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 =)

Sun-bathing and influenza

Putting on your sunglasses and lying on soft sandy beaches, taking 20 minutes of your time while enjoying the sun light, you flip once to get a uniform redness on the skin. A favourite hobby of my girlfriend apart from watching TV series and being industrious in the lab. She believes that the sun light she gets actually prevents her from falling ill. On the contrary, I would rather avoid the sun light and use the sun-block as I believe the harmful UV rays from the sun damage your skin and may also lead to skin cancer.
Apparently, both of our believes were true. In fact, she was right as the sun does prevent her from falling sick and this had already been proven scientifically. In 1981, Dr. Robert Edgar Hope-Simpson proposed that the cause of influenza epidemic is associated with the seasonal fluctuation of vitamin D especially during the winter and rainy seasons in tropical countries. These are the time when people tend to stay indoor to avoid from freezing their ass and getting wet. The reason for his proposal was simple as he discovered that influenza epidemics in Great Britain in the 17th and 18th century occurred in widely separated communities, before modern transportation could explain its wide spread of the disease. According to the chart, the number of influenza cases varies according to the latitude and specific months of the year.

Why is the sun significant? The answer is plain old vitamin D. Humans have always made vitamin D, when their naked skin meets with the ultraviolet B radiation from the sun. The liver then converts the vitamin D into 25-hydroxyvitamin D and then cells all over the body converts this into steroid hormone which increase the level of your immune system and other important functions. Apart from increasing our immunity, vitamin D increases antimicrobial peptides that destroys the influenza virus while simultaneously modulates macrophages (white blood cells within tissues) preventing them from releasing excessive inflammatory cells called chemokines and cytokines into infected lung tissue.

Instead of falling sick due to Vitamin D deficiency, why don't we grab our shades, put on our bikinis or shorts, lie on the couch and expose our skin under the sun. 15 minutes for 2 to 3 times a week is the easiest prescription. You may need more if you have darker skin due to regional pigmentation, and a little less if you live near the equator. But according to WHO, it is best to limit exposure of the sun's UV rays that are strongest between 10am to 4pm. A pair of sunglasses is essential as it provides 99 to 100 percent UVA and UVB protection before you start damaging your eyes which may lead to cataract. In addition, it is of interest to know that sometimes vitamin D is not made in your skin even though you see the sun. At latitude 52 deg North (particularly London), between October to March, no vitamin D is made in the skin because atmospheric ozone easily filters out UVB radiation.

The best way of getting sufficient sun for the necessary production of vitamin D is to follow the UV index. They are categorized from zero upward, and as the number goes higher the risk of damaging your eyes and skin increases. Below is a rough guideline from the WHO and you can even check for daily UV index of your area from wunderground.com. Do apply sunscreen if you do feel the sun rays are burning. A broad-spectrum sunscreen of SPF 15+ is sufficient and you can re-apply every two hours, but do apply 15-30 minutes before you start burning your lovely skin. The number 15+ does not refer to the UV index, it is called the sun protection factor. So, wearing a sunscreen with SPF 15+ means your skin will not burn until it has been exposed to 15-20 times the amount of solar energy that would normally cause it to burn. But this also depends on the time of the day you spend under the sun. Also take note that SPF 20 in America is the same as SPF 10 in Europe.

If you don't prefer sunbathing, there are other sources of vitamin D within your reach. For example, cod liver oil, and fishes like sardines, herring and salmon are sources of vitamin D that are within our reach for consumption. Other source of vitamin D includes erythemal doses of UV radiation which contains UVA and UVB radiation are typically administered to athletes.

Well, I guess it's time for me to get some sun now. I hope this article may help you a little.

References:

1. J.J Cannell, E. Giovannucci et al. "Epidemic influenza and vitamin D," Epidemiol Infect, 134, pp. 1129-1140, 2006.
2. Nina Shen Rastogi, "Is sunbathing good for you?" Slate, http://www.slate.com/id/2187566/
3. Dr. Dan Rutherford, "Sunbathing," Netdoctor, http://www.netdoctor.co.uk/health_advice/facts/sunbathing.htm

How scary is H1N1 pandemic?

In 1918 flu pandemic a similar strain of type A H1N1 influenza virus had taken the lives of 20 to 100 million. Also known as Spanish flu, the flu pandemic spread to the Arctic and Pacific islands.Today, early 2009, the type A H1N1 influenza virus is of a novel strain and many virology believed that it is a hybrid strain from North American swine flu, North American avian flu, human H1N1 flu and swine flu from Asia and Europe. The evolution of this new strain was caused by complex mutation of the virus. It was either due to our lust for bacon or according toconspiracy theorist, the virus was genetically doctored for the profit of certain evil group.

