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At least 1,693 records · Page 94Linked to original sources
PubMed1996

Magnetic resonance imaging of the musculoskeletal system: Part 3. The elbow.

Magnetic resonance imaging provides clinically useful information in assessing the elbow joint. Superior depiction of muscles, ligaments, and tendons as well as the ability to directly visualize nerves, bone marrow, and hyaline cartilage are advantages of magnetic resonance imaging relative to conventional imaging techniques. Ongoing improvements in surface coil design and newer pulse sequences have resulted in higher quality magnetic resonance images of the elbow. Traumatic and degenerative disorders of the elbow are well seen with MR imaging. The sequelae of medial traction and lateral compression from valgus stress include medial collateral ligament injury, common flexor tendon pathology, medial traction spurs, ulnar neuropathy, and osteochondritis dissecans. These conditions as well as lateral collateral ligament injury and lateral epicondylitis may be characterized with magnetic resonance imaging. Posttraumatic osseous abnormalities well seen by magnetic resonance imaging include radiographically occult fractures, stress fractures, bone contusions, and apophyseal avulsions. Magnetic resonance imaging also can be used to assess cartilaginous extension of fractures in children. Intraarticular loose bodies can be identified with magnetic resonance imaging, especially if fluid or contrast material is present within the elbow joint. Biceps and triceps tendon injuries can be diagnosed and characterized. Magnetic resonance imaging also can provide additional information regarding entrapment neuropathies about the elbow. Magnetic resonance imaging is perhaps most useful when patients have not responded to conservative therapy and therefore surgery and additional diagnoses are being considered.

Elbow↗
PubMed2003

A method to intraoperatively assess stapes prostheses for magnetic attraction.

OBJECTIVE: To present a technique used to assess metallic otologic prostheses for magnetic susceptibility during surgery. STUDY DESIGN: Description of a surgical technique. METHODS: A sterile handheld pacemaker magnet is used to evaluate the prosthesis prior to implantation. The magnet is placed over the prosthesis and the prosthesis is placed directly on the magnet. Any evidence of magnetic attraction and the prosthesis is rejected prior to implantation. RESULTS: None of the prostheses screened showed any magnetic attraction. As a control, steel wire was cut into pieces with dimensions similar to prostheses. These sections of wire were readily attracted to the magnet. CONCLUSIONS: Intraoperative screening of metallic prostheses for magnetic susceptibility is possible using a sterile handheld pacemaker magnet.

Intraoperative Period↗
PubMed1995

Magnetic resonance imaging of tuberculous spondylitis.

STUDY DESIGN: This retrospective study analyzed the magnetic resonance imaging characteristics of tuberculous spondylitis. OBJECTIVE: To describe the magnetic resonance imaging characteristics of tuberculous spondylitis and compare the diagnostic yield of magnetic resonance imaging versus other modalities. SUMMARY OF BACKGROUND DATA: Tuberculous spondylitis is not an uncommon occurrence with extrapulmonary disease. It requires prompt diagnosis and management. In the pre-magnetic resonance imaging era, computed tomography was used to delineate the associated radiologic changes. Data are limited that describe the magnetic resonance imaging pattern of tuberculous spondylitis and the effect of post-contrast enhancement. METHODS: The magnetic resonance imaging characteristics of 28 vertebrae in 12 patients with tuberculous spondylitis were studied. RESULTS: The thoracic spine was the most commonly involved region, with involvement occurring in the thoracic spine alone in 12 vertebrae (43%) and with other areas of the spine in an additional five (18%). Partial involvement was detected in the majority of the vertebral lesions (24; 86%). Magnetic resonance imaging evidence of disc space involvement was apparent in only 46% of the lesions. Paraspinal abscess and epidural extension were documented by magnetic resonance imaging in 71% and 61% of lesions, respectively. Decreased signal intensity on T1-weighted images was demonstrated in 13 vertebrae (46%), with increased signal intensity on T2-weighted images seen only in five (18%). CONCLUSION: Magnetic resonance imaging is a useful diagnostic modality for patients with suspected tuberculous spondylitis. Partial vertebral involvement and paraspinal and epidural extension were delineated. Study of the signal intensity on T1- and T2-weighted images revealed a pattern that may be dissimilar to that commonly reported. Post-contrast enhancement adds more certainty to the diagnosis of tuberculous spondylitis.

