antecedenteSAFIREescalas

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Purpose:
To evaluate the effect of iterative reconstruction on the
depiction of systemic sclerosis–related interstitial lung
disease (ILD) when the radiation dose is reduced by 60%.
Materials and
Methods:
This study was based on retrospective interpretation of
prospectively acquired data over a 12-month period and
approved by the institutional review board. The requirement to obtain informed consent was waived. Fifty-five
chest computed tomographic (CT) examinations were
performed in 38 women and 17 men (mean age, 55.8
years; range, 23–82 years) by using a dual-source CT unit
with (a) both tubes set at similar energy (120 kVp) and
(b) the total reference milliampere seconds (ie, 110 mAs)
split up in a way that 40% was applied to tube A and 60%
to tube B. Two series of images were generated simultaneously from the same dataset: (a) standard-dose images
(generated from both tubes) reconstructed with filtered
back projection (group 1, the reference standard) and (b)
reduced-dose images (generated from tube A; 60% dose
reduction) reconstructed with sinogram-affirmed iterative
reconstruction (SAFIRE) (group 2). In both groups, the
analyzed parameters comprised the image noise and the
visualization and conspicuity of CT features of ILD. Two
readers independently analyzed images from both groups.
Results were compared by using the Wilcoxon test for
paired samples; the 95% confidence interval was calculated when appropriate.
Results:
The mean level of objective noise in group 2 was significantly lower than that in group 1 (22.02 HU vs 26.23 HU,
respectively; P , .0001). The CT features of ILD in group
1 were always depicted in group 2, with subjective conspicuity scores (a) improved in group 2 for ground-glass
opacity, reticulation, and bronchiectasis and/or bronchiolectasis and (b) identical in both groups for honeycombing. The interobserver agreement for their depiction was
excellent in both groups (k, 0.84–0.98).
Conclusion:
Despite a 60% dose reduction, images reconstructed with
SAFIRE allowed similar detection of systematic sclerosis–
related ILD compared with the reference standard.
1
From the Department of Thoracic Imaging (EA 2694)
(F.P., A.S.B., J.B.F., J.R., M.R.J.), Department of Medical
Statistics (EA 2694) (A.D.), Department of Internal Medicine
(E.H.), and Department of Pulmonary Function (R.M.), Hôpital Calmette, Université Lille II, Boulevard Jules Leclercq,
59037 Lille, France; and Research and Development
Department, Siemens Healthcare, Forchheim, Germany
(B.S.). Received April 10, 2015; revision requested June 2;
revision received August 10; accepted September 2; final
version accepted September 21. Address correspondence to M.R.J. (e-mail: martine.remy@chru-lille.fr ).
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Radiology: Volume 279: Number 1—April 2016
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297
n Thoracic Imaging
François Pontana, MD
Anne-Sophie Billard, MD
Alain Duhamel, PhD
Bernhard Schmidt, PhD
Jean-Baptiste Faivre, MD
Eric Hachulla, MD, PhD
Régis Matran, MD
Jacques Remy, MD
Martine Remy-Jardin, MD, PhD
Original Research
Effect of Iterative Reconstruction
on the Detection of Systemic
Sclerosis–related Interstitial
Lung Disease: Clinical Experience
in 55 Patients1
THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
P
ulmonary involvement is common
in patients with systemic sclerosis, and lung complications represent the most frequent cause of death
in this population (1,2). In addition to
clinical findings, staging of disease severity usually relies on pulmonary function tests and high-spatial-resolution
computed tomography (CT), with the
latter enabling characterization and
quantification of lung changes. This
morphologic information is important
to identify early changes in asymptomatic patients and represents a method
with which to monitor lung disease
progression in patients with or without therapy (2–4). The CT features of
systematic sclerosis–related interstitial
lung disease (ILD) are characterized
by subtle parenchymal changes (eg,
ground-glass opacities, fine reticulation, and microcystic honeycombing),
the detection of which could be altered
on grainy images of reduced-dose acquisitions (5–8).
To minimize noise in CT images,
iterative reconstruction has been introduced as an alternative to the conventional reconstruction mode based
on filtered back projection (FBP). The
first generations of iterative reconstruction provided reduced-dose images
with a similar quality to that of images
acquired with a standard dose and reconstructed with FBP (9–11). However,
these reconstruction algorithms (ie, image domain–based iterative reconstruction) modified the visual appearance of
images, which could appear smooth (9)
or pixelated (11), thus raising concerns
about the possibility of maintaining the
diagnostic capability of CT. A second
generation of iterative reconstruction,
active in the raw data space, was introduced with the aim of reducing noise
and maintaining image sharpness.
