Radiology: understand what different scans show
Radiology helps solve medical questions with images of the body. In order to make sense of an image, you should decide what method was used before the image is interpreted. Each of the methods (X-ray, CT scan, MRI, ultrasound) works in different ways. The clinical question and the person being examined help determine which method the team selects.
Recognise methods that use X-rays
A standard x-ray generates a picture from ionizing radiation. CT scans create pictures of cross-sections as well, but use x-rays combined with computers. They can be used to help answer some questions that would not be answered through a standard X-ray. Also, they typically require greater exposure than standard x-rays. Clinicians weigh the potential benefits of a particular examination against its risks. Whether or not there will be radiation does not in itself determine if a study is needed.
The question being asked helps determine which examination can provide useful information. A detailed picture is not automatically the most appropriate investigation, and different methods have different strengths and limitations. When comparing X-ray and CT in a teaching case, state what needs to be seen and how the method produces that view. Keep the image's detail separate from the clinical value of the examination.
Understand the magnetic environment
MRI generates pictures with the help of a strong magnetic field and radio waves. It uses neither X-ray technology nor ionizing radiation. A patient must be screened for an appropriate MRI examination in relation to the presence of implants or other metallic objects. Some devices can be scanned under specified conditions. The imaging team must assess the device and scanning details before determining compatibility. Therefore, do not rely on a general web site to determine if your implant(s) are compatible with an MRI; follow the guidance of the Radiology Team.
Safety questions before MRI are part of planning the examination, rather than a reason to assume that every implant makes scanning impossible. The imaging team needs the particular device and circumstances. A general list on a website cannot establish compatibility for an individual. The relevant distinction is between understanding the magnetic environment and carrying out the specific safety assessment needed for a scan.
Follow the returning sound waves
Ultrasound creates images using a combination of high frequency sound waves and their echoes. However it does not utilise ionising radiation. The location in which the scan is to be taken will also determine whether a probe applied directly to the skin (some examples include liver and kidney scans) or an internally inserted probe can be used.
The position of the probe and the structure being examined influence the views obtained with ultrasound. A moving image may also provide information that is not captured by one still picture. When learning from an example, identify how the image was produced and what it is intended to show. Avoid assuming that every ultrasound examination uses the same approach or answers the same question.
Connect a finding with the question asked
An image is evaluated based on the examination technique, body region of interest, clinical background and prior imaging results. The written report of the radiologist includes description of findings and explanation of those findings along with any limitations to the report and/or recommended follow up testing. No single, isolated image will be able to supply all the needed context. Before describing an apparent abnormality, establish the view and orientation. Differentiate between describing an observable feature and making an interpretation that requires specialist evaluation.
A report may describe both a finding and a limitation of the examination. Those statements need to be read together. An image seen without the clinical question, full study or earlier comparisons can be misleading. A useful revision exercise separates the method, the visible features and the interpretation, then identifies which information would be needed to connect the report with a patient's care.
Check your understanding
A short quiz, with an explanation after each answer.
Which pair uses X-rays?
Choose one labelled teaching image and identify its method, body region and orientation. Write down what question the examination was intended to answer. Then distinguish a visible feature from an interpretation that would require a full clinical assessment and the complete imaging study.