“5.3 million people have Alzheimer’s. 172 billion dollars will be spent this year on health care services for people with Alzheimer’s.”
— 2010 Alzheimer’s Disease Facts and Figures
“Approximately 900,000 PET scans were performed in 2004. It is estimated that over 2 million PET scans will be performed in 2010.”
— PETNET Solutions
As a medical imaging researcher, I notice when medical imaging technologies are mentioned by popular news media or medical-themed television shows. Lately I’ve been seeing PET imaging mentioned more frequently, including on TV shows like House and Grey’s Anatomy. This probably just reflects the fact that dramatically increasing numbers of PET scans are being performed in real life in clinics and hospitals. So what is PET imaging? Funny that you ask, because I just happen to do research in this field.
In this context, PET stands for Positron Emission Tomography. During a PET scan, a trace amount of biologically-active, radioactive drug is injected into the patient’s vein. The drug localizes somewhere in the patient, depending on the metabolic properties of the selected drug. The drug then emits a positron (anti-particle of the electron), and the positron annihilates with an electron in the patient’s body. The resulting energy forms gamma ray pairs that pass through the patient and are detected by the PET scanner. These detected gamma ray signals are used to create a 3-D volumetric image or picture of the drug’s concentration in the body.
PET imaging technology is unique because it images a patient’s metabolism, whereas most other medical imaging techniques measure anatomical structure. For example, X-ray CT or MRI scans can be used to identify a tumor because they show the patient’s anatomy in detail. However, PET imaging can identify if the tumor is benign or cancerous, by measuring whether or not the tumor takes up the radioactive drug. In reality, you’d really like to know both though — detailed anatomical structure and metabolic function. Recent work has demonstrated the increased clinical diagnostic value of fusing imaging technologies based on function (e.g., PET, SPECT or functional MRI) with those based on structure (e.g., CT, MRI, or ultrasound). As a result, PET and CT scanners are now typically combined into a single gantry system, so that images can be taken from both devices sequentially during a single procedure.
Since PET measures metabolism instead of anatomical structure, it is mostly used to image organs whose size or shape does not indicate whether they are functioning properly, such as the brain or heart. It is also used to diagnose diseases that exhibit an abnormal metabolism, such as cancer.
Stay tuned this week when I discuss some Alzheimer’s research that utilizes PET imaging.
As you know, there was an aborted attempt to bomb Northwest Airlines Flight 253 last Christmas. The explosive (a.k.a., “crotch bomb”) was hidden in Mr. Abdulmutallab’s underwear to avoid detection. In the wake of this attempted terrorist attack, there was a lot of press on using full-body scanners at airport security checkpoints because such a scanner would have revealed the bomb. The news coverage focused primarily on the issue of privacy invasion weighed against the benefit of increased airport security.
Usually the news coverage included a frequent flier pleading for us to spend the money on full-body scanners to improve safety. However, I saw very little coverage on the potential health effect of frequent full-body scans. Now as a research scientist, I know just how much paperwork is required to scan humans even for medical purposes. So I know that these airport security scanners must pose very little health risk to humans. However, all the hype did get me curious about the technology used. There are two different technologies used for airport security full-body scanners — millimeter wave technology and backscatter technology.
Millimeter wave technology uses low-level electromagnetic waves. The millimeter wave is transmitted from two antennas simultaneously as they rotate around the body at high speed. A person walks into a large portal that resembles a glass elevator, pauses, and lifts his arms while being scanned for about 2 seconds. The wave energy reflected back from the body is then used to construct a 3-D image, which resembles a fuzzy photo negative that is displayed on a monitor in a nearby room. According to the Transportation Security Administration, the energy projected by a millimeter wave system is thousands of times less intense than a cell phone transmission.
Backscatter technology projects a very weak ionizing X-ray beam over the body surface. A person stands against a refrigerator-sized backscatter machine as a narrow, low-intensity X-ray beam scans his entire body at high speed. The beam of X-rays is sequentially scanned at a very high rate in the horizontal direction across the person’s body, while simultaneously moving down at a lower rate of speed. The entire scan takes a few seconds. The reflection ( “backscatter”) of the beam is detected, digitized and displayed on a monitor in a nearby room. The images look like a chalk drawing.
