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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
PubMed1991

Acute effects of exercise on MR imaging of skeletal muscle: concentric vs eccentric actions.

Eccentric (lengthening) muscle actions involve the forced lengthening of active muscles. Compared with concentric (shortening) muscle actions subjected to the same relative work load, eccentric actions have lower oxygen consumption requirements, fewer activated motor units, and less lactate production. This study was conducted to determine if T2-weighted MR could show any difference in muscles performing these specific types of actions and, therefore, be useful for physiologic investigations of eccentric and concentric actions. Five subjects performed exhaustive exercise by doing isolated concentric actions (raising a dumbbell, flexing at the elbow) and eccentric muscle actions (lowering a dumbbell, extending the contralateral arm). T2-weighted MR images of the arms were obtained immediately before and after exercise. Muscles that performed concentric actions had increases in signal intensity, whereas muscles that performed eccentric actions showed little or no change. T2 relaxation times increased significantly (p less than .01) in all volunteers, but T2 relaxation times for the muscles that performed concentric actions were significantly higher than those for muscles that performed eccentric actions (p less than .01). Therefore, T2 times increased with both concentric and eccentric actions, but the images failed to show the changes in the muscles that performed the eccentric actions. These data demonstrate that assessment of T2 values can be used to distinguish between muscles that perform concentric actions and those that perform eccentric actions, and this phenomenon may be useful for further physiologic investigations of these specific types of muscle actions.

Adult↗
PubMed1991

Do asymptomatic marathon runners have an increased prevalence of meniscal abnormalities? An MR study of the knee in 23 volunteers.

Excessive repetitive musculoskeletal loads and stresses associated with intense physical activity may lead to deterioration of the menisci of the knee. Therefore, MR imaging was performed on the knees of 23 asymptomatic marathon runners (eight men, 15 women; average age, 40 years; average number of years training, 10; average training distance per week, 41 miles) to determine the prevalence of meniscal signal abnormalities. None of the runners had previous knee injuries or surgery and each of them regularly competes in 26-mile, 50-mile, or 100-mile marathon races. T1-weighted coronal MR images and proton density-weighted and T2-weighted sagittal images were obtained with a 1.5-T MR system and a transmit/receive extremity coil. The medial and lateral menisci were divided into four portions, or horns, and a total of 92 horns were evaluated (i.e., four horns per knee: medial posterior, medial anterior, lateral posterior, and lateral anterior). Two meniscal horns (2%) had grade 3 signal (grade 3 indicates a meniscal tear), 12 (13%) had grade 2 signal, 29 (32%) had grade 1 signal (grades 1 and 2 are indicative of meniscal degeneration), and 49 (53%) had grade 0 signal (grade 0 is normal). Overall, the prevalence of meniscal tears was 9% (two meniscal tears found in 23 runners). This is lower than the prevalence of MR signal abnormalities indicative of meniscal tears reported for asymptomatic, nonrunner athletes (20% of 20 athletes) and for asymptomatic nonathletes (16% of 74 subjects). Fifty-three percent of the meniscal horns of the nonrunner athletes had grade 1 or 2 signal, indicative of meniscal degeneration. Our results indicate that the prevalence of meniscal tears in marathon runners is no higher than the prevalence reported for sedentary persons, and the runners have the same amount of meniscal degeneration as do nonrunner athletes.

Adult↗
PubMed1991

Exertional muscle injuries: magnetic resonance imaging evaluation.

Exertion-related muscle pain is frequent in athletes and patients alike; however, its severity and significance may be difficult to assess clinically. MRI can be used to evaluate myalgia, strains, delayed-onset muscle soreness, chronic muscle overuse syndromes, muscle contracture, and sequellae of muscle injuries such as myositis ossificans and compartment syndrome. MRI documents the distribution of affected muscles, the presence of focal hematoma, fascial herniation, and subsequent healing, fibrosis, or fatty infiltration. MRI is useful in evaluating acute and delayed exertional muscle injuries.

Athletic Injuries↗
PubMed1991

Kinematic magnetic resonance imaging of the joints: techniques and clinical applications.

Recently, kinematic magnetic resonance imaging (MRI) techniques have been developed to provide diagnostic information related to the functional aspects of the joints. The kinematic MRI evaluation of the joint is used to assess the various interactions of the soft tissues and bony anatomic structures that comprise the joint, and to evaluate the relative alignment of these structures through a specific range of motion. The use of kinematic MRI techniques for examination of the joints provides the radiologist and the clinician with augmented data of anatomic and movement-related information.

