Thermal responses in human subjects exposed to magnetic resonance imaging.
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Blood Pressure↗
Biomedical subjects
F G Shellock
Publications and source records attributed to F G Shellock.
Safety of patients with medical devices during application of magnetic resonance methods.
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Artificial Organs↗
Physiological cross-sectional area of human leg muscles based on magnetic resonance imaging.
Magnetic resonance imaging techniques were used to determine the physiological cross-sectional areas (PCSAs) of the major muscles or muscle groups of the lower leg. For 12 healthy subjects, the boundaries of each muscle or muscle group were digitized from images taken at 1-cm intervals along the length of the leg. Muscle volumes were calculated from the summation of each anatomical CSA (ACSA) and the distance between each section. Muscle length was determined as the distance between the most proximal and distal images in which the muscle was visible. The PCSA of each muscle was calculated as muscle volume times the cosine of the angle of fiber pinnation divided by fiber length, where published fiber length:muscle length ratios were used to estimate fiber lengths. The mean volumes of the major plantarflexors were 489, 245, and 140 cm3 for the soleus and medial (MG) and lateral (LG) heads of the gastrocnemius. The mean PCSA of the soleus was 230 cm2, about three and eight times larger than the MG (68 cm2) and LG (28 cm2), respectively. These PCSA values were eight (soleus), four (MG), and three (LG) times larger than their respective maximum ACSA. The major dorsiflexor, the tibialis anterior (TA), had a muscle volume of 143 cm2, a PCSA of 19 cm2, and an ACSA of 9 cm2. With the exception of the soleus, the mean fiber length of all subjects was closely related to muscle volume across muscles. The soleus fibers were unusually short relative to the muscle volume, thus potentiating its force potential.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
High-resolution MR imaging of the wrist and eye with short TR, short TE, and partial-echo acquisition.
High-resolution spin-echo and two- and three-dimensional gradient-recalled acquisition in the steady state (GRASS) and spoiled GRASS images of the wrist and eye were obtained with a whole-body magnetic resonance imager by using trapezoidal phase-encoding gradient waveforms and by lowering receiver bandwidth to +/- 8 kHz, which results in a minimum field of view (FOV) of 4 cm and pixel resolution of 156 microns for a 256 x 256 matrix. Short echo times were achieved by using partial-echo acquisition. Poor signal-to-noise ratio resulting from smaller voxel sizes was overcome by using prototype receive-only eye and wrist coils. Images were obtained in reduced time and were superior to those obtained in studies performed with an 8-12-cm FOV and commercially available coils.
Adult↗
Kinematic MR imaging of the patellofemoral joint: comparison of passive positioning and active movement techniques.
Thirteen patients underwent magnetic resonance (MR) imaging of the patellofemoral joint in an evaluation of passive positioning and active movement kinematic MR imaging techniques. Sixteen joints were symptomatic, and 10 were not. Delineation of normal and abnormal patellar alignment and tracking was similar with the two techniques, but kinematic MR imaging performed with active movement allowed a substantial reduction in examination time while permitting evaluation of the contribution of associated activated muscles and soft-tissue structures to patellofemoral joint function.
Adolescent↗
Patient monitoring during clinical MR imaging.
The impressive growth in the number of patients imaged with magnetic resonance (MR) technology has been accompanied by technical advances that have permitted more acutely ill patients to be studied with this diagnostic tool. Such patients, however, might require monitoring of vital functions during the examination. Unfortunately, the present construction of most MR imaging systems makes direct visualization of the patient difficult, if not impossible. Furthermore, the static and time-varying magnetic (and electric) fields associated with MR imaging systems may be incompatible with most physiologic monitoring devices, either because of safety or function. The authors review herein the data regarding presently available monitoring devices for various physiologic parameters and provide recommendations regarding what--and whom--to monitor during clinical MR examinations.
Humans↗
Increased corneal temperature caused by MR imaging of the eye with a dedicated local coil.