Many reports have erroneously stated that the X-rays from this backscatter technology penetrate clothing but not skin. In fact, the X-rays penetrate the skin but not much beyond it. However, the dose from the X-ray beam is truly negligible by any standard. It is equal to the dose that you receive from 15 minutes of natural background radiation (such as the sun’s rays). The dose from each scan is less than 10 microrem, which is equivalent to the dose you receive from two minutes of flying in an airplane at 30,000 feet. Or put in another way, the dose from the backscatter scan is less than 0.2% of the radiation received from a medical chest X-ray. Doctors and radiation experts argue that such a dose is inconsequential even for pregnant women.
The American College of Radiology states, “An airline passenger flying cross-country is exposed to more radiation from the flight than from screening by one of these devices.” However, these scans do have some limitations in terms of security effectiveness. For instance, these backscatter scanners cannot find weapons hidden in body cavities since the X-rays don’t penetrate much beyond the skin. Presumably the terrorists will adapt to account for the technology.
For those interested in health news blogs, I highly recommend “Health News from NHS.” This science blog looks at the science behind the international news headlines. The unique thing about this blog is its format:
- Summary of news reports
- Where did the story come from?
- What kind of research was this?
- What did the research involve?
- What were the basic results?
- How did the researchers interpret the results?
- Links to Headlines
- Links to Science
Given the long list above, you’ll justifiably conclude that the blog is a little bit longer than the average science news blog. However, you’ll come away with a more thorough understanding of the topic as a result. It may appeal particularly to scientists, but it could appeal to everyone on topics of specific interest.
A while back I used melatonin supplements in order to help with jet lag, since I was traveling for work to Germany. A friend that travels a lot had recommend melatonin to me, and it did seem to help me re-establish a normal sleep cycle when dealing with a large time shift.
Occasionally I have trouble sleeping through the night at home also. I usually fall asleep right away, but I wake up in the middle of the night and sometimes have trouble falling back to sleep. I have allergies and regularly take antihistamines, so the popular over-the-counter sleep aids like Tylenol PM (which has the same active ingredient as Benadryl as the sleep aid) don’t really work for me. So I wondered if I should take melatonin instead. Although melatonin is an herbal supplement, I did a little research to determine if I think it is safe to take as a normal sleep aid. This is what I found.
Melatonin is a hormone naturally produced by your pineal gland, which is a small pea-sized structure located deep inside your brain between the two hemispheres. Melatonin regulates your circadian rhythm, or basically your 24-hour internal clock. When the sun sets and darkness falls, you begin to naturally secrete increased levels of melatonin. As the melatonin levels rise in your blood, you start to feel sleepier. This hormone level is highest in your blood around bedtime and stays elevated for about 12 hours, then it falls back to the low daytime level around 9 am. Although nighttime melatonin levels remain at least an order of magnitude higher than at daytime throughout your life span, the concentration of melatonin continually decreases as you age. This helps explain why many older adults have problems with frequent insomnia.
Melatonin supplements have been shown to help “reset” the body’s internal clock in those suffering from jet lag, shift workers who work nights and sleep during the day, and blind people. There have been many studies on melatonin use, including studies on its effect to reduce insomnia for older adults. One such research study was performed by Richard Wurtman at the Department of Brain and Cognitive Sciences at MIT. He studied two groups of elderly subjects; one group had frequent insomnia and the other slept normally. Each subject received either a placebo or a melatonin dose about 30 minutes prior to bedtime, and those who received the melatonin were given a dose of either 0.1, 0.3, or 3.0 mg. Each subject was medicated for 7 days, followed by a “washout” period of 7 days. Wurton found that taking the hormone significantly improved the quality of sleep for the older adults. More importantly, he found that they were able to sleep through the night best when taking the 0.3 mg dose. Now perhaps this shouldn’t be surprising, because the body naturally produces melatonin at this “physiological” level. However, the typical over-the-counter melatonin dose is 3 mg and this was determined to be less effective in helping insomnia.
