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PubMed2006

Magnetic targeting of magnetoliposomes to solid tumors with MR imaging monitoring in mice: feasibility.

PURPOSE: To establish the feasibility of magnetoliposome tumor targeting with an extracorporeal magnet. MATERIALS AND METHODS: Animal experiments were performed in compliance with Institut National de la Santé Et de la Recherche Médicale animal protection guidelines and were approved by local government authorities. Magnetophoresis was used to measure the velocity of magnetoliposomes constituted of polyethylene glycol-lipids and anionic maghemite nanocrystals in a calibrated magnetic field in vitro. For in vivo studies, 38 male Swiss nude mice bearing a PC3 human prostate carcinoma tumor in each flank received an intravenous injection of magnetoliposomes (n = 27), saline (n = 9), or nonencapsulated superparamagnetic particles (n = 2) after a small magnet with a magnetic field of 0.3 T and a field gradient of 11 T/m was fixed to the skin above one tumor. The animals were examined at magnetic resonance (MR) imaging with eight different sequences, iron doses (13 mice), and magnet-application durations (12 mice). Their excised tumors were then stained with Perls Prussian blue and hematoxylin-eosin and were examined histologically. With use of the paired Student t test, signal intensity, tumor surface enhancement, and number of stained cells were compared between the control and magnet-exposed tumors to determine significant differences (P </= .01). RESULTS: The mean magnetoliposome velocity ranged from 10 to 40 mum/sec when the magnetic field equaled 0.13 T and the field gradient equaled 25 T/m. At T1-weighted three-dimensional spoiled gradient-echo MR imaging in vivo, the tumor exposed to the magnet showed strong negative enhancement, -52%, compared with the -7% enhancement of the other tumor. Maximal enhancement occurred after 3 hours of magnet application. After 24 hours of magnet application, intracapillary iron particle accumulation was observed in the targeted tumors only. CONCLUSION: Magnetic targeting of sterically stabilized magnetoliposomes after they are intravenously injected is feasible in vivo.

Animals↗
PubMed2005

Medical application of functionalized magnetic nanoparticles.

Since magnetic particles have unique features, the development of a variety of medical applications has been possible. The most unique feature of magnetic particles is their reaction to a magnetic force, and this feature has been utilized in applications such as drug targeting and bioseparation including cell sorting. Recently, magnetic nanoparticles have attracted attention because of their potential as contrast agents for magnetic resonance imaging (MRI) and heating mediators for cancer therapy (hyperthermia). Magnetite cationic liposomes (MCLs), one of the groups of cationic magnetic particles, can be used as carriers to introduce magnetite nanoparticles into target cells since their positively charged surface interacts with the negatively charged cell surface; furthermore, they find applications to hyperthermic treatments. Magnetite nanoparticles conjugated with antibodies (antibody-conjugated magnetoliposomes, AMLs) are also applied to hyperthermia and have enabled tumor-specific contrast enhancement in MRI via systemic administration. Since magnetic nanoparticles are attracted to a high magnetic flux density, it is possible to manipulate cells labeled with magnetic nanoparticles using magnets; this feature has been applied in tissue engineering. Magnetic force and MCLs were used to construct multilayered cell structures and a heterotypic layered 3D coculture system. Thus, the applications of these functionalized magnetic nanoparticles with their unique features will further improve medical techniques.

Animals↗
PubMed2001

Numerical computation of distortions in magnetic fields and induced currents in physiological solutions produced by microscope objectives.

Identifying distortions produced by commonly employed microscope objectives and their components in uniform DC and 60 Hz AC magnetic fields is important in imaging studies involving exposure of cells to spatially uniform or nonuniform magnetic fields. In this study, DC and 60 Hz AC magnetic flux densities were numerically computed in the presence of finite element models of various components of commonly utilized microscope objectives, as well as a model of a complete objective. Also computed were the distortions in the current density induced by an applied time-varying magnetic field in a physiological buffer contained within a Petri dish. We show that the magnetic flux density could be increased up to 65% in the presence of the nickel-chrome plating of an objective housing and that the presence of ferromagnetic components like a screw or spring could produce peaks that are 7% higher than the undistorted value of magnetic flux density. In addition, a slight tilt of 1% in the objective with respect to the magnetic field could cause a 93% deviation in magnetic flux density from the unperturbed value. These results correlate well with previously published experimental measurements that showed the presence of significant and sometimes asymmetric distortions in both DC and 60 Hz magnetic fields. Moreover, this study further reports that induced current density changed up to 37% compared to values in the absence of the objective. The existence of distortions in applied magnetic fields and induced currents could affect the interpretation of results of cell function studies if it is assumed that the cells are exposed to uniform magnetic flux densities in the presence of a microscope objective. Such assumptions of uniform magnetic flux density could also account for the lack of reproducibility in several studies that examined changes in intracellular calcium by imaging techniques.

