Cardiovascular imaging Flashcards
What is used for anatomical Studies/imaging?
- General X-Ray
- Computer Tomography
- Interventional Coronary Angiogram
What is the most common radiological examination?
The chest x-ray
How do the general chest x-rays work?
- 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 does the chest x-ray show about the heart?
- Size of heart
- Cardiac Thoracic Ratio
- Size and outline of aorta
- Evidence of stents, clips, wires and valves
What technique is used for general chest x-rays?
Projection - P-A (posterior to anterior projection, heart has to be as close as possible to the film)
What do Cardiac CTs show about the heart?
- General – look at the heart and structures
- Calcium Scoring
- CT Coronary angiography
How do Cardiac CTs work?
- 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.
What is calcium scoring?
It assesses calcification within coronary vessels
What is calcification a sign of?
Calcification of coronary arteries is a sign of atherosclerotic disease
How can we found about the amount and site of calcification?
Amount and site of calcification can be quantified with CT using visual interpretation and a computer algorithm
What are the benefits of using CT for detecting calcification/issues in the heart?
- 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
What is Cardiac CT ECG gating?
- Retrospective / Prospective Gating – we need to take pictures at a specific time/phase
- Image is acquired in seconds with ECG gating (1 breath hold)
What is a coronary artery CT?
- 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
What is vessel walking?
Reconstruction of 3D vessel path in one plane with Maximal Intensity Projection (MIP) – makes the images of the vessel clearer/detailed
What is CT Cardiac Angiography (CTCA)?
- 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!
CTCA Limitations?
- 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
What does the coronary angiogram involve?
Direct Arterial Access with advance of Catheter from Brachial, or Femoral or Approach all the way into Coronary Arteries
It's • Invasive • Direct intervention • Angioplatsy • Stenting
How is Digital Subtraction Angiography (DSA) carried out:
- Iodinated contrast used
* Contrast images electronically overlaid and subtracted from a negative template image
What are the treatments of acute coronary syndromes?
Balloon with a catheter inserted, balloon inflated when the site of plaque reached, balloon squishes the plaque against the wall and even after balloon is removed artery stays open
Coronary Stenting used if balloon doesn’t work:
• Bare metal Stent
• Drug Eluting Stent
o Anti-thrombotic
o Anti-inflammatory
Examples of functional imaging?
- Ultrasound
- MRI
- Nuclear Imaging
How does Cardiac Ultrasound Scan Echocardiography work?
- Uses soundwaves similar to echolocation to create an image
* Happens in real time
How does Duplex (Doppler Ultrasound) work?
- If the red blood cells are moving towards you the frequency is high
- If they are moving away the frequency will be lower
What is 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.
What is Pulsatility Index Flowrate?
The combination of Doppler and “M” mode demonstrates the haemodynamics of Blood flowing within the Heart
What are Cardiac MRI?
- Both Anatomical and Functional
* No radiation and ionising x-rays
How does Magnetic Resonance Imaging work?
- MRI uses a large magnet that surrounds the patient by a magnetic field up to 8,000 times stronger than that of the earth.
- 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 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
What patients cant undergo MRIs?
people dependent upon cardiac pacemakers and those with metallic foreign bodies in the brain or around the eye.
What are MRI Cine-Mode Projections?
Functional studies are obtained by stacking images acquired from separate time points of the cardiac cycle in a cine-loop.
How does a Cardiac Isotope Scan work?
Gamma Camera detects the source of the radiation to build a picture
Needed for this:
• Multihole collimator for direction of flux
• Lead shield to minimize background radiation
• Scintillation crystal
• Photo-multiplier tubes
• Detecto
Examples of Technetium Isotope Scans?
Hot-Spot Myocardial Imaging/Myocardial Infarction Scan
Technetium Heart Scans
How does a Hot-Spot Myocardial Imaging/Myocardial Infarction Scan work?
- 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 one hour.
- The technetium accumulates in heart tissue that has been damaged, leaving “hot spots” that can be detected by the scintillation camera.
How do Technetium Heart Scans work?
- The Nuclear heart scan uses technetium Tc-99m as it has a short physical half life of 6 hours, thus the amount of radioactive exposure is limited and 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
What is Nuclear Medicine Tomographic Imaging?
Single photon emission computer tomography SPECT scanner
• Multiple images taken at different rotation angles to obtain 2-D matrix
• 3-D picture can be reconstructed using the source information.
• The resolution isn’t as clear as the CT scan but shows how well perfused the heart is
What is a Myocardial Perfusion Scan?
- 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 myo cardium.
- 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.
What is the myocardial perfusion test?
- 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.
Pharmacologic stress agents for patients that cant do exercise?
- Adenosine
* Dobutamine
What are 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
How is Myocardial Perfusion Imaging done?
- 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 therefore cannot intervene directly
