CLINICAL STUDY
Reliability of High-Pitch Ultra-Low-Dose Paranasal Sinus Computed Tomography for Evaluating Paranasal Sinus Anatomy and Sinus Disease Elif Ayanoglu Aksoy, MD,* Sila Ulus Özden, MD,† Ercan Karaarslan, MD,† Ömer Faruk Ünal, MD,* and Hasan Tanyeri, MD* Objectives: The aim of this study was to evaluate the reliability of high-pitch ultra-low-dose computed tomography (CT) for detecting important paranasal sinus anatomic landmarks and pathologies. Materials and Methods: Sixty patients (22 females, 38 males) aged 15 to 67 years (mean age, 33.68 y; SD, 9.83 y) underwent high-pitch ultra-low-dose CT of the paranasal sinuses between February and June 2012. To determine the lowest possible dose for evaluation of the paranasal sinuses, the patients were divided into three groups randomly and prospectively. A different lowdose CT protocol was applied to each group. The image quality was assessed subjectively by a radiologist and an otorhinolaryngology head and neck surgeon independently using a 4-point grading scale (0 = structures could not be identified, 1 = indistinctly defined structures, 1.5 = relatively well-defined structures, 2 = very welldefined structures). Anatomic landmarks and mucosal structures were evaluated. Mean scores were evaluated to assess statistical significance. Results: According to the anatomic landmark scoring, excluding the ethmoid foramen for ethmoid artery identification, all of the structures in all 3 groups were very well-defined structures. The ethmoid foramen for ethmoid artery identification was scored as either could not be identified or an indistinctly defined structure in all groups. On evaluating the mucosa of the paranasal sinuses, normal and pathologic mucosal structures were scored as very well defined in all of the patients. The interobserver agreement was excellent. Conclusion: High-pitch ultra-low-dose CT is a safe, reliable paranasal sinus screening tool. Key Words: High-pitch ultra-low-dose CT, paranasal sinuses (J Craniofac Surg 2014;25: 1801–1804)
C
omputed tomography (CT) is the gold standard for investigating inflammatory sinus disease and has become a routine radiologic examination of the paranasal sinuses.1–4 Radiation exposure during this examination has always been a major concern. Dose-reduction strategies have been published in various recent
From the Departments of *Otorhinolaryngology and †Radiology, Faculty of Medicine, Acibadem University, Istanbul, Turkey. Received October 7, 2013. Accepted for publication March 13, 2014. Address correspondence and reprint requests to Elif Ayanoglu Aksoy, MD, Faculty of Medicine, Acibadem University, Maslak Hospital, Büyükdere cad. No: 40 Maslak, Istanbul, Turkey; E-mail: [email protected] The authors report no conflicts of interest. Copyright © 2014 by Mutaz B. Habal, MD ISSN: 1049-2275 DOI: 10.1097/SCS.0000000000000966
articles that investigated the impact of dose reduction on image quality.1–7 This study evaluated the image quality and reliability of ultra-low-dose CT for detecting important anatomic landmarks and mucosal pathologies of paranasal sinuses.
MATERIALS AND METHODS Sixty patients (22 females, 38 males) with clinically suspected sinusitis, aged 15 to 67 years (mean age, 33.68 y; SD, 9.83 y) underwent high-pitch ultra-low-dose CT of the paranasal sinuses (Somatom Definition Flash; Siemens Healthcare, Forchheim, Germany) between February and June 2012. This study was approved by the institutional review board of the institution in which the research was conducted. Adult patients who were referred for CT of the paranasal sinus were included in the study randomly and prospectively. To determine the possible lowest dose for evaluating the paranasal sinuses, the patients were divided into 3 groups, and different low-dose CT protocols were applied randomly to each group. The age and sex distributions of the groups were similar (Table 1). The CT examinations were performed with a second-generation dual-source CT (Somatom Definition Flash; Siemens Healthcare, Forchheim, Germany). The scans were obtained in axial sections ranging from the roof of the frontal sinus to the maxillary sinus with the upper jaw aligned to the gantry to reduce dental artifacts. The field of view was adapted to cover the paranasal sinuses, facial bones, and mastoid region. The scans were acquired in craniocaudal order. Collimation was 0.6 mm for all groups; pitches were 3.2, 1.55, and 0.8, respectively. The rotation times were 1 second for group 1 and 0.28 second for groups 2 and 3. The tube voltages and currents for the groups were 80 kV/18 mA, 80 kV/126 mA, and 120 kV/80 mA, respectively (Table 2). Multiplanar reconstructions were made from raw data: 3-mm slices with 3-mm image distances in the transverse (bone and soft tissue kernel), coronal (bone kernel), and sagittal (bone kernel) views.
