Cardiovascular Imaging Flashcards
What is the most common radiological exam?
chest x-ray
How does an X-ray work? (3)
The image is produced
when radiation passes
through the body to
expose sensitive film
on the other side.
The ability of radiation
to penetrate structures
depends on their
energy and density of
the tissues and bones .
The different absorption of the rays by different tissues creates the
image. The image is generally displayed as a negative
what is measured in a Heart x-ray? (5)
- Size of heart
- Cardiac Thoracic Ratio
CTR 1:2 - Size and outline of aorta
- Evidence of stents, clips,
wires and valves
Cardiac Hypertrophy
Dextrocardia
Sternotomy Wires, Aortic and Mitral Valve Prostheses
Thoracic Aortic Aneurysm
How does a computed tomography (CT) scan work? (3)
The scans are produced by having the source of the x-ray beam encircle
or rotate around the patient.
The X-rays passing through the body are detected by an array of sensors.
Information from the sensors is computer processed and then displayed as an image on a video screen showing organs of interest at selected levels of the body with each scan being a single slice - CT examinations produce detailed organ studies
by stacking individual image slices.
CT- Dissecting Aortic Aneurysm
why would you take a Cardiac CT? (3)
- General
- Calcium Scoring -Coronary calcification
- CT Coronary angiography
Cardiac CT Background
1st generation of scanners lacked the temporal and spatial
resolution to accurately image the coronary arteries
Invasive coronary angiography was the only way to directly
visualise the coronary vessels
Basic coronary anatomy (8)
Left coronary artery
circumflex artery
left marginal artery
diagonal arteries
left anterior descending artery
posterior descending artery
right marginal artery
right coronary artery
What is calcium scoring + how is it scored? (7)
- Calcification of coronary arteries is a sign of atherosclerotic
disease - Amount and site of calcification can be quantified with CT
using visual interpretation and a computer algorithm
score:
0 = no evid CAD
1-10 = minimal CAD
11-100 = mild CAD
101-400 = Moderate CAD
>400 = Severe CAD
calcium scoring advantages (6)
- Quick (10-20 seconds acquisition)
- Non-invasive
- Low dose <2mSv (10 CXR’s)
- No preparation required
- No contrast
- Useful prognostic indicator in low risk
group – 70% would have no calcium
therefore reassured
Coronary Artery CT facts (3)
- 1990’s - Development of 64 slice with multi-row
detector CT scanners allowed high resolution
and faster imaging for accurate coronary artery
visualisation - Dose 7-10mSv
- Non-invasive – only i.v. iodinated contrast
(need to check renal function) - patient is
monitored only for a short period before
discharge
Cardiac CT ECG gating (3)
Retrospective / Prospective Gating
Image is acquired in seconds with ECG gating
(1 breath hold)
Vessel walking
Reconstruction of 3D vessel path in one plane with Maximal Intensity
Projection (MIP)
- Right coronary artery
Cardiac CT angiography - Right coronary occlusion benefits (5)
Directly visualises vessel lumen, wall and plaque (including soft plaque)
- More accurate than any other non-invasive
imaging modality - Studies show excellent diagnostic accuracy in
detection of significant stenoses: Sensitivity
94% Specificity 97% - Negative predicative value 95%
-if it is reported as “normal” the patient will not have any significant CAD!
Direct Arterial Access with advance of Catheter from Brachial or Femoral or Approach all the way into Coronary Arteries
intervention
Angioplatsy
Stenting
CTCA Limitations (4)
- Slow Heart Rate required (<80/min)
- Medication can be given to slow heart rate
- Difficulty assessing narrowing with severe
calcification - No functional information
- Cannot Intervene
Invasive
Digital Subtraction Angiography DSA (2)
- Iodinated contrast used
- Contrast images electronically overlaid and subtracted
from a negative template image
Treatment of acute coronary syndromes (2)
Coronary angioplasty
Coronary stenting: Bare metal Stent or Drug Eluting Stent: Anti-thrombotic + Anti-inflammatory
Cardiac Ultrasound Scan
Echocardiography
Echolocation
Duplex (Doppler Ultrasound)
M (Motion) -Mode Trace Curves
The “M” mode using a stationary transducer but a moving recording scanning the ultrasound pattern across the screen
so it is possible to study the dynamics of moving structures such as the ventricular wall or the valve leaflets
Pulsatility Index Flowrate
The combination of Doppler and “M” mode demonstrates the Haemodynamics of Blood flowing within the Heart
What is Magnetic Resonance Imaging (MRI)? (2)
- MRI uses a large magnet that surrounds the patient by a
magnetic field up to 8,000 times stronger than that of the
earth.