Their effect on lung images has mainly
been evaluated with anthropomorphic
phantoms, showing a similar detection
of ground-glass opacities and pulmonary nodules on reduced-dose and standard-dose images (12–15). In clinical
situations, a few studies have evaluated
the visualization of lesions of lung infiltration in various disorders; however,
none, to our knowledge, has specifically
investigated ILD (9,11,16).
Because systemic sclerosis–related
ILD is characterized by mild forms of
lung infiltration on CT scans sequentially indicated for follow-up purposes,
this population can be considered as
an interesting target to investigate the
effect of a second-generation iterative reconstruction on reduced-dose
images in comparison with images
acquired with a standard dose and
reconstructed with FBP. The purpose
of this study was to evaluate the effect of iterative reconstruction on the
depiction of systematic sclerosis–related ILD when the radiation dose is
reduced by 60%.
Materials and Methods
One author (B.S., an employee of Siemens) provided technical support for
implementation of the research prototype enabling reconstruction of reduced-dose and full-dose images from
each data set.
One author received research
grants (M.R.J.) and one received consultant fees (J.R.) from Siemens. The
other authors (F.P., A.S.B., A.D.,
J.B.F., E.H., R.M.), who are not associated with Siemens, maintained full control of the data at all times. The study
was approved by the institutional ethics
committee, and the requirement to obtain informed consent was waived.
Advance in Knowledge
Implication for Patient Care
nn Mild interstitial lung abnormalities related to systemic sclerosis
are confidently depicted at radiation dose levels of 1.8 mSv, with
very good or excellent image
quality in 96% of reduced-dose
examinations
nn Reduced-dose chest CT examinations reconstructed with sinogram-affirmed iterative reconstruction allow accurate
depiction of CT features of
systemic sclerosis–related interstitial lung disease.
298
Pontana et al
Population
During a 12-month period (May 2011–
April 2012), 55 consecutive patients
with systematic sclerosis (mean age,
55.8 years; range, 23–82 years) underwent a chest CT examination indicated
for the diagnosis or follow-up of lung
disease; detailed information about
disease severity is given in the first paragraph of the Results section. The population comprised 38 women (mean age,
55.2 years; range, 23–77 years) and
17 men (mean age, 57.1 years; range,
32–82 years); there was statistically
significant difference in the mean age
of female and male patients (P = .64,
Student t test). Recruitment for CT and
assessment of clinical parameters was
done prospectively, and image analysis
was performed retrospectively.
CT Scan Acquisition
CT was performed with a dual-source
128-section multidetector CT system
(Somatom Definition Flash; Siemens
Healthcare, Germany) by using a dualsource research protocol provided by the
manufacturer. Both x-ray tubes of the CT
system were operated simultaneously at
the same tube potential (120 kV) with
the following parameters: collimation,
Published online before print
10.1148/radiol.2015150849 Content code:
Radiology 2016; 279:297–305
Abbreviations:
BMI = body mass index
FBP = filtered back projection
ILD = interstitial lung disease
SAFIRE = sinogram-affirmed iterative reconstruction
Author contributions:
Guarantors of integrity of entire study, F.P., A.S.B., R.M.,
J.R., M.R.J.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript
drafting or manuscript revision for important intellectual
content, all authors; manuscript final version approval,
all authors; agrees to ensure any questions related to the
work are appropriately resolved, all authors; literature
research, F.P., A.S.B., J.R., M.R.J.; clinical studies, F.P.,
A.S.B., J.B.F., R.M., J.R., M.R.J.; statistical analysis, F.P.,
A.S.B., A.D.; and manuscript editing, F.P., A.S.B., B.S., E.H.,
J.R., M.R.J.
Conflicts of interest are listed at the end of this article.
See also the editorial by Fletcher et al and articles by
Solomon et al and Mileto et al in this issue.
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THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
64 3 2 3 0.6 mm with z-flying focal
spot; rotation time, 0.28 second; and
pitch, 2. The total reference milliampere
second was split between both x-ray
tubes in a way that 40% of the reference
milliampere second was applied to tube
A (44 mAs) and 60% of the reference
milliampere second was applied to tube
B (66 mAs) with a four-dimensional
dose modulation system (Care Dose 4D,
Siemens Healthcare). There were 43 unenhanced and 12 contrast material–enhanced CT examinations.