Evaluation of Image Quality The image quality was assessed subjectively by a radiologist and an otorhinolaryngology head and neck surgeon independently using a 4-point grading scale (0 = structures could not be identified, 1 = indistinctly defined structures, 1.5 = relatively well-defined structures, 2 = very well-defined structures). Anatomic landmarks and mucosal structures were evaluated.
TABLE 1. Sex and Age Distribution of Groups Group 1
Group 2
Group 3
7 females, 13 males
7 females, 13 males 15–67 (34.05 ± 10.77) y
8 females, 12 males 18–61(35.66 ± 10.83) y
17–55 (31.7 ± 9.47) y
The Journal of Craniofacial Surgery • Volume 25, Number 5, September 2014
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
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TABLE 2. High-Pitch Ultra-Low-Dose CT Scan Parameters of the 3 Groups
Tube collimation, mm Rotation time, s Pitch Tube voltage, kV Quality tube current-time product, mAs DLP, mGy.cm Effective dose, mean (SD), mSv
Group 1
Group 2
Group 3
0.6 1 0.8 120 80 154 0.35 (0.026)
0.6 0.28 1.55 80 126 37 0.08 (0.01)
0.6 0.28 3.2 80 18 7 0.019 (0.0018)
kV, kilovolts; mAs, milliampere-seconds; mGy.cm, miligray.centimeters; mSv, milisievert.
The medial wall of the maxillary sinuses, posterior wall of the frontal sinuses, bony margins of the sphenoid sinuses, orbital floor and medial orbital wall, infundibulum, uncinate processes, uncinate attachment point, Keros classification, and anterior ethmoid artery identification were the anatomic landmarks scored. Normal and pathologic mucosal structures of the maxillary, ethmoid, frontal, and sphenoid sinuses were also scored. Nonspecific mucosal swelling, fluid collection with air-fluid levels, opacification of the entire sinus, retention cysts, and polyps were evaluated. Mean scores were evaluated to assess statistical significance.
Estimation of Radiation Doses To determine the radiation exposure, the dose-length product (DLP) was analyzed. The DLP is documented automatically by the CT and noted in the examination file. Following the European guidelines, an appropriate conversion factor of 0.0023 mSv/mGy. cm was used to estimate the effective dose.8
Statistical Analysis All statistical analyses were performed using Statistical Package for The Social Sciences software 17.0 (SPSS, Inc, Chicago, IL). Wilcoxon signed-rank test was used to compare the mean scores of the two observers in all groups.
RESULTS According to the anatomic landmark scoring, the medial wall of the maxillary sinuses, posterior wall of the frontal sinuses, bony
FIGURE 1. Coronal paranasal sinus CT section of a group 1 patient demonstrating medial wall of maxillary sinuses (M), uncinate process (U), and inferior turbinate (I).
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FIGURE 2. Coronal paranasal sinus CT section of a group 2 patient demonstrating medial wall of maxillary sinuses (M), uncinate process (U), and inferior turbinate (I).
margins of the sphenoid sinuses, orbital floor and medial orbital wall, infundibulum, uncinate processes, uncinate attachment point, and Keros classification of the patients in all 3 groups were very well-defined structures. The ethmoid foramen for ethmoid artery identification was scored as either could not be identified or an indistinctly defined structure in all groups (Figs. 1–3). While evaluating the mucosa of the paranasal sinuses, normal and pathologic mucosal structures were scored as very well-defined structures in all of the patients (Tables 3–4). According to the Wilcoxon signed-rank test, there was no significant difference between the mean scores of the two observers in all groups (P = 0.312, 0.232, and 0.383 for groups 1–3, respectively). The interobserver agreement was excellent.
