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H Kooijman

Publications and source records attributed to H Kooijman.

36 records · Page 2Linked to original sources
PubMed2000

Combined static-dynamic MR urography for the simultaneous evaluation of morphology and function in urinary tract obstruction. II. Findings in experimentally induced ureteric stenosis.

PURPOSE: To assess the diagnostic value of combined static-dynamic MR urography (MRU) for the functional-morphological evaluation of experimentally induced urinary tract obstruction in the piglet. MATERIALS AND METHODS: In 20 piglets unilateral ureteric stenosis was created operatively. Post-surgery repeated comparative examinations were obtained with MRU, diuretic renal scintigraphy (DRS), excretory urography (EU) and ultrasound (US). MRU was performed as a combination study with a static 3D-IR-TSE sequence and a dynamic 2D-FFE sequence after Gd-DTPA with frusemide administration. RESULTS: MRU allowed complete depiction of the prestenotic urinary tract and of the stenosis in all cases. In 43 comparative studies MRU was superior to EU in 36, EU to MRU in 2. When single kidney function was calculated with both MRU and DRS, results were highly correlated (r = 0.92). When urinary excretion was compared, significant agreement was achieved with concordant findings in 86% and slightly discordant results in 12%. CONCLUSIONS: Static-dynamic MR urography permits excellent depiction of experimentally induced urinary tract obstruction in piglets and reliable assessment of individual renal function and urinary excretion. Two advantages of the method stand out--it does not require radiation and it permits functional-morphological correlation.

Animals↗
PubMed1999

5'-N-substituted carboxamidoadenosines as agonists for adenosine receptors.

Novel as well as known 5'-N-substituted carboxamidoadenosines were prepared via new routes that provided shorter reaction times and good yields. Binding affinities were determined for rat A1 and A2A receptors and human A3 receptors. EC50 values were determined for cyclic AMP production in CHO cells expressing human A2B receptors. On all receptor subtypes relatively small substituents on the carboxamido moiety were optimal. Selectivity for the A3 receptor was found for several analogues (1a, 1d, 1h, and 1k). On A1 receptors a number of compounds, but not 5'-N-ethylcarboxamidoadenosine (NECA, 1b), showed small GTP shifts, which could be indicative of lower intrinsic activities at the A1 receptor. At the A2B receptor, derivatives 1i-k with modified ethyl substituents had reduced activities compared to the A2B reference agonist NECA (1b). Thiocarboxamido derivatives (8b and 8c) displayed considerable although decreased A2B receptor activity. The X-ray structure determination of compound 8b was carried out. Due to intramolecular hydrogen bonding between the carboxamido NH and the purine N3 in the crystal structure, the ribose moiety of this compound is in a syn conformation. However, theoretical calculations support that NECA (1b), and less so 8b, can readily adopt both the syn and the anti conformation, therefore not excluding the proposed anti mode of binding to the receptor.

Adenosine↗
PubMed1999

Diffusion-weighted imaging with navigated interleaved echo-planar imaging and a conventional gradient system.

PURPOSE: To demonstrate the technical feasibility and precision of a navigated diffusion-weighted (DW) MR imaging method with interleaved echo-planar imaging and test its diagnostic sensitivity for detection of ischemic stroke. MATERIALS AND METHODS: Apparent diffusion coefficient (ADC) measurements were performed in phantoms, and six healthy adult volunteers were examined to determine intrasubject (precision) and intersubject (reference range) variations in absolute ADC and relative ADC (rADC) measurements. DW imaging maps and lesion rADC values were also obtained in 34 consecutive stroke patients to evaluate the sensitivity and reliability of DW-interleaved echo-planar imaging for detection of ischemic brain damage. RESULTS: Phantom and volunteer ADC values were in excellent agreement with published data. The intrasubject variation of rADC was 6.2%. The ADC precision ranged from 6.5% in the subcortical white matter in the frontal lobe to 12.9% in the head of the caudate nucleus. Interleaved echo-planar imaging enabled rapid acquisition of high-quality images of the entire brain without substantial artifacts. Within the 1st week, the sensitivity of DW-interleaved echo-planar imaging for detection of acute infarction was 90% (18 of 20 true-positive studies) and independent of lesion location. CONCLUSION: DW-interleaved echo-planar imaging with phase navigation and cardiac triggering is robust, reliable, and fast. With high sensitivity for detection of early ischemic infarction, it is useful for examining stroke patients by using MR systems with conventional gradient hardware.

Adult↗
PubMed1994

Liver iron quantification: studies in aqueous iron solutions, iron overloaded rats, and patients with hereditary hemochromatosis.

For the noninvasive liver iron quantification by MRI in human iron overload diseases, fundamental proton relaxation mechanisms were studied in aqueous solutions with ferritin and other iron compounds, in experimentally iron overloaded rats, and in patients with iron overload diseases. MR-relaxation rates as a function of iron concentrations in the range of 0-7.5 mg Fe/g aqueous iron solutions, 0-5.4 mg Fe/g rat liver in vivo, and 0.16-4.9 mg Fe/g human liver in vivo were determined from multi- and sets of single-spin echo sequences (1.5 T imager). As predicted by theory, transverse relaxation rates (1/T2) in aqueous iron solutions, in liver tissue of rats, and in human liver tissue increased linearly with the iron concentration. A preliminary calibration for the liver iron quantification by MRI was performed from in vivo measurements of liver 1/T2-relaxation rates and liver iron quantification by atomic absorption spectroscopy in biopsies from 13 patients. With the single spin-echo method, precise in vivo liver iron quantification in humans also above 2.0 mg Fe/g liver tissue (T2 < 15 ms) should be accomplished on any imager with shortest spin-echo time available, at least TE < 20 ms.