Image Reconstruction
Two sets of lung images were reconstructed from each acquisition. The
first set of images were standard-dose
images (group 1) consisting of 1-mmthick contiguous images reconstructed
with FBP by using a high-spatial-resolution kernel (B50). The images were
generated by combining data from both
tubes so that the resulting images used
the total applied reference milliampere
second, that is, 110 mAs. The second
set of images were reduced-dose images (group 2) consisting of 1-mm-thick
contiguous images reconstructed with
sinogram-affirmed iterative reconstruction (SAFIRE). The images were generated only with data from tube A, which
used 40% of the total applied reference
milliampere second and thus represent
images acquired with 60% dose reduction. The manufacturer designed the
iterative reconstruction kernel (I50) to
closely match the spatial resolution of
the corresponding FBP kernel (B50).
The modulation transfer functions of
both kernels are designed to be very
similar in terms of their characteristic
spatial frequencies—namely the 50%
value, 10% value, and 2% value. Images
were viewed by using standard lung parenchymal window settings (window
width, 1600 HU; window center, 2600
HU).
Analyzed Parameters
Population characteristics and radiation dose estimation.—We recorded
the patients’ age, weight, body mass
index (BMI), CT dose index, doselength product, and size-specific dose
estimate.
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n
Image noise.—The objective assessment of noise was performed by measuring the standard deviation of pixel
values in homogeneous regions of interest within the tracheal lumen above the
aortic arch. Circular regions of interest within the tracheal lumen (mean 6
standard deviation of the region of interest surface: 1.48 cm2 6 0.53; range:
0.69–3.10 cm2) were placed by one
reader (A.S.B.), a junior radiologist
with 3 years of experience in chest CT.
The visual perception of noise, defined by the grainy appearance of images, was independently evaluated by
the junior reader (A.S.B.) and a senior
reader (F.P., with 8 years of experience in chest CT) with use of a threepoint scale, as follows: 1 = minimal, 2
= moderate, and 3 = severe. A noise
level score of 1 or 2 indicated that the
noise did not alter the identification of
normal and/or abnormal structures. A
noise level score of 3 indicated that the
identification of normal and/or abnormal structures was altered.
Overall image quality.—The overall
image quality of group 1 and group 2 images was rated by the same individuals by
using a five-point scale (11), as follows: 1
= excellent, 2 = very good, 3 = satisfactory, 4 = suboptimal, and 5 = nondiagnostic. Scores of 1–3 indicated diagnostic
image quality; scores of 4 and 5 corresponded to nondiagnostic image quality.
Visualization of normal and abnormal lung structures.—The following
anatomic structures were analyzed: (a)
fissures; (b) proximal bronchi and adjacent pulmonary vessels (ie, structures
down to the subsegmental level, further
referred to as proximal bronchi and
vessels); (c) peripheral bronchi and adjacent pulmonary vessels (ie, structures
beyond the subsegmental level); and
(d) vascular structures located within
10 mm of the pleura, further referred
to as subpleural vessels (17).
The presence of five abnormal
structures was determined at a lobar
level, considering six lobes per patient
(namely the right upper, middle, and
lower lobes; left upper culmen; and lingula and lower lobes) and a total of 330
lobes in our study group. The following
five abnormal structures were analyzed:
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Pontana et al
(a) ground-glass opacities; (b) reticulations; (c) CT features of lung fibrosis,
including bronchiectasis and/or bronchiolectasis; (d) signs of architectural
distortion (on bronchi, vessels, fissures, and/or interlobular septa); and
(e) honeycombing.
The visibility of normal and abnormal lung structures was analyzed on all
images by using a five-point scale (18),
as follows: 1 = excellent image quality
with sharp demarcation of structures;
2 = slight blurring of the structures,
with unrestricted image evaluation; 3
= moderate blurring of the interface
structures, with slight restricted assessment; 4 = severe blurring and poorly
defined structures, with uncertainty
about the evaluation; and 5 = severely
reduced image quality, making reliable
interpretation impossible. The rating of
abnormal structures also included (a)
an additional score (score, 0) in the
absence of abnormal findings (18) and
(b) comparison of the visibility of the
five abnormal structures within the 330
lobes examined in our study group.
Lung infiltration quantification
scores.—Because image quality can influence the analysis of the extent and
severity of ILD, the study included the
evaluation of the coarseness score, as
described by Desai et al (6), and the
extent score, as described by Goh et
al (19), on the group 1 and group 2
images from each patient. Lung images
were scored at five levels: (a) origin of
great vessels, (b) main carina, (c) pulmonary venous confluence, (d) halfway
between the third and fifth sections,
and (e) immediately above the right
hemidiaphragm. As proposed by Desai et al (6), the coarseness of fibrosis
was quantified semiquantitatively as
follows: 0 = ground-glass opacification
alone, 1 = fine intralobular fibrosis,
2 = microcystic reticular pattern (ie,
airspaces 4 mm), and 3 = macrocystic reticular pattern (ie, airspaces .4
mm).The total coarseness score was
the summed score for all five levels
(range, 0–15). The total extent of ILD
was estimated at the nearest 5% in
each of the five sections, with global
extent of disease on lung images (ie,
Goh score) as the mean of the scores.
