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Biomedical subjects

F G Shellock

Publications and source records attributed to F G Shellock.

162 records · Page 9Linked to original sources
PubMedDate not supplied

Ceramic surgical instruments: ex vivo evaluation of compatibility with MR imaging at 1.5 T.

The purpose of this study was to evaluate the MR compatibility of ceramic instruments. Nine different ceramic instruments were tested with respect to ferromagnetism, heating, and artifacts using previously described techniques. There was no magnetic field attraction, temperature increases were < or = 1 degree C, and artifacts involved a signal void similar to the size and shape of each instrument. The ceramic instruments were demonstrated to be compatible with MR imaging and acceptable for use during intraprocedural MR imaging.

Artifacts↗
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Peroneal tendons: use of kinematic MR imaging of the ankle to determine subluxation.

The purpose of this study was to develop a technique for kinematic MRI of the ankle to evaluate subluxation of the peroneal tendons. A special device was used to perform incremental, passive positioning of the ankle from dorsiflexed to plantarflexed positions for the kinematic MRI examination. A fast spoiled gradient-recalled acquisition in the steady state pulse sequence was used to obtain axial images to assess the peroneal tendons during different positions of the ankle. Seven asymptomatic volunteers and five patients with suspected peroneal tendon subluxation were studied. There was no transverse displacement of the peroneal tendons observed in the asymptomatic subjects nor in two of the patients. Two patients had peroneal tendon subluxation observed on the kinematic MRI studies, and one patient had the peroneal tendons maintained in a displaced position in all ankle positions. The preliminary results suggest that kinematic MRI of the ankle is a potentially useful technique to facilitate evaluation of patients with suspected subluxation of the peroneal tendons, particularly in instances in which subluxation is position-dependent, and spontaneous reduction of the tendons may occur.

Adult↗
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The effect of mechanical deformation on magnetic properties and MRI artifacts of type 304 and type 316L stainless steel.

The purpose of this study was to evaluate the influence of composition and deformation of biomedical stainless steels on mechanical properties, magnetic properties, and MRI artifacts. Type 304 and Type 316L samples were prepared using standard wire-drawing techniques. Mechanical properties were determined using standard test methods. The amount of ferromagnetic phase present was estimated using a Severn Gage and x-ray diffraction. Magnetic field attraction and artifacts were determined using previously described techniques. The strength of both steels increased significantly with increasing deformation. None of the type 316L wires transformed to the magnetic phase. The amount of magnetic phase in the type 304 wires increased with increasing deformation. There was no magnetic field attraction, and artifacts were minimal for all of type 316L wires and the undeformed type 304 wire. Deflection and artifacts were significant for the deformed type 304 stainless steel. These results provide guidance regarding the use of type 304 and type 316L stainless steels for bioimplants. In this regard, type 316L stainless steel seems to be a more acceptable material with respect to MR compatibility.

Artifacts↗
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Quantification of patellar tracking using kinematic MRI.

The purpose of this study was to describe a method to quantify dynamic patellar tracking using kinematic MRI (KMRI). Twelve normal females and three patients with patellofemoral pain participated. Imaging was performed with a 1.5-T/64-MHz MR system using a fast spoiled gradient-recalled acquisition in the steady state (GRASS) pulse sequence. A nonferromagnetic positioning device permitted active, bilateral knee extension against resistance (15% bwt) from 45 degrees knee flexion to full extension. Subjects were instructed to extend their knees at a rate of 9 degrees per second, which allowed images to be obtained at 45 degrees, 36 degrees, 27 degrees, 18 degrees, 9 degrees, and 0 degrees. All images were assessed for medial/lateral patellar displacement, patellar tilt, and sulcus angle using a computer-aided system. Normal patellar motion was characterized by medial movement from 45 degrees to 18 degrees, followed by a reversal toward lateral displacement from 18 degrees to full extension. The results for patellar tilt revealed a tendency toward decreasing lateral tilt as the knee extended. Sulcus angle measurements indicated that the patella was moving to a more shallow portion of the trochlear groove (superiorly) during extension.

Adult↗
PubMedDate not supplied

Determination of gradient magnetic field-induced acoustic noise associated with the use of echo planar and three-dimensional, fast spin echo techniques.

