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Ask a Radiologist: Q&A

CT and PET

A PET scan revealed a thin line with lymph nodes like beads separated a little from one another. Is having them arranged in a line a feature of cancer or can any lymph node be found in that arrangement?

Lymph nodes generally drain in a chain along your blood vessels, so it is not uncommon to see them somewhat lined up. There is no increased risk of cancer with this arrangement. In the lungs, this is actually more of a common feature as the lymph nodes are present within a fissure between different lobes of the lung. The main criteria we use in radiology to assess for whether a lymph node is normal or not is: size (> 1 cm in short axis), the overall appearance (normal lymph nodes contain a small amount of fat), and if they are “hot” on PET.

Is CT contrast necessary to diagnose an aortic aneurysm?

CT contrast isn’t technically necessary to diagnose an aortic aneurysm, though can add a lot of information. Without contrast, we can only roughly assess the size of the aorta. When performed with contrast, we generally use ECG-gating and can actually use special post-processing software to get very accurate measurements. It is generally preferred to have at least once CT with contrast to accurately characterize the aneurysm for a baseline. Future follow up exams can be performed without contrast or with contrast. Luckily, our contrast agents are very safe.

What are the risks of radiation exposure from CT scans?

The primary concern with radiation from modalities such as CT, is the potential development of cancer throughout one’s life. There has been a significant amount of research over the past several decades to try and estimate the level of risk associated with radiation. A currently accepted risk model uses a “linear no-threshold” model, which essentially assumes that there is a linear potential increase in cancer that correlates directly to the amount of radiation you receive (the more radiation you receive, the higher your risk of developing cancer throughout your lifetime). The “no threshold” part assumes that even a single x-ray has the potential to cause cancer, (though the odds of this are astronomically low).

  • Certain tissues/organs are more sensitive to radiation than others (e.g., ovaries/gonads, thyroid, breast tissue, etc.)
  • Younger patients have an increased risk compared to older patients (their organs are more sensitive to radiation and they are alive for a much longer period of time resulting in more time for a cancer to develop)
  • Cancers that develop depend on the area of the body radiated (i.e., which organs are exposed to the radiation, the radiation sensitivity of each organ, etc.)
  • Cancers generally don’t develop until >20 years following exposure
  • The general population already has a high baseline risk of cancer of ~40% over our lifetime (males are somewhat higher than females)
  • We are exposed to radiation everyday, with a background level of radiation of (on average) ~3 msV/year from background radiation (cosmic rays from space, naturally occurring radioactive compounds found on Earth such as Radon, etc.)
  • mSv is a unit used to estimate cancer risk. Our current risk models estimate that 1,000 mSv results in a ~5% excess/added lifetime cancer risk.
  • Not all cancers are/will be fatal. For example, if a chest CT results in a breast cancer in 30-40 years and you undergo annual screening mammography, there’s a good chance that the cancer would be caught at an early, curable stage during your screening.

Here is a statement from the RSNA, our primary radiologic society in the US: “Risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent. Predictions of hypothetical cancer incidence and deaths in patient populations exposed to such low doses are highly speculative and should be discouraged.”

Interventional Radiology

What is a Cerebral Angioplasty?

A cerebral angioplasty is a procedure where an interventional radiologist inserts a catheter, typically through the groin or arm, into the arterial system (the blood vessels that transport blood to our organs). In a nutshell, the physician injects contrast material to show what the blood vessels look like and if there are any areas/branches that are narrowed or occluded. If they find an area of narrowing, they insert a small balloon into the area of narrowing and blow it up, which opens the blood vessel back up to allow improved blood flow to the brain. For arteries in the neck (carotid arteries) they can also deploy stents, much like an interventional cardiologist does for patients with heart attacks. Stenting in the brain is generally considered dangerous, which is why a balloon is used (the balloon is removed at the end of the procedure whereas a stent remains).

MRI

Can a cardiac MRI be done in an open MRI?

Unfortunately, no. The open MRI scanner design comes at cost and that cost is a weaker magnet strength (1.2 Tesla for our Union magnet), which means it scans too slow for cardiac MRI and the images aren’t quite as good (lower resolution). For cardiac MRI, we need a high quality machine with a stronger magnetic field (we generally perform cardiac MRI on our upgraded 1.5 Tesla magnets) and they require special software.

Can an MRI with contrast 100% diagnose a lipoma to rule out liposarcoma?

Unfortunately, no, it cannot 100% rule out a liposarcoma as there could be small cancerous cells that are too small for us to see with any imaging modality (MRI, CT, or US). MRI can be used to look for suspicious features that could be biopsied. Rate of growth is one of the main ways that lipomas can be followed with rapid growth being considered suspicious. Statistically, lipomas are very common and liposarcomas (especially in the skin) are exceedingly rare.

Do you have a 3T MRI?

We do not have a 3T MRI, unfortunately. That said, our hospital partners both offer 3T MRI in the hospital setting – St. Joseph Medical  Center and MultiCare Tacoma General.

Can the MRI machine/scan can tell the difference between a saline vs a silicone breast implant?

Yes, MRI can tell the difference between the two.

What does it mean when a report says that contrast excretion into the contracted urinary bladder is noted after an MRI with contrast?

When intravenous contrast is administered, whether it’s for CT or MRI, our bodies have to get rid of it. For both CT and MRI, the contrast is filtered through our kidneys and eliminated (excreted) by passing from our kidneys into our bladder and eventually into the toilet. Seeing contrast in the bladder is a normal finding that we expect to see by the end of the exam.

Can I get an MRI scan when I have a tattoo?

Yes, you can get an MRI scan with a tattoo(s).

X-ray

Will you give me an idea of how much radiation exposure I received from multiple x-rays?

We typically always need at least 2-3 x-rays of bones so that we can look at the bones from different angles and find possible fractures that might not be apparent without these different views. As for the radiation, the amount of radiation you would have received from these x-rays is essentially negligible and is unlikely to have any noticeable effect over your lifetime.

When a trauma patient has a spinal injury and pleural effusion present in one lung, what x-ray image would you do to view the pleural effusion?

With a spinal cord injury, we are very limited in what we can do in terms of an X-ray. Upright and decubitus views are most helpful, which we would be unable to do safely if they have an unstable spinal cord injury. If the patient has had sufficient trauma to cause a spinal cord injury, however, they probably should get a CT to assess for further injury, which would be the best way to evaluate the effusion.

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