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THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
Conditions of Image Analysis
Images from groups 1 and 2 were anonymized and transferred to a clinical
workstation (Syngo CT Workplace,
Siemens Healthcare). Two readers
(A.S.B., F.P.) analyzed group 1 and
group 2 images from each patient in
random order while blinded to the reconstruction technique. This was possible because of the lack of pixilated and/
smooth appearance of images reconstructed with this second-generation
algorithm, a finding derived from our
daily use of SAFIRE on reduced-dose
chest CT examinations. After anonymization, the images from both groups
were randomized and mixed together.
The two types of images from one patient were not read at the same session.
Subjective noise, visibility of normal
and abnormal structures, and overall
image quality of group 1 and group 2
images were independently evaluated
by the two readers. Determination of
the coarseness and extent was obtained
by consensus between the two readers,
considering that the analysis of the effect of iterative reconstruction on the
extent and coarseness of ILD was a
secondary objective of this study. Measurement of objective image noise was
performed by one reader (A.S.B.). This
analysis had been undertaken before
the anonymization of images by positioning a circular region of interest at
the level of the trachea on group 1 and
group 2 images from each patient, both
being simultaneously available on the
workstation. This allowed the reader to
generate strictly similar regions of interest on both images for each patient.
Statistical Analysis
We did not calculate an a priori sample
size and decided to include all consecutive patients with systemic sclerosis
referred to our department during the
study period, that is, 55 patients. On
the basis of this study population, we
performed a post hoc power analysis
by calculating the smallest difference
(expressed as effect size by using the
standardized mean difference) that we
could detect with 80% power. The minimum effect size was 0.39, which was
considered moderate (20).
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Pontana et al
Table 1
Interobserver Agreement for Subjective Criteria Analysis
Parameter
Patient-based analysis (n = 55)*
Subjective noise
Overall image quality
Visibility of normal lung structures
Fissures
Proximal bronchi
Peripheral bronchi
Subpleural vessels
Lobar-based analysis (n = 330)†
Ground-glass opacities
Reticulation
Bronchiectasis and bronchiolectasis
Architectural distortion
Honeycombing
Group 1
Group 2
52 (94.5)
49 (89)
52 (94.5)
49 (89)
49 (89)
38 (69)
43 (78)
38 (69)
48 (87)
41 (74.5)
43 (78)
48 (87)
0.96
0.96
0.90
0.84
0.98
0.94
0.92
0.88
0.84
0.98
Note.—Group 1 = standard-dose images with FBP, group 2 = reduced-dose images with SAFIRE.
* Data are numbers of patients (n = 55), with percentages in parentheses, and are the concordance rate.
†
Data represent the visibility of the abnormal structures and are k values.
Statistical analyses were performed
by using software (SAS, version 9.3;
SAS Institute, Cary, NC). Results were
compared by using the Wilcoxon test
for paired samples. The 95% confidence interval was described when appropriate. The interobserver agreement
was expressed with a concordance
rate for the patient-based analysis and
with a weighted k value for the lobarbased analysis. The k coefficients were
interpreted as follows: less than 0, disagreement; 0.0–0.20, slight agreement;
0.21–0.40, fair agreement; 0.41–0.60,
moderate agreement; 0.61–0.80, good
agreement; and 0.81–1.00, almost perfect agreement (21). P , .05 was indicative of a statistically significant difference.
Results
Characteristics of the Study Population
The mean age (6standard deviation) of
the study population was 55.8 years 6
13.8 (range: 23–82 years), with a female
(38 women, 17 men) and nonsmoker (31
nonsmokers, 24 active or ex-smokers)
predominance. On the basis of clinical
findings, systemic sclerosis was limited in
38 of the 55 patients (69%) and diffuse
in 17 (31%). The mean duration of the
disease at the time of CT examination
was 7.6 years (range: 0.1–31 years; median, 5 years). The mean BMI was 27.2
kg/m2 6 5.8 (range, 16.9–37.8 kg/m2).
Two patients were underweight (BMI
,18.5 kg/m2), 20 were within the normal range (BMI, 18.5–24.9 kg/m2), 13
were overweight (BMI, 25–29.9 kg/m2),
and 19 were obese (BMI .30 kg/m2).