Humans↗
PubMed1990

Short-term exposure to a 1.5 tesla static magnetic field does not affect somato-sensory-evoked potentials in man.

The literature is contradictory regarding the effect of static magnetic fields on the function of the central nervous system of mammals. Since human subjects are exposed to intense static magnetic fields during magnetic resonance imaging, it is important to determine if the static magnetic field adversely affects the nervous system of man. Therefore, somato-sensory evoked potentials (SEPs) elicited from median nerve stimulation were measured in 11 normal subjects before and during short-term exposure to a 1.5 Tesla static magnetic field. Specially modified instrumentation was used to record SEPs that were unperturbed by the static magnetic field. There were no statistically significant differences in the N20 or P25 latencies or in the amplitude from N20 negative peak to P25 positive peak of the SEPs obtained before compared to those recorded during exposure to the static magnetic field. In addition, there were no changes in the waveforms associated with exposure to the static magnetic field. We conclude that short-term exposure to a 1.5 Tesla static magnetic field does not affect SEPs (i.e., nerve conduction and synaptic transmission were within normal limits) in normal human subjects.

Adult↗
PubMed1990

Evaluation of patients with persistent symptoms after lateral retinacular release by kinematic magnetic resonance imaging of the patellofemoral joint.

The arthroscopic lateral retinacular release is typically performed to treat patellar pain and instability. This procedure was previously considered to be relatively benign with a low associated complication rate. However, a high incidence of medial subluxation of the patella was recently reported in patients with persistent symptoms after lateral retinacular release. Because the use of physical examination criteria may not always be sufficient to assess patellar alignment, 40 patients (43 knees) were evaluated by the newly developed technique of kinematic magnetic resonance imaging of the patellofemoral joint. One (2%) patellofemoral joint had normal patellar alignment, 10 (23%) had lateral subluxation of the patella, 1 (2%) had excessive lateral pressure syndrome, 27 (63%) had medial subluxation of the patella, and 4 (9%) had lateral-to-medial subluxation of the patella. Seventeen of 40 patients (43%) with unilateral arthroscopic lateral retinacular releases had medially subluxated patellae on the unoperated joints. Because patellar malalignment commonly affects bilateral joints, medial subluxation of the patella may have been present before the lateral retinacular release but was not recognized in these patients.

Adult↗
PubMed1990

Safety considerations in MR imaging.

The authors identify eight areas of potential safety concern during clinical magnetic resonance (MR) imaging. These include (a) biologic effects of the static magnetic field; (b) ferromagnetic attractive "projectile" effects of the static magnetic field; (c) potential effects of the relatively slowly time-varying magnetic field gradients; (d) effects of the rapidly varying radio-frequency (RF) magnetic fields, including RF power deposition concerns; (e) auditory considerations from noise caused by the rapidly pulsed magnetic field gradients; (f) safety considerations concerning superconductive systems, including quenches, use of cryogens, and cryogen storage and handling; (g) psychological effects, such as claustrophobia and anxiety induced because of the examination; and (h) possible effects of the intravenous use of the MR contrast agent gadopentetate dimeglumine. The concerns in each of these categories are elaborated upon, and the available data are presented to clarify their status.

Accident Prevention↗
PubMed1990

Heating of the scrotum by high-field-strength MR imaging.

Sterility can occur in mammals if spermatogenic tissue is acutely or chronically heated to levels equal to or greater than body temperature. High-field-strength MR imaging has been shown to elevate tissue temperatures, particularly if high levels of RF radiation are used. To determine if MR imaging above the recommended level for RF radiation is associated with heating of the scrotum, scrotal skin temperatures were measured in eight subjects immediately before and after MR imaging of the scrotum with a 1.5-T, 64-MHz MR scanner at mean whole-body average specific absorption rates ranging from 0.56 to 0.84 W/kg (mean, 0.72 W/kg). The average imaging time was 23 min. A statistically significant (p less than .01) increase in average scrotal skin temperature was associated with MR imaging (before MR imaging, 30.8 degrees C; after MR imaging, 32.3 degrees C). The largest change in temperature was 3.0 degrees C, and the highest temperature measured was 34.1 degrees C. MR imaging at relatively high specific absorption rates produced a statistically significant increase in average scrotal skin temperature. However, the recorded temperatures were below the threshold known to affect spermatogenesis in mammals.

Adult↗
PubMed1990

Magnetic resonance imaging of injuries to bone and articular cartilage. Emphasis on radiographically occult abnormalities.

