Effect of filtered back projection and iterative reconstructions on cone beam computed tomography (CBCT) image quality and processing time

Objectives

To assess the effect of standard filtered back projection (FBP) and iterative reconstruction (IR) methods on cone beam computed tomography (CBCT) image noise and processing time (PT), acquired with various acquisition parameters with and without metal artifact reduction (MAR).

Methods

CBCT scans using the Midmark EIOS unit of a human mandible embedded in soft tissue−equivalent material with and without the presence of an implant at mandibular first molar region were acquired at various acquisition settings (milliamperages [4 mA-14 mA], field of view [5 × 5, 6 × 8, 9 × 10 cm], and resolutions [low, standard, high]) and reconstructed using FBP and IR, and with and without MAR. The processing time was recorded for each reconstruction. ImageJ was used to analyze specific axial images. Radial transaxial fiducial lines were created relative to the implant site. Standard deviations of the gray density values (image noise) were calculated at fixed distances on the fiducial lines on the buccal and lingual aspects at specific axial levels, and mean values for FBP and IR were compared using paired t tests. Significance was defined as P < .05.

Results

The overall mean for image noise (± SD) for FBP was 198.65 ± 55.58 and 99.84 ± 16.28 for IR. IR significantly decreased image noise compared to FBP at all acquisition parameters (P < .001). Percentage noise reduction ranged between 41.9% (protocols at 5 mA) and 70.3% (FBP / 9 × 10 cm / low resolution / no MAR). IR increased processing time by an average of 35.1 seconds.

Conclusions

IR significantly reduces CBCT image noise compared to standard FBP without substantially increasing processing time.