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Biomedical subjects

F G Shellock

Publications and source records attributed to F G Shellock.

At least 37 records · Page 2Linked to original sources
PubMed1999

Effect of bracing on patellar kinematics in patients with patellofemoral joint pain.

PURPOSE: Bracing is commonly used to correct patellar malalignment syndromes. However, there are little objective data documenting the effect of such supports on patellofemoral joint relationships. The purpose of this study was to assess the effectiveness of an elastic patellofemoral sleeve brace in altering patellar tracking in subjects with patellofemoral pain. METHODS: Ten female subjects (12 patellofemoral joints) between the ages of 17 and 46 participated in this study. All subjects had a diagnosis of patellofemoral pain and demonstrated lateral patellar tracking based on magnetic resonance imaging (MRI) assessment. Each subject underwent kinematic MRI of the patellofemoral joint through a range of 45 to 0 degrees of knee flexion against a resistance of 15% body weight. Imaging was performed with and without a patellofemoral joint brace (Bauerfeind Genutrain P3 brace, Atlanta, GA). Measurement of medial/lateral patellar displacement, medial/lateral patellar tilt, and the depth of the trochlear groove (sulcus angle) were obtained with midpatellar image sections at 45, 36, 27, 18, 9 and 0 degrees of knee flexion. RESULTS: No statistically significant differences in medial/lateral patellar displacement or tilt were found between braced and unbraced trials across all knee flexion angles (P < 0.05). A small but statistically significant increase in sulcus angle was found across all knee flexion angles with the braced trials (P > 0.05). CONCLUSIONS: These results do not support the hypothesis that the brace used in this study corrects patellar tracking patterns in subjects with patellofemoral pain. However, the increased sulcus angle indicates a change in patella position within the trochlea. It is possible that the clinical improvements seen with bracing may be the result of subtle differences in joint mechanics and not gross changes in alignment.

Adolescent↗
PubMed1999

Aneurysm clips: effects of long-term and multiple exposures to a 1.5-T MR system.

The authors evaluated the ferromagnetic properties of multiple nonferromagnetic aneurysm clips before and after long-term and multiple exposures to a 1.5-T magnetic resonance system. No alterations in the magnetic properties of these clips was observed. These findings suggest that repeated or chronic exposure of patients with implanted nonferromagnetic aneurysm clips to strong static magnetic fields is unlikely to result in any clinically significant alteration in the magnetic properties of these clips.

Contraindications↗
PubMed1999

Cardiac pacemakers and implantable cardioverter defibrillators are unaffected by operation of an extremity MR imaging system.

OBJECTIVE: The objective of our investigation was to determine whether an MR imaging system designed to obtain images of the extremities affects the safety and functionality of pacemakers or that of implantable cardioverter defibrillators (ICDs). MATERIALS AND METHODS: Ex vivo experiments were conducted in which seven pacemakers and seven ICDs were exposed to a 0.2-T extremity MR imaging system. Magnetic field attraction was assessed at three positions relative to the MR imaging system. In addition, the devices were placed into a test apparatus that was oriented parallel and perpendicular relative to the MR imaging system while imaging was performed on a phantom using T1-weighted spin-echo and gradient-echo sequences. Various functional aspects of the pacemakers and ICDs were evaluated before, during (pacemakers only), and after MR imaging. RESULTS: Magnetic field attraction was relatively minor for all devices. The quality of the MR images was unaffected by the devices. Operation of this MR system did not alter any of the functional aspects of the pacemakers or ICDs evaluated in this study. CONCLUSION: According to these data and in consideration of how patients are positioned during examinations--that is, positioned so that the thorax (where the pacemaker or ICD and the corresponding leads are located) does not enter the magnet bore--the results suggest that it should be safe to perform MR imaging in patients with the pacemakers and ICDs evaluated in this study.

Arm↗
PubMed1999

Metallic stents: evaluation of MR imaging safety.

