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Erschienen in: The International Journal of Cardiovascular Imaging 6/2017

Open Access 19.01.2017 | Original Paper

Influence of dose reduction and iterative reconstruction on CT calcium scores: a multi-manufacturer dynamic phantom study

verfasst von: N. R. van der Werf, M. J. Willemink, T. P. Willems, M. J. W. Greuter, T. Leiner

Erschienen in: The International Journal of Cardiovascular Imaging | Ausgabe 6/2017

Abstract

To evaluate the influence of dose reduction in combination with iterative reconstruction (IR) on coronary calcium scores (CCS) in a dynamic phantom on state-of-the-art CT systems from different manufacturers. Calcified inserts in an anthropomorphic chest phantom were translated at 20 mm/s corresponding to heart rates between 60 and 75 bpm. The inserts were scanned five times with routinely used CCS protocols at reference dose and 40 and 80% dose reduction on four high-end CT systems. Filtered back projection (FBP) and increasing levels of IR were applied. Noise levels were determined. CCS, quantified as Agatston and mass scores, were compared to physical mass and scores at FBP reference dose. For the reference dose in combination with FBP, noise level variation between CT systems was less than 18%. Decreasing dose almost always resulted in increased CCS, while at increased levels of IR, CCS decreased again. The influence of IR on CCS was smaller than the influence of dose reduction. At reference dose, physical mass was underestimated 3–30%. All CT systems showed similar CCS at 40% dose reduction in combinations with specific reconstructions. For some CT systems CCS was not affected at 80% dose reduction, in combination with IR. This multivendor study showed that radiation dose reductions of 40% did not influence CCS in a dynamic phantom using state-of-the-art CT systems in combination with specific reconstruction settings. Dose reduction resulted in increased noise and consequently increased CCS, whereas increased IR resulted in decreased CCS.
Abkürzungen
CCS
Coronary calcium score
CT
Computed tomography
FBP
Filtered back projection
HA
Hydroxyapatite
HU
Hounsfield units
IR
Iterative reconstruction

Introduction

The coronary calcium score (CCS) is known to be a strong predictor for major adverse cardiovascular events [1, 2]. Computed tomography (CT) is the first modality of choice for assessment of the presence and quantification of calcium in the coronary arteries. The number of CCS examinations with CT is expanding rapidly [3]. However, due to the expanding use of ionizing radiation in medicine, CT has become the main source of increased population dose in Western countries [4]. This dose issue is especially important when considering the 2013 guidelines from the American Heart Association that recommend CCS measurements if, after quantitative risk assessment, the risk-based treatment decision is uncertain in asymptomatic adults at intermediate and low-to-intermediate risk [5].
Recently, iterative reconstruction (IR) has become widely available on commercially available CT systems. IR allows for a dose reduction without the typical decrease in image quality [68]. It may therefore be possible to quantify CCS at lower dose levels, when using IR. Recent studies found that application of IR can result in spurious decreases in CCS in comparison with conventionally used filtered back projection (FBP) [911]. These effects of dose reduction and IR on CCS can be explained by their effect on image noise. At decreased dose an increase in noise is expected. This increase in noise can be associated with an increase in voxels above the calcium threshold of 130 Hounsfield Units (HU), which in turn increases CCS. Conversely, a decrease in CCS is expected with IR since it reduces noise [1215].
Moreover, cardiac motion imposes problems for the stability of CCS since calcium can be blurred and CCS can be over- or underestimated, depending on the density of the calcification [1618]. The combined effects of dose reduction, IR and heart rate on CCS for all major manufacturers have not been investigated before in a phantom study.
Therefore, the objective of this study was to evaluate the influence of dose reduction in combination with IR on CCS of moving calcifications in coronary CT on state-of-the-art CT systems from different manufacturers.

