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Schültke E, Fiedler S, Nemoz C, Ogieglo L, Kelly ME, Crawford P, Esteve F, Brochard T, Renier M, Requardt H, Le Duc G, Juurlink B, Meguro K. Synchrotron-based intra-venous K-edge digital subtraction angiography in a pig model: a feasibility study. Eur J Radiol 2009; 73:677-81. [PMID: 19233584 DOI: 10.1016/j.ejrad.2009.01.019] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2008] [Revised: 01/08/2009] [Accepted: 01/15/2009] [Indexed: 10/21/2022]
Abstract
BACKGROUND K-edge digital subtraction angiography (KEDSA) combined with the tunability of synchrotron beam yields an imaging technique that is highly sensitive to low concentrations of contrast agents. Thus, contrast agent can be administered intravenously, obviating the need for insertion of a guided catheter to deliver a bolus of contrast agent close to the target tissue. With the high-resolution detectors used at synchrotron facilities, images can be acquired at high spatial resolution. Thus, the KEDSA appears particularly suited for studies of neurovascular pathology in animal models, where the vascular diameters are significantly smaller than in human patients. MATERIALS AND METHODS This feasibility study was designed to test the suitability of KEDSA after intravenous injection of iodine-based contrast agent for use in a pig model. Four adult male pigs were used for our experiments. Neurovascular angiographic images were acquired using KEDSA with a solid state Germanium (Ge) detector at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. RESULTS After intravenous injection of 0.9 ml/kg iodinated contrast agent (Xenetix), the peak iodine concentrations in the internal carotid and middle cerebral arteries reached 35 mg/ml. KEDSA images in radiography mode allowed the visualization of intracranial arteries of less than 1.5mm diameter.
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Prezado Y, Fois G, Edouard M, Nemoz C, Renier M, Requardt H, Estève F, Adam JF, Elleaume H, Bravin A. Biological equivalent dose studies for dose escalation in the stereotactic synchrotron radiation therapy clinical trials. Med Phys 2009; 36:725-33. [DOI: 10.1118/1.3070538] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Renier M, Brochard T, Nemoz C, Requardt H, Bräuer E, Esteve F, Balosso J, Suortti P, Baruchel J, Elleaume H, Berruyer G, Berkvens P, Bravin A. The radiotherapy clinical trials projects at the ESRF: Technical aspects. Eur J Radiol 2008; 68:S147-50. [DOI: 10.1016/j.ejrad.2008.04.057] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2008] [Accepted: 04/28/2008] [Indexed: 10/21/2022]
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Verbeni R, D'Astuto M, Krisch M, Lorenzen M, Mermet A, Monaco G, Requardt H, Sette F. Energy calibration of a high-resolution inelastic x-ray scattering spectrometer. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2008; 79:083902. [PMID: 19044359 DOI: 10.1063/1.2968118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The energy scale of a triple-axis x-ray spectrometer with meV energy resolution based on perfect silicon crystal optics is calibrated, utilizing the most recent determination of the silicon lattice parameter and its thermal expansion coefficient and recording the dispersion of longitudinal acoustic and optical phonons in a diamond single crystal and the molecular vibration mode in liquid nitrogen. Comparison of the x-ray results with previous inelastic neutron and Raman scattering results as well as with ab initio phonon dispersion calculations yields an overall agreement better than 2%.
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Requardt H. Technology solutions for better outcomes: integrated information management in key to productivity increases in medicine. Br J Radiol 2006; 79:17-23. [PMID: 16421400 DOI: 10.1259/bjr/23726774] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
The challenges to healthcare systems around the world are primarily impacted by two topics: demographic factors and progress in medicine. An ageing population inherently needs more medical services which add financial burdens, in particular, to public healthcare. Since the level of medical education is growing at the same time, we are observing an increased demand for sophisticated (in general expensive) medicine. Drastic changes in financing seem unavoidable. Multiple diagnoses, repeated examinations, trial-and-error, overcapacities and other signs of missing economical considerations are reinforced by reimbursement systems. In a world where, in principle, all information is available everywhere, more than a patient's history should be accessible. Other industries have knowledge management systems in place that make state-of-the-art expertise available everywhere. Intelligent patient databases could consist of learning cycles that (i) enable the individual to benefit from structured knowledge, in addition to personal experience of the physician, and (ii) use the knowledge generated from the individual to extend the database. The novel area of molecular medicine fits perfectly well into these scenarios. Only attached to an IT backbone can the flood of information be managed in a beneficial way. Efficiency improvements in healthcare address the needs of all parties in the system: patients, providers, and payers. The opportunities, however, can only materialize if everyone is prepared to change. IT will set the standards for the biggest challenge in healthcare: The paradigm shift in medicine.
