Download Is Beta-blockade necessary to obtain diagnostic image

Is Beta-blockade necessary to obtain diagnostic image
quality at low radiation dose of coronary CT angiography
using a 2nd generation 320-row scanner?
Poster No.:
421
Congress:
ESCR 2014
Type:
Scientific Poster
Authors:
O. Ghekiere , J. Djekic , M. El Hachemi , D. Hansen , A.-S.
1
1
3
1
2
2
1 1
Vanhoenacker , P. Dendale , A. Nchimi Longang ; Liège/BE,
2
3
Hasselt/BE, Aalst/BE
Keywords:
Quality assurance, Radiation safety, CT-Angiography,
Radioprotection / Radiation dose, Cardiac
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Purpose
Coronary computed tomographic angiography (CCTA) is a noninvasive imaging tool for
evaluation of the coronary arteries, with high sensitivity and high negative predictive value
to exclude significant coronary artery disease (1).
In the early days, effective radiation doses of up to 21 mSv have been reported for
CCTA (2). Despite the recent advent of multidetector technologies allowing a better image
quality and lower radiation doses, heart rate control by beta-blockers has remained key
for improved cardiac image quality and radiation dose (3-5). Nevertheless, beta-blockers
are not harmless and can't be administered to all patients. Moreover, 20 to 30% of patients
do not achieve the target heart rate with preparation of beta-blockers (6-8).
nd
More recently, the 2 generation 320-detector row CT scanner with a gantry rotation
time of 275 msec and volume coverage up to 16 cm allows excellent image quality while
reducing the radiation dose over a wide range of body sizes and heart rates (9,10).
Given these recent advances, we aim to investigate if beta-blocker administration for
nd
CCTA using a 2 generation 320-detector rows CT scanner is required for diagnostic
image quality and low radiation dose.
Methods and Materials
1. Patients and study design are described in table 1
Study design
Prospective
Ethics Committee
Approved
Written informed consent
All patients
Inclusion criteria
CCTA referral
Exclusion criteria
- < 18 years
- Contraindications to X-ray exposure,
Allergy to iodinated contrast agents
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- Mild to severe renal insufficiency
(creatinine clearance < 60ml/min/1.73m²
body surface area)
Inclusion period
June - July 2013
Table 1: Study design and cohort
2. Coronary CT acquisition protocol and image processing.
nd
All patients underwent the same imaging protocol using a 2 generation CT scanner
(Aquilion ONE ViSION Edition; Toshiba Medical Systems, Otawara, Japan) equipped
with 320 rows and a gantry rotation time of 275 ms. The protocol included a coronary
calcium score scan (120kVp; 300mA; 3 mm slice thickness) and contrast-enhanced
CCTA using the parameters described in table 2.
Scanner
Aquilion ONE ViSION Edition; Toshiba
Medical Systems, Otawara, Japan
N° of rows
320
Maximum gantry rotation time
275 ms
Detector configuration; single step z-axis
coverage
320 x 0.5 mm; 160 mm
Scanning mode
Axial, ECG-Triggered, N° of rotation
depending on the heartrate
· 1 rotation HR < 75 bpm
· 2 rotations 75 bpm < HR < 100 bpm
Arrhythmia detection
Patient preparation
0.4 mg of sublingual nitroglycerine 2 min
before scanning
Tube voltage/current
Automatic based on scout views
SURE
(
exposure3D, Toshiba Medical
Systems).
Contrast injection protocol
•
Dual injection of 100%
Iomeron 400 (Bracco
Diagnostics, Milan, Italy; 400
mg of iodine/ml) for 9s (+ 1s
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•
for every supplementary tube
rotation) + 30 ml saline
Injection rate adapted to the
automatically set tube voltage/
current:
- 3.5 ml/sec for 80 kVp protocol
- 4 ml/sec for 100 kVp and < 450 mA
- 5 ml/sec for 100 kVp and > 450 mA
- 6 ml/sec for 120 kVp protocol.
