• CT Perfusion (CTP): Widely available, fast, ideal for emergencies like acute stroke.
• MR Perfusion (MRP): Uses either DSC (Dynamic Susceptibility Contrast), DCE (Dynamic Contrast Enhancement) or ASL (Arterial Spin Labeling) better tissue characterization, no ionizing radiation.

Many clinical situations where perfusion imaging is clinically warranted such as:

• Acute ischemic stroke- to determine tissue that is penumbra from infarct core.
• Brain tumors- evaluate tumor grade, vascularity, and treatment response.
• Dementia/neurodegeneration-to assess regional hypoperfusion patterns (e.g Alzheimer’s, FTD)
• Traumatic brain injury (TBI) or vasospasm- to assess perfusion deficits not visible on structural imaging.
• Pre-surgical/neurovascular planning-to evaluate collateral flow or steal phenomena.

Typical quantitative perfusion maps:

• CBF (Cerebral Blood Flow) – the rate of blood passing through brain tissue, usually measured in (mL/100g/min).
• CBV (Cerebral Blood Volume) – the total volume of blood in a given amount of brain tissue, usually measured in mL/100g.
• MTT (Mean Transit Time) – the average time it takes for blood to pass through a given region of tissue, measured in seconds.
• Tmax (Time to Maximum) – Delay in contrast bolus arrival, measured in seconds.

Imaging protocols in acute stroke settings for both CT and MR can be performed and processed for quick decision making and added to established stroke workflow protocols without adding a lot of time.

ASL and DCE MR Perfusion take longer to post process, and typically is used more for Neuro-oncology and Neurodegenerative exams where processing time is not STAT.

• CT Perfusion:~45-60 scan time: perfusion maps available in PACS ~2-3 mins.
• MR Perfusion: ~3-5 mins DSC acquisition time: maps available ~2-3mins, ~ 5-10 mins DCE acquisition time: maps available ~5-10mins, ~4-10 ASL acquisition time: maps available ~2-7 mins.

There is always a risk vs benefit from imaging like CT or MR that uses contrast agents. Ordering doctors will take into consideration’s any contraindications a patient may have to either CT or MR imaging.

• CT perfusion: involves radiation and iodine-based; safe if protocols are optimized, but not ideal for patients with renal insufficiency or contrast allergy.
• MR perfusion DSC/DCE/ASL: Uses gadolinium (DSC/DCE); safe for most, but caution in severe renal impairment. Some patients may have contraindications to MR environment due to implants.