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NITI TANK MD
Cardiovascular Imaging:Beyond US
Objectives
To understand common capabilities shared by CT and MRI
To understand strengths and limitations of CT and MRI
To learn the decision process from choosing CT versus MRI for cardiovascular imaging
Cardiac imaging
Indications for Cardiac CT
Diagnosis of coronary artery disease (CAD) in a patient with symptom(s) that may represent anginal equivalent:
Low or intermediate probability of stenotic CAD or stenotic bypass graft disease is sufficient. Stress testing is contraindicated, not tolerated, or likely to
generate artifact (body habitus, uncontrolled severe hypertension, large aortic aneurysm, left bundle branch block, suspicion of left main or severe multi-artery disease)
Stress testing result is equivocal or discrepant from clinical presentation
Persistence of symptoms despite normal stress test result – in place of catheterization
Evaluation of bypass graft anatomy – in place of catheterization
Concurrent evaluation of aorta is desired
Indications for Cardiac CTA
Coronary artery anomaly: < 40 years-old and symptoms or prior imaging suggests possible coronary anomaly
Evaluation of Fistula, AVM, aneurysm or pseudo- aneurysm
Planning interventional/surgical procedures Evaluation for stenotic CAD before valvular or aortic
surgery – in place of catheterization Evaluation of bypass graft and chest wall anatomy before
redo open heart surgery Left atrial / pulmonary vein evaluation before EP
procedures to treat atrial fibrillation Evaluation of left ventricular outflow tract and aorta before
TAVREvaluation of cardiac mass and/or thrombus
Cardiac CT Angiogram
Optimal patient characteristics* Resting sinus heart rate < 80 beats per minute Able to safely take metoprolol and nitroglycerin Able to hold breath for 10 seconds Body mass index (BMI) < 40 kg/m2
No stent or coronary artery bypass surgery *Expect sensitivity > 95% and specificity > 80% for
detecting stenotic CAD in patients meeting above criteria
Strong Contraindications Severe contrast allergy (anaphylaxis, shock, coma, seizure) Creatinine clearance < 30 ml/min or acute renal failure More than 10 PVCs/min Cannot follow instructions or cannot hold breath for 10 seconds High suspicion for acute coronary syndrome or stenotic CAD
Cardiac CT for Coronary artery disease
ECG synchronization- time image acquisition to cardiac cycle Retrospective Prospective
Contrast bolus types and timing depends on particular indication
Various reformats
Malignant right coronary artery
Cardiac Calcium Scoring
Addition of CACS to a prediction model based on traditional risk factors significantly improved the classification of risk
Calcium Score Presence of CAD0 No evidence of CAD1-10 Minimal evidence of CAD11-100 Mild evidence of CAD101-400 Moderate evidence of CADOver 400 Extensive evidence of CAD
Who should be screened using CT for calcium scoring?-Patient with risk factors for CAD (high cholesterol, DM, HTN, Smoker, obese, FH of CAD)What are the limitations of Cardiac CT for Calcium Scoring? - weight limit, CAD can still be present without calcium even if your calcium score is low, HR > 90, insurance coverage
Cardiovascular MRI - indications
CardiacGlobal and regional left and right ventricular function, and volumeCardiac and extracardiac massesCardiomyopathiesMyocarditisValvular function (qualitative/quantitative)Pericardial diseaseCongenital heart diseaseMyocardial viabilityPoor quality echocardiograms
Cardiac MRI technique
Morphology Wall motion Valve movement
Function Blood volume Flow Cardiac output
Tissue property Perfusion Delay enhancement Tumor/mass
Breath hold and ECG gated
Bright blood/dark blood sequence
Cine Phase encodingPerfusion and delay
postcontrast imaging
Subendocardial infarct vs. transmural infarct.
Infarct is bright on late-enhancement images.
When a coronary artery is occluded - subendocardially progresses towards the epicardium depending on the duration of the occlusion
Myocarditis
Myocarditis:
Delayed enhanced imaging demonstrate enhancement in the mid-myocardium
often in a patchy pattern
Nonvascular distribution
Interatrial septal aneurysm
an abnormal protrusion of the interatrial septum
ranging from >11mm to >15mm beyond normal excursion in adults
can be limited to the fossa ovalis or entire interatrial septum
Contraindications – Cardiac MRI
Severe claustrophobiaForeign body near vital structuresMetallic implants – Neurostimulators,
Cochlear implants, Bone growth stimulators, pacemakers/ICD
Intracranial aneurysm clipsVascular clampInsulin or infusion pump or implanted drug
infusion deviceAcute renal failure/ chronic renal dysfunction
Nephrotoxic Systemic Fibrosis (NSF)
occurs exclusively in patients with reduced renal function, including dialysis patients with gado use
Painful skin induration in extremities with contracture
Risk Factors: Any patient with eGFR <30 ml/min/1.73m2 Acute renal failure eGFR < 60 AND proinflammatory conditions/event
unenhanced MR may be a better approach for avoiding the potentially severe adverse effects associated with contrast materials.
