Key words
cardiac - contrast agents - technical aspects - CT angiography
Introduction
Technical advances in coronary computed tomographic angiography (CCTA) continuously
improved image quality [1]. Current technologies enable single-heartbeat CCTA with wide-area detectors [2], dual source technique or high pitch acquisition [3]. This leads to a substantial reduction in scan acquisition time (< 1 – 6 s, depending
on scan protocol) as well as a decrease in motion artifacts due to breathing and coronary
motion [4]. As these technical advances facilitate shorter scan acquisition times, smaller
volumes of contrast media (CM) may be used (total iodine dose [TID]) [5]
[6].
Previous studies demonstrated that enhancement levels in the coronary arteries above
325 Hounsfield units (HU) are necessary for optimal diagnosis [7]
[8]
[9]. Arterial attenuation depends on injection-related parameters (e. g. iodine delivery
rate [IDR; gI/s], injection rate [ml/s], CM concentration [mg/ml], TID, CM volume,
viscosity, saline flush, temperature of injected CM and injection needle type), scan-related
parameters (e. g. scan protocol, scan duration, scan delay, tube voltage, and reconstruction
parameters [kernel]) and patient-related factors (e. g. cardiac output, blood volume,
heart rate, breath hold and weight) [1]
[10]
[11]. The influence of these individual parameters is important as future directions
are aimed towards more individualized CM injection protocols. Previous research has
focused on the influence of saline flush, IDR, injection rate, CM concentration, injection
needle size, CM volume, viscosity as well as the temperature of injected CM on intravascular
attenuation with various outcomes [1]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]. Specifically, the influence of CM concentration has been studied extensively, and
current evidence is controversial as to whether a more highly concentrated CM is beneficial
in intravascular attenuation, when the calculated IDR (e. g. CM concentration × injection
rate) is kept identical [12]
[15]
[16]
[18]
[19]
[20]. To date, there is no consensus regarding the decisive injection parameters influencing
attenuation of the coronary arteries.
A systematic review of the literature on current CM application protocols for CCTA
was performed with the aim of providing an overview of the influence of various injection
factors on enhancement of the coronary arteries with a special focus on IDR, CM concentration
and injection rate.
Methods
Data sources and study selection
For this systematic review, we conducted a search through PubMed, Embase and MEDLINE
between January 2001 and May 2014 using the search terms coronary computed tomography
angiography, coronary computed tomography, iodine delivery rate, coronary attenuation,
coronary enhancement, total iodine load, coronary arteries, iodine concentration,
contrast media concentration, contrast material concentration.
Inclusion criteria were: (1) studies had to compare different CM injection protocols
in CCTA by providing attenuation levels in the coronaries achieved by a specific infusion
protocol, (2) an evaluation of image quality and/or diagnostic accuracy was reported,
(3) sample size of ≥ 30 (> 18 years old), (4) language English, German or French,
(5) MDCT ≥ 16 slice and (6) IDR, injection rate, CM concentration, TID, CM volume
had to be deduced. Studies conducted primarily on radiation dosage, other technical
aspects (e. g. reconstruction kernels, bolus tracking technique/test bolus method),
central venous or intra-arterial CM delivery, or focusing on patients with stents
or bypasses were excluded. Three readers (CM, JT, AS) independently performed the
searches and assessed the eligibility of the studies by reading the abstract and application
of these criteria. All potentially eligible articles were screened for references
to additional eligible studies. Disagreement on inclusion was solved by consensus
between the three readers.
Data extraction
Publications considered eligible were scored using a standardized extraction form,
for the following variables: design (retrospective/prospective/both), population region/size,
age, weight/body mass index (BMI), height, heart rate, cardiac output, blood pressure,
MDCT technique, slice collimation, rotation time, acquisition mode, kV settings, reconstructed
slice thickness, reconstruction kernel, intravenous (i. v.) needle size, CM concentration,
CM volume, injection rate, injection duration, saline flush, injection pattern, temperature,
IDR, TID and enhancement level at different coronary arteries.
In addition, the quality of the studies regarding selection and inclusion criteria,
study aims, patient characteristics and methodology was assessed and a flowchart was
created according to the Preferred Reporting Items for Systematic reviews and Meta-analyses
(PRISMA) guidelines [21]. Studies were also systematically assessed for quality based on the validated Quality
Assessment of Diagnostic Accuracy Studies (QUADAS)-II checklist [22]. This checklist assesses the risk of bias and clinical applicability of studies
based on different domains. Some of the domains are not applicable to the included
studies, as this review does not focus on strict diagnostic studies. Therefore, only
domains relevant to our study were selected from QUADAS-II for quality assessment.
Results from the QUADAS-II assessment are depicted in a graphical manner.
Additionally, the corresponding authors of all included studies were contacted to
fill out a questionnaire providing additional parameters that could not be retrieved
from the publication. The large heterogeneity observed between the included studies
regarding patient population, scanning technique and infusion parameters precluded
us from pooling the data and only allowed a systematic review. To account for heterogeneity
with regard to the outcome measure, a subgroup analysis of the most frequently studied
anatomical location (RCA) was performed (e. g. 30 studies) to evaluate the influence
of injection-related parameters on coronary attenuation. Since this study is a systematic
literature review, no approval from our institutional review board was necessary.
Results
In the primary literature search, 5007 potential studies (Pubmed: 2457, Embase: 1734,
Medline: 816) were identified, of which 2456 were duplicates, leaving 2551 potential
studies for analysis. 2403 studies were excluded from further evaluation after scanning
of the abstract. Of the remaining 148 studies, 91 studies did not meet the eligibility
criteria and were further excluded, leaving 57 studies to be reviewed using the extraction
form and consensus reading. Another 21 studies were excluded as they addressed other
technical aspects or because basic inclusion criteria and/or injection parameters
could not be derived [23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]. In total, 36 studies were included with a total of 4339 patients [7]
[15]
[16]
[19]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
[53]
[54]
[55]
[56]
[57]
[58]
[59]
[60]
[61]
[62]
[63]
[64]
[65]
[66]
[67]
[68]
[69]
[70]
[71]
[72]
[73]
[74]
[75]. Of the included studies, 18 authors responded to the questionnaire [7]
[19]
[49]
[51]
[54]
[55]
[56]
[57]
[60]
[61]
[63]
[64]
[65]
[66]
[67]
[70]
[72]
[75]. A detailed overview of the inclusion and data extraction process is depicted in
[Fig. 1].
Fig. 1 Detailed overview study selection.
Abb. 1 Detail Übersicht zu den ausgewählten Studien.
Data was prospectively collected in the vast majority (81 %) of the included studies.
According to the QUADAS-II assessment, there were some concerns regarding the risk
of bias and applicability mainly in the domain regarding patient selection. For the
other domains a low risk of bias was found. Results of the QUADAS-II assessment are
shown in [Fig. 2]. The quality assessment of all included publications is presented in the supplemental
material.
Fig. 2 Graphical display of different domains of the QUADAS II checklist for all included
studies (n = 36).
Abb. 2 Grafische Darstellung der QUADAS-II-Domänen der eingeschlossenen Studien (n = 36).
