AJR 2003; 181:939-944
© American Roentgen Ray Society
Comparison Between Low-Dose and Standard-Dose Multidetector CT in Patients with Suspected Chronic Sinusitis
Denis Tack1,
Jacques Widelec1,
Viviane De Maertelaer2,
Jean-Marie Bailly1,
Christian Delcour1 and
Pierre Alain Gevenois3
1 Department of Radiology, Centre Hospitalier Universitaire de Charleroi, 92
Blvd. Janson, Charleroi B-6000, Belgium.
2 Present address: Statistical Unit, Institut de Recherche Interdisciplinaire en
Biologie Humaine et Moléculaire, Université Libre de Bruxelles,
Brussels B-1070, Belgium.
3 Present address: Department of Radiology, Hôpital Erasme,
Université Libre de Bruxelles, Brussels B-1070, Belgium.
Received February 28, 2003;
accepted after revision April 16, 2003.
Address correspondence to D. Tack.
Abstract
OBJECTIVE. This study was designed to compare low- and standard-dose
multidetector CT (MDCT) findings in patients with suspected chronic
sinusitis.
SUBJECTS AND METHODS. Fifty patients underwent MDCT at 10 and 150
effective mAs. The low-dose MDCT protocol delivered a radiation dose of 0.047
mSv in men and 0.051 mSv in women, whereas the standard-dose MDCT protocol
delivered a radiation dose of 0.70 mSv in men and 0.76 mSv in women. Scans of
the right and left sides of sinonasal cavities were reviewed by three
radiologists, with each physician reviewing a scan twice over an interval of
more than 2 weeks. The reviewers were asked to evaluate the scans for eight
mucosal and two bone abnormalities. We calculated the number of discrepancies
in observed abnormalities between pairs of reviewers, among all three
reviewers, and between findings on scans acquired with the two radiation
doses.
RESULTS. The mean number of discrepancies in observed abnormalities
on scans acquired with different radiation doses ranged from 0 to 5.2.
Discrepancies between pairs of reviewers ranged from 1.0 to 12.8 for low-dose
scans and from 1.0 to 13.0 for standard-dose scans. Discrepancies among all
reviewers ranged from 1.0 to 10.3 for low-dose scans and from 1.0 to 8.7 for
standard-dose scans. In analyzing cases of significant discrepancies in
observations, we found greater variation between pairs of reviewers and among
all three reviewers than between findings obtained with different dose
levels.
CONCLUSION. Dose reduction played a far less important role in
discrepancies of detected abnormalities than did the human element of reviewer
observation. Given this finding and the fact that low-dose MDCT delivers a
radiation dose that is no higher than that delivered by a four-view
radiographic examination, low-dose MDCT should be considered the imaging
method of choice in patients with suspected chronic sinusitis.
Introduction
Chronic sinusitis is a frequent disorder that develops in up to one third
of patients with acute bacterial sinusitis. It may occur as a complication of
a dental infection or tooth extraction or may accompany systemic allergic
events [1]. CT has become the
method of choice for identifying and staging any inflammatory sinus disease
and is a routine examination for the diagnosis of chronic sinusitis
[2–5].
Chronic sinusitis is, by definition, frequently recurrent, and sensitive
organs such as eye lenses and the thyroid are potentially subject to high
cumulative doses of radiation from repeated CT examinations
[6].
Recommended acquisition parameters for single-detector CT are based on
studies using 3-mm-thick contiguous sections obtained with high milliampere
settings [2,
4–6].
Low-dose single-detector CT has been shown to provide scans of good image
quality leading to acceptable diagnostic performance compared with that
achieved using standard-dose single-detector CT
[7–12].