Materials and methods

An anthropomorphic chest phantom (Thorax, QRM, Moehrendorf, Germany) with artificial lungs, a spine insert and a shell of soft tissue equivalent material was used [16, 17]. An extension ring of tissue equivalent material was placed around the chest to simulate an averaged sized patient of 400 × 300 mm (QRM-Extensionring, QRM, Germany) [19]. The center compartment of the phantom was filled with water in which a motion simulator (Sim2D, QRM, Moehrendorf, Germany) translated an artificial coronary artery with two calcium hydroxyapatite (HA) inserts. The inserts had densities of 196 ± 3, 380 ± 2, 408 ± 2 and 800 ± 2 mg HA/cm3 and masses of 38.5 ± 1.7, 74.6 ± 3.1, 80.1 ± 3.3 and 157.1 ± 6.5 mg HA, respectively (Appendices 2, 3).
All inserts had equal dimensions; length 10.0 ± 0.1 mm, diameter 5.0 ± 0.1 mm, volume 196.3 ± 8.1 mm3. The artificial arteries were linearly translated in the horizontal plane at a velocity of 20 mm/s perpendicular to the scan direction. This velocity is comparable to typical velocities of the left anterior descending and right coronary arteries during the late diastolic scan phase of the R-R interval, at heart rates between 60 and 75 bpm [20, 21].
In order to assess the influence of IR and dose reduction on CCS in a clinical setting, daily used clinical CT protocols for coronary calcium scoring were used. These protocols were equal to the vendor recommended protocols if available or were adapted based on recommendation by the specific manufacturer consultants. Four different state-of-the-art CT systems (referred to as S1–S4) were used: Discovery CT 750 HD (GE Healthcare, Waukesha, Wisconsin, USA), Brilliance iCT (Philips Healthcare, Best, The Netherlands), Somatom Definition Flash (Siemens Healthcare, Forchheim, Germany) and Aquilion One (Toshiba Medical Systems, Otawara, Japan), respectively (Table 1).
Table 1
Acquisition and reconstruction parameters used on CT system S1–S4
CT system
S1
S2
S3
S4
Tube voltage (kV)
120
120
120
120
Tube charge per rotation (mA)
500
185
285
230
Collimation (mm)
64  ×  0.625
128  ×  0.625
128 ×  0.6
320 ×  0.5
Rotation time (s)
0.35
0.27
0.28
0.35
Temporal resolutiona (ms)
175
135
75
175
Slice thickness (mm)
2.5
3.0
3.0
3.0
Increment (mm)
2.5
3.0
3.0
3.0
Kernel
Standard
XCA
B35f
FC12
Levels of IR
20, 60, 100%
1, 5, 7
1, 3, 5
weak, standard, strong
Noise level (HU)
26
22
28
24
CTDIvol (mGy)
10.6
3.2
2.8
6.5
Software
Smartscore 4.0
Heartbeat-CS
Syngo
Vitrea FX 6.5.0
aAs defined in the isocenter
The phantom was scanned at three dose levels by reduction of the tube current: a reference dose at 100% tube current, and at reduced dose levels of 40 and 80% reduced tube current. Each scan was repeated five times with a small translation (2 mm) and rotation (2°) between each scan by manually repositioning the phantom. The internal ECG signal of the motion controller was used to simulate the heart rate of the patient and used as ECG trigger on all four CT systems. The triggering was carefully timed so that data acquisition was during linear motion of the phantom.
Images were reconstructed with FBP, and three increasing levels of IR: the lowest (L1), an intermediate (L2) and the highest level available on the CT system (L3) (Table 1). For each data set the noise level in the images was assessed by calculating the standard deviation in the average Hounsfield value in a uniform water region. The amount of calcium of each insert was quantified as Agatston and mass scores with manufacturer-recommended software (Table 1) with a default threshold of 130 Hounsfield units (HU). A semi-automatic method was used for selecting the calcification by one observer. On each CT system, the mass score calibration factors were determined as described by McCollough et al. [19]. Although mass scores are not used clinically, they were included for this study because of its potential to compare the score to the physical mass.
The design of this study resulted in 480 calcium scores per CT system (5 acquisitions at 3 dose levels with 4 reconstruction types for 4 calcifications and 2 calcium scores).
Agatston score and mass score were expressed as median and 25th–75th percentile for each calcification insert and CT system. For each insert, CCS from both the iteratively reconstructed and FBP reconstructed data sets for reduced dose levels were compared to the CCS from the FBP reconstructed data sets at reference dose using a Wilcoxon signed rank test. All statistical analyses were performed with SPSS for Windows, version 22.0. A p value of 0.05 was used to determine significant differences.

Results

Influence of dose reduction and iterative reconstruction on noise

For all CT systems and all reconstructions, a decrease in dose resulted in a vendor dependent increase in noise, whereas IR led to a decrease in noise (Fig. 1). Also, although the CTDIvol differed at most with a factor of 3.8 between the CT systems, the noise levels varied less than 18% at FBP reference dose.

