CT VISUALIZATION OF THE MAJOR PULMONARY FISSURES - VALUE OF 25-DEGREES CRANIALLY TILTED AXIAL SCANS

OBJECTIVE. CT visualization of the major (oblique) pulmonary fissures is often hampered by partial volume effects of adjacent lung parenchym a. We attempted to improve visualization of the fissures by using 25-d egrees cranially tilted axial scans. An initial in vitro study also wa s performed. MATERIALS AND METHODS. Both conventional and 25-degrees t ilted axial CT scans were obtained in 40 adult patients. After scans w ith 2-mm collimation were obtained at 1 cm and 6 cm below the carina, the gantry was tilted 25-degrees cranially to be perpendicular to the plane of the major fissures, and scans with 2-, 5-, and 10-mm collimat ion were obtained at the same two levels.The appearance of the fissure s was classified as linear opacity, bandlike opacity, or avascular are a for each lung at each level. RESULTS. On 2-mm conventional axial sca ns, the major fissures were seen as linear opacities in three to 23 pa tients (8-58%), as bandlike opacities in 13-31 (32-78%), and as avascu lar areas in one to seven (2-18%). (Ranges indicate lowest and highest values when data for tha two levels in the two lungs are grouped sepa rately.) On 2-mm tilted scans, the ranges were 32-38 patients (80-95%) , one to eight (2-20%), and zero to one (0-2%), respectively. The 2-mm tilted scans were significantly superior to the 2-mm conventional axi al scans for showing the fissures (p < .01). Direct visualization as l inear or bandlike opacities was possible even on 10-mm tilted scans in 15-32 cases (38-80%). CONCLUSION. Our results show that visualization of the major fissure is improved when tilted CT scans rather than con ventional axial scans are used.