MRI & CSF
Why Isn’t X-ray Always Good Enough?
Clinical radiography is an exceptionally vital tool in the diagnostic process for our patients. It is a fast efficient way to rule out very simple paths of diagnosis.
Radiography is wonderful in evaluating anatomic regions of stark contrast in density, but reveals its limitations when evaluating areas of minute tissue density differences. For example, when doing radiographs of the chest, X-ray provides a good representation of the anatomy because the majority of tissue is either air (no density) or bone (high density). There is little in the way of tissue between those two extremes, so abnormalities in the lung field are very obvious. The same goes with imaging of bones. In evaluating for fractures, the radiograph shows the presence or absence of bone, and reveals a fracture as a dark line in the cortical structure.
Beyond these situations, radiography is unfit to give an honest representation of the anatomical structures involved. Though radiography is established on a grey scale of contrast and density, the structures overlay each other and result in an image that roughly only contains four separate densities.
I know that the radiography purists out there might be upset by that comment, but please hear me out. If we were able to remove all of the contents of your body, and lay them out sided-by-side and take a radiograph, then we would see that each structure does have a unique tissue density to an extent. Unfortunately though, when all of those structures are mixed together in your body and we take a two-dimensional radiograph, all of those densities get averaged together and produce an image with a significantly lower dynamic image contrast.
We are able to improve this somewhat with Computed Tomography, but CT still falls short in the area of soft tissue evaluation. Even though CT gives a wider contrast range, the tissue structures are still so close that our brain averages them together and they look more similar than they actually are. MRI, however, does not rely solely on the physical density of tissue to create an image. It uses characteristic information from the tissue based on chemical make-up, position, resonant frequency, and magnetic susceptibility (to name a few) in order to give a more comprehensive breakdown of the structures involved.
Though diagnostic radiography is a vital part of the diagnostic process, rarely should we depend on it to give us all of the answers we desire. In this day and age with the resources we have available, we owe it to ourselves and our clients to utilize every opportunity to further diagnosis and promote health and longevity.
Spinal Tap (CSF Tap)
CSF, the abbreviation for cerebrospinal fluid, is a fluid that surrounds the brain and spinal cord and functions to protect, and support the central nervous system (CNS). Another important function, is that it helps remove waste from the normal CNS metabolism. Spinal fluid is constantly being produced in the brain and absorbed back by the body.
A CSF (or spinal) tap is used to evaluate the microscopic environment of the CNS. Some conditions diagnosed with CSF analysis include encephalitis, meningitis, CNS cancer, trauma, polyradioculoneuritis and hemorrhage. A spinal tap is usually interpreted in light of the patient, the presentation, history and results of other tests.
The CSF tap is typically performed after the MRI is complete. The supervising doctor will view the images, and if it is indicated, will do this while the patient is still under anesthesia. It is a generally safe procedure that can yield valuable diagnostic information.
Spinal taps are performed under general anesthesia, so the patient won’t feel any discomfort during the procedure. Side effects of spinal taps are rare, but can include bleeding, difficulty breathing, and rarely, brain herniation and death.