Cardiac CT in Pediatric Patients

1
Cardiac CT in Pediatric Patients
Marilyn J. Siegel, M.D. Mallinckrodt Institute of
Radiology Washington University School of
Medicine St. Louis, MO. USA
2
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

3
Cardiac CT Basic Facts

• Need multidetector CT
• Faster imaging times
• fewer motion artifacts
• Higher spatial resolution
• 0.5 to 1.25 mm
• superb 3D images
• Better contrast enhancement
• THE USE OF CT IS INCREASING

4
Frequency of Contrast Usage

• Contrast mandatory
• 100 of cases
• Inherent problems in children
• Small patient size
• Lack of perivisceral fat
• Poor differentiation of soft tissue structures on
  non-enhanced CT scans
• Solution IV contrast

5
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

6
Indications Pediatric Cardiac CT

• Detection of disease or pathology
• i.e., diagnosis
• Improve clinical decision making
• Need for other diagnostic testing
• Use of specific intervention
• No role in defining normal anatomy
• No role in assessing function
• Not a screening tool

7
Specific Disease States or Pathology

• Extracardiac great vessel anomalies
• Intracardiac shunt lesions
• Post-operative anatomy
• In children, CT is performed most often for
  congenital diseases

8
Pediatric Heart Diseases

• Common extracardiac lesions
• Aortic arch anomalies
• Aortic coarctation
• Interrupted arch
• Patent ductus arteriosus
• Pulmonary artery sling

9
Arch Anomalies
Right arch
Double Arch
Adolescent
Neonate
10
Pulmonary SlingLeft pulmonary artery arises
from right pulmonary artery
Neonate
Case from J. Schoepf
11
Aortic Coarctation
10-day old girl with CHF 8 cc contrast,
3D CT
CT
12
Patent Ductus Arteriosus
CT
MR
13
Other Indications for Pediatric Cardiac CT

• Diagnosis of cardiac shunts
• atrial septal defects
• ventricular septal defects
• Evaluate post-operative anatomy
• usually complex cyanotic heart disease

14
Shunt Lesion Septal Defects
ASD
ASD/VSD
Post ASD repair
15
Post-operative Evaluation
Graft right atrium to pulmonary artery
Grafts subclavian arteries to pulmonary arteries
16
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

17
Impact on Management

• Predict whether patient should undergo further
  invasive diagnostic testing (angiography)
• Clarify equivocal angiographic findings
• Predict whether patient needs surgery

18
Therapeutic InterventionIndications for
Re-operation
Leaking Baffle CT prompted angiography
Pseudoaneurysm Prompted surgery
19
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

20
Contrast Dosing

• Contrast volume is determined empirically based
  on patient weight
• Nonionic contrast medium
• 280 to 320 mg I
• Dose
• 2 mL/kg (max 4 mL/kg or 125 mL)

21
Contrast Injection

• Power Injection
• Antecubital catheter
• Flow rate variable
• 22g 1.5 -2.0 mL/sec
• 20 g 2.0 -3.0 mL/sec
• 24g or central line 1.0 mL/sec
• Hand Injection
• Peripherally positioned catheter

22
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

23
Limitations of Contrast-Enhanced CT

• Contrast-related
• Extravasation at injection site
• Adverse contrast reactions
• Device-related
• Radiation exposure

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Contrast-Related Risks

• Extravasation at injection site
• Power injector 0.4
• Manual injection 0.3

Kaste Pediatr Radiol 1995 26449
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Incidence Contrast ReactionsMeta-analysis

• LOCM(NICM)
• All 1-3
• Minor near 1
• Major (severe) .04 (110,000)
• Late 5-8
• Mortality rate - LOCM since 1980 1100,000

26
Adverse Contrast ReactionsPediatric Population

• 321 children
• Questionnaire (73 return rate)
• Omnipaque 300/450 (Iohexol)
• Acute reactions 1.9
• Minor (mild)
• Older patients (gt 24 kg)
• Late reactions 6.2
• Mild or intermediate
• Younger (lt 24 kg)

Mikkonen, Pediatr Radiol 1995 25350
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Adverse Contrast Reactions

• Nonionic n168,363 (1986-1988)
• Overall prevalence of ADRS 3.13
• Severe 0.04, deaths 0.004
• 70 within 5 minutes, remainder later
• Prevalence by age
• lt 10 yrs 0.4
• 10-19 yrs 2.52
• 20-49 yrs 4.1-4.6
• gt 50 yrs 1.5-2.6

