactions, MR imaging-related heating, and artifacts. Therefore, we evaluated these risks for aneurysm clips. MATERIALS AND METHODS: Three different MP35N aneurysm clips (Codman Slim-Line Aneurysm Clip, straight, blade length 25-mm; Codman Slim-Line Aneurysm Clip Graft, 5-mm diameter x 5-mm width; Codman Slim-Line Aneurysm Clip, reinforcing 30 degrees angle, 6-mm x 18-mm) that represented the largest mass for 155 additional clips made from MP35N were tested. The clips were evaluated at 3T for magnetic field interactions, heating, and artifacts. We studied MR imaging-related heating, placing the clip in a gelled-saline-filled phantom with MR imaging performed by using a transmit/receive radio-frequency body coil at a whole-body average SAR of 3 W/kg for 15 minutes. Artifacts were characterized by using T1-SE and GRE pulse sequences. RESULTS: Each aneurysm clip showed relatively minor magnetic field interactions, which would not cause movement in situ. Heating was not excessive (highest temperature change, <1.8 degrees C). Artifacts may create problems if the area of interest is in the same area or close to the aneurysm clip. CONCLUSIONS: The results of this investigation demonstrated that it would be acceptable (ie, "MR conditional" using current terminology) for patients with these aneurysm clips to undergo MR imaging at < or =3T. Notably, on the basis of the sizes of the clips that underwent testing, these findings pertain to 155 additional aneurysm clips made from the same material.

Programmable CSF shunt valve: in vitro assessment of MR imaging safety at 3T.

A programmable CSF shunt valve was assessed for magnetic field interactions, heating (transmit-receive body radio-frequency coil; whole-body averaged specific absorption rate, 2.1 W/kg), functional alterations, and artifacts at 3T. The programmable valve showed minor magnetic field interactions and heating was not excessive (+0.8 degrees C). The function of the programmable valve was not altered by multiple exposures to the 3T scanner or from exposure to various MR imaging conditions. Therefore, this implant is safe for a patient undergoing MR imaging at 3T or less when the radiologist follows specific safety guidelines. Artifacts for the programmable valve were relatively large in relation to the size and shape of the valve; this finding may impact the diagnostic use of MR imaging if the area of interest is in proximity to this implant.

MR safety in patients with implanted deep brain stimulation systems (DBS).

INTRODUCTION: While it is desirable to perform MRI examinations in patients with deep brain stimulators (DBS), a major safety concern exists regarding the potential for excessive heating secondary to magnetically induced electrical currents. This study was designed to determine the safety of MRI and DBS. METHODS: Standard configurations of DBS systems were tested. In vitro testing was performed using a 1.5-Tesla MR system, a gel-filled phantom, and the body and head RF coils with varying levels of RF energy (SAR). A fluoroptic thermometry system was used to record temperatures. RESULTS: Using the 1.5-T MRI and body RF transmit coil, the temperature changes ranged from 2.5 to 25.3 degrees C. Using the 1.5-T MRI and head RF transmit coil, the temperature changes ranged from 2.3 to 7.1 degrees C. CONCLUSIONS: Excessive heating does occur with certain MR imaging conditions. Under certain conditions determined in this study, patients with DBS may safely undergo anatomical MR imaging. In the future, standardized testing and more comprehensive studies will be needed to ensure the MR safety of neurostimulation systems.

Radiofrequency energy induced heating of bovine articular cartilage: comparison between temperature-controlled, monopolar, and bipolar systems.

