Assessment of MRI safety issues for stainless steel sutures used for microtia reconstruction.

INTRODUCTION: Potential magnetic resonance imaging issues for stainless steel sutures used for microtia reconstruction could be clinically significant for safety and diagnostic yield considerations. Therefore, the purpose of this investigation was to assess magnetic resonance issues (magnetic field interactions, heating, and artifacts) for different types of stainless steel sutures used for microtia reconstruction. METHODS: Small gauge, commonly used stainless steel sutures from four different manufacturers (5/0 Steelex, Aesculap/B, Braun Medical, Inc.; Nagata 38 Gauge Microtia Wire, Bear Medical Corporation; Auricular Reco Wire, Medicon Surgical Inc.; and 5-0 B&S 35 Surgical Steel Suture, Ethicon, Inc.) were tested using standardized ex vivo techniques to assess magnetic field interactions, heating, and artifacts at 3 Tesla. Before testing, the stainless steel sutures were configured in a manner same as that for cartilage reconstruction used to treat microtia. RESULTS: Each stainless steel suture exhibited minor magnetic field interactions at 3 Tesla (translational attraction, deflection angle <10°, and no torque). Heating associated with a whole-body averaged specific absorption rate of 2.9 W/kg was not excessive (highest temperature changes, ≤1.8 °C). Artifacts were relatively minor in relation to the size and shape of each stainless steel suture (artifact size in relation to the size and shape of each stainless steel suture extending ≤5 mm). CONCLUSIONS: The stainless steel sutures that underwent testing do not present additional risks to patients in a 3-Tesla or less magnetic field setting (i.e., magnetic resonance conditional). Artifacts for these sutures may only be an issue within close proximity to the reconstructed ear.

Programmable CSF shunt valve: in vitro assessment of MR imaging safety at 3T.

A programmable CSF shunt valve was assessed for magnetic field interactions, heating (transmit-receive body radio-frequency coil; whole-body averaged specific absorption rate, 2.1 W/kg), functional alterations, and artifacts at 3T. The programmable valve showed minor magnetic field interactions and heating was not excessive (+0.8 degrees C). The function of the programmable valve was not altered by multiple exposures to the 3T scanner or from exposure to various MR imaging conditions. Therefore, this implant is safe for a patient undergoing MR imaging at 3T or less when the radiologist follows specific safety guidelines. Artifacts for the programmable valve were relatively large in relation to the size and shape of the valve; this finding may impact the diagnostic use of MR imaging if the area of interest is in proximity to this implant.

Sustained benefits or oral pentaerythritol tetranitrate on ventricular function in chronic congestive heart failure.

The hemodynamic effects of a single oral dose of 80 mg of pentaerythritol tetranitrate (PETN) were determined over a 5-hr period in 16 patients with chronic congestive heart failure. PETN decreased (p < 0.05) pulmonary capillary wedge pressure (27 to 18 mm Hb), right atrial pressure (15 to 9 mm Hg), mean systemic arterial pressure (89 to 80 mm Hg), and systemic vascular resistance (1,812 to 1,466 dynes x sec x cm-5). There were increases (p < 0.01) in cardiac index (2.0 to 2.3 l/m2/min), stroke volume index (24 to 28 ml/m2), and stroke work index (25 to 31 gm-m/m2). Peak reduction in pulmonary capillary wedge pressure occurred 2 hr after PETN and hemodynamic effects were still apparent at 5 hr. In nine patients in whom left and right ventricular ejection fractions were determined by radionuclide ventriculography before and after PETN, no changes were found in left ventricular ejection fraction (0.20 to 0.22, p = NS) although there was a modest increase in right ventricular ejection fraction (0.29 to 0.34, p < 0.05). The data indicate that oral PTEN may induce beneficial effects on preload and afterload in congestive cardiac failure that may last 5 or more hours.

Brown adipose tissue in cancer patients: possible cause of cancer-induced cachexia.

