Monday, 11 August 2014

Investigations, Investigations, Investigations (Part 3)

Image courtesy of [anankkml] / FreeDigitalPhotos.net

The cornerstone of medicine remains the classic history and examination- let the patient tell their story, and the physician's hand of assessment can help pinpoint the diagnosis.

However, when diagnoses are unclear or can't be differentiated, that's where investigations come in. Sadly, today they're often over-used, but when used appropriately they offer a wealth of information that can help tailor all important management and get the patient on the path to recovery faster.

Following on from part one, where we looked at urine, and part two which look at bloods, this multi-part post will take a look at some of the common investigations performed, what they can tell us and the reasons why and when they should be used.

Part three deals with one of the more extravagant tests doctors can use- the various imaging that can visualise our internal anatomy.

Part Three- Imaging


A picture paints a thousand words, yes? Or a scan can reveal things that other tests can't. Scans are a double-edged sword, however, in that they required skilled interpretation, and some things seen on a scan may have nothing to do with the symptoms the patient is experiencing. This is why scans are often rationed, and radiologists need a good clinical history to correlate what they see to what the patient feels.

It can be frustrating for patients who often feel the doctor they see should review their scans in front of them, but while we're competent to look at simple X-rays, we're only taught at a basic level to recognise barn-door obvious things in the more complex scans such as CT/ CAT, MRI and ultrasound. This is why the specialty of radiology exists, as they see hundreds of thousands of these scans and thus are much better to analyse more subtle changes.

So let's delve into the types of imaging available to us today:

-X rays


The humble X-ray still has plenty of uses today, from finding bone fractures to looking for chest infections or heart failure. Every doctor, radiologist or not, usually knows how to interpret an X-ray. Of course, the drawback is the radiation risk, which while it's extremely low and is generally very very safe, it can't be used in some situations like pregnancy. Still, it remains a very useful test.

The other drawback to X-rays is that they are a 2D image of a 3D structure, so you can miss things (like lung cancers that are behind the heart shadow), and it can be difficult to visualise structures. This is where CT comes in...

-CT scan


Computed tomography, or computed axial tomography (CAT), is a step up from X-rays in that we can use it to picture the body in three dimensions and not two. The radiation dose is quite a step up, too, so again this imaging can't be used for everything, and certainly not in certain situations. It is excellent at assessing fractures, head injuries or brain pathology like stroke, looking at intra-abdominal organs (like liver, bowel, spleen, kidneys etc) and assessing spread of cancers. When used with contrast, it can also pick up blood clots in the lung or arterial dissections.

CT scans have become much more widely used, particularly by surgeons, as it allows them to visualise the organs in the abdomen without having to lay a scalpel on the patient and all the risks of laparotomy (open abdominal surgery), and hence they can plan surgery and hopefully account for otherwise unseen risks.

However, as it's based on X-rays, CTs are not so good for looking at soft tissues and can't see subtle changes. This is where the next imagine modality steps in...

-Magnetic Resonance Imaging (MRI)


This, as the name suggests, is based on magnets, and the alignment of water molecules. This allows for very detailed imaging of soft tissues, and hence MRI is the best for brain scans (showing subtle changes, such as old strokes or demyelination, which can be a sign of multiple sclerosis), scans to look at spread of tumours in the pelvis/ neck, and spinal scans to look for spinal cord compression. There's also no radiation risk, either.

However, MRIs are complex, and not a pleasant experience. Patients need to be still for a long period of time (making it harder to scan children without sedating them), MRIs are slow, and also they can pick up totally insignificant things that may not correlate to symptoms, but we can't tell that.

Spin-offs of MRI include MRAs (magnetic resonance arteriograms, which look at the arteries specifically).

-Ultrasound


Perhaps one of the safest imaging modalities, ultrasound has many uses, not just in pregnancy (as pictured above). It can assess abdominal and pelvic organs, look at complex joints such as the shoulder, help guide doctors to insert drains or central lines, it can assess lumps and bumps, and can help guide radiologist to take samples of said lumps (ultrasound guided biopsies or fine needle aspirations). It can even assess the heart, including the valves, the muscle wall, and how effective it's pumping blood. Best of all, there is no radiation risk. Sounds like the best of the lot, right?

However, as with all these imaging modalities, it does have its limits. The major one is that it can be very operator specific- that is, different ultrasonographers can interpret their findings differently. Also, things can get in the way, such as bowel gas, which can obscure the image, and with patients with a high BMI, it can be difficult to see, too.

Whew, so that's imaging! Oddly enough, there hasn't really been much change in the last few years, but who knows what the future will bring us...

The next and final part of this series will look at the leftovers, such as ECGs, 24hr tapes and the like.

Part 1- Urine

Part 2- Bloods



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