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Biomedical subjects

F G Shellock

Publications and source records attributed to F G Shellock.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1996

Specific tension of human plantar flexors and dorsiflexors.

Reported specific tension measurements for human skeletal muscle vary widely. This variability could be due, at least in part, to the determination of the physiological cross-sectional area (PCSA) of the muscles. In the present study, serial magnetic resonance images were taken every 10 mm along the lower leg of 8 male subjects to calculate the volume and subsequently the PCSAs of the individual muscles producing plantar flexor and dorsiflexor torques. Maximum plantar flexor and dorsiflexor voluntary isometric torques were determined at ankle joint angles of 90, 100, 110, and 120 degrees. Peak tendon force estimated from torque and moment arm measurements was more than fourfold higher in the plantar flexors (3,623 +/- 136 N) than in the dorsiflexors (832 +/- 19 N). PCSAs were about eight- and threefold higher than the anatomic cross-sectional areas at the level of maximum girth of the calf for the plantar flexor and dorsiflexor groups, respectively. Mean muscle volume and PCSA were 4.6 and 12 times larger in the plantar flexors compared with the dorsiflexors, respectively. The PCSAs of both plantar flexors (r = 0.92) and dorsiflexors (r = 0.80) were highly correlated with the tendon tension of the respective muscle groups. The maximum specific tension was more than twofold higher in dorsiflexors than in plantar flexors. These data suggest that factors other than PCSA contribute to the force output potential of ankle plantar flexors and dorsiflexors in humans.

Adult↗
PubMed1995

Technical note: magnetic resonance imaging-guided pre-operative breast localization using "freehand technique".

A 1.5 cm focus in the breast with intense gadolinium uptake was incidentally detected during magnetic resonance (MR) imaging evaluation of a cluster of microcalcifications. Because the apparent mass was both mammographically and sonographically occult, MR imaging was used to guide a needle by "freehand technique" to the lesion, permitting successful pre-operative localization and subsequent surgical excision of the area.

Breast↗
PubMed1995

Effect of a newly designed patellar realignment brace on patellofemoral relationships.

The effect of applying a newly developed patellar realignment brace to a patient with lateral subluxation of the patella was evaluated using active movement, loaded kinematic magnetic resonance (MR) imaging. The brace corrected the lateral displacement of the patella as shown on the kinematic MR imaging study. The patient underwent physical rehabilitation in conjunction with the use of the patellar realignment brace and has had resolution of her painful symptoms for the past 4 months.

Adult↗
PubMed1994

Measurement of acoustic noise during MR imaging: evaluation of six "worst-case" pulse sequences.

PURPOSE: To assess acoustic noise levels for ambient noise and magnetic resonance (MR) imaging at 1.5 T during use of six "worst-case" pulse sequences. MATERIALS AND METHODS: Acoustic noise measurements were obtained at the entrance, center, and exit of the magnet bore of the MR system by means of a specially modified device that is unaffected by electromagnetic radiation. RESULTS: The highest ambient noise level was 73 dB at both the entrance and exit of the magnet bore (A-weighted scale). The highest noise levels during MR imaging occurred during use of a gradient-echo (GRE) pulse sequence and was 102 dB at the entrance and exit of the magnet bore and 103 dB at the center (A-weighted scale). CONCLUSIONS: MR imaging performed with the worst-case pulse sequences did not produce noise levels that exceeded federal guidelines. Noise levels were, however, high enough to impair oral communication and annoy patients. Thus, techniques to attenuate acoustic noise and allow improved operator-patient communication should be used during MR imaging, especially during use of GRE pulse sequences.

Acoustics↗
PubMed1994

Physiologic responses to an MR imaging procedure performed at a specific absorption rate of 6.0 W/kg.