Computer Simulation↗
PubMed2002

Vagus nerve stimulation for epilepsy, clinical efficacy of programmed and magnet stimulation.

RATIONALE: Vagus nerve stimulation (VNS) by intermittent and programmed electrical stimulation of the left vagus nerve in the neck, has become widely available. It is an effective treatment for patients with refractory epilepsy. Patients can be provided with a magnet that allows to deliver additional stimulation trains. Since earlier studies have demonstrated the persistence of a stimulation effect after discontinuation of the stimulation train, we evaluated the clinical efficacy of VNS both in the programmed intermittent stimulation mode and magnet stimulation mode. METHODS: A group of 30 patients (16 F, 14 M) with medically refractory partial epilepsy, who were unsuitable candidates for resective surgery, were included in the study. The patients, their companions and caregivers were instructed on how to administer additional stimulation trains using a hand-held magnet when an aura or a seizure onset occurred. Patients or caregivers could recognize habitual seizures and were able to evaluate sudden interruption of these seizures. Using seizure diaries, detailed accounts of magnet use and regular clinic follow-up visits, data on seizure frequency and severity and number of magnet applications were collected. Patients who provided unreliable information were excluded from the analysis. RESULTS: Forty-seven percent of all patients had an improvement in seizure control with a reduction in seizure frequency of more than 50% during a mean follow-up of 33 months (range: 4-67 months). More than half of the patients used the magnet and provided reliable information. In 63% of patients who were able to self-administer or receive additional magnet stimulation, seizures could be interrupted, be it consistently or occasionally. More than half of the patients who reported a positive effect of magnet stimulation became responders. In most cases the magnet was applied by a caregiver. CONCLUSIONS: To our knowledge, this study is the first to explore the efficacy of magnet-induced vagus nerve stimulation. Results suggest that the magnet is a useful tool that provides patients and mainly caregivers with an additional means of controlling refractory seizures. Additional controlled studies comparing programmed stimulation and magnet-induced stimulation in monitoring conditions are warranted.

Adolescent↗
PubMed1999

Comparative study of transrectal ultrasonography, pelvic computerized tomography, and magnetic resonance imaging in preoperative staging of rectal cancer.

PURPOSE: The preoperative assessment of rectal cancer wall invasion and regional lymph node metastasis is essential for the planning of optimal therapy. This study was done to determine the accuracy and clinical usefulness of transrectal ultrasonography, pelvic computed tomography, and magnetic resonance imaging in preoperative staging. METHODS: A total of 89 patients with rectal cancer were examined with transrectal ultrasonography (n = 89), pelvic computed tomography (n = 69), and magnetic resonance imaging with endorectal coil (n = 73). The results obtained by these diagnostic modalities were compared with the histopathologic staging of specimens. RESULTS: In staging depth of invasion, the overall accuracy was 81.1 percent (72/89) by transrectal ultrasonography, 65.2 percent (45/ 69) by computed tomography, and 81 percent (59/73) by magnetic resonance imaging. Overstaging was 10 percent (9/89) by transrectal ultrasonography, 17.4 percent (12/69) by computed tomography, and 11 percent (8/73) by magnetic resonance imaging; and understaging was 8 of 89 (8.9 percent) by transrectal ultrasonography, 12 of 69 (17.4 percent) by computed tomography, and 6 of 73 (8 percent) by magnetic resonance imaging. In staging lymph node metastasis, the overall accuracy rate was 54 of 85 (63.5 percent) in transrectal ultrasonography, 39 of 69 (56.5 percent) in computed tomography, and 46 of 73 (63 percent) in magnetic resonance imaging. The sensitivity was 24 of 45 (53.3 percent) in transrectal ultrasonography, 14 of 25 (56 percent) in computed tomography, and 33 of 42 (78.5 percent) in magnetic resonance imaging; and specificity was 30 of 40 (75.0 percent) in transrectal ultrasonography, 25 of 44 (56.8 percent) in computed tomography, and 13 of 31 (41.9 percent) in magnetic resonance imaging. The accuracy in detection of positive lateral pelvic lymph nodes under magnetic resonance imaging (n = 8) was 12.5 percent. The accuracy in detection of posterior vaginal wall invasion was 100 percent in transrectal ultrasonography (n = 7) and 100 percent in magnetic resonance imaging (n = 3), but 28.5 percent in computed tomography (n = 7). CONCLUSIONS: Both transrectal ultrasonography and magnetic resonance imaging with endorectal coil exhibited similar accuracy and were superior to conventional computed tomography in preoperative assessment of depth of invasion and adjacent organ invasion. Because transrectal ultrasonography is a safer and more cost-effective modality than magnetic resonance imaging, transrectal ultrasonography is an appropriate method for preoperative staging of rectal cancer. Further efforts will be needed to provide a better staging of lymph node involvement.

