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Biomedical subjects

F G Shellock

Publications and source records attributed to F G Shellock.

At least 145 records · Page 8Linked to original sources
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Dynamic study of the upper airway with ultrafast spoiled GRASS MR imaging.

Dynamic magnetic resonance (MR) imaging of the upper airway was not possible previously because of poor temporal resolution. Recently, a rapid technique has been developed that provides the means to obtain multiple images at different section locations with sufficient image quality and temporal resolution to allow a comprehensive, dynamic study of the upper airway. The authors describe an ultrafast spoiled GRASS (gradient-recalled acquisition in the steady state) pulse sequence for dynamic studies of the upper airway. The authors believe that this procedure has potential for identifying and characterizing upper airway abnormalities such as nonfixed occlusions and/or narrowings that may exist in patients with obstructive sleep apnea.

Humans↗
PubMedDate not supplied

Phantom limb pain induced in amputee by strong magnetic fields.

An amputee (traumatic) experienced increased phantom limb pain when exposed to the magnetic fields of two magnetic resonance imagers. With a visual analog scale used to measure pain, electric stimulation studies demonstrated that the residual limb was unusually sensitive to subthreshold (for muscle twitch) levels of current. The painful symptoms produced mimicked those experienced in the presence of the imagers.

Adult↗
PubMedDate not supplied

MR imaging and metallic implants for anterior cruciate ligament reconstruction: assessment of ferromagnetism and artifact.

Magnetic resonance (MR) imaging is contraindicated for patients with certain ferromagnetic implants, primarily because of potential risks related to movement or dislodgment of the devices. An additional problem with metallic implants is the potential image distortion that may affect the interpretation of the MR study. Since MR imaging is frequently useful for the evaluation of postoperative anterior cruciate ligament (ACL) reconstruction, the ferromagnetic qualities and artifacts associated with MR imaging were determined for five metallic orthopedic implants commonly used for this surgery. Only the Perfix interference screw displayed a substantial deflection force and caused extensive signal loss. Images of the knee of one patient with two Perfix screws in place were not interpretable because of the image distortion caused by these implants. Therefore, alternative nonferromagnetic implants should be considered for reconstruction of the ACL.

Anterior Cruciate Ligament Injuries↗
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Policies, guidelines, and recommendations for MR imaging safety and patient management. SMRI Safety Committee.

The following are policies, guidelines, and recommendations from the Safety Committee of the Society for Magnetic Resonance Imaging (SMRI) concerning various issues related to magnetic resonance (MR) imaging safety and patient management. These policies, guidelines, and recommendations were developed to provide standardized and consistent information for use by health practitioners involved in clinical MR imaging.

Humans↗
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MR imaging of temporomandibular joint abnormalities associated with cervical hyperextension/hyperflexion (whiplash) injuries.

Patients often have temporomandibular joint (TMJ) dysfunction-related symptoms after cervical hyperextension/hyperflexion injuries ("whiplash") caused by rear-end motor-vehicle collisions. To determine abnormalities of the TMJ associated with these injuries, 33 consecutive symptomatic patients (66 joints) with no direct trauma to the jaw, mouth, head, or face due to the accident and no prior history of TMJ dysfunction underwent magnetic resonance (MR) imaging, and the images were retrospectively analyzed. Overall, 29 (88%) patients had some type of TMJ abnormality related to whiplash injury. Displacement of the disk was seen in 37 (56%) of the TMJs as follows: 21 (32%) had anterior displacement with reduction, nine (14%) had anterior displacement without reduction, six (9%) had lateral or medial displacement, and one (2%) had posterior displacement. On T2-weighted images, 43 (65%) TMJs had abnormal joint fluid or edema, predominantly affecting the joint capsule and/or lateral pterygoid muscles. The finding that many of the patients had joint fluid and/or soft-tissue edema indicates that T2-weighted images are especially useful for assessment of patients with a history of whiplash injury.

Adult↗
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Sedation, anesthesia, and physiologic monitoring during MR imaging: evaluation of procedures and equipment.

The authors developed safe standard sedation and general anesthesia procedures for adults and children, including adequate physiologic monitoring, during magnetic resonance (MR) imaging. Six-year results are reported from one institution; 75% of the 600 patients per year who require sedation or anesthesia are children who require sedation only. Testing was done to determine MR compatibility of various types of equipment essential for monitoring and supporting sedated or anesthetized patients in 1.0- and 1.5-T MR imagers. Use of sedation procedures that include oral chloral hydrate after sleep deprivation resulted in a failure rate of 3.8% in sedating outpatient children. Every physiologic parameter that can be monitored under normal circumstances in the critical care unit or operating room can be monitored during MR imaging. Our experience indicates that with careful consideration of the unique MR environment and with rigorous testing of monitoring equipment, MR imaging can be performed safely in sedated or anesthetized patients.

Adult↗
PubMedDate not supplied

Ex vivo evaluation of ferromagnetism and artifacts of cardiac occluders exposed to a 1.5-T MR system.