Adult↗
PubMed1997

Bony vibration stimulation test combined with magnetic resonance imaging. Can discography be replaced?

STUDY DESIGN: The results of two noninvasive methods, magnetic resonance imaging and a bony vibration test, were compared with discographic pain provocation findings. OBJECTIVES: To evaluate whether the combination of magnetic resonance imaging and vibration pain provocation tests could be used to replace discography in low back pain diagnostics. SUMMARY OF BACKGROUND DATA: Magnetic resonance imaging gives a wealth of visual information on anatomic changes of the spine with often unknown clinical significance. Discographic examination of the spine is still the only widely accepted diagnostic method that can relate the pathoanatomic changes to the patient's clinical pain. Internal anular rupture has been shown to be one of the sources of back pain. The bony vibration test of the spinal processes has been shown correlate well with discographic pain provocation tests in cases of internal anular rupture. METHODS: The three lowest lumbar discs of 33 patients with back pain were examined by means of magnetic resonance imaging and a bony vibration stimulation test, and the results were compared with those from computed tomography-discography. RESULTS: In cases of intradiscal magnetic resonance imaging findings, the vibration provocation test showed a sensitivity of 0.88 and a specificity of 0.50 compared with the discographic pain provocation test. If the patients with previous back surgery were excluded, the specificity was 0.75. In the cases of total anular rupture, the sensitivity was 0.50, and the specificity was 0.33. CONCLUSION: The combination of the two noninvasive methods, vibration stimulation and magnetic resonance imaging, gives more information on the origin of the back pain than magnetic resonance imaging alone. The pathoanatomic changes seen in magnetic resonance imaging can be correlated with the patient's disorder more reliably using the vibration provocation test in the cases of partial anular ruptures. The use of discography can be limited mostly to cases with total anular ruptures detected by magnetic resonance imaging.

Adult↗
PubMed1997

Magnetic resonance appearance of monoclonal gammopathies of unknown significance and multiple myeloma. The GRI Study Group.

STUDY DESIGN: A prospective multicenter study. OBJECTIVES: To evaluate the use of magnetic resonance imaging, in the differentiation between monoclonal gammopathies of unknown significance and multiple myeloma. SUMMARY OF BACKGROUND DATA: Although multiple myeloma has been studied extensively with magnetic resonance imaging, to the authors' knowledge, no study has evaluated the clinical interest of magnetic resonance imaging in the differentiation between monoclonal gammopathies of unknown significance and multiple myeloma. METHODS: The magnetic resonance examinations of the thoracolumbar spine in 24 patients with newly diagnosed monoclonal gammopathies of unknown significance were compared with those performed in 44 patients with newly diagnosed nontreated multiple myeloma. RESULTS: All findings on magnetic resonance examination performed in patients with monoclonal gammopathies of unknown significance were normal, whereas findings on 38 (86%) of the 44 magnetic resonance examinations performed in patients with multiple myeloma were abnormal. CONCLUSION: Magnetic resonance imaging can be considered as an additional diagnostic tool in differentiating between monoclonal gammopathies of unknown significance and multiple myeloma, which may be helpful when routine criteria are not sufficient. An abnormal finding on magnetic resonance examination in a patient with monoclonal gammopathies of unknown significance should suggest the diagnosis of multiple myeloma after other causes of marrow signal abnormalities are excluded. Magnetic resonance imaging also may be proposed in the long-term follow-up of monoclonal gammopathies of unknown significance when a new biologic or clinical event suggests the diagnosis of malignant monoclonal gammopathy.

Bone Marrow↗
PubMed1998

A comparison of magnetic resonance and computed tomographic image quality after the implantation of tantalum and titanium spinal instrumentation.