Adult↗
PubMed2006

Protein purification using magnetic adsorbent particles.

The application of functionalised magnetic adsorbent particles in combination with magnetic separation techniques has received considerable attention in recent years. The magnetically responsive nature of such adsorbent particles permits their selective manipulation and separation in the presence of other suspended solids. Thus, it becomes possible to magnetically separate selected target species directly out of crude biological process liquors (e.g. fermentation broths, cell disruptates, plasma, milk, whey and plant extracts) simply by binding them on magnetic adsorbents before application of a magnetic field. By using magnetic separation in this way, the several stages of sample pretreatment (especially centrifugation, filtration and membrane separation) that are normally necessary to condition an extract before its application on packed bed chromatography columns, may be eliminated. Magnetic separations are fast, gentle, scaleable, easily automated, can achieve separations that would be impossible or impractical to achieve by other techniques, and have demonstrated credibility in a wide range of disciplines, including minerals processing, wastewater treatment, molecular biology, cell sorting and clinical diagnostics. However, despite the highly attractive qualities of magnetic methods on a process scale, with the exception of wastewater treatment, few attempts to scale up magnetic operations in biotechnology have been reported thus far. The purpose of this review is to summarise the current state of development of protein separation using magnetic adsorbent particles and identify the obstacles that must be overcome if protein purification with magnetic adsorbent particles is to find its way into industrial practice.

Adsorption↗
PubMed2003

Prospective comparison of hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging of perianal fistulas.

PURPOSE: This study was conducted to determine agreement between hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging in the preoperative assessment of perianal fistulas and to compare these results with the surgical findings. METHODS: Twenty-one patients (aged 26-71 years) with clinical symptoms of a cryptoglandular perianal fistula and a visible external opening underwent preoperative hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography, endoanal magnetic resonance imaging, and surgical exploration. The results were assessed separately by experienced observers blinded as to each other's findings. Each fistula was described with notice of the following characteristics: classification of the primary fistula tract according to Parks (intersphincteric, transsphincteric, extrasphincteric, or suprasphincteric), horseshoe, or not classified; presence of secondary tracts (circular or linear); and location of an internal opening. RESULTS: The median time between hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging was 66 (interquartile range, 21-160) days; the median time between the last study (hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography or endoanal magnetic resonance imaging) and surgery was 154 (interquartile range, 95-189) days. Agreement for the classification of the primary fistula tract was 81 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and surgery, 90 percent for endoanal magnetic resonance imaging and surgery, and 90 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging. For secondary tracts, agreement was 67 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and surgery, 57 percent for endoanal magnetic resonance imaging and surgery, and 71 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging in case of circular tracts and 76 percent, 81 percent, and 71 percent, respectively, in case of linear tracts. Agreement for the location of an internal opening was 86 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and surgery, 86 percent for endoanal magnetic resonance imaging and surgery, and 90 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging. CONCLUSIONS: For evaluation of perianal fistulas, hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging have good agreement, especially for classification of the primary fistula tract and the location of an internal opening. These results also show good agreement compared with surgical findings. Therefore, hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging can both be used as reliable methods for preoperative evaluation of perianal fistulas.

Adult↗
PubMed1993

Treatment of arteriovenous malformations with stereotactic radiosurgery employing both magnetic resonance angiography and standard angiography as a database.

