가상현실 기관지 내시경(virtual bronchoscopy) : 기관지내 병변의 크기 측정에 영향을 주는 요소들에 관한 실험적 연구

Abstract

본 연구에서는 가상현실 기관지 내시경 (virtual bronchoscopy, VB)상 병변의 크기에 영향을 미칠 수 있는 요소를 알아보고, 실제값을 가장 잘 반영할 수 있는 지표를 찾고자 하였다. 적출하여 고정한 돼지 폐의 기관과 기관지내에 구슬을 무작위로 넣고, helical CT를 이용하여 각각 절편두께 와 pitch가 3mm/1, 3mm/1.5, 5mm/1로 영상을 얻고, 이를 각각 1mm, 1.5mm, 2mm 간격으로 재구성 하여, 각각의 VB를 재구성 하였다. 기관내 10mm 구슬 한 개와 기관지내 8mm 구슬 두개를 선택하여, VB상 역치(threshold)를 -800에서 -200로 바꾸면서 구슬의 최대 직경을 측정하였다. 절편두께, pitch, 재구성값, 역치, 구슬이 위치한 기관 혹은 기관지 내경의 변화에 따른 크기의 변화를 알아 보았다. 측정된 기관지내 구슬 크기를 실제값의 %로 표시 하였을때, 측정된 값은 1) 절편두께와 pitch가 3mm/1일때 78.9% (100-61%), 3mm/1.5일때 77.5% (98-45%), 5mm/1일때 73.7% (100-46%); 2) 재구성을 1mm일때 77.9% (100-45%), 1.5mm일때 76.9% (96-49%), 2mm일때 75.1% (98-46%); 3) 역치가 각각 -800/-700/-600/-500/-400/-300/-200일때 86.2% (100-71%)/ 83.4% (100-70%)/ 80.4% (94-69%)/ 77.0% (94-66%)/ 74.8% (89-65%)/ 70.2% (83-58%)/ 64.5% (82-45%);4) 구슬이 위치한 기관 혹은 기관지 내경이 23mm일때 85.6% (98-67%), 17mm일때 75.0% (100-59%), 11mm일때 69.3% (85-45%)였다. VB상 측정된 기관지내 구슬의 크기는 실제값보다 작았으며, 역치값이 낮을수록, 절편두께와 pitch를 작게 할수록, 병변이 위치한 기관지 내경이 클수록 실제값에 유사하였고, 이중 역치값과 기관지 내경에 의한 영향이 가장 컸다. ; The purpose of this study is to evaluate scanning parameters affecting apparent sizes of endoluminal lesions of tracheobronchial tree on virtual bronchoscopy (VB) and to find optimal CT parameters for demonstrating real sizes of endobronchial lesions. Spherical beads of 8mm - 10mm in diameter were randomly placed into the airways of the fixed and inflated pig lung. CT scans were obtained with three kinds of CT parameters by helical CT, collimation and pitch of 3mm/1, 3mm/1.5, and 5mm/1. The volume data were reconstructed with 1mm-, 1.5mm-, and 2mm-collimation for each parameters. Therefore, a total of nine kinds of scan and reconstruction data were acquired. VBs were reconstructed with shaded-surface technique and soft tissue algorithm. A 10mm-sized bead in the trachea and two 8mm-sized beads in the left main bronchus were selected and their longest diameters were measured on VB at varying thresholds from -800 to -200. Effects of collimation, pitch, reconstruction interval, threshold, and luminal diameter of lesion location on the measurement of the diameter of beads were evaluated. When the measured diameters of beads on VB were recorded as % of real sizes, they were 1) 78.9% (100-61%), 77.5% (96-45%), and 73.7% (100-46%) at collimations and pitches of 3mm/1, 3mm/1.5, and 5mm/1,respectively; 2) 77.9% (100-45%), 76.9% (96-49%), and 75.1% (98-46%) at 1mm, 1.5mm and 2mm reconstructions,respectively; 3) 86.2% (100-71%)/ 83.4% (100-70%)/ 80.4% (94-69%)/ 77.0% (94-66%)/ 74.8% (89-65%)/ 70.2% (83-58%)/ 64.5% (82-45%) at isosurface thresholds of -800/-700/-600/-500/-400/-300/-200,respectively; 4) 85.6% (98-67%), 75.0% (100-59%), 69.3% (85-45%) at 23mm, 17mm and 11mm luminal diameters of lesion location,respectively. Overall, the diameters of beads simulating endobronchial lesions are underestimated on VB, compared to those of real size. As the isosurface threshold values, collimations, and pitches decrease in size, the measured diameters approach to real diameter of the beads. Beads of the peripheral airways appear smaller than beads of the proximal airways.