STUDY DESIGN: Tantalum- and titanium-based lumbar interbody fusion devices were implanted into two fresh human cadavers, and magnetic resonance and computed tomographic imaging were performed to evaluate adjacent spinal structures and the amount of metallic artifact. OBJECTIVE: The objective of this study was to prospectively compare the preliminary results of magnetic resonance imaging and computed tomography scanning image quality after the implantation of both titanium and tantalum spinal implants. SUMMARY OF BACKGROUND DATA: The availability of tantalum and titanium spinal implants brings theoretical magnetic resonance imaging compatibility along with several other desirable characteristics. The magnetic resonance imaging and computed tomographic imaging of tantalum spinal instrumentation has never been studied previously or compared with titanium instrumentation. METHODS: Titanium and tantalum spinal implants produced for anterior spinal fusion were each placed at two levels in the lumbar spine of two fresh cadaver specimens. Sequential spin echo T1-weighted and T2-weighted magnetic resonance imaging studies and computed tomographic scans were obtained. The resulting images were then graded to describe and compare the behavior of tantalum metal in magnetic resonance imaging and computed tomographic studies. RESULTS: Good T1 and T2 images were obtained that allowed visualization of the neural structures with minimal artifact. The optimal T1 images for tantalum metal were similar in quality to the optimal T1 parameters for titanium metal. T2 images for both tantalum and titanium metal were obtained with similar results for both metals. Gradient echo magnetic resonance imaging scans of both were poorly imaged with a large amount of artifact. Computed tomographic studies of tantalum implants produced a large amount of metal artifact when compared with computed tomographic studies of titanium implants. CONCLUSIONS: High-quality magnetic resonance imaging studies can be obtained after the implantation of both titanium and tantalum spinal instrumentation. Both of the metals produce similar images on magnetic resonance imaging studies with comparable amounts of metallic artifact. High-quality computed tomographic scans of titanium implants can be obtained with minimal distortion secondary to artifact. However, computed tomographic scanning is not the imaging modality of choice for the tantalum spinal implants because of the large amounts of artifact.

Artifacts↗
PubMed2003

Detection of traumatic brain injury with magnetic resonance imaging and S-100B protein in children, despite normal computed tomography of the brain.

OBJECTIVE: The objective of this study was to obtain data to further define the extent of traumatic brain injury by using S-100B protein and standard noncontrast magnetic resonance imaging with added fluid-attenuated inversion recovery (FLAIR) and gradient echo sequence in children with normal head computed tomography. DESIGN: Pilot, single cohort, prospective, clinical diagnostic study. SETTING: Pediatric intensive care and intermediate care unit in a tertiary care children's hospital. PATIENTS: Children ages 5-18 yrs who sustained traumatic brain injury, had a negative computed tomography of the brain, and were admitted to hospital were eligible for enrollment. INTERVENTIONS: Two blood samples were drawn for S-100B protein analysis: the first (t-1) as soon as possible or close to 6 hrs of injury and the second (t-2) close to 12 hrs from the time of injury. A magnetic resonance image of the brain was obtained within 96 hrs of injury. MEASUREMENTS AND MAIN RESULTS: Seven of 17 patients (41%) had positive magnetic resonance image. Of the seven patients with positive magnetic resonance image, 100% (seven of seven) had a positive magnetic resonance image with FLAIR sequence, 85% (six of seven) with axial T2 sequence and 50% (three of six) with gradient echo sequence. There was no statistically significant difference in S-100B protein concentrations in patients with a positive magnetic resonance image (n = 7) and those with a negative magnetic resonance image (n = 10; p =.40 at t-1 and p =.13 at t-2). The concentration of S-100B protein was statistically significantly higher in patients with head and other bodily injury (n = 9) compared with isolated head injury (n = 6; p =.018 at t-1 and p =.025 at t-2). Patients with a positive magnetic resonance image had a lower Glasgow Coma Scale score and longer duration of hospital stay. CONCLUSIONS: Magnetic resonance imaging seems to be a useful modality to better define the spectrum of brain injury in children with mild head trauma. The addition of S-100B protein measurement does not seem to be useful in this setting.

Adolescent↗
PubMed2004

A pilot safety study of repetitive transcranial magnetic stimulation (rTMS) in Tourette's syndrome.

