Radiology Q&A
There was a lot of good questions and feedback from the last post. Here are some thoughts.
Since I started practicing radiology, one of the ideas I have kept ruminating on are the limitations of imaging (within a broader criticism of limitations of testing).
Whereas most people and clinicians think of radiology as some snapshot into the truth, I see it as a limited and narrow means of communicating with the body.
After all, any time you transmit signals toward an object and wait for feedback, you are communicating.
Radiology is a snapshot of communication with the body.
Thus, the choice of which imaging to use, is deciding which language to communicate with.
In addition to the limits of radiology, there are also the assumptions that underlie many of its teachings.
For example, most radiologists believe that stochastic somatic mutations lead to cancer. In easy to understand terms, this is the belief that a random mutation in cellular DNA is the proximate cause of cancer.
I don’t believe the somatic mutation hypothesis to be true, and so I have to unpack a lot when I tell people that “I am not really concerned about radiation dose.”
It is interesting to observe the contradiction of assumptions when both clinicians and patients ask me questions about a given scan or imaging modality.
Because of the above, I am limited in what I can address in an article like this.
There are some questions I can answer here, there are some that require a deeper dive, and then there are those questions which must be addressed in another medium altogether.
Frequently Asked
Today I’ve consolidated all the questions into clusters, and will address what I can.
What is “x” (X-ray, CT, US, MRI) modality used for?
The most important thing to know is that every single one of these modalities complement one another, and the choice of which scan(s) to use to solve a problem depends on the problem.
For example, what most people don’t know is that X-Ray imaging has the highest spatial resolution available to us. In fact, the transition from analog to digital X-Ray came with costs, including a reduction in spatial resolution.
The high spatial resolution is useful in evaluating things like hardware failure, like hip or spine implants we are concerned may be slipping or fractured. I have seen cases of screw fractures which were imperceptible on CT, but obvious on X-ray.
As the first lesson above states, radiology is communication.
The choice of modality depends on what you are trying to understand, and how you will communicate with the body.
As you can imagine, this requires a lot more space to explore.
What are the harms (radiation, procedure, contrast) of imaging?
In my opinion, the most harmful aspect of radiology is inappropriate use of imaging.
Whatever harms people can bring up about radiation exposure, contrast agents, and even some procedures…I am willing to bet that the potential harm that can be brought about from inappropriate imaging is far greater.
The classic example of this would be something like a whole-body CT or MRI, that reveals a random nodule somewhere in the body (termed an incidentaloma). This incidental nodule will now undergo a series of testing and imaging, and at one or more points along this work-up or “treatment” the patient will undergo severe harm that could have been avoided altogether.
Not to mention the psychosocial stress, and financial burden. After all, many radiologic tests and procedures are quite costly.
There are rare instances in which either radiation dose or contrast causes harm greater than the above pathway (which is far more common).
Is contrast harmful?
To be entirely honest with you, I am not sure.
If we are talking about CT contrast, which is an iodine based contrast medium…then I think it’s probably of low concern. There used to be a time when iodine-based CT contrast were indeed harmful.
But, my current understanding is that modern non-ionic water-soluble agents which are around 40-50% iodine by weight…are relatively safe and readily excreted by the kidneys.
Depending on the length of the scan, I can actively see the kidneys excreting the contrast into the bladder.
But, MRI contrast is a different beast.
This is where I am more uncertain.
The current teaching is that modern MRI contrast (which is gadolinium-based) is safer because it is “macrocyclic” and blah, blah, blah.
But, you are fundamentally injecting a heavy metal into your bloodstream. Simultaneously, you are inside the bore of a very powerful magnet, which has been shown to disrupt membrane integrity.
For example, an MRI of less than 1 Tesla (which is virtually non-existent in modern human imaging, since all magnets are now at least 1.5T in strength, and up to 7T) has been shown to weaken the blood brain barrier.
Taken together with the known phenomenon that patients who undergo repeat MRI with contrast (the best example of this is in people with multiple sclerosis) demonstrate contrast staining of the brain, it is difficult to say just how benign Gadolinium may be, and indeed the safety of MRI itself.
Is radiology overused?
Yes. Incredibly overused.
What do different modalities image better?
This is very rudimentary, but a reasonable approximation of the utility of different techniques.
X-Ray: acute phase triage, hardware integrity, and dynamic imaging (e.g. it is very easy to repeatedly image your spine in different position - flexion, extension, neutral, side-bending, etc).
CT or “CAT” Scan: As CT technology has evolved, it is has emerged as a fast, cheap, and reliable way to solve all sorts of problems. It’s only limitation is tissue contrast. Although it does a great job of differentiating tissue by density (like all radiography), it cannot provide a lot of contrast resolution information beyond that. Which is why iodinated contrast is often used in CT imaging.
MRI: Tissue contrast. Because of the nature of how MRI works, it is incredible at differentiating tissue by characteristics other than density. To the extent that IV contrast is needed in far fewer instances than with CT.
Ultrasound: The unsung hero of radiology, but also the lost art. Ultrasound imaging is highly dependent on the knowledge and skill of the person operating the machine, which in modern America, is not the radiologist. Ultrasound’s greatest strength is that it truly dynamic imaging. The technology around ultrasound has also evolved tremendously, to the extent that you can have a probe at home connected to your iPhone and obtain incredible information in the comfort of your home.
There may even be an emerging role in empowering patient with their own probes, similar to how we do it with other wearable devices that monitor health metrics.
There are other modalities which we can get into in the future, but these are the basics.
Radiology 101 Seminar
Given the high interest I’ve received on this topic, I am putting together a Radiology Seminar (presentation + Q&A format) which will be on Zoom (or a similar platform).
Paid subscribers will have complimentary access to this seminar, and free subscribers can attend with a one-time fee.
Topics covered will include:
Basics of imaging
Role of the radiologist
Gaps in medical care associated with imaging
Incidental findings
Things your radiologist doesn’t report, and why that is the case
What can patients do to optimize imaging
Radiologists recommending more imaging
and more…
From there, we can determine if there are people interested in doing even deeper dives into specifics of imaging.
If you are interested, drop your info on this sheet!
Or, you can simply e-mail me at remnantmd@pm.me
I will follow-up with more information and a date in the coming weeks.
Since people have been asking about mammography, it is important to note that by and large mammography is a cancer screening and workup specialty.
Mammography is also, pretty unanimously, the most boring specialty in radiology for many reasons.
I have little to no interest in mammography other than as a technical analysis, insofar as the utility of screening, the way the imaging works, and if there is a clinical benefit to widespread screening.
The literature on the final point is mixed, at best.
A radiology seminar for patients and for non radiology health care professionals could improve vigilance and prevent errors.