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Magnetic bones in human sinuses.
Baker RR, Mather JG, Kennaugh JH.
Studies on the interaction of magnetic fields and biological
organisms have centred on the influence of applied magnetic fields on
the physiology and behaviour of organisms, including humans, and a
search for magnetic sources within the organisms themselves. Evidence
continues to accumulate that a wide range of organisms, from bacteria to
vertebrates, can detect and orient to ambient magnetic fields (for
examples see refs 2-4). Since the discovery that magnetic orientation by
bacteria was due to the presence within the organism of magnetic
particles of the ferric/ferrous oxide, magnetite, the search has begun
for other biogenic deposits of inorganic magnetic material and ways in
which the possession of such material might confer on the organism the
ability to orient to ambient magnetic fields. Such magnetic material,
often identified as magnetite, has been discovered in bees, homing
pigeons, dolphins and various other organisms, including man. A variety
of hypotheses for the use of magnetite in magnetic field detection have
been proposed. We report here that bones from the region of the
sphenoid/ethmoid sinus complex of humans are magnetic and contain
deposits of ferric iron. The possible derivations and functions of these
deposits are discussed.
Nature. 1983 Jan 6;301(5895):79-80.
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High-field magnetic resonance imaging of paranasal sinus inflammatory disease.
Moore J, Potchen M, Waldenmaier N, Sierra A, Potchen EJ.
Magnetic resonance imaging using a 1.5 tesla magnet and a spin echo
technique has revealed a remarkably intense signal from abnormal tissue
in the human paranasal sinuses. Inflammatory disease in the maxillary,
sphenoid, ethmoid, and frontal sinuses has been detected and
demonstrated with greater clarity than any other available technique.
The pathophysiologic basis for the intense signal has not been defined.
These observations do, however, provide an opportunity to discover,
clarify, and study paranasal sinus disease. Acute upper respiratory
disease, allergic episodes, and the effect of drug treatment based on
the MR signal and pathology can now be investigated with this technique.
In addition, this may form a basis for assessing the epidemiology of
paranasal sinus pathology.
Laryngoscope. 1986 Mar;96(3):267-71.
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Effect of field strength on susceptibility artifacts in magnetic resonance imaging.
Farahani K, Sinha U, Sinha S, Chiu LC, Lufkin RB.
Department of Radiological Sciences, UCLA School of Medicine 90024.
In magnetic resonance imaging susceptibility artifacts occur at the
interface of substances with large magnetic susceptibility differences,
resulting in geometric distortions of the image at those boundaries. The
susceptibility artifacts are often subtle on clinical images and if not
carefully examined they may lead to misdiagnosis. Magnetic
susceptibility artifacts are prevalent on the boundary of air-containing
paranasal sinuses, as well as bone-soft tissue interfaces in the spinal
canal. The appearance of these artifacts on images from three different
magnetic field strength instruments, 0.3, 0.5, and 1.5 Tesla were
studied. T1- and T2-weighted spin echo and gradient recalled echo pulse
sequences were selected to image a water phantom containing substances
of varying susceptibilities. The effects were also studied in MR images
of the head in a normal human volunteer. At any given field strength the
artifacts were more prominent in the gradient echo imaging than in the
corresponding spin echo pulse sequence. As expected, the distortions
were also greater at higher field strengths. The results in human
subjects paralleled the findings in the phantom study.
Comput Med Imaging Graph. 1990 Nov-Dec;14(6):409-13.
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Measurements of magnetic field variations in the human brain using a 3D-FT multiple gradient echo technique.
Ericsson A, Weis J, Hemmingsson A, Wikstrom M, Sperber GO.
Department of Diagnostic Radiology, University Hospital, Uppsala University, Sweden.
A magnetic resonance 3DFT multiple gradient-echo technique was used
for measurements of the proton spectrum for each voxel in the measured
slice. Water, fat, magnetic field and T2 distributions in the head of a
normal volunteer and a patient with intracerebral hematoma were
computed. Magnetic field variations caused by the head were calculated
after correction for the static magnetic field inhomogeneity. Large
local magnetic field variations up to 3 ppm were found in the human
brain near interfaces between air or bone and brain tissues and 0.5 ppm
between hematoma and brain tissue. Information about magnetic field
variations could be useful for shimming procedures in vivo and for
correcting artifacts in imaging and spectroscopy.
Magn Reson Med. 1995 Feb;33(2):171-7.
