Low-Dose Noncontrast Examination of the Paranasal ...

ORIGINAL ARTICLE

Low-Dose Noncontrast Examination of the Paranasal Sinuses Using Volumetric Computed Tomography Berhan Pirimoglu, MD,* Recep Sade, MD,* Muhammed Sedat Sakat, MD,† Hayri Ogul, MD,* Akin Levent, MD,* and Mecit Kantarci, MD, PhD*

Objectives: The objective of this study was to evaluate image quality of low dose in noncontrast paranasal sinus computed tomography (CT) using single volumetric 320-row multidetector CT technique. Methods: The low-dose protocol including tube voltage of 135 kV and tube current of 5 mAs was chosen based on results of the present phantom study. Forty-six patients were assigned to control group with factory standard settings (120 kVp, 75 mAs), and 46 patients were assigned to study group and underwent noncontrast CT of paranasal sinus with low-dose protocol using single volumetric 320-row multidetector CT device. Objective and subjective image qualities were performed. Results: Effective radiation dose calculated for control group scans was 0.45 (SD, 0.39) mSv. It was 0.038 (SD, 0.004)mSv for study group scans. The effective radiation dose of study group was statistically significant lower than control group (P < 0.001). Conclusions: Noncontrast paranasal sinus CT imaging can be performed at very low radiation exposure maintaining high image quality with 135 kVp and 5 mAs. Key Words: low dose, paranasal sinus, 320-row detector CT (J Comput Assist Tomogr 2017;00: 00–00)

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omputed tomography (CT) is the primary imaging technique used to assess inflammatory diseases. It is the criterion standard radiologic examination of the paranasal sinuses. Multidetector volumetric row CT is a useful diagnostic tool and has the high spatial resolution. It usually performs to diagnose acute and chronic sinusitis to differentiate mucosal disease patterns. It is also beneficial before functional endoscopic sinus surgery to evaluate individual anatomic variants and extension of disease.1–3 Radiation exposure during paranasal sinus CT examination has usually around a major concern, because the radiation-sensitive optic lens is included in the scanning field.4 According to the ALARA (as low as reasonably achievable) principle, different approaches to lower radiation exposure have been proposed including reducing the tube voltage and, to acquire isotropic volumes of an entire organ with a single rotation of the gantry, it is possible with a volumetric 320-row detector CT systems. Low kVp and mAs imaging is also strategy to effectively reducing radiation dose that recently become popular.5–7 Scanning with 320-detector row CT provides 16-cm z axis coverage in a single 0.35-second rotation.

From the *Department of Radiology, Medical Faculty, Ataturk University; and †Department of Otorhinolaryngology, Medical Faculty, Ataturk University, Erzurum, Turkey. Received for publication July 31, 2017; accepted October 16, 2017. Correspondence to: Berhan Pirimoglu, MD, Department of Radiology, Faculty of Medicine Ataturk University, 25040 Erzurum, Turkey (e‐mail: [email protected]). Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.jcat.org). The authors declare no conflict of interest. Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/RCT.0000000000000699

J Comput Assist Tomogr • Volume 00, Number 00, Month 2017

Concordantly, it has minimized dose requirements and reduced the need for sedation.6 Recently, CT imaging procedures have seen emerging technologies such as larger detectors, faster rotation tubes, new multidetectors, and image reconstruction algorithms as well as combinations of those.8–10 The most recent developments like the 320-row detector facilitate volume CT and helps to avoid the overbeaming effect of helical scanning. This significantly contributes to dose minimization for CT imaging examinations while speeding up the investigation and thus decreasing the duration time. The 320-row multidetector volume CT offers several advantages to reduce CT dose while maintaining image quality. There are many advantages of the single volume CT acquisition including no helical overlap, decreased radiation dose, and no helical scan. As a result, radiation dose can decrease by as much as 80%.11,12 Therefore, the purpose of our study was also to assess the impact of single volumetric 320-row multidetector CT on image quality and radiation dose in phantom and patient studies. In recent years, various articles about dose reduction strategies have been published.2,4,5,7,13 However, to the best of our knowledge, our study is the first original research evaluation of the paranasal sinus CT imaging protocols using volumetric 320-row detector CT system. In this study, we aim to compare between different tube voltages (120 kVp and 135 kVp) and currents (75 mAs and 5 mAs) and we also aim to evaluate image quality of low-dose CT of the paranasal sinus using a volumetric 320-row multidetector CT technique.

MATERIALS AND METHODS Phantom Study Examinations were performed on a phantom head. For this study, a 320-row multidetector CT device (Aquillion ONE Vision; Toshiba Medical Systems Corporation, Otawara, Japan) was used to examine the phantom head. All CT scans were performed with a wide volume acquisition technique with parameters recommended by the manufacturer (slice thickness, 0.5 mm; rotation time, 0.5 second; and scan range, 160 mm [320 slices 0.5 mm, see Supplemental Digital Content 1, http://links.lww.com/RCT/ A65]). Nineteen examinations were conducted with different settings of the tube voltage and current (Table 1). Dose measurements were derived from the study protocol as volume CT dose index and dose-length product (DLP). Table 1 summarizes the examination parameters for the phantom imaging studies. Image qualities of all the phantom images were assessed using a 5-point scale (1, not diagnostic, to 5, excellent image quality) with consensus between observers 1 and 2. The lowest dose that our 320-row multidetector CT device can perform was chosen based on the results of the present phantom study (see Supplemental Digital Content 2, http://links.lww.com/RCT/A66). The study group included a tube voltage 135 kV and tube current 5 mAs (Table 1). www.jcat.org

Copyright © 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. This paper can be cited using the date of access and the unique DOI number which can be found in the footnotes.

