1

Introduction

Cone beam CT (CBCT) was first introduced for clinical use in 1982 at the Mayo Clinic Biodynamic Research Laboratory with the idea of utilizing it in angiography.

It is recently getting recognized as a step ahead in CT imaging as it provides a better quality cross sectional technique for visualizing bony structures of the head and neck using a lower dose of radiation, when compared with conventional CT scans. This is particularly relevant in sinus surgeries where the main interest is preserving bony demarcation. CBCT allows visualizing bony structures of the head and neck while using relatively low isotropic spatial resolution of osseous structures with a reduced radiation dose compared with conventional CT scans. This made it an attractive alternative to conventional CT scan imaging.

Since its discovery, many CBCT systems have emerged. This led to intense interest and growth in the utilization of CBCT in neuro-interventional procedures , radiation therapy guidance , and in surgical planning and intraoperative guidance . The first CBCT scanner became commercially available for dento-maxillo-facial imaging in 2001.

As CBCT systems have become more used in surgical procedures, there has been an increasing interest in applying CBCT in otolaryngology, specifically in the field of rhinology, particularly using CBCT to image in cases with sinusitis needing surgical intervention, as this condition is one of the most common ENT chronic diseases in the United States and the fifth most common reason for antibiotics to be prescribed , with its chronic form affecting approximately 12.5% of people .

2

Materials and methods

‘Ethical considerations’: we have chosen patients who had both types of CT scans for medical purpose and not for the benefit of the study as this was a retrospective collection of data, hence at time of requesting the scans there was no intention of comparing the image quality for the benefit of the study.

In the current study we explored the application of CBCT in diagnostic imaging of the paranasal sinuses, comparing both the effective dose and imaging characteristics to conventional MDCT sinus examinations.

The data were collected retrospectively using the Computerized Radiology Information System (CRIS). All CBCT scans of paranasal sinuses performed at Queen Elizabeth Hospital Birmingham over a period of one year (2013) were reviewed. The mean effective dose of CBCT scans was then compared to fifty consecutive standard MDCT scans of paranasal sinuses performed in year 2012, and fifty consecutive low doses MDCT scans of paranasal sinuses performed in year 2014. The low dose scans were carried out using the sinogram-affirmed iterative reconstruction algorithm (SAFIRE; Siemens, Erlangen, German), which is used as a standard for sinus imaging in our hospital since the end of year 2013. MDCT sinus scans performed with IV contrast, and MDCT sinus scans which also included the brain, temporal bone or neck, were excluded from the study.

The CBCT scans of paranasal sinuses were performed with the Care stream 9300 scanner, Care stream Health. The dose for the CBCT was calculated using the PCXMC dose evaluation software, the dose for MDCT – the ImPACT CT patient dosimetry calculator.

The image quality comparison of CBCT versus conventional scans was determined subjectively by evaluating visualization of surgically relevant bony structures of the ostiomeatal complex (OMC), ethmoid roof and frontal sinus drainage pathway by 2 senior ENT surgeons and 2 senior radiologists.

2

Materials and methods

‘Ethical considerations’: we have chosen patients who had both types of CT scans for medical purpose and not for the benefit of the study as this was a retrospective collection of data, hence at time of requesting the scans there was no intention of comparing the image quality for the benefit of the study.

In the current study we explored the application of CBCT in diagnostic imaging of the paranasal sinuses, comparing both the effective dose and imaging characteristics to conventional MDCT sinus examinations.

The data were collected retrospectively using the Computerized Radiology Information System (CRIS). All CBCT scans of paranasal sinuses performed at Queen Elizabeth Hospital Birmingham over a period of one year (2013) were reviewed. The mean effective dose of CBCT scans was then compared to fifty consecutive standard MDCT scans of paranasal sinuses performed in year 2012, and fifty consecutive low doses MDCT scans of paranasal sinuses performed in year 2014. The low dose scans were carried out using the sinogram-affirmed iterative reconstruction algorithm (SAFIRE; Siemens, Erlangen, German), which is used as a standard for sinus imaging in our hospital since the end of year 2013. MDCT sinus scans performed with IV contrast, and MDCT sinus scans which also included the brain, temporal bone or neck, were excluded from the study.

The CBCT scans of paranasal sinuses were performed with the Care stream 9300 scanner, Care stream Health. The dose for the CBCT was calculated using the PCXMC dose evaluation software, the dose for MDCT – the ImPACT CT patient dosimetry calculator.

The image quality comparison of CBCT versus conventional scans was determined subjectively by evaluating visualization of surgically relevant bony structures of the ostiomeatal complex (OMC), ethmoid roof and frontal sinus drainage pathway by 2 senior ENT surgeons and 2 senior radiologists.