Scan and patient-related parameters are described in [Table 1], [2]. Baseline characteristics were poorly described, only reporting mean age, heart
rate and weight. Approximately 20 publications state one or more additional baseline
characteristics (e. g. BMI, cardiac output or blood pressure) [7]
[48]
[52]
[54]
[55]
[56]
[57]
[63]
[64]
[65]
[66]
[67]
[68]
[69]
[70]
[71]
[72]
[73]
[74]
[75]. In the vast majority of the included publications, a tube voltage of 120 kV was
used. Some of the included papers either did not mention tube voltage or mention lower
or various kV settings [48]
[59]
[63]
[70]
[73]
[74]. As different vendors and scanners were used, scan-related parameters such as collimation,
slice reconstruction and kernel were not comparable and occasionally missing.
Table 1
Scan characteristics of the included studies listed according to year of publication.
Tab. 1 Scan-Parameter der eingeschlossenen Studien. Reihenfolge nach Jahr der Publikation.
author
|
coll (mm)
|
rot time (ms)
|
acquisition mode
|
kV setting
|
slice reconstr (mm)
|
kernel
|
Cademartiri [44]
|
12x× 0.75
|
420
|
ECG gating
|
120
|
1
|
medium smooth (B30f)
|
Cademartiri [15]
|
16 × 0.75
|
420
|
ECG gating
|
120
|
1
|
medium smooth (B30f)
|
Cademartiri [45]
|
16 × 0.75
|
420
|
ECG gating
|
120
|
1
|
|
Cademartiri [16]
|
16 × 0.75
|
375
|
ECG gating
|
120
|
1
|
medium smooth (B30f)
|
Rist [19]
|
16 × 0.75
|
375
|
ECG gating
|
120
|
1
|
B20f
|
Utsunomiya [46]
|
16 × 0.5
|
400
|
ECG gating
|
120
|
|
|
Yamamuro [47]
|
64 × 0.5
|
400
|
|
120
|
0.5
|
|
Husmann [48]
|
64 × 0.625
|
350
|
ECG triggering
|
|
|
|
Kerl [49]
|
2 × 32 × 0.6
|
330
|
ECG gating
|
120
|
0.75
|
medium smooth (B25f)
|
Kim [50]
|
64 × 0.6
|
370
|
ECG gating
|
120
|
|
medium smooth (B25f)
|
Nakaura [51]
|
64 × 0.625
|
420
|
ECG gating
|
120
|
0.67
|
medium cardiac
|
Tsai [52]
|
40 × 0.625
|
420
|
ECG gating
|
120
|
1.4 – 3
|
|
Wuest [53]
|
64 × 0.6
|
330
|
ECG gating
|
120
|
0.75
|
medium sharp (B26f)
|
Halpern [54]
|
64 × 0.9
|
420
|
ECG gating/triggering
|
120
|
0.8
|
cardiac sharp C
|
Seifarth [55]
|
2 × 32 × 0.6
|
330
|
|
120
|
|
|
Kim [56]
|
64 × 0.5
|
400
|
ECG gating
|
120
|
0.5
|
FC43
|
Lu [57]
|
64 × 0.625
|
350
|
ECG gating
|
120
|
|
|
Ozbulbul [58]
|
16 × 0.625
|
500
|
ECG gating
|
120
|
0.625
|
medium soft tissue
|
Pazhenkottil [59]
|
64 × 0.625
|
350
|
ECG triggering
|
100 – 120
|
0.625
|
|
Tatsugami [60]
|
320 × 0.5
|
350/375
|
ECG gating
|
120
|
0.5
|
FC13
|
Tatsugami [61]
|
64 × 0.5
|
350/400
|
ECG triggering
|
135
|
0.5
|
FC13
|
Becker [62]
|
|
330
|
ECG gating
|
120
|
0.6
|
B26
|
Isogai [7]
|
64 × 0.625
|
350
|
ECG gating
|
120
|
0.625
|
cardiac
|
Kumamaru [63]
|
320 × 0.5
|
350
|
ECG triggering
|
80/100/120
|
|
FC03
|
Nakaura [64]
|
64 × 0.625
|
420
|
ECG gating
|
120
|
0.67
|
medium cardiac (XCB)
|
Zhu [65]
|
2 × 64 × 0.6
|
330
|
ECG gating
|
120
|
0.75
|
medium soft tissue (B26f)
|
Zhu [66]
|
2 × 64 × 0.6
|
330
|
ECG gating
|
120
|
0.75
|
medium soft tissue (B26f)
|
Zhu [67]
|
2 × 64 × 0.6
|
330
|
ECG gating
|
120
|
0.75
|
medium soft tissue (B26f)
|
Kidoh [68]
|
64 × 0.625
|
420
|
ECG gating
|
120
|
0.67
|
medium cardiac (XCB)
|
Kidoh [69]
|
64 × 0.625
|
420
|
ECG gating
|
120
|
0.67
|
medium cardiac (XCB)
|
Liu [70]
|
2 × 128 × 0.6
|
280
|
ECG triggering
|
100
|
0.75
|
medium smooth (B26)
|
Yang [71]
|
2 × 128 × 0.6
|
280
|
ECG triggering
|
120
|
0.6
|
media smooth (B26f)
|
Tomizawa [72]
|
320 × 0.5
|
350/375/400
|
ECG triggering
|
120
|
0.5
|
FC04, AIDR
|
Zheng [73
|
2 × 64 × 0.6
|
280
|
ECG triggering
|
80/100
100/120
|
0.75
|
I26F
B26f
|
Lembcke [74]
|
2 × 128 × 0.6
|
280
|
ECG triggering
|
100
|
|
|
Kawaguchi [75]
|
2 × 128 × 0.625
|
270
|
ECG gating
|
120
|
0.8
|
medium cardiac (XCB)
|
Coll: collimation, rot: rotation, reconstr: reconstruction, BMI: body mass index.
Coll: Kollimation, Rot: Rotation, Reconstr.: Rekonstruktion, BMI: Body Maß Index.
Table 2
Patient characteristics of the included studies listed according to year of publication.
Tab. 2 Patienten Charakteristika der eingeschlossenen Studien. Reihenfolge nach Jahr der
Publikation.
