Biomedical subjects
D Matthaei
Publications and source records attributed to D Matthaei.
Biophysica and medical aspects of fast NMR-imaging.
Nuclear magnetic resonance (NMR) imaging is a promising new technique for non-invasive medical diagnosis. Following a decade of technical improvements and preliminary medical experiences, the measuring time of several minutes remained the major drawback of the method. The recent development of a fast NMR-imaging technique, the so-called FLASH (Fast Low Angle SHot) method, opens a new field of medical applications. This article deals with a few applications and aspects of FLASH imaging. Using the technique cross-sectional images can be taken within a few seconds without loss in spatial resolution. Therefore dynamic investigations of the function of internal organs and images of blood vessels become possible. Furthermore three-dimensional volume imaging of the whole object provides the full anatomical information. FLASH imaging is also applicable in combination with localized NMR-spectroscopy. Thus, biochemical information from NMR-spectroscopy and structural and functional information from NMR-tomography can easily be combined.
[FLASH-tomography. A rapid imaging procedure for magnetic resonance tomography].
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Nuclear magnetic resonance imaging of mummified corpses.
Clinical applications of nuclear magnetic resonance (NMR) imaging have demonstrated its great potential for noninvasive examinations of soft tissues. Here preliminary experiments are reported on mummified human tissue by means of NMR cross-sectional and transmission imaging. For this purpose the natural viscosity of the tissues has been lowered by rehydration with an aqueous solution of 20% acetone.
Rapid NMR imaging of dynamic processes using the FLASH technique.
FLASH (Fast Low-Angle SHot) imaging is a new method for rapid NMR imaging which has been demonstrated to provide abdominal images without artifacts due to respiratory or peristaltic motions. The sequence typically employs 15 degrees radiofrequency excitation pulses and acquires a free induction decay signal in the form of a gradient echo. Here FLASH images are recorded in the presence of dynamic processes with time constants even smaller than the measuring time of about 2 s for an image with a 128 X 128-pixel resolution. Experiments are carried out on flow phantoms and on rabbits yielding heart images without gating of the cardiac motion.
Multipurpose NMR imaging using stimulated echoes.
STEAM (stimulated-echo acquisition mode) imaging techniques recently introduced by the authors are demonstrated to provide a versatile tool for improving the parametric specificity in NMR imaging. Stimulated echoes can be excited by a sequence of at least three rf pulses with flip angles of 90 degrees or less. The main characteristics of the STEAM method are based on the great functional flexibility of an imaging sequence comprising three rf pulses unequal to 180 degrees and three intervals prior to acquisition of the data. Major advantages are the easy access to contiguous multiplanar images, to CHESS (chemical-shift-selective) images, and to T1 information. Moreover, the rf power deposition is considerably reduced as compared to spin-echo NMR imaging sequences. Here first in vivo results on human extremities are presented including contiguous multislice images, multiple CHESS images, and spin-lattice relaxation time images calculated from a series of simultaneously recorded T1-weighted STEAM images.
Dynamic digital subtraction imaging using fast low-angle shot MR movie sequence.
High-quality magnetic resonance (MR) images can be recorded within seconds with the use of fast low-angle shot (FLASH) MR imaging. This technique also gives new access to the time evolution of both periodic functions, such as cardiac motion, and nonperiodic physiologic processes, such as flow within internal organs. The time course and regional distribution of dynamic processes detectable by FLASH MR movies are often demonstrated best within series of difference images obtained by digital subtraction of the original data, especially after the use of MR contrast agents. In addition, quantitative information is provided by the analysis of time-intensity profiles for selected regions of interest. Dynamic digital subtraction MR imaging was evaluated in rabbit brain and kidney using a 2.3-T, 40-cm-bore magnet. The time resolution was 1.5 seconds for brain studies and 28 seconds for kidney studies. The total examination times were 1.5 and 30 minutes, respectively.
MR imaging using stimulated echoes (STEAM).
The introduction of STEAM (stimulated echo acquisition mode) magnetic resonance (MR) sequences provides access to a variety of MR parameters. T1-weighted and calculated T1 proton MR images of the head of healthy volunteers and a patient with an astrocytoma are presented. MR examinations were performed with a 2.0-T whole-body system. The STEAM T1 method can be used to characterize multiexponential relaxation behavior, to evaluate T1 relaxation times, and to improve the T1 contrast within MR images. Both the measuring time and the spatial resolution are the same as for a conventional image.
Multiple chemical shift selective (CHESS) MR imaging using stimulated echoes.
