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P van Dijk

Publications and source records attributed to P van Dijk.

68 records · Page 4Linked to original sources
PubMed1987

R 8110, a new short-acting hypnotic in dogs.

The clinical, respiratory and cardiovascular effects of intravenous injections of R 8110, a fluor analogue of etomidate, were studied in unpremedicated dogs. Clinical observations were carried out after intravenous injections of 3 and 4 mg kg-1 of R 8110. Cardiovascular studies were conducted after an intravenous injection of 3 mg kg-1. The drug proved to be a safe and reliable agent for induction and produced a short-lasting hypnosis and some analgesia. Both induction and recovery were smooth and rapid. Heart rate and systolic and diastolic blood pressure decreased significantly (P less than or equal to 0.05) 10 minutes after injection; the influence on arterial blood parameters was minimal.

Anesthesia, General↗
PubMed1984

Derivation of quantitative information in NMR imaging: a phantom study.

The use of NMR imaging as a quantitative research tool requires insight into the relationship between various imaging techniques and their resultant images. Work was undertaken to elucidate this relationship by using the following procedure. First, a theoretical model of NMR imaging under various pulse sequences was elaborated. Subsequently, a series of inversion recovery and saturation recovery images of a particular object slice was generated by varying the sequence parameters. Finally, pure rho, T1 and T2 images of that slice were obtained by solving the corresponding model equations. This procedure was applied to a test phantom containing tubes with suitable reference substances, including aqueous solutions of agar, manganese chloride and deuterium, and water-fat mixtures. The concentration of various samples was chosen such as to yield rho, T1 and T2 values usually encountered in clinical NMR imaging. Experiments were carried out with a prototype resistive NMR imager with a static magnetic field of 0.14 T, corresponding to a hydrogen proton resonance frequency of 5.9 MHz. For most samples a weighted non-linear regression analysis showed the theoretical model to produce an adequate parametrisation of the data at the 5% significance level, given the number of data points and the experimental accuracy. The quantitative information extracted from the NMR imaging experiments, i.e. rho, T1 and T2, appeared to be in good agreement with the results of conventional methods, including NMR spectroscopy. The clinical efficacy of the proposed methods is currently being investigated.

Humans↗
PubMed1984

Direct cardiac NMR imaging of heart wall and blood flow velocity.

Nuclear magnetic resonance (NMR) imaging is used to produce in the same scan both anatomical and functional information of the heart and great vessels. A method is described to generate velocity images by the use of phase shifts for moving spins induced by imaging gradients under electrocardiogram (ECG) synchronized imaging conditions. The influence of the different gradients is discussed together with methods to obtain velocity information for each gradient direction separately. The results, obtained with a 0.14 T resistive NMR scanner and normal volunteers, show the spatial velocity distribution in the aorta and heart walls in color scale images. The feasibility of velocity calculations is demonstrated and some applications are given. The present results indicate the possibility of quantitative flow and motion analysis with ECG synchronized NMR imaging.

Aorta↗
PubMed1984

ECG-triggered NMR imaging of the heart.

The relatively long scan time needed for an NMR image gives rise to motion artifacts when imaging the heart. These can be strongly reduced by synchronizing the imaging sequences to the ECG (cardiac gating). Using an adjustable delay between the ECG pulse and the trigger pulse for the repeated imaging sequence, detailed heart images can be made in any phase of the cardiac cycle. Images made at systole and diastole in different planes can be used for the accurate assessment of left ventricular volume and ejection fraction. NMR imaging can provide heart images in any slice orientation without the use of contrast medium or obstruction from bones.

Diastole↗
PubMed1983

Interpretation of nuclear magnetic resonance tomograms of the brain.

Nuclear magnetic resonance tomography is an imaging method based on the magnetic resonance behavior of protons, as they occur predominantly in tissue water or in fatty acids. This behavior, as characterized by the relaxation times T1 and T2, is determined by the chemical and physical environment of the protons. The relaxation properties of the tissue can be accentuated by selection of the appropriate pulse sequence. Interpretation of the images requires an understanding of the principles of the technique with which the relaxation times are expressed in the images, and acquaintance with the composition of the tissue in terms of relaxation properties (as in computerized tomography, tissue composition is expressed as attenuation coefficients).

Adult↗
PubMedDate not supplied

MR imaging of poststenotic flow phenomena: experimental studies.

Poststenotic flow patterns were analyzed in a flow phantom with a 1.5-T magnetic resonance (MR) imager, with use of different MR imaging and MR angiographic pulse sequences. Spin-echo, fast field-echo, two-dimensional inflow (multiple single-section technique), and flow-adjusted-gradient sequences were applied. For the spin-echo sequences, modulus and phase images were reconstructed from each data set. The length of the region of poststenotic changes in signal amplitude and phase measured at a constant flow rate increased with stenosis grade. Likewise, the length of the region of poststenotic changes measured at a constant stenosis grade increased with flow rate. Moreover, the results depended on the alignment of the flow direction with the readout gradient. Comparison of modulus and phase images allowed discrimination of turbulent and nonturbulent flow, which yields additional information on stenosis grade in clinical MR angiography.

Arterial Occlusive Diseases↗
PubMedDate not supplied

MR lesion detection in a breast cancer population.

Implementation of MR imaging of the breast as an extension of the existing imaging modalities in the diagnosis of breast cancer was evaluated in a university cancer center, MR imaging of the breast was performed in 54 patients, in whom the MR results were compared with the triple test (the combination of clinical examination, mammographic evaluation, and cytology) and the final histological diagnosis. MR imaging of the breast depicted 30 of the 33 malignancies (sensitivity, 91%). In two of the malignancies, the carcinoma was clinically and mammographically occult. For the three patients with a false-negative MRI diagnosis, the conventional mammography showed suspicions clustered microcalcifications as a sign of in situ carcinoma. For seven patients, MR imaging of the breast incorrectly suggested the presence of a malignant lesion (specificity, 67%). To improve MR specificity, we perform MR-guided ultrasonographic fine-needle aspiration biopsy (FNAB). Although MR imaging of the breast is a highly sensitive examination, conventional x-ray mammography remains the most efficient imaging modality in the diagnosis of breast cancer. In our patient population, MR imaging of the breast had additional value for women with mammographically dense breast tissue and especially for patients with clinical evidence of breast carcinoma that could not be detected with conventional diagnostic methods.

Adenocarcinoma↗