This in vitro investigation characterized temperature changes associated with radiofrequency (RF) energy induced heating of bovine articular cartilage using temperature-controlled, monopolar (Vulcan RF system and Vulcan, TAC-S Electrothermal Probe) and bipolar (VAPR II RF system and VAPR TC RF electrode) electrosurgical equipment. The RF generators were used at the same setting (set temperature 70 degrees C; 30 W). The cartilage tissue sample was placed in a saline bath maintained at room temperature. Temperatures were recorded using fluoroptic thermometry at the RF electrode-tissue interface at 1-s intervals before, during deliver of RF energy (1- and 2-s), and after (1- to 3-s). For both electrosurgical systems the mean RF electrode-tissue interface temperatures were significantly ( P<0.05) higher than the mean baseline value during delivery of RF energy (monopolar, highest mean temperature, 65.7 degrees C; bipolar, highest mean temperature, 54.1 degrees C). In general, during and after the deliver of RF energy, the monopolar RF system produced tissue temperatures that were significantly ( P<0.05) higher than those produced by the bipolar RF system. Neither electrosurgical system exceeded the set temperature of 70 degrees C. These findings provide basic tissue temperature characteristics for the newly developed, temperature-controlled RF devices applied to articular cartilage.

Evaluation of the rotator cuff and glenoid labrum using a 0.2-Tesla extremity magnetic resonance (MR) system: MR results compared to surgical findings.

The purpose of this investigation was to evaluate the diagnostic capabilities of magnetic resonance imaging (MRI) performed using a dedicated-extremity MR system in detecting lesions of the rotator cuff and glenoid labrum. This retrospective study compared the MR results obtained in 47 patients that underwent MRI using a 0.2-Tesla extremity MR system (E-scan) to the surgical findings. MR images of the shoulder were obtained as follows: shoulder coil, T1-weighted, coronal-oblique and axial images; short Tau inversion recovery (STIR), coronal-oblique images; and T2-weighted, coronal-oblique, sagittal-oblique, and axial images. The MR examinations were interpreted by three highly experienced, musculoskeletal radiologists. Open surgical (N = 26) or arthroscopic (N = 21) procedures were performed within a mean time of 33 days after MRI. The surgical findings revealed rotator cuff tears in 28 patients and labral lesions in 9 patients. For the rotator cuff tears, the sensitivity, specificity, positive predictive value, and negative predictive value were 89%, 100%, 100%, and 90%, respectively. For the labral lesions, the sensitivity, specificity, positive predictive value, and negative predictive value were 89%, 95%, 80%, and 97%, respectively. The findings indicated that there was good agreement comparing the MR results obtained using the low-field extremity MR system to the surgical findings for determination of lesions of the rotator cuff and glenoid labrum. Notably, the statistical values determined for the use of this MR system were comparable to those reported in the peer-reviewed literature for the use of whole-body, mid- and high-field-strength MR systems.

Metallic neurosurgical implants: evaluation of magnetic field interactions, heating, and artifacts at 1.5-Tesla.

The purpose of this study was to use ex vivo testing to determine the magnetic resonance imaging (MRI) safety aspects for seven different metallic neurosurgical implants in association with the 1.5-T MR environment. Ex vivo testing was performed using previously-described techniques for the evaluation of magnetic field interactions (deflection angle and torque), heating (gel-filled phantom and fluoroptic thermometry; 15 minutes of MRI at a specific absorption rate [SAR] of 1.4 W/kg), and artifacts (using T1-weighted, spin-echo and gradient-echo pulse sequences). None of the metallic implants displayed interactions with the magnetic field. The highest temperature change was +0.6 degrees C for the representative implant that was evaluated. Artifacts were relatively minor. The lack of magnetic field interactions and negligible heating indicate that MR procedures may be conducted safely in patients with these neurosurgical implants using MR systems with static magnetic fields of 1.5-T or less. Furthermore, these implants may be considered for use in interventional MR procedures insofar as the MR safe qualities and relatively small artifacts would likely be desirable for such procedures.

Radiofrequency energy-induced heating of bovine capsular tissue: Temperature changes produced by bipolar versus monopolar electrodes.

