Lecture 6 - Cardiac Imaging 1

What is the leading cause of death worldwide

Cardiovascular disease

What’re the layers of the heart

Pericardium → Epicardium → Myocardium → Endocardium

Role of pericardium

• Protective

• Fluid containing sac around heart

Role of epicardium

Outer surface of the heart

Role of myocardium

• Muscular layer

• Responsible for contraction

Role of endocardium

• Smooth inner lining of the chambers and valves

• Ensures blood an flow through heart without friction

Name the atrioventricular valves

• Tricuspid

• Mitral

Name the semilunar valves

• Pulmonary

• Aortic

Flow of mitral valve and what phase of cardiac cycle

• LA → LV

• Diastole

Flow of tricuspid valve and what phase of cardiac cycle

• RA → RV

• Diastole

Flow of pulmonary valve and what phase of cardiac cycle

• RV → pulmonary trunk

• Systole

Flow of aortic valve and what phase of cardiac cycle

• LV → aorta

• Systole

What is the difference between diastole and systole

• Diastole: Heart muscles relax and and ventricles fill with blood

• Systole: Heart muscles contract and pump blood to body

Explain why there is a difference in pressure between the RV and LV

• LV pumps blood into the high resistance systemic circulation

• RV pumps blood into the low resistance pulmonary circulation

• Both hearts pump the same amount of blood

Describe the pulmonary circulation

• RV → pulmonary trunk → pulmonary arteries → lungs → pulmonary veins → LA

• Low pressure

What kind of blood do the pulmonary arteries carry

Deoxygenated

What kind of blood do the pulmonary veins carry

Oxygenated

Describe the systemic circulation

• LA → mitral valve → LV → aorta → systemic arteries → tissues → veins → IVC/IVC → RA

• High pressure

What is cardiac hypertrophy

Abnormal thickening of cardiac walls

What is the cardiac output formula

CO = HR x SV

• CO: cardiac output (mL/min)

• HR: heart rate (beats/min)

• SV: stroke volume (mL/beat)

What is the stroke volume formula

SV = EDV - ESV

• SV: stroke volume

• EDV: end diastolic volume

• ESV: end systolic volume

What is the typical resting adult CO

5-6 L/min

What’re the branches of the aorta

• Brachiocephalic trunk

• Left common carotid

• Left subclavian artery

Where do the pulmonary veins attach to the heart

Posterior aspect of the LA

Which vessel carries the least amount of oxygen

SVC/IVC

Which vessel carries the most amount of oxygen

Pulmonary veins

What is a CTPA and what is it used for

• Pulmonary angiogram

• Uses IV contrast to display the vessels supplying the lungs

• Done to diagnose PE

What is CCTA and what is it used for

• Coronary CT angiogram

• To see if the coronary lumens patent

Where is the trigger ROI placed for a CTPA

Pulmonary trunk

Where is the trigger ROI placed for a CCTA

Ascending aorta

Name the vessel

Right coronary artery (RCA)

Name the vessel

Left circumflex artery (LCX)

Name the vessel

Left anterior descending (LAD)

CTPA or CCTA contrast timing earlier

CTPA

• Contrast reaches lungs and pulmonary vessels before coronary arteries

Where does the coronary tree lie in relation to the aortic valve

Superior

What plane is used to image coronary vessels

Epicardial fat

Origin of right coronary artery

Right aortic sinus

What does the RCA supply

• RA

• RV

• SA node

• AV node

Origin of left coronary artery

Left aortic sinus

Branches of the left coronary artery

• Left anterior descending

• Left circumflex

What does the LAD artery supply

Anterior LV

What does the LCX artery supply

Lateral LV

Why does CCTA need high resolution scanning

Coronary arteries are only 2-5mm in diamter

Why is diastole preferred for cardiac imaging

• Ventricles are full

• AV valves open

• Semilunar valves closed

What does the P wave represent

• Atrial depolarisation

• When the atria are contracting to push blood into the ventricles

What does the QRS complex represent

• Ventricular repolarization

• R wave is used as the trigger for ECG gated imaging

• Ventricles contract to eject blood into the pulmonary trunk and aorta

What does the T wave represent

• Ventricular repolarisation

• Ventricles relax and prepare to fill with blood

Describe the route of electrical signal in the heart

SA node → AV node → bundle of His → Purkinje fibers

Normal or nah

• No P wave

• Atrial fibrillation

Normal or nah

• Ventricular fibrillation

• Chaotic and irregular

What is eh ideal HR for CCTA

60 bpm

What is atherosclerosis

Inflammatory disease that causes build up of fat to block the lungs

Describe the inflammatory process of atherosclerosis

Endothelial dysfunction (inner layer of arteries)

↓

LDL (low density lipoprotein) enters vessel intima

↓

LDL oxidises

↓

Monocytes enter

↓

Inflammatory mediators released

↓

Plaque grows

↓

Fibrous cap weakens

↓

Plaque rupture

↓

Thrombus

↓

Myocardial infarction

What’re the AHA plaque stages

1-2: Adaptive intimal thickening fatty streak, below CCTA spatial resolution

3: Pathological intimal thickening

4: Atheroma with necrotic lipid core (can be seen on CCTA)

5: Fibroatheroma (calcified)

