Validity of Maxillary Sinus Volume Measurements Using Dolphin3D

Objectives: Previous studies showed that mucosal tissues and fluids in maxillary sinuses influenced computerized sinus volume measures. The purpose of this 3-dimensional cone-beam computed tomograph (3D CBCT) study was to evaluate methods of measuring maxillary sinus volume using Dolphin3D software.
Methods: A dry left human maxilla was overlaid with wax to increase radiographic density and to close the ostium. Wax also was placed into the sinus to simulate mucosal tissue. The maxilla was weighed on ten separate days followed by a second round at least a week later. Measured water (72^o F) was added to fill the sinus, and the maxilla reweighed. Volume of the maxillary sinus in a CBCT image was analyzed using Dolphin3D software (-1000 Hounsfield units) and compared with manual volume measurements. On two separate rounds, the image was segmented manually based on landmark identification into 2mm thick slices. The bone and airspace areas of each slice were measured and multiplied by 2mm to calculate sinus volume for bone and air. The number of slices for bone and airspace measures was determined. Manual measures were compared for significant differences (p<.05) using Student’s t- test.
Results: Dolphin3D measures for sinus volume (Avg. = 10340+152. 0 and 10446.8+69.2 mm³), water weight (Avg. = 10566.4+82.1 and 10458.9+67.7 gm) and volume (Avg. = 10.6+.1 and 10.6+.1 ml), and manually outlined measures of airspace (Avg. = 94382.4 and 94778 mm³) were similar. Bone sinus volume (156312 and 156884.2 mm³) and airspace volume of the slices measured manually using Dolphin3D were significantly different (p<0.0001). Fewer slices contained the airspace compared with the bony sinus border, but the number of slices was the same for airspace and for bony border.
Conclusions: Conclusion: Dolphin3D software measures sinus airspace only and might not be valid for total sinus volume depending on Hounsfield units.