Pediatr Cardiol (2011) 32:426–432 DOI 10.1007/s00246-010-9873-8
ORIGINAL ARTICLE
Use of 320-Detector Computed Tomographic Angiography for Infants and Young Children with Congenital Heart Disease Faris Al-Mousily • Roger Y. Shifrin • Frederick J. Fricker • Nicholas Feranec Nancy S. Quinn • Arun Chandran
•
Received: 16 September 2010 / Accepted: 8 December 2010 / Published online: 6 January 2011 Ó Springer Science+Business Media, LLC 2010
Abstract Pediatric patients with complex congenital heart disease (CHD) face a lifetime of treatment with interventional therapeutic and palliative procedures. Echocardiography remains the mainstay for noninvasive imaging of congenital heart lesions. This often is supplemented with diagnostic cardiac catheterization for additional anatomic and physiologic characterization. However, recent technological improvements in computed tomography (CT) and magnetic resonance imaging (MRI) have led to an increased focus on the use of these techniques given their better safety profile. This study aimed to review the authors’ experience with a 320-slice multidetector CT scanner in the evaluation of CHD in children. This retrospective case study investigated 22 infants and young children with a provisional diagnosis of CHD. Their anatomic evaluation was performed using a 320-slice Aquilon ONE CT scanner. Of these 22 patients, 14 were examined without cardiac gating. This was subsequently modified to a prospective gated, targeted protocol to decrease the radiation dose. The images were interpreted by an experienced radiologist and a pediatric cardiologist. Continuous variables were expressed as mean and standard deviation or range, and the two imaging protocols were compared. A comparison of exposure rates with those from other pediatric studies that had used the 64-slice
F. Al-Mousily F. J. Fricker A. Chandran (&) Department of Pediatrics, University of Florida, P.O. Box 100296, Gainesville, FL 32610-0266, USA e-mail:
[email protected] R. Y. Shifrin N. Feranec N. S. Quinn Department of Radiology, University of Florida, P.O. Box 100296, Gainesville, FL 32610-0266, USA
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CT angiography also was performed. For the first group of patients, with nongated CT examinations, the mean effective whole-body radiation dose was 1.8 ± 0.71 millisieverts (mSv) (range, 0.96–3.2 mSv). For the second group, the mean was 0.8 ± 0.39 mSv (range, 0.4–1.5 mSv). Although the radiation dose was reduced dramatically, clinicians must be vigilant about the cumulative risk of radiation exposure. Keywords Congenital heart disease CT scan Radiation exposure 320-Slice scanner
Echocardiography remains the primary imaging method for children with congenital heart disease (CHD). This frequently is supplemented with diagnostic cardiac catheterization for additional anatomic and functional data. However, the radiation exposure associated with cardiac catheterization and computed tomography (CT), has caused some concern, especially in relation to patients with complex CHD, who are increasingly treated with interventional therapeutic and palliative procedures [6, 17]. Recent studies have demonstrated increased risks for radiation-induced chromosomal DNA damage and a lifetime cancer risk with increasing cumulative doses of radiation for children with CHD who have undergone either CT or cardiac catheterization procedures [3, 4]. Previous studies [7, 8, 11, 16] have demonstrated the accuracy of cardiac computed tomographic angiography (CTA) in delineating complex cardiac anatomy as well as airway and lung disease. This study aimed to report our experience using a 320slice multidetector CT scanner to evaluate CHD in children and to report the radiation dose associated with these examinations.