What is positive remodeling

• Outward growing of plaque

• Vessel expands as plaque grows outwards, away from lumen

• High risk feature

What is negative remodeling

• Inward growing of plaque

• Vessel shrinks inwards

What're the high risk plaque features on CCTA

• Low attenuation plaque (lipid rich core)

• Spotty calcium (small calcifications)

• Positive remodeling

• Napkin ring sign (high attenuation rim with low attenuation core)

If plaque shows up very bright on CCTA what kind of plaque is this

Calcified

What is going on here

Nothing

What is going on here

Negative remodeling

What is going on here

• Negative remodeling

• Soft lipid plaque

What is the FAI

• Fat attenuation intext

• Evaluates the perivascular inflammation around the coronary arteries

How does inflammation change fat

• Normal lipid rich fat has strong negative HU

• Inflammation changes adjacent fat so it becomes more positive (moves towards 0)

-60 HU vs -90 HU, which is more inflamed

-60 HU due to the FAI

What is the high risk cut off for FAI

FAI ≥ −70.1 HU = high-risk perivascular inflammation (moving towards 0 = higher risk)

What is CAC

• Coronary artery calcium scoring

• measures atherosclerotic calcified burden not the degree of coronary narrowing

Describe prospective gating

• Tube current only on during a chosen cardiac phase, mid-late diastole

• Scanner waits for R wave

What’re the disadvantages of prospective gating

• Slow HR

• Regular rhythm required

• Predictable RR interval

Describe retrospective ECG gating

• Scanner acquires data throughout the cardiac cycle

• ECG trace is recorded and images can later be reconstructed at different phases

What’re the advantages of using retrospective ECG gating

• High HR

• Irregular rhythm

• Functional assessment

• Reconstructing multiple phases

Explain what partial-volume averaging is and how it relates to slice thickness

• Image artifact that happens when a single voxel contains a mix of tissue types

• Having thicker slices leads to partial-volume averaging and can obscure pathology

What is the slice thickness for CCTA

0.5-0.75mm recons

What is the slice thickness for calcium scoring

2.5-3mm

Purpose of beta-blockers

• Control HR/rhythm

• Decreases HR

• Regularizes rhythm

• Lengthens diastole

• Improves motion free imaging window

What is the role of GTN

• Coronary vasodilation

• Increases coronary vessel caliber

• Improves lumen visualization (bigger coronary lumen)

• Does not control HR

Process of CCTA

Preparation → HR target (tall R wave) → GTN → acquisition → contrast → recon

What’re the contraindications for GTN

• Hypotensive

• Server aortic stenosis

• Recent PDE-5 inhibitor (Viagra)

What is the HU of calcium

≥130 HU

What’re the levels of Agatston scoring

0: No detectable calcium

1-99: Mild

100-299: Moderate

≥300–400: High burden

High calcium score ≠ proof of severe stenosis

What’re the post processing ways for CCTA

• cMPR/CPR

• Orthogonal MPR

• MIP

• Volume rendering

What is cMPR/CPR

• Curved multiplanar/planar reconstruction

• Follows the coronary centerline and unrolls the artery

• Useful for seeing a long coronary segment

What is orthogonal MPR

• Cross section perpendicular to vessel centerline

• Can help measure lumen diameter, vessel wall, stenosis

What is stenosis

Narrowing of the lumen

What is MIP

• Highlights highest attenuating structures

• Useful for calcium

• Contrast filled vessels

• Can conceal soft plaque

What is volume rendering

• Useful for overview of anatomy

• Not used for stenosis grading

• HU measurements

What is a myocardial perfusion used for

• Evaluates contrast distribution through the myocardium

• Uses stress agent (adenosine)

• Anatomy and physiology

Why is cardiac MRI used

• Non-ionizing radiation

• issue characterization

• Follow ups

• Congenital heart disease

• Gives good values for ejection rate, stroke volume, mass

When would you use CMR vs CCTA

CMR: muscle related clinical question

CCTA: coronary artery disease

What is the magnetohydrodynamic effect

• The current of blood flow behaves like conductive fluid while interacting with the magnet

• Interferes with the ECG signal and produces abnormal T wave

• Scanner can confuse R with T wave

Cine on CMR = ?

Retrospective gating

What is steady state free precession (cine) CMR

• Blood = bright

• Myocardium = dark

Used for:

• Wall motion

• Ventricular volumes

• Valve motion Jets

What is T1/T2 black blood CMR

• Blood appears dark

T1:

• Anatomy

• Fat infiltration

T2:

• Oedema

• Myocardial infarction

What is late gadolinium enhancement used for

• 10-15min after GAD

• Scar tissue

• Infarction

Describe the vertical long axis view

• 2 chamber view

• LA and LV

• LV → mitral valve → LA

Describe the 4 chamber view (horizontal long axis view)

• RA

• RV

• LA

• LV

• Mitral valve

• Tricuspid valve

Describe the short axis view

• Base → apex

• Volume

• Wall motion

Outflow tract views

LVOT: Aortic outflow

RVOT: Pulmonary outflow

What is tetralogy fallot

• Ventricular spetal defect

• Overriding aorta

• Pulmonary stenosis

• RV hypertrophy

What is TGA

• Transposition of the great arteries

• When the aorta arises from RV

• When the pulmonary artery arises from LV

What is ebstein anomaly

• Abnormal tricuspid valve

Causes:

• Apical displacement

• Arterialization of part of the RV

• Enlarged RA