DISCUSSION In recent decades, CT has become the gold standard imaging method for diagnosing and grading the severity of inflammatory
FIGURE 3. Coronal paranasal sinus CT section of a group 3 patient demonstrating medial wall of maxillary sinuses (M), uncinate process (U), and inferior turbinate (I).
© 2014 Mutaz B. Habal, MD
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
The Journal of Craniofacial Surgery • Volume 25, Number 5, September 2014
Reliability of Paranasal Sinus CT
TABLE 3. Anatomic Landmark Scoring: Mean (SD) Scores of Observers 1 and 2 Group 1 Observer 1 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 0.66 (0.92)
Medial wall of maxillary sinuses Posterior wall of frontal sinuses Bony margins of sphenoid sinuses Orbital floor and medial orbital wall Infundibulum Uncinate processes Uncinate attachment point Keros classification Anterior ethmoid artery identification
Group 2 Observer 2 2 (0) 2 (0) 2 (0) 2 (0) 1.97 (0.17) 1.97 (0.17) 1.97 (0.17) 1.91 (0.28) 0.88 (0.91)
paranasal sinus diseases with adequate spatial resolution. Besides inflammatory findings, relevant anatomic variants are shown in detail with the isotropic data set obtained from CT. However, the radiation exposure associated with CT is a concern, especially for radiation-sensitive tissues such as the eye lenses and thyroid gland in the head and neck area and the frequent need for repeated examinations.6,9–11 The current trend in paranasal sinus CT is lowering the radiation dose to the minimum possible without decreasing diagnostic reliability.1–7 However, CT requires high-radiation doses if the examinations are performed following the standardized protocols recommended by the various CT scanner manufacturers. An effective dose as high as 0.76 mSv has been reported.12 Even studies of low-dose protocols reported effective doses as high as 0.48 mSv.13 In this study, we evaluated subjects using a recently introduced second-generation dual-source CT. Compared with earlier scanners, it has more detectors and a faster gantry rotation speed. Dual-source modes permit high-pitch values up to 3.2, and a gapless data set with reliable image quality for various indications is obtained. In addition to the large detector coverage, the scan speed can be increased dramatically. In our study, the highest effective dose was 0.35 (SD, 0.026) mSv in group 1 and was reduced by 94.5% to 0.019 (SD, 0.0018) mSv in group 3. Despite significant lowering of the radiation doses, image quality was sufficient for identifying important anatomic and mucosal structures. Although the mean observer scores were nonsignificantly lower in group 3, even the lowest mSv protocol provided reliable diagnostic images. According to our results, significantly lowering the radiation dose does not decrease diagnostic reliability. During mucosal evaluation of the paranasal sinuses, normal and pathologic mucosal structures were identified with all 3 low-dose CT protocols used in the patients included in our study. Important anatomic structures were defined as very well-defined or relatively well-defined structures, except for the ethmoid foramen for ethmoid artery identification. Our
TABLE 4. Paranasal Sinus Mucosal Evaluation: Mean (SD) Scores of Observers 1 and 2 Group 1 Maxillary sinus Ethmoid sinus Frontal sinus Sphenoid sinus
Group 2
Group 3
Observer 1 Observer 2 Observer 1 Observer 2 Observer 1 Observer 2 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
Observer 1 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 1.9 (0.46) 1.9 (0.46) 1.92 (0.35) 0.62 (0.9)
Group 3 Observer 2 2 (0) 2 (0) 2 (0) 2 (0) 1.8 (0.58) 1.8 (0.58) 1.38 (0.7) 1.5 (0.66) 0.31 (0.63)
Observer 1 2 (0) 2 (0) 2 (0) 1.45 (0.52) 2 (0) 1.57 (0.83) 1.57 (0.83) 1.9 (0.44) 0.066 (0.25)
Observer 2 2 (0) 2 (0) 2 (0) 1.71 (0.47) 1.59 (0.51) 1.40 (0.65) 1.10 (0.55) 1.14 (0.65) 0.08 (0.27)
