Accuracy of computer-aided design models of the jaws produced using ultra-low MDCT doses and ASIR and MBIR

Asma’A A Al-Ekrish,Wadea Ameen,Sara A Alfadda,Wolfgang Puelacher,Romed Hörmann,Gerlig Widmann

doi:10.1007/s11548-018-1809-4

Abstract

PurposeTo compare the surface of computer-aided design (CAD) models of the maxilla produced using ultra-low MDCT doses combined with filtered backprojection (FBP), adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) reconstruction techniques with that produced from a standard dose/FBP protocol.MethodsA cadaveric completely edentulous maxilla was imaged using a standard dose protocol (CTDIvol: 29.4 mGy) and FBP, in addition to 5 low dose test protocols (LD1-5) (CTDIvol: 4.19, 2.64, 0.99, 0.53, and 0.29 mGy) reconstructed with FBP, ASIR 50, ASIR 100, and MBIR. A CAD model from each test protocol was superimposed onto the reference model using the ‘Best Fit Alignment’ function. Differences between the test and reference models were analyzed as maximum and mean deviations, and root-mean-square of the deviations, and color-coded models were obtained which demonstrated the location, magnitude and direction of the deviations.ResultsBased upon the magnitude, size, and distribution of areas of deviations, CAD models from the following protocols were comparable to the reference model: FBP/LD1; ASIR 50/LD1 and LD2; ASIR 100/LD1, LD2, and LD3; MBIR/LD1. The following protocols demonstrated deviations mostly between 1–2 mm or under 1 mm but over large areas, and so their effect on surgical guide accuracy is questionable: FBP/LD2; MBIR/LD2, LD3, LD4, and LD5. The following protocols demonstrated large deviations over large areas and therefore were not comparable to the reference model: FBP/LD3, LD4, and LD5; ASIR 50/LD3, LD4, and LD5; ASIR 100/LD4, and LD5.ConclusionsWhen MDCT is used for CAD models of the jaws, dose reductions of 86% may be possible with FBP, 91% with ASIR 50, and 97% with ASIR 100. Analysis of the stability and accuracy of CAD/CAM surgical guides as directly related to the jaws is needed to confirm the results.

Highlights

Multidetector computed tomography (MDCT) is considered one of the most accurate modalities in production of computer-aided design (CAD) models of the jaws
The maximum and mean deviations and the root-mean-square of the difference (RMSD) between the test models and the reference model increased with each dose reduction with all the reconstruction techniques, but the increase in deviations was markedly less with Model-Based Iterative Reconstruction (MBIR) (Table 2), and were less with increasing Adaptive Statistical Iterative Reconstruction (ASIR) percentage
The present study investigated the comparability of the surface of CAD models of an edentulous maxilla produced using ultra-low doses combined with filtered backprojection technique (FBP), ASIR and MBIR with the surface of a model produced from a standard dose/FBP protocol

Summary

Introduction

Multidetector computed tomography (MDCT) is considered one of the most accurate modalities in production of computer-aided design (CAD) models of the jaws. Using MDCT images produced with an 88% reduction in dose (compared to a standard clinical protocol), Loubel et al [4] obtained accurate CAD models of the jaws. The iterative reconstruction techniques (IRTs) of Adaptive Statistical Iterative Reconstruction (ASIR) and Model-Based Iterative Reconstruction (MBIR) have allowed the use of ultra-low MDCT doses with reduced noise levels, as compared with the traditionally used filtered backprojection technique (FBP) [6,7]. Such noise reduction may potentially improve the thresholding of the MDCT datasets

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