Imaging of Aorta
Aneurysm Incidence of AAA – 4% of ppl > 50 yrs of age Thoracic Aortic aneurysm: increase incidence with
age, 7.5 per 100000, male predomiance
DissectionCongenital – Coartation, Vasculitis – GCA, Takayasu Arteritis
CTA of aorta
Great for evaluation of acute aortic disorder (dissection, aneurysm rupture) and endovascular rx planning/stent followup
short scan time and easy to performLarge FOVBetter spatial resolution (vs. MRA)
DisadvantagesLong post-processing timeRadiationBeam Harding from metallic artifact
MRA of aorta
Better for congenital abnormalities, serial follow up of Aneurysm, vasculitis, younger patient population
Endovascular rx planning in ascending aortic aneurysm with visualization of aortic valve on cine imaging
Large FOV Shorter post processing time No artifact related to calcifications Greater soft tissue contrast
Disadvantage Technically complex Longer scan time - Claustrophobia/motion artifact Breath holding: chest/abd Metallic artifact from stents
Coarctation of Aorta
Peripheral Vascular Disease
Occurs in approximately 1/3 of patients Over age 70 Over age 50 who smoke or have DM
Strong association with CAD Obvious associated risk of stroke, MI, cardiovascular death
Progressive disease in 25% with progressive intermittent claudication/limb threatening ischemia
Outcomes Impaired QoL Limb Loss Premature Mortality
Diagnosis modalities
Ankle Brachial Index (ABI)Noninvasive vascular laboratoryUltrasoundAngiography: MRA, CT, DSA
Location based on symptoms
Buttock/hip Usually indicates aortoiliac occlusive disease
(Leriche's syndrome) Some cases, thigh claudication too Question diagnosis of bilateral disease if erectile
dysfunction is not presentThigh
Occlusion of the common femoral artery leads to claudication in the thigh, calf, or both.
Calf Symptoms in upper 2/3 is usually due to SFA Lower 1/3 is due to popliteal disease.
Ankle Brachial Index
Cornerstone of lower extremity vascular evaluation Blood pressure cuffs, Doppler Ankle (DP or PT) to brachial artery pressure
Limitations
Noncompressible vessels Diabetes Renal Failure ABI >1.5 Use toe-brachial index
Normal >0.7 Rest pain <0.2
Subclavian/Brachiocephalic Occlusive disease
Duplex Doppler
Non-invasive method of evaluating the blood vessels.
Can obtain both anatomic and hemodynamic information. Anatomical detail
vessel wall intraluminal obstructive lesions perivascular compressive structures
Sensitivity of 92.6% and specificity of 97% (angiography gold standard) Inaccurate at adductor canal and the aorto-iliac regions. 95% accuracy in the detection of bypass graft stenosis, but can overestimate stenosis
Sensitivity of 92.6% and specificity of 97% (angiography gold standard) Inaccurate at adductor canal and the aorto-iliac regions. 95% accuracy in the detection of bypass graft stenosis, but can overestimate stenosis
Doppler Waveform Analysis: Hemodynamic Information
Doppler Waveform Analysis: Hemodynamic Information
Polack JF. Duplex Doppler in peripheral arterial disease. Radiol Clin N Amer 1995; 33 : 71-88.