OBJECTIVE: We designed a randomized, blinded, crossover study to assess safety and test whether transcranial magnetic stimulation at specific regions and frequencies might modify tics. We administered repetitive transcranial magnetic stimulation over prefrontal cortex or motor cortex, with either fast or slow repetitive transcranial magnetic stimulation, to 8 Tourette's syndrome patients. METHODS: Over 5 days, we applied repetitive transcranial magnetic stimulation at 110% of the motor threshold over left motor cortex (twice) or left prefrontal cortex (twice), using either 1 Hz or 15 Hz transcranial magnetic stimulation, or sham transcranial magnetic stimulation (once). RESULTS: All 8 subjects completed the study with minimal side effects and no worsening of tics or other involuntary movements. Ignoring site and frequency, tic symptoms improved significantly over the week of the study. The study design does not allow one to address whether this was due to the presence or frequency of transcranial magnetic stimulation or to nonspecific factors involved in study participation. CONCLUSIONS: Repetitive transcranial magnetic stimulation at these sites, doses, and use parameters appears to be safe in adults with Tourette's syndrome. Further studies using repetitive transcranial magnetic stimulation in Tourette's syndrome are warranted, using balanced parallel designs.

Adult↗
PubMed2007

Assessment of right ventricular infarction with contrast-enhanced magnetic resonance imaging.

OBJECTIVE: Evaluation of contrast-enhanced magnetic resonance imaging to assess right ventricular infarction in patients with acute inferior myocardial infarction. BACKGROUND: Contrast-enhanced magnetic resonance imaging has been used for assessing scar tissue after left ventricular infarction. The value of contrast-enhanced magnetic resonance imaging to assess right ventricular infarction is unknown and was evaluated. METHODS: Consecutive patients (n=18) with first acute inferior infarction were included. Resting electrocardiogram and right-sided electrocardiogram were acquired to assess right ventricular involvement. Resting cine magnetic resonance imaging was performed to evaluate right ventricular function and volumes, whereas the extent of right ventricular scar tissue was assessed by contrast-enhanced magnetic resonance imaging. Cine magnetic resonance imaging was repeated at 6-months follow-up to re-assess right ventricular function and volumes. RESULTS: Sensitivity and specificity of magnetic resonance imaging were 100 and 78%, respectively, to detect right ventricular infarction (using the right-sided electrocardiogram as the gold standard). At 6 months follow-up, patients with scar tissue on contrast-enhanced magnetic resonance imaging showed right ventricular dilatation. Moreover, the extent of right ventricular scar tissue was linearly related to the severity of right ventricular dilatation. CONCLUSIONS: Contrast-enhanced magnetic resonance imaging permits accurate assessment of right ventricular scar tissue. Patients with extensive right ventricular infarction demonstrate right ventricular dilatation at 6 months follow-up.

Adult↗
PubMed2001

Ultrafast magnetic resonance imaging of central nervous system abnormalities in utero in the second and third trimester of pregnancy: comparison with ultrasound.

OBJECTIVE: To assess the ability of ultrafast magnetic resonance imaging to visualise abnormalities in the central nervous system of third trimester fetuses in utero and to compare the results with the current 'reference standard' of ultrasound and postnatal imaging or post-mortem data. DESIGN: A prospective, observational study comparing the diagnostic accuracy of two imaging methods: antenatal ultrasound and antenatal magnetic resonance with each other and postnatal or post mortem data. POPULATION: Twenty-one pregnant women of 19-36 weeks of gestation whose fetus were thought to have a central nervous system abnormality on the basis of antenatal ultrasound. The women had either not been offered or had refused a termination and were willing to have a magnetic resonance scan. METHODS: A 1.5T magnetic resonance scanner used a single shot fast spin echo sequence, in three image planes. The results were compared with the ultrasound results obtained by an experienced investigator independently. A series of 21 patients, with a range of pathologies of central nervous system, were imaged. Postnatal ultrasound and/or magnetic resonance imaging, or post-mortem data were used for additional confirmation of the pathology in all cases. RESULTS: The magnetic resonance report was different to the ultrasound in 10/21 (47.6%), magnetic resonance provided information additional to the ultrasound in 5/21 (23.8%), ultrasound and magnetic resonance results agreed in 6/21 cases (28.6%). CONCLUSION: Magnetic resonance in the third trimester provides a useful adjuvant to ultrasound imaging of the fetus when assessing abnormalities of the central nervous system after 19 weeks of gestation particularly if the abnormality involves the posterior fossa.