The recent development of multidetector CT (MDCT) enables us to obtain
1-mm-collimation scans and subsequent high-quality multiplanar reformations,
but this protocol requires a radiation dose approximately 20% higher than that
delivered with the formerly used 3-mm collimation. Regardless of the CT
acquisition parameters used, the radiation dose has not yet been reduced to
that delivered by a four-view radiographic examination
[13]. The aim of our study
was, therefore, to compare low-dose MDCT scans obtained at a radiation dose no
higher than that delivered during a four-view radiographic examination with
MDCT scans obtained with the standard radiation dose.
Subjects and Methods
From January to March 2001, 50 consecutive patients (20 men and 30 women;
age range, 18–79 years; mean age, 44 years) who presented with a
headache suspected to be caused by chronic sinusitis were referred for MDCT of
the head and the sinonasal cavities. They underwent both low-dose MDCT of the
sinonasal cavities and standard-dose MDCT of the head. The study protocol was
approved by the institutional review board. Informed consent was obtained from
all patients.
MDCT Examinations
Scans were obtained using a commercially available four-channel MDCT
scanner (Somatom Plus Volume Zoom, Siemens Medical Systems, Forschheim,
Germany). Patients were examined while in a supine position, and none received
contrast material. A lateral 25.6-cm scout scan was first obtained at 120 kVp
and 50 mAs. We then obtained a low-dose MDCT scan that covered the region from
maxillary dental arch to the top of the frontal sinuses, with simultaneous
acquisition of 4 x 1 mm collimations at 120 kVp and 10 effective mAs. As
defined by Mahesh et al. [14],
effective milliampere-seconds is determined by dividing the number of
milliampere-seconds by the pitch, which, as defined by Silverman et al.
[15], is the ratio between the
table feed per rotation and the X-ray beam width. Table feed was 8 mm per 0.5
sec of scanner rotation (16 mm/sec). These parameters result in a pitch of
2:1. Low-dose scanning was followed by a standard-dose MDCT scanning of the
head that covered the area from the maxillary dental arch to the upper limit
of the vertex with simultaneous acquisition of 4 x 1 mm collimations at
120 kVp and 150 effective mAs. Table feed was 3 mm per 1 sec of scanner
rotation (3 mm/sec). These parameters result in a pitch of 0.75:1. From the
raw data, 1.25-mm-thick sections were reconstructed with a 0.8-mm increment
using a bone algorithm. From these scans, 2-mm-thick axial, frontal, and
sagittal reformations were obtained with a 2-mm increment.
Effective Dose Calculations
The effective dose was simulated on a personal computer using commercially
available software (CT Expo, Medizinische Hochschule, Hanover, Germany) that
requires no phantom measurements. Inputs corresponding to MDCT parameters, the
patient's sex, and the scanned region as represented on a graph of the Monte
Carlo phantom model [16] were
given to the program. The effective dose was then computed according to the
Monte Carlo simulations for anthropomorphic phantoms as recommended by Nagel
[17] and conversion factors as
reported by Zankl et al. [16,
18]. The calculated effective
doses were expressed according to the International Commission on Radiological
Protection recommendations
[19]. We also used this
software to calculate the effective dose delivered by previously reported CT
protocols (Table 1)
[2,
5–8,
10,
11,
20,
21]. For all calculations, we
considered the height of the scanned region to be 12 cm.
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TABLE 1 Comparison of Effective Radiation Doses Delivered During Imaging of the
Head by Low-Dose and Standard-Dose Multidetector CT (MDCT) and CT and
Radiology Protocols Used in Previous Studies
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Image Analysis
The multiplanar reformations were stored on compact disks and reviewed on a
clinical workstation (Wizard, Siemens Medical Systems) by a general
radiologist who had 14 years' experience in interpreting CT scans and by two
neuroradiologists—one who had 14 years' and one who had 19 years'
experience in interpreting head and neck CT scans. To meet quality criteria
for clinical studies as recommended by Arrive et al.
[22], we organized scan
interpretations as follows: Multiplanar reformations from low-dose MDCT scans
were reviewed before multiplanar reformations from standard-dose MDCT scans,
each interpretation being performed in separate sessions more than 2 weeks
apart. Therefore, each multiplanar reformation was interpreted twice by all
three reviewers.
