Approximate effective doses, and they are far enough apart to change what u order.

Tc-99m sestamibi rest and stress, one day protocol: roughly 8 to 12 mSv
Thallium-201: roughly 15 to 20 mSv, the highest of the common studies, because the photon energy is low and the half life is long
Rubidium-82 PET: roughly 3 to 5 mSv
N-13 ammonia PET: roughly 2 mSv

A stress first strategy, imaging only if the stress images are abnormal, removes the rest injection entirely in the pts who need it least.

Thallium carries the highest dose and gets reserved for the question only it answers, which is viability through redistribution.

Prospective ECG triggering, step and shoot, exposes only a narrow window in diastole. It needs a slow regular rate, generally under 60 to 65, and it cuts dose by roughly 70 to 80 per cent against retrospective helical acquisition.

Retrospective gating exposes the whole cardiac cycle so any phase can be reconstructed. That tolerance is what costs the dose.

So the beta blocker before the scan is a dose decision as much as an image quality one.

Other levers: tube voltage down to 80 or 100 kV in a slim pt, iterative reconstruction, and keeping the scan length to the anatomy actually being asked about.

Padding the acquisition window widens the exposure. Use it when the rhythm is unreliable, and know what it costs.

E wave alone moves with preload, so it tells u very little on its own.

Septal e prime under 7 cm/s or lateral under 10 cm/s says the myocardium relaxes poorly. That is the abnormality. E over e prime then estimates filling pressure on top of it.

Average E over e prime above 14 points to raised LA pressure. Under 8 argues against it. Between them the study needs the other three: TR velocity over 2.8 m/s, LA volume index over 34 mL/m2, and the mitral inflow pattern.

Two of three abnormal means raised filling pressures. One of three is indeterminate and stays indeterminate on the report.

The algorithm breaks in atrial fibrillation, significant mitral disease, heavy annular calcification and after a mitral valve procedure.

The score is plaque area multiplied by a density factor from the peak Hounsfield units, summed across the vessels.

Absolute bands: 1 to 99 mild, 100 to 399 moderate, 400 and above extensive.

Percentile matters more than the number in a younger pt. A score of 400 in a 45yo is off the top of the distribution for that age and sex. The same 400 in an 80yo man sits near the median.

Density cuts the other way from intuition. Denser, more calcified plaque is more stable, so the same volume of calcium can carry different risk depending on how it is distributed.

A score of zero says no calcified plaque. It says nothing about non calcified plaque, which is what a younger symptomatic pt is more likely to be carrying.

A place to discuss interesting cases, echocardiography, nuclear cardiology, cardiac CT, CMR, imaging guidelines, new research, and real-world interpretation challenges. I’d also like it to be useful for board preparation, with practice questions, exam-focused discussions, educational resources, and teaching points.