Adult↗
PubMed1993

Stereochemistry of charged nitrogen-aromatic interactions and its involvement in ligand-receptor binding.

Recently, new evidence was found for the involvement of charged nitrogen-aromatic interactions in ligand-receptor binding. In this study we report two favourable orientations of a phenyl ring with respect to a R-N+(CH3)3 group, based on crystal structure statistics from the Cambridge Structural Database. In the first orientation, the phenyl ring is situated in between the substituents at about 4.5 A from the nitrogen atom, and the ring is approximately oriented on the sphere around the nitrogen atom. In the second orientation, the phenyl ring is situated in the same direction as one of the N-C bonds at about 6.0 A from the nitrogen atom, and the ring is tilted with respect to the sphere around the nitrogen atom. The same two orientations were also found in the crystal structures of three ligand-receptor complexes, which implies that these orientations probably play a major role in molecular recognition mechanisms.

Benzene Derivatives↗
PubMed1989

[Measurement of noise levels in MR tomography at 1.5 Tesla].

The noise levels at the isocentrum of an MR apparatus with a field strength of 1.5 Tesla was measured during various sequences. The rapid switching of the gradients exerts effects on the gradient coils, which result in the development of noise as from a loudspeaker. Measurements were carried out using gradients of 3 and 9.3 mT/m with head and body coils and a variety of sequences. The noise level depended largely on the type of sequence and, under extreme conditions, may attain 96 dB. Because of the short exposure times, we do not consider it necessary to use any form of protection. During the examination of patients with damaged hearing, some protection may be advisable.

Humans↗
PubMed1988

[High-resolution MRT with increased magnetic field gradients and a 512(2)-data matrix: initial clinical experiences].

By increasing the strength of the magnetic field gradients of a whole-body imager to 9.4mT/m, it was possible to obtain spin-echo images with short echo delays and high spatial resolution. The reduction of the pixel size was effected either by decreasing the field of view or by increasing the scan matrix (512(2) pixel). To prevent loss of signal-to-noise ratio, the scan parameters had to be carefully selected. With the 512(2) matrix, the resolution could be increased without decreasing the field of view, so that backfolding artifacts were avoided. In comparison with the 256(2) matrix, the 256 x 512 matrix provided improved resolution in the frequency encoded direction without an increase in acquisition time.

Humans↗
PubMed1988

[Cine-MRT for studying regional myocardial function].

Cine-MRT was performed in 8 healthy subjects and in 16 patients with myocardial infarction, in whom regional wall motion abnormalities had been demonstrated by left ventricular angiography. Short axis and long axis slices were obtained by angulation of the imaging planes according to the orientation of the cardiac axes. From the end-diastolic and end-systolic images, systolic wall thickening and radial wall motion were determined. In healthy subjects, regional variation in wall thickening was not significant. Patients with myocardial infarction demonstrated abnormal wall motion within the infarct region. Discrepancies between wall thickening and wall motion were observed in 8 patients.

Adult↗
PubMed1987

[Pulse triggering in magnetic resonance tomography in high-field strength].

Gated images of patients with stronger pulsation artefacts in the brain stem were produced on a 1.5 tesla MR-imager, registering blood pulsations by means of a finger plethysmograph. A minimization of movement artefacts was achieved and thus sufficient diagnostic-value of images in these patients was noticeable. This gating method seems to be a promising simple alternative compared to the well known cardiac gating for imaging of the head and neck area. Its advantages and limitations are demonstrated.

Brain Stem↗
PubMed1987

[Risks and artifacts in MRT (1.5 tesla) caused by metallic foreign bodies. Studies on phantoms and 60 patients].

Our experience of the effects of metallic foreign bodies on MRT high field examinations is described. In vitro measurements showed moderate magnetic torsion or displacement in a few cases. The findings in 60 patients with various metal foreign bodies and the resulting artifacts are discussed. Despite local loss of information, in the majority of cases there is additional evidence provided by MRT, which suffers less from foreign body artifacts than does CT. Stainless steel implants result in some signal loss and geometric distortion, but do not usually constitute a danger to the patient and do not affect the diagnostic information from surrounding structures.

Foreign Bodies↗
PubMed1987

[Methodologic variants on rapid MR imaging of the liver].

The development of rapid imaging methods makes it possible to obtain T1 and T2-weighted MR images in less than 15 seconds. Consequently images can be obtained without respiratory artefacts. An attempt has been made to obtain optimal factors for the fast-field-echo procedure in order to obtain satisfactory images of the liver with T1 and T2 sequences. By moving the examination couch, it is possible to obtain 10 mm transverse sections without gaps throughout the entire liver in a reasonable time. The additional use of contrast medium (Gd-DTPA) provides information about perfusion and leads to an increase in contrast between lesions and normal liver tissue with adequate image quality. The method is particularly valuable before surgery for liver metastases.

Contrast Media↗