These reviewers were asked to judge whether the appearance of 10 distinct
features was normal, abnormal, or indeterminate (Figs.
1A,
1B,
2A,
2B,
3A,
3B,
4A,
4B). The first eight features
were mucosal abnormalities that could potentially be found in the anatomic
structures defined by Rao and El-Noueam
[4] and by Zinreich et al.
[2]: the sphenoethmoidal
recess, including the ostium of the sphenoid sinus; the osteomeatal unit,
including the maxillary ostium, uncinate process, and infundibulum; the
nasofrontal duct, including the frontal sinus; the maxillary sinus, excluding
the osteomeatal unit; the anterior ethmoid cells; the posterior ethmoid cells;
the ethmoid bulla; and the basal lamina. Mucosa was considered to be normal if
it was not visible and was considered abnormal (thickened) if it was visible.
Indeterminate findings included those instances in which a reviewer was
doubtful or in which the anatomic structure was not seen (e.g., the
osteomeatal unit after a previous surgery of the maxillary sinus). The ninth
feature consisted of bony abnormalities such as sclerosis, thickening, or
lysis of any structures excluding the periodontal space, and the 10th feature
was an enlargement of the periodontal space. As suggested by Fuhrmann et al.
[23], the appearance of the
periodontal space was scored as normal if it was not visible, abnormal if it
was visible, and indeterminate if a patient had no teeth. In each patient,
right and the left sides were reviewed separately, resulting in a total number
of scans equivalent to the number obtained in 100 patients.
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Fig. 1A. —Axial multiplanar reformations of multidetector CT (MDCT)
scans obtained at level of sphenoethmoidal recess in 35-year-old man who
presented with headache suspected to be caused by chronic sinusitis. R =
right; a = anterior ethmoid cell; b = basal lamina (arrowhead); p =
posterior ethmoid cell. Reformation of low-dose MDCT scan shows normal right
(curved arrow) and abnormal left (straight arrow)
sphenoethmoidal recess. No discrepancies among reviewers or between pairs of
reviewers were noted.
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Fig. 1B. —Axial multiplanar reformations of multidetector CT (MDCT)
scans obtained at level of sphenoethmoidal recess in 35-year-old man who
presented with headache suspected to be caused by chronic sinusitis. R =
right; a = anterior ethmoid cell; b = basal lamina (arrowhead); p =
posterior ethmoid cell. Reformation of standard-dose MDCT scan shows normal
right (curved arrow) and abnormal left (straight arrow)
sphenoethmoidal recess. As with A, no discrepancies among reviewers or
between pairs of reviewers were noted.
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Fig. 2A. —Coronal multiplanar reformations of multidetector CT (MDCT)
scans obtained at level of osteomeatal units (straight arrows) in
24-yearold woman who presented with headache suspected to be caused by chronic
sinusitis. R = right; m = maxillary sinus; b = right ethmoid bulla.
Reformation of low-dose MDCT scan shows abnormal left ethmoid bulla
(curved arrow). No discrepancies were noted.
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Fig. 2B. —Coronal multiplanar reformations of multidetector CT (MDCT)
scans obtained at level of osteomeatal units (straight arrows) in
24-yearold woman who presented with headache suspected to be caused by chronic
sinusitis. R = right; m = maxillary sinus; b = right ethmoid bulla.
Reformation of standard-dose MDCT scan shows abnormal left ethmoid bulla
(curved arrow) seen in A. Discrepancies in findings of ethmoid
bulla were noted between first and second interpretation sessions of reviewer
1 and between reviewer 1 and reviewers 2 and 3 in first interpretation
session.
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Fig. 3A. —Sagittal multiplanar reformations of multidetector CT (MDCT)
obtained at level of left maxillary sinus (m) in 52-year-old woman who
presented with headache suspected to be caused by chronic sinusitis. Enlarged
periodontal space (arrow) was consistently identified throughout all
interpretations. P = posterior; f = frontal sinus; m = maxillary sinus.
