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Biomedical subjects

H W Fischer

Publications and source records attributed to H W Fischer.

At least 19 recordsLinked to original sources
PubMed1990

Nuclear relaxation of human brain gray and white matter: analysis of field dependence and implications for MRI.

The dependence of 1/T1 on the magnetic field strength (the relaxation dispersion) has been measured at 37 degrees C on autopsy samples of human brain gray and white matter at field strengths corresponding to proton Larmor frequencies between 10 kHz and 50 MHz (0.0002-1.2 T). Additional measurements of 1/T1 and 1/T2 have been performed at 200 MHz (4.7 T) and 20 MHz (0.47 T), respectively. Absolute signal amplitudes are found to be proportional to the sample water content, not to the "proton density," and it is concluded that the myelin lipids do not contribute to the signal. Transverse magnetization decay data can be fitted with a triple exponential function, giving characteristic results for each tissue type, and are insensitive to variations of the pulse spacing interval. The longitudinal relaxation dispersion curves show characteristic shapes for each tissue type. The most striking difference is a large dispersion for white matter at very high fields. As a consequence, the relative difference in 1/T1 between gray and white matter shows a marked maximum around 10 MHz. Possible implications for MRI are discussed. A weighted least-squares fit of the dispersions has been performed using a four-parameter function of the form 1/T1 = 1/T1,w + D + A/(1 + (f/fc)beta'). The quality of the fit is superior to that of other functions proposed previously. The results of these fits are used to predict image contrast between gray and white matter at different field strengths.

Brain↗
PubMed1979

[Intravenous cholangiography in hyperbilirubinaemia (author's transl)].

The effect of bilirubin on biliary and renal excretion of methylglucamine-iodipamide at an infusion rate of 1.3, 2.6 and 5.2 mu mol/min/kg was studied by intravenous injection into five dogs with normal liver functions and chronic duodenal fistulas. Unconjugated bilirubin administered in a dose of 0.1 mu mol/min/kg reduced biliary iodipamide excretion and concentration significantly, but did not affect renal contrast material excretion. This indicates that the unsatisficatory radiological results of intravenous cholangiography in hepatic and obstructive jaundice depend not only on the reduced excretion capacity of the liver, but are also due to a direct inhibitory effect of bilirubin on biliary contrast material excretion. In the presence of hyperbilirubinaemia, the highest iodine concentrations in the bile were obtained with the highest iodipamide serum levels; a reduction in contrast material dose or prolongation of the period of contrast material infusion therefore does not appear to be indicated in jaundiced patients.

Animals↗
PubMed1978

Ventricular fibrillation from diatrizoate with and without chelating agents.

The toxicity of Renografin 76% was compared with that of Hypaque 76% by selective injection of each into the right coronary artery of dogs. Renografin contains the chelating agents sodium citrate and disodium edetate, while Hypaque contains calcium disodium edetate and no sodium citrate. Ventricular fibrillation occurred significantly more often with Renografin, suggesting that chelating agents contribute to toxicity in coronary angiography.

Angiography↗
PubMed1976

Whole-gut irrigation as a means of cleaning the colon.

The authors describe a whole-gut irrigation method of cleaning the colon. Normal volunteers drank an irrigant solution at varying rates, and all but one achieved a radiologically clean colon within several hours. This method is proposed for use in the occasional study where a clean colon must be obtained in a relatively short period of time.

Adult↗
PubMed1976

Pharmaco-cholangiography with anticholinergic drugs in the dog.

The effect of atropine and pipenzolate bromide (PB) in different dosage levels was investigated in intravenous cholangiography with 0.6 ml/kg iodipamide infused over 30 minutes in six cholecystectomized dogs (20-36 kg) equipped with Thomas cannulas through which the common bile duct could be cannulated. Doses of 1 mg atropine and 20 mg PB, half the dose given intravenously just prior to the contrast agent and the other half with the iodipamide infusion, had the greatest effect in decreasing the bile flow (atropine-24% at 60, PB-23% at 30 minutes) and increasing the bile iodine concentration (atropine + 16%, PB + 14%). The biliary iodipamide excretion rate was not affected.

Animals↗
PubMed1976

The effect of sodium taurocholate on biliary iodipamide excretion in the dog.