Recently, stimulated echo acquisition mode (STEAM) magnetic resonance (MR) imaging has been demonstrated as a new tool for multiparametric MR imaging studies. Applications of the chemical shift selective (CHESS) STEAM technique using a 2.0-T whole-body MR imaging system are reported in which a series of contiguous cross-sectional images of the head and the pelvis were acquired. Because selective excitation of the desired component is employed rather than elimination of the unwanted component, this method yields an improved degree of spectral resolution which is dependent only on the homogeneity of the static magnetic field. For routine medical applications, no sophisticated adjustment of the CHESS pulse is needed, as reported in previous methods.
Gas chromatography of amino acids in urine and haemofiltrate.
Capillary gas chromatography of amino acid derivatives obtained from biological material shows a large number of previously unknown constituents. The profiles of amino acids obtained from urine of healthy individuals and haemofiltrate of uraemic patients indicate that haemofiltration removes some amino acids to a considerably higher extent from uraemic patients than the kidney does from healthy persons. For instance, if haemofiltration is required three times a week, an approximately ten-fold amount of the essential amino acid methionine and a forty-fold amount of the essential amino acid leucine is lost compared to their excretion in urine by a healthy individual over the same period.
[Methods and importance of the separation of lipids and water in NMR tomography].
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Regional physiological functions depicted by sequences of rapid magnetic resonance images.
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Chemical-shift-selective magnetic-resonance imaging of avascular necrosis of the femoral head.
Chemical-shift-selective (CHESS) nuclear-magnetic-resonance (NMR) imaging is a new method for separating "water" and "fat" (CH2) resonances in proton NMR imaging. Its major advantage over conventional composite NMR imaging is the contrast enhancement, which in particular allows the detection of small water-containing structures, such as vessels or joint surfaces, normally obscured by fat signals. First clinical findings in the femoral head with avascular necrosis are reported.
1H NMR chemical shift selective (CHESS) imaging.
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Chemical shift selective MR imaging using a whole-body magnet.
We have applied a new method for separating water and fat resonances in proton magnetic resonance (MR) imaging to human studies using a whole-body MR imaging system at 2.0 T. Chemical shift selective (CHESS) MR imaging provides either a water or fat image in a single experimental run within the same time needed for a conventional composite image. Although the technique requires a spectral resolution of about 1 ppm over the entire imaging region, first images of the human head and hip indicated that CHESS MR imaging is extremely promising for use in clinical investigations. Moreover, CHESS MR imaging can be combined arbitrarily with other imaging modalities and is easy to implement in any high-field MR imaging system.
[Nuclear magnetic resonance spectroscopy in medicine].
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Influence of insulin on blood levels of branched chain keto and amino acids in man.
Branched chain keto acids, their corresponding amino acids, glucose, glucagon, growth hormone, C-peptide and gastric inhibitory polypeptide were determined in 8 healthy subjects after an intravenous bolus injection of 0.1 U/kg insulin. Branched chain keto acids declined within 60 min, the corresponding amino acids within 20 min or later. Amino acids tended to return towards normal earlier than their keto acids. Blood glucose levels were normal 2 hr after insulin injection while keto and amino acids remained diminished for more than 3 hr. In 8 healthy controls, given physiological saline instead of insulin, the branched chain keto acids did not decline throughout the test. It is suggested that insulin diminishes blood levels of branched chain keto acids, that the intraorgan flux of branched chain keto acids is different from the flux of branched chain amino acids and that branched chain keto acids may serve to correct for hypoglycemia.
The identification of urinary bile alcohols by gas chromatography-mass spectrometry in patients with liver disease and in healthy individuals.
The neutral steroid fractions in the urine of eleven patients suffering from various forms of liver disease with cholestasis and of ten healthy individuals were studied by glass capillary gas chromatography-mass spectrometry. The steroid conjugates in urine were enzymatically solvolysed, the liberated steroids extracted and transformed into the trimethylsilylether for measurements. The excretion rates of androstane and pregnane metabolites of patients with liver disease were far lower than those of healthy persons. The main compounds in the urine of the former were the bile alcohols 27 - nor - 3 alpha, 7 alpha, 12 alpha, 24 xi, 25 xi - pentahydroxy - 5 beta - cholestane and 3 alpha, 7 alpha, 12 alpha, 25 xi, 26 - pentahydroxy - 5 beta - cholestane. Our data suggest a correlation between the excretion rates of these bile alcohols and the serum levels of bilirubin. While the excretion rate of the two bile alcohols in the urine of healthy individuals was approximately 0.24 mg/24 h (0.6 mumol/24 h) a patient with a serum bilirubin of 841 mumol/l excreted 4 mg/24 h (9 mumol/24 h). The accumulation of bile alcohols described in this study possibly indicates alternative pathways of cholic acid formation in liver disease.