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A computer simulation of the static magnetic field distribution in the human head.
Li S, Williams GD, Frisk TA, Arnold BW, Smith MB.
Department of Radiology (Division of NMR Research), Pennsylvania
State University, College of Medicine, Hershey Medical Center, Hershey
17033, USA.
Distortion of the static magnetic field inside the human head is
dependent on regional tissue susceptibility variations and geometrical
shape. These effects result in resonance line broadening and frequency
shifts and consequently, intensity and spatial errors in both magnetic
resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To
calculate the field distortion due to the susceptibility's geometry, two
dimensional (2D) finite element analysis was applied to simulate the
field distribution in a 2D model of the human head, placed in a uniform
magnetic field. The model contains air-filled cavities and sinuses, and
the remainder is treated as water. The magnetic field deviation was
evaluated using gray scale plots and histograms of the magnetic field.
The shifts in parts/million and broadening of the histograms correspond
to the NMR of the sampled region. The field distribution of the human
head was also experimentally mapped using the DANTE tagging sequence.
The calculated and experimental field maps are in good agreement. Thus,
geometric considerations with uniform susceptibilities are sufficient to
explain most of the static magnetic field distribution in the human
head.
Magn Reson Med. 1995 Aug;34(2):268-75.
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Analysis and correction of geometric distortions in 1.5 T magnetic resonance images for use in radiotherapy treatment planning.
Moerland MA, Beersma R, Bhagwandien R, Wijrdeman HK, Bakker CJ.
Department of Radiotherapy, University Hospital Utrecht, The Netherlands.
The aim of this study is to investigate and correct for machine- and
object-related distortions in magnetic resonance images for use in
radiotherapy treatment planning. Patients with brain tumours underwent
magnetic resonance imaging (MRI) in the radiotherapy position with the
head fixed by a plastic cast in a Perspex localization frame. The
imaging experiments were performed on a 1.5 T whole body MRI scanner
with 3 mT m-1 maximum gradient capability. Image distortions, caused by
static magnetic field inhomogeneity, were studied by varying the
direction of the read-out gradient. For purposes of accuracy assessment,
external and internal landmarks were indicated. Tubes attached to the
cast and in the localization frame served as external landmarks. In the
midsagittal plane the brain-sinus sphenoidalis interface, the pituitary
gland-sinus sphenoidalis interface, the sphenoid bone and the corpora of
the cervical vertebra served as internal landmarks. Landmark
displacements as observed in the reversed read-out gradient experiments
were analysed with respect to the contributions of machine-related
static magnetic field inhomogeneity and susceptibility and chemical
shift artifacts. The machine-related static magnetic field inhomogeneity
in the midsagittal plane was determined from measurements on a grid
phantom. Distortions due to chemical shift effects were estimated for
bone marrow containing structures such as the sphenoid bone and the
corpora of the cervical vertebra using the values obtained from the
literature. Susceptibility-induced magnetic field perturbations are
caused by the patient and the localization frame. Magnetic field
perturbations were calculated for a typical patient dataset.
Phys Med Biol. 1995 Oct;40(10):1651-4.
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Three-dimensional numerical simulations of susceptibility-induced magnetic field inhomogeneities in the human head.
Truong TK, Clymer BD, Chakeres DW, Schmalbrock P.
Department of Radiology, The Ohio State University, Columbus, Ohio 43210, USA.
Three-dimensional numerical simulations of the static magnetic field
in the human head were carried out to assess the field inhomogeneity due
to magnetic susceptibility differences at tissue interfaces. We used a
finite difference method and magnetic permeability distributions
obtained by segmentation of computed tomography images. Computations
were carried out for four models, consisting of the head and the neck;
the head, neck, and shoulders; the head, neck, and thorax; and the head
tilted backwards, including the neck and the shoulders. Considerable
magnetic field inhomogeneities were observed in the inferior frontal
lobes and inferior temporal lobes, particularly near the sphenoid sinus
and the temporal bones. Air/tissue interfaces at the shoulders were
found to induce substantial magnetic field inhomogeneities in the
occipital lobes and the cerebellum, whereas air/tissue interfaces in the
lungs appeared to have less influence on the magnetic field in the
brain. Tilting the head backwards could significantly reduce the field
inhomogeneities superior to the planum sphenoidale as well as in the
occipital lobes and the cerebellum.
Magn Reson Imaging. 2002 Dec;20(10):759-70.
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