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1.
PAPER
ISSN: 1352-8661
Source: Springer Online Journal Archives 1860-2000
Type of Medium: 1
2.
PAPER
ISSN: 1352-8661
Keywords phase-contrast velocity encoding ; heart wall motion ; myocardial contraction
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract We present a noninvasive MR technique to assess the regional myocardial wall motion quantitatively. The method uses a phase-contrast sequence in conjunction with a masking program allowing for exact myocardial wall demarcation. Five healthy volunteers, aged 24 to 36 years, were studied to evaluate normal heart motion. These data served as a normal reference to myocardial motion patterns determined in five patients, aged 51 to 73 years, with known coronary artery disease induced wall motion abnormalities. Tangential motion in normal subjects showed a clockwise rotation at the cardiac base and counterclockwise rotation at the apex. The maximal radial velocity was 30.45±5.9 mm/s−1. Dyskinetic myocardial motion could be differentiated from normal ventricular motion: The number of hypomotile segments as well as hypokinetic and paradox phases determined with this method correlated well with patients' ejection fractions (r 2=0.95). This preliminary study demonstrates the ability of velocity-encoded MR to characterize myocardial motion and differentiate normal from dyskinetic heart motility.
Type of Medium: 1
3.
PAPER
Interactive drawing of the left ventricular borders from cine magnetic resonance images (1994)
Springer
ISSN: 1352-8661
Keywords cardiac borders ; digital image processing ; heart functions ; left ventricular contours ; magnetic resonance imaging ; reproducibility
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract The calculation of the left ventricular (LV) function requires the endocardial and epicardial contours of the cavity to be accurately defined beforehand. This identification is generally achieved by manual tracing of the LV borders. Such manual methods are tedious and time-consuming, limiting their clinical usefulness for cardiac quantitative analysis. The purpose of this study was to evaluate an efficient method for drawing the LV borders from magnetic resonance (MR) images. This technique, based on the use of cubic B-spline curves to modelize the shape of the cavity, allows an interactive and real-time remodeling of the contours. The variability and the accuracy of this contour tracing tool have been evaluated on standard cine-MR images obtained in 10 healthy volunteers in a short-axis view. Theendocardial and epicardial areas and themean local error between the contours were compared through interobserver and intraobserver analyses. A good correlation was observed between the enclosed areas in both studies (r>0.98 for endocardium,r=0.99 for epicardium). The mean local error between the contours was less than 2.8% for the endocardial borders and less than 1.4% for the epicardial borders. This method has a high degree of flexibility for the interactive trace and deformation of contours. Although further validation is needed, this method may prove useful in clinical application to permit the measurement of LV function from MR imaging.
Type of Medium: 1
4.
PAPER
Electrostimulation by time-varying magnetic fields (1994)
Springer
ISSN: 1352-8661
Keywords electrostimulation ; magnetostimulation ; neurostimulation ; cardiac stimulation ; electrical safety ; magnetic field ; electric field
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract Despite several investigations and publications on possible effects due to time-varying magnetic fields, the question remains as to the magnitude of the field, or its derivative with respect to time, that is capable of stimulating the human heart. It is quite surprising how little information on cardiac stimulation has entered the discussion to date. If the law of induction and the fundamental law of stimulation, both in their field forms, are combined, the result is quite different from what has been published: (1) It is the amplitude of the gradient field that is responsible for stimulation and notdB/dt. (2) The shape of the time-varying pulse has no influence on stimulation but only its mean value. (3) Owing to different rheobase and chronaxie values for cardiac tissue and peripheral nerves, the threshold for magnetostimulation of the myocardium is up to 200-fold higher than that for nerves. These results allow for the determination of safety limits that are certainly above those proposed to date. Based on these limits, technological advancement can be achieved without neglecting the patient safety requirement.
Type of Medium: 1
5.