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Murphy BM, Requardt H, Stettner J, Serrano J, Krisch M, Müller M, Press W. Phonon modes at the 2H-NbSe2 surface observed by grazing incidence inelastic x-ray scattering. PHYSICAL REVIEW LETTERS 2005; 95:256104. [PMID: 16384477 DOI: 10.1103/physrevlett.95.256104] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2005] [Revised: 08/09/2005] [Indexed: 05/05/2023]
Abstract
We have determined the dispersion of acoustic and optical surface phonon modes 2H-NbSe2 at the by inelastic x-ray scattering under grazing incidence conditions. Already, at room temperature, an anomaly is observed close to the charge density wave -vector position located at about one-third along the Gamma-M direction of the Brillouin zone. Our results indicate that the anomaly for the surface mode occurs at a lower energy than that measured in bulk sensitive geometry in the same experiment, showing evidence of a modified behavior in the uppermost layers. We demonstrate that inelastic x-ray scattering in grazing incidence conditions provides a unique tool to selectively study either surface or bulk lattice dynamics in a single experiment.
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Bräuer-Krisch E, Requardt H, Régnard P, Corde S, Siegbahn E, LeDuc G, Brochard T, Blattmann H, Laissue J, Bravin A. New irradiation geometry for microbeam radiation therapy. Phys Med Biol 2005; 50:3103-11. [PMID: 15972983 DOI: 10.1088/0031-9155/50/13/009] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Microbeam radiation therapy (MRT) has the potential to treat infantile brain tumours when other kinds of radiotherapy would be excessively toxic to the developing normal brain. MRT uses extraordinarily high doses of x-rays but provides unusual resistance to radioneurotoxicity, presumably from the migration of endothelial cells from 'valleys' into 'peaks', i.e., into directly irradiated microslices of tissues. We present a novel irradiation geometry which results in a tolerable valley dose for the normal tissue and a decreased peak-to-valley dose ratio (PVDR) in the tumour area by applying an innovative cross-firing technique. We propose an MRT technique to orthogonally crossfire two arrays of parallel, nonintersecting, mutually interspersed microbeams that produces tumouricidal doses with small PVDRs where the arrays meet and tolerable radiation doses to normal tissues between the microbeams proximal and distal to the tumour in the paths of the arrays.
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Antonangeli D, Krisch M, Fiquet G, Farber DL, Aracne CM, Badro J, Occelli F, Requardt H. Elasticity of cobalt at high pressure studied by inelastic x-ray scattering. PHYSICAL REVIEW LETTERS 2004; 93:215505. [PMID: 15601029 DOI: 10.1103/physrevlett.93.215505] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2004] [Indexed: 05/24/2023]
Abstract
The five independent elastic moduli of single-crystalline hcp cobalt were determined by inelastic x-ray scattering to 39 GPa and compared to ultrasonic measurements and first principles calculations. In general the agreement is good, in particular, for the evolution of the longitudinal sound velocity in the a-c plane. This confirms the calculations, suggesting that a similar evolution is valid for hcp iron, the main constituent of the Earth's inner core, up to the highest investigated pressure. Our results represent an important benchmark to further refine ab initio calculations.
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Ayari A, Danneau R, Requardt H, Ortega L, Lorenzo JE, Monceau P, Currat R, Brazovskii S, Grübel G. Sliding-induced decoupling and charge transfer between the coexisting Q1 and Q2 charge density waves in NbSe3. PHYSICAL REVIEW LETTERS 2004; 93:106404. [PMID: 15447429 DOI: 10.1103/physrevlett.93.106404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Indexed: 05/24/2023]
Abstract
Using high-resolution x-ray scattering in the presence of an applied current, we report evidence for a dynamical decoupling between the two NbSe3 charge-density waves (CDWs), Q1 (T(C1)=145 K) and Q2 (T(C2)=59 K), coexisting below T(C2). Simultaneous and oppositely directed shifts of the relevant CDW superlattice spots develop above a threshold current which we identify as the depinning threshold I(C1) for the more strongly pinned upper CDW Q1 (I(C1) approximately 10I(C2)). In contrast with shifts induced by current conversion processes, the present effect is not current polarized and is not limited to the current-contact regions. We propose a model which explains this instability through a sliding-induced charge transfer between the two electronic reservoirs corresponding to the Q1 and Q2 CDWs.