Results of pulmonary function tests,
expressed as mean percentages (6standard deviations) of predicted values,
were within normal limits except for
diffusing capacity of lung for carbon
monoxide. Results are as follows : (a)
total lung capacity, 87.7% 6 20.4; (b)
forced vital capacity, 91.5% 6 23; (c)
forced expiratory volume in 1 second,
85.5% 6 19.5; (d) ratio of forced expiratory volume in 1 second to vital
capacity, 78.7% 6 8.8; and (e) diffusing capacity of lung for carbon monoxide, 53.5% 6 22.4. The population
comprised 35 patients with diffusing
capacity of lung for carbon monoxide
less than 70% predicted, 10 with forced
expiratory volume in 1 second less than
70% predicted, and 11 with total lung
capacity less than 70% predicted.
CT features of lung infiltration were
present in 38 of the 55 patients (69%)
and included ground-glass opacities in 38
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THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
patients (69%), reticulation in 38 (69%),
bronchiectasis and/or bronchiolectasis in
27 (49%), architectural distortion in 27
(49%), and honeycombing in 17 (31%).
The mean number of lobes with abnormal CT features was 5.2 6 1.4 (range:
2–6), and the mean number of abnormal CT features per lobe was 3.3 6 1.5
(range: 1–5). The mean dose-length
product of CT examinations was 216.09
mGy · cm 6 58.83 (range: 118–343
mGy · cm). The mean size-specific dose
estimate was 9.94 mGy 6 3.62 (range:
4.98–25.52 mGy). The mean effective
dose, calculated by multiplying the doselength product by a conversion factor of
0.017 (22), was 3.67 mSv 6 1.00 (range:
2.01–5.83 mSv). In group 2, the theoretical mean dose-length product was 86.44
mGy · cm (range: 48.8–208.8 mGy ·
cm), which corresponds to a mean effective dose of 1.8 mSv.
Interobserver Agreement for Subjective
Analysis
Concordance rates were similar between groups 1 and 2 for subjective
noise analysis and overall image quality
and higher in group 2 for the visibility of proximal bronchi and subpleural
vessels, whereas they were similar for
peripheral bronchi in both groups and
inferior for fissure analysis in group 2
(Table 1). The interobserver agreement
was excellent for the analysis of abnormal lung structures (k: 0.84–0.98).
Noise and Overall Image Quality
The mean level of objective noise in
group 2 images was significantly lower
than that in group 1 images (P , .0001,
Table 2). There was no significant difference in the distribution of subjective
noise scores between the two groups,
which was mainly rated as moderate (94%) in both groups and never
downgraded in group 2 compared with
group 1 images. There was no significant difference in the distribution of
image quality scores between the two
groups, with images classified as very
good (score, 2) for 52 of 55 patients
in group 1 (94.5%) and 49 of 55 patients in group 2 (89%); the proportion
of images with excellent image quality
(score, 1) was higher in group 2 (four
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Table 2
Comparison of Noise and Image Quality between Groups 1 and 2
Parameter
Objective noise (HU)
Mean
Range
Median
Subjective noise
Minimal (score, 1)
Moderate (score, 2)
Severe (score, 3)
Overall image quality
Excellent (score, 1)
Very good (score, 2)
Satisfactory (score, 3)
Suboptimal (score, 4)
Nondiagnostic (score, 5)
Group 1
Group 2
26.23 6 9.40
15.6–52.4
22.6
22.02 6 6.95
13.2–44
19.6
2 (3.6)
52 (94.5)
1 (1.8)
3 (5.5)
52 (94.5)
0
1 (1.8)
52 (94.5)
2 (3.6)
0
0
4 (7.3)
49 (89)
2 (3.6)
0
0
P Value
,.0001
NA
NA
Note.—Except where indicated, data are numbers of patients (n = 55), with percentages in parentheses. Group 1 = standarddose images with FBP, group 2 = reduced-dose images with SAFIRE. NA = not applicable.
Table 3
Comparison of Normal Lung Structure Visibility between Groups 1 and 2
Parameter
Fissures
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Proximal bronchi and vessels
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Peripheral bronchi and vessels
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Subpleural vessels
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Group 1
Group 2
5 (9.1)
49 (89.1)
1 (1.8)
0
0
7 (12.7)
47 (85.5)
1 (1.8)
0
0
7 (12.7)
47 (85.5)
1 (1.8)
0
0
10 (18.2)
45 (81.8)
0
0
0
2 (3.7)
52 (94.5)
1 (1.8)
0
0
7 (12.7)
47 (85.5)
1 (1.8)
0
0
1 (1.8)
50 (90.9)
4 (7.3)
0
0
2 (3.7)
51 (92.6)
2 (3.7)
0
0
Note.—Data are numbers of patients (n = 55), with percentages in parentheses. Group 1 = standard-dose images with FBP,
group 2 = reduced-dose images with SAFIRE.