Cachexia is a common manifestation of advanced cancer and frequently contributes to physical disability and mortality. An increased metabolic rate has been suggested to be one of the causes of cancer-induced cachexia, although the mechanisms producing this hypermetabolism remain unclear. The presence and activation of brown adipose tissue, a highly thermogenic tissue, may result in a hypermetabolic state and be partially responsible for weight loss in cancer patients. To investigate this hypothesis, we examined necropsy samples of peri-adrenal tissues using light microscopy to identify the prevalence of brown adipose tissue in 25 cachectic patients who died from cancer and 15 age-matched subjects who died from other illnesses. Brown adipose tissue was observed in 20 of the cancer patients (80%) compared to 2 of the age-matched subjects (13%). Therefore, our preliminary results indicate that a high prevalence of brown adipose tissue is associated with cancer-induced cachexia and may reflect an abnormal mechanism responsible for profound energy expenditure and weight loss.

Muscle and femoral vein temperatures during short-term maximal exercise in heart failure.

Core temperature decreases throughout short-term maximal exercise in heart-failure patients. To investigate possible causes for this unusual response to exercise, we studied core (pulmonary arterial blood), femoral vein, muscle, and skin temperatures in eight patients with severe heart failure who performed maximal upright incremental bicycle exercise to 50 W. A normal group (n = 4) was exercised for comparison. In the heart-failure patients, core temperature was 36.95 +/- 0.37 degrees C at rest, significantly (P less than 0.05) decreased at 25 W of exercise to 36.59 +/- 0.40 degrees C, and at 50 W remained decreased to 36.57 +/- 0.40 degrees C. In comparison, we found that the resting core temperature in the normal subjects was 37.28 +/- 0.34 degrees C, was the same at 25 W (37.29 +/- 0.41 degrees C), and increased significantly (P less than 0.05) to 37.50 +/- 0.32 degrees C at 50 W of exercise. Femoral vein temperature in heart-failure patients (n = 6) was below core temperature throughout exercise to 25 and 50 W (36.22 +/- 0.62 and 36.34 +/- 0.65 degrees C, respectively). Muscle temperature (n = 7) was significantly (P less than 0.05) lower in the heart-failure patients (34.8 +/- 1.1 degrees C) at rest compared with the normal subjects (36.2 +/- 1.0 degrees C). During exercise, muscle temperature increased above core temperature in only four of the heart-failure patients and was significantly (P less than 0.05) lower (36.5 +/- 1.3 degrees C) compared with the normal subjects (38.0 +/- 0.2 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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)

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.

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.

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)

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.

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.

Development and clinical application of kinematic MRI of the patellofemoral joint using an extremity MR system.

PURPOSE: Kinematic magnetic resonance imaging (MRI) of the patellofemoral joint provides diagnostic information pertaining to patellar alignment and tracking during the earliest increments of joint flexion, when abnormalities that affect this joint are the most apparent. Recently, a low-field strength (0.2 Tesla) dedicated extremity MR system has been designed, such that only the body part that is being imaged is placed inside of the magnet bore. The purpose of this investigation was to develop a kinematic MRI technique for the patellofemoral joint using the extremity MR system and to apply this procedure in the clinical setting. METHODS: An incremental, passive positioning kinematic MRI technique was developed for the patellofemoral joint that involved obtaining three different axial section locations with the patellofemoral joint extended and then imaging these same section locations repeatedly as the patellofemoral joint was flexed in four increments up to 36 degrees of flexion. MR images were obtained using a T1-weighted spin echo sequence. Five (10 PFJ) asymptomatic volunteers and nine patients (9 PFJ) with patellofemoral joint symptoms were studied. RESULTS: Volunteers had normal kinematic MRI examinations. Seven patients had lateral subluxation, and two patients had excessive lateral pressure syndrome. Two patients with lateral subluxation seen on their kinematic MRI studies had Merchant views (x-rays obtained at 45 degrees) that showed "normal" patellar alignment, illustrating the importance of imaging the patellofemoral joint at 30 degrees or less. CONCLUSIONS: A kinematic MRI technique was successfully developed for the low-field extremity MR system and utilized for clinical applications. This procedure may be used to determine the presence and severity of patellar malalignment and abnormal tracking patterns.

The effects of eccentric velocity on activation of elbow flexors: evaluation by magnetic resonance imaging.