author
|
no. of subjects (m;f)
|
mean age (years)
|
mean weight (kg)
|
BMI (kg/m2)
|
heart rate (bpm)
|
CO (l/min)/EF (%)
|
BP (syst; diast, mmHg)
|
Cademartiri [44]
|
21 (16;5)
|
59 (34 – 74)
|
72 (53 – 90)
|
|
60 (48 – 72)
|
|
|
21 (14;7)
|
59 (39 – 79)
|
74 (60 – 95)
|
|
60 (49 – 80)
|
|
|
Cademartiri [15]
|
25 (22;3)
|
58 ± 11
|
74 ± 7
|
|
59 ± 8
|
|
|
25 (20;5)
|
60 ± 11
|
72 ± 7
|
|
59 ± 7
|
|
|
25 (21;4)
|
58 ± 13
|
72 ± 7
|
|
61 ± 9
|
|
|
25 (21;4)
|
57 ± 11
|
74 ± 9
|
|
60 ± 9
|
|
|
25 (20;5)
|
63 ± 12
|
71 ± 8
|
|
57 ± 8
|
|
|
Cademartiri [45]
|
15 (11;4)
|
58 (34 – 74)
|
71 (55 – 90)
|
|
58 (46 – 72)
|
|
|
15 (14;1)
|
58 (28 – 73)
|
72 (60 – 88)
|
|
56 (45 – 65)
|
|
|
15 (14;1)
|
59 (45 – 79)
|
73 (60 – 95)
|
|
56 (45 – 68)
|
|
|
Cademartiri [16]
|
20 (15;5)
|
59 ± 12
|
73 ± 9
|
|
61 ± 7
|
|
|
20 (14;6)
|
63 ± 10
|
75 ± 11
|
|
60 ± 8
|
|
|
Rist [19]
|
30
|
58.13 ± 11.16
|
77.68 ± 14.76
|
|
57.3 ± 3.7
|
|
|
30
|
62.17 ± 8.22
|
84.86 ± 16.24
|
|
57.4 ± 4.3
|
|
|
Utsunomiya [46]
|
13 (total: 30;8)
|
68.6 ± 8.4
|
59.5 ± 7.0
|
|
61 ± 11
|
|
|
12
|
63.9 ± 8.9
|
62.1 ± 8.5
|
|
59 ± 11
|
|
|
13
|
68.0 ± 8.8
|
64.3 ± 7.1
|
|
58 ± 8
|
|
|
Yamamuro [47]
|
30 (16;14)
|
68.7 ± 12.1
|
59.5 ± 11.7
|
|
70.1 ± 13.1
|
|
|
30 (17;13)
|
68.0 ± 11.0
|
57.3 ± 7.8
|
|
72.7 ± 18
|
|
|
Husmann [48]
|
70 (48;22)
|
58 ± 12
|
79 ± 16
|
26.5 ± 4.0
|
57.7 ± 7.0
|
|
|
70 (51;19)
|
60 ± 11
|
80 ± 15
|
26.7 ± 4.2
|
57.6 ± 6.0
|
|
|
Kerl [49]
|
25 (14;11)
|
53.32
|
82.2
|
|
|
|
|
25 (20;5)
|
65.40
|
87.7
|
|
|
|
|
25 (14;11)
|
65.84
|
86.9
|
|
|
|
|
Kim [50]
|
20 (total: 59;41)
|
62 (44 – 82)
|
62 (54 – 78)
|
|
55 (42 – 67)
|
|
|
20
|
56 (43 – 76)
|
67 (53 – 79)
|
|
58 (47 – 74)
|
|
|
20
|
57 (37 – 76)
|
61 (51 – 75)
|
|
59 (43 – 79)
|
|
|
20
|
58 (39 – 77)
|
64 (53 – 79)
|
|
58 (41 – 71)
|
|
|
20
|
57 (38 – 72)
|
66 (52 – 83)
|
|
61 (51 – 74)
|
|
|
Nakaura [51]
|
30 (13;17)
|
62.4 ± 12.5
|
60.1 ± 14.2
|
|
66.5 ± 12.5
|
|
|
30 (16;14)
|
67.5 ± 12.9
|
59.5 ± 12.8
|
|
65.8 ± 12.9
|
|
|
Tsai [52]
|
38 (22;16)
|
61.7 ± 12.5
|
64.9 ± 10.9
|
|
71.5 ± 13.2
|
58.8 ± 6.5
|
120.7 ± 14.5; 75.4 ± 10.5
|
34 (21;13)
|
61.7 ± 11.3
|
65.9 ± 8.4
|
|
76.7 ± 11.2
|
57.0 ± 5.6
|
118.9 ± 12.6; 75.8 ± 9.0
|
Wuest [53]
|
53 (38;15)
|
58 ± 11.82
|
|
|
|
|
|
53 (40;13)
|
62 ± 13.08
|
|
|
|
|
|
Halpern [54]
|
260 (%: 57;43)
|
58 ± 12
|
89 ± 25
|
30.3 ± 7.6
|
61.5 ± 0.8
|
|
Syst> 100
|
168 (%: 45;55)
|
50 ± 12
|
85 ± 21
|
29.6 ± 6.7
|
63.0 ± 1.0
|
|
|
Seifarth [55]
|
40
|
62.3 ± 10.8
|
80.8 ± 14.2
|
26.3 ± 3.0
|
64.7 ± 13.0
|
|
|
40
|
62.6 ± 9.6
|
82.0 ± 13.4
|
26.2 ± 3.7
|
63.1 ± 11.4
|
|
|
40
|
62.9 ± 13.3
|
81.7 ± 15.3
|
26.3 ± 3.8
|
63.7 ± 13.3
|
|
|
Kim [56]
|
151 (87;64)
|
55 ± 9
|
67 ± 10.2
|
24.6 ± 3.0
|
70 ± 11
|
|
124 ± 18 (85 – 169)
|
146 (88;58)
|
52 ± 11
|
68 ± 9.9
|
24.8 ± 2.7
|
71 ± 11
|
|
128 ± 19 (92 – 181)
|
Lu [57]
|
30 (total: 71;79)
|
55.6 ± 10.9
|
|
23.4 ± 2.4
|
58.0 ± 8.0
|
|
|
30
|
58.8 ± 12.2
|
|
23.8 ± 2.6
|
58.4 ± 6.3
|
|
|
30
|
58.8 ± 10.5
|
|
23.7 ± 2.5
|
57.9 ± 7.5
|
|
|
30
|
58.3 ± 11.5
|
|
23.5 ± 2.3
|
57.6 ± 6.7
|
|
|
30
|
56.1 ± 11.2
|
|
24.3 ± 2.5
|
56.1 ± 6.8
|
|
|
Ozbulbul [58]
|
24 (total: 20;32)
|
56.4 ± 13.6
|
|
|
61.0 ± 8.9
|
|
|
28
|
54.1 ± 17.1
|
|
|
62.8 ± 7.0
|
|
|
Pazhenkottil [59]
|
80 (59;21)
|
59 ± 11
|
82 ± 12
|
|
56 ± 7
|
|
|
80 (68;12)
|
57 ± 11
|
82 ± 12
|
|
56 ± 7
|
|
|
Tatsugami [60]
|
48 (57;41)
|
69.8 ± 9.8
|
59.3 ± 8.4
|
|
57.1 ± 9.7
|
|
|
50
|
68.7 ± 9.0
|
58.0 ± 8.1
|
|
58.8 ± 6.4
|
|
|
Tatsugami [61]
|
16 (total: 27;18)
|
68.2 ± 10.6
|
57.4 ± 6.0
|
|
53.8 ± 7.6
|
|
|
15
|
69.1 ± 10.3
|
55.3 ± 5.9
|
|
55.7 ± 7.7
|
|
|
14
|
69.6 ± 9.6
|
56.2 ± 7.8
|
|
59.0 ± 12.2
|
|
|
Becker [62]
|
50 (28)
|