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Maultzsch J, Reich S, Thomsen C, Requardt H, Ordejón P. Phonon dispersion in graphite. PHYSICAL REVIEW LETTERS 2004; 92:075501. [PMID: 14995866 DOI: 10.1103/physrevlett.92.075501] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2003] [Indexed: 05/24/2023]
Abstract
We measured the dispersion of the graphite optical phonons in the in-plane Brillouin zone by inelastic x-ray scattering. The longitudinal and transverse optical branches cross along the Gamma-K as well as the Gamma-M direction. The dispersion of the optical phonons was, in general, stronger than expected from the literature. At the K point the transverse optical mode has a minimum and is only approximately 70 cm(-1) higher in frequency than the longitudinal mode. We show that first-principles calculations describe very well the vibrational properties of graphene once the long-range character of the dynamical matrix is taken into account.
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Danneau R, Ayari A, Rideau D, Requardt H, Lorenzo JE, Ortega L, Monceau P, Currat R, Grübel G. Motional ordering of a charge-density wave in the sliding state. PHYSICAL REVIEW LETTERS 2002; 89:106404. [PMID: 12225211 DOI: 10.1103/physrevlett.89.106404] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2002] [Indexed: 05/23/2023]
Abstract
We have used high-resolution x-ray scattering, in the presence of an applied direct current, for studying the correlation lengths in the sliding charge-density wave (CDW) state. Transport properties were simultaneously measured in situ during the experiment. We find that, while the transverse correlation is reduced when the CDW moves, the CDW becomes more ordered in the direction of motion. This is the first report of a motional ordering process in a periodic system other than a vortex lattice.
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Abstract
The dispersion of longitudinal acoustic phonons was measured by inelastic x-ray scattering in the hexagonal closed-packed (hcp) structure of iron from 19 to 110 gigapascals. Phonon dispersion curves were recorded on polycrystalline iron compressed in a diamond anvil cell, revealing an increase of the longitudinal wave velocity (VP) from 7000 to 8800 meters per second. We show that hcp iron follows a Birch law for VP, which is used to extrapolate velocities to inner core conditions. Extrapolated longitudinal acoustic wave velocities compared with seismic data suggest an inner core that is 4 to 5% lighter than hcp iron.
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Requardt H, Nad F, Rideau D, Monceau P, Currat R, Lorenzo J, Smilgies D, Grübel G. X-ray diffraction studies on charge-density-wave deformation by carrier injection in the quasi-one-dimensional compound NbSe 3. Acta Crystallogr A 2000. [DOI: 10.1107/s0108767300023631] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Requardt H, Nad FY, Monceau P, Currat R, Lorenzo JE, Rideau D, Smilgies D, Grübel G. Space- and time-resolved X-ray diffraction from pinned and sliding charge-density-waves in NbSe3. ACTA ACUST UNITED AC 1999. [DOI: 10.1051/jp4:19991034] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Mäurer J, Mitrovic T, Knollmann FD, Lüdtke E, Requardt H. In vitro delineation of human brain-stem anatomy using a small resonator: correlation with macroscopic and histological findings. Neuroradiology 1996; 38:217-20. [PMID: 8741190 DOI: 10.1007/bf00596532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Our purpose was to investigate the potential of an experimental animal coil using a commercial MRI unit to delineate the anatomical structure of the human brain stem. Three formaldehyde-fixed brain-stem specimens were examined by MRI and sectioned perpendicular to their longitudinal axis. The images were compared with gross anatomy and myelin-stained histological sections. Fibre tracts and nuclei which were not evident on examination of the unstained specimen were readily identified by MRI. Due to its inherent grey/white matter contrast, MRI with a high-resolution coil delineates anatomical structures in a way comparable to the myelin-stained histological sections. However, pigmented structures, readily visible on examination of the unstained specimen were discernible on neither MRI nor on myelin-stained sections. The excellent anatomical detail and grey/white matter contrast provided by these images could make MRI a useful adjunct to the pathologist investigating brain disease.