results indicate that the proposed ultra-low-dose dual-source protocol has sufficient diagnostic validity, while resulting in only minimal radiation exposure to the patient, and the proposed ultra-low-dose examination protocol can be used to screen for inflammation of the paranasal sinuses. The maximum dose reduction (group 3, 80 kV and 18 mAs; effective dose, 0.0019 mSv) was considered sufficient for defining anatomic structures and mucosal pathologies and has subsequently been used in clinical practice in our institution (when sinusitis was the clinical question at issue), replacing the standard CT protocol using the scan parameters recommended by the CT manufacturer. For the clarity of the anatomic structures, especially for the delineation of bones and vascular structures, which are important to surgeons for preoperative assessment, standard low-dose protocols should be preferred. We believe that plain radiographic images are inadequate for evaluating the complex anatomy of the paranasal sinus comprehensively and should be discouraged and avoided. Conebeam CT (CBCT), primarily introduced for dental examinations and orthodentic indications, is considered an alternative modality to have reasonable diagnostic value for the evaluation of rhinosinusitis.14,15 According to the literature, radiation exposure, especially of the thyroid gland by scattered radiation, is lower with CBCT compared with multislice CT devices.16,17 However, with recent improvements in the CT technology, the use of appropriate tube voltage and current settings enable the evaluation of paranasal sinuses with much lower radiation doses comparable with the values of CBCT and diagnostically conclusive image quality. Future studies with optimized CBCT parameters and comparison of image quality with low-dose CT would be beneficial. The paranasal sinuses can also be visualized and evaluated by magnetic resonance imaging (MRI). The presence of inflammation or retention cysts can be determined by MRI, whereas bony structures are visualized with superior spatial resolution in CT images. In addition, MRI is more expensive, and the examination time is longer compared with the very-short 0.3-second scan time with CT. Considering these facts, low-dose CT should be the gold standard imaging method in the work-up of sinusitis, and optimization of the radiation dose is an important issue. Furthermore, our findings of equally high interrater agreement in detecting pathology and characterizing different pathologies, as well as previous reports of high interrater agreement in defining a number of anatomic landmarks,9,12 suggest that the radiation doses used in standard sinus CT protocols, such as before functional endoscopic sinus surgery, are higher than needed. Performing paranasal sinus CT with the lowest acceptable dose must be the prime aim in each examination. One of the drawbacks of our study is that we did not quantify noise. With iterative reconstruction in image space, the image quality of the ultra-low-dose images can be increased. We did not routinely use iterative reconstruction in image space in our series.
© 2014 Mutaz B. Habal, MD
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
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In summary, our data demonstrate that ultra-low-dose protocols provide significant dose reduction without the loss of diagnostic image quality for paranasal sinus CT.
REFERENCES 1. Bulla S, Blanke P, Hassepass F, et al. Reducing the radiation dose for low-dose CT of the paranasal sinuses using iterative reconstruction: feasibility and image quality. Eur J Radiol 2012;81:2246–2250 2. Abul-Kasim K, Strömbeck A, Sahlstrand-Johnson P. Low-dose computed tomography of the paranasal sinuses: radiation doses and reliability analysis. Am J Otolaryngol 2011;32:47–51 3. Lam S, Bux S, Kumar G, et al. A comparison between low-dose and standard-dose non-contrasted multidetector CT scanning of the paranasal sinuses. Biomed Imaging Interv J 2009;5:e13 4. Schulz B, Potente S, Zangos S, et al. Ultra-low dose dual-source high-pitch computed tomography of the paranasal sinus: diagnostic sensitivity and radiation dose. Acta Radiol 2012;53:435–440 5. Schell B, Bauer RW, Lehnert T, et al. Low-dose computed tomography of the paranasal sinus and facial skull using a high-pitch dual-source system—first clinical results. Eur Radiol 2011;21:107–112 6. Schulz B, Beeres M, Bodelle B, et al. Performance of iterative image reconstruction in CT of the paranasal sinuses: a phantom study. AJNR Am J Neuroradiol 2012 7. Brem MH, Zamani AA, Riva R, et al. Multidetector CT of the paranasal sinus: potential for radiation dose reduction. Radiology 2007;243:847–852 8. Bongartz G, Golding SJ, Jurik AG, et al. European guidelines on quality criteria for computed tomography. Available at: http://www.drs.dk/ guidelines/ct/quality/. Accessed July 7, 2014.
