Tissue perfusion is blood flow through the capillary bed of a tissue — the last stretch that delivers oxygen and nutrients and takes waste away. It is a flow. It is not a standard uptake value. It is not a Hounsfield unit. It is not a liver segment or a chamber mask.
If you meant PET SUV (activity / dose / weight) → standard uptake values. If you meant the SUVbw calculator → SUV calculator. If you meant CT density → Hounsfield units. If you meant drawing an organ → medical image segmentation. If you meant liver anatomy → liver segmentation CT.
706 left this URL on purpose. Tissue blood-flow ≠ SUV. PYCAD builds custom web DICOM viewers and imaging models. It does not ship a perfusion workstation.
Flow, not activity, not density
Circulation is the highway (heart → arteries → veins → heart). Perfusion is the last street: capillaries exchanging with cells. You can have a pulse and still have a capillary bed that is not being fed — a local blockage, a failed microcirculation, a territory downstream of a stenosis.
Four things have to work at once:
- Cardiac output. Volume the heart puts out per minute. No output, no delivery.
- Driving pressure. Enough arterial pressure to push blood into the bed, not so much it wrecks the vessel.
- Resistance. Open, flexible arterioles versus a plaque, a spasm, or a squeezed capillary.
- Cargo. Hemoglobin that actually carries oxygen. A perfect flow of anemic blood is still a failed delivery.
Hypoperfusion is that system failing: low volume (bleed, dehydration), a blocked vessel (ischemic stroke, coronary occlusion, PAD), or a pump that cannot push (cardiogenic shock). Cells switch to anaerobic metabolism and lactate rises. That lactate number is a distress flag, not a perfusion map.
How a clinic sees it (and how imaging sees it)
| Method | What it actually measures | What it is not |
|---|---|---|
| Bedside | Skin colour / temperature, capillary refill, cuff pressure | Not a millilitre-per-minute number |
| Lactate | A blood marker that anaerobic metabolism is on | Not where the failure is |
| Doppler | Velocity in a named vessel | Not capillary exchange |
| CT / MR perfusion | A time-density or time-intensity curve after contrast; maps of blood flow / volume / transit | Not HU as a density, not a segment label |
| PET (perfusion tracers) | Flow, with the right tracer and a flow model (e.g. 15O-water, 13N-ammonia) | Not FDG SUV. SUV is uptake, not mL/min/g |
Stroke CT perfusion and cardiac MR / PET perfusion are the imaging jobs that use this word correctly. An FDG SUV on a tumour is a different number on a different page. Do not 301 this URL into standard uptake values or the calculator.
What this page is not
- Not SUV. Activity concentration over injected dose over weight → 6258. Calculator → 8098.
- Not HU. CT density → 6213.
- Not a liver or heart map. Segments and chamber masks stay on those URLs.
- Not a lifestyle FAQ. Exercise and smoking advice is not why this URL exists.
- Not a PYCAD perfusion product. No workstation, no “perfusion AI” SKU.
If a viewer has to show a perfusion map next to the source series, that is the imaging piece. Case studies.