Biomedical subjects

P N Maniatis

Publications and source records attributed to P N Maniatis.

2 recordsLinked to original sources

PubMed2004

Threshold selection in virtual bronchoscopy: phantom study and clinical implications.

PURPOSE: To investigate the effect of the threshold selection on the apparent diameter of a virtual bronchus and the virtual wall morphology and to examine the parameters that can affect the selection of the appropriate threshold for virtual bronchoscopy with single slice computed tomography. MATERIAL AND METHODS: A bronchial phantom containing plastic tubes simulating the airways of the tracheobronchial tree was constructed. The diameters of the virtual images of these tubes were measured using various thresholds for two different materials surrounding the tubes: air and water. These measurements were correlated with the density in HU of the walls. Furthermore, data from 20 virtual bronchoscopies in patients were retrospectively analyzed in the same way. RESULTS: The diameter of a virtual bronchus is strongly affected by the selected threshold. The appropriate threshold for accurate diameter representation depends on the density of the bronchial wall. CONCLUSION: Our results suggest that in clinical practice a single threshold value cannot be used for imaging all segments of the tracheobronchial tree. While a value of -520 is appropriate for the trachea and lobar segments, values down to -720 could be needed on the level of segmental and subsegmental bronchi. At these levels, a threshold value about 65 HU more negative than the value where the artificial holes appear on the virtual bronchial walls could be used.

Bronchoscopes↗

PubMed2003

Radiation doses to patients from endoscopic retrograde cholangiopancreatography examinations and image quality considerations.

The purpose of this investigation was to measure the dose-area product (DAP) and the other relevant dosimetric quantities in diagnostic and therapeutic endoscopic retrograde cholangiopancreatography (ERCP). Furthermore, the dependence of patient dose and image quality on the tube potential was investigated. A DAP meter was used for dose monitoring in seven diagnostic and 21 therapeutic ERCPs. For each ERCP the DAP meter readings, fluoroscopy time, number of radiographs and exposure data were recorded. From these data the fluoroscopy and radiography contributions to DAP, the entrance skin dose and the effective dose for each examination were estimated. For the investigation of the effect of tube potential on patient dose and image quality, a water phantom containing syringes filled with diluted contrast media was used. The average DAP was 13.7 Gy cm2 in diagnostic and 41.8 Gy cm2 in therapeutic ERCP whereas the average fluoroscopy times were 3.1 and 6.0 min respectively. DAP was strongly correlated to the fluoroscopy time. Measurements in the phantom showed that a good compromise between image quality and patient dose is obtained for tube potentials around 80 kV. Therapeutic ERCPs deliver on average higher doses to patients than diagnostic ERCPs. However, for a difficult diagnostic ERCP more patient exposure may be required than for a simple therapeutic ERCP.

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