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

Pediatric Heart Diseases Common extracardiac lesions –Aortic arch anomalies –Aortic coarctation –Interrupted arch –Patent ductus arteriosus –Pulmonary artery sling

Arch Anomalies Neonate Adolescent Right arch Double Arch

Pulmonary Sling: Left pulmonary artery arises from right pulmonary artery Case from J. Schoepf Neonate

Aortic Coarctation 10-day old girl with CHF; 8 cc contrast, 3D CT CT

Patent Ductus Arteriosus CT MR

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 Post ASD repair ASD/VSD ASD

Post-operative Evaluation: Graft right atrium to pulmonary artery Grafts subclavian arteries to pulmonary arteries

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 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 Leaking Baffle CT prompted angiography Pseudoaneurysm Prompted surgery

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 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 mL/sec »20 g mL/sec »24g or central line 1.0 mL/sec Hand Injection: –Peripherally positioned catheter

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

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 LOCM(NICM) –All1-3% –Minornear 1% –Major (severe).04%(1:10,000) –Late5-8% Mortality rate - LOCM since :100,000

Adverse Contrast Reactions: Pediatric Population 321 children Questionnaire (73% return rate) Omnipaque 300/450 (Iohexol) Acute reactions1.9% –Minor (mild) –Older patients (> 24 kg) Late reactions6.2% –Mild or intermediate –Younger (< 24 kg) Mikkonen, Pediatr Radiol 1995; 25:350

Adverse Contrast Reactions Nonionic n=168,363 ( ) 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: % –> 50 yrs: % Katayama H. Radiology 1990; 175:621

Radiation Exposure

Radiation Risks CT –10% of all radiological procedures –65% effective dose of all medical x-rays Chest X-ray0.10 mSv Pediatric chest CT 1-10 mSv Adult chest CT 7-15 mSv Cardiac Cath20-30 mSvCardiac Cath20-30 mSv –(3.5 min fluoro/75 sec cine)

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

Safety Monitoring Radiation Dose Directly proportional to: –Tube current –Kilovoltage –Scan time –Slice thickness –Total number of slices

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

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 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 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  injection rate increases contrast enhancement Bae 2002

 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

Concentration vs. Enhancement Varying iodine concentrations Total iodine mass and flow rate constant (5mL/s)  iodine concentration =  contrast enhancement Bae 2002

Concentration vs. Flow Rate Left ventricular density ( 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 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 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 Potential for studying perfusion abnormalities associated with heart/lung disease

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