The purpose of this study was to assess gradient magnetic-field-induced acoustic noise levels associated with the use of echo planar imaging (EPI) and three-dimensional fast spin echo (3D-FSE) pulse sequences. Acoustic noise measurements were obtained from two different high field-strength MR systems (1.5 T, Siemens and General Electric Co.) under ambient noise conditions and the use of EPI and 3D-FSE pulse sequences. Parameters were selected to produce "worst case" acoustic noise levels. Acoustic noise recordings were made at the entrance, the center, and at the exit of the magnet bores with a specially designed microphone that was unperturbed by electromagnetic fields. The highest ambient noise levels (A-weighted scale) were 67 dB (Siemens: the same values were recorded at the center and at the exit) and 78 dB (General Electric Co.; recorded at the exit). The highest acoustic noise levels recorded during activation of the gradient magnetic fields were 114 dB (Siemens) and 115 dB (General Electric Co.) and those occurred at the centers of the MR systems with the use of the EPI technique. Gradient magnetic fields associated with the use of EPI and 3D-FSE techniques produced acoustic noise levels that were within permissible levels recommended by federal guidelines.

Echo-Planar Imaging↗
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Cardiovascular catheters and accessories: ex vivo testing of ferromagnetism, heating, and artifacts associated with MRI.

The purpose of this study was to evaluate the MR safety of cardiovascular catheters and accessories. Intravascular cardiovascular catheters and accessories were tested for MR safety at 1.5 T using previously described techniques with respect to the evaluation of magnetic field attraction (deflection angle method), heating (temperature measured immediately before and after performing MRI), and artifacts (using a fast spoiled gradient-recalled acquisition in steady state [GRASS] pulse sequence). Two devices were attracted (RV pacing lead and Oximetrix 3 SO2 optical module) by the static magnetic field. Each of the other objects displayed no attraction. Heating was +0.2 degrees C for the sample cardiovascular catheter tested (Opticath). Artifacts varied from moderate to severe, depending on the amount and type of metal present in the device. Despite these ex vivo test results, further safety consideration should be given to the cardiovascular devices that have a conductive wire component (ie, certain types of the cardiovascular catheters) because of the potential for inducing current and excessive heating in these devices during MRI, especially using a high-field-strength MR system. The cardiovascular catheters evaluated in this study or those with a similar design are not recommended for use in patients undergoing MRI procedures.

Artifacts↗
PubMedDate not supplied

Temperature changes associated with radiofrequency energy-induced heating of bovine capsular tissue: evaluation of bipolar RF electrodes.

SUMMARY: This in vitro study determined the temperature changes associated with radiofrequency (RF) energy-induced heating of bovine capsular tissue using bipolar RF electrodes. Tissue samples were placed in a saline bath (37 degrees C) and RF energy was applied using 2 different types of bipolar electrodes (VAPR T End Effect and Vapor T Side Effect; Mitek, Westwood, MA). Each electrode was activated for 3 seconds at 10 W, 16 W, and 20 W, for 6 separate data acquisitions. Fluoroptic thermometry designed to be unperturbed by RF fields was used to record temperatures on the tissue surface and at depths of 2 mm, 4 mm, and 5 mm, at 1-second intervals before (5 seconds), during (3 seconds), and after (7 seconds) the application of RF energy. The highest mean temperatures were recorded at the tissue surfaces for the different power settings for each RF electrode type, as follows: End Effect: 48.9 degrees C (10 W), 57.0 degrees C (16 W), and 67.3 degrees C (20 W). Side Effect: 51.5 degrees C (10 W), 62.1 degrees C (16 W), and 71.2 degrees C (20 W). All recorded surface temperatures were within the range known to be acceptable for tissue shrinkage. Gradient effects (i.e., higher-to-lower) were observed for the tissue temperatures measured at the different depth positions. None of the temperatures recorded at the different depths were excessive, suggesting that sensitive anatomic structures should not be damaged by RF energy-induced heating under the conditions described above.

Animals↗
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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.

Animals↗
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Warming-up and stretching for improved physical performance and prevention of sports-related injuries.

