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Cardiac CT in Pediatric Patients. Marilyn J. Siegel, M.D. Mallinckrodt Institute of Radiology Washington University School of Medicine St. Louis, MO. USA. FDA Questions: Contrast-enhanced Pediatric Cardiac CT. Indications for CT Impact of CT on diagnosis & treatment

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cardiac ct in pediatric patients
Cardiac CT in Pediatric Patients

Marilyn J. Siegel, M.D.

Mallinckrodt Institute of Radiology

Washington University School of Medicine

St. Louis, MO. USA

fda questions contrast enhanced pediatric cardiac ct
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
cardiac ct basic facts
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
frequency of contrast usage
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
fda questions contrast enhanced pediatric cardiac ct1
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
indications pediatric cardiac ct
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
specific disease states or pathology
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
pediatric heart diseases
Pediatric Heart Diseases
  • Common extracardiac lesions
    • Aortic arch anomalies
    • Aortic coarctation
    • Interrupted arch
    • Patent ductus arteriosus
    • Pulmonary artery sling
arch anomalies
Arch Anomalies

Right arch

Double Arch

Adolescent

Neonate

pulmonary sling left pulmonary artery arises from right pulmonary artery
Pulmonary Sling:Left pulmonary artery arises from right pulmonary artery

Neonate

Case from J. Schoepf

aortic coarctation
Aortic Coarctation

10-day old girl with CHF; 8 cc contrast,

3D CT

CT

other indications for pediatric cardiac ct
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
shunt lesion septal defects
Shunt Lesion: Septal Defects

ASD

ASD/VSD

Post ASD repair

post operative evaluation
Post-operative Evaluation:

Graft right atrium to pulmonary artery

Grafts subclavian arteries to pulmonary arteries

fda questions contrast enhanced pediatric cardiac ct2
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
impact on management
Impact on Management
  • Predict whether patient should undergo further invasive diagnostic testing (angiography)
  • Clarify equivocal angiographic findings
  • Predict whether patient needs surgery
therapeutic intervention indications for re operation
Therapeutic Intervention:Indications for Re-operation

Leaking Baffle

CT prompted angiography

Pseudoaneurysm

Prompted surgery

fda questions contrast enhanced pediatric cardiac ct3
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
contrast dosing
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)
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

Contrast Injection
fda questions contrast enhanced pediatric cardiac ct4
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
limitations of contrast enhanced ct
Limitations of Contrast-Enhanced CT
  • Contrast-related:
    • Extravasation at injection site
    • Adverse contrast reactions
  • Device-related:
    • Radiation exposure
contrast related risks
Contrast-Related Risks
  • Extravasation at injection site
    • Power injector: 0.4%
    • Manual injection: 0.3%

Kaste Pediatr Radiol 1995; 26:449

incidence contrast reactions meta analysis
Incidence Contrast Reactions:Meta-analysis
  • LOCM(NICM)
    • All 1-3%
    • Minor near 1%
    • Major (severe) .04% (1:10,000)
    • Late 5-8%
  • Mortality rate - LOCM since 1980 1:100,000
adverse contrast reactions pediatric population
Adverse Contrast Reactions:Pediatric Population
  • 321 children
  • Questionnaire (73% return rate)
  • Omnipaque 300/450 (Iohexol)
  • Acute reactions 1.9%
    • Minor (mild)
    • Older patients (> 24 kg)
  • Late reactions 6.2%
    • Mild or intermediate
    • Younger (< 24 kg)

Mikkonen, Pediatr Radiol 1995; 25:350

adverse contrast reactions
Adverse Contrast Reactions
  • Nonionic n=168,363 (1986-1988)
  • Overall prevalence of ADRS: 3.13%
    • Severe 0.04%, deaths 0.004%
  • 70% within 5 minutes, remainder later
  • Prevalence by age:
    • < 10 yrs: 0.4%
    • 10-19 yrs: 2.52%
    • 20-49 yrs: 4.1-4.6%
    • > 50 yrs: 1.5-2.6%

Katayama H. Radiology 1990; 175:621

radiation risks
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)
relative risks
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 CT’s 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.

fda questions contrast enhanced pediatric cardiac ct5
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
safety monitoring
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
mitigating preventing adverse contrast reactions
Mitigating & Preventing Adverse Contrast Reactions
  • Identify patients at risk:
    • Prior moderate contrast reaction
    • Medically treated asthma
  • Premedication with corticosteroids
safety monitoring radiation dose
Safety MonitoringRadiation Dose
  • Directly proportional to:
    • Tube current
    • Kilovoltage
    • Scan time
    • Slice thickness
    • Total number of slices
radiation risks recommendations
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
fda questions contrast enhanced pediatric cardiac ct6
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
efficacy data
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
coronary artery stenosis
Coronary Artery Stenosis
  • Several studies have shown that CT allows reliable detection of coronary artery disease
  • 95% sensitivity, 86% specificity
      • detecting > 50% stenosis
      • vessels 2-4 mm in diameter

Nieman: Circulation 2002; 106:2051Fayad: Circulation 2002; 106:2026

pediatric aortic arch anomalies
Pediatric Aortic Arch Anomalies
  • 22 pediatric patients
  • Confirmatory studies:
    • Echocardiography (n=7)
    • Angiography (n=7)
    • Surgery (n=8)
  • Accuracy CT: 96%
    • Stenotic vessels: 2 to 5 mm in diameter

Lee E, Siegel MJ. AJR, In Press

fda questions contrast enhanced pediatric cardiac ct7
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
future directions in contrast enhanced ct
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
injection rate vs arterial enhancement

350

5

mL/s

300

3

mL/s

1

mL/s

250

Contrast Enhancement (HU)

200

150

100

50

0

50

75

100

125

150

175

0

25

200

Time (sec)

Injection Rate vs. Arterial Enhancement

Bae 2002

 injection rate increases contrast enhancement

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

350

400 mgI/mL

300

350 mgI/mL

300 mgI/mL

250

200

Aortic CE (HU)

150

100

50

0

0

10

20

30

40

50

Time (sec)

Concentration vs. Enhancement

Varying iodine concentrations

Total iodine mass and flow rate constant (5mL/s)

Bae 2002

 iodine concentration =  contrast enhancement

concentration vs flow rate
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

effect of iodine concentration
Effect of Iodine Concentration
  • Implication in children
  • Use of higher concentration contrast material at may result in smaller contrast volumes
  • Disadvantage
    •  Viscosity (not usable > 400 mgI/mL)
  • Challenge for future research
ct future clinical utilization
CT: Future Clinical Utilization
  • Ventricular function studies based on images in systole and diastole
  • Pulmonary perfusion studies
    • Peak attenuation & time to peak attenuation measured
pulmo ct color coded display
Pulmo CT: Color Coded Display

Potential for studying perfusion abnormalities associated with heart/lung disease

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