| ObjectiveCT virtual bronchoscopy(VB) are greatly developed with the occurence of multislice CT (MSCT). These studys aim at optimizing the scan parameters and the reconstruction parameters of CTVB and investigating the impact of bronchial orientation on virtual bronchoscopy. Also, we apply these techniques into the cases of lung cancer and benign airway disease.Materials and MethodsAmong 120 normal volunteers, forty normal volunteers were equally divided into two groups: group 1 (slice thickness 6.5mm,collimation 5mm) and group 2 (slice thickness 3.2mm,collimation 2.5mm).which included pitch1.25, exposure dosage 195mAs,and resolution ST. Five reconstructive methods were employed with different reconstruction intervals and filters of the inherence setting. The groups3-6 were studied according to the setting itself about kV, filter and RI, namely 120kV, B, 50% overlapping.Pitch is normed as 1.25, comparing with the high figure. Exposure dosage is normed as 195mAs, comparing with the low figure. Resolution is normed as ST, comparing with the high figure. Slice thickness 6.5 and 3.2mm were chose from the offering choices of CT (6.5\3.2\1.3mm). Segment(S1\S4\S6\S8\S10)bronchi were observed and the luminal diameters of the distal bronchi were measured under VB. 66 cases of lung cancer and 29 benign airway disease were studied with the above techniques.Results1. Among scan parameter, the slice thickness was the number one influence factor on VB. In the group of 3.2mm slice thickness,the luminal diameter of S1 ranged 2.18～2.63mm,which was better than that of 6.5mm. mAs had influence on VB as well．The dosage of 195mAs was the best among the three choices (F=5.98,P<0.01). The pitch and scan resolution had little influence on VB(P>0.05). 2. Among reconstruction parameter, the reconstruction intervals had significant effects on VB．In group B,0.5mm interval was the best(F=3.53,P＜0.05), and the average luminal diameter of S1 was 1.68±0.21mm. There was no difference between 1.6mm and 1.0 mm intervals or 1.0mm and 0.5mm intervals, and the diameter was 2.10±0.36mm (1.6mm interval)．In group A, 3.2mm interval was the worst(F=3.20,P＜0.05), and there was no difference between 2.0mm and 1.0 mm intervals. The average luminal diameter of S1 was 2.65±0.69mm(2.0mm interval)．Combining with practice, 50% overlapping was the best. The filter had little influence on VB(F=1.85,P=0.177). 3. The bronchial orientation had influence on VB. The luminal diameter of S1/S10 (these bronchi were vertical to axial section) under VB was the smallest. That of S4/S6 (these bronchi were parallel to axial section) was the largest, and that of S8 was the median.4. CTVB can play a supplimentary role in evaluating the lung cancer, but can clearly reveal the anatomy of the central airway disease.ConclusionVariable slice thickness had a marked effect on MSCT VB, and the thin slices had a better outcome than the thick slices. The exposure dosage had influence on VB too, but the pitch and resolution had little influence on VB. A protocol for1. MSCT-VB including 3.2mm slice thickness and common mAs (195mAs) is recommended. 2. The optimal reconstruction parameters varied with the collimations. We suggest that no less than 50% overlapping reconstruction should be routinely applied and more than 50% when the thicker slices were apllied． Filter might have little influence on VB.3. The bronchial orientation had direct influence on VB, and the bronchi vertical to axial section were best evaluated．4. CTVB can play a supplimentary role in evaluating the lung cancer, but can clearly reveal the anatomy of the central airway disease. |
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