Twenty-one arteriovenous malformations were prospectively evaluated using magnetic resonance angiography and compared with stereotactic angiography. The goals were to establish the feasibility of magnetic resonance angiography, compare it to stereotactic angiography, employ magnetic resonance angiography in follow-up, and semiquantify flow. A correlative evaluation between flow and response to stereotactic radiosurgery was carried out. Phase contrast angiograms were obtained at flow velocities of 400, 200, 100, 60, and 20 cm/sec. The fractionated velocities provided images that selectively demonstrated the arterial and venous components of the arteriovenous malformations. Qualitative assessment of the velocity within the arteriovenous malformations and the presence of fistulae were also determined by multiple velocity images. In addition, 3-dimensional time-of-flight magnetic resonance angiograms were obtained to define the exact size and shape of the nidus. This technique also permitted evaluation of the nidus and feeding arteries for the presence of low flow aneurysms. Correlation between the two imaging modalities was carried out by subjective and semiquantitative estimation of flow velocity and estimation of nidus size. The following velocity parameters were employed: fast, intermediate, slow, and none (arteriovenous malformation obliterated). In 19 of 21 (90.5%) arteriovenous malformations, magnetic resonance angiography was equal or superior to stereotactic angiography for flow quantification and visualization of the nidus. Only 2 of 21 arteriovenous malformations were better demonstrated by stereotactic angiography than by magnetic resonance angiography (failure rate of 9.5%). The nidus size in one case was clearly underestimated by stereotactic angiography and would have resulted in a geographic miss without magnetic resonance angiography. Seven post-radiosurgery arteriovenous malformations were evaluated for follow-up with both magnetic resonance angiography and stereotactic angiography. In 6 of 7 arteriovenous malformations, magnetic resonance angiography response matched stereotactic angiography response. Correlation of flow with outcome was carried out for 14 arteriovenous malformations using magnetic resonance angiography only. Interestingly, all nine arteriovenous malformations with intermediate or slow flow demonstrated partial or complete obliteration; whereas only 3 of 5 fast flow arteriovenous malformations achieved a response with a median follow-up of 10 months. This early analysis suggests that slower flowing arteriovenous malformations may obliterate faster after stereotactic radiosurgery and flow parameters could be employed to predict response. In conclusion, magnetic resonance angiography permits semiquantitative flow velocity assessment and may therefore be superior to stereotactic angiography. An additional advantage of magnetic resonance angiography is the generation of serial transverse images which can replace the conventional CT scan employed for stereotactic radiosurgery treatment planning.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebral Angiography↗
PubMed1992

Bio-effects of high magnetic fields: a study using a simple animal model.

The desire to do clinical imaging and spectroscopy at magnetic field strengths greater than 2 Tesla (T) necessitates investigation of possible bioeffects at these high fields. A simple T-maze was utilized to evaluate the aversive effects of exposure to three levels of static magnetic field (0, 1.5, and 4 T). The right arm of the maze extended into the center of a 30-cm horizontal bore magnet, while the left arm extended into a mock magnet bore with the same dimensions. The self-shielded design of the magnet reduces the fringe field to zero within 1 m of the bore, placing the start box of the maze outside the 5-G line of the magnet. Each rat performed a total of ten trials at each level of magnetic field strength. A follow-up subset was run at 4 T with the maze reversed. At 0 T, the rats entered the magnet freely. No significant differences from the control were observed at 1.5 T. At 4 T, however, in 97% of the trials the rats would not enter the magnet. In the maze-reversed subset a majority of the rats turned toward the magnet, indicating that they had learned an aversive response from the previous trials at 4 T. However, in only 4 decisions out of 58 did the rats actually enter the magnet. Eighteen decisions to turn around were made at the edge of the magnet in a region of strong field gradients (up to 13 T/m) and a field strength up to 1.75 T.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Biological effects due to weak magnetic field on plants.