57.0 ± 11.2
|
77.4 ± 17.7
|
|
66.5 ± 14.26
|
|
|
54 (31)
|
60.4 ± 11.6
|
78.0 ± 19.1
|
|
68.1 ± 15.86
|
|
|
Isogai [7]
|
20 (16;4)
|
63.5 ± 11.4
|
63.9 ± 13.7
|
|
62.1 ± 10.9
|
|
133.8 ± 14.3; 79.9 ± 8.8
|
20 (12;8)
|
64.4 ± 11.7
|
64.4 ± 13.3
|
|
63.0 ± 8.2
|
|
133.± 17.9; 82.0 ± 11.8
|
20 (5;15)
|
65.4 ± 7.8
|
66.0 ± 8.5
|
|
62.9 ± 10.5
|
|
138.3 ± 16.9; 80.6 ± 12.7
|
Kumamaru [63]
|
36 (18;18)
|
56.7 ± 12.9
|
79.7 ± 15.4
|
22.8 ± 4.8
|
57.4 ± 5.9
|
|
|
72 (41;31)
|
54.8 ± 11.9
|
80.8 ± 18.0
|
27.8 ± 4.8
|
56.7 ± 5.9
|
|
|
Nakaura [64]
|
30 (21;9)
|
69.9 ± 9.1
|
56.8 ± 9.2
|
22.4 ± 3.1
|
60.0 ± 9.7
|
4.2 ± 0.9
|
|
30 (20;10)
|
70.9 ± 11.6
|
57 ± 10
|
22.9 ± 3
|
59.8 ± 10.9
|
4.2 ± 1.0
|
|
Zhu [65]
|
96 (57;39)
|
58.2 (29 – 85)
|
67.1 (39 – 101)
|
24.5 (15.8 – 34)
|
71.7 (48 – 106)
|
6.2 ± 1.7
|
|
100 (53;47)
|
58.1 (27 – 84)
|
67.9 (40 – 101)
|
24.6 (17.9 – 35.4)
|
74.5 (51 – 107)
|
|
|
100 (53;47)
|
59.8 (30 – 83)
|
65.9 (41 – 104)
|
24.1 (15.2 – 34.9)
|
73.0 (50 – 104)
|
|
|
Zhu [66]
|
114 (60;54)
|
60.8 (30 – 85)
|
66.9 (34 – 100)
|
24.7 (16.4 – 32.7)
|
74.5 (49 – 107)
|
|
|
119 (67;52)
|
59.8 (28 – 83)
|
67.1 (38 – 94)
|
24.7 (16.9 – 32.0)
|
75.7 (50 – 111)
|
|
|
Zhu [67]
|
113 (60;53)
|
58.2 (30 – 85)
|
66.9 (34 – 100)
|
24.7 (16.4 – 32.7)
|
74.5 (49 – 107)
|
|
|
94 (54;40)
|
60.4 (32 – 87)
|
64.8 (42 – 101)
|
23.9 (16.4 – 33.0)
|
74.3 (37 – 106)
|
|
|
Kidoh [68]
|
50 (32;18)
|
70.7 ± 9.5
|
57.2 ± 10.4
|
22.6 ± 3.2
|
60.1 ± 10.3
|
4.2 ± 1.5
|
|
50 (32;18)
|
68.5 ± 11.4
|
56.8 ± 10.2
|
22.3 ± 2.9
|
60.6 ± 11.8
|
4.1 ± 1.2
|
|
Kidoh [69]
|
30 (18;12)
|
68.1 ± 12
|
57.7 ± 13.3
|
|
64.1 ± 11.0
|
4.6 ± 1.3
|
|
30 (21;9)
|
59.9 ± 14.3
|
61.6 ± 10.0
|
|
62.8 ± 11.4
|
4.6 ± 1.2
|
|
Liu [70]
|
30 (total: 60;30)
|
55 ± 13
|
71 ± 12
|
25.0 ± 2.8
|
56 ± 6
|
> 55 %
|
150;80
|
30
|
59 ± 10
|
71 ± 9
|
24.9 ± 2.4
|
58 ± 5
|
|
|
30
|
52 ± 11
|
73 ± 13
|
25.3 ± 3.2
|
57 ± 5
|
|
|
Yang [71]
|
120 (81;39)
|
58.5 ± 9.8
|
68.7 ± 11.1
|
24.1 ± 3.0
|
59.1 ± 7.5
|
|
|
80 (53;27)
|
59.6 ± 9.7
|
69.0 ± 10.1
|
23.7 ± 2.8
|
59.3 ± 6.8
|
|
|
Tomizawa [72]
|
36 (20;16)
|
66.1 ± 14.4
|
59.3 ± 12.1
|
23 ± 3.6
|
67.5 ± 11.5
|
|
|
36 (16;20)
|
67.9 ± 12.6
|
55.9 ± 8.8
|
22.3 ± 3.0
|
65.8 ± 13.6
|
|
|
36 (17;19)
|
67.1 ± 9.8
|
61.3 ± 13.7
|
23.7 ± 3.2
|
57.4 ± 11.2
|
|
|
Zheng [73]
|
50 (25;25)
|
54.53 ± 10.71
|
65.45 ± 11.13
|
22.31 ± 2.77
|
75.61 ± 9.59
|
|
|
25 (12;13)
|
BMI< 25: 56.39 ± 12.79
|
BMI< 25: 57.57 ± 6.65
|
BMI< 25: 20.9 ± 1.49
|
BMI< 25: 75.35 ± 10.13
|
|
|
25(13;12)
|
BMI≥ 25: 52.88 ± 8.39
|
BMI≥ 25: 72.42 ± 9.56
|
BMI≥ 25: 25.44 ± 1.63
|
BMI≥ 25: 75.85 ± 9.29
|
|
|
50 (31;19)
|
55.24 ± 9.38
|
64.55 ± 12.91
|
23.73 ± 3.39
|
72.67 ± 9.89
|
|
|
25 (12;13)
|
BMI< 25: 58.56 ± 9.43
|
BMI< 25: 54.28 ± 6.36
|
BMI< 25: 20.79 ± 1.32
|
BMI< 25: 72.76 ± 10.49
|
|
|
25 (19;6)
|
BMI≥ 25: 52.04 ± 8.30
|
BMI≥ 25: 74.42 ± 9.35
|
BMI≥ 25: 26.56 ± 2.09
|
BMI≥ 25: 72.58 ± 9.49
|
|
|
Lembcke [74]
|
20 (8;12)
|
75.7 ± 7.4
|
76 ± 7.8
|
25.9 ± 2.9
|
|
|
|
20 (13;7)
|
|
76.1 ± 8.1
|
25.2 ± 2.2
|
|
|
|
20 (8;12)
|
|
76.6 ± 6.6
|
26.4 ± 2.6
|
|
|
|
20 (9;11)
|
|
74.5 ± 7.1
|
25.9 ± 2.1
|
|
|
|
20 (10;10)
|
|
75.9 ± 8.0
|
26.2 ± 2.5
|
|
|
|
Kawaguchi [75]
|
50 (32;18)
|
63.3 ± 12
|
64.7 ± 11.1
|
24.6 ± 3.5
|
66.1 ± 11.7
|
|
|
50 (27;23)
|
65.3 ± 11.5
|
62.5 ± 12.7
|
24.1 ± 3.8
|
63.7 ± 7.2
|
|
|
M: male, F: female, kg: kilograms, BMI: body mass index, BPM: beats per minute, CO:
cardiac output, EF: ejection fraction, BP: blood pressure, syst: systolic, diast:
diastolic.
M: männlich, F: weiblich, kg: Kilogramm, BMI: Body Maß Index, BPM: Beats pro Minute,
CO: Kardialer Output, EF: Ejektion Fraktion, BP: Blutdruck, Syst.: Systole, Dias:
Diastole.