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THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
of 55 patients, 7.3%) than in group 1
(one of 55 patients, 1.8%). A single set
of group 2 images was rated with lower
image quality (score, 3) compared with
the corresponding group 1 set of images
(score, 2) (one of 55 patients, 1.82%
[95% confidence interval = 0.05%,
9.72%]). No series of images was classified as having suboptimal (score, 4) or
nondiagnostic (score, 5) image quality.
Visualization of Normal and Abnormal
Lung Structures
There was no difference between groups
in the distribution of conspicuity scores
of normal lung structures (Table 3).
Most structures were given a score of 2
in both groups; there was a higher proportion of scores of 1 in group 2 than
in group 1 and no scores of 4 or 5 in
either group.
There was no significant difference
in the distribution of scores with regard
to the visibility of abnormal lung structures (Table 4). Most CT features were
given a score of 2 in both groups. Except
for the honeycombing, which received
a similar rating for both groups, there
was a higher proportion of scores of 1 in
group 2 than in group 1 (Figs 1–4).
Extent of ILD
Because the coarseness score was
based on the analysis of five sections
per patient, a total of 275 sections were
analyzed in the study group; 164 of the
275 sections (60%) had signs of infiltration in groups 1 and 2. There was no
difference in the mean coarseness score
between the two groups (group 1: mean
= 6.34 6 3.17, range = 0–12, median =
5; group 2: mean = 6.29 6 3.17, range
= 0–12, median = 5). The extent score
was similar in both groups: 39 of the 55
patients (70.9%) had lung infiltration of
less than 20% and 16 (29.1%) had lung
infiltration of more than 20%.
Discussion
The results of our study showed no significant difference in the distribution of
overall image quality scores between
our two groups. All series of images
were rated with a diagnostic image
quality—even those in group 2, which
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Pontana et al
Table 4
Comparison of Abnormal Lung Structure Visibility between Groups 1 and 2
Parameter
Ground-glass opacity
Absent (score, 0)
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Reticulation
Absent (score, 0)
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Bronchiectasis and bronchiolectasis
Absent (score, 0)
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Honeycombing
Absent (score, 0)
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Architectural distortion
Absent (score, 0)
Sharp delineation (score, 1)
Slight blurring (score, 2)
Moderate blurring (score, 3)
Severe blurring (score, 4)
Unreliable analysis (score, 5)
Group 1
Group 2
127 (38.5)
4 (1.2)
199 (60.3)
0
0
0
127 (38.5)
14 (4.2)
189 (57.3)
0
0
0
143 (43.3)
4 (1.2)
183 (55.5)
0
0
0
143 (43.3)
14 (4.2)
173 (52.4)
0
0
0
188 (57.0)
4 (1.2)
134 (40.6)
4 (1.2)
0
0
188 (57.0)
7 (2.1)
130 (39.4)
5 (1.5)
0
0
244 (73.9)
0
82 (24.8)
3 (0.9)
0
0
244 (73.9)
0
82 (24.8)
3 (0.9)
0
0
186 (56.4)
3 (0.9)
138 (41.8)
3 (0.9)
0
0
186 (56.4)
8 (2.4)
131 (39.7)
5 (1.5)
0
0
Note.—Data are numbers of lobes (n = 330), with percentages in parentheses. Group 1 = standard-dose images with FBP, group
2 = reduced-dose images with SAFIRE.
were generated with a 60% dose reduction corresponding to a mean effective
dose of 1.8 mSv. A higher proportion of
images were rated with excellent image
quality in group 2 than in group 1 that
is likely to be linked to the significantly
lower noise level, a major factor in the
analysis of subjective image quality
(23). Our findings are consistent with
those of Baumueller et al (24), who reported a significant reduction in image
noise on submillisievert images reconstructed with SAFIRE compared with
standard-dose images with FBP. In contrast to studies performed with the first
generations of iterative reconstruction
(9,11), we did not observe a pixelated
and/or smoothed appearance for images reconstructed with SAFIRE.