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9. Sohaib SA, Peppercorn PD, Horrocks JA, et al. The effect of decreasing mAs on image quality and patient dose in sinus CT. Br J Radiol 2001;74:157–161 10. Mulkens TH, Broers C, Fieuws S, et al. Comparison of effective doses for low-dose MDCT and radiographic examination of sinuses in children. AJR Am J Roentgenol 2005;184: 1611–1618 11. Gogos KA, Yakoumakis EN, Tsalafoutas IA, et al. Radiation dose considerations in common paediatric x-ray examinations. Pediatr Radiol 2003;33:236–240 12. Tack D, Widelec J, De Maertelaer V, et al. Comparison between low-dose and standard-dose multidetector CT in patients with suspected chronic sinusitis. AJR Am J Roentgenol 2003;181: 939–944 13. Damilakis J, Prassopoulos P, Mazonakis M, et al. Tailored low dose three-dimensional CT of paranasal sinuses. Clin Imaging 1998;22:235–239 14. Batra PS, Kanowitz SJ, Citardi MJ. Clinical utility of intraoperative volume computed tomography scanner for endoscopic sinonasal and skull base procedures. Am J Rhinol 2008;22:511–515 15. Zoumalan RA, Lebowitz RA, Wang E, et al. Flat panel cone beam computed tomography of the sinuses. Otolaryngol Head Neck Surg 2009;140:841–844 16. Cohnen M, Kemper J, Mobes O, et al. Radiation dose in dental radiology. Eur Radiol 2002;12:634–637 17. Schulze D, Heiland M, Thurmann H, et al. Radiation exposure during midfacial imaging using 4- and 16-slice computed tomography, cone beam computed tomography systems and conventional radiography. Dentomaxillofac Radiol 2004;33:83–86
© 2014 Mutaz B. Habal, MD
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
Reliability of High-Pitch Ultra-Low-Dose Paranasal Sinus Computed Tomography for Evaluating Paranasal Sinus Anatomy and Sinus Disease Elif Ayanoglu Aksoy, MD,* Sila Ulus Özden, MD,† Ercan Karaarslan, MD,† Ömer Faruk Ünal, MD,* and Hasan Tanyeri, MD* Objectives: The aim of this study was to evaluate the reliability of high-pitch ultra-low-dose computed tomography (CT) for detecting important paranasal sinus anatomic landmarks and pathologies. Materials and Methods: Sixty patients (22 females, 38 males) aged 15 to 67 years (mean age, 33.68 y; SD, 9.83 y) underwent high-pitch ultra-low-dose CT of the paranasal sinuses between February and June 2012. To determine the lowest possible dose for evaluation of the paranasal sinuses, the patients were divided into three groups randomly and prospectively. A different lowdose CT protocol was applied to each group. The image quality was assessed subjectively by a radiologist and an otorhinolaryngology head and neck surgeon independently using a 4-point grading scale (0 = structures could not be identified, 1 = indistinctly defined structures, 1.5 = relatively well-defined structures, 2 = very welldefined structures). Anatomic landmarks and mucosal structures were evaluated. Mean scores were evaluated to assess statistical significance. Results: According to the anatomic landmark scoring, excluding the ethmoid foramen for ethmoid artery identification, all of the structures in all 3 groups were very well-defined structures. The ethmoid foramen for ethmoid artery identification was scored as either could not be identified or an indistinctly defined structure in all groups. On evaluating the mucosa of the paranasal sinuses, normal and pathologic mucosal structures were scored as very well defined in all of the patients. The interobserver agreement was excellent. Conclusion: High-pitch ultra-low-dose CT is a safe, reliable paranasal sinus screening tool. Key Words: High-pitch ultra-low-dose CT, paranasal sinuses (J Craniofac Surg 2014;25: 1801–1804)
C
omputed tomography (CT) is the gold standard for investigating inflammatory sinus disease and has become a routine radiologic examination of the paranasal sinuses.1–4 Radiation exposure during this examination has always been a major concern. Dose-reduction strategies have been published in various recent
From the Departments of *Otorhinolaryngology and †Radiology, Faculty of Medicine, Acibadem University, Istanbul, Turkey. Received October 7, 2013. Accepted for publication March 13, 2014. Address correspondence and reprint requests to Elif Ayanoglu Aksoy, MD, Faculty of Medicine, Acibadem University, Maslak Hospital, Büyükdere cad. No: 40 Maslak, Istanbul, Turkey; E-mail: [email protected] The authors report no conflicts of interest. Copyright © 2014 by Mutaz B. Habal, MD ISSN: 1049-2275 DOI: 10.1097/SCS.0000000000000966
articles that investigated the impact of dose reduction on image quality.1–7 This study evaluated the image quality and reliability of ultra-low-dose CT for detecting important anatomic landmarks and mucosal pathologies of paranasal sinuses.