Injection-related parameters are described in [Table 3]. The temperature of the injected CM concentration was only stated in a limited number
of publications [15]
[19]
[52]
[56]
[58]
[60]
[61]
[62]
[65]
[66]
[67]
[72]. A saline flush was initially not used in all injection protocols but has gained
increasing popularity in more recent publications with only a few publications using
injection protocols without a saline flush [44]
[45]
[46]
[49]
[57]
[58]
[72]. Only eight publications state usage of a biphasic protocol, often in comparison
to a uniphasic injection protocol [45]
[46]
[47]
[49]
[53]
[54]
[55]
[57]. The total injected CM volume ranged between 30 ml and 140 ml. Within the period
of inclusion, a gradual decrease in total injected CM volume is noted, as earlier
publications make mention of a total injected CM volume of 140 ml [15]
[44]
[45], whereas more recent publications reported CM injection protocols with total injected
CM volumes below 40 ml [69]
[70]
[74]
[75]. Subsequently, the TID has substantially lowered from anywhere between 44 – 56 g
[15]
[44]
[45] to less than 15 g (range: 11.1 – 56.0 g) [7]
[47]
[60]
[61]
[64]
[68]
[69]
[70]
[71].
Table 3
Injection parameters of the included studies listed according to year of publication.
Tab. 3 Kontrastinjektionsparameter der eingeschlossenen Studien. Reihenfolge nach Jahr der
Publikation.
author
|
needle
|
CM (mg/ml)
|
CM volume (ml)
|
flow rate (ml/s)
|
saline
|
injection pattern
|
temp (°C)
|
IDR (gI/s)
|
TID (g)
|
Cademartiri [44]
|
18G
|
iodixanol 320
|
140
|
4
|
no
|
uniphasic
|
|
1.28
|
44.8
|
|
iodixanol 320
|
100
|
4
|
yes
|
uniphasic
|
|
1.28
|
32
|
Cademartiri [15]
|
18G
|
iohexol 300
|
140
|
4
|
no
|
uniphasic
|
|
1.2
|
42
|
|
iodixanol 320
|
140
|
4
|
no
|
uniphasic
|
37
|
1.28
|
44.8
|
|
iohexol 350
|
140
|
4
|
no
|
uniphasic
|
37
|
1.4
|
49
|
|
iomeprol 350
|
140
|
4
|
no
|
uniphasic
|
37
|
1.4
|
49
|
|
iomeprol 400
|
140
|
4
|
no
|
uniphasic
|
37
|
1.6
|
56
|
Cademartiri [45]
|
18 – 20G
|
iodixanol 320
|
140
|
4
|
no
|
uniphasic
|
|
1.28
|
44.8
|
|
iodixanol 320
|
140
|
5→3
|
no
|
biphasic
|
|
1.6→0.96
|
44.8
|
|
iodixanol 320
|
100
|
4
|
no
|
uniphasic
|
|
1.28
|
32
|
Cademartiri [16]
|
18G
|
iopromide 370
|
100
|
4
|
yes
|
uniphasic
|
|
1.48
|
37
|
|
iomeprol 400
|
100
|
4
|
yes
|
uniphasic
|
|
1.6
|
40
|
Rist [19]
|
18G
|
iomeron 300
|
83
|
3.3
|
yes
|
uniphasic
|
37
|
0.99
|
24.9
|
|
iomeron 400
|
63
|
2.5
|
yes
|
uniphasic
|
37
|
1.0
|
25.2
|
Utsunomiya [46]
|
20G
|
iohexol 350
|
60 + mix 80 (50 %)
|
3→1.5
|
no
|
biphasic
|
|
1.05→0.26
|
35
|
|
iohexol 350
|
100
|
3
|
yes
|
uniphasic
|
|
1.05
|
35
|
|
iohexol 350
|
100
|
3
|
no
|
uniphasic
|
|
1.05
|
35
|
Yamamuro [47]
|
|
iomeron 350
|
40
|
3.5→2.8
|
yes
|
biphasic
|
|
1.23→0.98
|
14
|
|
iomeron 350
|
50
|
3.5→2.8
|
yes
|
biphasic
|
|
1.23→0.98
|
17.5
|
Husmann [48]
|
18G
|
iodixanol 320
|
80
|
5
|
yes
|
uniphasic
|
|
1.6
|
25.6
|
|
iodixanol 320
|
73.9 ± 11.2
|
4.0 – 5.0
|
yes
|
uniphasic
|
|
1.28 – 1.6
|
23.6
|
Kerl [49]
|
18G
|
iopamidol 370
|
50 – 75
|
5
|
no
|
uniphasic
|
|
1.85
|
18.5 – 27.8
|
|
iopamidol 370
|
50 – 75
|
5
|
yes
|
uniphasic
|
|
1.85
|
18.5 – 27.8
|
|
iopamidol 370
|
(50 – 75) + mix 50 (30 %)
|
5
|
yes
|
biphasic
|
|
1.85→0.56
|
18.5 – 27.8 + 5.6
|
Kim [50]
|
|
iobitridol 350
|
60
|
4
|
yes
|
uniphasic
|
|
1.4
|
21
|
|
iobitridol 350
|
60
|
4
|
yes
|
uniphasic
|
|
1.4
|
21
|
|
iobitridol 350
|
60
|
4
|
yes
|
uniphasic
|
|
1.4
|
21
|
|
iobitridol 350
|
60
|
4
|
yes
|
uniphasic
|
|
1.4
|
21
|
|
iobitridol 350
|
60
|
4
|
yes
|
uniphasic
|
|
1.4
|
21
|
Nakaura [51]
|
20G
|
iopamiron 370
|
80
|
4
|
yes
|
uniphasic
|
|
1.48
|
29.6
|
|
iopamiron 370
|
59.5 ± 12.8
|
3.96 ± 0.85
|
yes
|
uniphasic
|
|
1.47
|
22.0 ± 4.7
|
Tsai [52]
|
20G
|
iohexol 350
|
100
|
4
|
yes
|
uniphasic
|
37
|
1.4
|
35
|
|
iodixanol 320
|
100
|
4
|
yes
|
uniphasic
|
37
|
1.28
|
32
|
Wuest [53]
|
|
iomerol 350
|
45 – 65
|
5
|
yes
|
uniphasic
|
|
1.75
|
15.75 – 22.75
|
|
iomerol 350
|
55 – 75 (incl mix 20 %)
|
5
|
yes
|
biphasic
|
|
1.75→0.35
|
22.75 – 29.75
|
Halpern [54]
|
18 – 20G
|
ioversol 350
|
70
|
5.5
|
yes
|
uniphasic
|
|
1.93
|
24.5
|
|
ioversol 350
|
70 + mix 50 (50 %)
|
5
|
yes
|
biphasic
|
|
1.75→0.88
|
33.25
|
Seifarth [55]
|
18G
|
iopromide 370
|
80 + mix 50 (30 %)
|
6
|
yes
|
biphasic
|
|
2.22→0.67
|
35.2
|
|
iopromide 370
|
82.5 ± 8.8 + mix 34.3 ± 10.8(30 %)
|
5.1 ± 0.6
|
yes
|
biphasic
|
|
1.89→0.57
|
35.6
|
|
iopromide 370
|
73.5 ± 12.9 + mix 50 (30 %)
|
5
|
yes
|
biphasic
|
|
1.85→0.56
|
32.8
|
Kim [56]
|
18G
|
iomeprol 370