Influence of dose reduction on Agatston score with FBP

Dose reduction resulted in significant increases in Agatston scores for almost all calcifications and CT systems (Fig. 2). This increase, in combination with an increase in noise, is depicted in the top row of Fig. 3.
For S1 at FBP and averaged over all inserts, Agatston scores increased by 8 and 25% at 40 and 80% reduced dose respectively. For the other CT systems similar increases in Agatston scores at FBP were observed at reduced dose with a corresponding average increase of 7 and 64% for S2, 4 and 26% for S3, and 1 and 23% for S4. The largest increase in Agatston score at reduced dose was observed for the 38 mg insert at 80% dose reduction: 58, 160, 48, and 71 for S1–S4, respectively.

Influence of dose reduction on mass score with FBP

Also, dose reductions resulted in significantly increased mass scores at FBP for almost all inserts and CT systems, albeit that the increase was smaller than the increase in Agatston scores (Fig. 4).
At 40% reduced dose, mass scores increased on average by 0, 3, 1 and 0% for S1–S4 respectively in comparison with the mass score at reference dose. At 80% reduced dose, mass scores increased 35, 15 and 13% for S2–S4, whereas for S1 the mass score decreased 11%.

Influence of iterative reconstruction on Agatston scores

With increased IR levels, a significant decrease in Agatston scores was observed for almost all calcifications and CT systems (Fig. 5). This decrease in Agatston score was accompanied by decrease in noise, as can be seen from the left column in Fig. 3.
Averaged over all inserts, Agatston scores for S1 decreased on average 0, 2 and 5% at L1–L3 respectively. For S2 the corresponding decrease was 1, 4, and 5%; for S3 1, 4, and 9% and for S4 1, 4, and 7%. The largest decrease in Agatston score was again observed for the 38 mg calcification: 22% with L3 on S3, and 19% with L3 on S4.

Influence of iterative reconstruction on mass scores

The decrease in mass scores at increased levels of IR was smaller than the observed decrease in Agatston scores (Fig. 6). Mass score decreased on average between 0 and 6% for all CT systems and inserts.

Combination of dose reduction and iterative reconstruction on Agatston and mass scores

Representative images of the reconstructed datasets are shown in Fig. 3.
For all four CT systems 40% dose reduction in combination with varying levels of IR did not result in significantly different Agatston and mass scores with respect to the reference dose (Table 2). For 80% dose reduction, only S2 in combination with L2 and L3 did not result in significantly different Agatston scores. For the other CT systems, there was no combination of investigated imaging parameters that resulted in Agatston scores which were unchanged from the reference protocol and dose.
Table 2
Reconstructions per CT system S1–S4 that did not result in significantly different Agatston and mass scores at 60–75 bpm and at a dose reduction of 40 and 80% with respect to the FBP-reference dose
CT system
Dose reduction (%)
Agatston score
Mass scores
S1
40
L1
FBP, L1
 
80
n/a
n/a
S2
40
FBP, L1, L2, L3
FBP, L1, L2, L3
 
80
L2, L3
L1
S3
40
FBP, L1, L2
FBP, L1, L2, L3
 
80
n/a
L2, L3
S4
40
FBP
FBP
 
80
n/a
n/a
FBP  filtered back projection, L1, L2, L3 increasing levels of iterative reconstruction
On all CT systems, mass scores generally underestimated the physical mass of the calcifications. Mass scores at FBP and reference dose and deviations from the physical mass are listed in Table 3. Averaged over all inserts the physical mass was underestimated by 23, 12, 30, and 3% for S1–S4 respectively. The largest underestimation was again observed for the 38 mg insert, where the underestimation was 39, 33, 30, and 31%, respectively for S1–S4. At 40% reduced dose the underestimation was 24, 9, 29, and 3%. At 80% reduced dose the underestimation was 24 and 29% on S1 and S3, whereas S2 and S4 showed an overestimation of on average 16 and 9%. The influence of IR on mass scores was relatively small compared to the influence of dose reduction. At the maximum IR level, the underestimation of the physical mass at reference dose was 23, 15, 32, and 8% for S1–S4, respectively (averaged over all inserts).
Table 3
Physical mass and corresponding mass scores for all CT systems and calcification masses
CT system
Physical mass (mg)
Mass score (mg)
Deviation (%)
S1
38
23 (20–26)
−39 (−47; −32)
 