With regard to the visibility of CT
features of systematic sclerosis–related
ILD, there was no significant difference
in the distribution of ratings between the
two groups. The extent of disease and the
severity of lung infiltration, as assessed
with the coarseness and extent scores,
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THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
Figure 1
Figure 1: Transverse CT scans obtained in lower lung zones (magnified view of right lower lobe) in
27-year-old patient with normal BMI (23.8 kg/m2). Subpleural ground-glass opacity with fine reticulation
was given a similar rating (score, 2) on (a) standard-dose image reconstructed with FBP and (b) reduceddose image reconstructed with SAFIRE. Objective noise was 17.8 HU on group 1 images and 17.2 HU on
group 2 images.
Figure 2
Figure 2: Transverse CT scans obtained in lower lung zones (magnified view of right lower lobe) in
65-year-old patient with normal BMI (23.4 kg/m2). Ground-glass opacity of low attenuation, which is diffusely
distributed in lower lobe and disseminated in right middle lobe, was given a similar rating (score, 2) on
(a) standard-dose image reconstructed with FBP and (b) reduced-dose image reconstructed with SAFIRE.
Objective image noise was lower in group 2 images (16.8 HU) than in group 1 images (17.4 HU).
did not significantly differ between the
two groups. These results demonstrate
the effectiveness of SAFIRE in restoring
a diagnostic image quality of reduceddose acquisitions. In a recent study performed to evaluate the ability of low-dose
CT to depict and help characterize the
most common patterns of pulmonary
disease, Christe et al (8) reported a 20%
Radiology: Volume 279: Number 1—April 2016
n
decrease in sensitivity but also a drift
in recognition of faint abnormalities on
images reconstructed with FBP instead
of iterative reconstruction. Because
honeycombing is known to be detectable even on grainy images (8), it was
not surprising to observe similar ratings
in our two groups. More interesting to
note was the higher scores of excellent
radiology.rsna.org
Pontana et al
visibility observed in group 2 for the
other subtle interstitial patterns. These
results are consistent with the improved
depiction of ground-glass opacities, pulmonary nodules, and emphysema previously reported with the first generation
of iterative reconstruction compared
with FBP (9). They also confirm in vivo
the results recently reported in an experimental study concerning the detection
of ground-glass nodules (25). They are
comparable to the excellent intermethod
agreement demonstrated by Ohno et al
(16) for the detection of emphysema,
ground-glass opacities, bronchiectasis, honeycombing, and nodules when
reduced-dose images are reconstructed
with iterative reconstruction. The absence of negative effect of iterative reconstruction on the detection of groundglass opacities is particularly important
for systematic sclerosis when keeping
in mind that it may reflect not only the
presence of interstitial inflammation but
also fibrotic changes (26). The excellent
interobserver agreement observed in our
study is in keeping with that reported by
Baumueller et al (24) in a wide variety
of chest diseases and should be linked to
the low level of image noise (27).
Our study design provided a means
of comparing image quality on full-dose
and reduced-dose images for each patient. This situation is more appropriate
for image quality analysis than is relying
on the comparison of distinct groups of
patients. Although often paired according to BMI, populations may differ in
chest dimension, degree of inspiration,
and/or underlying disorders that may affect comparative analysis of image quality. Our approach also allows more accurate intertechnique comparison because
the whole lung volume is analyzed on the
two sets of images. This is more robust
than the methodology proposed by Sverzellati et al (28), who added three CT
sections acquired at reduced dose to a
standard-dose study covering the whole
chest volume. Iterative reconstructions
are expected to influence the dose reduction strategy that can be proposed
to patients with systematic sclerosis–related ILD. The similarities in radiation
dose levels reported in our study (1.8
mSv in group 2) and with sequential
303
THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
Pontana et al
Figure 3
Figure 3: Transverse CT scans obtained in lower lung zones (magnified view of right lower lobe) in
66-year-old overweight patient (BMI: 26.2 kg/m2). CT features of lung fibrosis in right middle lobe and right
lower lobe are ground-glass opacities of high attenuation, traction bronchiolectasis, and fissural distortion.
Visibility scores of individual CT features were worse on (a) standard-dose image reconstructed with FBP
(ground-glass opacity: score, 2; traction bronchiolectasis: score, 2; distortion: score, 2) than on (b) reduceddose images reconstructed with SAFIRE (ground-glass opacity: score, 1; bronchiolectasis: score, 1; distortion:
score, 1). Objective noise was lower in group 2 images (17.4 HU) than in group 1 images (19.6 HU).
