Comparison of Micro-Computed Tomography and Clinical Computed Tomography Protocols for Visualization of Nasal Cartilage Before Surgical Planning for Rhinoplasty

Abstract

Importance: There is no imaging standard to model nasal cartilage for the planning of rhinoplasty procedures. Preoperative visualization of cartilage may improve objective evaluation of nasal deformities, surgical planning, and surgical reconstruction.

Objectives: To evaluate the feasibility of visualizing nasal cartilage using high resolution micro-computed tomography (CT) compared with the criterion standard of pathologic findings in a cadaveric specimen and to evaluate its accuracy compared with various clinical CT protocols.

Design, setting, and participants: Anatomic study at the University of Washington using single human cadaveric nasal specimens performed from July 10, 2017, to March 30, 2018.

Interventions: A micro-CT acquisition with 60-micron resolution was obtained of a nasal specimen. The specimen was then scanned with 5 different clinical CT protocols to span both clinical care and machine limits. The specimen was then sectioned in 5-mm axial slices for pathologic analysis.

Main outcomes and measures: Micro-CT images were registered to pathologic specimen cross-sections using a graphite fiducial system. Cartilage substructures were manually segmented and analyzed. A library of matched images across the micro-CT and various clinical CT protocols was then developed. Region of interest analysis was performed for each of the cartilage structures and their boundaries on clinical CT protocols and micro-CT, with the outcome of mean (SD) density using Hounsfield units.

Results: A single human cadaveric nasal specimen was used to obtain the following results. Lower lateral cartilage, upper lateral cartilage, and septal cartilage were accurately delineated on the micro-CT images compared with pathologic findings. The mean absolute deviation from pathologic findings was 0.30 mm for septal cartilage thickness, 0.98 mm for maximal upper lateral cartilage length, and 1.40 mm for maximal lower lateral cartilage length. On clinical CT protocols, only septal cartilage was well discriminated from boundary. Higher radiation dose resulted in more accurate density measurements of cartilage, but it did not ultimately improve ability to discriminate cartilage.

Conclusions and relevance: The results of this anatomic study may represent a notable step toward advancing knowledge of the capabilities and pitfalls of nasal cartilage visualization on CT. Nasal cartilage visualization was feasible on the micro-CT compared with pathologic findings. Future research may further examine the barriers to accurately visualizing upper lateral cartilage and lower lateral cartilage, a prerequisite for clinical application.

Level of evidence: NA.

Figure 1.. Nasal Cartilage Visualization on Micro-CT Compared With Pathologic Findings

The masks show an axial cross-section of a pathologic specimen (A) and registration of micro–computed tomography (CT) to the pathologic specimen (B). The total surface area of cartilage was calculated from nasal cartilage segmentation on micro-CT (C) and on axial pathology (D). d indicates distance.

Figure 2.. Library Data Set of Micro-CT and Clinical Images

The micro–computed tomography (CT) and clinical protocols are seen on axial section in columns A through F (images arranged from highest to lowest radiation dose). The first 2 rows show nasal cartilage visualization on the micro-CT. The third and fourth rows show the corresponding nasal cartilage visualization after manual segmentation.

Figure 3.. Region of Interest Analysis for Cartilage vs Boundary Across Micro-CT and Clinical CT Protocols

The mean (SD) of cartilage substructures and boundary was calculated in 3D Slicer for septal cartilage (A), upper lateral cartilage (B), and lower lateral cartilage (C) across the micro-computed tomography (CT) and clinical CT protocols (arranged from highest to lowest radiation dose). Less overlap in density variance between the cartilage and boundary indicates better discrimination of cartilage from boundary.