PURPOSE: To determine temperature changes associated with radiofrequency (RF) energy-induced heating of bovine capsular tissue using a bipolar RF electrode versus a temperature-controlled, monopolar RF electrode. TYPE OF STUDY: In vitro laboratory investigation using bovine capsular tissue. METHODS: Samples of bovine tissue were placed in a saline bath (37 degrees C) and RF energy was applied using bipolar and monopolar RF electrodes at manufacturer-recommended settings for tissue shrinkage. Fluoroptic thermometry was used to record temperatures on the tissue surface and at depths of 1 mm and 2 mm during continuous delivery of RF energy at 1, 2, 3, 4, 5, and 10 second time increments. RESULTS: The highest mean temperatures were recorded on the tissue surface, as follows (mean +/- SD; *P <.05, value compared with baseline): 1 sec 2 sec 3 sec 4 sec 5 sec 10 sec Bipolar 40.1 +/- 1.0* 48.2 +/- 4.7* 62.8 +/- 6.9* 76.0 +/- 7.6* 84.7 +/- 5.7* 94.7 +/- 1.9* Monopolar 39.0 +/- 0.7* 48.2 +/- 4.3* 67.7 +/- 7.0* 86.6 +/- 6.1* 93.8 +/- 2.7* 59.5 +/- 2.6* For the bipolar RF electrode, there was a strong linear relationship (R =.926) between mean surface temperatures versus time. The temperature-controlled, monopolar RF electrode did not appear to properly regulate the delivery of RF energy to maintain tissue temperatures at the selected level (i.e., 65 degrees C). The bipolar RF electrode produced a smaller temperature gradient (average difference, 9.2 degrees C) at the 1-mm tissue depth compared with the monopolar RF electrode (average difference, 14.6 degrees C). Temperature profiles at the 2-mm tissue depth were comparable for both types of RF electrodes. CONCLUSIONS: These data provide basic information pertaining to the temperature profiles produced by bipolar and monopolar RF electrodes applied to collagen-based tissue.

The effects of eccentric velocity on activation of elbow flexors: evaluation by magnetic resonance imaging.

PURPOSE: To compare magnetic resonance imaging (MRI) signal intensity changes in the primary elbow flexors during two isotonic exercise protocols varying in eccentric velocity and the ratio of eccentric to concentric activity. METHODS: Twelve men performed two exercise protocols. The right and left arms were randomly assigned to one of two protocols that had the same workload (60% 1RM) and same total time of exercise (144 s) but differed in the velocity and ratio of eccentric to concentric activity (1:1 and 5:1 for the fast and slow protocols, respectively). MRI signal intensity changes were quantified pre- and post-exercises using an inversion recovery sequence with a 1.5T MRI system (TR = 2500 ms, TE = 90 ms, TI = 140 ms). Percent change in MRI signal intensity, rate of perceived exertion (RPE), and delayed onset muscle soreness (DOMS) were recorded and analyzed. RESULTS: The biceps brachii was found to be preferentially recruited during the fast protocol compared with the brachialis, whereas the brachialis was found to be preferentially recruited during the slow protocol (P < 0.05). The fast exercise protocol was perceived as being more strenuous (RPE = 8.3 +/- 2.1) than the slow (RPE = 5.4 +/- 1.5, P < 0.05) and produced DOMS in 58% of the tested subjects. CONCLUSIONS: These results suggest that agonists respond to various loading conditions nonhomogeneously. These findings may have implications with respect to exercise prescriptions for specific muscles.

Metallic surgical instruments for interventional MRI procedures: evaluation of MR safety.

This investigation evaluated metallic surgical instruments for magnetic resonance (MR) safety in association with a 1.5-Tesla/64-MHz MR system. Seven different instruments (mallet, bone punch, curette, Weil-Blakesley ethmoid forceps, suction cannula, septum speculum, and Kocher-Langenbeck retractor; Aesculap, Inc. (South San Francisco, CA) were tested for magnetic field interactions, heating, and generation of artifacts by using previously described techniques. Heating was evaluated for the septum speculum and Kocher-Langenbeck retractor by using a special gel-filled phantom and a fluoroptic thermometer to record temperatures immediately before and during MRI performed at a whole-body averaged SAR of 1.3 W/kg. Artifacts were assessed with the instruments placed inside of a gel-filled phantom and performing MRI using T1-weighted spin-echo and gradient-echo pulse sequences. Magnetic field interactions were relatively minor (deflection angles, 0 to 7 degrees; torque, 0 to +1), the highest temperature changes were < or = +0.8 degrees C, and the artifacts should not create substantial problems considering the "intended use" for these instruments. The findings of the MR safety tests indicated that the seven different metallic surgical instruments (Aesculap, Inc.) would be safe and acceptable for use in interventional MRI procedures performed with MR systems with static magnetic fields of 1.5 T or less. J. Magn. Reson. Imaging 2001;13:152-157.