Adolescent↗
PubMed2001

Magnetic resonance imaging in the assessment of complex Müllerian anomalies.

OBJECTIVE: To evaluate the accuracy of magnetic resonance imaging in assessment of adolescent patients with complex Müllerian anomalies and its contribution towards operative management. DESIGN: A retrospective review of magnetic resonance imaging and operative findings. SETTING: A London teaching hospital that is a tertiary referral centre for complex reproductive tract disorders. SAMPLE: All adolescents referred for assessment of complex Müllerian anomalies, from 1996 to 1999, and undergoing both magnetic resonance imaging and surgical assessment. METHOD: In the nine suitable patients magnetic resonance imaging and surgical findings were compared and the role of magnetic resonance imaging in determining the route and type of surgery was evaluated. MAIN OUTCOME MEASURES: Magnetic resonance imaging data on reproductive tract anatomy and surgical findings detailing reproductive tract anatomy. RESULTS: There was good correlation of magnetic resonance imaging and operative findings in all cases. The best correlation was with uterine structure. In four cases the magnetic resonance imaging findings were essential for the appropriate choice of the surgical approach and type of procedure. CONCLUSIONS: Magnetic resonance imaging is a valuable tool in the management of this particular complex group of patients.

Adolescent↗
PubMed1990

A large-scale magnetic separator for selective cell separations with paramagnetic microbeads.

An improved magnetic separator has been developed for use in large-scale cell separations. This separation method uses paramagnetic microbeads coated with antibodies that selectively bind to target cells. The magnetic separator attracts the microbead-target cell aggregates and holds these aggregates at its surface while the suspending fluid and nontarget cells flow past. The optimum separator design was determined to be two magnetic assemblies in series along with a peristaltic pump. The assemblies consist of neodymium-iron-boron magnet bars sandwiched between steel bars (magnetic pole pieces). The size and pole spacing of the two magnetic assemblies are designed to be different, so that the first assembly, which captures greater than 99.99% of the microbeads, has good magnetic reach-out and a high magnetic holding force at its surface, while the second assembly has an even higher magnetic holding force at its surface. Studies show that the separator can remove 1 x 10(10) microbeads from a suspension of red blood cells processed at a flow rate of 9 ml/min, so that no microbeads are detected in the effluent.

Animals↗
PubMed1992

Force-distance relation and properties of repelling Sm-Co5 magnets in orthodontic clinical use: an experimental model.

In recent years, magnets and magnetic forces have been suggested as an alternative to traditional orthodontic devices such as elastics, springs and wires. The purpose of this study was to analyze the reliability and the output of forces for prefabricated orthodontic repelling Sm-Co5 magnets and the force conditions for the magnets after 5 months of maximal loading. The test-machine consisted of a jig where the tested pair of repelling magnets was mounted close to the clinical situation. With a cylindrical strain gauge transducer, a micrometer screw, a bridge-amplifier, and a Mingograph jet recorder, force-distance diagrams were constructed. The force-distance diagrams showed that the force-distance curve was hyperbolic and that the mean force when the magnetic pole faces were almost in contact with each other was 214.9 g, SD 13.42 g. The variation of magnetic force between different Sm-Co5 magnets was 6-9%. The difference in force before and after 5 months of maximal loading of the magnets was not significant. The test results indicate that with proper handling of the forces according to the new force diagrams, the system is reliable for orthodontic use.

Cobalt↗
PubMed1994

Comparison of magnetic resonance angiography, duplex ultrasound, and digital subtraction angiography in assessment of extracranial internal carotid artery stenosis.

