Danny Cho Wai Man, Rad I (DR), Queen Mary HospitalApril 2011

Outline

Introduction Clinical investigations of IHD MRI in the assessment of IHD Safety in Cardiac MR

examination Imaging protocol for IHD in

QMH

Introduction

In Hong Kong, heart disease is the second leading cause of death in 2009 (after cancer)

More than six thousand and four hundred people died from heart disease in 2009

It accounts for 15% of all death

Introduction

Diagnosis of IHD requires careful history taking and physical examination, along with direct investigation

Diagnostic imaging plays an important role in the proper assessment and management of coronary artery disease

Clinical investigations of IHD

Electrocardiography (ECG) Echocardiography Nuclear medicine Positron emission tomography (PET) Computed tomography (CT) Coronary angiography Magnetic resonance imaging (MRI)

Electrocardiography(ECG) One of the standard investigation

performed in patients with chest pain Exercise stress electrocardiography is

the most widely applied test to obtain objective evidence of myocardial ischaemia and significant coronary artery disease

Echocardiography Provides a good estimate of

ventricular size as well as regional and generalized left ventricular wall motion

Stress echocardiography either by exercise or by pharmacological means is comparable in accuracy to radionuclide testing for diagnosis of coronary artery disease

Radionuclide Imaging

Provides higher sensitivity and specificity for the diagnosis of IHD than exercise ECG testing

It can provide functional or physiological and prognostic information, is quantifiable and reproducible

Positron Emission Tomography (PET)

Provides more accurate result for the detection of CAD

Provides an estimate of coronary blood flow and coronary flow reserve as well as myocardial viability

Popularity limited by the high cost

Computed Tomography (CT)

CT angiography provides high resolution imaging of the heart and give good visualization of the coronary arteries

Coronary Angiography Gold standard in the

diagnosis of ischaemic heart disease

It has a very good spatial resolution of 300m

Ascertains the anatomic extend and severity of the atherosclerotic involvement of the coronary arteries

Magnetic Resonance Imaging (MRI)

Global cardiac function and regional wall motion abnormalities

Regional perfusion Myocardial infarction Coronary MRA

Cardiac function & regional wall motion

For patients with heart failure or myocardial infarction due to IHD

Assessment of cardiac function is important prior to commencement and for monitoring of therapy

Cardiac function & regional wall motion

Good spatial and temporal resolution Allowing imaging of systolic and diastolic

phases of both right and left ventricles Cine short-axis images from base to

apex Yields reproducible data for myocardial

mass and ventricular size Regional wall thickness of ventricle,

valvular motion, and regional wall motion can be clearly defined

Good contrast between blood pool and myocardium

Cardiac function & regional wall motion Commercially available software

yields calculations of stroke volume, ejection fraction, end-systolic volume, end-diastolic volume, myocardial wall thickening within few minutes

Advantages of non-invasiveness, no irradiation, high reproducibility, and high repeatability of results make it an ideal tool for serial measurement and monitoring of cardiac function

First-pass Myocardial Perfusion For the detection of regional ischaemia Good temporal resolution to image

first-pass of contrast medium through myocardium

Adequate contrast between normal and ischaemic myocardium

Adequate coverage from apex to base of the heart (multiple short axis slices in basal, mid-ventricular, and apical regions of left ventricle)

First-pass Myocardial Perfusion In view of the auto-regulatory function

of coronary arteriolar beds, stenosed coronary arteriolar beds will vasodilate to maintain adequate blood supply to myocardium

Stenosed coronary arteries usually have normal myocardial perfusion at rest

First-pass myocardial perfusion during stress condition is necessary for demonstration of perfusion defects

Stress Cardiac MRI Exam.

Physical stress may not be feasible within the MRI environment

Pharmacological stress will be more easily to implement using vasodilator e.g. adenosine

Myocardial blood flow will increase fourfold to fivefold downstream of normal coronary arteries, but does not increase downstream of stenosed arteries because the related arteriolar beds have already vasodilated maximally

Stress Cardiac MRI Exam. Myocardium receiving

blood supply from an significantly stenosed coronary artery will show hypoperfusion compared with normal myocardium

Normally perfused myocardium shows greater enhancement at a faster rate than hypoperfused myocardium

LV

Normalmyocardium

Infarcted orIschaemic

myocardium

Adenosine Stress Cardiac MRI Exam.

