Transcript Peripheral Vascular Disease: Beyond US

Cardiovascular Imaging:
Beyond US
NITI TANK MD
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.
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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 pseudoaneurysm
 Planning interventional/surgical procedures
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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 TAVR
 Evaluation 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
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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 CAD
0
No evidence of CAD
1-10
Minimal evidence of CAD
11-100
Mild evidence of CAD
101-400
Moderate evidence of CAD
Over 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
Cardiac
 Global and regional left and right ventricular
function, and volume
 Cardiac and extracardiac masses
 Cardiomyopathies
 Myocarditis
 Valvular function (qualitative/quantitative)
 Pericardial disease
 Congenital heart disease
 Myocardial viability
 Poor quality echocardiograms
Cardiac MRI technique
 Morphology
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Wall motion
Valve movement
 Breath hold and ECG
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 Function
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Blood volume
Flow
Cardiac output
 Tissue property
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Perfusion
Delay enhancement
Tumor/mass
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gated
Bright blood/dark blood
sequence
Cine
Phase encoding
Perfusion and delay
postcontrast imaging
Infarct is bright on lateenhancement images.
When a coronary artery
is occluded subendocardially
progresses towards the
epicardium depending
on the duration of the
occlusion
Subendocardial infarct vs.
transmural infarct.
Myocarditis:
Delayed enhanced
imaging demonstrate
enhancement in the
mid-myocardium
often in a patchy pattern
Nonvascular distribution
Myocarditis
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
Interatrial septal aneurysm
Contraindications – Cardiac MRI
 Severe claustrophobia
 Foreign body near vital structures
 Metallic implants – Neurostimulators, Cochlear
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implants, Bone growth stimulators, pacemakers/ICD
Intracranial aneurysm clips
Vascular clamp
Insulin or infusion pump or implanted drug infusion
device
Acute 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:
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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
 Dissection
 Congenital – 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 perform
 Large FOV
 Better spatial resolution (vs. MRA)
Disadvantages
 Long post-processing time
 Radiation
 Beam Harding from metallic artifact
MRA of aorta
 Better for congenital abnormalities, serial follow up of Aneurysm,
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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
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Impaired QoL
Limb Loss
Premature Mortality
Diagnosis modalities
 Ankle Brachial Index (ABI)
 Noninvasive vascular laboratory
 Ultrasound
 Angiography: 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
present
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 Thigh
 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
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 Subclavian/Brachiocephalic Occlusive disease
Duplex Doppler
 Non-invasive method of evaluating the blood vessels.
 Can obtain both anatomic and hemodynamic
information.
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Anatomical detail
vessel wall
 intraluminal obstructive lesions
 perivascular compressive structures
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Doppler Waveform Analysis: Hemodynamic
Information
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
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
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80-150 cc
Automated Scan Delay
 Renal arteries to ankles
 10-minute exam
 Post processing software crucial
CT angiogram
Advantages
 Faster study
 Intervention planning
 Excellent renal to ankle imaging – high spatial
resolution
 Images soft tissue and bone as well
CT limitations
 Radiation
 Pregnancy
Blooming artifact from calcification
• overestimate stenosis
 Need contrast:
 renal function
 contrast allergy
 Uncooperative patient
 Bad Pump
 Inconsistent pedal vessel visualization
 Longer 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 exam
 Pooled sensitivity 97%, specificity
96%
 Higher temporal resolution
MR angiogram - Advantage
 Localizing disease extent and severity
 Providence guidance for intervention
 No radiation
 Can 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. DSA
Limitations of MRI
 Longer scan time
 Pre-screening is required- Pacemakers/ICDs,
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metallic implants
More costly
Metal artifacts can be mistaken for stenosis
Unable to characterize vascular calcification
Uncooperative 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.
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Risk of no treatment is 26%.
Risk of CEA is 9%.
Carotid Ultrasound
 Most accurate, noninvasive cost-effective method for
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diagnosis of extracranial cerebrovascular disease
Intimal thickening and plaque morphology
Doppler velocity spectral analysis
High negative predictive value
Vertebral artery evaluation (assess for subclavian
steal)
CTA of Carotid artery
 Accurate quantitation and anatomic localization
 Luminal and non-luminal information
 Tandem stenosis
 Longitudinal follow-up
 3D visualization
 Extended coverage
 pooled sensitivity of 95% and a specificity of 98% for
the detection of >70% stenosis
 Greater for assessment of dissection
Limitations of CTA
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Contrast allergy
Renal dysfunction
Radiation
Gross patient motion artifacts
Artifacts
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Beam hardening artifacts: amalgam, hyper-concentrated contrast
Reconstruction artifacts
Contrast gradient artifacts
Stent blooming artifacts
 Simultaneous arterial and venous imaging
 Low ejection fraction (heart failure)
 Overestimation of stenosis in thick calcific plaque
MRA - Technique
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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.
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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
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TOF vs.CEM
MRA – CEM vs. TOF
Advantages
 Shorter scan time – less artifact from motion
 Large coverage
 More accurate stenosis and occlusion
 Contrast independent of flow direction
 Less contamination from short T1 materials
 Better SNR vs. TOF-MRA
 Less signal loss from slow/turbulent flow
 Great for evaluation of dissection
MRA – CEM vs. TOF
Disadvantages
 Longer prep time – more venous signal
 Lower spatial resolution (vs. TOF-MRA and CTA)
 Stents and metallic artifact
 T2* effects with bolus
 Maki effect (k-space ordering)
 Vessel diameter varies during contrast bolus cycle
 No calcifications
Advantage of CTA over MRA
 Provides information about vessel lumen and vessel
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wall in single study vs. contrast enhanced MRA (CEMRA) and TOF-MRA
No vascular signal artifacts arising from
slow/complex/turbulent/in-plane flow vs. TOF MRA
Higher spatial resolution
Widely available
Easier to acquire
Lower cost
Disadvantage of CTA over MRA
 Radiation
 Contrast allergy (1:30,000)
 Longer processing time
 Renal insufficiency
 Simultaneous venous contamination
 Limited 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
Subclavian Steal
Thromboangiitis
obliterans
MRA upper extremity
 Great for Large and medium vessels
 Great for small vessels below the wrist
 Evaluation of stenosis, occlusion, trauma,
vasculitides
 No radiation, can be done without contrast
 Longer study
 Usual contraindications.
MRA hand
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