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!