Throughout the evolution process, Earth's magnetic field (MF, about 50 microT) was a natural component of the environment for living organisms. Biological objects, flying on planned long-term interplanetary missions, would experience much weaker magnetic fields, since galactic MF is known to be 0.1-1 nT. However, the role of weak magnetic fields and their influence on functioning of biological organisms are still insufficiently understood, and is actively studied. Numerous experiments with seedlings of different plant species placed in weak magnetic field have shown that the growth of their primary roots is inhibited during early germination stages in comparison with control. The proliferative activity and cell reproduction in meristem of plant roots are reduced in weak magnetic field. Cell reproductive cycle slows down due to the expansion of G1 phase in many plant species (and of G2 phase in flax and lentil roots), while other phases of cell cycle remain relatively stable. In plant cells exposed to weak magnetic field, the functional activity of genome at early pre-replicate period is shown to decrease. Weak magnetic field causes intensification of protein synthesis and disintegration in plant roots. At ultrastructural level, changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells were observed in pea roots exposed to weak magnetic field. Mitochondria were found to be very sensitive to weak magnetic field: their size and relative volume in cells increase, matrix becomes electron-transparent, and cristae reduce. Cytochemical studies indicate that cells of plant roots exposed to weak magnetic field show Ca2+ over-saturation in all organelles and in cytoplasm unlike the control ones. The data presented suggest that prolonged exposures of plants to weak magnetic field may cause different biological effects at the cellular, tissue and organ levels. They may be functionally related to systems that regulate plant metabolism including the intracellular Ca2+ homeostasis. However, our understanding of very complex fundamental mechanisms and sites of interactions between weak magnetic fields and biological systems is still incomplete and still deserve strong research efforts.

Calcium↗
PubMed2007

Magnetic Mini-Mover Procedure for pectus excavatum: I. Development, design, and simulations for feasibility and safety.

BACKGROUND/PURPOSE: Correction of pectus excavatum (PE) results in measurable improvement in lung capacity and cardiac performance as well as improved appearance and self-image. The Nuss and modified Ravitch approaches attempt to correct the chest wall deformity by forcing the sternum forward in 1 step and holding it in place using a metal strut. The initial operation requires extensive manipulation under general anesthesia and results in postoperative pain, requiring hospitalization and regional anesthesia. Pain and disability may last for weeks. Both procedures are expensive. A better principle would be a gradual bit-by-bit repair via small increments of pressure applied over many months. We developed the Magnetic Mini-Mover Procedure and applied this strategy to correct PE. METHODS: The Magnetic Mini-Mover Procedure uses magnetic force to pull the sternum forward. An internal magnet implanted on the sternum and an external magnet in a nonobtrusive custom-fitted anterior chest wall orthosis produce an adjustable outward force on the sternum. Outward force is maintained until the abnormal costal cartilages are remodeled and the pectus deformity is corrected. RESULTS: We implanted a magnet in human skeletons and measured the force applied to the sternum when the distance between the internal and external magnets was varied in increments. With the 2 magnets 1 cm apart, the outward force was adequate to move the sternum at least 1 cm. We also mapped the magnetic field in the two-magnet configuration and found that maximum field strengths at the surface of the heart and at the outer surface of the orthosis were at safe levels. CONCLUSIONS: The Magnetic Mini-Mover Procedure allows correction of PE by applying magnetic force over a period of months. Crucial questions raised during our design, redesign, and simulation testing have been satisfactorily answered, and we have received a Food and Drug Administration Investigation Device Exemption (G050196/A002) to proceed with a phase I to II clinical trial.

Feasibility Studies↗
PubMed2006

Parthenogenetic activation of domestic cat oocytes using ethanol, calcium ionophore, cycloheximide and a magnetic field.

The objective of this study was to evaluate parthenogenetic activation of domestic cat oocytes after being exposed to either ethanol, magnetic field, calcium ionophore A23187, or cycloheximide and a combination of these agents. We also wished to evaluate the usefulness of the magnetic field for oocyte activation. In vitro matured oocytes subjected to artificial activation were randomly assigned into eight groups according to activating agents: (1) 10% ethanol; (2) the magnetic field (slow-changing, homogenous magnetic field with low values of induction); (3) 10% ethanol plus magnetic field; (4) 10 microM calcium ionophore A23187; (5) 10 microM calcium ionophore A23187 plus magnetic field; (6) 10% ethanol and 10 microg/mL of cycloheximide; (7) 10% ethanol and 10 microg/mL of cycloheximide plus magnetic field; (8) oocytes were not exposed to any of the activating agents. After activation oocytes were stained with Hoechst 33258 and parthenogenetic activation was defined as oocytes containing pronuclei and second polar bodies or two to four or six nuclei (embryonic cleavage). The total activation rate by using different activation treatments was 40%. The addition of the magnetic field to ethanol or calcium ionophore treatments resulted in increased parthenogenetic activation rates from 47% to 75%, and from 19% to 48%, respectively (P<0.001). Instead, when the magnetic field was added to ethanol and cycloheximide treatment, activation rate decreased from 48% to 30%. Oocytes activated with magnetic field only gave the lowest activation rate (12%). We concluded that a magnetic field can be used as an activating agent, and the combination of ethanol and magnetic field is an effective method for domestic cat oocyte activation.