The effect of sodium taurocholate in stepwise increasing infusion rates, 0.3 to 9.6 mumoles per min per kg, on the biliary excretion rate of iodipamide was investigated in 6 dogs (10 experiments) with complete bile diversion under general anesthesia. Iodipamide was administered intravenously with an initial priming dose of 33 mumoles per kg followed by a constant infusion of 1.3 mumoles per min per kg. Although the bile flow continuously increased with an increasing taurocholate dose, the iodipamide excretion rate reached a plateau with a 0.6 mumoles per min per kg of taurcholate infusion, which was 20% higher than with the lowest taurocholate dose. With a taurocholate dose over 2.4 mumoles per min per kg, a significant decrease in the iodipamide rate was found, amounting to 22% of its maximum value with the largest taurocholate dose. The bile iodipamide concentration was already at its maximum with the lowest taurocholate dose, and it decreased with an increasing taurocholate dose. Since the bile iodipamide concentration is probably the most important determinant in clinical cholangiography, low bile salt plasma levels should result in the best radiographic visualization of the biliary tree.

Animals↗
PubMed1975

[Slow infusion cholangiography in jaundice. An experimental study in the dog].

56 intravenous cholangiograms were performed in eleven dogs with either advanced hepatic damage or complete common bile duct obstruction. If radiographic visualization of the biliary system did not occur within 8 hours after a 30 minute infusion with 0.6 ml/kg iodipamide 52%, the result could not be improved by just extending the infusion time to 2 and 6 hours. However, a slight improvement was obtained, when the iodipamide dose was increased up to 1.8 ml/kg. Nevertheless we do not recommend a massive increase of the dose in the icteric patient, because it is likely that the risk of toxic side effects increases with an increasing iodipamide dose.

Animals↗
PubMed1975

[Renal blood flow after selective injection of different dosages of diatrizoate into the renal artery. An experimental study in the dog (author's transl)].

The characteristic biphasic renal haemodynamic response to diatrizoate injected into the renal artery was shown in the dog with the 133-Xenon washout technique. A brief increase in renal blood flow (RBF) during the first ten seconds is followed by a more prolonged period of diminuished RBF. A dose of 4 ml. diatrizoate 60% resulted in the maximum RBF increase of 43% after ten seconds, but even 1 ml. diatrizoate raised the RBF 24%. The initial vasodilator effect of diatrizoate compares well in its extent with the most potent renal vasodilators.

Animals↗
PubMed1975

[Selective renal angiography with fractionated contrast medium injection. An experimental study in the dog (author's transl)].

Fractionated contrast medium was compared with the conventional technique in 96 selective renal angiograms in the dog. The only possible clinical significance might be that improved visualisation of the renal vein was obtained with this technique without increasing the total administered dose. The overall best result in this regard was obtained with 2 and 6 ml. diatrizoate 60% injected with an interval of five seconds. Compared with other vasodilators, contrast material reflux into the aorta was not reduced and the vasodilator effect on the main renal, segmental and interlobar arteries was not constant and less marked.

Angiography↗
PubMed1975

Intravenous cholangiography in normal and subsequently liver-damaged dogs.

When a 30-minute infusion is chosen for intravenous cholangiography, the optimal dose in subjects with normal and decreased hepatic function seems to be 0.6 ml/kg iodipamide. Delayed visualization of the ducts and gallbladder occurs in hepatic dysfunction, therefore, radiographs should be taken up to eight hours after the start of the examination if the cholangiogram is not diagnostic sooner. Prolonged infusion time, increased dosage, or both did not improve the radiographic results significantly when this method was not diagnostic. Contary to what is seen in obstructive jaundice, a markedly reduced gallbladder size, compared to its own baseline, was found in hepatic dysfunction.

Animals↗
PubMed1975

Contraction of the canine gallbladder in different degrees of common bile duct obstruction.

C-terminal octapeptide of cholecystokinin was administered at six dose levels, 4-128 ng/kg, by 184 intravenous injections to three mongrel dogs under several pressure conditions of the biliary system. Gallbladder contraction was monitored radiographically. A good, dose-dependent contraction response resulted with intraductal pressures of 0 and 10 cm water. At 20 cm water, a markedly reduced and dose-independent response occurred. No contraction response was found with an intraductal pressure of 30 cm water. This animal experimental work suggests that in man, a contraction response of 30% or more may rule out significant common bile duct obstruction.

Animals↗
PubMed1975

Retrograde hepatography and indirect lymphography of the liver: an experimental study in the dog.

Retrograde infusion of large amounts of water-soluble contrast agents into the biliary system results in only a brief hepatogram. A dense hepatogram lasting for several weeks and visualization of hepatic and celiac lymph nodes equal to that in direct lymphography can be obtained after retrograde biliary infusion of Ethiodol. In serching for metastasis from tumor in the liver, gall-bladder, bile ducts, pancreas, stomach, and duodenum, radiographic visualization of these nodes may help. If proved safe, the procedure can be performed by endocopic cannulation of the common bile duct.

Animals↗