74
58 (54–62)
−22 (−27; −16)
 
80
70 (60–78)
−13 (−25; −3)
 
157
125 (108–138)
−20 (−31; −12)
S2
38
25 (22–26)
−33 (−43; −31)
 
74
63 (59–68)
−15 (−20; −8)
 
80
76 (75–79)
−5 (−6; −1)
 
157
165 (161–175)
5 (3; 11)
S3
38
20 (16–22)
−46 (−57; −42)
 
74
49 (47–53)
−34 (−37; −28)
 
80
62 (59–65)
−23 (−26; −19)
 
157
131 (128–136)
−17 (−19; −13)
S4
38
26 (23–29)
−31 (−40; −24)
 
74
69 (66–72)
−7 (−11; −3)
 
80
86 (80–94)
7 (0; 18)
 
157
188 (186–191)
20 (19; 21)
The mass scores are expressed as median and range
The difference between the median and physical mass is also given as median and range

Discussion

To our knowledge this is the first multivendor study to evaluate the effects of dose reduction and IR on CCS in a dynamic phantom. We have shown that dose reduction in dynamic coronary calcium CT can result in a substantial increase in CCS, whereas the use of IR results in modestly decreased CCS. The most important clinically relevant finding is the ability to reduce dose by 40% in routinely used clinical protocols on state-of-the-art CT systems of four major manufacturers, without compromising the calcium score. This result is not only valid for high plaque burden, but also for the clinically more important mild to moderate coronary plaque burden, represented by the 38 and 74 mg calcifications respectively.
Since risks of radiation dose increase with growing numbers of CT examinations, dose reduction techniques in CCS are highly relevant. Because new guidelines recommend CCS measurements if, after quantitative risk assessment, the risk-based treatment decision is uncertain, it is expected that the number of CT examinations for CCS will further increase in coming years [5]. In the current study we found for all CT systems that dose reductions of 40%, in combination with the in Table 2 specified reconstruction methods, did not significantly affect Agatston scores. For one vendor, the Agatston scores were even similar at 80% reduced dose, and for two vendors there was no significant difference in mass scores at 80% reduced dose in combination with IR.
These results are consistent with those of Hecht et al. [15] who showed in a patient study that for one CT system (equal to S2) CCS can be performed at reduced radiation dose (50%) in combination with IR, without significantly affecting Agatston scores [15]. Ode et al. showed, for a pulsating phantom at 60 bpm and one CT system (similar to S4), that increased IR resulted in decreased Agatston scores, which is in agreement with our results [22]. In comparison with full dose FBP, Agatston scores were not influenced at IR levels L2 and L3 in combination with dose reduction up to 75%, for all used calcifications combined. In our study however, Agatston scores at 40 and 80% reduced dose were found to be significantly different for all IR levels. The reason for this difference is that we only included combinations of dose reduction and IR, when valid for all calcifications separately. Our results also correspond well with a recent study which showed that IR has the potential to reduce radiation dose with 27–54% using a non-dynamic phantom and the same CT systems [23]. With non-dynamic ex vivo human hearts it was shown that a dose reduction of 80% was possible for the four CT systems [23, 24]. This study, however, used static calcifications, did not report on a reference standard of true calcification mass, and used a small-sized phantom. In our dynamic study, we found that a dose reduction of 80% was only feasible for one CT system, and a dose reduction of 40% was possible for all four CT systems, even for low-density calcifications in combination with specific reconstruction methods. Because iterative CT reconstruction significantly reduces calcium scores [10, 25], which potentially alters perceived cardiovascular risk [26], this effect may be counter balanced by the use of reduced dose levels. Moreover, it has been shown that the application of IR significantly improves objective image quality [12], and does not alter quantitative analysis of coronary plaque volume, composition and luminal area [27].
Our results showed a relatively large variation in calcium scores between the CT systems, with Agatston scores ranging from 450 to 738, for the 157 mg calcification. This is in line with previous studies that found that state-of the-art CT scanners of different manufacturers produce substantially different Agatston scores, which can result in reclassification of patients to high- or low-risk categories in up to 6.5% of the cases [28]. Moreover, mass scores generally underestimated the physical mass of the inserts by 3–23% depending on the specific CT system. Underestimations of the physical mass up to 68% were also observed with a static calcium phantom [29].
Reference dose levels, from routinely used clinical protocols of the four high-end CT systems, showed large differences (2.8–10.6 mGy). Despite of these differences in dose levels, similar noise levels were found (22–28 HU). It is important to note, however, that noise is not only determined by dose, but—among other parameters—also by reconstruction kernel. A sharper kernel results in more noise as compared to a softer kernel, if the dose levels are the same. Therefore, different CT acquisition and reconstruction settings may result in different dose levels but similar noise levels. The noise levels behaved as expected as a function of dose reduction and IR: noise levels increased at decreasing dose, and noise levels decreased at increased IR. Our findings indicate that even in the presence of comparable noise levels CCS differed up to 39% between different CT systems at full dose FBP. These differences are surprising for a relatively straightforward metric as the coronary calcium score.
This study has limitations. First, this was an in-vitro study with artificial arteries with calcified inserts. However, the inserts where embedded in an anthropomorphic phantom and were translated at a velocity that is generally observed in in-vivo studies, and the masses of the inserts were in range with calcium masses clinically detected in patients [30]. Second, movement of the calcifications was linear. In vivo, coronary arteries perform a complex movement in three dimensions, which was not feasible in our setup. However, because a linear movement can approximate the movement in 3D during the acquisition time of the CT data, we estimate that addition of 3D movement would result in minor changes in our results. Third, analysis on the inter and intra variability for the different CT systems has not been performed. The associated CT specific correlation between noise reduction and CCS accuracy was also not within the scope of this study. However, these analysis can answer questions about current practice. For example specificity, sensitivity, variations in CCS score between different vendors and the possibility to reduce dose without impact on the metric. Finally, only sequential scan modes were used. With the current appearance of high-pitch spiral mode scanning for coronary calcium it would be interesting to assess the differences in the accuracy of coronary calcium assessment between sequential and high-pitch spiral mode. However, that was not within the scope of this study.
We conclude that for all CT systems a dose reduction of 40% in combination with specific reconstruction gives a CCS comparable for reference protocols. For several systems, even higher dose reductions are possible. Dose reduction results in increased noise and consequently increased CCS, whereas increased IR results in decreased CCS. Mass scores generally underestimated physical mass of the calcifications.