Magnetic resonance imaging safety: implications for cardiovascular patients.

The potential bioeffects associated with magnetic resonance (MR) procedures result from exposure to the static, gradient, and radiofrequency electromagnetic fields. Each electromagnetic field represents a possible health risk at sufficiently high levels of exposure. The presence of certain biomedical implants and devices may pose hazards for patients undergoing MR procedures. Additionally, other safety issues must be considered for patients in the MR environment. This review article discusses the bioeffects of MR exposures and provides an overview of safety considerations, with an emphasis on information pertinent to cardiovascular patients.

Prosthetic heart valves and annuloplasty rings: assessment of magnetic field interactions, heating, and artifacts at 1.5 Tesla.

The purpose of this study was to determine the magnetic resonance (MR) safety aspects and artifacts for three different heart valve prostheses and two different annuloplasty rings that have not been evaluated previously in association with the 1.5-T MR environment. Ex vivo testing was performed using previously described techniques for the evaluation of magnetic field interactions (deflection angle and torque), heating (gel-filled phantom and fluoroptic thermometry; 15 min of MR imaging at a whole body-averaged specific absorption rate of 1.2 W/kg), and artifacts (using T1-weighted, spin echo, and gradient echo pulse sequences). One heart valve prosthesis and one annuloplasty ring showed no magnetic field interactions. Two heart valve prostheses and one annuloplasty ring displayed relatively minor magnetic field interactions (i.e., deflection angle < or = 6 degrees, torque, +1). Heating was < or = 0.7 degrees C for the five different implants. Artifacts varied depending on the amount and type of metal used to make the implants. For the three heart valve prostheses and two annuloplasty rings, the lack of substantial magnetic field interactions and relatively minor hearing indicated that MR procedures may be conducted safetly in patients with these implants using MR systems operating with static magneticfields of 1.5 T or less. Notably, these findings essentially apply to 54 different heart valve prostheses and 37 different annuloplasty rings (i.e., based on the various models and sizes available for these implants).

Radiofrequency energy-induced heating of bovine articular cartilage using a bipolar radiofrequency electrode.

Radiofrequency energy is used for thermal-assisted chondroplasty to treat grade II and III chondromalacia with the lowest possible energy setting that achieves the desired result. The purpose of this in vitro study was to determine the temperature changes associated with the use of radiofrequency energy delivered at different settings to bovine articular cartilage using a bipolar electrode. Cartilage samples were placed in a temperature-controlled (37 degrees C) saline bath for the delivery of radiofrequency energy. A fluoroptic thermometry probe was positioned to record the temperatures at the electrode-tissue interface. The electrode was activated for 2 seconds at settings of V2-120, V2-60, V2-40, and V2-20 in two modes: ablation and desiccation. Additionally, the cartilage samples were visually inspected to determine changes in appearance. The highest average temperatures were as follows: ablation mode, 78.5 degrees C (V2-120), 62.6 degrees C (V2-60), 58.1 degrees C (V2-40), and 54.1 degrees C (V2-20); desiccation mode, 71.8 degrees C (V2-120), 61.4 degrees C (V2-60), 57.7 degrees C (V2-40), and 53.3 degrees C (V2-20). There were statistically significant increases in temperatures associated with each of the respective settings. There were no substantial visual changes produced by the V2-20 settings, while the other settings produced a gradation of effects. These data provide information to help guide the use of a bipolar radiofrequency electrode and electrosurgical system for thermal-assisted chondroplasty.