OBJECTIVE: The objective of our investigation was to evaluate safety during MR imaging (i.e., magnetic field interactions, heating, and artifacts) for metallic stents. MATERIALS AND METHODS: Different types of metallic stents were tested for magnetic field interactions, heating, and artifacts using a 1.5-T MR system. Magnetic field-related translational attraction and torque were assessed using previously described techniques. Heating was evaluated using an infrared thermometer to record temperatures immediately before and after performing MR imaging using a whole-body-averaged specific absorption rate of 1.3 W/kg. Artifacts were assessed by placing the stents inside a fluid-filled phantom and performing MR imaging using fast spoiled gradient-echo and T1-weighted spin-echo pulse sequences. RESULTS: For the 10 different stents evaluated, we found no magnetic field interactions. the highest temperature change was < or = +0.3 degrees C, and the artifacts involved signal voids that would not create diagnostic problems as long as the area of interest was not positioned exactly where a particular stent was located. CONCLUSION: The findings of the safety tests indicated that the 10 different metallic stents would be safe for patients undergoing MR imaging procedures using MR systems with static magnetic fields of 1.5 T or less.

Artifacts↗
PubMed1998

Spetzler titanium aneurysm clips: compatibility at MR imaging.

To evaluate the compatibility of a commercially pure titanium aneurysm clip associated with magnetic resonance (MR) imaging at 1.5 T. Artifacts of the Spetzler titanium aneurysm clip were compared with those produced by six different nonferromagnetic aneurysm clips. With the titanium clip, no magnetic attraction was present, heating was minor, and the artifacts involved a small signal void. With the six other aneurysm clips, artifacts were larger. The presence of Spetzler titanium aneurysm clips is safe at MR imaging at 1.5 T or less.

Artifacts↗
PubMed1998

Yasargil aneurysm clips: evaluation of interactions with a 1.5-T MR system.

PURPOSE: To evaluate the magnetic field interactions with Yasargil aneurysm clips exposed to a 1.5-T MR system. MATERIALS AND METHODS: Sixteen Yasargil aneurysm clips made with Phynox (10 clips returned to the manufacturer due to suspected magnetic field interactions and six clips obtained from the manufacturer in sterile packages) were tested for magnetic field interaction at 1.5 T by using techniques to assess magnetic field-induced translational (deflection angle test) and torque (changes in alignment or rotation) forces. RESULTS: None of the aneurysm clips demonstrated magnetic field interactions; that is, deflection angles were zero and there were no changes in alignment or evidence of rotational forces present. CONCLUSION: It is safe to perform MR procedures at 1.5 T or less in patients with Yasargil aneurysm clips made with nonferromagnetic material.

Alloys↗
PubMed1998

Cranial bone flap fixation clamps: compatibility at MR imaging.

Metallic cranial bone flap fixation clamps were tested for compatibility at 1.5-T magnetic resonance (MR) imaging with standardized techniques. There was no magnetic field attraction, heating was minor, and artifacts involved a relatively small signal void. These data indicate that bone flap fixation clamps will not present risks to patients undergoing MR imaging procedures with MR systems of 1.5 T or less.

Artifacts↗
PubMed1998

Aneurysm clips: assessment of magnetic field interaction associated with a 0.2-T extremity MR system.

Twenty-two different aneurysm clips were tested by means of the deflection angle test for magnetic field interaction associated with a 0.2-T extremity magnetic resonance (MR) system. At the opening of the magnet bore and 5 inches (13 cm) and 10 inches (25 cm) away from the magnet bore, respectively, deflection angles were 14 degrees, 2 degrees, and 0 degree for one clip and were 17 degrees, 4 degrees, and 0 degree for another, and were 0 degree for the remaining 20 clips. Because the patient's head does not enter the magnet bore, extremity MR imaging of patients with the aneurysm clips evaluated in this study should be safe.

Aneurysm↗
PubMed1998

Aneurysm clips: evaluation of MR imaging artifacts at 1.5 T.

Magnetic resonance (MR) imaging-related artifacts associated with five different aneurysm clips made of five different metals (commercially pure titanium, titanium alloy, Phynox, Elgiloy, and cobalt alloy) were evaluated. Aneurysm clips made of commercially pure titanium and titanium alloy produced the smallest artifacts, whereas the aneurysm clip made of Elgiloy produced the largest artifacts. These results have implications for the selection of aneurysm clips in patients who may require MR procedures.