|
70
|
4
|
yes
|
uniphasic
|
37
|
1.48
|
25.9
|
|
iomeprol 400
|
70
|
4
|
yes
|
uniphasic
|
37
|
1.6
|
28
|
Lu [57]
|
20G
|
iohexol 350
|
67 ± 5.3
|
5
|
no
|
uniphasic
|
|
1.75
|
23.45
|
|
iohexol 350
|
59.9 ± 4.9
|
5
|
yes
|
uniphasic
|
|
1.75
|
20.97
|
|
iohexol 350
|
(56.9 ± 3.2) + mix 20 (30 %)
|
5
|
yes
|
biphasic
|
|
1.75→0.53
|
22.02
|
|
iohexol 350
|
(59.2 ± 5.7) + mix 20 (50 %)
|
5
|
yes
|
biphasic
|
|
1.75→0.88
|
24.22
|
|
iohexol 350
|
(56.9 ± 4.6) + mix 20 (70 %)
|
5
|
yes
|
biphasic
|
|
1.75→1.23
|
24.82
|
Ozbulbul [58]
|
18G
|
iodixanol 320
|
130
|
4
|
no
|
uniphasic
|
37
|
1.28
|
41.6
|
|
iopamidol 370
|
130
|
4
|
no
|
uniphasic
|
37
|
1.48
|
48.1
|
Pazhenkottil [59]
|
18G
|
iodixanol 320
|
80
|
5
|
yes
|
uniphasic
|
|
1.6
|
25.6
|
|
iodixanol 320
|
70.9 ± 14.1
|
3.5 – 5.0
|
yes
|
uniphasic
|
|
1.1 – 1.6
|
22.7
|
Tatsugami [60]
|
20G
|
iomeron 350
|
47.5 ± 7.4
|
4 ± 0.56
|
yes
|
uniphasic
|
37
|
1.4
|
16.6
|
|
iomeron 350
|
41.5 ± 5.5
|
4.06 ± 0.57
|
yes
|
uniphasic
|
37
|
1.42
|
14.5
|
Tatsugami [61]
|
20G
|
iomeron 350
|
46.5 ± 5.25
|
3.3 ± 0.37
|
yes
|
uniphasic
|
37
|
1.16
|
16.28
|
|
iomeron 350
|
44.3 ± 4.71
|
4.4 ± 0.48
|
yes
|
uniphasic
|
37
|
1.54
|
15.5
|
|
iomeron 350
|
39.3 ± 5.41
|
4.0 ± 0.55
|
yes
|
uniphasic
|
37
|
1.40
|
13.76
|
Becker [62]
|
18G
|
iodixanol 320
|
80
|
5
|
yes
|
uniphasic
|
37
|
1.6
|
25.6
|
|
iomeprol 400
|
80
|
5
|
yes
|
uniphasic
|
37
|
2
|
32
|
Isogai [7]
|
18G
|
iohexol 300
|
44.7
|
4.5
|
yes
|
uniphasic
|
|
1.35
|
13.42
|
|
iohexol 350
|
38.6
|
3.9
|
yes
|
uniphasic
|
|
1.37
|
13.52
|
|
iohexol 350
|
46.2
|
4.6
|
yes
|
uniphasic
|
|
1.61
|
16.17
|
Kumamaru [63]
|
20G
|
iopamidol 370
|
60
|
6
|
yes
|
uniphasic
|
|
2.22
|
22.2
|
|
iopamidol 370
|
80
|
6
|
yes
|
uniphasic
|
|
2.22
|
29.6
|
Nakaura [64]
|
20G
|
iohexol 350
|
57 ± 10.1
|
3.8 ± 0.7
|
yes
|
uniphasic
|
|
1.33 ± 0.23
|
20
|
|
iohexol 350
|
39.7 ± 6.4
|
4.4 ± 0.7
|
yes
|
uniphasic
|
|
1.55 ± 0.25
|
13.9
|
Zhu [65]
|
20G
|
iopromide 370
|
66.3 (42 – 92)
|
4.15 (2.6 – 5.7)
|
yes
|
uniphasic
|
37
|
1.54
|
24.5
|
|
iopromide 370
|
66.4 (40 – 92)
|
4.19 (2.6 – 6)
|
yes
|
uniphasic
|
37
|
1.55
|
24.6
|
|
iopromide 370
|
66.4 (37 – 95)
|
4.08 (2.7 – 5.9)
|
yes
|
uniphasic
|
37
|
1.51
|
24.6
|
Zhu [66]
|
20G
|
iopromide 370
|
73.6 ± 13.5
|
4.69 ± 0.95
|
yes
|
uniphasic
|
37
|
1.74
|
27.23
|
|
iopromide 370
|
67.9 ± 8.3
|
4.38 ± 0.66
|
yes
|
uniphasic
|
37
|
1.62
|
25.12
|
Zhu [67]
|
20G
|
iopromide 370
|
73.6 (37 – 110)
|
4.69 (2.3 – 7.4)
|
yes
|
uniphasic
|
37
|
1.74
|
27.2
|
|
iopromide 370
|
68.5 (42 – 111)
|
4.37 (2.5 – 6.6)
|
yes
|
uniphasic
|
37
|
1.62
|
25.3
|
Kidoh [68]
|
20G
|
iohexol 350
|
40.6 ± 7.6
|
4.5 ± 0.9
|
yes
|
uniphasic
|
|
1.58
|
14.21
|
|
iohexol 350
|
39.7 ± 7.1
|
5
|
yes
|
uniphasic
|
|
1.75
|
13.90
|
Kidoh [69]
|
20G
|
iohexol 350
|
36.9 ± 9.2
|
4.1
|
yes
|
uniphasic
|
|
1.44
|
12.92
|
|
iohexol 350
|
43.1 ± 7.0
|
4.8
|
yes
|
uniphasic
|
|
1.68
|
15.09
|
Liu [70]
|
18G
|
iopromide 370
|
47 ± 8
|
5.0/6.0
|
yes
|
uniphasic
|
|
1.85/2.22
|
17.39
|
|
iopromide 370
|
44 ± 8
|
5.0/6.0
|
yes
|
uniphasic
|
|
1.85/2.22
|
16.28
|
|
iopromide 370
|
36 ± 6
|
5.0/6.0
|
yes
|
uniphasic
|
|
1.85/2.22
|
13.32
|
Yang [71]
|
18G
|
iopamidol 370
|
30 – 60
|
4
|
yes
|
uniphasic
|
|
1.48
|
11.1 – 22.2
|
|
iopamidol 370
|
60
|
4
|
yes
|
uniphasic
|
|
1.48
|
22.2
|
Tomizawa [72]
|
20 – 22G
|
iopamidol 370
|
49.3 ± 10.1
|
3.5 ± 0.7
|
no
|
uniphasic
|
37
|
1.3
|
18.24
|
|
iopamidol 370
|
46.8 ± 7.6
|
3.3 ± 0.5
|
yes
|
uniphasic
|
37
|
1.22
|
17.32
|
|
iopamidol 370
|
43.9 ± 9.6
|
3.6 ± 0.8
|
yes
|
uniphasic
|
37
|
1.33
|
16.24
|
Zheng [73]
|
18G
|
iodixanol 270
|
65.5 ± 11.1
|
5
|
yes
|
uniphasic
|
|
1.35
|
17.69
|
|
iopromide 370
|
64.6 ± 12.9
|
5
|
yes
|
uniphasic
|
|
1.85
|
23.9
|
Lembcke [74]
|
18G
|
iopromide 370
|
30
|
5
|
yes
|
uniphasic
|
|
1.85
|
11.1
|
|
iopromide 370
|
40
|
5
|
yes
|
uniphasic
|
|
1.85
|
14.8
|
|
iopromide 370
|
50
|
5
|
yes
|
uniphasic
|
|
1.85
|
18.5
|
|
iopromide 370
|
60
|
5
|
yes
|
uniphasic
|
|
1.85
|
22.2
|
|
iopromide 370
|
70
|
5
|
yes
|
uniphasic
|
|
1.85
|
25.9
|
Kawaguchi [75]
|
20G
|
iohexol 350 or
iopamidol 370
|
38.6 ± 7.6
43.9 ± 6.9
|
5
|
yes
|
uniphasic
|
|
1.75 or 1.85
|
14.8 ± 2.9
|
|
iopamidol 370
|
37.6 ± 7.6
|
3.7 ± 0.7
|
yes
|
uniphasic
|
|
1.37
|
13.9 ± 2.8
|
CM: contrast media, mg: milligram, ml: milliliter, s: second, mix: mixed bolus (presented
as total volume of mixed bolus), %: percentage of CM in mixed bolus, → indicates second
injection phase, IDR: iodine delivery rate, TID: total iodine dose.