PAPER
A time-efficient method for combinedt 1 andt 2 measurement in magnetic resonance imaging: Evaluation for multiparameter tissue characterization (1994)
Springer
ISSN: 1352-8661
Keywords mr imaging ; relaxation times ; proton density ; double delay multiecho ; high resolution parameter images ; tissue characterization
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract A new magnetic resonance imaging high-resolution sequence is presented that allows for the collection of all data for determination ofT 1 and ρ as well as for multiexponentialT 2 analysis within one measurement cycle. Noise preprocessing is performed in order to avoid systematic errors in relaxation parameter analysis and to increase the interexperimental reproducibility of the results. ForT 2 analysis, an optimized Marquardt algorithm is used, in combination with image processing methods for both automatic detection of voxels with partial volume effects, and for speedup of the iterative nonlinear regression steps. Determination of longitudinal relaxation time is based on a sophisticated signal intensity ratio technique that computesT 1 as the mean of up to eight individualT 1 values, each weighted with its relativeT 2 decay. Relative proton density is computed using results of the evaluations of both relaxation times. Validation of the method is accomplished by comparing phantom measurements with reference data acquired with spectroscopic sequences.In vivo examples of the computed parameter images taken from a study of experimental cerebral infarcts in rats are presented. The method allows one to acquire high-resolution parameter images within a measurement time that is tolerable even in clinical routine. Furthermore, the chosen evaluation concepts guarantee a short computation time. Therefore, an on-line computation of the parameter images and, in consequence, their direct use for diagnostic purposes appears feasible.
Type of Medium: 1
6.
PAPER
Pannus-induced destruction of joint cartilage and subchondral bone. Visualization and staging by MRI (1994)
Springer
ISSN: 1352-8661
Keywords rheumatoid arthritis ; synovitis ; arthritis ; magnetic resonance imaging ; cartilage ; knee
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract To investigate whether characterization and reliable staging of pannus-induced cartilage destructions in the knee could be achieved by magnetic resonance imaging (MRI), we examined 13 patients with arthritis, 2 patients with osteoarthritis (OA) and 5 healthy controls. A regional staging of bone and cartilage erosions was performed by two independent observers. In each of six regions, pannus-induced cartilage erosions were staged 0 (not present), 1 (present, but not penetrating), or 2 (penetrating). Pannus-induced cartilage erosions were demonstrated by MRI in 11 patients with arthritis and in no controls or OA patients. In the 11 patients, synovial masses overlying joint cartilage and a corresponding thinning of the cartilage, reflecting degradation, could be precisely delimited following gadolinium-DTPA I.V. Eight patients had bone erosions on MRI, either marginal caused by direct synovial invasion and/or in continuity with cartilage destructions caused by overlying pannus. By contrast, only two patients had radiographic erosions. The kappa values of interobserver variation with respect to regional presence or absence of bone and cartilage erosions were 0.94 and 0.92, respectively, indicating almost full concordance. This study suggests that MRI allows early description and reliable staging of pannus-induced cartilage and bone erosions. The destructions can be assessed by MRI at a time when plain radiographs are normal. The different pathways of joint destruction by pannus could be demonstrated. Description and staging of pannus-induced cartilage erosions by MRI could be clinically useful for early assessment of disease severity and for determination of progression in rheumatoid arthritis, particularly in early/radiologically nonerosive disease.
Type of Medium: 1
7.