Influenza virus consists of three major types, namely type A, B and C in which belong to the family of Orthomyxviridae. And each of type A virulent has two proteins attached to the surface of the virus, one is hemagglutinin (H) and neuraminidase (N). There are all together 16 H and 9 N subtypes known in birds but only H 1, 2, and 3 and N 1 and 2 are commonly known in human. Type B and C virulent are not common as these types mutates 2-3x slower than type A, and because of limited host range (only seals and pigs) they have a lower chance to create a pandemic.

Type A influenza virus particularly originated from wild aquatic birds predominantly ducks, geese, and gulls. This type A avian influenza are commonly spread when these birds start to migrate to different regions of the world. So, can we really blame the pigs (swine) for this pandemic? How did avian flu evolve into swine flu? One resource mentioned that swine barns which usually get pond water to wash down the barns contains avian viruses. As a result, pigs became the host of the avian flu virus. But, pigs are also susceptible to infection from both avian host virus and human host virus. Sometimes when pigs contracted two viruses, these viruses will experience reassortment or antigenic shift in the pigs and this new strain of virus can ocassionally transmit to humans. The reason pigs are susceptible to both avian and human flu virus because the cells of the respiratory tract are susceptible to infection.

Below are the symptoms that we can watch out for or if you prefer, you can seek medical attention from "Dr. Gregory House" so that he can criticized how you are wasting his time. *grin*

1. Fever (38-39 deg C)

2. Sore throat

3. Cough

4. Nasal congestion

5. Chills and fatigue

6. Body aches

7. Headache

8. Occasionally vomiting and diarrhea

These symptoms may look vague and as far as I know, common cold also follows these symptoms. It is common even the 1918 influenza was initially misdiagnosed as dengue, cholera, or typhoid.

However, for children and particularly in the high risk groups which cover adults > 65 years of age, pregnant women, low immune system after organ transplant, people infected with diabetes, heart disease and HIV should seek immediate medical attention or advised to take vaccination from your local doctors. According to World Health Organization (WHO), a single dose of swine flu vaccine is enough to immunize adults and children over 10 years. In addition, regular flu vaccine will not be effective for this newly discovered strain of H1N1 virus. Also it means one needs to take two flu shots to be fully covered. In my opinion, vaccination is still under clinical trial and it is entirely up to the local government and health department to decide what is reasonable and who should take the shots.

If you suspect you have swine flu and doctors have vigilantly verified that, there are two types of prescriptions. They are anti-viral drug which are also known as neuraminidase inhibitors which basically stop the virus from spreading by disabling one of the proteins on the surface of the virus. One of the anti-viral drugs, Tamiflu is the most common prescription while the other is Relenza, which I think is a little sophisticated as it is administered to the respiratory tract by oral inhalation. And since my girlfriend is lactose intolerance, I also want to emphasize that each blister of Relenza contains powder mixture of 5mg zanamivir and 20mg of lactose. So, it is best to describe your lactose allergy to the doctors you visit.

To those who are healthy and still having fun outside, please be very cautious especially on your personal hygiene. As droplets of virus which are air-borne can always land on the things you touch. And under certain humidity and temperature conditions, the virus can survive for a longer period of time. So, be sure to:

1. Always wash hands

2. Use hand disinfectants

3. Avoid spitting

4. Covering nose and mouth while sneezing or coughing

5. Use surface sanitizing (at home you can use diluted bleach to wipe surface)

6. Use masks (those used in the hospitals, preferably N95 respirators)

References:

1. Ron A M Fouchier et al. “Animal influenza virus surveillance,” Vaccine, Vol. 21, Issue. 16, pp. 1754-1757,May2003.

2. Jason Gale, “Swine flu Source Traced to Birds and People; Don’t blame pigs,” Bloomberg, May 2009, http://www.bloomberg.com/apps/news?pid=20601085&sid=axlmGLLc9Too&refer=europe

3. Michael Le Page, “Is swine flu a bioterrorist virus?,” NewScientist, April 2009, http://www.newscientist.com/blogs/shortsharpscience/2009/04/is-swine-flu-a-bioterrorist-vi.html

4. Frank Jordans, “WHO experts: Single dose swine flu vaccine enough,” PHYSORG, Oct 2009, http://www.physorg.com/news176120744.html