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Mäurer J, Requardt H, Herrling T, Knollmann FD, Schedel H, Vogl TJ, Felix R. [Theoretical principles and technical realization of high resolution nuclear magnetic resonance tomography with the example of a dedicated coil system]. BILDGEBUNG = IMAGING 1996; 63:40-6. [PMID: 8653008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The theory of high-resolution magnetic resonance imaging (MRI) and the physical properties of a dedicated coil system with its clinical application are reviewed. To evaluate the spatial resolution of the system, a phantom sample was depicted by a transverse T1-weighted sequence (time of repetition 500 ms, time of echo 25 ms, 256 x 256 matrix, 3 acquisitions, field of view 25 mm2). Relative signal intensity decrease was less using the 5-cm coil, as signal intensity field distribution depends on coil diameter. The phantom appeared as an attainable resolution of 100-microns pixel width using the 2.5-cm coil. For the 5-cm coil the pixel width was 200 microns, not accomplishing clear resolution of the phantom. Coil head choice depends on the anatomic depth of the target organ. Work-up of the skin and musculoskeletal lesions is the main indication for high-resolution MRI using surface coils.
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Mäurer J, Requardt H, Sander B, Knollmann FD, Lemke AJ, Vogl TJ, Felix R. Applications of specialized coils for high-resolution MRI on a whole-body scanner. MAGMA (NEW YORK, N.Y.) 1996; 4:27-33. [PMID: 8773999 DOI: 10.1007/bf01759777] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
To investigate the application of a mini-coil surface system for high-resolution MRI, 60 volunteers were examined in a 1.5-T whole-body scanner. Two replaceable probe heads were available: a circular 2.5-cm coil and a quadratic 5-cm coil, both of which were placed directly on the skin. The skin layers, Achilles tendon and finger joints were examined with the 2.5-cm coil and a FOV of 25 X 25 mm2. A matrix of 256 pixels resulted in a pixel size of 0.098 X 0.098 mm2. For imaging of the carpal tunnel, the 5-cm coil was used in transverse orientation. The FOV was 50 X 50 mm2 so that a matrix of 256 X 256 pixels led to a pixel size of 0.195 X 0.195 mm2. The resulting spatial resolution permitted visualization of the epidermis, dermis and subcutis, resulting in clear definition of anatomical detail of the musculoskeletal system. MRI measurement of skin-layer thickness did not correlate with histometric data (p < 0.05). This discrepancy was due in part to shrinkage of the tumor specimen on histologic preparation. Other causes include the motion artifacts and the limited accuracy of determining thickness on the MRI display unit.
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Hosten N, Lemke A, Sander B, Requardt H, Wassmuth R, Mäurer J, Anders N, Felix R. [MRT of the eye: the normal anatomy and detection of the smallest lesions with a high-resolution surface coil]. ROFO-FORTSCHR RONTG 1996; 164:126-31. [PMID: 8679974 DOI: 10.1055/s-2007-1015624] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
PURPOSE A new, high-resolution surface coil for MRI of the eye was evaluated with regard to practicability, image quality and sensitivity for small lesions. MATERIAL AND METHODS 48 patients in whom a space-occupying lesion of the eye or orbit was suspected were examined (1.5 T tomograph, 5 cm surface coil, T1- and T2-weighted spin-echo sequences, the former before and after i.v. gadolinium DTPA). RESULTS 45/48 patients tolerated MR with the high-resolution surface coil. No adverse effects were experienced by the patients. In 11/48 patients a space occupying lesion of the eye was detected (melanoma, 5; metastases, 2; haemorrhage, 1; malformation, hamartoma and scarring after melanoma, one each). The smallest detectable lesion had a thickness of < 1 mm. CONCLUSION First experiences with the high-resolution surface coil indicate that this device is suited for detection of very small lesions of the eye.
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Heywang-Köbrunner SH, Huynh AT, Viehweg P, Hanke W, Requardt H, Paprosch I. Prototype breast coil for MR-guided needle localization. J Comput Assist Tomogr 1994; 18:876-81. [PMID: 7962793 DOI: 10.1097/00004728-199411000-00006] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
OBJECTIVE Evaluation of breast lesions detected by MR alone is a problem: Preoperative MR-guided localization is difficult, since the breast is not accessible by a needle within the breast coil. Magnetic resonance-guided core biopsy and needle aspiration are impossible. Together with Siemens Erlangen, a prototype localization breast coil has been developed and tested. MATERIALS AND METHODS The device consists of a circular polarized coil, which contains two plates for mediolateral breast compression. They are perforated with numerous holes and thus allow access to the breast from both sides. By means of bushings, which fit into the holes, sterile needle insertion in a horizontal path is possible. RESULTS So far, precise needle insertion has been possible in 10 of 11 lesions, allowing exact needle insertion into 5 invasive carcinomas (1 MR-detected), 1 MR-detected additional focus, 2 in situ carcinomas (1 MR-detected), and 3 benign lesions. CONCLUSION Our studies show that MR-guided needle localization is possible.