Magnetic resonance imaging (MRI) has emerged as the premier noninvasive imaging method for evaluation of the musculoskeletal system. Among the most widely recognized and accepted applications of MRI is that of trauma-related imaging. While the initial emphasis on MRI was directed toward the assessment of soft-tissue structures previously difficult to image (eg, knee menisci and cruciate ligaments), it has become increasingly apparent that MRI is superbly suited to the depiction of a wide spectrum of injuries to bone and articular cartilage. MRI has proved capable of depicting abnormalities ranging from clinically innocuous bone bruises to posttraumatic osteonecrosis. Many of the abnormalities that have been detected by MRI have been radiographically occult and often clinically unsuspected. MRI has become established in the assessment of chondral and osteochondral injuries, insufficiency and stress fractures, occult proximal femoral fractures, tibial plateau fractures, and scaphoid injuries. This review will attempt to present the current state of the art with respect to the application of MRI to the assessment of injuries to bone and articular cartilage. Particular emphasis will be placed on radiographically occult abnormalities.

Bone Diseases↗
PubMed1989

The safety of MRI.

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Body Temperature↗
PubMed1989

Exposure to a 1.5-T static magnetic field does not alter body and skin temperatures in man.

The literature has conflicting reports concerning the effect of static magnetic fields on body and skin temperatures in mammals. Since temperature changes induced by static magnetic fields would have important safety implications for clinical magnetic resonance imaging body (sublingual pocket) and skin (abdomen, forehead, chest, upper arm, forearm, thigh, and calf) temperatures were determined in six normal subjects using a fluoroptic thermometry system during a 20-min exposure to a 1.5-T static magnetic field. Ambient conditions were controlled and held constant. An analysis of variance for repeated measures revealed that there were no statistically significant changes in body or any of the skin temperatures recorded. We conclude that exposure for 20 min to a 1.5-T static magnetic field does not alter body and skin temperatures in man.

Air Movements↗
PubMed1989

Patellar tracking abnormalities: clinical experience with kinematic MR imaging in 130 patients.

A kinematic magnetic resonance (MR) imaging technique for assessment of malalignment of the patella, involving the acquisition of multiple sequential axial images of the patellofemoral joint during the early increments of passive knee flexion, was used to evaluate 130 patients (235 symptomatic patellofemoral joints) showing clinical evidence of having patellar tracking abnormalities. Twenty-three of the patellofemoral joints had undergone previous surgical procedures for patellar realignment. In addition, 14 (28 patellofemoral joints) asymptomatic control subjects were studied. Normal patellar tracking was observed in all of the asymptomatic subjects and in 43 (17%) of the 260 patellofemoral joints in the patient population, 18 (7%) of which were symptomatic. Sixty-nine (26%) of the patellofemoral joints had lateral subluxation of the patella, 106 (41%) had medial subluxation of the patella, 21 (8%) had excessive lateral pressure syndrome, 19 (7%) had lateral-to-medial subluxation of the patella, and two (1%) had dislocation of the patella. Of the 235 patellofemoral joints with suspected abnormalities, 217 (93%) had patellar malalignment. Of the 23 patellofemoral joints that had undergone prior surgery, 20 (87%) had abnormal patellar tracking. Thirteen of 14 (93%) patellofemoral joints that had undergone a prior arthroscopic lateral retinacular release had a medially displaced patella.

Adult↗
PubMed1989

Alterations in body and skin temperatures caused by magnetic resonance imaging: is the recommended exposure for radiofrequency radiation too conservative?

Increases in tissue temperature caused by exposure to radiofrequency (RF) radiation are a primary safety concern of magnetic resonance imaging (MRI). Therefore, body and skin temperatures were measured in six subjects before (20 min), during (30 min) and after (20 min) MRI procedures performed at specific absorption rates (SARs) six to 10 times higher than the limit recommended by the UK National Radiological Protection Board. Body temperature was unchanged throughout the experiment. Abdominal skin temperature increased significantly (p less than 0.05) during MRI, decreased significantly post-MRI, but was still significantly (p less than 0.05) higher than baseline. The highest abdominal skin temperature recorded was 36 degrees C. Upper arm, forearm and chest skin temperatures increased significantly (p less than 0.05) during MRI and remained elevated post-MRI. The highest skin temperatures recorded on the upper arm, forearm and chest were 38.1, 36.0 and 34.5 degrees C, respectively. Thigh and calf skin temperatures were not significantly changed during MRI. These alterations in tissue temperatures were physiologically trivial and easily tolerated by the subjects, suggesting that the recommended exposure to RF radiation during MRI of the body for patients with normal thermoregulatory function may be too conservative.

Abdomen↗