Reformation of low-dose MDCT scan reveals enlarged periodontal space
(arrow).
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Fig. 3B. —Sagittal multiplanar reformations of multidetector CT (MDCT)
obtained at level of left maxillary sinus (m) in 52-year-old woman who
presented with headache suspected to be caused by chronic sinusitis. Enlarged
periodontal space (arrow) was consistently identified throughout all
interpretations. P = posterior; f = frontal sinus; m = maxillary sinus.
Reformation of standard-dose MDCT scan reveals enlarged periodontal space
(arrow) as clearly as seen in A.
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Fig. 4A. —Axial multiplanar reformations of multidetector CT (MDCT)
obtained at level of maxillary sinus in 49-year-old man who presented with
headache suspected to be caused by chronic sinusitis. Bony remodeling was
consistently identified throughout all interpretations. R = right; m = left
maxillary sinus. Reformation of low-dose MDCT scan shows osseous lysis
(arrow) of anterior wall of right maxillary sinus.
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Fig. 4B. —Axial multiplanar reformations of multidetector CT (MDCT)
obtained at level of maxillary sinus in 49-year-old man who presented with
headache suspected to be caused by chronic sinusitis. Bony remodeling was
consistently identified throughout all interpretations. R = right; m = left
maxillary sinus. Reformation of standard-dose MDCT scan reveals osseous lysis
(arrow) of anterior wall of right maxillary sinus as clearly as seen
in A.
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Two weeks before the first interpretation session, reviewers were
familiarized with observation recording procedures in an exercise involving
multiplanar reformations obtained in 20 patients not included in our study
population.
Statistical Methods
Because a definite diagnosis from an independent method of reference cannot
be obtained and because standard-dose MDCT is not an a priori gold standard,
our study compared discrepancies among all three reviewers and between pairs
of the reviewers and discrepancies between the MDCT findings obtained using
the two radiation doses. For every 10 observations recorded, we calculated the
number of scoring discrepancies among the 100 sets of patient data. In all,
five sets of comparisons were made: two-by-two comparisons between pairs of
the three reviewers (i.e., between reviewers 1 and 2, 1 and 3, and 2 and 3) of
both interpretation sessions of the low-dose scans, producing six comparative
combinations; two-by-two comparisons between pairs of the three reviewers for
both interpretation sessions of the standard-dose scans, producing six
comparative combinations; intrareviewer comparisons of each reviewer's
interpretations of the low-dose scans, producing three comparative
combinations; intraviewer comparisons of each reviewer's interpretations of
the standard-dose scans, producing three comparative combinations; and
comparisons between the low- and standard-dose findings for each of the three
reviewers and for both interpretation sessions, producing six different
comparative combinations.
For every 10 observations, a one-way analysis of variance was performed to
globally compare the mean discrepancies in these five sets of combinations. In
cases of statistically significant discrepancies, we then performed Tukey
tests [24] to detect which set
statistically differed from the others. Statistical significance for all tests
was set at a p value of less than 0.05. The statistical software used
was SPSS for Windows (release 11.0, SPSS, Chicago, IL).
Results
The mean number of discrepancies for the five sets of comparisons ranged
from one to 13 overall. Global differences in mean discrepancies reached
statistical significance for the mucosal abnormalities in the sphenoethmoidal
recess, osteomeatal unit, nasofrontal duct, posterior ethmoid cells, ethmoid
bulla, basal lamina, and periodontal space. Tukey tests revealed which set of
comparisons differed from the others. Figures
5,
6,
7,
8,
9,
10,
11 show these differences with
the corresponding p values. Differences in discrepancies for the
mucosal abnormalities in the anterior ethmoid cells and maxillary sinus and
for bony abnormalities did not reach statistical significance. We found that
in the scoring for any abnormality in which discrepancies reached statistical
significance, the discrepancies between the findings obtained with the two
radiation doses were smaller than the discrepancies among all reviewers or
between pairs of reviewers.