CM: Kontrastmittel, mg: Milligramm, ml: Milliliter, s: Sekunde, mix: Mischbolus (angegeben
als Gesamtvolumen), %: Prozent Kontrastmittel im Mischbolus, → Indiziert eine zweite
Injektionsphase, IDR: Iodine Delivery Rate (Jodapplikationsrate), TID: Totale-Jod-Dosis.
Injection-related parameters and coronary attenuation
The results of all included publications in relation to its three major injection
parameters are presented in the supplemental material. The CM concentration varied
between 270 mg/ml and 400 mg/ml. However, only four CM injection protocols make use
of CM concentrations below 320 mg/ml [7]
[15]
[19]
[73]. The variation in injection rate was higher than for CM concentrations, varying
between 2.5 ml/s [19] and 6 ml/s [55]
[63]
[70]. The majority of the included papers keep injection rate relatively constant when
comparing different groups. Only a few studies mention substantial differences in
flow rates between groups [19]
[55]
[61]
[75]. IDR ranged between 0.99gI/s and 2.22gI/s and proved to be very heterogeneous. A
limited number of injection protocols stated usage of an IDR above 1.9gI/s [54]
[55]
[63]
[70]. All included publications that stated a flow rate below 4 ml/s also reported an
IDR < 1.4gI/s [7]
[46]
[47]
[61]
[64]
[75]. However, lower CM concentrations were not always associated with lower IDR levels,
as some publications state IDR levels ≥ 1.4gI/s with usage of lower (e. g. 320 mg/ml)
CM concentrations, indicating that the CM injection rate might have a greater influence
on the calculated IDR [45]
[48]
[59].
Conflicting results were reported with regard to the influence of IDR on coronary
attenuation. When the IDR differed between subgroups, various publications found significant
differences in the attenuation of the coronary arteries in favor of a higher IDR [7]
[15]
[16]
[55]
[61]
[62]
[68]
[69]
[75]. When the IDR between subgroups was kept identical, numerous publications did not
find statistically significant differences in coronary attenuation [7]
[15]
[19]
[44]
[45]
[46]
[49]
[51]
[60]
[70]
[71]. In both groups (variable and identical IDR), other injection-related parameters
varied substantially, making it difficult to determine the true influence of IDR on
coronary attenuation [47]
[50]
[53]
[55]
[57]
[63]
[74]. Three studies report significant differences between CM concentrations in favor
of higher CM concentrations [15]
[16]
[62]. However, other injection parameters such as IDR were not kept identical between
groups.
Diagnostic attenuation levels of the RCA were reached in the vast majority of the
included studies when IDR levels ≥ 1.4gI/s were used. Only seven studies report non-diagnostic
attenuation levels of the RCA with usage of an IDR ≥ 1.4gI/s [16]
[45]
[46]
[47]
[49]
[54]
[58], of which four studies report the lack of usage of a saline chaser [45]
[46]
[49]
[58]. When no saline flush was applied, almost all publications report attenuation values
of the RCA below a diagnostic level (< 325HU), stressing the importance of a saline
chaser [44]
[45]
[46]
[49]
[58].
Discussion
The aim of this systematic review was to provide an update on the effect of different
CM injection parameters on the attenuation in CCTA. A large variation regarding scan
technique, patient characteristics and CM injection protocols was found. This heterogeneity
makes it difficult to draw conclusions and stresses the need for studies in which
such heterogeneity is avoided.
The findings in this systematic review confirm the need for an additional saline flush
in a CM injection protocol. A saline flush pushes the tail of the injected CM bolus
into the central blood volume thus utilizing CM that would otherwise remain behind
in the injection tubing and peripheral veins [4]. Cademartiri et al. divided patients into two groups: group 1 (140 ml at 4 ml/s,
no saline flush) and group 2 (100 ml at 4 ml/s followed by 40 ml of saline chaser
at 4 ml/s) with an identical IDR (1.28gI/s). No significant differences in the attenuation
of the coronary arteries were found [44]. As group 1 did not receive a saline flush, it is quite possible that some of the
injected CM bolus was not dispensed into the central blood volume, leading to a decrease
in the effective CM volume and subsequently to the non-significant differences in
intracoronary attenuation.
The influence of CM concentration solely on attenuation has been an ongoing topic
of interest. The majority of the included studies evaluating differences in CM concentrations
did not find statistically significant differences in attenuation between groups [19]
[52]
[56]
[58]. Some studies do attribute higher attenuation to higher CM concentrations [15]
[16]
[62]. Becker et al. conducted a double-blind multicenter randomized controlled trial,
which randomized patients in 2 CM groups (iodixanol 320 mg/ml and iomeprol 400 mg/ml)
in order to assess whether CM characteristics affect diagnostic quality. In both groups
80 ml CM was injected at an identical injection rate of 5 ml/s [62]. A significant difference was found in coronary attenuation in favor of the 400 mg/ml
group. They concluded that CM with a higher iodine concentration was beneficial to
attenuation when administered at an identical injection rate and volume. However,
administering different CM concentrations at an identical injection rate leads to
differences in IDRs (320 mg/ml: 1.6gI/s vs. 400 mg/ml: 2.0gI/s). Therefore, the higher
attenuation values in the 400 mg/ml group might not be attributed to the CM concentration
solely, but rather to the calculated product of CM concentration and injection rate
(e. g. higher IDR).
Comparable results are reported by Cademartiri et al. [15] who evaluated coronary attenuation in five different CM groups where both injection
rate and CM volume were kept identical. Mean attenuation values were significantly
lower in the lower CM group and higher in the highly concentrated CM group. Again,
due to the use of an identical injection rate in both groups, the IDR varied significantly
(1.2 to 1.6gI/s), rendering doubtful conclusions with regard to the sole superiority
of higher CM concentrations. The results of this systematic review show diagnostic
attenuation levels of the RCA in the vast majority of the included studies when IDR
levels ≥ 1.4gI/s were used and suggest that IDR levels are easier to modify through
usage of a large variety in flow rates rather than a limited variety in CM concentrations
(e. g. 270 – 400 mg/ml).
Recent studies have confirmed the hypothesis that a CM with a lower iodine concentration
provides attenuation levels equal to those obtained using a more highly concentrated
CM when the IDR is kept identical [76]
[77]. In both in vivo and phantom studies, comparison of protocols using different CM
concentrations (varying between 240 – 400 mg/ml) established comparable intravascular
enhancement patterns when the IDR and other CM- and scan-related factors were kept
standardized. These findings are supported by a double-blind randomized controlled
study, in which both the objective and the subjective image quality were evaluated
with usage of different iodine concentrations (e. g. 240 mg/ml, 300 mg/ml and 370 mg/ml)
while maintaining an identical IDR and total iodine load [78]. In addition, patient comfort and pain at the injection site with usage of flow
rates varying 5.4 – 8.3 ml/s and incidence of contrast extravasation have been evaluated.
