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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. Indications for CT Impact of CT on diagnosis & treatment

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Cardiac CT in Pediatric Patients

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  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 Sling:Left 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 MR CT

  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 Intervention:Indications 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. 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

  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

  24. Contrast-Related Risks • Extravasation at injection site • Power injector: 0.4% • Manual injection: 0.3% Kaste Pediatr Radiol 1995; 26:449

  25. 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

  26. 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

  27. 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

  28. Radiation Exposure

  29. 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)

  30. 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.

  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

  33. 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 > 50% stenosis • vessels 2-4 mm in diameter Nieman: Circulation 2002; 106:2051Fayad: Circulation 2002; 106:2026

  39. 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

  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. 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

  43.  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

  44. 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

  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 > 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

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

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