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Methods Patient Selection This retrospective case study investigated consecutive infants and young children referred to the Congenital Heart Center at the University of Florida between January 2009 and December 2009. These children had a provisional diagnosis of congenital heart defect as determined by clinical examination and echocardiography, and CT had been ordered for further delineation of their diagnosis. The exclusion criteria for this study ruled out known hypersensitivity to iodine-containing agents and renal dysfunction. The study was approved by the institutional review board of the hospital. The study enrolled 22 patients (12 boys and 10 girls). Multidetector CT The examinations were performed using a 320-slice Aquilion ONE scanner (Toshiba Medical Systems Corp., Tustin, CA). All the patients were in sinus rhythm, and none required beta-blockers despite heart rates exceeding 80 beats/min (bpm) in all cases. No sedation was given, and breath holding was not required. The CT scanning was performed using intravenous contrast comprising 2 ml/kg of low-osmolar iodine contrast medium (Visipaque 320) injected via a 24-gauge or larger peripheral catheter or a single-lumen peripherally inserted central catheter (PICC) line at the rate of 0.5 ml/s manually. The scanning was initiated after the contrast bolus had been delivered. Bolus tracking, either automatic or manual, was not used. The scan volume extended typically from the thoracic inlet superiorly to just below the diaphragm inferiorly. In cases of suspected heterotaxy and anomalous inferior vena cava drainage, the scan volume was extended to the infrarenal region. All scans were performed in a cranial-caudal direction, with CT parameters adapted to the patient’s weight. A total of 14 patients were scanned using a nongated volume scan mode with a rotation time of 0.4 s, a tube voltage of either 80 or 100 kVp (weight based), and scan ranges from 10 to 16 cm. The remaining eight patients were scanned using a prospective gated target CTA volume scan mode with a rotation time of 0.35 s and a tube voltage of 80 kVp. The scan range, dependent on patient size, heart rate, and area to be evaluated, varied from 8 to 16 cm, and the tube current was set at 150 to 450 mA (automatic dose modulation based on the size and shape of the individual patient). The effective dose was derived from the dose-length product and conversion coefficients for the chest, taking into account the patient’s age [1]. Postprocessing of the multidetector CT (MDCT) scans was performed on a dedicated Vital Images workstation
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using Vitrea 2 software 4.0 (Vital Images, Inc., Minnetonka, MN). The studies also were scored by two boardcertified radiologists with experience interpreting CT scans of patients with CHD in a range of 1 to 5 based on overall diagnostic quality and image noise, as defined by the average amount of mottling or graininess. Diagnostic quality was considered excellent (score of 5) if sharpness of different structures, contrast resolution, and lesion visualization were superior, leading to high confidence in the diagnosis. Diagnostic quality was described as unacceptable (score of 1) if these image attributes were unsatisfactory. A breakdown of the intermediate scores included 2 (suboptimal), 3 (adequate), and 4 (good). An average quality score was calculated for each patient on the basis of the individual scores for relevant vascular structures and anatomic anomalies. Diagnostic quality was considered sufficient when the mean score was rated 3 or higher [11, 13, 14, 18]. Analysis of Data All images were interpreted by an experienced radiologist and a pediatric cardiologist. Full volumes were reconstructed in 0.5-mm-thickness slices and analyzed in twodimensional mode in the three standard orthogonal planes, with oblique planes when necessary. This was followed by three-dimensional volume rendering of these images. Echocardiogram, CT, and intraoperative findings then were compared (Figs. 1, 2, 3, 4).
Fig. 1 Interrupted aortic arch with arch hypoplasia. The posterior projection of the three-dimensional reconstruction shows the interruption with a closing ductus arteriosus
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Fig. 2 Interrupted aortic arch with arch hypoplasia. The coronal twodimensional image set shows the aortic arch and the site of the interruption Fig. 4 Truncus arterosus type A posterior projection showing an interrupted aortic arch type B with anomalous left subclavian artery (LSCA) and patent ductus arteriosus (PDA)
were calculated using weighted kappa statistics with both linear and quadratic off-diagonal weighting.
Results
Fig. 3 Posterior coronal projection of total anomalous pulmonary venous return (TAPVR) with the common pulmonary vein connecting to the right innominate vein