Katayama H. Radiology 1990 175621
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Radiation Exposure
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Radiation Risks

• CT
• 10 of all radiological procedures
• 65 effective dose of all medical x-rays
• Chest X-ray 0.10 mSv
• Pediatric chest CT 1-10 mSv
• Adult chest CT 7-15 mSv
• Cardiac Cath 20-30 mSv
• (3.5 min fluoro/75 sec cine)

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Relative Risks

• To individual
• Lifetime risk of cancer 20-25 (1 in 4 or 5)
• Added risk 0.05 (negligible, 1 in 2000)
• To population
• 600,000 pediatric CTs in the US / year
• Without CT 135,000 will die of cancer
• With CT 135,300 will die of cancer

Courtesy Jim Brink, M.D.
31
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

32
Safety Monitoring

• Dosing
• IV contrast drawn up by technologist
• Dose verified by radiologist prior to injection
• Contrast administered by radiologist
• Procedural
• Catheter site monitored for extravasation

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Mitigating Preventing Adverse Contrast Reactions

• Identify patients at risk
• Prior moderate contrast reaction
• Medically treated asthma
• Premedication with corticosteroids

34
Safety MonitoringRadiation Dose

• Directly proportional to
• Tube current
• Kilovoltage
• Scan time
• Slice thickness
• Total number of slices

35
Radiation Risks Recommendations

• Optimize CT settings
• Reduce tube current and voltage
• Increase table speed (mm/sec)
• Limit number of scans
• Use automated dose reduction technology
• Eliminate inappropriate referrals for CT

36
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

37
Efficacy Data

• In adults, large amount of data related to CT
  angiography of the coronary arteries and acute
  aortic events
• In children, overall paucity of data
• Minimal data on aortic imaging
• Several review articles on CT angiography of
  congenital heart disease

38
Coronary Artery Stenosis

• Several studies have shown that CT allows
  reliable detection of coronary artery disease
• 95 sensitivity, 86 specificity
• detecting gt 50 stenosis
• vessels 2-4 mm in diameter

Nieman Circulation 2002 1062051 Fayad
Circulation 2002 1062026
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Pediatric Aortic Arch Anomalies

• 22 pediatric patients
• Confirmatory studies
• Echocardiography (n7)
• Angiography (n7)
• Surgery (n8)
• Accuracy CT 96
• Stenotic vessels 2 to 5 mm in diameter

Lee E, Siegel MJ. AJR, In Press
40
FDA Questions Contrast-enhanced Pediatric
Cardiac CT

• Indications for CT
• Impact of CT on diagnosis treatment
• Contrast-specific questions
• Methods of determining dosing
• Limitations of contrast-enhanced CT
• Methods of safety monitoring
• Efficacy data (adults children)
• Direction of future drug development or
  utilization for contrast agents in children

41
Future Directions in Contrast-Enhanced CT

• Goal To get the highest contrast enhancement
  with the least amount of contrast agent
• 2 main factors affect contrast enhancement
• Flow rate or injection duration
• Iodine concentration

42
Injection Rate vs. Arterial Enhancement
Bae 2002
? injection rate increases contrast enhancement
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? Injection rate

• Higher levels of enhancement may result in
  smaller volumes of contrast
• But in children there is a limit how fast we can
  inject, because small gauge catheters and
  catheters in hand and foot need slower injection
  rate

44
Concentration vs. Enhancement
Varying iodine concentrations Total iodine mass
and flow rate constant (5mL/s)
Bae 2002
? iodine concentration ? contrast enhancement
45
Concentration vs. Flow Rate

• Left ventricular density (200-300 HU)
• 300 mgI/mL at 3.5 mL/sec
• 400 mgI/mL at 2.5 mL/sec
• Injecting low-concentration contrast at high flow
  rate or higher-concentration at lower flow rate
  produces similar enhancement density

Becker Appl Radiol 2003 S50
46
Effect of Iodine Concentration

• Implication in children
• Use of higher concentration contrast material at
  may result in smaller contrast volumes
• Disadvantage
• ? Viscosity (not usable gt 400 mgI/mL)
• Challenge for future research

47
CT Future Clinical Utilization

• Ventricular function studies based on images in
  systole and diastole
• Pulmonary perfusion studies
• Peak attenuation time to peak attenuation
  measured

48
Pulmo CT Color Coded Display
Potential for studying perfusion abnormalities
associated with heart/lung disease
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Summary

• Role of CT will increase
• Challenges
• Optimize contrast enhancement
• Lower radiation dose