Figure 4
Figure 4: Transverse CT scans obtained at level of right inferior pulmonary vein (magnified view centered
on right lung) in 47-year-old obese patient (BMI: 31.3 kg/m2). CT features of lung fibrosis were traction
bronchiectasis in right middle lobe and microcystic changes, reticulation, and signs of distortion in right lower
lobe, with concurrent presence of mild ground-glass opacities in both lobes. Visibility scores of individual
CT features were identical for both (a) standard-dose image reconstructed with FBP and (b) reduced-dose
image reconstructed with SAFIRE (traction bronchiectasis: score, 1; microcystic changes suggestive of honeycombing: score, 2; reticulation: score, 2; distortion: score, 2). Objective noise was lower in group 2 images
(24.1 HU) than in group 1 images (28.8 HU).
scanning (1.6 mSv) strongly favor reduced-dose volumetric acquisitions with
images reconstructed with iterative
304
reconstruction instead of sequential
scanning at 10-mm intervals with images reconstructed with FBP (29). This
approach can be extended to the entire
spectrum of ILDs because it allows a
more comprehensive assessment than
that provided by a reduced number of
sections (30). This approach should also
facilitate quantitative assessment of ILD,
which is useful for screening but also for
longitudinal monitoring (28,31–33).
Our study has some limitations.
With regard to the scanning parameters,
we used the same kilovoltage and same
reference milliampere second for all patients regardless of their BMI. Although
this had no adverse consequence for thin
patients, it could have been responsible
for high noise levels in obese patients–especially with reduced-dose images. This
limitation was partly compensated for by
the systematic use of automatic tube current modulation but could not be avoided
because of our study design. Second, the
study population was composed of only
55 patients, a situation linked to the low
prevalence of this disease and the limited
availability of the research prototype.
Third, we should underline that 12 chest
CT examinations were performed after
injection of contrast material, which may
influence the assessment of ground-glass
opacity on lung images (34). Fourth, a
limitation related to the power of the
study must be underlined. We cannot exclude that some differences between the
two groups could have been overlooked
because of the effect size. However, results of post hoc analysis showed that a
moderate range of differences between
the two techniques was accessible, thus
limiting the risks of overestimation of the
effect of iterative reconstructions. Fifth,
one should underline a limitation of the
subjective scoring system used. The use
of a five-point scale may have obscured
small image quality differences between
the two series of images. Last, the CT
features studied did not include all categories of lung abnormalities that can
be encountered in respiratory diseases.
However, the absence of a negative effect of iterative reconstruction for the
depiction of subtle lesions suggests that
similar conclusions could be drawn for
more severe forms of infiltration and/or
pulmonary destruction.
Despite a 60% dose reduction,
SAFIRE allows evaluation of systematic
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Radiology: Volume 279: Number 1—April 2016
THORACIC IMAGING: Detection of Systemic Sclerosis–related Interstitial Lung Disease
Pontana et al
sclerosis–related ILD on reduced-dose
images as accurate as that provided by
standard-dose images reconstructed
with FBP.
10. Pontana F, Pagniez J, Flohr T, et al. Chest
computed tomography using iterative reconstruction vs filtered back projection. I.
Evaluation of image noise reduction in 32
patients. Eur Radiol 2011;21(3):627–635.
23. Mayo JR, Hartman TE, Lee KS, Primack SL,
Vedal S, Müller NL. CT of the chest: minimal tube current required for good image
quality with the least radiation dose. AJR
Am J Roentgenol 1995;164(3):603–607.
Disclosures of Conflicts of Interest: F.P. disclosed no relevant relationships. A.S.B. disclosed no relevant relationships. A.D. disclosed
no relevant relationships. B.S. Activities related
to the present article: disclosed no relevant relationships. Activities not related to the present
article: is an employee of Siemens Healthcare.
Other relationships: disclosed no relevant relationships. J.B.F. disclosed no relevant relationships. E.H. disclosed no relevant relationships.
R.M. disclosed no relevant relationships. J.R.
disclosed no relevant relationships. M.R. disclosed no relevant relationships.
11. Prakash P, Kalra MK, Ackman JB, et al.
Diffuse lung disease: CT of the chest with
adaptive statistical iterative reconstruction
technique. Radiology 2010;256(1):261–269.
24. Baumueller S, Winklehner A, Karlo C, et al.
Low-dose CT of the lung: potential value of
iterative reconstructions. Eur Radiol 2012;
22(12):2597–2606.
12. Higuchi K, Nagao M, Matsuo Y, et al. Detection of ground-glass opacities by use of
hybrid iterative reconstruction (iDose) and
low-dose 256-section computed tomography: a phantom study. Radiol Phys Technol
2013;6(2):299–304.
25. Christe A, Lin MC, Yen AC, et al. CT patterns
of fungal pulmonary infections of the lung:
comparison of standard-dose and simulated
low-dose CT. Eur J Radiol 2012;81(10):2860–
2866.
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