MATERIALS AND METHODS Sixty patients (22 females, 38 males) with clinically suspected sinusitis, aged 15 to 67 years (mean age, 33.68 y; SD, 9.83 y) underwent high-pitch ultra-low-dose CT of the paranasal sinuses (Somatom Definition Flash; Siemens Healthcare, Forchheim, Germany) between February and June 2012. This study was approved by the institutional review board of the institution in which the research was conducted. Adult patients who were referred for CT of the paranasal sinus were included in the study randomly and prospectively. To determine the possible lowest dose for evaluating the paranasal sinuses, the patients were divided into 3 groups, and different low-dose CT protocols were applied randomly to each group. The age and sex distributions of the groups were similar (Table 1). The CT examinations were performed with a second-generation dual-source CT (Somatom Definition Flash; Siemens Healthcare, Forchheim, Germany). The scans were obtained in axial sections ranging from the roof of the frontal sinus to the maxillary sinus with the upper jaw aligned to the gantry to reduce dental artifacts. The field of view was adapted to cover the paranasal sinuses, facial bones, and mastoid region. The scans were acquired in craniocaudal order. Collimation was 0.6 mm for all groups; pitches were 3.2, 1.55, and 0.8, respectively. The rotation times were 1 second for group 1 and 0.28 second for groups 2 and 3. The tube voltages and currents for the groups were 80 kV/18 mA, 80 kV/126 mA, and 120 kV/80 mA, respectively (Table 2). Multiplanar reconstructions were made from raw data: 3-mm slices with 3-mm image distances in the transverse (bone and soft tissue kernel), coronal (bone kernel), and sagittal (bone kernel) views.
Evaluation of Image Quality The image quality was assessed subjectively by a radiologist and an otorhinolaryngology head and neck surgeon independently using a 4-point grading scale (0 = structures could not be identified, 1 = indistinctly defined structures, 1.5 = relatively well-defined structures, 2 = very well-defined structures). Anatomic landmarks and mucosal structures were evaluated.
TABLE 1. Sex and Age Distribution of Groups Group 1
Group 2
Group 3
7 females, 13 males
7 females, 13 males 15–67 (34.05 ± 10.77) y
8 females, 12 males 18–61(35.66 ± 10.83) y
17–55 (31.7 ± 9.47) y
The Journal of Craniofacial Surgery • Volume 25, Number 5, September 2014
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
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Aksoy et al
TABLE 2. High-Pitch Ultra-Low-Dose CT Scan Parameters of the 3 Groups
Tube collimation, mm Rotation time, s Pitch Tube voltage, kV Quality tube current-time product, mAs DLP, mGy.cm Effective dose, mean (SD), mSv
Group 1
Group 2
Group 3
0.6 1 0.8 120 80 154 0.35 (0.026)
0.6 0.28 1.55 80 126 37 0.08 (0.01)
0.6 0.28 3.2 80 18 7 0.019 (0.0018)
kV, kilovolts; mAs, milliampere-seconds; mGy.cm, miligray.centimeters; mSv, milisievert.
The medial wall of the maxillary sinuses, posterior wall of the frontal sinuses, bony margins of the sphenoid sinuses, orbital floor and medial orbital wall, infundibulum, uncinate processes, uncinate attachment point, Keros classification, and anterior ethmoid artery identification were the anatomic landmarks scored. Normal and pathologic mucosal structures of the maxillary, ethmoid, frontal, and sphenoid sinuses were also scored. Nonspecific mucosal swelling, fluid collection with air-fluid levels, opacification of the entire sinus, retention cysts, and polyps were evaluated. Mean scores were evaluated to assess statistical significance.