Animals↗
PubMed2003

RGD-anchored magnetic liposomes for monocytes/neutrophils-mediated brain targeting.

Negatively charged magnetic liposomes were prepared using soya lecithin (Soya PC), cholesterol and phosphatidyl serine (PS) for their preferential presentation to circulating blood phagocytes (monocytes and neutrophils). PS ratio was optimized in terms of drug and magnetite loading, in vitro magnetic responsiveness and ex vivo monocytes/neutrophils uptake. RGD peptide was covalently coupled to the negatively charged liposomes composed of PC, cholesterol, PS and phopsphatidyl ethanolamine (PE) via carbodiimide-mediated coupling. In vivo cellular sorting study under magnetic guard indicated an increase in relative count of neutrophils and monocytes. Results suggest that selective uptake of RGD-anchored magnetic liposomes by these cells imparts them magnetic property. High levels of a model drug diclofenac sodium was quantified in target organ brain. In case of negatively charged uncoated magnetic liposomes brain levels of the drug was 5.95-fold compared to free drug and 7.58-fold in comparison to non-magnetic formulation, while for RGD-coated magnetic liposomes this ratio was 9.1-fold compared to free drug solution, 6.62-fold compared to non-magnetic RGD-coated liposomes and 1.5-fold when compared to uncoated magnetic liposomes. Liver uptake was significantly bypassed (37.2% and 48.3% for uncoated and RGD-coated magnetic liposomes, respectively). This study suggested the potential of negatively charged and RGD-coated magnetic liposomes for monocytes/neutrophils-mediated active delivery of drugs to relatively inaccessible inflammatory sites, i.e. brain. The study opens a new perspective of active delivery of drugs for a possible treatment of cerebrovascular diseases.

Animals↗
PubMed1996

The physical properties and behavior of magnets used in the treatment of anterior open bite.

This investigation examined the magnetic flux and repulsive force of neodymium-iron-boron (Nd-Fe-B) magnets used in repulsion in the treatment of anterior open bite. Three different grades of magnets each of five different dimensions were used. Magnetic flux was measured by a Hall probe and the repulsive force by an Instron mechanical testing machine. Results showed that the different grades of magnet displayed similar magnetic flux with a relationship between thickness and flux. There was a significant difference between the flux measured at the end as opposed to the center of the magnet. The force between two magnets and the flux above each magnet was directly related. Using magnets in groups did not produce higher forces than using single magnets of an equivalent size. It was concluded that Nd-Fe-B magnets can be used to give predictable repulsive forces in the mouth.

Boron↗
PubMed1996

The performance of bonded magnets used in the treatment of anterior open bite.

This investigation examined the magnetic flux and repulsive force of neodymium-iron-boron (Nd-Fe-B) magnets based on Nd2Fe14B with acrylic coatings in different orientations. The flux was measured with a Hall probe and the force measured by electronic scales with the magnets mounted on a laboratory jack. Results show that there were no magnetic losses after embedding the magnets in acrylic bite-blocks, although there were significant flux losses when the magnet blocks were directly heated. The alignment of the magnets over each other was of the utmost importance and significantly affected the repulsive force between the magnets. When the magnets were mounted in an articulator to simulate jaw movement, the force levels between the magnets was further reduced as a result of the effects of the rotation of the articulator. It is concluded that Nd-Fe-B type magnets embedded in acrylic can be used to give predictable repulsive forces in the mouth. The dramatic reduction in force levels when the magnets are not in optimal alignment, however, makes their effectiveness in aiding intrusion of teeth doubtful.

Acrylic Resins↗
PubMed1998

Role of magnetization transfer imaging in bone tumors.