To determine the existence of tissue heating-associated risks to the eye with magnetic resonance (MR) imaging performed at high specific absorption rates (SARs), corneal temperature was measured in 14 patients immediately before and after MR imaging performed with a 1.5-T, 64-MHz unit and a quadrature-driven body coil for radio-frequency transmission and a receive-only local coil designed for eye imaging. Fast spin-echo pulse sequences were used predominantly. Estimated peak SARs ranged from 3.3 to 8.4 W/kg. A statistically significant (P < .001) increase in average corneal temperature (32.2 degrees C +/- 0.7 before imaging, 33.1 degrees C +/- 0.6 after) was associated with MR imaging of the eye. The changes in corneal temperature ranged from 0.2 degrees to 1.8 degrees C (average, 0.9 degrees C). The highest corneal temperature measured after MR imaging was 35.1 degrees C. MR imaging performed with a dedicated local coil at the SARs studied produced elevations in corneal temperature that were physiologically inconsequential and below the temperature threshold (41 degrees to 55 degrees C) for radio-frequency radiation-induced cataractogenesis.
Adult↗
Hematopoietic bone marrow hyperplasia: high prevalence on MR images of the knee in asymptomatic marathon runners.
In a prior study of marathon runners, we noticed that MR scans of the knee frequently showed hyperplasia of red (i.e., hematopoietic) bone marrow. Because the frequency of this finding in various populations is unknown, the purpose of this study was to determine the relative prevalences of hematopoietic bone marrow hyperplasia on MR examinations of the knees of healthy volunteers (n = 74), patients with symptoms of knee disorders (n = 54), and asymptomatic marathon runners (n = 23). The prevalence of hematopoietic bone marrow hyperplasia was 3% (2/74) for the healthy volunteers, 15% (8/54) for the patients, and 43% (10/23) for the marathon runners. The difference in prevalence between each of the three groups was statistically significant at p less than .05 in each case with hematopoietic bone marrow hyperplasia, the distal femur was the only area affected, while the epiphysis and proximal tibia were uninvolved. This pattern of affected bone marrow with hyperplasia of the hematopoietic marrow may be useful for the differential diagnosis. We postulate that the high prevalence of hematopoietic bone marrow hyperplasia in marathon runners may develop as a response to "sports anemia", which is commonly found in highly conditioned, aerobically trained athletes. Furthermore, this is considered to be a normal variant when found in the pattern described here.
Bone Marrow↗
Monitoring heart rate and oxygen saturation with a fiber-optic pulse oximeter during MR imaging.
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Adolescent↗
Occlusion and narrowing of the pharyngeal airway in obstructive sleep apnea: evaluation by ultrafast spoiled GRASS MR imaging.
Morphologic abnormalities of the pharyngeal airway are frequently found in patients with obstructive sleep apnea. These structural alterations in the pharyngeal airway can be detected in awake patients by using rapid imaging techniques. Ten patients with clinically proved obstructive sleep apnea had ultrafast spoiled gradient-recalled acquisition in the steady state (GRASS) MR imaging of the pharyngeal airway to determine the presence of occlusions and/or narrowings. Twelve sequential images were obtained at one midsagittal plane and at eight transverse planes through the pharyngeal airway. The scans were obtained at the rate of one image per 1.04 sec while the patient was breathing quietly. Occlusions or narrowings of the pharyngeal airways were detected on MR images in all patients. The site(s) of the occlusions and the site(s) and extent of the narrowings varied. Six patients had occlusions and four had narrowings of one or more sites. This study shows that ultrafast spoiled GRASS MR imaging can be used to evaluate patients with obstructive sleep apnea during tidal breathing and is useful for determining the presence of occlusions and narrowings of the pharyngeal airway.
Adult↗
The use of nuclear magnetic resonance to evaluate muscle injury.
Magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) are new and powerful tools to study tissue biochemistry, and to provide precise anatomical visualization of soft tissue structures. This review focuses on the use of these techniques to study exercise-induced muscle injury. MRS measurements show an increase in the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) 1-7 d after eccentric exercise. This increase in Pi/PCr could be due to either increases in extracellular Pi or small increases in resting muscle metabolism. Increased Pi/PCr is also seen during training programs and may indicate persistent muscle injury. Increased resting Pi/PCr with injury was not associated with altered metabolism during exercise. Elevations in resting Pi/PCr have been used to show increased susceptibility of dystrophic muscle to exercise-induced injury. Progressive clinical deterioration in dystrophic dogs is marked by impaired muscle metabolism, and the presence of low oxidative muscle fibers not seen in normal dogs. MRI shows increased proton T2 relaxation times following eccentric exercise that last up to 80 d after injury, and can reflect muscle edema as well as longer lasting changes in the characteristics of cell water. MRI demonstrate precise localization of the injured area, with large differences in both location and degree of injury in different subjects following the same exercise protocol. Thus, MRS can provide information on the metabolic response to injury, while MRI provides information regarding the site and extent of the injury. These tools have promise in helping to understand exercise-induced muscle injury.
Animals↗
Effects of a topically applied counterirritant (Eucalyptamint) on cutaneous blood flow and on skin and muscle temperatures. A placebo-controlled study.
This study was designed to investigate the effects of a new product of counterirritant, Eucalyptamint, on the cutaneous circulation and on skin and muscle temperatures. Ten normal subjects (six males and four females, with an average age of 34 +/- 6 yr) were involved in this study. Eucalyptamint was applied to the anterior forearm skin of one side, and placebo was applied to the contralateral forearm. The subjective feelings, cutaneous blood flow, and skin temperature were measured before and periodically (5-min intervals) after the application of the compound. Muscle temperature was measured before and 30 min after the application of the Eucalyptamint. There was no significant effect on the subjective sensation. However, there were statistically significant (P less than 0.05) increases in cutaneous blood flow (up to 4 times base-line) and skin temperatures (up to 0.8 degrees C higher than base-line) after the application of Eucalyptamint with the effects lasting up to 45 min after the application. The muscle temperature was also increased (0.4 degrees C) significantly (P less than 0.05) 30 min after application of the Eucalyptamint. There were no significant changes in the placebo application. The results of this study suggested that the new product of counterirritant, Eucalyptamint, produced significant physiologic responses that may be beneficial for pain relief and/or useful to athletes as a passive form of warm-up.
Adult↗
Patellofemoral joint abnormalities in athletes: evaluation by kinematic magnetic resonance imaging.
The patellofemoral joint is one of the most common sources of painful symptoms encountered by athletes and is one of the most frequently injured joints. Patellar incongruency is the primary pathologic condition that affects the patellofemoral joint and has been reported to be associated with patellar subluxation, patellar dislocation, chondromalacia, and arthrosis. The diagnosis of patellofemoral incongruency by physical examination alone is extremely difficult because the clinical signs may stimulate other types of internal derangements of the knee, and there is a high incidence of combined abnormalities. In consideration of these issues, a kinematic MRI technique was developed to identify and characterize abnormal anatomic and functional aspects of the patellofemoral joint. Because the patellofemoral joint is often injured in athletes and patellofemoral incongruency is a common site of their pain, this article will discuss the use of kinematic MRI to assess the anatomy and function of the patellofemoral joint, with an emphasis toward special problems that may be found in relation to sports-related activities.
Athletic Injuries↗
Cross-sectional imaging of the patellofemoral joint and surrounding structures.
Computed tomography (CT) and magnetic resonance (MR) imaging are extremely useful in the accurate diagnosis of anterior knee pain, a common complaint arising from numerous causes (including fracture, chondromalacia patellae, and alignment and tracking abnormalities). Plain CT is effective for evaluating intraosseous lesions of the knee. Although CT arthrography provides excellent visualization of the patellar articular cartilage, the technique is expensive and invasive. Cine CT is an excellent method for assessing patellofemoral tracking and alignment. Kinematic MR imaging can also perform this function. In addition, MR imaging can provide valuable information concerning the status of patellar cartilage. Although MR imaging can accurately show high-grade chondromalacia patellae, it is less accurate in the detection of low-grade disease. The authors believe that MR imaging and plain radiography offer radiologists the greatest latitude in making a specific diagnosis of the cause of anterior knee pain; however, CT is a useful alternative.