PAD
Advances in noninvasive imaging methods: computed tomography (CT) magnetic resonance (MR) imaging
replaced invasive angiographic procedures lowering the cost and morbidity of diagnosis
CTA – current technique
Multidetector CT scanner necessary (4+)- most are now 64 Slice
Iodinated contrast volume similar to conventional angiography 80-150 cc Automated Scan Delay
Renal arteries to ankles10-minute examPost processing software crucial
AdvantagesAdvantages
Faster studyIntervention planningExcellent renal to ankle imaging – high
spatial resolutionImages soft tissue and bone as well
CT angiogram
CT limitations
Radiation PregnancyBlooming artifact from calcification• overestimate stenosis
Need contrast: renal function contrast allergy
Uncooperative patientBad PumpInconsistent pedal vessel visualizationLonger postprocessing time
MRA current technique
2D or 3D Time of Flight Unsaturated blood produces
bright signal and background tissue is saturated
Contrasted Enhanced 20-40 cc gadolinium injection Automated Scan delay
45-min examPooled sensitivity 97%,
specificity 96%Higher temporal resolution
MR angiogram - Advantage
Localizing disease extent and severityProvidence guidance for interventionNo radiationCan do with and without contrast (better for
patient with renal issue or contrast allergies)Better for foot and ankle vascular imaging
(esp in calcified vessels) Evaluate inflow grafts: (aorto–biiliac,
aortobifemoral, axillobifemoral)
MRA vs. DSAMRA vs. DSAMRA vs. DSAMRA vs. DSA
Limitations of MRI
Longer scan timePre-screening is required- Pacemakers/ICDs,
metallic implantsMore costlyMetal artifacts can be mistaken for stenosisUnable to characterize vascular calcificationUncooperative patient/ Claustrophobia
Carotid arterial disease
Carotid disease and Stroke
Up to 83% of all stroke, TIA or amaurosis fugax – maybe from carotid bifurcation atheromatous disease
CEA produces an absolute reduction of 17% in stroke at 2 years when compared to ASA in symptomatic patients with 70% or greater ICA stenosis. Risk of no treatment is 26%. Risk of CEA is 9%.
Carotid Ultrasound
Most accurate, noninvasive cost-effective method for diagnosis of extracranial cerebrovascular disease
Intimal thickening and plaque morphologyDoppler velocity spectral analysisHigh negative predictive valueVertebral artery evaluation (assess for
subclavian steal)
CTA of Carotid artery
Accurate quantitation and anatomic localization
Luminal and non-luminal informationTandem stenosisLongitudinal follow-up3D visualizationExtended coveragepooled sensitivity of 95% and a specificity of
98% for the detection of >70% stenosisGreater for assessment of dissection
Limitations of CTA
Contrast allergyRenal dysfunctionRadiationGross patient motion artifactsArtifacts
Beam hardening artifacts: amalgam, hyper-concentrated contrast
Reconstruction artifacts Contrast gradient artifacts Stent blooming artifacts
Simultaneous arterial and venous imagingLow ejection fraction (heart failure) Overestimation of stenosis in thick calcific plaque
MRA - Technique
TOF: Noncontract imaging which captures blood flow information 2d TOF – rapid acquisition but susceptible to motion
artifact 3d TOF – high spatial resolution (sensitive to medium to
high flow) but insensitive to low flow. Contrast enhanced MRA
May be performed in 2d imagine along any plane as well as 3d
Usually performed in coronal plane with reformats Fast imaging approximately 10 minutes
TOF vs.CEM
MRA – CEM vs. TOF
AdvantagesShorter scan time – less artifact from motionLarge coverageMore accurate stenosis and occlusion Contrast independent of flow directionLess contamination from short T1 materialsBetter SNR vs. TOF-MRALess signal loss from slow/turbulent flowGreat for evaluation of dissection
MRA – CEM vs. TOF
DisadvantagesLonger prep time – more venous signalLower spatial resolution (vs. TOF-MRA and CTA)Stents and metallic artifactT2* effects with bolusMaki effect (k-space ordering)Vessel diameter varies during contrast bolus cycleNo calcifications
Advantage of CTA over MRA
Provides information about vessel lumen and vessel wall in single study vs. contrast enhanced MRA (CE-MRA) and TOF-MRA
No vascular signal artifacts arising from slow/complex/turbulent/in-plane flow vs. TOF MRA
Higher spatial resolutionWidely availableEasier to acquireLower cost
Disadvantage of CTA over MRA
RadiationContrast allergy (1:30,000)Longer processing timeRenal insufficiencySimultaneous venous contaminationLimited direct hemodynamic information.Gross motion and beam hardening.
Upper extremity vascular disease
broad spectrum of diseases ranging from acute limb-threatening ischemia to chronic disabling disease.
less common than lower extremity vascular disease
affects as much as 10% of the population
CTA Upper extremity
evaluate for stenosis, occlusion, aneurysm, or embolic events, especially when they affect vessels proximal to the wrist.
vasculitis of large and medium arteries: Takayasu arteritis (TA), giant cell arteritis (GCA), and thromboangiitis obliterans
Limitation - imaging of small vessels of the hand due to inconsistent enhancement of these vessels.
Giant cell arteritis Thromboangiitis obliterans
Subclavian Steal
MRA upper extremity
Great for Large and medium vesselsGreat for small vessels below the wristEvaluation of stenosis, occlusion, trauma,
vasculitidesNo radiation, can be done without contrastLonger studyUsual contraindications.
MRA hand
When in doubt…call us!