CTP has two common meanings in medicine. It most often refers to Computed Tomography Perfusion, an imaging technique that measures blood flow through organs in real time. It can also stand for the Child-Turcotte-Pugh score, a classification system used to assess how well the liver is functioning in people with cirrhosis. Which meaning applies depends on context: if you’re reading about stroke or heart disease, it’s the imaging scan; if the topic is liver disease, it’s the scoring system.
CT Perfusion: Measuring Blood Flow in Real Time
Computed Tomography Perfusion is a specialized type of CT scan that goes beyond showing the structure of an organ. A standard CT tells you what tissue looks like. CTP tells you how blood is actually moving through that tissue, revealing areas that are starved of oxygen before permanent damage sets in. It works by injecting a contrast dye into a vein (typically 35 to 50 mL) while the scanner takes rapid, repeated images of the same area. Software then tracks how the dye travels through the smallest blood vessels, generating color-coded maps of blood flow.
The scan produces several measurements that doctors use to assess tissue health:
- Cerebral blood flow (CBF): the volume of blood reaching a section of tissue per second
- Cerebral blood volume (CBV): the total amount of blood present in a given area of tissue, normally around 4 to 5 mL per 100 grams
- Mean transit time (MTT): how long it takes blood to pass through a region
- Time to maximum (Tmax): the delay between dye arriving in a major artery and reaching the surrounding tissue
When blood flow drops and transit times increase, it signals that tissue isn’t getting enough oxygen. These maps let doctors see exactly where the problem is and how severe it is.
CTP in Stroke Diagnosis
The most common use of CTP is in emergency stroke care. When someone arrives at the hospital with stroke symptoms, the critical question is whether brain tissue can still be saved. A standard CT can show a large clot or bleeding, but it can’t distinguish between brain cells that are already dead and brain cells that are struggling but still viable. CTP fills that gap.
The scan identifies two key zones. The first is the ischemic core, the area where blood flow has dropped so severely that the tissue is likely beyond rescue. The second is the penumbra, a surrounding region where blood flow is reduced but the cells haven’t died yet. This is the tissue that treatment can potentially save. If CTP shows a large penumbra relative to a small core, there’s a strong case for clot-removal procedures even hours after symptoms began. In fact, CTP is specifically used to evaluate whether patients arriving in a delayed time window are still good candidates for treatment.
The radiation dose for a head CTP is around 4.9 millisieverts, roughly comparable to one to two years of natural background radiation. The main safety concern is the iodinated contrast dye. Patients are screened for prior allergic reactions to contrast material. In emergency stroke situations, doctors may skip pre-scan kidney function tests if the potential benefit of rapid diagnosis outweighs the risks.
CTP in Heart Disease
CTP also plays a growing role in evaluating coronary artery disease. When arteries supplying the heart are narrowed, a CT angiogram can show the narrowing itself, but it can’t always tell you whether that narrowing is actually reducing blood flow to the heart muscle. Adding a perfusion scan solves this. The combination of anatomy (from the angiogram) plus function (from the perfusion scan) creates what cardiologists call a “one-stop-shop” evaluation.
This combined approach has shown 95 to 96% accuracy in detecting significant blockages, compared to 68 to 75% for the angiogram alone. CT perfusion of the heart has demonstrated sensitivity of 93% and specificity of 82% for detecting reduced blood flow, performing comparably to cardiac MRI and PET scans while outperforming older nuclear imaging techniques. For many patients, this means fewer follow-up tests and a lower chance of being sent for an invasive catheter procedure unnecessarily.
The Child-Turcotte-Pugh Score
In liver disease, CTP refers to the Child-Turcotte-Pugh score, a point-based system that grades how much damage cirrhosis has caused. It was originally developed to predict survival in cirrhosis patients and remains one of the most widely used tools for that purpose. The score is calculated from five factors, each rated 1 to 3 points based on severity:
- Bilirubin (a waste product the liver clears): under 2 mg/mL scores 1 point, 2 to 3 scores 2, over 3 scores 3
- Albumin (a protein the liver produces): above 3.5 mg/mL scores 1 point, 2.8 to 3.5 scores 2, below 2.8 scores 3
- Prothrombin time (how long blood takes to clot): less than 4 seconds prolonged scores 1 point, 4 to 6 seconds scores 2, over 6 seconds scores 3
- Ascites (fluid buildup in the abdomen): none scores 1 point, slight scores 2, moderate scores 3
- Encephalopathy (confusion or brain fog from toxin buildup): none scores 1 point, mild scores 2, severe scores 3
What CTP Classes Mean for Prognosis
The total score ranges from 5 to 15 and places patients into one of three classes. Class A (5 to 6 points) indicates relatively well-preserved liver function. Class B (7 to 9 points) reflects significant compromise. Class C (10 to 15 points) signals advanced liver failure.
These classes translate directly to survival expectations. One-year survival for Class A and B patients is above 85%, while Class C drops to roughly 52%. Mortality rates follow the same pattern: essentially 0% for Class A, about 30% for Class B, and nearly 39% for Class C. These numbers guide major clinical decisions, including whether a patient should be listed for liver transplant, whether they can safely undergo surgery, and how aggressively other conditions should be treated.
The CTP score’s strength is its simplicity. Three of the five components come from routine blood tests, and the other two are assessed during a standard physical exam. It gives doctors and patients a quick, shared language for describing how much function the liver has left and what that means going forward.