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TABLE 1. Examination Parameters, the Corresponding Radiation Doses, and Image Quality Scores Obtained via Consensus Between Observers 1 and 2 in Phantom Study

Tube Voltage, kVp

Tube Current, mA–mAs

120 135 120 100 135 100 80 120 80 135 100 120 80 100 135† 120 80 100 80

150–75 100–50 100–50 150–75 50–25 100–50 150–75 50–25 100–50 25–12.5 50–25 25–12.5 50–25 25–12.5 10–5 10–5 25–12.5 10–5 10–5

CTDIvol, mGy*

DLP,* mGy cm

Image Quality Scores Obtained via Consensus Between Observers 1 and 2

13.7 12 9.1 8.8 6 5.8 4.7 4.6 3.1 3 2.9 2.3 1.6 1.5 1.2 0.9 0.8 0.6 0.3

191.2 168.5 127.5 122.6 84.3 81.8 65.7 63.7 43.8 42.1 40.9 31.9 21.9 20.4 16.9 12.7 10.9 8.2 4.4

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 4 3 2 1

*The corresponding radiation doses are listed from the highest to the lowest. †Bold italic line refers to the low-dose protocol including tube voltage 135 kV, and tube current 5 mAs was chosen based on the results of present phantom study. CTDIvol, volume CT dose index.

Patients Between September and December 2016, a total of 97 consecutive patients scheduled for paranasal sinus CT for suspected inflammatory mucosal disease were included into our study. Consecutive patients scheduled for paranasal sinus CTwith contrast media administration (suspicious for abscess of neoplasm) were excluded (n = 5). A total of 92 patients met the inclusion criteria. Patients were randomly selected in a 1:1 ratio, and the first 46 (50%) of 92 patients were assigned to the control group (120 kVp and 75 mAs). The next remaining 46 (50%) of 98 patients were also assigned to study group (135 kVp and 5 mAs). All patients signed informed consent; the study protocol was approved by the local institutional review board.

CT Acquisition Protocols All paranasal CTexaminations were performed on a 320-row detector CT (Aquillion ONE Vision; Toshiba Medical Systems Corporation, Otawara, Japan) in single volume mode with an acquisition in single volume covering the paranasal region. The paranasal CT protocols for control and study groups were performed concurrently. In the control group, the CT acquisition protocol was performed with the following parameters: 0.5-second gantry rotation time, collimation of 192 0.6 mm using a z-flying focal spot, and 75 mAs tube current at 120 kVp tube voltage. In the study group, the CT acquisition protocol also performed with the following parameters: 0.5-second gantry rotation time, collimation of 192 0.6 mm using a z-flying focal spot, and 5 mAs tube current

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at 135 kVp tube voltage. Patient position was supine with a slight reclination of the head to obtain a parallel alignment of the upper jaw to the gantry, to minimize artefacts from dental hardware in both groups. One-millimeter axial, 1-mm coronal, and 1-mm sagittal images were reconstructed from the raw data set, using both bone and soft tissue kernels.

Evaluation of the Objective Image Quality To compare the objective parameters between the control and study group images, noise was measured by three 10 mm2 region of interest placed on the axial soft tissue reconstructions in both eye bulbs, retrobulbar fat, and maxillary sinuses to obtain different values for aqueous tissue, soft tissue, and air, respectively. Noise was defined as the mean (SD) of attenuations measured in Hounsfield units.

Evaluation of the Subjective Image Quality All the imaging parameters were evaluated independently by 2 radiologists with 5 (R.S.) and 3 (B.P.) years of experience in neuroradiology imaging, respectively, who were blinded to all clinical data on a 3D workstation (SyngoVia VB10B, Siemens Health care, Forchheim, Germany). The conspicuity of important anatomic landmarks was assigned a score using a 5-point scale (1, not diagnostic; 2, limited diagnostic image quality with image noise and artefacts; 3, sufficient image quality; 4, good image quality; 5, excellent image quality). The following anatomic landmarks were assessed for each side: bone structures (including ethoidal bony septae, lamina papryrace, uncinate process, conchas, maxillary © 2017 Wolters Kluwer Health, Inc. All rights reserved.

Copyright © 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. This paper can be cited using the date of access and the unique DOI number which can be found in the footnotes.


Low-Dose CT of Paranasal Sinuses

agreements for all observers. An interobserver reliability analysis using the κ statistic was performed to determine consistency among observers. The degree of agreement based on κ values was as follows: less than 0, none; 0 to 0.20, slight; 0.21 to 0.40, fair; 0.41 to 0.60, moderate; 0.61 to 0.80, substantial; and 0.81 to 1.00, almost perfect. P values