Despite the many studies that have demonstrated melatonin to be an effective sleep aid, there is still controversy about melatonin use though. Some doctors consider it harmless and others potentially harmful. This is true, in part, because the function of the melatonin hormone may not be fully understood. What is understood is that melatonin does more than just regulate the internal clock, such as affecting the onset of puberty. It is also clear that melatonin is only available as a prescription in many European countries and Canada (although this seems to be due more to ingredient regulatory issues than medical concerns), whereas in the US it is an herbal supplement that isn’t regulated by the FDA.
So what does this all mean? Mostly it means that the human body is a complicated system that we don’t entirely understand. But from what I’ve read, I’ve concluded that melatonin is probably a safe and effective sleep aid for adults (at least those over age 50). Of course, I’m a scientist and not a medical doctor. All in all, it is probably best to speak with your physician before taking it regularly as a sleep aid. If you consider taking melatonin, you do need to remember that it is a sleep regulator rather than a sleep inducer. It isn’t the same as taking something like Ambien or Tylenol PM. You also probably want to somehow chop up the over-the-counter pills into smaller pieces (doses) without getting a crumbled mess. For now, I’m just going to stick with daily exercise, relaxing before bedtime, Advil for sore muscles, and the World Finest Ear Plugs for peace and quiet. Sweet dreams.
My brother-in-law was seemingly the healthiest person we knew. He hikes up and down steep hills as part of his daily work. He kayaks intense oceans as part of his weekend play. He never even gets a cold. So he rarely sees a doctor. Luckily he did finally go for a general checkup when he turned 50, and those simple blood tests saved his life. Turned out, he had aggressive prostate cancer. Standard screening, to find prostate cancer in people who do not have symptoms, allowed him to be treated in time.
Against a backdrop of uncertainty and controversy, the American Cancer Society recently updated their prostate screening guidelines for the first time in almost a decade. This was largely in response to the findings of a massive federal study that was published in the New England Journal of Medicine last year. This study evaluated the usefulness of a popular prostate screening test that measures the amount of prostate-specific antigen (PSA) in your blood. Basically, PSA is a protein produced by the prostate gland. PSA is present in small quantities for normal men, but it is generally elevated for men with prostate cancer or other prostate disorders.
Some recent news coverage sensationalized the results of this federal study, so here are the basics of the report. The research findings are based on 10 years of follow-up of nearly 77,000 men (ages 55-74). Half of the men received annual PSA tests for six years, and the other half received “usual care” from their own doctors (physicals that in some cases included PSA tests). After 10 years, the men that received annual screening were diagnosed with prostate cancer 17 percent more than those in the “usual care” group. However, the screening didn’t reduce the rate of death from the disease. (Various possible and plausible explanations are discussed in the report, but I’m not going to get into the gory details here.) This brings into question whether the PSA test should be used for general screening, because prostate cancer over-diagnosis leads to unnecessary treatment and potential lasting side effects such as impotence and incontinence.
So, what is a man to do? Since I work in the area of prostate cancer research, friends and family members have been asking my opinion on whether or not they should be regularly checked for prostate cancer.
To me, it seems like these new screening guidelines assume that ignorance is less stressful than having faith in your doctor. Namely, it is better to not even perform a simple PSA blood test, because patients with low PSA levels are often over-treated. I understand the issues that they are addressing, but I think the reasoning is somewhat flawed. Why not instead just change how you treat patients with low PSA levels? Such PSA test results would indicate that you probably have some non-aggressive cancer cells in your prostate but they are unlikely to harm you. Scary yes, but so are impotence and incontinence treatment side effects. So why not just repeat the blood test in 6 months or a year to see if PSA levels have risen? Is this common practice of “watchful waiting” by your doctor really more stressful than not having the blood test at all? Because, for some, that simple blood test could also indicate that you have aggressive prostate cancer that needs immediate treatment.
Based on my personal and professional experience, I recommend that men get at least one initial PSA test when they are in their early 40’s. Doctors can use this as an important baseline in the future. This agrees with the American Urological Association’s guidelines. However, I am not a medical physician and some men have higher risk for prostate cancer, so it is important to speak about your health and concerns with your physician