Compliance with ethical standards

Conflict of interest

The Radiology Department of the University Medical Center Utrecht received institutional grants from Philips Healthcare. Martin Willemink received personal fees for lectures from Philips Healthcare.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://​creativecommons.​org/​licenses/​by/​4.​0/​), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Anhänge

Appendix 1

See Tables 4 and 5.
Table 4
Agatston scores (median and range) for all CT systems, calcification masses, reconstructions and dose values
CT system
Mass
Recon.
Full dose
40% reduction
80% reduction
Median (range)
p value
Median (range)
p-value
Median (range)
p-value
S1
38 mg
FBP
95
(92–109)
Ref
109
(99–127)
0.041
150
(137–159)
0.043
  
L1
97
(92–107)
0.593
96
(93–108)
0.686
139
(133–147)
0.043
  
L2
93
(88–98)
0.042
93
(90–105)
0.141
121
(94–128)
0.225
  
L3
91
(87–95)
0.042
91
(88–95)
0.080
94
(88–107)
0.066
 
74 mg
FBP
328
(315–345)
Ref
323
(308–336)
0.042
331
(320–345)
0.684
  
L1
328
(311–345)
0.102
318
(308–337)
0.068
325
(319–332)
0.498
  
L2
326
(306–336)
0.042
305
(296–311)
0.043
314
(303–326)
0.225
  
L3
305
(302–323)
0.043
302
(294–307)
0.043
306
(299–311)
0.042
 
80 mg
FBP
388
(336–446)
Ref
377
(347–464)
0.893
419
(388–465)
0.043
  
L1
388
(333–441)
0.068
376
(329–459)
0.343
409
(381–459)
0.043
  
L2
381
(327–441)
0.042
372
(325–452)
0.078
405
(370–446)
0.046
  
L3
375
(322–435)
0.043
362
(317–445)
0.043
398
(366–433)
0.225
 
157 mg
FBP
497
(490–636)
Ref
595
(561–638)
0.043
664
(602–707)
0.080
  
L1
492
(473–631)
0.041
586
(559–623)
0.080
644
(591–692)
0.080
  
L2
480
(453–618)
0.043
573
(538–596)
0.138
629
(580–667)
0.080
  
L3
463
(432–608)
0.043
569
(528–584)
0.345
616
(566–646)
0.138
S2
38 mg
FBP
102
(90–125)
Ref
106
(89–144)
0.854
265
(202–331)
0.043
  