Short half life (<10 secs) Better patient tolerence Side effects of Adenosine

Mild decrease in systemic blood pressure Mild increase in heart rate Increase respiratory rate Headache Dizziness Shortness of breath Nausea flushing

Contraindications of Adenosine

Acute Myocardial infarction within few days

Asthma Second- or third-degree atrio-

ventricular block Sick sinus syndrome Symptomatic bradycardia

Patient Preparation for Adenosine Stress MRI Exam. Refrain from caffeinated food and

drink for 24 hoursSuch as coffee, tea, coke and chocolateAdenosine antagonist Interfere with the ability of Adenosine to

dilate arteriesFalse negative examination result

Adenosine Stress Cardiac MRI Exam. Adenosine at 140g/kg/min

intravenously for 4 mins Gadolinium-DTPA (0.05 mmol/kg) is

rapidly infused (4ml/sec) First-pass imaging is performed using

gradient echo pulse sequence on multiple short axis slices (basal, middle, and apex) of the left ventricle during a breath hold

Adenosine Stress Cardiac MRI Exam. Normal myocardium shows a

“blush” of bright signal throughout the cardiac cycle

Ischaemic or infarcted myocardium will show a persistent dark signal, either subendocardial or transmural in location

The perfusion defect shall follow the supply territory of the coronary arteries

Myocardial Viability Differentiation between

viable and non-viable myocardium is important

Transmural extent Viable myocardium may

benefit from revascularization and resume normal cardiac function

Function cannot be restored to nonviable tissue

Myocardial Infarction

Post-gadolinium myocardial delay enhancement technique

Areas of infarct or scar have increased volume of distribution of gadolinium as compared to normal myocardium

There is more efficient egress of gadolinium from normal myocardium compared to infarcted tissue

Hyperenhancement of infarcted myocardium 10-20mins after contrast administration

Ischaemia vs Infarction

Ischaemic and infarcted myocardium can be differentiated by first-pass myocardial perfusion and myocardial delay enhancement techniques

Ischaemic but viable myocardium

Non-viablemyocardium

Rest perfusion Normal signal Signal lossStress perfusion Signal loss Signal lossMyocardial delay enhancement

None Presence

Safety of Stress Cardiac MRI Exam. Staff of multiple

disciplines (including Radiographers, Radiologists, Nurses & Cardiologists will be involved in stress cardiac MRI examination Only properly screened

personnel shall be allowed to enter the control access area of MRI Scanner Room

Safety of Stress Cardiac MRI Exam. Patient screening for any contra-indications of MRI and

Adenosine e.g. cardiac pacemaker or asthmatic history ECG investigation will be performed before stress MRI

examination to assess any second- or third –degree heart block or acute myocardial infarction, which are contraindications for Adenosine stress examination

Adequate patient preparation ECG investigation will be performed after stress MRI

examination to exclude Adenosine induced infarction

Safety of Stress Cardiac MRI Exam. A total of 0.2mmol/kg Gd-based

contrast medium will be administered for rest perfusion, stress perfusion and myocardial delay enhancement imaging

In view of the risk of Nephrogenic Systemtic Fibrosis (NSF) for patients with severe or end-stage renal disease, renal function test result should be checked for high-risk patients

Informed consent shall be obtained if necessary

Safety of Stress Cardiac MRI Exam. Multiple MRI-safe ancillary equipment

are necessary for stress MRI examination Infusion pump Power injector Vital sign monitoring system

NIBP, Pulse rate, SaO2

ECG electrode and leads

Safety of Stress Cardiac MRI Exam. Examination checklist Patient monitoring records

Safety of Stress Cardiac MRI Exam. Aminophylline shall be ready for

emergency situation Belongs to a group of medicines

known as xanthines Treat breathing difficulties associated

with reversible airway obstruction, as in bronchial spasm

Safety of Stress Cardiac MRI Exam. Cardiologist will stay in

the MRI scanner room during administration of Adenosine to monitor the patient’s condition

The infusion of Adenosine will be terminated in case of symptoms of flushing, SOB and chest pain

Continuous monitoring of vital signs during entire stress MRI examination

Protocols of Adenosine Stress MRI Exam. in DR, QMH

MyocardialPerfusion(Stress*)

Short axis view

Myocardial Perfusion

(Rest)Short axis view

Myocardial Viability Study:

Short axis, 2-, 3- & 4-chamber views

0.05mmol/KgMR Contrast

Media

0.05mmol/KgMR Contrast

Media

Localizer Sequences

Additional 0.1mmol/KgMR Contrast Media injected immediately

after rest perfusion study

Delay 10mins

FIESTA Cine Short Axis View

FIESTA Cine2-chamber, 4-chamber or 3-chamber view

Delay 10mins

Total Imaging Time: about 45mins

Localizers

3-plane localizer, 2-chamber, 4-chamber localizer

The goal is to prescribe imaging planes along short- and long-axis of the heart Short axis view 2-chamber view 3-chamber view 4-chamber view

Localizers3-plane localizer

Short Axis View Cover from base to apex Quantification of LV & RV volumes,

ejection fraction and myocardial mass

Evaluation of regional wall motion

Long Axis Views2-Chamber 3-Chamber

4-Chamber

Left Ventricular Segmentation

First-pass Myocardial Perfusion

Rest Stress

Myocardial Delay Enhancement

Conclusion

MRI has a definite role in the assessment and management of patients with IHD

It is an ideal imaging technique for serial follow-up and screening due to being non-invasive and involves no irradiation

An single examination can assess cardiac function, regional wall motion, regional perfusion, and the extent of infarction

Thank you