Magnetic resonance (MR) procedures are contraindicated for patients with certain ferromagnetic biomedical implants, primarily owing to the risk of movement or dislodgment of the implants by the static magnetic field. An additional concern is the amount of artifact that the implant produces, which can affect image quality and interpretation of the examination. Therefore, an ex vivo assessment of ferromagnetism and artifact was conducted for 12 different occluders used to treat patients with patent ductus arteriosus, atrial septal defects, and ventricular septal defects, in a 1.5-T MR system. Seven of the occluders, made of 304 stainless steel, were ferromagnetic and displayed deflection forces of 248-299 dynes. Five of the implants, made of MP35n, were nonferromagnetic. Artifacts were variable and depended primarily on the type and amount of metal used to construct the implant. The authors conclude that patients with ferromagnetic cardiac occluders may undergo MR procedures approximately 6 weeks after placement of these devices, to allow tissue growth to provide additional retentive force. After this time, it is highly unlikely that the magnetic fields associated with a 1.5-T MR system are capable of moving or dislodging any of these cardiac occluders.

Alloys↗
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Effect of a patellar realignment brace on patellofemoral relationships: evaluation with kinematic MR imaging.

The effect of a newly developed patellar realignment brace was evaluated in 21 patellofemoral joints (19 patients) with patellar subluxation (13 joints with lateral subluxation and eight with medial subluxation) by using active-movement, loaded kinematic magnetic resonance (MR) imaging. Sixteen patellofemoral joints (76%) demonstrated a qualitative correction of or improvement in patellar subluxation (ie, centralization of the patella or a decrease in the displacement of the patella) after application of the brace. Four of the five "failures" occurred in patellofemoral joints that had patella alta and/or dysplastic bone anatomy. These results indicate that the patellar realignment brace was able to counteract patellar subluxation in the majority of patellofemoral joints studied, as shown by active-movement, loaded kinematic MR imaging. This brace appears to be useful for conservative treatment of patients with patellofemoral joint pain secondary to patellar malalignment and maltracking.

Adolescent↗
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Guidelines and recommendations for MR imaging safety and patient management. III. Questionnaire for screening patients before MR procedures. The SMRI Safety Committee.

The authors present the third installment of the guidelines and recommendations from the Safety Committee of the Society for Magnetic Resonance Imaging (now the Society of Magnetic Resonance) concerning various issues related to the safety and management of patients undergoing magnetic resonance (MR) procedures. This document was developed to provide standardized and consistent information for use by health practitioners involved in screening patients or other individuals for MR procedures.

Artifacts↗
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Ex vivo evaluation of ferromagnetism, heating, and artifacts produced by heart valve prostheses exposed to a 1.5-T MR system.

Ex vivo testing techniques were used to determine the ferromagnetic qualities of, presence of heating in, and artifacts produced by 13 different heart valve prostheses exposed to a 1.5-T (64-MHz) magnetic resonance (MR) system. None of the heart valve prostheses showed a measurable deflection in the 1.5-T static magnetic field. Only minimal artifacts were produced during MR imaging with a fast spoiled GRASS (gradient-recalled acquisition in the steady state) pulse sequence. The largest temperature changes measured during a "worst case" MR imaging sequence (estimated average specific absorption rate, 2.5 W/kg; estimated spatial peak specific absorption rate, 7.6 W/kg) were +0.2 degree C with the implant imaged "in air" and +0.3 degrees C with the implant imaged in normal saline. Therefore, MR procedures performed with a 1.5-T (64-MHz) MR system may be performed safely in patients with any of the 13 different heart valve prostheses evaluated in this study.

Absorption↗
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Biopsy needles and devices: assessment of ferromagnetism and artifacts during exposure to a 1.5-T MR system.

Forty-eight biopsy devices (needles, stylets, guide wires, biopsy guns, etc) were evaluated for ferromagnetism (n = 48) and artifacts (n = 43) in a 1.5-T magnetic resonance (MR) system, with previously described techniques. Forty-five of the 48 devices were found to be ferromagnetic. Artifacts varied, depending on the type and size of the component material(s) of the device. Most of the commercially available biopsy devices are not useful for MR imaging-guided biopsy procedures because of the presence of ferromagnetism and associated artifacts.

Artifacts↗
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MR imaging and vascular access ports: ex vivo evaluation of ferromagnetism, heating, and artifacts at 1.5 T.

The purpose of our study was to assess ferromagnetism, heating, and artifacts associated with vascular access ports exposed to a 1.5-T MR system. Twenty-eight different vascular access ports were evaluated in this investigation. Ferromagnetism was determined by using two previously described techniques. Temperature changes were measured immediately before and after performing a pulse sequence on the vascular access ports for 60 min at a specific absorption rate of 3.1 W/kg. Artifacts were assessed in association with the use of a fast GRASS pulse sequence. None of the vascular access ports displayed ferromagnetism. Heating was 0.2 degrees C or less. The presence of artifacts varied, depending on the component materials. The lack of ferromagnetism and negligible heating indicates that MR imaging performed at 1.5 T or less may be conducted safely in patients with any of the vascular access ports tested. None of the associated artifacts produced by the vascular access ports is considered to pose a substantial problem for MR imaging.

Artifacts↗
PubMedDate not supplied

Ex vivo evaluation of ferromagnetism, heating, and artifacts of breast tissue expanders exposed to a 1.5-T MR system.

Three breast tissue expanders were evaluated for compatibility with MR imaging (1.5 Tesla). The metallic components of the breast tissue expanders were shown to be nonferromagnetic, heating < or = .2 degrees C and the artifacts varied. These results indicate that MR procedures may be performed safely in patients with these implants; however, artifacts may obscure implant leaks or breast lesions if located near and metal portion of the breast tissue expanders.

Artifacts↗