L1
99
(89–107)
0.042
103
(84–112)
0.686
132
(108–209)
0.043
  
L2
95
(89–107)
0.043
96
(82–111)
0.104
124
(84–205)
0.225
  
L3
95
(89–104)
0.042
95
(69–108)
0.080
99
(70–203)
0.893
 
74 mg
FBP
313
(297–342)
Ref
336
(306–351)
0.138
411
(382–514)
0.043
  
L1
312
(294–340)
0.041
323
(307–347)
0.225
343
(307–421)
0.043
  
L2
295
(284–335)
0.043
317
(297–344)
1.000
315
(294–364)
0.892
  
L3
291
(283–329)
0.043
311
(287–337)
0.785
309
(287–354)
0.893
 
80 mg
FBP
350
(313–390)
Ref
374
(331–425)
0.225
448
(438–456)
0.043
  
L1
349
(307–383)
0.066
376
(328–423)
0.225
389
(371–404)
0.043
  
L2
348
(305–369)
0.042
368
(322–412)
0.893
361
(346–373)
0.893
  
L3
332
(299–371)
0.068
364
(299–408)
0.893
340
(334–364)
0.500
 
157 mg
FBP
505
(439–571)
Ref
551
(449–657)
0.225
690
(472–714)
0.080
  
L1
499
(444–568)
0.416
543
(449–652)
0.345
561
(469–652)
0.225
  
L2
494
(432–567)
0.043
532
(442–643)
0.345
544
(455–631)
0.345
  
L3
490
(433–566)
0.043
520
(434–625)
0.345
528
(446–613)
0.500
S3
38 mg
FBP
102
(80–120)
Ref
105
(93–132)
0.225
151
(145–172)
0.043
  
L1
101
(77–118)
0.109
93
(87–116)
0.892
142
(135–161)
0.043
  
L2
93
(73–101)
0.043
87
(75–97)
0.080
111
(92–117)
0.225
  
L3
80
(72–93)
0.043
77
(70–95)
0.080
88
(85–99)
0.223
 
74 mg
FBP
278
(275–309)
Ref
294
(226–311)
0.498
303
(287–377)
0.042
  
L1
274
(274–305)
0.042
292
(224–310)
0.715
295
(282–367)
0.042
  
L2
273
(267–298)
0.042
267
(202–308)
0.225
281
(248–324)
0.892
  
L3
270
(262–278)
0.043
264
(198–302)
0.080
269
(237–312)
0.345
 
80 mg
FBP
320
(303–356)
Ref
338
(321–354)
0.138
397
(337–495)
0.043
  
L1
318
(298–355)
0.042
332
(313–338)
0.686
391
(334–415)
0.043
  
L2
318
(291–330)
0.042
322
(306–331)
0.893
362
(311–378)
0.080
  
L3
303
(286–325)
0.043
311
(300–318)
0.225
339
(204–370)
0.686
 
157 mg
FBP
450
(420–460)
Ref
459
(425–461)
0.465
561
(517–579)
0.043
  
L1
446
(412–456)
0.042
451
(417–453)
0.893
546
(501–552)
0.043
  
L2
434
(403–444)
0.043
432
(398–439)
0.345
516
(469–524)
0.043
  
L3
414
(398–437)
0.042
420
(392–435)
0.043
484
(450–500)
0.043
S4
38 mg
FBP
109
(93–125)
Ref
107
(94–130)
0.500
186
(166–204)
0.043
  