Statistical Analysis Data were stored in an Excel spreadsheet (Microsoft Excel 2003, Redmond, WA). Continuous variables were expressed as mean and standard deviation or range. Because this was a case series, no specific null hypothesis had been created before this pilot study. In our attempts to compare radiation exposure data from this study to other pediatric studies that had used the 64-slice CTA, we made a direct comparison of the mean and respective exposure rates. Interrater agreement for the quality scores of the CT scans
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A total of 22 patients underwent evaluation. All scans were performed successfully without breath holding or sedation. The image acquisition time was within 350 to 400 ms in all cases. Manual injection of the contrast agent was used in all cases, and no complications occurred. The first 14 patients were evaluated without cardiac gating (marked with * in Tables 1 and 2). Subsequently, this protocol was modified to a prospectively gated, targeted protocol (marked with r in Tables 1 and 2) in an attempt to decrease the radiation dose and provide less cardiac motion. The remaining eight patients were evaluated using the modified protocol. Table 1 summarizes the age, sex, weight, and diagnosis of the patients. The age and weight characteristics of the two groups were almost identical. The mean age was 8.8 months (range, 0.2–55 months) for the first group and 8.1 months (range 0.1–49 months) for the second group. The mean weight was 5.65 kg (range, 2.4–16 kg) for the first group and 5.24 kg (range 2.2–15.9) for the second group. All the MDCT findings correlated well with the intraoperative surgical findings, and no major discrepancies were noted. Table 2 lists all the relevant radiation data,
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Table 1 Age, weight, and diagnosis of the two groups Patienta
Sex
Age (months)
1*
F
4
5.3
DORV, MA, PS, BDG
2*
M
4
4.5
As, CoA, Shone’s complex
3*
F
8
6.3
CoA, PDA
4*
M
0.2
2.4
Abnormal arch
5*
F
24
16
PAPVR, ASD
6*
F
5
6
Vascular ring
7*
M
55
12
8*
F
6
7
TOF, PA, Systemic venous thrombosis
9*
M
0.2
3.5
TGA, VSD, CoA
10*
F
2
3.9
Unbalanced AVSD with borderline hypoplastic LV and Asc Ao
11* 12*
M M
0.2 (6 days) 1
3 3.3
TGA, PA, VSD, ASD, PDA Vascular sling
13*
M
2
3.2
DORV, MA, PS, BDG, PAPVR
14*
F
0.5 (15 days)
2.7
Absent RPA/ right pulmonary veins
Weight
Diagnosis
Unbalanced AVC, S/P bilat Glenn
15r
F
0.1 (4 days)
2.27
IAA Aberrant RSCA
16r
M
6
8.16
Plueropericardial effusion
17r
M
0.3 (11 days)
2.2
Hypoplastic arch with CoA
18r
M
0.5 (14 days)
3.1
Hypoplastic arch with CoA
19r
F
3
3.1
TA RPA stenosis
20r
M
5
4.5
CoA, pulmonary artery hypoplasia
21r
M
49
15.9
22r
M
1
2.7
TOF, hypoplastic LPA PAPVR Tracheobronchial stenosis, Emphysema
DORV double-outlet right ventricle, MA mitral atresia, PS pulmonary stenosis, BDG bidirectional Glenn, As aortic stenosis, CoA coarctation of the aorta, PDA patent ductus arteriosus, PAPVR partial anomalous pulmonary venous return, ASD atrial septal defect, AVC atrioventricular canal, S/P status post, TOF tetralogy of Fallot, PA pulmonary atresia, TGA transposition of the great arteries, VSD ventricular septal defect, AVSD atrioventricular septal defect, LV left ventricle, Asc Ao ascending aorta, RPA right pulmonary artery, IAA interrupted aortic arch, RSCA right subclavian artery, TA truncuc arteriosus, LPA left pulmonary artery a
The * denotes no cardiac gating, whereas the r denotes prospectively gated image acquisition
with the effective radiation dose equivalent expressed in millisieverts (mSv). The mean effective whole-body dose was 1.8 ± 0.71 mSv (range, 0.96–3.2 mSv) for the first group and 0.8 ± 0.39 mSv (range, 0.4–1.5 mSv) for the second group. The results of the image quality analysis demonstrated an average score of 2.24 for intracardiac structures using the nongated protocol, with an increase to 2.92 for the gated protocol. For the pulmonary arteries, the mean score was 3.74 for the nongated protocol, with an increase to 4.38 for the gated protocol (Table 3). Finally, the mean score for the aorta was 3.80 using the nongated protocol, with an increase to 4.10 with the gated protocol. The weighted kappa statistic for intracardiac structures was 0.12 with a linear off-diagonal weighting using the nongated protocol. This statistic rose to 0.34 with the gated protocol, whereas the quadratic off-diagonal weighting yielded 0.17 for the nongated protocol but increased to 0.45 for the gated protocol. Similarly, for the pulmonary arteries, the weighted kappa statistic using a linear off-diagonal weighting was
0.17 for the non-gated protocol, with an increase to 0.42 using the gated protocol, whereas the quadratic off-diagonal weighting yielded 0.29 for the nongated protocol, with an increase to 0.54 for the gated protocol. Finally, for the aorta, the weighted kappa statistic using a linear off-diagonal weighting was 0.11 for the nongated protocol, with an increase to 0.44 using the gated protocol, whereas the quadratic off-diagonal weighting yielded 0.14 for the nongated protocol, with an increase to 0.55 for the gated protocol.