Estimation of Radiation Doses To determine the radiation exposure, the dose-length product (DLP) was analyzed. The DLP is documented automatically by the CT and noted in the examination file. Following the European guidelines, an appropriate conversion factor of 0.0023 mSv/mGy. cm was used to estimate the effective dose.8
Statistical Analysis All statistical analyses were performed using Statistical Package for The Social Sciences software 17.0 (SPSS, Inc, Chicago, IL). Wilcoxon signed-rank test was used to compare the mean scores of the two observers in all groups.
RESULTS According to the anatomic landmark scoring, the medial wall of the maxillary sinuses, posterior wall of the frontal sinuses, bony
FIGURE 1. Coronal paranasal sinus CT section of a group 1 patient demonstrating medial wall of maxillary sinuses (M), uncinate process (U), and inferior turbinate (I).
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FIGURE 2. Coronal paranasal sinus CT section of a group 2 patient demonstrating medial wall of maxillary sinuses (M), uncinate process (U), and inferior turbinate (I).
margins of the sphenoid sinuses, orbital floor and medial orbital wall, infundibulum, uncinate processes, uncinate attachment point, and Keros classification of the patients in all 3 groups were very well-defined structures. The ethmoid foramen for ethmoid artery identification was scored as either could not be identified or an indistinctly defined structure in all groups (Figs. 1–3). While evaluating the mucosa of the paranasal sinuses, normal and pathologic mucosal structures were scored as very well-defined structures in all of the patients (Tables 3–4). According to the Wilcoxon signed-rank test, there was no significant difference between the mean scores of the two observers in all groups (P = 0.312, 0.232, and 0.383 for groups 1–3, respectively). The interobserver agreement was excellent.
DISCUSSION In recent decades, CT has become the gold standard imaging method for diagnosing and grading the severity of inflammatory
FIGURE 3. Coronal paranasal sinus CT section of a group 3 patient demonstrating medial wall of maxillary sinuses (M), uncinate process (U), and inferior turbinate (I).
© 2014 Mutaz B. Habal, MD
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
The Journal of Craniofacial Surgery • Volume 25, Number 5, September 2014
Reliability of Paranasal Sinus CT
TABLE 3. Anatomic Landmark Scoring: Mean (SD) Scores of Observers 1 and 2 Group 1 Observer 1 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 0.66 (0.92)
Medial wall of maxillary sinuses Posterior wall of frontal sinuses Bony margins of sphenoid sinuses Orbital floor and medial orbital wall Infundibulum Uncinate processes Uncinate attachment point Keros classification Anterior ethmoid artery identification
Group 2 Observer 2 2 (0) 2 (0) 2 (0) 2 (0) 1.97 (0.17) 1.97 (0.17) 1.97 (0.17) 1.91 (0.28) 0.88 (0.91)
paranasal sinus diseases with adequate spatial resolution. Besides inflammatory findings, relevant anatomic variants are shown in detail with the isotropic data set obtained from CT. However, the radiation exposure associated with CT is a concern, especially for radiation-sensitive tissues such as the eye lenses and thyroid gland in the head and neck area and the frequent need for repeated examinations.6,9–11 The current trend in paranasal sinus CT is lowering the radiation dose to the minimum possible without decreasing diagnostic reliability.1–7 However, CT requires high-radiation doses if the examinations are performed following the standardized protocols recommended by the various CT scanner manufacturers. An effective dose as high as 0.76 mSv has been reported.12 Even studies of low-dose protocols reported effective doses as high as 0.48 mSv.13 In this study, we evaluated subjects using a recently introduced second-generation dual-source CT. Compared with earlier scanners, it has more detectors and a faster gantry rotation speed. Dual-source modes permit high-pitch values up to 3.2, and a gapless data set with reliable image quality for various indications is obtained. In addition to the large detector coverage, the scan speed can be increased dramatically. In our study, the highest effective dose was 0.35 (SD, 0.026) mSv in group 1 and was reduced by 94.5% to 0.019 (SD, 0.0018) mSv in group 3. Despite significant lowering of the radiation doses, image quality was sufficient for identifying important anatomic and mucosal structures. Although the mean observer scores were nonsignificantly lower in group 3, even the lowest mSv protocol provided reliable diagnostic images. According to our results, significantly lowering the radiation dose does not decrease diagnostic reliability. During mucosal evaluation of the paranasal sinuses, normal and pathologic mucosal structures were identified with all 3 low-dose CT protocols used in the patients included in our study. Important anatomic structures were defined as very well-defined or relatively well-defined structures, except for the ethmoid foramen for ethmoid artery identification. Our