Like CT, MRI produces images, which are the visual equivalent of a
slice of anatomy. MRI, however, is also capable of producing those
images in an infinite number of projections through the body
Who can’t get MRI’s? (2)
people dependent upon cardiac pacemakers
those with metallic foreign bodies in the brain or around the eye.
Cardiac MRI
Both Anatomical and Functional
How does an MRI work? (3)
MRI produces images by
decoding radiofrequency
signals emitted from the
body’s hydrogen atoms
The scanner subjects nuclei of the body’s atoms to a radio signal, temporarily knocking select ones out of
alignment.
When the signal stops, the nuclei return to the aligned position,
releasing their own faint radio frequencies from which the scanner
and computer produce detailed images of the human anatomy
MRI Cine-Mode Projection
Functional studies are
obtained by stacking images acquired from separate time points of the cardiac cycle in a cine-loop
Cardiac Isotope Scan (5)
Gamma Camera detects the source of the radiation to build a picture:
- Multihole collimator for
direction of flux - Lead shield to minimize background radiation
- Scintillation crystal
- Photo-multiplier tubes
- Detector
Technetium Isotope Scan -Hot-Spot Myocardial Imaging +
Myocardial Infarction Scan (3)
The test is done 12 hours after a suspected heart attack.
The scanning is performed 3 hours
after the isotope is injected and the image acquisition takes about 1hr
The technetium accumulates in
heart tissue that has been damaged,
leaving “hot spots” that can be detected by the scintillation camera.
Technetium Heart Scan (3)
- The Nuclear heart scan uses technetium Tc-99m as it has a short physical half life = 6 hours= the amount of radioactive exposure is limited + provides better image
quality than previously used radioactive agents such as thallium because it has a shorter half life and can thus be given
in larger doses. - The study is repeated after several weeks to determine if any
further damage has occurred - Clinical studies demonstrate that technetium heart scans are just as or more accurate in detecting heart attacks as
electrocardiogram findings
Nuclear Medicine Tomographic Imaging:
Single photon emission computer tomography SPECT scanner (2)
Multiple images taken at different rotation angles to obtain 2-D matrix
3-D picture can be reconstructed using the source information
Anatomical Correlation
Myocardial Perfusion Scan (4)
- These scans are used to study blood flow to the heart and can
indicate conditions that could lead to a heart attack. - MPS is a non-invasive nuclear imaging technique that uses
radioactive imaging agents to assess the coronary blood flow
to the LV myocardium. - Radioactive tracer injected into vein travels through coronary
arteries and settles into LV myocardium. - A narrowed/diseased coronary artery will not allow as much
tracer through it as a normal one resulting in reduced amount of tracer to settle in the effected area of myocardium
Myocardial Perfusion Study
A narrowed vessel results in less tracer reaching the effected myocardium
MP Stress Test (5)
- Exercise causes coronary dilation
- In patients that have CAD exercise exaggerates the narrowing of coronary arteries.
- Comparison of rest and stress images differentiates between
reversible ischemia and established myocardial infarct - Treadmill exercise
- Pharmacologic stress agents: Adenosine + Dobutamine
Summed Perfusion Images
- Summed images are used to assess cardiac perfusion.
Rest and Stress images are compared to determine if a region of the heart is “ischemic” – starved of oxygen
- In the study below, the rest image indicates normal blood flow, but the stress image indicates abnormal blood flow in the Inferior-lateral region.
This indicates a stenosis in the left coronary artery
Normal Perfusion on both Rest and Stress
Good perfusion seen on both Stress (top line) and Rest (lower line)
Reversible Ischemia: Defect on Stress only
Poor perfusion on stress (top) but better perfusion on rest to indicate
reversible ischemia (lower)
Fixed defect on both studies: established Infarct
Poor perfusion on both Stress (top) and Rest (lower) imaging to
indicate established MI
3D View Reconstruction: Integrated 3D Function View
Myocardial Perfusion Imaging
- MP scans provide excellent negative predictive value.
Patients from the general population with normal
scans have <1% annual risk of cardiac events. - MPS is a non-invasive test and therfore cannot
intervene directly
Cardiac Pathway
mindmap