PURPOSE: To assess the physiologic responses to a magnetic resonance (MR) procedure performed at a whole-body-averaged specific absorption rate (SAR) of 6.0 W/kg. MATERIALS AND METHODS: Tympanic membrane temperature, skin temperature at seven sites, heart rate, blood pressure, oxygen saturation, and cutaneous blood flow in six volunteers were assessed before, for 16 minutes during, and immediately after MR imaging performed at 1.5 T, 64 MHz. RESULTS: Statistically significant (P < .05) increases in temperature of the tympanic membrane and the skin of the chest, abdomen, upper arm, hand, and thigh and in heart rate and cutaneous blood flow were associated with exposure to high SAR. None of these physiologic changes, however, were considered deleterious to the study subjects. CONCLUSION: MR imaging procedures performed at the high SAR studied can be tolerated by persons with normal thermoregulatory function.

Adult↗
PubMed1993

MR imaging of silicone breast implants: comparison of different coil arrays.

To determine the optimal coil and patient position for magnetic resonance imaging of patients with silicone breast implants, images obtained with body, circular surface, flexible, single shoulder, and dual shoulder coils in various numbers of patients were compared with regard to signal-to-noise ratio (S/N), decay of signal intensity, resolution, and key area coverage. Images obtained with the dual shoulder coil and prone position, with a customized positioning device, gave the best S/N, resolution, and coverage of the breasts and axillae.

Breast↗
PubMed1993

Survey of reproductive health among female MR workers.

Epidemiologic data were obtained to evaluate potential risks from exposure to the static and time-varying magnetic fields used in magnetic resonance (MR) imaging. A questionnaire sent to women workers in more than 90% of clinical MR facilities in the United States addressed menstrual-reproductive experiences, work activities, and potential confounders (eg, age, smoking, alcohol use). In 1,915 completed questionnaires, 1,421 pregnancies were reported: 280 occurred in an MR worker (technologist or nurse), 894 in an employee in another job, 54 in a student, and 193 in homemakers. Comparing MR-worker pregnancies with those occurring in employees at other jobs, a relative risk ratio of 1.27 (95% confidence interval [CI], 0.92-1.77) was found for spontaneous abortions; for conception taking more than 12 months, 0.90 (CI, 0.54-1.51); for delivery before 39 weeks, 1.19 (CI, 0.76-1.88); for birth weight below 5.5 lb (2.5 kg), 1.01 (CI, 0.50-2.04); and for male gender of the offspring, 0.99 (CI, 0.80-1.22). Adjustment for maternal age, smoking, and alcohol use also failed to markedly change any of the associations. These results suggest that there is not a substantial increase in these common adverse reproductive outcomes.

Female↗
PubMed1993

Patellofemoral joint: identification of abnormalities with active-movement, "unloaded" versus "loaded" kinematic MR imaging techniques.

A positioning device was used to apply a "load" to stress the patellofemoral joint during active-movement, kinematic magnetic resonance (MR) imaging. Twenty-three symptomatic patellofemoral joints were studied by using "unloaded" versus "loaded" techniques. With the unloaded technique, seven joints were normal, nine had lateral subluxation, three had lateral tilt, and four had medial subluxation. With the loaded technique, one was normal, 13 had lateral subluxation, four had lateral tilt, and five had medial subluxation. The active-movement, loaded kinematic MR imaging technique provides improved ability to identify patellofemoral joint abnormalities.

Adolescent↗
PubMed1993

Adverse reaction to intravenous gadoteridol.

Moderate and severe anaphylactoid reactions--while extremely rare--have been reported in association with intravenous administration of gadopentetate dimeglumine. There has been no similar experience related to use of the newly released magnetic resonance (MR) imaging contrast agent gadoteridol. The authors describe a case of vasovagal response and anaphylactoid reaction during intravenous administration of gadoteridol. MR users should be aware of the potential for adverse effects to occur in association with use of gadoteridol and be prepared by implementing appropriate observation procedures for patients receiving this as well as other MR contrast agents. In addition, physiologic monitoring devices and resuscitation equipment should be readily available in the clinical MR setting for proper treatment of patients who may experience moderate to severe adverse reactions.

Adult↗