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Fig. 5. —Graphs representing mean (± SEM) number of
discrepancies in identifying abnormalities of sphenoethmoidal recess (Fig. 5),
osteomeatal unit (Fig. 6),
nasofrontal duct (Fig. 7), and
ethmoid bulla (Fig. 8).
X-axis represents sets of comparisons: 1, two-by-two comparisons
between pairs of reviewers at both sessions interpreting low-dose
multidetector CT (MDCT) scans; 2, two-by-two comparisons between pairs of
reviewers at both sessions interpreting standard-dose MDCT scans; 3,
intrareviewer comparisons between two interpretation sessions of low-dose MDCT
scans; 4, intrareviewer comparisons between two interpretation sessions of
standard-dose MDCT scans; 5, comparisons between interpretations of low- and
standard-dose MDCT scans for each reviewer and for both interpretation
sessions. In cases of statistically significant discrepancies, p
values from Tukey tests [24]
are given. Solid line represents significant difference involving comparisons
of low-dose and standard-dose scans among reviewers. Dashed line represents
significant difference involving another comparison. Vertical bars extending
on either side of mean point represent range.
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Fig. 6. —Graphs representing mean (± SEM) number of
discrepancies in identifying abnormalities of sphenoethmoidal recess
(Fig. 5), osteomeatal unit
(Fig. 6), nasofrontal duct (Fig.
7), and ethmoid bulla (Fig.
8). X-axis represents sets of comparisons: 1, two-by-two
comparisons between pairs of reviewers at both sessions interpreting low-dose
multidetector CT (MDCT) scans; 2, two-by-two comparisons between pairs of
reviewers at both sessions interpreting standard-dose MDCT scans; 3,
intrareviewer comparisons between two interpretation sessions of low-dose MDCT
scans; 4, intrareviewer comparisons between two interpretation sessions of
standard-dose MDCT scans; 5, comparisons between interpretations of low- and
standard-dose MDCT scans for each reviewer and for both interpretation
sessions. In cases of statistically significant discrepancies, p
values from Tukey tests [24]
are given. Solid line represents significant difference involving comparisons
of low-dose and standard-dose scans among reviewers. Dashed line represents
significant difference involving another comparison. Vertical bars extending
on either side of mean point represent range.
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Fig. 7. —Graphs representing mean (± SEM) number of
discrepancies in identifying abnormalities of sphenoethmoidal recess
(Fig. 5), osteomeatal unit
(Fig. 6), nasofrontal duct
(Fig. 7), and ethmoid bulla (Fig.
8). X-axis represents sets of comparisons: 1, two-by-two
comparisons between pairs of reviewers at both sessions interpreting low-dose
multidetector CT (MDCT) scans; 2, two-by-two comparisons between pairs of
reviewers at both sessions interpreting standard-dose MDCT scans; 3,
intrareviewer comparisons between two interpretation sessions of low-dose MDCT
scans; 4, intrareviewer comparisons between two interpretation sessions of
standard-dose MDCT scans; 5, comparisons between interpretations of low- and
standard-dose MDCT scans for each reviewer and for both interpretation
sessions. In cases of statistically significant discrepancies, p
values from Tukey tests [24]
are given. Solid line represents significant difference involving comparisons
of low-dose and standard-dose scans among reviewers. Dashed line represents
significant difference involving another comparison. Vertical bars extending
on either side of mean point represent range.