Competitive and recreational athletes typically perform warm-up and stretching activities to prepare for more strenuous exercise. These preliminary activities are used to enhance physical performance and to prevent sports-related injuries. Warm-up techniques are primarily used to increase body temperature and are classified in 3 major categories: (a) passive warm-up - increases temperature by some external means; (b) general warm-up - increases temperature by nonspecific body movements; and (c) specific warm-up - increases temperature using similar body parts that will be used in the subsequent, more strenuous activity. The best of these appears to be specific warm-up because this method provides a rehearsal of the activity or event. The intensity and duration of warm-up must be individualised according to the athlete's physical capabilities and in consideration of environmental factors which may alter the temperature response. The majority of the benefits of warm-up are related to temperature-dependent physiological processes. An elevation in body temperature produces an increase in the dissociation of oxygen from haemoglobin and myoglobin, a lowering of the activation energy rates of metabolic chemical reactions, an increase in muscle blood flow, a reduction in muscle viscosity, an increase in the sensitivity of nerve receptors, and an increase in the speed of nervous impulses. Warm-up also appears to reduce the incidence and likelihood of sports-related musculoskeletal injuries. Improving flexibility through stretching is another important preparatory activity that has been advocated to improve physical performance. Maintaining good flexibility also aids in the prevention of injuries to the musculoskeletal system. Flexibility is defined as the range of motion possible around a specific joint or a series of articulations and is usually classified as either static or dynamic. Static flexibility refers to the degree to which a joint can be passively moved to the end-points in the range of motion. Dynamic flexibility refers to the degree which a joint can be moved as a result of a muscle contraction and may therefore not be a good indicator of stiffness or looseness of a joint. There are 3 basic categories of stretching techniques: (a) ballistic--which makes use of repetitive bouncing movements; (b) static--which stretches the muscle to the point of slight muscle discomfort and is held for an extended period; and (c) proprioceptive neuromuscular facilitation - which uses alternating contractions and stretching of the muscles. Each of these stretching methods is based on the neurophysiological phenomenon involving the stretch reflex.(ABSTRACT TRUNCATED AT 400 WORDS)

Athletic Injuries↗
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Metallic otologic implants: in vitro assessment of ferromagnetism at 1.5 T.

MR imaging is contraindicated for patients with certain ferromagnetic implants because of potential risks related to movement or dislodgement. This is especially true for metallic implants located in sensitive areas of the body, such as those placed in and around the ear. Therefore, the ferromagnetic qualities of 35 different metallic otologic implants were assessed by placing them individually on a millimeter scale in a plastic petri dish that was slowly moved into the center of a 1.5-T MR imaging system. None of the metallic otologic implants moved during this procedure. The results demonstrate that each of these implants are made from nonferromagnetic materials and do not pose a risk to patients undergoing high-field-strength MR imaging. These data effectively expand the list of metallic implants that appear to be safe for MR imaging.

Cochlear Implants↗
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Temperature changes caused by MR imaging of the brain with a head coil.

Tissue heating caused by exposure to RF radiation is a primary safety concern in MR imaging. Therefore, to determine temperature changes caused by high field strength MR imaging of the brain with a head coil, we measured body and skin temperatures in 35 patients immediately before and after clinical MR imaging. MR imaging was performed with a 1.5 T MR system using a 28-cm, open-bore RF transmit/receive head coil specifically designed for examinations of the brain. The average body temperature was 36.6 +/- 0.2 degrees C before MR imaging and 36.6 +/- 0.2 degrees C immediately afterward (mean +/- SD, p = not significant). The average forehead skin temperature increased from 32.6 +/- 0.6 to 32.8 +/- 0.5 degrees C (p less than .01), and the average outer canthus skin temperature increased from 32.1 +/- 0.6 to 32.7 +/- 0.6 degrees C (p less than .01) after MR imaging. The highest skin temperature recorded was 34.2 degrees C, and the largest temperature change was +2.1 degrees There were no statistically significant changes in the average skin temperatures of the upper arm and hand. We conclude that patients undergoing MR imaging of the brain with a head coil at the RF radiation exposure we studied experience no significant changes in average body temperature and statistically significant increases in local (i.e., areas within the head coil) skin temperatures. The observed elevations in skin temperatures were physiologically inconsequential.

Body Temperature↗
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Reading pulmonary artery and pulmonary capillary wedge pressure waveforms with respiratory variations.

Various techniques for reading pulmonary artery and pulmonary capillary wedge pressures have been described. We feel that the most easily obtained and accurate method for reading pressures with respiratory variations should be with reference to end expiration. This is a relatively constant period of intrathoracic pressure and allows for a stable pressure waveform, which can be measured easily. No matter which technique is utilized, a standard procedure should be adopted by those reading the pressures and understood by those who must interpret them. Consistency in the method of pressure waveform reading is important to ensure meaningful measurements and subsequent appropriate treatment of the patient.

Blood Pressure Determination↗