PAPER
Experimental31p nmr study of the influence of ionic strength on the apparent dissociation constant of mgatp (1994)
Springer
ISSN: 1352-8661
Keywords 31p nmr spectroscopy ; intracellular free magnesium ; mgatp dissociation constant ; ionic strength
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract The classical method for31P NMR determination of intracellular free magnesium concentration ([Mg free 2+ ]) requires an accurate knowledge of the apparent dissociation constant (K D ) of MgATP. There is a large difference between the previously determined values ofK D . Although the value of 50 µM, determined by a31P NMR method, is now largely accepted, a value of 86 µM has more recently been measured with a fitting method derived from the original one, and with a different ionic strength. The purpose of our study was to assess if the cause of the difference between these two previously reportedK D values was due to the measuring method or to the ionic strength value used. Working at pH=7.2,T=37°C, and [KCl]=0.25 M, we performedK D measurements with the original31P NMR method and with the fitting method. The results (67±13 µM and 61±20 µM, respectively) were not significantly different. Then, with the first method, we measured KD at [KCl]=0.12 M and found a value of 19±5 µM. We conclude that the main cause of difference between theK D values measured by31P NMR reside in the disparity of ionic strength values used for their measurement. OurK D measurements at [KCl]=0.25 and 0.12 M demonstrate the importance of the ionic strength value used for imitating the intracellular medium on the absolute value of ([Mg free 2+ ]) measured by31P NMR spectroscopy.
Type of Medium: 1
8.
PAPER
Mri and mrs of human tendon xanthoma at 1.5 t: Anin vivo study (1994)
Springer
ISSN: 1352-8661
Keywords magnetic resonance imaging ; magnetic resonance spectroscopy ; tendon xanthoma ; familial hypercholesterolemia ; atherosclerosis
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract We studied a xanthomatous Achilles tendon and a normal Achilles tendon with the proton magnetic resonance imaging (MRI) and spectroscopy (MRS) at 1.5 T in a standard head coil. TheT 2 maps and the localized proton spectra of the Achilles tendon were reconstructed. The normal tendon revealed no MR signal, whereas the xanthomatous tendon image consisted of variable signal intensities, for which the value ofT 2 was significantly shorter (p=0.0002) than that of adipose tissue. The proton spectrum of this tendon xanthoma showed an increased water peak and unsaturated olefinic group intensity compared with the spectrum of the normal Achilles tendon area. The complex cholesterol molecule itself cannot be proven directly in a xanthomatous tendon, but its presence can be revealed with the help of the increased methyl and methylene groups of the fatty acids of the cholesteryl esters. This and other typical features describedin vitro for atheromatous tissue can be detectedin vivo in xanthomas.
Type of Medium: 1
9.
PAPER
A new MRI formulation for flow and motion applications (1994)
Springer
ISSN: 1352-8661
Keywords flow-imaging ; MR motion artifacts ; MR phase shifts
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract A rigorous reformulation of the magnetic resonance (MR) image formulation model (IFM) can use the integrally cumulative nature of MRI phase shifts for encoding and of time-of-flight travel corrections for magnitude. This approach characterizes each independent gradient element by its cumulant waveforms,K N (t), instead of by particular time expansion in gradient moments. The lowest-order cumulant gradient that gives a simple monopolar waveform governs all resulting phase-encoding properties. Each gradient element specifically encodes one and only one motion-order variable. Phase sensitizations to “higher order” do not exist; they are mathematical psuedophasings. Magnetization isochromats may have arbitrarily complicated velocity history,V(t), appearing in both time-of-flight and motion phase-shift formulas. The subject's intravoxel motion subdistributions each automatically reference the correct mean time of encoding action and its encoding duration. This formulation yields very simple and generalizable IFM expressions for MRI acquired data, with no theoretical confusion regarding higher-order phase shifts and nonphased time-of-flight effects.
Type of Medium: 1
10.
PAPER
The significance of MRI in myelin disorders (1994)
Springer
ISSN: 1352-8661
Keywords white matter disorders ; myelin disorders ; MRI of myelin disorders ; pattern recognition
Source: Springer Online Journal Archives 1860-2000
Notes: Abstract Systematic analysis of white matter changes on magnetic resonance (MR) images has increased the diagnostic quality of MR interpretation. For that purpose, structural elements were defined, relevant to the distinction of disease groups. Per disease group histograms were obtained of the frequency of involvement of these structural elements. On the reverse, this database could be used as the basis of an expert system. Loaded with the data of a new case, the program comes up with a differential diagnosis and probability percentage with confidence intervals per diagnostic item. The program has helped in identifying MR patterns in rare disorders.
Type of Medium: 1