The results of a prospective study comparing ultrasound, intra-arterial digital subtraction angiography, and magnetic resonance angiography in the assessment of the degree of extracranial internal carotid artery stenosis are reported in patients with symptoms of recent carotid territory ischaemia. A total of 70 patients and 137 vessels were examined by all three techniques. The results obtained by each technique were reported blind. The mean difference (SD) for the comparison of magnetic resonance angiography and digital subtraction angiography was -0.7 (14)%, for ultrasound and digital subtraction angiography 3.1 (15)%, and for magnetic resonance angiography and ultrasound -3.8 (15)%. The level of agreement was greater for the more tightly stenosed vessels. With the assumption that the results of the digital subtraction angiogram reflect the true situation, the sensitivity and specificity in the detection of > or = 30% stenoses were 93% and 82% with ultrasound and 89% and 82% with magnetic resonance angiography; for stenoses > or = 70% 93% and 92% with ultrasound and 90% and 95% with magnetic resonance angiography; and for stenoses of 70-99% 89% and 93% with ultrasound and 86% and 93% with magnetic resonance angiography. For occlusion the values were 93% and 99% with ultrasound and 80% and 99% with magnetic resonance angiography. Increased sensitivity and specificity were obtained when analysis was confined to those vessels in which ultrasound and magnetic resonance angiography were in agreement over classification. It is thus possible to accurately categorize the degree of stenosis of the extracranial internal carotid artery from a combination of ultrasound and magnetic resonance angiography. The adoption of this combination for the investigation of patients before carotid endarterectomy removes the risk associated with conventional angiography and represents an important advance in the management of carotid stenosis.

Adult↗
PubMed2003

Effects of atropine, scopolamine and xylazine on the placement of an orally administered magnet in cows.

This study was carried out to determine whether the administration of atropine, scopolamine or xylazine to cows before the administration of a magnet orally would help to position it in the reticulum. The transit time of the magnet through the oesophagus was also measured. Sixty Swiss Braunvieh cows were examined by radiography and ultrasonography to locate the reticulum. They were then divided into six groups of 10. Before the administration of the magnet, a control group received 4 ml saline solution subcutaneously, one group received 0.10 mg/kg of atropine subcutaneously, a second received 0.05 mg/kg of atropine intravenously, a third received 0.15 mg/kg of scopolamine intravenously, a fourth group received 0.02 mg/kg of xylazine intravenously, and the cows in the fifth group were positioned so that their forelimbs were 30 cm lower than their hindlimbs during the administration of the magnet. The passage of the magnet through the oesophagus was timed with a stopwatch and monitored with a compass. In the control group the magnet passed through in less than 60 seconds, but in four of the cows receiving either atropine or xylazine intravenously, or having their forelimbs positioned lower than their hindlimbs, it took longer than 60 seconds. In the cows receiving atropine subcutaneously or scopolamine intravenously, it took the same time as in the control group. All the cows were radiographed one-and-a-half hours after the administration of the magnet to determine its location. In seven of the 10 cows in the control group, the magnet was located in the reticulum, but in the other three it was in the cranial dorsal blind sac of the rumen. In the other five groups the magnet was located in the reticulum of between four and seven of the 10 cows, but in the cranial dorsal sac of the rumen, the rumen or in other sites in the other cows.

Administration, Oral↗
PubMed2004

Vascular guide wire navigation with a magnetic guidance system: experimental results in a phantom.

PURPOSE: To investigate the efficacy of a second-generation prototype magnetic guidance system in complex vessel phantoms versus conventional navigation in simulated interventional radiology procedures and to analyze procedure and fluoroscopy times. MATERIALS AND METHODS: The magnetic guidance system consists of two focused-field permanent magnets on each side of the body that create a 0.1-T navigation field and is integrated with a modified C-arm single-planar digital angiography system. Forty-nine navigations in a glass phantom and 80 navigations in a three-dimensional liver phantom were performed with a magnetically tipped floppy 0.014-inch guide wire and a conventional 0.014-inch microcatheter system. Rates of success and fluoroscopy and procedure times were quantified for both techniques. For the liver phantom experiment, the Mann-Whitney U test was used. For the glass phantom experiment, the Wilcoxon matched pair test was used with the Hodges-Lehmann estimator. RESULTS: In the glass phantom experiments, 42 of 49 turns were successfully performed with both methods. Procedure time to reach a target did not differ significantly between methods, while fluoroscopy time was significantly different when compared with that of the magnetic guidance system (P <.01). Navigation in the liver phantom was successful in 80 of 80 turns with the magnetic guidance system and in 76 of 80 turns with conventional navigation. With the support of the magnetic guidance system, procedure time and fluoroscopy time were significantly different from those with conventional navigation (P <.001). CONCLUSION: The magnetic guidance system allows the precise navigation of a magnetic guide wire in complex vessel phantoms with significantly shorter fluoroscopy and procedure times.