Alloys↗
PubMed1997

MR compatibility of Guglielmi detachable coils.

Guglielmi detachable endovascular coils were evaluated for magnetic resonance (MR) compatability at 1.5 T. Tests to determine magnetic field attraction (deflection angle and Petri-dish displacement methods), heating (infrared thermometry), and artifact production (beef phantom) were performed. Adverse event data were reviewed for MR imaging in 142 patients in whom the coils were implanted to treat intracranial aneurysms. There was no magnetic field attraction, the temperature increased 0.2 degrees C, and only a mild signal void relative to the size and shape of the coil was produced. All patients underwent MR imaging without incident. The Guglielmi coils are compatible with MR imaging at static magnetic field strengths of 1.5 T or less.

Aneurysm↗
PubMed1996

Vascular access ports and catheters: ex vivo testing of ferromagnetism, heating, and artifacts associated with MR imaging.

The purpose of this study was to evaluate ferromagnetic qualities, heating, and artifacts associated with MR imaging of implantable vascular access ports (IVAPs, N = 9) and catheters (N = 8). Ferromagnetism was determined using previously described techniques. Heating was assessed for the IVAPs by measuring temperature immediately before and after performing a 3D GRASS, MTC pulse sequence for 60 min at an SAR of 2.8 W/kg. Artifacts were evaluated in association with the use of a fast GRASS pulse sequence and graded according to the severity of image distortion. None of the IVAPs or catheters were attracted by the magnetic field of the MR system. The largest temperature change measured was -0.3 degree C. Artifacts varied, depending on the component materials used for the construction of the IVAPs and catheters. The lack of ferromagnetic qualities and negligible heating indicates that MR imaging performed at 1.5 T or less may be conducted safely in patients with each of the IVAPs and catheters tested. None of the artifacts produced by the presence of the IVAPs or catheters is considered to impair the diagnostic aspects of MR imaging, especially if the device is not positioned directly in the imaging area of interest.

Artifacts↗
PubMed1996

MR imaging and cervical fixation devices: evaluation of ferromagnetism, heating, and artifacts at 1.5 Tesla.

The purpose of this study was to assess ferromagnetism, heating, and artifacts for cervical fixation devices exposed to a 1.5 T MR system. Cervical fixation devices (three halos, one tong and two halo vests) were evaluated for compatibility with MR procedures. Ferromagnetism was determined using a previously described technique. Heating was evaluated by measuring temperatures at various positions on the cervical fixation devices while applied to a volunteer subject before and during the use of various pulse sequences, including an magnetization transfer contrast (MTC) sequence. Artifacts associated with routine clinical MR imaging of the cervical spine were qualitatively evaluated with the cervical fixation devices applied to a volunteer subject. None of the devices displayed attraction to the magnetic field. The temperature changes were +/-1.5 degrees C in each instance. The MTC pulse sequence produced a sensation of "heating" the skull pins that may have been caused by vibration of the cervical fixation device. The MR images of the cervical spine were obtained without apparent artifacts using each routine, clinical pulse sequence. The lack of ferromagnetism, negligible heating, and capability of obtaining diagnostically acceptable studies of the cervical spine indicate that MR imaging performed at 1.5 T or less may be conducted safely in patients with each of the cervical fixation devices tested using conventional pulse sequences.

Artifacts↗
PubMed1996

Aneurysm clip testing for ferromagnetic properties: clip variability issues.

To assess ferromagnetic properties of intracranial aneurysm clips reported to be nonferromagnetic, 1,765 Yasargil, 11 Sugita, and 15 Perneczky aneurysm clips were studied for rotation or translation on plate glass in a 1.5-T MR imager. Sixty-three clips (52 Yasargil, 11 Perneczky) weakly reoriented along the static magnetic resonance (MR) field. These results confirm the need for standardized testing for ferromagnetic properties for implantable metallic devices.

Contraindications↗