MFF0039: X-rays


Medical Fun Facts logo from Gary Lum

If I’ve timed this correctly, tonight’s show is dropping on Monday 13 February 2017.

Tonight’s episode is about something beginning with the letter X. There aren’t too many infections whose name starts with an X, except perhaps XDR TB.

I have to confess, my knowledge of physics and medical physics is limited. I struggled at school and university with physics and higher mathematics. I didn’t mind organic chemistry but I couldn’t get my head around inorganic chemistry and I was just plain stupid when it came to biochemistry. I think school teachers and university lecturers also struggled with my inane questions and inability to grasp the basic concepts. If it wasn’t for zoölogy, microbiology and evolutionary biology at school and university I would not have contemplated medicine as a career.

So getting my head around x-rays is a struggle. I will rely heavily on Wikipedia and other sources apart from my memory.

Did you know x-rays and γ-rays are very similar except for their source, x-rays come from electrons and γ-rays from the atomic nucleus.

Apparently, there are hard x-rays and soft x-rays. So, like many things in life hard is good. Hard x-rays have high photon energy and these x-rays are used in medical imaging and airport security. So when your bags and laptop and other sensitive electronic equipment is on the conveyor belt, in that dome is a source of hard x-rays I assume.

Because the wavelengths of hard x-rays are similar in size to atoms, they are used to examine the structure of crystals, hence, x-ray crystallography.

On the other hand, soft x-rays, are easily absorbed in air, and they can only penetrate about a micron when they hit the water.

X-ray photons contain enough energy to ionise atoms and disrupt atomic bonds, so you really don’t want to be spending too long near a source of x-rays. Props to radiographers and radiologists I reckon. Mind you, pathologists and medical laboratory scientists are constantly exposed to carcinogenic chemicals, as well as biological threats.

Really high doses of x-rays can cause radiation sickness while exposure to low doses over a long period can increase the risk of radiation-induced malignancies. X-rays can also be used in the treatment of some malignancies.

As an aside, you’ll hear me use terms like malignancy, neoplasm, carcinoma, benign neoplasm but I rarely use the word cancer. Why is that?

I was taught by some amazing pathologists, one of them being Professor John Kerr. While he never received the accolades of a Nobel prize, he was instrumental in our understanding of the process of apoptosis. Anyway, he always impressed on medical students, that the word cancer is an imprecise term and best avoided by medical practitioners and especially pathologists.

Because hard x-rays can penetrate objects without being scattered or absorbed, hard x-rays are used to examine the inside of visually opaque objects.

So radiology is a medical speciality associated with the use of x-rays and other forms of diagnostic imaging. I am constantly struggling in my head when at work I hear the word radiological in the context of chemical, biological and radiological weaponry. In that context, the issue is radiation, mainly ionising radiation and it’s about radioactivity. Still, when working with nonmedical people, you have to make allowances.

So in medicine and particularly clinical microbiology and infectious diseases, how do x-rays help?

In medical school, we’re all taught the art of physical examination. The physical examination requires a good appreciation of tactile and auditory inputs. Percussion and auscultation are traditionally important, especially when examining the chest and abdomen. We use a stethoscope to listen (auscultation) and our fingers and hands to feel and our ears to hear subtle changes when we percuss with a pounding finger on another finger. If you’ve ever wondered what the hell your doctor is doing when she or he has a hand on your chest or back or belly and then a bent finger, on the other hand, is used to sharply tap the flattened finger of the hand on you, that’s percussion. Mostly, everything should sound and feel hollow, if there is dullness to percussion or if the breath sounds are accentuated, that may mean you have consolidation in your lungs. That means your lungs are filled with lovely pus.

As I said, a physical examination is more art than science. It’s subjective and not everyone is good at hearing subtle changes. The truth, that is a fundamental truth of disease is the domain of the pathologist and medical laboratory scientist. Unfortunately, most of the time our specimens have been carved out, secreted or excreted (not faeces is NOT excreted) or we have a dead patient available for the ultimate in diagnosis, viz., the post-mortem examination. The ultimate truth.

Somewhere in between, in dark rooms, in the shadows of medicine, radiologists and radiographers, work their dark art, which is more science than art. A good diagnosis can be made using x-rays, especially of infectious processes like osteomyelitis and pneumonia. Now the radiologist can’t tell you the name of the bacterium causing the infection, but common things are common, and they can have a good stab at it.

So props to the radiologists and radiographers. May they continue to be like mushrooms. Valuable and tasty and full of goodness.

If you disagree with anything in these podcasts or if you would like to voice a different view, please feel free to write a comment. If I have said something incorrect I welcome correction. Please also feel free to share your comments on social media.

You can find me on Twitter and Facebook. Please follow me on Twitter and like my Facebook page.

Go on, leave a comment, you know you want to

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s