Scan triggering
Automated bolus tracking
Slice thickness/increments
0.5/0.25 mm
Image reconstruction matrix
512²
Reconstruction, algorithms and kernel
Asymmetric cone beam reconstruction
AIDR3D (Toshiba Medical Systems)
Kernel FC03 (Standard) Best diastolic
phase ± increments of 3%, in case of
movements, depending on the heartrate.
Table 2: Imaging consisted of calcium scoring and CCTA protocols.
3. Analysis of image quality
Images were evaluated by 2 independent experienced readers on a dedicated
workstation equipped with software enabling automatic centerline determination of each
of the coronary segments. The window level and width levels were set to 300 and 800
respectively. They evaluated independently motion-related image quality on longitudinal
and orthogonal reconstructions for all coronary segments # 1.5 mm in diameter according
to the American Heart Association segmentation (S1-S15) by using a four-point Likert
scale (Table 3).
Grade
1
no artifact
2
minor, mild artifact
3
moderate artifact but still interpretable
4
Severe artifacts rendering
interpretation not possible
diagnostic
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Table 3: 4-point Likert scale for motion-related image quality
Consensus readings were performed to resolve all discordant inclusion criteria and
segment location. Image noise was evaluated by assessing the noise levels in the
ascending aorta and the endobronchial air (Hounsfield unit and standard deviation).
Signal to noise ratio (SNR) is defined as the ratio between the mean attenuation and the
standard deviation in the ascending aorta.
4. Statistical analysis
All patient and examination data were stored in excel sheet. Interobserver agreement for
image quality was calculated using Cohen's # test by using the following scale: # values
of less than 0.20 are indicative of poor agreement; 0.21-0.40, fair agreement; 041-0.60,
moderate agreement; 0.61-0.80, good agreement; 0.81-1.00, excellent agreement.
The student t test was used to compare continuous variables, and chi-square test was
used to compare nonparametric variables. A p-value of less than 0.05 is considered to
express a statistically significant.
To identify the predictors of the radiation dose (mSv), a linear regression model was
used with continuous variable mSv as outcome and the following variables as potential
predictors: age, beta-blocker administration, the number of heart beats, presence of
arrhythmia, scanning length, Agatston calcification score, heart rate, BMI and SNR.
A general linear model was fitted with a backwards model selection. The model
assumptions of normality, constant variance and linearity were checked.
For identifying the factors with impact on image quality, the following potential risk factors
are investigated using a generalized linear mixed model (GLMM): diameter of the vessel,
the age of the patient, use of beta-blockers, the number of heart beats (1, 2 or 3),
arrhythmia, scan length, Agatston calcification score, SNR, heart rate, radiation dose
and BMI. The original outcome for the mean quality of the two readers is a multinomial
variable with an ordinal scale (grade 1, 1.5, 2 and 3).
Results
208 consecutive and unselected patients were eligible. 8 were not included because
of refusal (n =3), coronary bypass surgery (n = 3), and calcium channel blockade
administration (n = 2). The remaining 200 patients (mean age 60±12, range 20-86 years;
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92 females) were enrolled in this prospective study (Flowchart, figure 1); their clinical
characteristics and cardiovascular risk factors are given in table 1, and in figures 2 and 3.
47 patients were receiving an oral beta-blocker as part of baseline medication, and
56 patients were prepared by receiving 5mg of Bisoprolol both the evening before
and the morning of the examination (Emconcor mitis, Merck, Overijse, Belgium) and/
or intravenous bolus administration of 5 to15mg of metoprolol (Seloken, AstraZeneca,
Brussels, Belgium) at the time of imaging. Therefore, a total number of 103 patients had
beta-blockade administration and 97 patients had no beta-blockade prior to CCTA.
Comparaison between the group with beta-blockade administration and the group
without beta-blockade
No significant difference (p>0,05) was observed between the two groups of patients
regarding the BMI, the age of the patient, the radiation dose (mSv), the scan length,
coronary stenting, Agatston coronary calcification score and the SNR, although the mean
HR tended to be higher in the group without beta-blocker administration (63.1 versus
59.77 bpm) (p =0.05) (Table 2). This result may be regarded as a selection bias in our
study population with only beta-blockade preparation in patients with high baseline HR.