Arthrography↗
Knees of trained long-distance runners: MR imaging before and after competition.
A previous report indicated that recreational runners had increased meniscal signal intensity and visible joint effusions on magnetic resonance (MR) images after jogging. Therefore, the knees of trained long-distance runners were evaluated by means of MR imaging before and after competition to determine the presence of any structural alterations, particularly changes in intrameniscal signal intensity and/or joint effusions. T1-weighted coronal, proton-density and T2-weighted sagittal, and short T1 inversion recovery sagittal images were obtained in five trained runners 24 hours before and within 24 hours after completion of a long-distance race (distance range, 17-50 miles). Pre- and postrace images were filmed and windowed with standardized techniques. All ligaments were normal before and after the race. No alteration in meniscal signal intensity was noted for any menisci, and there was no increase in joint fluid after running. These data indicate that the knees of trained long-distance runners do not demonstrate changes similar to those found in recreational runners, suggesting that these athletes may have adapted to the stresses of their activity.
Adult↗
Exertional muscle injury: evaluation of concentric versus eccentric actions with serial MR imaging.
Eccentric muscular actions involve the forced lengthening or stretching of muscles and tend to produce exertional injuries. This study used magnetic resonance (MR) imaging to serially evaluate muscles in five healthy, untrained subjects who performed exhaustive biceps exercise by doing isolated eccentric and concentric actions with a dumbbell. Symptoms were assessed, and T2-weighted images of the arms were obtained before exercise and 1, 3, 5, 10, 25, 40, 50, 60, and 80 days after exercise. Statistically significant increases in T2 relaxation times indicative of muscle injury occurred on each day of MR imaging evaluation in muscles performing eccentric actions, peaking on day 3 in two subjects; day 5, two subjects; and day 10, one subject. The pattern and extent of the abnormalities on MR images were variable. Pain, soreness, and joint stiffness were present on days 1, 3, and 5 in muscles that performed eccentric actions. MR imaging showed subclinical abnormalities that lasted as long as 75 days after the disappearance of symptoms (two subjects). Muscles that performed concentric actions had no changes in T2 relaxation times and were asymptomatic throughout the study.
Adult↗
MR imaging and biomedical implants, materials, and devices: an updated review.
Certain ferromagnetic metallic implants, materials, and devices are regarded as contraindications for magnetic resonance imaging, primarily because of the risks associated with their movement or dislodgment. More than 40 publications have reported the ferromagnetic qualities of 261 different metallic objects (aneurysm and hemostatic clips, 32; carotid artery vascular clamps, five; dental devices or materials, 16; heart valve prostheses, 29; intravascular coils, filters, and stents, 14; ocular implants, 12; orthopedic implants, materials, and devices, 15; otologic implants, 56; pellets and bullets, 23; penile implants, nine; vascular access ports, 33; and miscellaneous, 17) on the basis of measurements of deflection forces or attraction during exposure to static magnetic fields at strengths of 0.147-4.7 T. The results of these studies are listed with respect to the specific object tested, the material used to construct the object (if known), whether or not the object was deflected or moved during exposure to the static magnetic field, and the highest static magnetic field strength used for testing the object.
Biocompatible Materials↗
Patellofemoral joint: evaluation during active flexion with ultrafast spoiled GRASS MR imaging.
An ultrafast spoiled gradient-recalled acquisition in the steady state pulse sequence was developed that permits multiple images to be obtained at a temporal resolution suitable for examining the patellofemoral joint during active flexion. This pulse sequence was used to perform kinematic magnetic resonance imaging of patellar alignment and tracking in five healthy subjects and seven patients with a provisional clinical diagnosis of abnormal patellofemoral joints.
Female↗