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Fig. 8. —Graphs representing mean (± SEM) number of
discrepancies in identifying abnormalities of sphenoethmoidal recess
(Fig. 5), osteomeatal unit
(Fig. 6), nasofrontal duct
(Fig. 7), and ethmoid bulla
(Fig. 8). X-axis represents sets of comparisons: 1, two-by-two
comparisons between pairs of reviewers at both sessions interpreting low-dose
multidetector CT (MDCT) scans; 2, two-by-two comparisons between pairs of
reviewers at both sessions interpreting standard-dose MDCT scans; 3,
intrareviewer comparisons between two interpretation sessions of low-dose MDCT
scans; 4, intrareviewer comparisons between two interpretation sessions of
standard-dose MDCT scans; 5, comparisons between interpretations of low- and
standard-dose MDCT scans for each reviewer and for both interpretation
sessions. In cases of statistically significant discrepancies, p
values from Tukey tests [24]
are given. Solid line represents significant difference involving comparisons
of low-dose and standard-dose scans among reviewers. Dashed line represents
significant difference involving another comparison. Vertical bars extending
on either side of mean point represent range.
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Fig. 9. —Graphs representing mean (± SEM) number of
discrepancies in identifying abnormalities of posterior ethmoid cells (Fig.
9), basal lamina (Fig. 10),
and periodontal space (Fig.
11). X-axis represents sets of comparisons: 1, two-by-two
comparisons between pairs of reviewers at both sessions interpreting low-dose
multidetector CT (MDCT) scans; 2, two-by-two comparisons between pairs of
reviewers at both sessions interpreting standard-dose MDCT scans; 3,
intrareviewer comparisons between two interpretation sessions of low-dose MDCT
scans; 4, intrareviewer comparisons between two interpretation sessions of
standard-dose MDCT scans; 5, comparisons between interpretations of low- and
standard-dose MDCT scans for each reviewer and for both interpretation
sessions. In cases of statistically significant discrepancies, p
values from Tukey tests [24]
are given. Solid line represents significant difference involving comparisons
of low-dose and standard-dose scans among reviewers. Dashed line represents
significant difference involving another comparison. Vertical bars extending
on either side of mean point represent range.
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Fig. 10. —Graphs representing mean (± SEM) number of
discrepancies in identifying abnormalities of posterior ethmoid cells
(Fig. 9), basal lamina (Fig.
10), and periodontal space (Fig.
11). X-axis represents sets of comparisons: 1, two-by-two
comparisons between pairs of reviewers at both sessions interpreting low-dose
multidetector CT (MDCT) scans; 2, two-by-two comparisons between pairs of
reviewers at both sessions interpreting standard-dose MDCT scans; 3,
intrareviewer comparisons between two interpretation sessions of low-dose MDCT
scans; 4, intrareviewer comparisons between two interpretation sessions of
standard-dose MDCT scans; 5, comparisons between interpretations of low- and
standard-dose MDCT scans for each reviewer and for both interpretation
sessions. In cases of statistically significant discrepancies, p
values from Tukey tests [24]
are given. Solid line represents significant difference involving comparisons
of low-dose and standard-dose scans among reviewers. Dashed line represents
significant difference involving another comparison. Vertical bars extending
on either side of mean point represent range.
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Fig. 11. —Graphs representing mean (± SEM) number of
discrepancies in identifying abnormalities of posterior ethmoid cells
(Fig. 9), basal lamina
(Fig. 10), and periodontal
space (Fig. 11). X-axis represents sets of comparisons: 1, two-by-two
comparisons between pairs of reviewers at both sessions interpreting low-dose
multidetector CT (MDCT) scans; 2, two-by-two comparisons between pairs of
reviewers at both sessions interpreting standard-dose MDCT scans; 3,
intrareviewer comparisons between two interpretation sessions of low-dose MDCT
scans; 4, intrareviewer comparisons between two interpretation sessions of
standard-dose MDCT scans; 5, comparisons between interpretations of low- and
standard-dose MDCT scans for each reviewer and for both interpretation
sessions. In cases of statistically significant discrepancies, p
values from Tukey tests [24]
are given. Solid line represents significant difference involving comparisons
of low-dose and standard-dose scans among reviewers. Dashed line represents
significant difference involving another comparison. Vertical bars extending
on either side of mean point represent range.