RATIONALE AND OBJECTIVES: The authors evaluated the role of magnetization transfer imaging in differentiation of bone tumors, with special emphasis on cartilaginous tumors. MATERIALS AND METHODS: Fifty-one patients with skeletal tumors or tumor-like lesions who had undergone magnetic resonance (MR) imaging were included. The tumors were divided into three groups according to their gross appearance and the origin of tissue: cyst, cartilaginous tumor, and noncartilaginous solid tumor. A gradient-recalled acquisition in the steady state sequence was used for MR imaging, and examinations were performed both with and without off-resonance magnetization transfer pulses. Magnetization transfer ratios were obtained as an indicator of magnetization transfer effect of the lesions and were compared. Then, the magnetization transfer ratios of all tumors in the cartilaginous tumor group were compared. The magnetization transfer ratios of benign and malignant solid tumors were also compared. RESULTS: The mean magnetization transfer ratio for cartilaginous tumors was 0.31 +/- 0.08 (standard deviation), and that of cysts and noncartilaginous solid tumors was 0.07 +/- 0.03 and 0.40 +/- 0.14, respectively. Comparisons between the three groups showed statistically significant intergroup differences in magnetization transfer ratio (P < .05). In the cartilaginous tumor category, enchondroma and low-grade chondrosarcoma had a lower magnetization transfer effect than chondroblastoma and mesenchymal chondrosarcoma. The mean magnetization transfer ratios of benign (n = 28) and malignant (n = 18) tumors were 0.35 +/- 0.11 and 0.39 +/- 0.15, respectively; there was no statistically significant intergroup difference (P = .14). CONCLUSION: Magnetization transfer imaging could be useful for categorizing bone tumors as cysts, cartilaginous tumors, or noncartilaginous solid tumors.

Adolescent↗
PubMed1992

Force generation by orthodontic samarium-cobalt magnets.

The use of samarium-cobalt (Sm-Co) magnets for light force application is a relatively new concept in orthodontic tooth movement. This study reports on the forces generated by these magnets. Magnets were attached to aluminum rods mounted in a universal testing machine. The magnets were initially separated by 10 mm were moved toward each other at 2.5mm/min in repulsion or attraction, depending upon the magnetic pole orientation. The magnets were also positioned initially in contact and then moved apart at a rate of 2.5mm/min, again producing repulsion or attraction, depending upon the pole orientation. The Sm-Co magnets exhibit very large forces when in close approximation but forces decrease markedly at separations greater than 2mm. The force, P, generated between magnets is determined by their separation, d, and follows the relationship P = dn. At magnet separations of 0 to 2mm, the exponent n is equal to -0.4; at separations of 2mm to 7mm, exponent n equals -2.1 for both attraction and repulsion. Thus the classic Coulomb law of magnetic force was followed only at magnet separations of greater than 2mm. Force-separation behavior and the high cost of these magnets may not justify their routine clinical use.

Cobalt↗
PubMedDate not supplied

Permanent magnetic-levitation of rotating impeller: a decisive breakthrough in the centrifugal pump.

Magnetic bearings have no mechanical contact between the rotor and stator, and a rotary pump with magnetic bearings therefore has no mechanical wear and thrombosis. The magnetic bearings available, however, contain electromagnets, are complicated to control and have high energy consumption. Therefore, it is difficult to apply an electromagnetic bearing to a rotary pump without disturbing its simplicity, reliability and ability to be implanted. The authors have developed a levitated impeller pump using only permanent magnets. The rotor is supported by permanent radial magnetic forces. The impeller is fixed on one side of the rotor; on the other side the rotor magnets are mounted. Opposite these rotor magents, a driving magnet is fastened to the motor axis. Thereafter, the motor drives the rotor via magnetic coupling. In laboratory tests with saline, where the rotor is still or rotates at under 4,000 rpm, the rotor magnets have one point in contact axially with a spacer between the rotor magnets and the driving magnets. The contacting point is located in the center of the rotor. As the rotating speed increases gradually to more than 4000 rpm, the rotor will disaffiliate from the stator axially, and become fully levitated. Since the axial levitation is produced by hydraulic force and the rotor magnets have a giro-effect, the rotor rotates very stably during levitation. As a left ventricular assist device, the pump works in a rotating speed range of 5,000-8,000 rpm, and the levitation of the impeller is assured by use of the pump. The permanent maglev impeller pump retains the advantages of the rotary pump but overcomes the disadvantages of the leviated pump with electromagnetic-bearing, and has met with most requirements of artificial heart blood pumps, thus promising to have more applications than previously.

Equipment Design↗