The heart Flashcards
Features of
- Heart disease
- Angina
- Heart Attack
- Heart disease - plaque builds up in artery
- Angina - harder for blood to get through artery
- Heart Attack - plaque cracks and blood clot blocks artery
Why is it diagnostically useful to stress the heart?
2 ways to do it?
At rest blood flow, normal and stenosed vessel could have the same bloodlow. At stress, the stenosing is much more noticable as reduced perfusion.
Two ways to stress:
- Get patient to exercise: Inject RN at 90% predicted max heart rate
- Pharacological stress - inject vasodilator, e.g. Rapiscan; inject 0.4mg slowly followed 10-20s later by the radionuclide. Side effects can be headache or in more rare cases cardiac arrest.
Stress with Adenosine
How does it work?
Why was it used?
- vasoldilation by stimulation of all adenosine receptors in smooth muscle
- increases coronary blood flow 3-4x
- this was the old method and was combine with exercise, known to work and cheap. But can get 8-10 patients done in 1 session.
Stress with Rapiscan
How does it work?
Why is it preferred?
- Coronary vasodilator only.
- No side-effects.
- 2-3 min biological half life
- Stress protocal with single bolus
- Not effected by b-blockers
- More expensice
- 12-15 throughput per session
Heart protocol features:
1 or 2 days
which first?
how much Tc
2-day
- Should do stress first, if notmal you might not need to do the rest.
- 2x400MBq
1-day
- Stress and rest on same day
- Half of life of Tc is 6hours, so you have to swamp the early scan activity with late. i.e. you need to give a lot more on the second one to differentiate it from what would still be present in the first scan.
- Typical dose 250MBq early scan 750 late
How is RP taken up in heart?
How do sestamibi and myoview compare?
Both are taken up by passive diffusion. Uptake is determined by SA of vascular beds, myocardial uptake is related to blood flow. At rest, accumulates in ciable myocardial tissue. (infarct, dead tissue - lack of uptake). At stress, accumulates in myocardial tissue depending on blood flow, ischemia is present as loss of accumulation.
Sestamibi
- Need higher counts
- Better image quality (better heart:lung ratio)
Myoview
- shorter biological half life = higher patient throughput and easier to do 1 day protocol
- Faster liver clearence = lower effective dose
What should patients od on the day of the scan>
- Fast / light breakfast
- Stop smoking – Blocks vasodilatory effect of stress agents
- Stop certain drugs
- Avoid caffeine – Binds to adenosine receptors
- Cannula inserted
What does normal and abnormal heart anatomy look like in 3 axis
short
vertical long
horizontal long
What is a bulls-eye plot ?
Why do we use it?
Split up the left ventrical into a cont, with each region corresponding to clinically significant area of heart. Converting 3D volume to 2D topographic map, allos you to quantitatively compare with normal data.
17 segments, score uptake defect 0 (normal) -4 (no uptake) for each segment.
ECG gated heart filter
How does it work?
How do you deal with variability in length of cycle (R-R)
Detecting the heart’s cycle, can see how signals spread through atrial nodes, apex, ventricles.
Use their ECG to gate the acquisition to compare how the heart looks in diastole or systole parts of the cycle.
You can do beat rejection, look at the number of counts in the edge bins, and decide whether to accept or reject it.
Our patient volunteer, Mrs Coron Alartery, is undergoing a cardiac scan to determine her ejection fraction ahead of receiving chemotherapy.
Coron’s end diastolic volume is 125ml and her end systolic volume is 58ml what is her ejection fraction?
- EJF = (EDV – ESV) / EDV x 100%
- EJF = (125 – 58)/125 x 100% = 67/125 x 100%
- EJF = 53.6%
EDV (end-diastolic volume) – ESV (end-systolic volume) – LVEF (Left ventricular ejection fraction)
Brief summary of PET
- Decay produces positiron which goes on to anihilate with an electron. result is two 180 deg separated gammas 511keV
- Ring of detectors around patient to record events
- Only record if the events occur at same time.
How do you do cardiac PET?
- CT attenuation correction at rest
- inject 82Rb 1110MBq, acts as potassiun analogue
- PET rest
- Adenosine infusion
- Rb infusion 1110MBq
- PET stress
- CTAC stress
Cardiac PET vs SPECT
Resolution
Efficiency
Radiation Dose 1.4 – 1.9mSv ~8mSv
AC
Sensitivity
Specificity
Cost / Patient
- Resolution: ~5mm, ~10mm
- Radiation Dose: 1.4 – 1.9mSv, ~8mSv
- AC: CT, CT (less common)
- Sensitivity 91% 87%
- Specificity 89% 73%
- Cost / Patient: 400Euro/patient, 230Euro/Patient
- Cost Equipment: £2M for PET Scanner, £0.5M SPECT Scanner
PET GIVES SUPERIOR IMAGE QUALITY BUT MORE EXPENSIVE
SUMMARY
Why we do myocardial imaging? – To image areas of hypo-perfusion in the myocardium as an indicator of coronary artery disease
What does the test involve? – Tc99m agent, stress agent, comparison of myocardium at stress and at rest
How do we gate images using ECG? – Using “bins” to split up the count data, caution of gating artefacts
What is Cardiac PET and how does it compare to SPECT? – A myocardial imaging technique using PET, superior image quality but more expensive