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Mäurer J, Requardt H, Müller F, Steinkamp HJ, Hosten N, Langer R, Felix R. [Indications for the application of a high resolution coil in MR tomography]. ROFO-FORTSCHR RONTG 1994; 160:353-60. [PMID: 8161750 DOI: 10.1055/s-2008-1032437] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
This is the first study with high spatial resolution Magnetic Resonance Imaging (MRI), performed with a high resolution coil in a clinical whole-body system. Measurements were recorded with a slice thickness of 2 mm. A 256 x 256 matrix and a 2.5 cm field of view were used resulting in a pixel size of 0.01 mm2. MR images of the skin, hand, wrist, knee and ankle of 14 healthy volunteers, of three anatomic pathology tissue specimens and of three formalin-fixed specimens were obtained. Normal anatomy was identified and compared with the three gross anatomic pathology sections. The skin, hands, wrists and ankles of 30 patients were examined and a variety of pathological lesions were detected, including cutaneous neoplasms and ulceration, acute and chronic tendon lesions and pathologic features of the bone and wrist. Based on the excellent imaging of anatomic detail and superior contrast resolution, high resolution MRI proved an important complement for preoperative diagnosis.
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Krasny R, Casser HR, Requardt H, Botschek A. A new holder and surface MRI coil for the examination of the newborn infant hip. Pediatr Radiol 1993; 23:538-40. [PMID: 8309758 DOI: 10.1007/bf02012143] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A special holder was developed for examination of the infant hip joint using MRI. This holder allows the infant hip joint to be examined both in a neutral position and in various defined functional positions. A special integrated surface coil, also developed for this purpose, provides the high spatial resolution required for assessment of the fine joint structures. Thirty infants were examined and the new device has proved useful in advanced hip dysplasia, therapy-resistant subluxation and luxation, and for operative therapy planning (reconstruction of the acetabular roof, redirectional osteotomies). Interpretation errors due to misprojection can be eliminated to a large extent since the holder allows standardized and reproducible positioning.
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Martos J, Petersen D, Klose U, Requardt H, Buchholz R, Ohneseit P, Schabet M, Voigt K. MR imaging of experimental meningeal melanomatosis in nude rats. J Neurooncol 1992; 14:207-11. [PMID: 1460485 DOI: 10.1007/bf00172596] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
MR imaging of the rat brain has become an increasingly frequently used method in experimental neuroradiology. On a generally available 1.5 T whole body tomograph, supplemented with an individually made small coil and a special SE sequence we obtained fairly fine images of the structures of the rat brain. With gadolinium-DTPA, we were able to visualize posterior fossa and cervical leptomeningeal growth of intrathecally injected B16 melanoma in nude rats. Using MRI to follow experimental leptomeningeal metastasis, may provide a new means for diagnostic evaluation and preclinical testing of treatment modalities.
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Abstract
Switched array coils (SACs) are a useful tool in local coil imaging since they allow in a user-friendly manner one to make the best choice in the trade-off between field of view and signal-to-noise ratio. This is done by selecting the current path within a conductor array equipped with suitable switches. Since the switching can be controlled by the system, this allows changing of the coil dimensions within multislice sequences. Thus image quality can be improved due to smaller coil dimensions for a given slice and a larger area can be covered by electronically shifting this sensitive area. The principle can be applied to surface--as well as volume--coil designs.
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Bongartz G, Requardt H, Laub G, Peters PE. [A simplified technic in high-resolution MR tomography of the shoulder: ZEPRA (Zoom of Eccentric Positioned Regions by active Aliasing)]. ROFO-FORTSCHR RONTG 1989; 150:421-4. [PMID: 2539620 DOI: 10.1055/s-2008-1047050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A fairly easy method for high-resolution MR imaging of the shoulder is described. The combination of a defined arrangement of the gradients with a small-volume Helmholtz coil provides the possibility of a high zoom of structures apart from the magnet's centre. The maximal achievable zoom factor depends on the ratio of FOV/sensitive coil volume. The ZEPRA method acts by phase-encoded aliasing only. With this technique all interesting soft tissue of the shoulder may readily be visualized in every direction and with every type of sequence.
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