No significant differences were found between groups regarding comfort, stress, and
pain [78]. This study also shows that the reluctance towards the usage of higher flow rates
as a possible cause for an increased incidence of extravasation due to increased injection
pressures is merely based on hypothetical flow-related issues. In a recent feasibility
study, the latter was confirmed in an in vitro and in vivo setup [79]. The results from these studies confirm in a standardized way that the injection
with high flow rates does not have any negative side effects. No extravasation or
flow-related problems were observed and the maximum injection pressure of 325psi was
not reached. As CMs with a lower concentration are attractive due to their lower viscosity
and, hence, lower injection pressure, these findings might stimulate a shift in paradigm
towards clinical usage of CMs with lower iodine concentrations (e. g. 240 mg/ml) for
individually tailored contrast protocols with subsequently higher flow rates.
Attenuation values cannot be attributed to a saline flush and the product of CM concentration
and flow rate solely. Lembcke et al. assessed the effect of lower CM volumes on image
quality in high-pitch CCTA [74]. Patients were randomly assigned to one of five groups with different CM volumes
(e. g. 30 – 70 ml). The flow rate and CM concentration remained identical in all groups
(5 ml/s and 370 mg/ml, respectively). As the volumes in all groups were different,
the calculated TID is also different (varying between 11.1 g and 25.9 g). They reported
significantly higher mean attenuation values in groups with higher CM volumes [74]. An increased total CM volume injected at the same flow rate leads to a prolonged
injection duration, which increases the magnitude of vascular enhancement. Similarly,
injection of a dedicated CM with higher flow rates affects both the magnitude and
timing of contrast enhancement, leading to a shorter, earlier and higher peak enhancement
and a proportional increase in vascular and parenchymal enhancement [1]
[4]
[11]
[80]
[81]. A short injection duration might be challenging and requires careful timing of
CM bolus injection and data acquisition, especially in patients with abnormal hemodynamic
parameters (e. g. irregular heart rate or low/high cardiac output) [74]. The authors recommend taking into account the patient’s hemodynamic status, especially
cardiac output, before imaging. Information regarding cardiac output has only been
supplied in a very limited number of included publications [52]
[64]
[65]
[68]
[69]
[70]. Body weight and BMI are known to have a substantial impact on vascular attenuation
and time-to-peak in CTA [11]
[82]
[83]
[84]. Many included publications evaluated the applicability of different body weight-adjusted
CM injection or biphasic injection protocols with various outcomes. Seifarth et al.
investigated whether individually tailored CM injection software resulted in higher
vascular attenuation of coronary arteries compared to fixed injection protocols [55]. They evaluated a body weight adapted individualized CM injection software in comparison
to two different standard injection protocols and found comparable or increased attenuation
values in favor of the individualized CM injection software. However, besides overall
mean attenuation of the coronary arteries between groups, an analysis for differences
in attenuation values between weight classes was not performed. Another group evaluated
the vascular attenuation of the coronary arteries as well as image quality and injection
parameters within different weight classes by using identical body weight-adapted
CM bolus injection software in comparison to a standardized injection protocol with
fixed parameters [85]. Diagnostic attenuation in the entire coronary tree and a more homogeneous enhancement
pattern between different weight groups was found with usage of the body weight-adapted
injection software. The fixed injection protocol showed a large variation in the attenuation
of the coronary arteries between different weight groups with higher attenuation levels
in patients with a lower body weight and low attenuation levels in the heavier patients.
These findings indicate suboptimal use of CM in different patient weight groups and
show a clear benefit for individually tailored CM injection software in CCTA.
A thorough understanding of the influence of different injection parameters is considered
a necessity for achieving the ultimate goal of individualized medicine. Disentangling
the influence of patient-related parameters on attenuation and overall image quality
will be helpful in defining optimal bolus shaping in future injection protocols, hereby
creating a doorway towards individualized CM application. Though a large variation
in IDR is applied in CCTA in the daily clinical routine, there is no literature or
consensus regarding the optimal IDR for the attenuation of the coronary arteries.
The goal is to create a personalized CM injection protocol, where some patients (e. g.
lower weight and/or length or heart rate ≤ 60 bpm) might require less CM with a different
scan timing protocol than other patients (e. g. higher BMI or heart rate ≥ 60 bpm)
to reach the same attenuation value. Research needs to be directed towards defining
individualized optimal IDR tailored towards patient-related factors (e. g. weight,
heart rate, cardiac output) with further incorporation of different scan and injection
parameters into computer modeling software.
This study has several limitations. The study population inclusion criterion was set
to a minimum of 30 patients. Furthermore, a limited number of prospective randomized
trials are available on this topic. A known limitation in all systematic reviews is
that studies with less favorable results have a tendency not to be published. A publication
bias, therefore, cannot be ruled out. Another potential limitation is the heterogeneity
of vendors and scanner types. Although technical advances have improved image quality
substantially, image quality can vary between vendors and scanner types. Most studies
provided only limited data concerning injection, scanning, and patient parameters.
Not all corresponding authors of the included articles completed and sent back the
questionnaire or provided additional information. Therefore, possible effects of patient
level characteristics (e. g. BMI, cardiac output) could not be accounted for. Nevertheless,
these factors have a significant impact in the clinical routine and should be addressed
by individualized scan and CM injection protocols. Finally, most of the included studies
were scanned with a tube voltage of 120 kV. The use of lower kV settings subsequently
leads to a higher contrast enhancement, as a lower tube voltage translates into lower
effective photon energy, bringing the latter closer to the K-edge of iodine (33.2keV)
[86]
[87]. Technical developments of the CT technique have made the use of lower tube voltage
(kV) possible. Using the newest CT technology has made kV settings as low as 70 kV
and 80 kV feasible, also for a broader range of patients, as a higher tube current
(mA) is available. These technical developments add to the importance of adapting
CM injections. As current technical developments are moving towards broad clinical
application of lower kV settings, a substantial decrease in various determinant injection
parameters (e. g. IDR, CM volume) is expected.
Conclusion
This systematic review shows that an adequate attenuation in the coronary arteries
can be achieved with different CM injection protocols. Given the substantial variability
between studies, it remains unclear which of the injection parameters is the most
important determinant for adequate attenuation. It is highly likely that one parameter
that combines multiple parameters (e. g. IDR) will be the most determinant factor
for coronary attenuation in CCTA protocols. Research needs to be directed towards
unraveling the influence of injection parameters and defining individualized optimal
IDRs tailored to patient-related factors. This will make it possible to offer a CM
injection protocol with applicability of a broad variety of injection and scan-related
parameters tailored to each individual patient.
List of abbreviations
CCTA:
Coronary Computed Tomographic Angiography
CM:
Contrast Media
TID:
Total Iodine Dose
HU:
Hounsfield Units
IDR:
Iodine Delivery Rate
MDCT:
Multidetector Computed Tomography
BMI:
Body Mass Index
RCA:
Right Coronary Artery
LAD:
Left Anterior Descending artery
Cx:
Circumflex artery