Discussion Over the years, echocardiography has remained the standard for noninvasive imaging of CHD. In many instances, however, limitations in technology and poor patient acoustic windows affect the accuracy and scope of diagnosis. Currently, other noninvasive methods such as magnetic resonance imaging (MRI) and CT are being used
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Table 2 Corresponding relevant radiation data and system setup with effective radiation dose equivalent expressed in millisieverts (mSv) Patient no.a
Eff mA
kVp
Rotation time (s)
CTDI (vol.e)
DLPe
Dose (mSv.)
1*
36
100
0.4
3.6
42.9
1.6
2*
56
100
0.4
5.6
66.8
2.6
3*
40
100
0.4
4.3
68.8
1.7
4*
60
80
0.4
3.1
24.8
0.96
5*
35
100
0.35
3.8
60.2
1.56
6*
108
80
0.4
6.1
84.7
3.2
7*
48
100
0.4
5.2
82.5
1.4
8*
48
100
0.4
5.2
82.5
2.1
9*
36
80
0.4
3.6
42.9
1.6
10*
104
80
0.4
5.8
81.6
3.1
11* 12*
28 80
100 100
0.4 0.4
2.5 4.3
25.2 51.0
0.9 1.9
13*
36
80
0.4
3.6
42.9
1.6
14*
28
100
0.4
2.8
33.4
1.3
15r
44
80
0.35
1.40
14.34
0.55
16r
55
80
0.35
2.80
38.86
1.5
17r
43
80
0.35
2.80
22.10
0.86
18r
43
80
0.35
2.80
22.19
0.86
19r
33
80
0.35
1.10
10.73
0.42
20r
33
80
0.35
1.30
15.00
0.6
21r
55
80
0.35
2.90
45.85
1.19
22r
33
80
0.35
1.10
10.77
0.4
Eff mA effective tube current, kVp tube voltage, CTDI CT dose index, vol.e effective volume, DLPe effective dose length product a
The * denotes no cardiac gating, whereas the r denotes prospectively gated image acquisition
widely to supplement echocardiography. Although cardiac MRI is emerging as an alternative tool for both functional and anatomic evaluation, it is limited by its availability, the need for sedation or anesthesia, and the duration of time required for image acquisition in a potentially hemodynamically unstable patient. Consequently, cardiac CTA has gained popularity because it allows delineation of the complex cardiac and extracardiac anatomy in a rapid fashion, thus obviating the need for sedation. In addition, CT has the advantage of being more readily available in many centers. The accuracy of the CT scan in defining both the pre- and postoperative anatomy in children has already been well established by various studies including one from our center [7]. The greatest disadvantage of CT, however, remains the risk for exposure of the child to ionizing radiation, especially during infancy. This risk cannot be underestimated [2–4] considering the increased rate of DNA mutations in children as well as a 1.9 to 2 times higher lifetime attributable risk for fatal and nonfatal cancers in infants compared with older children (15 years of age). This was with a median lifetime cumulative dose of 7.7 mSv per patient. A large study evaluating pediatric cardiovascular disease with a 64-slice scanner that had automatic anatomic
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tube current modulation using low-voltage settings (mean age, 5.8 years; range, 1 day to 15 years; mean weight, 21.9 kg; range, 2.3–74.2 kg) had radiation doses of 2.5 ± 2.1 mSv [11]. A more recent study [16] of the coronary artery anatomy after an arterial switch operation (mean age, 5.6 ± 1.1 years; weight, 19.7 ± 9 kg) had radiation doses of 4.5 ± 0.5 mSv. Kuettner et al. [15] studied children with CHD using a dual-source scanner with gating (mean age, 8.9 ± 7 years; mean weight, 29 ± 26 kg), applying a radiation dose of 5 ± 3.9 mSv. In the current study, the cohort of patients had a different age and weight range. However, this was in part compensated by the currently available conversion coefficients used to determine the effective radiation dosages in millisieverts. The initial nongated protocol was an adaptation from a protocol used previously with a 64-slice scanner at our institution. Subsequently, we used a gated protocol to reduce cardiac motion, with the additional possibility of reducing the radiation dose. Compared with other published studies using CT to evaluate congenital heart defects [6, 10, 12, 16], our study examined much younger patients and had a significantly lower average radiation dose. In the first nongated protocol,