Conversely, it may be regarded as a failure of beta-blockade to control HR, as reported
in other studies (7,8).
The scanning conditions and parameters in the two groups were also quite similar (Table
3).
Radiation dose
The median DLP of all CCTA examinations was 105.3 ± 96.1 (range: 10.6-627.1)
mGy.cm. Using a (k = 0,014) CT organ-specific effective dose index, the median radiation
dose was 1.47± 1.35 (range: 0.15-8.78 mSv). Overall, the radiation dose was # 1 mSv in
98 (49 %) patients, and more than 4 mSv in 11 (5.5%) patients, including 6 with arrhythmia
(Figure 4), one with (BMI>35) (Figure 5) and 4 with both overweight (BMI>25) and 2heartbeat scan.
Image quality
695 of the 3200 coronary segments were absent or < 1.5 mm diameter, the image
quality of the remaining 2505 (78.3%) was graded 1 or 2 in 2500 (99.8%) segments. The
agreement between the two readers was good (#=0.61). 5 segments were scored "3" by
both readers (Figure 6).
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The image quality score was not significantly impacted by beta-blockade administration
(p = 0.27).
Identifying the predictors for the radiation dose (mSv) of CCTA
The distribution of the effective radiation dose (mSv) is skewed (Figure 7). The adjusted
coefficient of determination R²adjusted is 0.6448. There was a significant impact of the
number of heart beats, patient age, BMI, arrhythmia, scan length and the Agatston
calcification score on the effective radiation dose (p < 0.001), while the use of betablockers, HR and the SNR had no significant impact (Table 4).
Identifying the risk factors that are associated with image quality (mean quality of
the two readers)
A greater caliber and a higher SNR have a positive effect on the image quality, while the
age of the patient, a higher Agatston calcification score, and a higher HR have a negative
effect (Table 5).
Cut-off values for heart rate
To determine a HR cut-off value for good to excellent image quality (mean image quality
grade 1 or 1.5 of the two readers), a population-averaged cumulative probability with
p=0.90 and p=0.95 is calculated. For patients with median values of the variables Age
(61 years), Caliber (2.8 mm), Calcification Agatston score (75) and SNR (21.91), HR cutoff values with 90% and 95% probability for good to excellent image quality were 73 and
60 bpm respectively (Figure 7). This curve has a quadratic fit and the probability for good
image quality seems to decrease rapidly above a HR of 80 bpm.
HR cut-off values for good to excellent image quality are also measured for different
scenarios using the minimal and maximum values of age, coronary artery caliber,
Calcification Agatston score and SNR (Table 6). This confirms the impact of these
parameters on the HR cut-offs for mean image quality grade 1 or 1.5.
Images for this section:
Page 7 of 22
Fig. 1: Flowchart
Page 8 of 22
Table 1: Patients demographics and cardiovascular risk factors
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Fig. 2: Distribution of the Body Mass Index (BMI) (n=200 patients)
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Fig. 3: Heart rate during acquisition (n=200 patients)
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Table 2: Comparaison of patients demographics and cardiovascular risk factors between
both groups of patients with regard to the use of beta-blockers
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Table 3: CCTA parameters with regard to the use of beta-blockers
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Table 4: Risk factors associated with radiation dose
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Table 5: Risk factors associated with image quality
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Fig. 4
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Fig. 5
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Fig. 6
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Fig. 7
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Table 6: HR cut-off values of 90 and 95% probability for image quality grade 1 or 1.5
according to scenarios combining the minimal and maximum values of age, coronary
artery caliber, calcification Agatston score and SNR
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Conclusion
In our study, the use of beta-blockers did not result into a significant difference in HR.
Although HR remains a key determinant for image quality, it does not affect the effective
nd
radiation dose when using a 2 generation 320-row scanner. Furthermore, HR cutoff with
a 90% probability for good to excellent image quality in an "average" patient is sufficiently
high (73 bpm) to obviate the need for HR control in most subjects, even though this cut-off
may vary on a per-patient basis according to other parameters such as the calcification
score, age, SNR and the caliber of the coronary arteries.
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