The wonders of PET scan

Positron Emission Tomography, or commonly known as PET scan is the most advanced medical imaging that a hospital can have. Works like any other medical imaging like CT (computer tomography) scan, X-ray and MRI (magnetic resonance imaging), PET scan can also produce 2-D anatomical structure of the whole body or specific organs. However, it does one thing others can't which is mapping out the metabolic activities of tissues especially malignant (cancerous) tissues. By injecting a small amount of radioactive substance typically behind the elbow of a patient, this radionuclide or commonly known as tracer will accumulate and absorbed by tissues within the body. It is known that healthy tissues and un-healthy tissues absorbed this tracer at different rate, thus, the emission of positron from different tissues enables the detector of PET scan to map out the energy of positron emitted from the body. The detected signals are then reconstructed by sophisticated computer to be revealed as colour-coded images on the monitor. Physicians like oncology and neurology are able to interpret these images and form a more accurate and better non-invasive diagnosis of their patients. Diseases like Alzheimer, cancer, and cardio vascular disease are some of the chronic diseases proven to be diagnosed successfully by PET scan with high specificity and sensitivity. And typically this diagnostic is followed by another CT scan which will reveal a clearer picture of the tissues especially on cancer patients.

These are some of the PET scan results which showed some lavish colour-coded images. The first one is a scan of the brain to compare a patient with and without Alzheimer's disease. Second is a full body scan of a patient with lung cancer before chemotherapy. I got it from his blog which he described his experiences as a lung cancer patient.

The high-lighted area of the brain are plaques that formed between brain nerve cells which are induced by amyloid protein deposits. There are three promising drugs for Alzheimer's patients. First which is the Exebryl-1 which attacks the amyloid deposits. Second is the Dimebon which boosts the brain cell energy and improves memory. Thirdly, is Rember which attacks the Tau protein tangles and slows down the damage of brain cells done by Tau protein.

How does a PET scan look like? The first image shows the real PET scan at full scale, and the second image shows the schematic diagram or a cartoon of a PET scan.

The PET scan is indeed an advance medical imaging tool which is also a part of the nuclear medicine procedure. This machine cost $2.5 million and not many hospitals can afford to own such high-cost machine. Even if they have this machine, they will charge twice as much compared to a CT or MRI scan. A PET scan fee is typically around $3000. This is also partly induced by the high cost of producing the tracer which has to be used within hours of production. Requiring a huge machine called a cyclotron, particles are accelerated in a spiral path under vacuum and they will hit a target at the circumference of the machine. This collision produces short-lived positron-emitting isotopes suitable for PET imaging. A typical tracer is 18-fluorine compound.

Another new type of tracer under development is a vitamin B-12 compound with radioactive atoms attached to them. By injecting this substance, cancer cells which in nature are growing aggressively consume a greater quantity of vitamin B-12 as compared to other healthy cells. Therefore, this type of tracer does show promising results from PET scans. And ultimately, researchers are working on treating vitamin B-12 as a conduit to attack specific cancer cells by carrying a lethal substance on the back of vitamin B-12. It sounds like vitamin B-12 will act like a "Trojan horse" in our body. Interestingly, I have already seen a huge trojan horse with my girlfriend =)