PET or MRI, that is the question – Part 1

In our previous blogs, we discussed that doctors can diagnose Moyamoya disease using medical imaging systems, such as positron emission tomography (PET) and magnetic resonance imaging (MRI). But which one is better?

According to some recent studies performed by Dr. Moss Zhao (AHA Postdoctoral Fellow, 2021) at Stanford University, MRI is better thanks to its accessibility, safety, and affordability.

For decades, PET has been the gold standard technique for diagnosing Moyamoya disease based on imaging the blood flow in the abnormal blood vessels in the brain. However, PET uses radioactive tracers to create the images, making it complex and expensive. Although the amount of radiation is less than a 5-hour flight, doctors have sought for alternative and less invasive techniques to replace PET, especially for children. In recent years, arterial spin labeling (ASL), an advanced MRI technique, has emerged to replace PET imaging to measure blood flow in the brain. Because ASL MRI is more accessible at most hospitals and the procedure is less complex than PET, ASL has gained popularity in many research and clinical institutions for Moyamoya patients.

At Stanford University, Dr. Moss Zhao demonstrated that ASL could replace the conventional PET imaging technique without exposing patients to radiation and causing side effects. The image quality and measurement accuracy of ASL are compatible with PET, implying that ASL can be used to characterize the abnormal blood flow and circulation in Moyamoya patients. Among the different implementations of ASL, Dr. Zhao developed an advanced technique dubbed ‘multi-delay ASL’ that gives the best image quality with the least amount of scanning time. For less than 5 minutes, multi-delay ASL can produce images that require more than 20 minutes for PET imaging. The image in this blog shows the images collected by ASL and PET at the same time from normal and healthy people. Using the latest ASL techniques, doctors can identify patients with a high risk for stroke based on their MRI scans for just under 5 minutes without using any radioactive substances. Dr. Zhao’s team is currently testing this technique on the pediatric population to enable this non-invasive imaging technology to be accessible to patients across the lifespan.

Image source: NeuroImage




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High Sodium Consumption: The Next Public Health Endeavor?

We hear it everywhere. “Don’t put too much salt on your food, it’s not good for you.” It is a statement that is so frequently said by doctors to their patients, by concerned family members to their loved ones, that it has almost become part of our culture. Off the top of my head, I can think of a dozen movies where the main protagonist gets the table salt taken away from them because they have high blood pressure.

With that said, as noted by the AHA’s “Common High Blood Pressure Myths” article1, adding table salt to your food is not the main culprit causing medical problems. It is the hidden sodium in our processed foods.

Recently, I took it upon myself to pay a closer look at my diet. Like many American, I eat out a lot. Given that most fast food restaurants are starting to note the calories within their food, I started to realize it was easy to keep up with the CDC-recommended calorie count of roughly 2,300 calories per day2. However, the one variable that always kept coming up high in my diet was sodium.

It’s not like I was eating hamburgers everyday either. I started to realize simple condiments pushed the sodium in my food to astronomical numbers. A serving of hot sauce, broth in my ramen noodles, even pickles, would cause my sodium intake to leap despite a low-calorie count. On restaurant menus, I always saw in small letters the warning that “guidelines recommend a 2,000 mg daily sodium consumption”, and next to it, I would find a food entrée that had twice that amount in a single serving. As a physician, I was recommending sodium restriction to all my patients as an easy treatment for their many comorbidities, and yet, I had a difficulty following my own recommendations. Sodium is everywhere and trying to keep its consumption in check is a challenge.

So why is high sodium bad?

Initially, clinicians attributed sodium’s harmful effects to its association with high blood pressure3. Multiple meta-analysis and randomized control trials have shown a strong positive correlation between high sodium intake and elevated systolic blood pressure. As we know, high blood pressure is associated with a myriad of health complications affecting the heart, kidneys, and the brain. Thus, given sodium’s relationship with the number one cause of cardiovascular related death worldwide, it would make sense that sodium restriction has become the first-line treatment for hypertension.

Yet, new research presented at this year’s AHA Scientific Sessions is suggesting that there may be more adverse effects associated with high sodium consumption than just its effect on blood pressure. During the “Cutting Edge in Cardiovascular Science” presentation at Sessions, Dr. Constantino Ladecalo of Weill Cornell Medicine presented evidence in mice studies correlating high sodium consumption to neurovascular and cognitive impairment in the absence of hypertension. Outlined in a paper published recently in Nature Neuroscience4, Dr Ladecola presented a molecular pathway that may connect the effect of sodium in the small intestine with reduced resting blood flow to the brain, leading to cognitive impairment. The “gut-brain connection” as so called by Dr. Ladecola, may be a new frontier in medicine.

While Dr. Ladecola and his team suggested that this molecular pathway may be a new target for prevention of cognitive impairment, to me, their findings reinforced the fact that we need to return to the basics in our treatment of cardiovascular disease: lifestyle changes and nutrition. Previous endeavors in public health have helped eliminate several illnesses that were common such as thiamine deficiency, so why not attempt the same with sodium? As the evidence builds against high sodium consumption, it may be time for us to take a more active look at how we can address it. Can we work together with major food distributors to reduce sodium in their food? Should chain restaurants inform consumers of the sodium value in their foods as they do with calories currently? I am not sure of the answer to these questions as they can be very difficult endeavors to focus on.

What are your thoughts on sodium?

  1. American Heart Association. “Common High Blood Pressure Myths” October 31, 2016 “http://www.heart.org/en/health-topics/high-blood-pressure/the-facts-about-high-blood-pressure/common-high-blood-pressure-myths”
  2. Kotchen TA, Cowley AW, Frohlich ED. Salt in health and disease–a delicate balance. N Engl J Med. 2013;368(26):2531-2.
  3. Center for Disease Control. “Most Americans Should Consume Less Salt” June 11, 2018 National Center for Chronic Disease Prevention and Health Promotion , Division for Heart Disease and Stroke Prevention “https://www.cdc.gov/salt/index.htm”
  4. Faraco G, Brea D, Garcia-bonilla L, et al. Dietary salt promotes neurovascular and cognitive dysfunction through a gut-initiated TH17 response. Nat Neurosci. 2018;21(2):