Angiography, Digital Subtraction↗
PubMed2005

Modulation of cardiovascular excitatory responses in rats by transcutaneous magnetic stimulation: role of the spinal cord.

This study investigated the efficacy of magnetic stimulation on the reflex cardiovascular responses induced by gastric distension in anesthetized rats and compared these responses to those influenced by electroacupuncture (EA). Unilateral magnetic stimulation (30% intensity, 2 Hz) at the Jianshi-Neiguan acupoints (pericardial meridian, P 5-6) overlying the median nerve on the forelimb for 24 min significantly decreased the reflex pressor response by 32%. This effect was noticeable by 20 min of magnetic stimulation and continued for 24 min. Median nerve denervation abolished the inhibitory effect of magnetic stimulation, indicating the importance of somatic afferent input. Unilateral EA (0.3-0.5 mA, 2 Hz) at P 5-6 using similar durations of stimulation similarly inhibited the response (35%). The inhibitory effects of EA occurred earlier and were marginally longer (20 min) than magnetic stimulation. Magnetic stimulation at Guangming-Xuanzhong acupoints (gallbladder meridian, GB 37-39) overlying the superficial peroneal nerve on the hindlimb did not attenuate the reflex. Intravenous naloxone immediately after termination of magnetic stimulation reversed inhibition of the cardiovascular reflex, suggesting involvement of the opioid system. Also, intrathecal injection of delta- and kappa-opioid receptors antagonists, ICI174,864 (n=7) and nor-binaltorphimine (n=6) immediately after termination of magnetic stimulation reversed inhibition of the cardiovascular reflex. In contrast, the mu-opioid antagonist CTOP (n=7) failed to alter the cardiovascular reflex. The endogenous neurotransmitters for delta- and kappa-opioid receptors, enkephalins and dynorphin but not beta-endorphin, therefore appear to play significant roles in the spinal cord in mediating magnetic stimulation-induced modulation of cardiovascular reflex responses.

Afferent Pathways↗
PubMed1995

Magnetic and electrical responses of the human brain to texture-defined form and to textons.

1. We searched for a neurophysical correlate of preattentive texture discrimination by recording magnetic and electric evoked responses from the human brain during the first few hundred milliseconds following the presentation of texture-defined (TD) checkerboard form. The only two textons that changed when the TD checkerboard appeared or disappeared were the local orientation and line termination textons. (Textons are conspicuous local features within a texture pattern). 2. Our evidence that the magnetic response to TD form cannot be explained in terms of responses to the two associated textons is as follows: 1) by dissociating the two responses we showed that the magnetic response to TD form is almost entirely independent of the magnetic response to the local orientation texton; 2) a further distinction between the two responses is that their distributions over the head are different; and 3) the magnetic response to TD form differs from the magnetic response to the line termination texton in both distribution over the head and waveform. We conclude that this evidence identifies the existence of a brain response correlate of preattentive texture discrimination. 3. We also recorded brain responses to luminance-defined (LD) checkerboard form. Our grounds for concluding that magnetic brain responses to the onset of checkerboard form are generated by different and independent neural systems for TD and LD form are as follows: 1) magnetic responses to the onset of TD form and LD form had different distributions over the skull, had different waveforms, and depended differently on check size; and 2) the waveform of the response to superimposed TD and LD checks closely approximated the linear sum of responses to TD checks and LD checks alone. 4. One possible explanation for the observed differences between the magnetic and electric evoked responses is that responses to both onset and offset of TD form predominantly involve neurons aligned parallel to the skull, whereas that is not the case for responses to LD form.

Adolescent↗