Z Tarjàn | PubMed Health

PubMed1996

Three-dimensional reconstructions of carotid bifurcation from CT images: evaluation of different rendering methods.

Three-dimensional computed tomographic angiography (3D-CTA) and digital subtraction angiography of the cervical carotid artery were performed bilaterally in 15 patients with suspected stenoses. A new semi-automatic segmentation and new rendering methods were used. The degree of stenosis of internal carotid arteries, as determined both by axial slices and 3D images (surface, integral, maximum-intensity-projection, and raysum-rendered images), was compared qualitatively and quantitatively to angiographic findings. In correlation to angiography, the accuracy in determining the stenosis classification of internal carotid arteries was of 97% for axial slices and 59-90% for 3D images, respectively. Raysum (pseudoradiograph) rendering was found to be the most reliable rendering method and gave the most similar results to angiography. The accuracy of all rendering methods was improved by applying calcification removing algorithm, with a statistically significant difference between surface rendering without plaque removal and raysum rendering using the removing algorithm.

Adult↗

PubMed1995

[Optimization of scanning and processing parameters for the three-dimensional reconstruction in computerized tomography of the facial bones].

The evolution of computer technology has significantly improved the performances of three-dimensional reconstructions from Computed Tomographic images. The authors discuss the examination technique and the modalities of three-dimensional reconstruction based upon a new advanced workstation. This unit is based on a Sun Sparkstation linked with the main computer of the CT scanner. The workstation is extremely fast, the processing time for a high resolution three-dimensional image of the maxillofacial region being about 3 minutes. The scanning parameters, image reconstruction and visualization were investigated on cases of maxillofacial (mainly posttraumatic) conditions. The most important scanning parameters are slice thickness, table incrementation, dose, scan plane. Slice thickness and table incrementation are the parameters bearing the greatest influence on the quality of the three-dimensional images. Dose is also important but bears no influence on image quality: therefore it can be kept as low as possible to reduce patient exposure. The scanning plane has some minor effect; coronal images have some advantages over axial images but in many cases only axial images can be acquired. The reconstruction parameters are the threshold and the matrix. The threshold may range 70 to 300 HU but in most cases ranges 120 to 200 HU. An advantage offered by this system is that it allows threshold values to be changed after the reconstruction has been completed, without performing a new reconstruction. The visualization parameters include four rendering methods, i.e. the surface mode, the integral mode, the maximum intensity projection and the ray sum. The surface mode is the one yielding the best results for bones while the others are used for the reconstruction of soft tissues and vessels. The workstation enables the three-dimensional images to be processed with shading parameters, and to be modified with cut planes, disarticulation methods and other interactive methods.

Bone Diseases↗