X-ray Vision
Well Halloween has just past and kids are now busy enjoying their candy and driving their parents nuts. The decorations are getting packed up for another year - including the hoards of skeletons that were out hanging from trees, emerging from the ground or posed doing various activities around the yards of our neighbourhoods. Seeing bones scattered about everywhere, I figure it may be a fitting time to help decode some of the common imaging techniques used to take “pictures” of our insides!
Imaging is one tool used by health care providers to “get a better look” at the source of your concern. With all of the abbreviations and different types of imaging methods out there, it can be confusing what test you are being sent for and why. Always defer to your healthcare providers to know which test is best to order for your personal circumstances. While each type of imagining is slightly more specific or sensitive at illuminating different tissues, there is often overlap. Sometimes, we must also consider the availability of the test, the wait times, the suspected underlying pathology (what we are looking to rule in or rule out), access to the machines and any associated costs for the patient.
True to the Halloween spirit - let’s start with X-rays!
Most are familiar with X-rays and have had them taken at least a time or two. It is a fairly easily accessible and cost-effective test used primarily to take pictures aka “radiographs” of our bones. Helping to rule out (or better visualize) the presence of a fracture or pathology in a bone, check for skeletal alignment, or to help assess the amount and type of arthritis in a joint are all common reasons to have an X-ray done. In addition to being able to be done quickly in a trauma or emergency setting and as they are more available, faster to conduct, and cheaper than other types of imaging, we often use X-rays as the first test for a lot of things. Though the test may not give us as much detailed information as other technologies, it can still be very useful - even for more than just bones. While we can’t see the “soft tissues” (such as muscles, tendons, ligaments, spinal discs, organs, vessels etc) very well, we can still use the initial information gained on radiographs to help determine what the next best steps would be.
Different structures in the body have different densities depending on their make-up. X-ray technology generates a “picture” of our insides and allows us to visualize these different densities as different shades of white or black on the radiograph. Metal (like in the case of a surgical screw or plate), will show up a bright bright white as it would be the most dense, bones show up pretty white, muscles and organs kinda grey-ish or hazy (we often call them “soft tissue “shadows”), fat/fluid - like swelling or adipose tissue around organs or between skin and muscle - is pretty dark, and air - the least dense of all, is black. Using this knowledge, along with knowing what structure “should” be where in the body and whether or not each has any air, bone/calcium or fluid density in it normally, can give us clues about structures other than bones - even though we can’t see them in great detail.
Here’s just a few examples of how we might use radiographs to help us check for problems in structures that aren’t bones:
Sometimes muscle or organ “shadows” can show up and if they are not where they should be - or are larger or smaller than expected, we may get a sense of what could be happening. Is something pushing them out of their usual spot? Is there a density in there that shouldn’t be? Maybe there are round white densities in the spot where the kidney, gall bladder or bladder is - this could be stones inside there. Streaks of calcification may also be present in artery walls when there is plaque build up (atherosclerosis); when this occurs, looking at the radiograph we can get an idea of the extent of build up in the vessel and check for expansion or bulging (aneurysm). Significant swelling also “leaves a mark” on the radiographs. Our bowels generally have air bubbles in them - a deviation in the normal pattern of gas inside here can give us hints of where a disruption or blockage could be. The spinal discs sit between each vertebrae and obviously take up space, so we know if we see a reduced space between two vertebrae then the disc sitting in that space is likely a bit squished. Depending on the patient’s symptoms we can estimate what might be happening to it and whether or not we need a closer look. Similarly, by knowing which nerves and vessels travel through various “holes” (aka foramen) in the spine and the skull, even though we can’t see them on the radiograph, we can get a sense of whether or not they may be getting compressed by looking at the bone structure at these important entry and exit points. If the patient is having a lot of nerve or vascular symptoms and we see on their radiograph that the foramen is smaller than it should be due to perhaps an arthritic process or a shift in the bones (as could occur in trauma) then we’ve got some clues to work with.
When we know each part of each bone that should be seen using X-ray technology, we can also “see” when something is missing. Admittedly, sometimes the hardest thing to see is something that isn’t there - but when we can’t see something that we know should be there - we must pause. For example, when we see spots or “rain drop marks” in bones, fuzzy parts in them or around them, or parts of them missing completely - no matter how small, this tells us to watch out! There might be something at play that is destroying them and we need to do more testing to find out what.
While X-rays are sometimes used to get an idea of the extent of bone mineral loss (osteopenia if mild or osteoporosis if more severe), plain x-ray it is not the best test for this. It is well accepted that we need at least 30% bone mineral loss for the loss to be visualized on plain film radiographs - aka “regular” x-rays. A more specific type of X-ray technology called a “DEXA scan” is much better suited to measure bone loss like this.
No bones about it, there’s a little more to looking at X-rays than just dancing skeletons! Stay tuned next time for a little insight and decoding of some other common types of imaging.