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Table 3 Reader scores for both groups and corresponding kappa statistics using both linear and quadratic off-diagonal weighting Group 1
Group 2
Weighted Kappa Group 1
Weighted Kappa Group 2
Linear
Linear
Reader 1
Reader 2
Mean 1
Reader 1
Reader 2
Mean
Quadratic
Quadratic
Atrial septum
2.75
2.00
2.35
3.29
3.50
3.43
0.22
0.37
0.70
0.77
Muscular IVS
3.21
2.57
2.89
3.38
3.63
3.39
0.17
0.40
0.62
0.73
Membranous IVS
3.30
1.60
2.36
3.33
2.71
2.93
0.20
0.22
0.29
0.31
Moderator band
2.57
2.00
2.25
3.13
2.63
2.88
-0.19
-0.44
0.35
0.55
Papillary muscles
3.14
2.07
2.61
3.50
2.63
3.06
0.07
0.25
0.14
0.32
Coronary arteries
1.64
1.07
1.36
2.75
1.50
2.13
0.11
0.06
0.23
0.29
Coronary sinus Main PA
2.14 4.18
1.57 3.25
1.86 3.67
3.38 4.63
1.88 4.38
2.63 4.50
0.22 0.38
0.35 0.51
0.02 0.30
0.19 0.27
Right PA
4.23
3.38
3.81
4.43
4.14
4.29
0.07
0.25
0.56
0.75
Left PA
4.14
3.36
3.75
4.43
4.29
4.36
0.06
0.12
0.39
0.58
Subsegmental PAs
3.21
2.43
2.82
3.29
2.63
2.88
0.27
0.56
0.14
-0.01
Asc Ao
3.93
3.29
3.61
3.88
4.13
4.00
0.22
0.36
0.20
0.36
Arch
4.07
3.43
3.75
4.00
4.00
4.10
0.25
0.38
0.79
0.89
Arch branches
4.14
3.57
3.86
3.57
3.86
3.71
0.03
-0.17
0.53
0.63
Desc Ao
4.29
3.79
4.04
4.25
4.13
4.19
-0.05
-0.03
0.25
0.33
Mean intracardiac
2.68
1.84
2.24
3.25
2.64
2.92
0.12
0.17
0.34
0.45
Mean PAs
4.19
3.33
3.74
4.49
4.27
4.38
0.17
0.29
0.42
0.54
Mean Ao
4.10
3.50
3.80
4.04
4.08
4.10
0.11
0.14
0.44
0.55
IVS interventricular septum, PA pulmonary artery, PAs pulmonary arteries, Asc Ao ascending aorta Scoring scale: 1 unsatisfactory, 2 suboptimal, 3 adequate, 4 good, 5 excellent
our dose of 1.8 ± 0.7 mSv was lower than in other published studies. The second protocol, using cardiac gating, demonstrated a further dose reduction to 0.8 ± 0.39 mSv. The protocol then was revised and standardized for all young children weighing less than 20 kg to use prospective gating with an exposure window of 350 ms and a minimum necessary field of view. The images obtained using the gated protocol were improved with better conspicuity of small cardiac and vascular structures and less radiation exposure. The two readers rated the quality and conspicuity of depicted intracardiac structures as less than satisfactory, with a slight increase using the gated protocol. Scores for the pulmonary arteries indicated good to excellent conspicuity and quality, with an increase using the gated protocol. Similarly, scores for the aorta indicated satisfactory to good conspicuity and quality, with an increase using the gated protocol. There was moderate inter-reader agreement based on the weighted kappa statistics, with a significant increase in the kappa statistic (increased interreader agreement) with use of the gated protocol compared with the nongated protocol. To the best of our knowledge, only one previous case report publication has dealt with the potential to reduce radiation dosage significantly using a wide-channel multidetector scanner [5]. However, our study remains the first
to examine a large group of patients with CHD using the 320-slice CT scanner. Although the radiation dose was reduced dramatically, we need to continue being vigilant about the cumulative risk of radiation exposure, especially in children, for whom the risk is estimated to be three to four times higher for the development of malignancy after radiation exposure than for adult patients using the same exposure [9]. Recommendation The decision whether to use MRI or CT to delineate congenital cardiac pathology should be made on a caseby-case basis. The decision criteria should include the availability of the required technology and local expertise, the type of data required (e.g., functional vs anatomic), and the risks of sedation or anesthesia versus the risks of radiation exposure. In the event that CT is used, available protocols should be tailored to minimize the dose of radiation. We suggest that centers using CTA for children should review their technique periodically and refine their protocols to decrease the radiation dose. Acknowledgment The authors thank Danielle Sessions for her assistance in submission of the manuscript for this article.
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