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C N de Graaf

Publications and source records attributed to C N de Graaf.

8 recordsLinked to original sources
PubMed1988

Precision in calculated rho, T1 and T2 images as a function of data analysis method.

In NMR imaging rho, T1 and T2 images are usually calculated from a set of partial saturation, saturation recovery or inversion recovery experiments with multiple echoes and multiple repetition times. Several methods can be envisaged to extract parameter images from such a set of source images. These methods to a greater or lesser extent take advantage of the fact that a multiple echo/multiple repetition time experiment provides a set of largely independent T1 and T2 measurements. In this study several data analysis methods, including weighted and non-weighted averaging of results of independent T1 and T2 measurements, weighted and non-weighted averaging of source images prior to data reduction and simultaneous three-parameter fitting, were compared against another in terms of precision, computational efficiency and robustness. The predicted performance of the examined methods was verified by stochastic simulation experiments.

Humans↗
PubMed1986

Simulation procedure to determine nuclear magnetic resonance imaging pulse sequence parameters for optimal tissue contrast.

In order to permit a more optimized selection of acquisition parameters for nuclear magnetic resonance (NMR) imaging a simulation procedure is proposed to determine the pulse sequences for optimal tissue contrast for a variety of clinical indications. In selected patient studies an adequate set of source images is measured, which allows computation of images of all possible pulse sequences, and measurement of tissue contrast within selected regions of interest. Data concerning promising sequences for specific clinical indications can then be filed, so as to aid the investigator's experience in setting up future NMR acquisitions.

Breast Neoplasms↗
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↗
PubMed1978

Selective scintiangiography of the kidney with xenon-133.

Measurement of the spatial distribution of the clearance rate of xenon-133 from the kidney after its injection into the renal artery for estimating intrarenal blood flow can easily be combined with selective X-ray angiography as a routine method. Using a gamma camera as detection equipment anand applying a special computer analysis technique, 'functional images' can be obtained, by which the spatial distribution of the blood flow in the kidney is quantitatively mapped. Experiments with a rather heterogenous group of 12 patients suggest that in at least one type of renal pathology the xenon-133 flow study is more indicative for clinical evaluation than the X-ray angiography

Adult↗