L1
105
(93–113)
0.197
103
(77–107)
0.225
99
(83–112)
0.225
  
L2
96
(88–111)
0.080
100
(76–104)
0.068
98
(80–112)
0.225
  
L3
88
(82–103)
0.043
97
(75–102)
0.043
82
(75–94)
0.043
 
74 mg
FBP
372
(346–391)
Ref
367
(335–397)
0.223
438
(367–462)
0.043
  
L1
370
(334–389)
0.336
350
(309–377)
0.043
314
(300–363)
0.043
  
L2
365
(327–384)
0.042
350
(308–355)
0.042
308
(297–357)
0.043
  
L3
352
(309–367)
0.043
344
(298–350)
0.043
296
(293–314)
0.043
 
80 mg
FBP
452
(427–503)
Ref
467
(396–494)
0.225
488
(459–494)
0.892
  
L1
462
(423–476)
0.345
445
(392–453)
0.043
402
(370–438)
0.080
  
L2
452
(421–480)
0.068
439
(390–451)
0.043
399
(367–438)
0.080
  
L3
438
(420–448)
0.042
411
(390–446)
0.043
370
(349–425)
0.043
 
157 mg
FBP
738
(672–752)
Ref
706
(603–743)
0.078
716
(659–749)
0.500
  
L1
736
(657–744)
0.041
698
(597–726)
0.042
666
(585–675)
0.043
  
L2
730
(657–742)
0.066
697
(600–724)
0.043
660
(585–668)
0.042
  
L3
736
(660–748)
0.042
694
(606–725)
0.042
654
(584–661)
0.043
P values of the Wilcoxon signed rank test are given for each combination of dose value and reconstruction type, compared to the reference FBP full dose value
Table 5
Mass scores (median and range) for all CT systems, calcification masses, reconstructions and dose values
CT system
Mass
Recon.
Full dose
40% reduction
80% reduction
Median
(range)
p value
Median
(range)
p value
Median
(range)
p value
S1
38 mg
FBP
23
(20–26)
Ref
25
(20–27)
0.059
26
(21–30)
0.041
  
L1
23
(19–26)
0.317
24
(21–26)
0.157
28
(25–29)
0.041
  
L2
22
(18–25)
0.034
23
(19–25)
0.043
27
(24–27)
0.038
  
L3
22
(16–24)
0.039
22
(16–24)
0.039
26
(21–26)
0.414
 
74 mg
FBP
58
(54–62)
Ref
58
(45–62)
0.180
43
(36–54)
0.042
  
L1
57
(52–62)
0.059
58
(52–62)
0.180
48
(44–58)
0.039
  
L2
57
(55–61)
0.157
58
(52–61)
0.109
53
(50–59)
0.039
  
L3
57
(50–60)
0.041
57
(53–60)
0.038
58
(50–58)
0.043
 
80 mg
FBP
70
(60–78)
Ref
71
(61–74)
0.892
56
(50–64)
0.043
  
L1
69
(61–78)
1.000
70
(65–74)
1.000
58
(51–66)
0.042
  
L2
71
(69–76)
0.684
69
(65–74)
0.893
67
(64–72)
0.414
  
L3
70
(64–76)
0.680
70
(66–73)
1.000
69
(62–73)
0.785
 
157 mg
FBP
125
(108–138)
Ref
110
(105–120)
0.225
111
(108–116)
0.078
  
L1
125
(108–138)
0.317
113
(108–118)
0.223
110
(107–116)
0.080
  
L2
132
(115–141)
0.077
112
(104–122)
0.225
111
(105–114)
0.080
  
L3
135
(118–142)
0.080
119
(112–124)
0.225
112
(111–127)
0.225
S2
38 mg
FBP
25
(22–26)
Ref
24
(22–30)
0.854
43
(34–55)
0.043
  
L1
25
(21–26)
0.157
23
(21–28)
0.465
28
(21–38)
0.225
  
L2
24
(20–26)
0.180
22
(19–27)
0.257
25
(19–37)
0.500
  
L3
23
(20–26)
0.063
22
(18–27)
0.176
24
(17–37)
0.581
 
74 mg
FBP
63
(59–68)
Ref
65 (61–70)
0.279
81
(74–101)
0.043
  
L1
62
(59–68)
0.157
64
(59–69)
0.892
64
(61–80)
0.684
  
L2
61
(58–67)
0.038
63
(58–68)
0.414
60
(58–79)
0.893
  
L3
60
(58–66)
0.041
62
(58–67)
0.221
60
(57–77)
1.000
 
80 mg
FBP
76
(75–79)
Ref
81
(73–86)
0.138
92
(86–93)
0.043
  
L1
75
(75–78)
0.157
80
(72–85)
0.279
76
(71–78)
0.276
  
L2
75
(74–78)
0.025
79
(70–84)
0.683
72
(68–74)
0.042
  
L3
75
(74–76)
0.109
78
(70–83)
1.000
71
(66–73)
0.042
 
157 mg
FBP
165
(161–175)
Ref
174
(163–187)
0.144
200
(181–207)
0.042
  
L1
164
(161–174)
0.063
170
(161–186)
0.225
164
(162–188)
0.336
  
L2
163
(159–173)
0.025
169
(160–184)
0.498
161
(159–185)
0.498
  
L3
163
(159–173)
0.038
168
(159–182)
0.498
160
(157–183)
0.345
S3
38 mg
FBP
20
(16–22)
Ref
20
(18–21)
0.496
24
(23–28)
0.042
  