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The effective dose delivered by the low-dose MDCT protocol was 0.047 mSv in
men and 0.051 mSv in women, whereas the effective dose delivered by the
standard-dose MDCT protocol was 0.70 mSv in men and 0.76 mSv in women. The
calculated effective doses delivered by previously reported protocols are
listed in Table 1.
Discussion
Our results show that when identifying mucosal and bone abnormalities in
the sinonasal cavities, the number of discrepancies between findings on the
low-dose and findings on standard-dose MDCT scans either did not differ or
were even fewer than the number of discrepancies among all reviewers and
between pairs of reviewers, depending on the feature considered. In other
words, observational variations associated with a decrease in radiation dose
are fewer than those that can be attributed to the reviewers themselves.
Interpretation of MDCT scans showed discrepancies among all reviewers and
between pairs of reviewers even for scans obtained with a standard radiation
dose. Standard-dose MDCT, therefore, should not be considered the absolutely
perfect method of reference, as has been suggested in previous studies
[21]. Indeed, if we had
considered the findings obtained with standard-dose MDCT as representing the
gold standard, we would have misclassified 1–13% of the low-dose MDCT
findings (depending on the observation considered). Consequently, calculated
diagnostic performances would not have reflected the real value of low-dose
MDCT. Because we had no actual diagnosis established by an independent method
of reference, we compared only discrepancies in the interpretations of the
three reviewers against discrepancies between scans obtained at different
radiation doses.
The CT technique for imaging the sinonasal cavities may vary depending on
numerous factors, such as whether one is using a helical versus an incremental
technique or scanning in the axial versus the coronal planes in addition to
the peak kilovoltage and milliampere-seconds presets and selection of
collimation, pitch, and slice increment. All these factors greatly influence
the radiation dose. In our study, the acquisition protocol was intended to
provide high-quality imaging in all planes, to prevent attenuation artifacts
caused by metallic dental restorations in the coronal acquisitions, and to
reduce the radiation dose to the dose delivered by a four-view radiographic
examination. To attain this dose, we used 10 effective mAs. As shown in
Table 1, this effective dose is
three to 10 times lower than the one delivered in previously reported studies
with incremental or helical single-detector CT scanning. In a recent study,
Hagtvedt et al. [21] used
noncontiguous incremental acquisitions to obtain 10 coronal CT sections with a
radiation dose 50% lower than that delivered in our study using the low-dose
MDCT protocol. However, because their scans were not contiguous, Hagtvedt et
al. might have not been able to identify clinically relevant data such as
mucosal abnormalities in the sphenoethmoidal recess or enlargement of the
periodontal space. An MDCT acquisition protocol using 15 effective mAs., 80
KVp, and 4 x 1 mm collimation could achieve a radiation dose similar to
the one proposed by Hagtvedt et al. but provide all advantages of
three-dimensional imaging.
Discrepancies vary from observation to observation. For example,
discrepancies were higher for the mucosal abnormalities in the ethmoid bulla
than in the maxillary sinus. These differences may be explained by anatomic
variants. Indeed, the ethmoid bulla is a tiny structure close to the
osteomeatal unit in a region with numerous anatomic variants
[25]. In comparison, the
maxillary sinus is a large sinonasal cavity that is quite easy to evaluate.
Although delineation of bone structures is widely believed to require a high
radiation dose, our study did not find any difference in discrepancies in
recording bone abnormalities (including the periodontal space) between
judgments based on low-dose scans and those based on standard-dose scans, as
illustrated in Figures 3A,
3B and
4A,
4B.
In conclusion, low-dose MDCT should be considered as the method of choice
for imaging sinonasal cavities in patients with suspected chronic sinusitis
because it exposes patients to a radiation dose no higher than that used for a
four-view radiographic examination.
Acknowledgments
We thank Alain Van Muylem for preparing the figures.
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Abstract
Introduction