Radiofrequency energy-induced heating during MR procedures: a review.

During an MR procedure, most of the transmitted RF power is transformed into heat within the patient's tissue as a result of resistive losses. Not surprisingly, the primary bioeffects associated with the RF radiation used for MR procedures are directly related to the thermogenic qualities of this electromagnetic field. This review article discusses the characteristics of RF energy-induced heating associated with MR procedures, with an emphasis on thermal and other physiologic responses observed in human subjects.

Auditory noise associated with MR procedures: a review.

This review article discusses the various types of acoustic noise produced during the operation of MR systems, describes the characteristics of the acoustic noise, and presents information regarding noise control techniques. In addition, the problems related to acoustic noise for patients and healthcare workers are discussed.

Pre-MRI procedure screening: recommendations and safety considerations for biomedical implants and devices.

Maintaining a safe MR environment is a daily challenge for MR healthcare workers, especially in consideration of the increasing number of clinical MR applications and the large and growing variety of biomedical implants and devices that are currently used in patients. This review article presents policies and procedures that should be used to screen all patients and individuals before allowing them to enter the magnetic resonance (MR) environment. Information pertaining to MR safety and the relative risk factors for implants, devices and materials is discussed. A comprehensive pre-MRI procedure screening form that is recommended for use by MR facilities is also included.

Aneurysm clips: evaluation of magnetic field interactions with an 8.0 T MR system.

This study was conducted to evaluate magnetic field interactions for aneurysm clips exposed to an 8.0 T magnetic resonance (MR) system. Twenty-six different aneurysm clips were tested for magnetic field translational attraction (deflection angle test) and torque (qualitative assessment method) using previously described techniques. Six of the specific aneurysm clips (i.e. type, model, blade length) made from stainless steel alloy (Perneczky) and Phynox (Yasargil, models FE 748 and FE 750) displayed deflection angles above 45 degrees and torque measurements of +4, indicating that these aneurysm clips maybe unsafe for patients or individuals in an 8.0 T MR environment. The specific aneurysm clips (i.e. type, model, blade length) made from commercially pure titanium (Spetzler), Elgiloy (Sugita), titanium alloy (Yasargil, model FE 750T), and MP35N (Sundt) displayed deflection angles less than 45 degrees and torque that ranged from + 1 to +4. Accordingly, these aneurysm clips are likely to be safe for patients or individuals exposed to an 8.0 T MR system. Depending on the actual dimensions and mass, an aneurysm clip made from Elgiloy may or may not be acceptable for a patient or individual in the 8.0 T MR environment.

Implantable spinal fusion stimulator: assessment of MR safety and artifacts.

The objective of this investigation was to perform magnetic resonance (MR) imaging safety and artifact testing of an implantable spinal fusion stimulator. Magnetic field interactions, artifacts, and operational aspects of an implantable spinal fusion stimulator were evaluated in association with a 1.5 T MR system. Magnetic field-related translational attraction was measured using the deflection angle test. A special test apparatus was used to determine torque at 4.7 T. Artifacts were characterized using fast multiplanar spoiled gradient-echo, T1-weighted spin-echo, and T1-weighted fast spin-echo sequences. Operational aspects of the implantable spinal fusion stimulator before and after exposure to MR imaging at 1.5 T were assessed. In addition, nine patients (six lumbar spine and three cervical spine) with implantable spinal fusion stimulators underwent MR imaging. The findings indicated that magnetic field interactions were relatively minor, artifacts were well characterized and should not create diagnostic problems, and there were no changes in the operation of the spinal fusion stimulator. The nine patients underwent MR procedures without substantial adverse events or complaints. Based on the results of this investigation and in consideration of the findings from previous studies of MR imaging safety for the implantable spinal fusion stimulator, MR imaging may be performed safely in patients using MR systems operating at 1.5 T or less following specific recommendations and precautions.