L1
20
(16–21)
0.317
19
(17–20)
0.854
23
(22–25)
0.042
  
L2
20
(15–21)
0.083
18
(16–19)
0.197
20
(19–20)
0.684
  
L3
19
(14–20)
0.038
17
(15–18)
0.104
17
(16–18)
0.225
 
74 mg
FBP
49
(47–53)
Ref
50
(39–54)
0.713
55
(46–60)
0.141
  
L1
48
(47–53)
0.317
50
(38–53)
1.000
54
(44–59)
0.225
  
L2
47
(47–53)
0.180
49
(38–53)
0.414
50
(42–55)
1.000
  
L3
47
(46–53)
0.059
48
(37–52)
0.131
46
(39–52)
0.176
 
80 mg
FBP
62
(59–65)
Ref
64
(59–65)
0.357
72
(62–93)
0.068
  
L1
61
(59–65)
0.317
63
(59–65)
0.416
71
(61–78)
0.080
  
L2
62
(58–65)
0.083
62
(58–64)
1.000
66
(58–70)
0.176
  
L3
62
(58–65)
0.083
62
(57–64)
0.892
64
(56–65)
0.713
 
157 mg
FBP
131
(128–136)
Ref
132
(129–134)
0.496
145
(138–150)
0.043
  
L1
131
(127–136)
0.317
131
(128–133)
1.000
139
(135–146)
0.043
  
L2
130
(127–135)
0.025
130
(127–132)
0.680
133
(131–141)
0.273
  
L3
130
(127–135)
0.025
130
(126–132)
0.257
130
(126–137)
0.854
S4
38 mg
FBP
26
(23–29)
Ref
27
(23–28)
0.705
32
(29–41)
0.041
  
L1
25
(22–28)
0.102
26
(21–27)
0.102
23
(19–27)
0.066
  
L2
25
(21–28)
0.102
25
(20–26)
0.068
23
(18–24)
0.068
  
L3
23
(20–26)
0.034
24
(20–27)
0.042
21
(17–25)
0.043
 
74 mg
FBP
69
(66–72)
Ref
67
(66–69)
0.285
78
(74–80)
0.043
  
L1
66
(65–69)
0.066
64
(61–66)
0.042
62
(60–66)
0.042
  
L2
65
(64–68)
0.042
64
(61–67)
0.039
60
(59–61)
0.043
  
L3
65
(61–66)
0.042
62
(59–65)
0.043
59
(56–62)
0.042
 
80 mg
FBP
86
(80–94)
Ref
87
(81–88)
0.496
96
(93–101)
0.039
  
L1
85
(79–89)
0.059
82
(76–88)
0.042
79
(76–79)
0.043
  
L2
84
(78–87)
0.039
81
(76–85)
0.041
78
(75–80)
0.043
  
L3
82
(76–86)
0.034
79
(74–84)
0.042
74
(72–80)
0.042
 
157 mg
FBP
188
(186–191)
Ref
185
(176–192)
0.102
197
(189–201)
0.043
  
L1
186
(183–194)
0.216
179
(169–186)
0.043
168
(167–173)
0.042
  
L2
185
(182–187)
0.039
178
(169–183)
0.043
166
(165–171)
0.042
  
L3
181
(178–186)
0.039
175
(168–179)
0.041
162
(160–168)
0.043
P values of the Wilcoxon signed rank test are given for each combination of dose value and reconstruction type, compared to the reference FBP full dose value

Appendix 2

See Fig. 7.

Appendix 3

See Fig. 8.
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Metadaten
Titel
Influence of dose reduction and iterative reconstruction on CT calcium scores: a multi-manufacturer dynamic phantom study
verfasst von
N. R. van der Werf
M. J. Willemink
T. P. Willems
M. J. W. Greuter
T. Leiner
Publikationsdatum
19.01.2017
Verlag
Springer Netherlands
Erschienen in
The International Journal of Cardiovascular Imaging / Ausgabe 6/2017
Print ISSN: 1569-5794
Elektronische ISSN: 1875-8312
DOI
https://doi.org/10.1007/s10554-017-1061-y

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