TABLE 4. Paranasal Sinus Mucosal Evaluation: Mean (SD) Scores of Observers 1 and 2 Group 1 Maxillary sinus Ethmoid sinus Frontal sinus Sphenoid sinus
Group 2
Group 3
Observer 1 Observer 2 Observer 1 Observer 2 Observer 1 Observer 2 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
2 (0)
Observer 1 2 (0) 2 (0) 2 (0) 2 (0) 2 (0) 1.9 (0.46) 1.9 (0.46) 1.92 (0.35) 0.62 (0.9)
Group 3 Observer 2 2 (0) 2 (0) 2 (0) 2 (0) 1.8 (0.58) 1.8 (0.58) 1.38 (0.7) 1.5 (0.66) 0.31 (0.63)
Observer 1 2 (0) 2 (0) 2 (0) 1.45 (0.52) 2 (0) 1.57 (0.83) 1.57 (0.83) 1.9 (0.44) 0.066 (0.25)
Observer 2 2 (0) 2 (0) 2 (0) 1.71 (0.47) 1.59 (0.51) 1.40 (0.65) 1.10 (0.55) 1.14 (0.65) 0.08 (0.27)
results indicate that the proposed ultra-low-dose dual-source protocol has sufficient diagnostic validity, while resulting in only minimal radiation exposure to the patient, and the proposed ultra-low-dose examination protocol can be used to screen for inflammation of the paranasal sinuses. The maximum dose reduction (group 3, 80 kV and 18 mAs; effective dose, 0.0019 mSv) was considered sufficient for defining anatomic structures and mucosal pathologies and has subsequently been used in clinical practice in our institution (when sinusitis was the clinical question at issue), replacing the standard CT protocol using the scan parameters recommended by the CT manufacturer. For the clarity of the anatomic structures, especially for the delineation of bones and vascular structures, which are important to surgeons for preoperative assessment, standard low-dose protocols should be preferred. We believe that plain radiographic images are inadequate for evaluating the complex anatomy of the paranasal sinus comprehensively and should be discouraged and avoided. Conebeam CT (CBCT), primarily introduced for dental examinations and orthodentic indications, is considered an alternative modality to have reasonable diagnostic value for the evaluation of rhinosinusitis.14,15 According to the literature, radiation exposure, especially of the thyroid gland by scattered radiation, is lower with CBCT compared with multislice CT devices.16,17 However, with recent improvements in the CT technology, the use of appropriate tube voltage and current settings enable the evaluation of paranasal sinuses with much lower radiation doses comparable with the values of CBCT and diagnostically conclusive image quality. Future studies with optimized CBCT parameters and comparison of image quality with low-dose CT would be beneficial. The paranasal sinuses can also be visualized and evaluated by magnetic resonance imaging (MRI). The presence of inflammation or retention cysts can be determined by MRI, whereas bony structures are visualized with superior spatial resolution in CT images. In addition, MRI is more expensive, and the examination time is longer compared with the very-short 0.3-second scan time with CT. Considering these facts, low-dose CT should be the gold standard imaging method in the work-up of sinusitis, and optimization of the radiation dose is an important issue. Furthermore, our findings of equally high interrater agreement in detecting pathology and characterizing different pathologies, as well as previous reports of high interrater agreement in defining a number of anatomic landmarks,9,12 suggest that the radiation doses used in standard sinus CT protocols, such as before functional endoscopic sinus surgery, are higher than needed. Performing paranasal sinus CT with the lowest acceptable dose must be the prime aim in each examination. One of the drawbacks of our study is that we did not quantify noise. With iterative reconstruction in image space, the image quality of the ultra-low-dose images can be increased. We did not routinely use iterative reconstruction in image space in our series.
© 2014 Mutaz B. Habal, MD
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
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The Journal of Craniofacial Surgery • Volume 25, Number 5, September 2014
Aksoy et al
In summary, our data demonstrate that ultra-low-dose protocols provide significant dose reduction without the loss of diagnostic image quality for paranasal sinus CT.
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© 2014 Mutaz B. Habal, MD
Copyright © 2014 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