PURPOSE: To compare magnetic resonance imaging (MRI) signal intensity changes in the primary elbow flexors during two isotonic exercise protocols varying in eccentric velocity and the ratio of eccentric to concentric activity. METHODS: Twelve men performed two exercise protocols. The right and left arms were randomly assigned to one of two protocols that had the same workload (60% 1RM) and same total time of exercise (144 s) but differed in the velocity and ratio of eccentric to concentric activity (1:1 and 5:1 for the fast and slow protocols, respectively). MRI signal intensity changes were quantified pre- and post-exercises using an inversion recovery sequence with a 1.5T MRI system (TR = 2500 ms, TE = 90 ms, TI = 140 ms). Percent change in MRI signal intensity, rate of perceived exertion (RPE), and delayed onset muscle soreness (DOMS) were recorded and analyzed. RESULTS: The biceps brachii was found to be preferentially recruited during the fast protocol compared with the brachialis, whereas the brachialis was found to be preferentially recruited during the slow protocol (P < 0.05). The fast exercise protocol was perceived as being more strenuous (RPE = 8.3 +/- 2.1) than the slow (RPE = 5.4 +/- 1.5, P < 0.05) and produced DOMS in 58% of the tested subjects. CONCLUSIONS: These results suggest that agonists respond to various loading conditions nonhomogeneously. These findings may have implications with respect to exercise prescriptions for specific muscles.

Magnetic resonance imaging evaluation of muscle usage associated with three exercises for rotator cuff rehabilitation.

PURPOSE: Methods of determining muscle usage for exercises involving rotator cuff muscles are limited. Therefore, this investigation used magnetic resonance imaging (MRI) to evaluate the effect of three different exercises used for rehabilitation of the rotator cuff. METHODS: Five normal volunteer subjects (3 men, 2 women, mean age 31.4 yr) were studied. The exercises were scaption with internal rotation (SIR), military press (MP), and side-lying 45 degrees abduction (SLA). MR imaging was performed immediately before and after exercise using a "fast" spin echo STIR sequence and oblique coronal plane imaging. Changes in signal intensity pre- and post-exercise were measured at comparable section locations for the MR images of the supraspinatus, infraspinatus, teres minor, subscapularis, deltoid, and trapezius. RESULTS: The SLA showed the greatest increase in signal intensity in all the muscles (percent change, P < 0.01) except for the trapezius, which was used more by the MP and SIR. None of the exercises activated the teres minor (percent change, P = not significant). CONCLUSION: These findings have important implications in efficacy of physical rehabilitation of the rotator cuff and avoidance of subacromial impingement exercise motions.

Effect of bracing on patellar kinematics in patients with patellofemoral joint pain.

PURPOSE: Bracing is commonly used to correct patellar malalignment syndromes. However, there are little objective data documenting the effect of such supports on patellofemoral joint relationships. The purpose of this study was to assess the effectiveness of an elastic patellofemoral sleeve brace in altering patellar tracking in subjects with patellofemoral pain. METHODS: Ten female subjects (12 patellofemoral joints) between the ages of 17 and 46 participated in this study. All subjects had a diagnosis of patellofemoral pain and demonstrated lateral patellar tracking based on magnetic resonance imaging (MRI) assessment. Each subject underwent kinematic MRI of the patellofemoral joint through a range of 45 to 0 degrees of knee flexion against a resistance of 15% body weight. Imaging was performed with and without a patellofemoral joint brace (Bauerfeind Genutrain P3 brace, Atlanta, GA). Measurement of medial/lateral patellar displacement, medial/lateral patellar tilt, and the depth of the trochlear groove (sulcus angle) were obtained with midpatellar image sections at 45, 36, 27, 18, 9 and 0 degrees of knee flexion. RESULTS: No statistically significant differences in medial/lateral patellar displacement or tilt were found between braced and unbraced trials across all knee flexion angles (P < 0.05). A small but statistically significant increase in sulcus angle was found across all knee flexion angles with the braced trials (P > 0.05). CONCLUSIONS: These results do not support the hypothesis that the brace used in this study corrects patellar tracking patterns in subjects with patellofemoral pain. However, the increased sulcus angle indicates a change in patella position within the trochlea. It is possible that the clinical improvements seen with bracing may be the result of subtle differences in joint mechanics and not gross changes in alignment.

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.

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.

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.

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.